KR102493369B1 - Humic Acid-Derived Conductive Foams and Devices - Google Patents

Abstract

A humic acid-derived foam composed of multiple pores and pore walls, the pore walls containing single or few-layer humic acid-derived hexagonal carbon atom planes or sheets, The layered hexagonal carbon atom plane or sheet has from 2 to 10 layers of stacked hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm, as measured by X-ray diffraction, wherein the single layer or The multi-layered hexagonal carbon atom plane contains from 0.01% to 25% by weight of non-carbon atoms, and the humic acid is oxidized humic acid, reduced humic acid, fluorinated humic acid, chlorinated humic acid, brominated humic acid, iodinated humic acid. A humic acid-derived foam selected from humic acid, hydrogenated humic acid, nitrogenated humic acid, doped humic acid, chemically functionalized humic acid, or combinations thereof.

Description

Humic Acid-Derived Conductive Foams and Devices

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Serial No. 15/251,841 (Aug. 30, 2016) and U.S. Patent Application No. 15/251,849 (Aug. 30, 2016), which are incorporated herein by reference. do.

technology field

The present invention relates generally to the field of carbon/graphite foam, and more specifically to a new type of conductive foam derived from humic acid, and to devices containing such humic acid-derived foam. , and its production process.

Carbon includes diamond, fullerene (0-D nanographitic material), carbon nanotubes or carbon nanofibers (1-D nanographitic material), graphene (2-D nanographitic material), and graphite (3-D graphite material). It is known to have five unique crystalline structures including Other than fullerenes, all of these materials can be made into foamed structures.

Carbon nanotubes (CNTs) refer to single- or multi-walled grown tubular structures. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have diameters on the order of a few nanometers to hundreds of nanometers. Its longitudinal hollow structure gives the material unique mechanical, electrical and chemical properties. CNT or CNF is a one-dimensional nanocarbon or one-D nanographitic material. However, CNTs are difficult to produce and very expensive. In addition, CNTs are known to be difficult to disperse in solvents or water and difficult to mix with other materials. These characteristics have severely limited their application scope.

A single-layer graphene sheet consists of carbon atoms occupying a two-dimensional hexagonal lattice. Multilayer graphene is a platelet composed of more than one graphene plane. Individual monolayer graphene sheets and multilayer graphene platelets are collectively referred to herein as nanographene platelets (NGPs) or graphene materials. NGPs include pristine graphene (essentially 99% carbon atoms), slightly oxidized graphene (less than 5% oxygen by weight), and graphene oxide (more than 5% oxygen by weight).

NGPs have been found to have a wide range of unconventional physical, chemical, and mechanical properties. Our research group first discovered graphene (see B. Z. Jang and W. C. Huang, "Nano-scaled Graphene Plates," US Patent Application Serial No. 10/274,473 (October 21, 2002); current US Patent 7,071,258 (April 7, 2006)]). The process for producing NGPs and NGP nanocomposites has previously been reviewed by the present inventors (Bor Z. Jang and A Zhamu, "Processing of Nano Graphene Platelets (NGPs) and NGP Nanocomposites: A Review," J. Materials Sci 43 (2008) 5092-5101]). NGPs have been created according to four main prior art approaches. Their advantages and disadvantages are briefly summarized as follows:

Approach 1: Chemical Formation and Reduction of Graphene Oxide (GO)

The first approach (FIG. 1) involves treating natural graphite powder with an intercalating agent and an oxidizing agent (e.g., concentrated sulfuric acid and nitric acid, respectively) to obtain a graphite intercalation compound (GIC) or, in practice, graphite oxide (GO). (William S. Hummers, Jr., et al., Preparation of Graphitic Oxide, Journal of the American Chemical Society, 1958, p. 1339). Before intercalation or oxidation, graphite has a graphene interplanar spacing of approximately 0.335 nm ( L _d = 1/2 d ₀₀₂ = 0.335 nm). By intercalation and oxidation treatment, the intergraphene spacing is typically increased to values greater than 0.6 nm. This is the first expansion step that graphitic materials undergo during this chemical pathway. The obtained GIC or GO then undergoes further expansion (sometimes referred to as exfoliation ), which is done using thermal shock exposure or solution-based ultrasound-assisted graphene layer exfoliation approaches.

In the thermal shock exposure approach, the GIC or GO is exposed to a high temperature (typically 800 to 1,050 °C) for a short period of time (typically 15 to 60 seconds) to exfoliate the GIC or GO to form exfoliated or further expanded graphite. or expanded, wherein the exfoliated or further expanded graphite is typically in the form of a "graphite worm" consisting of still interconnected graphite flakes. This thermal shock procedure may produce some isolated graphite flakes or graphene sheets, but typically most of the graphite flakes remain interconnected. Typically, the exfoliated graphite or graphite worms are then subjected to a flake separation treatment using air milling, mechanical shearing, or ultrasound in water. Thus, Approach 1 basically involves three distinct procedures: first expansion (oxidation or intercalation), further expansion (or "exfoliation"), and separation .

In the solution-based separation approach, the swollen or exfoliated GO powder is dispersed in water or aqueous alcohol solution, which is subjected to ultrasonication. It is important to note that in these processes, ultrasound is used after intercalation and oxidation of the graphite (i.e., after the first expansion) and typically after thermal shock exposure of the resulting GIC or GO (after the second expansion). Alternatively, GO powder dispersed in water can undergo ion exchange or a lengthy purification procedure in such a way that the repulsive force between ions present in the interplanar space overcomes the inter-graphene van der Waals forces, resulting in the separation of the graphene layers. go through

There are several major problems associated with these conventional chemical production processes.

(1) This process requires the use of large quantities of some undesirable chemicals (eg, sulfuric acid, nitric acid, and potassium permanganate or sodium chlorate).

(2) The chemical treatment process requires a long intercalation and oxidation time, typically ranging from 5 hours to 5 days.

(3) Strong acids consume significant amounts of graphite during these long intercalation or oxidation processes by "corrosing the graphite" (by converting the graphite to carbon dioxide, which is lost in the process). It is common to lose 20 to 50% by weight of the graphite material immersed in strong acids and oxidizing agents.

(4) Thermal exfoliation requires high temperatures (typically 800 to 1,200° C.) and is therefore a highly energy-intensive process.

(5) Both the heat-induced exfoliation approach and the solution-induced exfoliation approach require very cumbersome washing and purification steps. For example, 2.5 kg of water is typically used to wash and recover 1 g of GIC, generating a huge amount of wastewater, which needs to be properly disposed of.

(6) In both the thermal-induced exfoliation approach and the solution-induced exfoliation approach, the obtained product is GO platelets, which must undergo an additional chemical reduction treatment to reduce the oxygen content. Typically even after reduction, the electrical conductivity of GO platelets remains much lower than that of pristine graphene. In addition, reduction procedures often involve the use of toxic chemicals such as hydrazine.

(7) Additionally, the amount of intercalating solution retained on the flakes after draining may range from 20 to 150 parts by weight (pph) per 100 parts by weight of graphite flakes (pph), more typically from about 50 to 120 pph of solution. During hot exfoliation, residual intercalating species retained by the flakes decompose to produce various species of sulfuric acid and nitrous compounds (eg, NO _x and SO _x ), which are undesirable. The effluent requires costly cleanup procedures in order not to have harmful environmental effects.

Approach 2: Direct Formation of Pristine Nanographene Platelets

In 2002, the research team of the present inventors succeeded in isolating mono- and multi-layer graphene sheets, from partially carbonized or graphitized polymer carbon obtained from polymer or pitch precursors (B. Z. Jang and W. C. Huang, "Nano- scaled Graphene Plates," US Patent Application Serial No. 10/274,473 (October 21, 2002); now US Patent No. 7,071,258 (April 7, 2006)]. Mack et al. ("Chemical manufacture of nanostructured materials" U.S. Patent No. 6,872,330 (March 29, 2005)) described the steps of intercalating a potassium melt into graphite and contacting the resulting K-intercalated graphite with an alcohol, vigorously A process was developed involving the production of properly exfoliated graphite-containing NGPs. This process must be carried out carefully in a vacuum or in an extremely dry glove box environment, since the pure alkali metals, such as potassium and sodium, are very sensitive to moisture and pose an explosion hazard. This process is not suitable for mass production of NGPs.

Approach 3: Epitaxial growth and chemical vapor deposition of nanographene sheets on inorganic crystal surfaces

Small-scale production of ultrathin graphene sheets on substrates can be achieved by thermal decomposition-based epitaxial growth and laser desorption-ionization techniques (Walt A. DeHeer, Claire Berger, Phillip N. First, “Patterned thin film graphite devices and method for making same" U.S. Patent No. 7,327,000 B2 (June 12, 2003)]). Epitaxial films of graphite with only one or several atomic layers are of technological and scientific importance due to their unique properties and great potential as device substrates. However, these processes are not suitable for mass production of isolated graphene sheets for composite materials and energy storage applications.

Another process for producing graphene in thin film form (typically less than 2 nm thick) is a catalytic chemical vapor deposition process. Such catalytic CVD involves the catalytic decomposition of a hydrocarbon gas (eg, C ₂ H ₄ ) on a Ni or Cu surface to form single- or few-layer graphene. Using Ni or Cu as a catalyst, carbon atoms obtained through decomposition of hydrocarbon gas molecules at a temperature of 800 to 1,000 ° C. are directly deposited on the surface of the Cu foil or precipitated on the surface of the Ni foil from the Ni-C solid solution state to form a single Forms sheets of layered or multilayer graphene (fewer than 5 layers). Ni- or Cu-catalyzed CVD processes by themselves do not provide for the deposition of more than 5 graphene planes (typically less than 2 nm), beyond which the underlying Ni or Cu layer no longer has any catalyst. effect cannot be provided. CVD graphene films are very expensive.

Approach 4: Bottom-Up Approach (Synthesis of Graphene from Small Molecules)

Yang et al. ("Two-dimensional Graphene Nano-ribbons," J. Am. Chem. Soc. 130 (2008) 4216-17) reported that 1,4-diiodo-2,3,5,6-tetra Nanographene sheets up to 12 nm in length were synthesized using a method starting with Suzuki-Miyaura coupling of phenyl-benzene and 4-bromophenylboronic acid. The obtained hexaphenylbenzene derivative was further derivatized and ring-fused to form small graphene sheets. This is a slow process that has so far produced very small graphene sheets.

Thus, we have a new class of carbon nanomaterials that are comparable to or superior to graphene in terms of properties, but can be produced more cost-effectively, faster, more scalably, and in a more environmentally benign manner. There is an urgent need for The production process for such new carbon nanomaterials includes reduced amounts of undesirable chemicals (or removal of all of them), shortened process times, lower energy consumption, and the introduction of undesirable chemicals into the drainage. species (eg, sulfuric acid) or undesirable chemical species (eg, SO ₂ and NO ₂ ) into the air. In addition, it should be possible to easily fabricate these new nanomaterials into thermally and electrically relatively conductive foam structures.

Generally speaking, a foam or foamed material consists of pores (or cells) and pore walls (solid materials). The pores can be interconnected to form an open cell foam. As an example, graphene foam is composed of pores and pore walls containing graphene material. There are three main methods of producing graphene foam, all of which are time consuming, energy intensive, and slow:

The first method involves sealing an aqueous suspension of graphene oxide (GO), typically in a high pressure autoclave, under high pressure (tens or hundreds of atm) for an extended period of time (typically 12 to 36 hours), typically in the range of 180 to 300 °C. It is a hydrothermal reduction of a graphene oxide hydrogel comprising heating a GO suspension at a temperature of A useful reference for this method is provided below: Y. Xu, et al., “Self-Assembled Graphene Hydrogel via a One-Step Hydrothermal Process,” ACS Nano 2010, 4, 4324-4330. There are several major problems associated with this method: (a) The high pressure requirements make the method impractical for industrial scale production. For one thing, this process cannot be carried out continuously. (b) It is difficult, if not impossible, to exert control over the pore size and porosity level of the resulting porous structure. (c) there is no flexibility to vary the shape and size of the resulting reduced graphene oxide (RGO) material (eg it cannot be made into a film form); (d) The method involves the use of very low concentrations of GO suspended in water (e.g., 2 mg/mL = 2 g/L = 2 kg/kL). By removing non-carbon elements (up to 50%), it is possible to produce less than 2 kg of graphene material (RGO) per just 1000 liters of suspension. In addition, it is practically impossible to operate a 1000 liter reactor that must withstand conditions of high temperature and high pressure. Clearly, this is not a scalable process for mass production of porous graphene structures.

A second method is based on a mold-assisted catalytic CVD process, involving the CVD deposition of graphene on a sacrificial mold (eg, Ni foam). The graphene material depends on the shape and dimensions of the Ni foam structure. The Ni foam is then etched away using an etchant, leaving a monolith of the graphene framework that is essentially an open cell foam. A useful reference for this method is provided below: Zongping Chen, et al., "Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition," Nature Materials, 10 (June 2011) 424-428. There are several problems associated with this process: (a) catalytic CVD is an inherently very slow, highly energy intensive and expensive process; (b) The etchant is typically a highly undesirable chemical, and the resulting Ni-containing etching solution is a source of contamination. Recovering or recycling dissolved Ni metal from the etchant solution is very difficult and expensive. (c) When the Ni foam is etched, it is difficult to maintain the shape and dimensions of the graphene foam without damaging the cell walls. The resulting graphene foam is typically very brittle and brittle. (d) transport of the CVD precursor gas (e.g., hydrocarbon) into the interior of the metal foam may be difficult, resulting in a non-uniform structure, since certain spots inside the sacrificial metal foam may because it is not accessible.

A third method of producing graphene foam also uses a sacrificial material (eg, colloidal polystyrene particles, PS) coated with graphene oxide sheets using a self-assembly method. For example, Choi, et al. prepared chemically modified graphene (CMG) paper in two steps: free-standing PS/ by vacuum filtration of a mixed aqueous colloidal suspension of CMG and PS (2.0 μm PS spheres). Fabrication of CMG film, then removal of PS beads to generate 3D macropores (B. G. Choi, et al., "3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities," ACS Nano, 6 (2012) 4020- 4028]). Choi, et al. fabricated well-aligned free-standing PS/CMG paper by filtration, which discloses separately prepared negatively charged CMG colloidal and positively charged PS suspensions. A mixture of CMG colloidal and PS suspensions was dispersed in solution under controlled pH (=2), where the two compounds had the same surface charge (+13±2.4 mV for CMG and +68±5.6 for PS). zeta potential value in mV). When the pH was raised to 6, CMGs (zeta potential = -29 ± 3.7 mV) and PS spheres (zeta potential = +51 ± 2.5 mV) assembled due to their electrostatic interaction and hydrophobic character, which were subsequently and incorporated into the PS/CMG composite paper through a filtration process. This method also has several disadvantages: (a) This method requires a very tedious chemical treatment of both graphene oxide and PS particles. (b) Removal of PS by toluene also weakens the macroporous structure. (c) Toluene is a highly regulated chemical and must be handled with extreme caution. (d) Pore sizes are typically excessively large (e.g., several microns) and too large for many useful applications.

The above discussion clearly indicates that all prior art methods or processes for producing graphene and graphene foam have significant deficiencies. It is therefore an object of the present invention to provide a new class of foam materials that are thermally and electrically conductive and mechanically robust and to provide a cost-effective method for producing this class of foam.

Humic acid (HA) is an organic substance commonly found in soil and can be extracted from soil using a base (eg KOH). HA can also be extracted in high yield from a type of coal called leonardite, which is a highly oxidized form of lignite. HA extracted from soft brown coal contains a number of oxygenated groups (eg, carboxyl groups) located around the edges of the graphene-like molecular center (SP ² core of hexagonal carbon structure). This material is slightly similar to graphene oxide (GO) produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5% to 42% by weight (other major elements being carbon and hydrogen). The HA after chemical or thermal reduction has an oxygen content of 0.01% to 5% by weight. For purposes of claim definition in this application, humic acid (HA) refers to a total oxygen content ranging from 0.01% to 42% by weight. Reduced humic acid (RHA) is a special type of HA with an oxygen content of 0.01% to 5% by weight.

The present invention relates to a new class of graphene-like 2D materials (ie humic acid), which can be converted into foamed structures with surprisingly high structural integrity. Accordingly, another object is to provide a cost-effective process for producing such nanocarbon foams (specifically, humic acid-derived foams) in large quantities. The process does not involve the use of chemicals that are not environmentally friendly. The method allows flexible design and control of porosity level and pore size.

Another object of the present invention is to provide a humic acid-derived foam that exhibits thermal conductivity, electrical conductivity, elastic modulus, and/or strength comparable to or greater than conventional graphite foam, carbon foam, or graphene foam. Another object of the present invention is to provide a humic acid-derived foam preferably having a mesoscale pore size range (2 to 50 nm).

Another object of the present invention is to provide products (eg, devices) containing the humic acid-derived foams of the present invention and methods of operating these products.

The present invention provides a humic acid-derived foam composed of a plurality of pores and pore walls, wherein the pore walls contain single-layer or multi-layer humic acid-derived hexagonal carbon sheets, and the multi-layer hexagonal carbon sheets have X-ray diffraction properties. It has 2 to 10 layers of stacked hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.60 nm (preferably 0.40 nm or less), as measured by . The single-layer or multi-layer hexagonal carbon sheet contains from 0.01% to 25% by weight of non-carbon elements. Humic acid (HA) is oxidized humic acid, reduced humic acid, fluorinated humic acid, chlorinated humic acid, brominated humic acid, iodinated humic acid, hydrogenated humic acid, nitrogenated humic acid, doped humic acid acids, chemically functionalized humic acids, or combinations thereof.

The humic acid-derived foams of the present invention are divided into three types: (a) at least 10 wt% (typically 10 wt% to 42 wt%, most typically 10 wt% to 25 wt%), which can be used in a wide range of applications; % by weight) of a humic acid (HA) foam containing non-carbon elements, wherein the original humic acid molecules remain substantially the same, but some chemical linkages between the HA molecules occur; (b) a chemically merged and reduced humic acid-based foam in which extensive linking and coalescing between original HA molecules has occurred to form pristine graphene-like hexagonal carbon sheets constituting the pore walls, resulting in HA molecules chemical species containing non-carbon elements originally attached to are released (thus, the non-carbon element content is generally reduced to 2% to 10% by weight); and (c) a humic acid-derived graphite foam containing essentially all carbon (non-carbon content of less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.1% by weight), wherein the pore walls are , containing monolayer or multilayer (2 to 10) graphene-like sheets that are hexagonal carbon atom planes.

Preferably and typically, the HA-derived foam has a density of 0.005 to 1.7 g/cm ³ , a specific surface area of 50 to 3,200 m ² /g, and/or a thermal conductivity per unit of specific gravity of at least 100 W/cm 3 . mK, and/or an electrical conductivity per unit of specific gravity of at least 500 S/cm. More typically, the humic acid-derived foam has a density of 0.01 to 1.5 g/cm ³ or an average pore size of 2 nm to 50 nm. In one embodiment, the foam has a specific surface area of 200 to 2,000 m ² /g or a density of 0.1 to 1.3 g/cm ³ .

Typically, when the HA-derived foam is produced from a process that does not include a heat treatment temperature (HTT) greater than 300° C., the foam has a content of non-carbon elements ranging from 10% to 42% by weight. The pore walls may still contain identifiable humic acid molecules, which are sheet-like hexagonal carbon atom structures. The non-carbon element may include an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. In a specific embodiment, the pore walls contain a fluorinated humic acid and the foam has a fluorine content of 0.01% to 25% by weight. In another embodiment, the foam has an oxygen content of 0.01% to 25% by weight.

For HTTs higher than 300 °C, closely packed and well-ordered neighboring HA molecules can chemically link together to form multi-ring aromatic structures similar to the initial graphene-like hexagonal carbon atom structure. As heat treatment continues, these highly aromatic molecules merge together in an edge-to-edge manner to increase the length and width of the graphene-like hexagonal planes, while at the same time, several hexagonal carbon planes are stacked together to form multilayer graphene. It is possible to form a multi-layered carbon atom structure similar to the structure. The interplanar spacing is typically reduced to << 0.60 nm, more typically less than 0.40 nm. When the HTT is from 300 °C up to 1,500 °C, it typically produces a chemically coalesced and reduced humic acid-based foam, in which extensive linking and coalescing between the pristine HA molecules takes place, resulting in pristine graphene-constituting the pore walls. A pseudo-hexagonal carbon sheet is formed. The specific carbon content in the foam is typically reduced from 2% to 10%.

When the HTT is between 1,500°C and 3,200°C, the foam may be essentially a graphite foam, in which the pore walls contain monolayer or multilayer graphene-like hexagonal carbon planes and the non-carbon content is less than 2% by weight. is reduced

In a preferred embodiment, the foam is in the form of a continuous-length roll sheet having a thickness of 200 μm or less and a length of at least 1 meter, preferably at least 2 meters, more preferably at least 10 meters, and most preferably at least 100 meters. (rolls of continuous foam sheet). These sheet rolls are produced by a roll-to-roll process. There are no HA-derived graphene-like foams made in the form of sheet rolls in the prior art.

In a preferred embodiment, the HA-derived foam has an oxygen content or specific carbon content of less than 1% by weight, and the pore walls have an interplanar spacing of less than 0.35 nm and/or a thermal conductivity per unit of specific gravity of at least 200 W/mK; / or has stacked graphene-like planes having an electrical conductivity per unit of specific gravity greater than or equal to 1,000 S/cm.

In a further preferred embodiment, the HA-derived foam has an oxygen content or specific carbon content of less than 0.1% by weight, and the pore walls have an interplanar spacing of less than 0.34 nm and/or a thermal conductivity per unit of specific gravity of at least 250 W /mK and/or contain layered graphene-like hexagonal carbon atom planes having an electrical conductivity per unit of specific gravity of at least 1,500 S/cm.

In another preferred embodiment, the graphene foam has an oxygen content or non-carbon content of 0.01% by weight or less, and the pore walls have an inter-graphene spacing of less than 0.336 nm and/or a mosaic dispersion value of 0.7 or less and/or , containing layered graphene-like planes having a thermal conductivity per unit of specific gravity of at least 300 W/mK and/or an electrical conductivity per unit of specific gravity of at least 2,000 S/cm.

In another preferred embodiment, the graphene foam has an interplanar spacing of less than 0.336 nm, a mosaic dispersion value of 0.4 or less, and/or a thermal conductivity per unit of specific gravity greater than 400 W/mK, and/or per unit of specific gravity. It has pore walls containing stacked graphene-like atomic planes with an electrical conductivity greater than 3,000 S/cm.

In a preferred embodiment, the pore walls contain layered graphene-like hexagonal carbon atom planes with an interplanar spacing of less than 0.337 nm and a tessellation dispersion value of less than 1.0. In a preferred embodiment, the foam exhibits a degree of graphitization greater than 80% (preferably greater than 90%) and/or a mosaic variance value less than 0.4. In a preferred embodiment, the pore walls contain a 3D network of interconnected graphene-like hexagonal carbon atom planes.

In a preferred embodiment, the solid foam contains mesoscale pores with a pore size of 2 nm to 50 nm. Solid foams can also be made to contain micro-scale pores (1 to 500 μm).

The HA-derived foam of the present invention may be produced by a process comprising the steps of: (a) preparing a humic acid dispersion having a plurality of humic acid molecules or sheets dispersed in a liquid medium, wherein the humic acid is Oxidized humic acids, reduced humic acids, fluorinated humic acids, chlorinated humic acids, brominated humic acids, iodinated humic acids, hydrogenated humic acids, nitrogenated humic acids, doped humic acids, chemically functionalized a humic acid, or a combination thereof, wherein the dispersion contains an optional blowing agent, wherein the blowing agent to humic acid weight ratio is from 0/1.0 to 1.0/1.0; (b) dispensing and depositing the graphene dispersion onto the surface of a supporting substrate (eg, plastic film, rubber sheet, metal foil, glass sheet, paper sheet, etc.) to form a wet layer of humic acid; (c) partially or completely removing the liquid medium from the wet layer of humic acid to form a dry layer of humic acid; and (d) a blowing agent or which induces the formation and release of volatile gas molecules from non-carbon elements (e.g., O, H, N, B, F, Cl, Br, I, etc.) to produce humic acid-derived foam. Heat treating the dry layer of humic acid at a first heat treatment temperature of 80° C. to 3,200° C. at a desired heating rate sufficient to activate the humic acid. Preferably, the dispensing and deposition procedure includes subjecting the humic acid dispersion to an orientation-induced stress.

This optional blowing agent is such that the HA material contains at least 5% by weight (preferably at least 10% by weight, more preferably at least 20% by weight, even more preferably at least 30% by weight) of non-carbon elements (eg O, H, N, B, F, Cl, Br, I, etc.). Subsequent high-temperature treatment serves to remove most of these non-carbon elements from the edges of the HA molecule, generating volatile gaseous species that create pores or cells in the solid foam structure. In other words, quite surprisingly, these non-carbon elements act as blowing agents. Accordingly, an externally added blowing agent is optional (but not essential). However, the use of a blowing agent may provide additional flexibility to control or tune the porosity level and pore size for a desired application. Blowing agents are typically required when the non-carbon element content in the humic acid is less than 5%.

The blowing agent may be a physical blowing agent, a chemical blowing agent, a mixture thereof, a dissolution-and-leaching agent, or a mechanically introduced blowing agent.

The process may further include heat treating the solid foam at a second heat treatment temperature higher than the first heat treatment temperature for a length of time sufficient to obtain a graphene-like foam, wherein the pore walls are between 0.3354 nm and 0.3354 nm. It contains stacked hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.40 nm and a content of non-carbon elements of less than 5% by weight (typically between 0.001% and 2% by weight). When the obtained non-carbon element content is 0.1% to 2.0%, the interplanar spacing d ₀₀₂ is typically 0.337 nm to 0.40 nm.

When the original HA molecules in the dispersion contain a non-carbon element content higher than 5% by weight, the hexagonal carbon atom planes (after heat treatment) in the solid foam contain structural defects induced during the heat treatment step (d). The liquid medium may simply be water and/or alcohol, which is environmentally friendly.

In a preferred embodiment, the present process includes steps (b) and (c) feeding the support substrate from a feeder roller to the deposition zone and continuously applying an HA dispersion on the surface of the support substrate to form a wet layer of HA material thereon. or intermittently, drying the wet layer of HA material to form a dried layer of HA material, and collecting the dried layer of HA material deposited on the supporting substrate on a collector roller. It is a two-roll process. This roll-to-roll or reel-to-reel process is a real industrial-scale high-volume manufacturing process that can be automated.

In one embodiment, the first heat treatment temperature is 100 °C to 1,500 °C. In another embodiment, the second heat treatment temperature comprises a temperature selected from at least (A) 300 to 1,500 °C, (B) 1,500 to 2,100 °C, and/or (C) 2,100 to 3,200 °C. In certain embodiments, the second heat treatment temperature includes a temperature in the range of 300 to 1,500 °C for at least 1 hour, followed by a temperature in the range of 1,500 to 3,200 °C for at least 1 hour.

There are several surprises as a result of performing the first and/or second heat treatment on the dried HA layer, different heat treatment temperature ranges allow achieving different objectives: (a) the release of non-carbon elements from the HA material. removal (e.g., thermal reduction of fluorinated humic acid to obtain reduced humic acid), which generates volatile gases to create pores or cells in the HA foam; (b) activates a chemical or physical blowing agent to (c) chemical linking or incorporation of humic acid molecules into highly aromatic molecules, and edge-to-edge incorporation of aromatic ring structures or hexagonal carbon planes in foam walls (solid parts of the foam) to create pores or cells; Significantly increase the lateral dimensions (length and width) of graphene-like hexagonal carbon sheets of (d) repair defects naturally present in HA or caused during fluorination, oxidation, or nitrogenation of humic acid molecules, and (e) Reorganization and perfection of graphite domains or graphite crystals. These different purposes or functions are achieved to different degrees within different temperature ranges. Non-carbon elements typically include elements selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. Quite surprisingly, even under low-temperature foaming conditions, heat treatment often results in edge-to-edge (some, face-to-face) chemical linking, coalescence, or induce chemical bonds.

In one embodiment, the HA-derived foam has a specific surface area of 200 to 2,000 m 2 /g. In one embodiment, the solid foam has a density of 0.1 to 1.5 g/cm 3 . In one embodiment, step (d) of heat treating the HA material layer at the first heat treatment temperature is performed under compressive stress. In another embodiment, the process includes a compression step to reduce the thickness, pore size, or porosity level of the film of the HA-derived foam. In some applications, the foam has a thickness of 200 μm or less.

In one embodiment, the HA dispersion has at least 5% by weight of HA dispersed in a liquid medium to form a liquid crystalline phase. In one embodiment, the first heat treatment temperature contains a temperature in the range of 80 ° C to 300 ° C, and as a result, the HA foam has an oxygen content or non-carbon element content of less than 5%, and the pore walls are less than 0.40 nm. interplanar spacing, a thermal conductivity per unit of specific gravity of at least 150 W/mK (more typically, at least 200 W/mk), and/or an electrical conductivity per unit of specific gravity of at least 1,000 S/cm.

In a preferred embodiment, the first heat treatment temperature and/or the second heat treatment temperature contains a temperature in the range of 300° C. to 1,500° C. As a result, the HA-derived foam has an oxygen content or non-carbon content of less than 2%. and the pore walls have an interplanar spacing of less than 0.35 nm, a thermal conductivity per unit of specific gravity of at least 250 W/mK, and/or an electrical conductivity per unit of specific gravity of at least 1,500 S/cm.

When the first heat treatment temperature and/or the second heat treatment temperature contain a temperature in the range of 1,500°C to 2,100°C, the HA-derived foam has an oxygen content or non-carbon content of less than 1%, and a pore wall of 0.34 nm an intergraphene spacing of less than or equal to, a thermal conductivity per unit of specific gravity of at least 300 W/mK, and/or an electrical conductivity per unit of specific gravity of at least 3,000 S/cm.

When the first heat treatment temperature and/or the second heat treatment temperature contain a temperature higher than 2,100°C, the HA-derived foam has an oxygen content or non-carbon content of 0.1% or less, and the pore walls are less than 0.336 nm interplanar. spacing, a mosaic dispersion value of 0.7 or less, a thermal conductivity per unit of specific gravity of at least 350 W/mK, and/or an electrical conductivity per unit of specific gravity of at least 3,500 S/cm.

When the first heat treatment temperature and/or the second heat treatment temperature contain a temperature of 2,500° C. or higher, the HA-derived foam has an interplanar spacing of less than 0.336 nm, a mosaic dispersion value of 0.4 or less, and a specific gravity greater than 400 W/mK per unit. It has pore walls containing stacked graphene-like hexagonal carbon planes with high thermal conductivity and/or electrical conductivity greater than 4,000 S/cm per unit of specific gravity.

In one embodiment, the pore walls contain stacked graphene-like hexagonal carbon planes with an interplanar spacing of less than 0.337 nm and a tessellation dispersion value of less than 1.0. In another embodiment, the solid wall portion of the HA-derived foam exhibits a degree of graphitization of 80% or greater and/or a mosaic dispersion value of less than 0.4. In another embodiment, the solid wall portion of the HA-derived foam exhibits a graphitization degree of 90% or greater and/or a mosaic dispersion value of 0.4 or less.

Typically, after heat treatment at HTT higher than 2,500 °C, the pore walls in HA-derived graphite foam contain a 3D network of interconnected hexagonal carbon atom planes that are electron-conducting pathways. The cell wall is 20 nm or greater, more typically and preferably 40 nm or greater, even more typically and preferably 100 nm or greater, even more typically and preferably 500 nm or greater, often greater than 1 μm, and sometimes 10 μm. It contains graphitic domains or graphitic crystals with a lateral dimension (L _a , length or width) greater than The graphitic domains typically have a thickness of 1 nm to 20 nm, more typically 1 nm to 10 nm, even more typically 1 nm to 4 nm.

Preferably, the HA-derived foam contains mesoscale pores with a pore size of 2 nm to 50 nm (preferably 2 nm to 25 nm).

In a preferred embodiment, the present invention provides a roll-to-roll process for producing a solid HA foam or HA-derived foam composed of multiple pores and pore walls. The process includes the following steps: (a) preparing a humic acid dispersion having a plurality of humic acid molecules or sheets dispersed in a liquid medium, wherein the humic acid is oxidized humic acid, reduced humic acid, fluorinated humic acid selected from humic acids, chlorinated humic acids, brominated humic acids, iodinated humic acids, hydrogenated humic acids, nitrogenated humic acids, doped humic acids, chemically functionalized humic acids, or combinations thereof; wherein the dispersion contains an optional blowing agent, wherein the blowing agent to humic acid weight ratio is from 0/1.0 to 1.0/1.0; (b) distributing and depositing the HA dispersion continuously or intermittently on the surface of a supporting substrate to form a wet layer of HA material, wherein the supporting substrate is a continuous thin film supplied from a supply roller and collected on a collecting roller; phosphorus, step; (c) partially or completely removing the liquid medium from the wet layer of humic acid in one or more heating zones to form a dry layer of humic acid; and (d) a temperature of 80° C. to 500° C. at a desired heating rate sufficient to activate the blowing agent to produce a humic acid-derived foam having a density of 0.01 to 1.7 g/cm ³ or a specific surface area of 50 to 3,000 m ² /g. Heat treating the dry layer of humic acid in one of these heating zones comprising a heating temperature. In this process, heat treatment takes place in situ during the roll-to-roll process. This is a very cost-effective process suitable for mass production of sheets of HA-derived graphite foam rolled onto rollers for ease of transport and handling, and subsequently, ease of cutting and slitting.

Orientation-induced stress may be shear stress. As an example, shear stress can be encountered in situations as simple as a "doctor blade", which guides the spreading of the HA dispersion onto a plastic or glass surface at a sufficiently high shear rate during the manual casting process. As another example, effective orientation-induced stress can be achieved by automated roll-to-roll, in which a "knife-on-roll" configuration dispenses a graphene dispersion onto a moving solid substrate, such as a plastic film. -to-roll) produced in the coating process. The relative movement between this moving film and the coating knife serves to achieve orientation of the graphene sheet along the shear stress direction. Comma coating and slot-die coating are particularly effective methods for this function.

This orientation-induced stress is such that the shear stress moves the HA molecules or sheets in a specific direction (e.g., the X-direction or the longitudinal-direction) to create a preferred orientation and facilitate contact between the HA molecules or sheets along the foam walls. ) is a very important step in the production of HA-derived foams of the present invention. Also surprisingly, this preferred orientation and improved HA-to-HA contact facilitates chemical incorporation or linkage between HA molecules or sheets during subsequent heat treatment of the dried HA layer. This preferred orientation and improved contact are essential to finally achieve the exceptionally high thermal conductivity, electrical conductivity, elastic modulus, and mechanical strength of the resulting HA-derived foam. In general, these superior properties could not be obtained without such shear stress-induced orientation control.

The present invention also provides an oil-removing device or oil-separating device containing humic acid-derived foam as an oil-absorbing element. A solvent-removal device or solvent-separation device containing humic acid-derived foam as a solvent-absorbing or solvent-separating element is also provided.

The invention also provides a method for separating oil from water. The method includes the following steps: (a) providing an oil-absorbing element comprising integral humic acid-derived foam; (b) contacting the oil-water mixture with urea to absorb oil from the mixture; (c) reprocessing urea from the mixture and extracting oil from the urea; and (d) reusing the element.

Additionally, the present invention provides methods for separating organic solvents from solvent-water mixtures or from multi-solvent mixtures. The method includes the following steps: (a) providing an organic solvent-absorbing or solvent-separating element comprising an integral humic acid-derived foam; (b) contacting the urea with an organic solvent-water mixture or a multi-solvent mixture containing a first solvent and at least a second solvent; (c) enabling the urea to absorb the organic solvent from the mixture or at least to separate the first solvent from the second solvent; (d) reprocessing the urea from the mixture and extracting the organic solvent or first solvent from the urea; and (e) reusing the element.

A thermal management device containing humic acid-derived foam as a heat spreading or heat dissipating element is also provided. Thermal management devices include heat exchangers, heat sinks, heat pipes, high-conductivity inserts, conductive plates between heat sinks and heat sources, heat-spreading components, heat-dissipating components, thermal interface media, or thermoelectric or Peltier devices. (Peltier) may include a device selected from cooling devices.

Humic acid (HA) is an organic substance commonly found in soil and can be extracted from soil using a base (eg KOH). HA can also be extracted from a type of coal called soft coal, which is a highly oxidized form of lignite. HA extracted from soft brown coal contains a number of oxygenated groups (eg, carboxyl groups) located around the edges of the graphene-like molecular center (SP ² core of hexagonal carbon structure). This material is slightly similar to graphene oxide (GO) produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5% to 42% by weight (other major elements being carbon, hydrogen, and nitrogen). An example of the molecular structure of humic acids, with various components including quinones, phenols, cafecol and sugar moieties, is provided in Scheme 1 below (source: Stevenson FJ "Humus Chemistry: Genesis, Composition, Reactions ," John Wiley & Sons, New York 1994 ]).

[Scheme 1]

Non-aqueous solvents for the humic acid include polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine solvents, amide solvents, alkylene carbonates, organic acids, or inorganic acids.

The present invention provides a humic acid-derived foam composed of multiple pores and pore walls and a process for producing the same. The pores in the foam are such that the sheet-like humic acid molecules are (1) chemically linked/merged together (edge-to-edge and/or face-to-face), typically at temperatures of 100 to 1,500° C., and/or or (2) formed during or after organization (referred to herein as graphitization) into larger graphitic crystals or domains along the pore walls at high temperatures (typically greater than 2,100° C., more typically greater than 2,500° C.).

The present invention also provides a production process comprising the following steps: (a) preparing a humic acid dispersion having a plurality of humic acid molecules or sheets dispersed in a liquid medium, wherein the humic acid is an oxidized humic acid, a reduced humic acid humic acid, fluorinated humic acid, chlorinated humic acid, brominated humic acid, iodinated humic acid, hydrogenated humic acid, nitrogenated humic acid, doped humic acid, chemically functionalized humic acid, or any of these wherein the dispersion contains an optional blowing agent, wherein the blowing agent to humic acid weight ratio is from 0/1.0 to 1.0/1.0; (b) dispensing and depositing the graphene dispersion onto the surface of a supporting substrate (eg, plastic film, rubber sheet, metal foil, glass sheet, paper sheet, etc.) to form a wet layer of humic acid; (c) partially or completely removing the liquid medium from the wet layer of humic acid to form a dry layer of humic acid; and (d) to induce volatile gas molecules from non-carbon elements (e.g., O, H, N, B, F, Cl, Br, I, etc.) or activate blowing agents to produce humic acid-derived foams. Heat treating the dry layer of humic acid at a first heat treatment temperature of 80° C. to 3,200° C. at a sufficient desired heating rate. Preferably, the dispensing and deposition procedure includes subjecting the humic acid dispersion to an orientation-induced stress. When these non-carbon elements are removed through heat-induced decomposition, they produce volatile gases that act as foaming or blowing agents.

The resulting humic acid-derived foam typically has a density of 0.005 to 1.7 g/cm ³ (more typically 0.01 to 1.5 g/cm ³ , even more typically 0.1 to 1.0 g/cm ³ , most typically 0.2 to 1.0 g/cm 3 ). 0.75 g/cm ³ ), or a specific surface area of 50 to 3,000 m ² /g (more typically 200 to 2,000 m ² /g, most typically 500 to 1,500 m ² /g).

A foaming agent or foaming agent is a material capable of producing cells or foamed structures through a foaming process in a variety of materials that undergo curing or phase transition, such as polymers (plastics and rubbers), glass, and metals. This is typically applied when the material being foamed is in a liquid state. Previously, it was not known that a blowing agent could be used to create a foamed material while in the solid state. More significantly, it has not been previously taught or suggested that aggregates of humic acid molecules can be converted to graphene-like foams via a blowing agent. Cellular structures in the matrix are typically created with the goal of reducing density and increasing heat and sound insulation while increasing the thickness and relative stiffness of the original polymer.

Blowing agents or related foaming mechanisms that create pores or cells (bubbles) in a matrix to produce foamed or cellular materials can be classified into the following groups:

(a) Physical blowing agents: eg, hydrocarbons (eg, pentane, isopentane, cyclopentane), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and liquid CO ₂ . The bubble/foam-generating process is an endothermic process, ie it requires heat (e.g., from a melting process or chemical exotherm due to crosslinking) to volatilize the liquid blowing agent.

(b) Chemical blowing agents: eg isocyanates, azo-, hydrazine, and other nitrogen-based materials (for thermoplastic and elastomeric foams), sodium bicarbonate (eg baking soda, used in thermoplastic foams) . Here, gaseous products and other by-products are formed by chemical reactions, catalyzed by the exothermic heat of the process and reacting polymers. Since the foaming reaction involves forming a low molecular weight compound that acts as a foaming gas, additional exothermic heat is also released. Titanium hydride powder is used as a foaming agent in the production of metal foam as it decomposes at elevated temperatures to form titanium and hydrogen gas. Zirconium(II) hydride is used for the same purpose. Immediately after being formed, the low molecular weight compound will never return to the original blowing agent(s), ie the reaction is irreversible.

(c) Mixed physical/chemical blowing agents: used, for example, to produce flexible polyurethane (PU) foams with very low densities. Both chemical and physical foaming can be used together to balance each other with respect to released/absorbed thermal energy. Accordingly, the temperature rise is minimized. For example, isocyanates and water (which react to form CO ₂ ) together with liquid CO ₂ (which boils to give a gaseous form) in the production of very low density flexible PU foam for mattresses. used

(d) Mechanically Injected Agents: Mechanically prepared foams involve incorporating bubbles into a liquid polymerizable matrix (e.g., unvulcanized elastomer in the form of liquid latex). These methods include whisking-in of air or other gases or low-boiling volatile liquids into a low-viscosity grid, injecting the gas into an extruder barrel or die or into an injection molding barrel or nozzle, and injecting very fine bubbles or gases into the melt. and uniformly dispersing the gas by the shearing/mixing action of the screw to form a solution of When the melt is molded or extruded and the part is at atmospheric pressure, gases come out of solution just before solidification to expand the polymer melt.

(e) Soluble and Leachable Agents: Soluble fillers, for example solid sodium chloride crystals that are mixed into a liquid urethane system and then shaped into solid polymer parts, which then form solid molded parts in water for a while. Cleaned by impregnation, it forms small interconnected holes in a relatively high-density polymer product.

(f) We have found that all of the above five mechanisms can be used to create pores in HA-derived materials while in the solid state. Another mechanism for creating pores in HA materials is through vaporization and evolution of volatile gases by removing such non-carbon elements in a high temperature environment. This is a unique self-foaming process that has never been taught or suggested before.

The pore walls (cell walls) in the foams of the present invention contain chemically bonded and merged graphene-like hexagonal carbon atom planes. The carbon atoms of these planar aromatic molecules or hexagonal structures are well interconnected physically and chemically. The lateral dimensions (length or width) of these planes are large (20 nm to greater than 10 μm), typically many or even tens of times the maximum length/width of the starting humic acid molecules. Hexagonal carbon atom planes are intrinsically interconnected to form long electron-conducting pathways with low resistance. This is a unique and novel class of substances that have not been previously discovered or developed or suggested to be likely to exist.

In step (b), the HA suspension is preferably formed into a wet layer on a solid substrate surface (eg PET film or glass) under the influence of shear stress. One example of such a shearing procedure is to cast or coat a thin film of HA suspension using a coating machine. This procedure is similar to a layer of varnish, paint, coating, or ink being coated onto a solid substrate. A roller, "doctor's blade," or wiper is capable of generating shear stress at sufficiently high relative motion velocities as the film is being shaped, or when there is relative motion between the roller/blade/wiper and the supporting substrate. can Quite unexpectedly and remarkably, this shear action causes the planar HA molecules to align well, eg along the shear direction. Even more surprisingly, this state of molecular alignment or preferred orientation is not destroyed when the liquid component of the HA suspension is subsequently removed to form a well-packed layer of at least partially dried, highly ordered, sheet-like HA molecules. The dried HA film has a high birefringence coefficient between the in-plane direction and the normal-to-plane direction.

In one embodiment, this HA layer is then subjected to a thermally-induced reaction to remove non-carbon elements (eg, F, O, etc.) from the HA molecules to generate volatile gases as by-products and/or It is treated with a heat treatment to activate the blowing agent. These volatile gases generate pores or bubbles inside the solid HA material, pushing sheet-like HA molecules into the wall structure, forming the HA foam. When no blowing agent is added, the non-carbon elements in the HA material preferably account for at least 10% by weight (preferably at least 20% by weight, and more preferably at least 30% by weight) of the HA material. The first (initial) heat treatment temperature is typically greater than 80°C, preferably greater than 100°C, more preferably greater than 300°C, even more preferably greater than 500°C, and may be as high as 1,500°C. Blowing agents are typically activated at temperatures from 80° C. to 300° C., but higher may be possible. The foaming procedure (formation of pores, cells or bubbles) is typically completed within a temperature range of 80 to 1,500°C. Quite surprisingly, chemical linking or merging between hexagonal carbon atom planes in an edge-to-edge and face-to-face manner ( FIG. 2 ) can occur at relatively low annealing temperatures (e.g., as low as 150 to 300° C.). there is.

The HA-derived foam may be subjected to an additional heat treatment comprising at least a second temperature significantly higher than the first heat treatment temperature.

A suitably programmed heat treatment procedure may include only a single heat treatment temperature (e.g., only a first heat treatment temperature), at least two heat treatment temperatures (a first temperature for a period of time, and then, a second temperature raised for a predetermined period of time). maintained at this second temperature), or any other combination of heat treatment temperatures (HTT) including an initial treatment temperature (first temperature) and a final heat treatment temperature (HTT) (second) (higher than the first temperature). can include The highest or final HTT over which the dried HA layer is formed can be divided into four distinct HTT regimes:

Mode 1 (80° C. to 300° C.): In this temperature range (chemical linking and thermal reduction mode, and also activation mode for the blowing agent, if present), the HA layer undergoes heat-induced chemical linking of neighboring HA molecules. mainly suffered, as schematically illustrated in the upper part of FIG. 2 . This also involves the removal of some non-carbon atoms, such as O and H, resulting in a reduction of the oxygen content, typically from 20 to 42% (of O in HA) to approximately 10 to 25%. This treatment reduces the interplanar spacing in the foam wall from approximately 0.6 to 1.2 nm (dry) to approximately 0.4 to 0.6 nm, and increases the thermal conductivity to 100 W/mK per unit of specific gravity and/or up to 2,000 S per unit of specific gravity. It causes an increase in electrical conductivity up to /cm. (Because you can vary the level of porosity, and thus the specific gravity, of the graphene foam material, and given the same graphene material, both the thermal and electrical conductivities vary with specific gravity, Values for these properties should be divided by specific gravity to facilitate fair comparisons). Even in this low temperature range, some chemical linkages occur between HA molecules. The interplanar spacing remains relatively large (0.4 nm or greater). A number of O-containing functional groups exist (eg, -OH and -COOH).

Method 2 (300° C. to 1,500° C.): In this chemical linking and merging method, extensive chemical combination, polymerization, and crosslinking between adjacent HA molecules or linked HA molecules occur, resulting in initial graphene-like hexagonal carbon forming an atomic plane, as illustrated in the lower part of FIG. 2 . The oxygen content is typically reduced to between 2% and 10% (eg, after chemical coupling and merging), resulting in a reduced interplanar spacing to approximately 0.345 nm. This is in stark contrast to conventional graphitizable materials (e.g., carbonized polyimide films), which typically require temperatures as high as 2,500°C to initiate graphitization, suggesting that some initial graphitization has already initiated at these low temperatures. it means. This is another distinct feature of the graphene foam of the present invention and its production process. This chemical coupling reaction results in an increase in thermal conductivity up to greater than 250 W/mK per unit of specific gravity, and/or an increase in electrical conductivity up to 2,500 to 4,000 S/cm per unit of specific gravity.

Mode 3 (1,500 to 2,500° C.): In this alignment and graphitization mode, extensive graphitization or merging of graphene-like planes takes place, significantly improving the degree of improved structural alignment in the foam wall. As a result, the oxygen content is typically reduced by 0.1% to 2%, and the inter-graphene spacing is reduced to approximately 0.337 nm (depending on the actual HTT and time length, achieving a degree of graphitization of 1% to approximately 80%). The improved degree of alignment is also reflected by an increase in thermal conductivity to greater than 350 W/mK per unit of specific gravity, and/or an increase in electrical conductivity to greater than 3,500 S/cm per unit of specific gravity.

Manner 4 (greater than 2,500 °C): In this recrystallization and finishing scheme, extensive migration and removal of grain boundaries and other defects occurs, leading to the formation of nearly complete mono- or polycrystalline graphene-like crystals with large grains in the foam walls. , which can be several orders of magnitude larger than the original size of the HA molecule. The oxygen content is essentially eliminated and is typically between 0% and 0.01%. The interplanar spacing is reduced to approximately 0.3354 nm (80% to nearly 100% graphitization), corresponding to the interplanar spacing of perfect graphite single crystals. The foamed structure thus obtained exhibits a thermal conductivity of greater than 400 W/mK per unit of specific gravity and an electrical conductivity of greater than 4,000 S/cm per unit of specific gravity.

The HA-derived foam structure of the present invention is prepared by adding dried HA to a temperature program comprising at least a first mode, typically requiring 1 to 4 hours in this temperature range if the temperature does not exceed 500°C. , more typically including the first two modalities (preferably 1 to 2 hours), even more typically the first three modalities (preferably 0.5 to 2.0 hours in modality 3), all four modalities (including modality 4 for 0.2 to 1 hour, which can be run to achieve the highest conductivity).

X-ray diffraction patterns were obtained with an X-ray diffractometer equipped with CuKcv radiation. Shifts and broadening of the diffraction peaks were corrected using silicon powder standards. The degree of graphitization (g) is calculated using Mering's equation, d ₀₀₂ = 0.3354 g + 0.344 (1 - g), where d ₀₀₂ is the interlayer spacing of graphite- or graphene-type crystals in units of nm. was calculated from the X-ray pattern. This equation is valid only when d ₀₀₂ is approximately 0.3440 nm or less. HA-derived foam walls with d ₀₀₂ higher than 0.3440 nm have oxygen-containing functional groups acting as spacers to increase the interplanar spacing (e.g., -OH on graphene-like molecular planar surfaces or edges, >0, and -COOH).

Another structural index that can be used to characterize the degree of alignment of the stacked and bonded hexagonal carbon atom planes in the foam walls of HA-derived graphene-like and conventional graphite crystals is the "mosaic spread", which is It is expressed by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection. This degree of alignment characterizes the graphite or graphene crystallite size (or grain size), the amount of grain boundaries and other defects, and the degree of preferred grain orientation. Almost perfect monocrystals of graphite are characterized by having mosaic dispersion values between 0.2 and 0.4. Most of the graphene walls of the present invention have mosaic dispersion values in this range of 0.2 to 0.4 (when produced with a heat treatment temperature (HTT) of 2,500° C. or higher). However, some values range from 0.4 to 0.7 for HTT from 1,500 to 2,500 °C and from 0.7 to 1.0 for HTT from 300 to 1,500 °C.

The most likely chemical linking and merging mechanism is illustrated in Figure 2, where only two aligned HA molecule segments are shown as an example, but multiple HA molecules can be chemically linked together, and multiple "linked "HA molecules" can be chemically incorporated to form a foam wall. In addition, chemical linking can occur face-to-face, not just edge-to-edge to HA molecules or sheets. These linking and merging reactions proceed in such a way that the molecules are chemically merged, linked, and integrated into one single entity. The resulting product is not a simple aggregate of individual HA sheets, but a single entity that is essentially a network of interconnected macromolecules with essentially infinite molecular weight. All of the constituent hexagonal carbon planes have very large lateral dimensions (length and width), and if the HTT is sufficiently high (eg, above 1,500° C. or even higher), these planes are essentially bonded together.

In-depth studies using a combination of SEM, TEM, selected area diffraction, X-ray diffraction, AFM, Raman spectroscopy and FTIR have revealed that HA-derived foam walls are composed of several large hexagonal carbon atom planes (typically >> 20 nm, more typically, >> 100 nm, often >> 1 μm, and in many cases, >> 10 μm, or even >> 100 μm). These giant graphene-like planes are often formed in the thickness direction (crystallographic c-axis direction) via van der Waals forces (as in conventional graphite crystallites) as well as covalent bonds, when the final heat treatment temperature is lower than 2,500 °C. are laminated and combined along In this case, without wishing to be bound by theory, Raman and FTIR spectroscopy studies appear to indicate the coexistence of sp ² (dominant) and sp ³ (present but weak) electronic configurations, rather than the usual sp ² in graphite. .

(1) These HA-derived graphite foam walls are not made by gluing or bonding separate flakes/plates together with a resin binder, linker, or adhesive. Instead, the HA molecules are incorporated into integrated graphene-like crystalline entities via linkage or formation of covalent bonds with each other, without the use of any externally added linker or binder molecules or polymers.

(2) Foam walls are typically polycrystalline, composed of large grains with imperfect grain boundaries. This entity is derived from multiple HA molecules, and these aromatic HA molecules have lost their original identity. Upon removal of the liquid component from the suspension, the resulting HA molecules essentially form an amorphous structure. Upon heat treatment, these HA molecules are chemically merged and linked to form monolithic or monolithic graphite entities that make up the foam walls. This foam wall is highly ordered.

(3) their distinctive chemical composition (including oxygen or non-carbon content), morphology, crystal structure (including interplanar spacing), and structural characteristics (e.g., high degree of orientation, very few defects, imperfect grain boundaries, Due to the chemical bonding and the absence of gaps between the graphene sheets, and virtually no breaks in the hexagonal carbon plane), the HA-derived foam exhibits remarkable thermal conductivity, electrical conductivity, mechanical strength, and stiffness (elasticity). modulus).

It may be further mentioned that certain desired hydrophilicities can be imparted to the pore walls of humic acid-derived foams when the content of non-carbon elements (H and O) is between 2 and 20% by weight. These features enable separation of oil from water by selectively absorbing oil from an oil-water mixture. In other words, such HA-derived foam materials can recover oil from water, which helps clean up oil-spill rivers, lakes, or oceans. The oil absorption capacity is typically 50% to 500% of the foam's own weight. It is a very useful material for environmental protection purposes.

If high electrical or thermal conductivity is required, the HA-carbon foam can be subjected to a graphitization treatment at temperatures higher than 2,500 °C. The resulting material is particularly useful for thermal management applications (eg, for use in making finned heat sinks, heat exchangers, or heat spreaders).

It may be said that the HA-carbon foam may undergo compression during and/or after the graphitization process. This operation allows tuning of the graphene sheet orientation and porosity.

In order to characterize the structure of the resulting graphite material, an X-ray diffraction pattern was obtained using an X-ray diffractometer equipped with CuKcv radiation. Silicon powder standards were used to correct the shift and broadening of the diffraction peaks. Degree of graphitization from the X-ray pattern using Mering's Eq, d ₀₀₂ = 0.3354 g + 0.344 (1 - g ), where d ₀₀₂ is the interlayer spacing of graphite or graphene crystals (unit: nm), g was calculated. This equation is valid only when d ₀₀₂ is approximately 0.3440 nm or less. In this study, graphene-like (HA or RHA) foam walls with d ₀₀₂ greater than 0.3440 nm have oxygen-containing functional groups (e.g., -OH, >O, and -COOH on graphene molecular planar surfaces or edges). , these oxygen-containing functional groups act as spacers to increase the spacing between graphenes.

Another structural index that can be used to characterize the degree of order of the stacked and bonded RHA planes in the foam walls of graphene and conventional graphite crystals is the "mosaic spread", which is either (002) or (004). ) expressed by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the reflection. This degree of order characterizes the graphite or graphene crystallite size (or grain size), the amount of grain boundaries and other defects, and the degree of preferred grain orientation. Almost perfect single crystals of graphite are characterized by mosaic dispersion values of 0.2 to 0.4. Most of the RHA walls of the present invention (when produced with a heat treatment temperature (HTT) of 2,500° C. or higher) have mosaic dispersion values within this range of 0.2 to 0.4. However, some values are in the range of 0.4 to 0.7 for HTT of 1,500 to 2,500 °C, and in the range of 0.7 to 1.0 for HTT of 300 to 1,500 °C.

Thorough studies using a combination of SEM, TEM, selected area diffraction, X-ray diffraction, AFM, Raman spectroscopy, and FTIR have shown that the humic acid-carbon foam walls have several large graphic planes (length/width typically >> 20 nm, more typically >> 100 nm, often >> 1 μm, and in many cases >> 10 μm). This is very unexpected, since the lateral dimensions (length and width) of the pristine humic acid sheet or molecule before heat treatment are typically less than 20 nm, more typically less than 10 nm. This implies that multiple HA sheets or molecules can be merged edge-to-edge through covalent bonds with each other to form larger (longer or wider) sheets.

These large graphene-like planes can also be stacked and bonded along the thickness direction (crystallographic c- axis direction), which is often due to the final heat treatment temperature, as well as van der Waals forces (as in conventional graphite crystallites). is also achieved through covalent bonding if is less than 2,500 °C. In these cases, without wishing to be limited by theory, Raman and FTIR spectroscopy studies indicate the coexistence of sp ² (predominant) and sp ³ (weak but present) electron configurations, as well as the usual sp ² in graphite. see.

Integral HA-derived foams are composed of multiple pores and pore walls, and the pore walls contain single- or multi-layer HA sheets chemically bonded together, wherein the multi-layer HA sheets are determined by X-ray diffraction. 2 to 10 layers of stacked graphene-like merged HA planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.36 nm, and the single-layer or multi-layer graphene-like HA sheet has 0.01 wt. It contains 25% by weight of non-carbon elements (more typically less than 15%).

Typically, the integral HA-derived foam has a density of 0.001 to 1.7 g/cm ³ , a specific surface area of 50 to 3,000 m ² /g, and/or a thermal conductivity per unit of specific gravity of at least 200 W/mK and/or , the electrical conductivity per unit of specific gravity is 2,000 S/cm or more. In a preferred embodiment, the pore walls contain stacked graphene-like RHA planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm as measured by X-ray diffraction.

Most of the HA sheets can merge edge-to-edge through covalent bonds with each other to form a unified reduced HA (RHA) entity. Their distinctive chemical composition (including oxygen or hydrogen content, etc.), morphology, crystal structure (including interplanar spacing), and structural characteristics (eg, degree of orientation, very few defects, chemical bonding, and graphene- Due to the absence of gaps between like sheets, and virtually no breaks along the hexagonal planar direction), HA-derived foams exhibit a unique combination of remarkable thermal conductivity, electrical conductivity, mechanical strength, and stiffness (elastic modulus). have

thermal management applications

The above mentioned features and properties make integral HA-derived foams an ideal component for a wide range of engineering and biomedical applications. For example, for thermal management only purposes, the foam can be used in the following applications:

a) HA-derived foams that are compressible and have high thermal conductivity are ideally suited for use as a thermal interface material (TIM) that can be implemented between a heat source and a heat spreader or between a heat source and a heat sink.

b) HA-derived foam can be used as a heat spreader itself due to its high thermal conductivity.

c) HA-derived foam as a heat sink or heat dissipation material due to its high heat-diffusion ability (high thermal conductivity) and high heat-dissipation ability (many surface pores lead to huge air-convection micro- or nano-channels) can be used

d) light weight (low density adjustable between 0.001 and 1.8 g/cm ³ ), high thermal conductivity per unit of specific gravity or per unit of physical density, and high structural integrity (HA sheets are merged together to form long electron-conducting pathways) makes these HA-derived foams ideal materials for durable heat exchangers.

HA-derived foam-based thermal management or heat dissipation devices include heat exchangers, heat sinks (e.g., finned heat sinks), heat pipes, high-conductivity inserts, thin or thick conductive plates (heat sinks and heat sources). between), thermal interface media (or thermal interface materials, TIMs), thermoelectric or Peltier cooling plates, and the like.

A heat exchanger is a device used to transfer heat between one or more fluids; For example, gas and liquid flow separately in different channels. Fluids are typically separated by solid walls to prevent mixing. The HA-derived foam material of the present invention is an ideal material for such a wall, unless the foam is a fully open cell foam allowing the mixing of fluids. The method of the present invention enables the creation of both open cell foam structures and closed cell foam structures. A high surface pore area enables very rapid heat exchange between two or multiple fluids.

Heat exchangers are widely used in refrigeration systems, air conditioning units, heaters, power plants, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. A well-known example of a heat exchanger is found in internal combustion engines, where circulating engine coolant flows through radiator coils while air flows past the coils, which cools the coolant and heats the incoming air. The solid walls (eg those that make up the radiator coils) are typically made of high thermal conductivity materials such as Cu and Al. HA-derived foams of the present invention with higher thermal conductivity or higher specific surface area are excellent replacements for Cu and Al, for example.

There are many types of heat exchangers available commercially: shell and tube heat exchanger, plate heat exchanger, plate and shell heat exchanger, adiabatic wheel heat exchanger ( adiabatic wheel heat exchanger), plate fin heat exchanger, pillow plate heat exchanger, fluid heat exchanger, waste heat recovery unit, dynamic scraped surface heat exchanger, Phase change heat exchangers, direct contact heat exchangers, and microchannel heat exchangers. All of these types of heat exchangers can take advantage of the exceptionally high thermal conductivity and specific surface area of the foam material of the present invention.

The solid HA-derived foams of the present invention can also be used in heat sinks. Heat sinks are widely used in electronic devices for heat dissipation purposes. Central processing units (CPUs) and batteries in portable microelectronic devices (eg, notebook computers, tablets, and smart phones) are well-known sources of heat. Typically, a metal or graphite object (eg Cu foil or graphite foil) is brought into contact with a hot surface, and such object transfers heat (mainly by conduction and convection and to a lesser extent by radiation) to an outer surface or It helps diffuse into the outside air. In most cases, a thin thermal interface material (TIM) mediates between the hot surface of the heat source and the heat-spreading surface of the heat spreader or heat sink. (The HA-derived foam of the present invention can also be used as a TIM.)

A heat sink is a structure of highly conductive material having one or more flat surfaces to ensure good thermal contact with the components to be cooled, and a comb to increase the surface contact with air and thus the rate of heat dissipation. It usually consists of an array of comb or fin-like protrusions. A heat sink may be used in conjunction with a fan to increase the speed of airflow over the heat sink. Heat sinks may have multiple fins (extended or raised surfaces) to improve heat transfer. In an electronic device with a limited amount of space, the shape/arrangement of fins must be optimized to maximize heat transfer density. Alternatively or additionally, a cavity (inverted fin) may be embedded in the region formed between adjacent fins. These cavities are effective in extracting heat from the various heat generating bodies to the heat sink.

Typically, an integrated heat sink includes a heat collection member (core or base) and at least one heat dissipation member (eg, fin or plurality of fins) integral to the heat collection member (base) to be a finned heat sink. form Without the use of externally applied adhesives or mechanical fastening means to connect the pins to the core, the pins and cores are naturally connected or integrated together to form an integrated body. The heat collection base has a surface in thermal contact with a heat source (eg, an LED), collects heat from this heat source, and dissipates the heat through fins into the air.

As an illustrative example, FIG. 10 provides schematic diagrams of two heat sinks 300 and 302 . The first one houses a heat collecting member (or base member) 304 and a number of fins or heat dissipating members (eg, fins 306 ) connected to the base member 304 . Base member 304 is shown having a heat collection surface 314 intended to be in thermal contact with a heat source. A heat dissipating member or fin 306 is shown having at least a heat dissipating surface 320 .

A particularly useful embodiment is an integral radial heat sink 302 comprising a radially finned heat sink assembly comprising: (a) a base 308 comprising a heat collection surface 318 ; and (b) a plurality of spaced apart parallel planar fin members (eg, 310 , 312 , as two examples) supported by or integral with base 308 , wherein planar fin members (eg 310 ) includes at least one heat dissipating surface ( 322 ). The plurality of parallel plane fin members are preferably equally spaced.

The HA-derived foam of the present invention, which is highly resilient and resilient, is itself an excellent thermal interface material and likewise a very effective heat spreading element. Additionally, these highly conductive foams can also be used as inserts for electronic cooling and to enhance heat removal from small chips to heat sinks. Since the space occupied by the high-conductivity material is a major concern, it is a more efficient design to use a high-conductivity pathway that can be embedded into the heat generating body. The elastic and highly conductive solid graphene foam disclosed herein fully meets these requirements.

The high elasticity and high thermal conductivity make the solid HA-derived foam of the present invention an excellent conductive thick layer for placement as a heat transfer interface between a heat source and a cold-flowing fluid (or any other heat sink) to improve cooling performance. make it a plate In such an arrangement, the heat source is cooled under a thick HA-derived foam plate instead of being cooled in direct contact with the cooling fluid. A thick plate of HA-derived foam can significantly improve the heat transfer between the heat source and the cooling fluid by conducting the heat current in an optimal way. No additional pumping power and no extra heat transfer surface area is required.

HA-derived foam is also an excellent material for constructing heat pipes. A heat pipe is a heat transfer device that uses the evaporation and condensation of a two-phase working fluid or coolant to transport large amounts of heat with a very small difference in temperature between a hot interface and a cold interface. A typical heat pipe consists of a sealed hollow tube made of a thermally conductive metal, such as Cu or Al, and a wick that returns the working fluid from the evaporator to the condenser. The pipe contains both vapor and a saturated liquid of the working fluid (eg water, methanol or ammonia), all other gases being excluded. However, both Cu and Al are prone to oxidation or corrosion, and thus their performance degrades relatively quickly over time. In contrast, HA-derived foams are chemically inert and do not have these oxidation or corrosion problems. A heat pipe for thermal management of an electronic device may have a foam envelope and a wick, wherein water is used as a working fluid. HA-derived foam/methanol can be used if the heat pipe needs to operate at temperatures below the freezing point of water, and HA-derived foam/ammonia heat pipes can be used for cooling electronics in space.

Peltier cooling plates operate in the Peltier effect to create a heat flux between the junctions of two dissimilar electrical conductors by applying an electrical current. This effect is commonly used to cool electronic components and small appliances. In practice, multiple such junctions can be arranged in series to increase the effect on the amount of heating or cooling required. HA-derived foams can be used to improve heat transfer efficiency.

Filtration and fluid absorption applications

HA-derived foams can be prepared to contain microscopic pores (less than 2 nm) or mesoscale pores with a pore size of 2 nm to 50 nm. HA-derived foams can also be made to contain microscale pores (1 to 500 μm). Based solely on sufficiently controlled pore size, the present HA-derived foam may be an exceptional filter material for air or water filtration.

In addition, the humic acid (HA) pore wall chemistry can be controlled to impart different amounts and/or types of functional groups to the pore walls (e.g., as reflected by the percentages of O, F, N, H, etc. in the foam). can In other words, the parallel or independent control of both pore size and chemical functionality at different sites of the internal structure has many unexpected properties, synergistic effects, and any unique combination of properties normally considered mutually exclusive (e.g. , providing unprecedented flexibility or ultimate freedom in designing and manufacturing HA-derived foams that exhibit some portions of the structure being hydrophobic and others being hydrophilic; or the foam structure being both hydrophobic and lipophilic. A surface or material is said to be hydrophobic if water is repelled from the material or surface and water droplets lying on the hydrophobic surface or material form a large contact angle. A surface or material is said to be lipophilic if it has a strong affinity for oil and otherwise for water. This method allows precise control over hydrophobicity, hydrophilicity, and lipophilicity.

The present invention also provides an oil-removing, oil-separating, or oil-recovery device containing the HA-derived foam of the present invention as an oil-absorbing or oil-separating element. A solvent-removal or solvent-separation device containing an HA-derived foam as a solvent-absorbing element is also provided.

A major advantage of using the present HA-derived foam as an oil-absorbing component is its structural integrity. Due to the concept that HA sheets are chemically incorporated and thus have high structural integrity, the resulting foam will not disintegrate upon repeated oil soaking operations. In contrast, it was found that graphene-based oil-absorbing elements prepared by hydrothermal reduction, vacuum-assisted filtration, or freeze-drying disintegrated after absorbing oil for two or three times. There is nothing to hold these otherwise separated graphene sheets together (other than the weak van der Waals forces that existed before initial contact with the oil). Once these graphene sheets are wetted by oil, they can no longer return to the original shape of the oil-absorbing element.

Another major advantage of the present technology is the flexibility in designing and manufacturing the oil-absorbing element to absorb oil in amounts as high as 400 times its own weight while still maintaining its structural shape (without significant swelling). am. This amount depends on the specific pore volume of the foam, which can be mainly controlled by the ratio between the amount of original carrier polymer particles and the amount of HA molecules or sheets before heat treatment.

The present invention also provides a method for separating/recovering oil from an oil-water mixture (eg, oil-spill water or wastewater from oil sands). The method includes the following steps: (a) providing an oil-absorbing element comprising integral HA-derived foam; (b) contacting the oil-water mixture with urea to absorb oil from the mixture; and (c) reprocessing the oil-absorbing component from the mixture and extracting the oil from the component. Preferably, the method includes the additional step of (d) reusing the element.

Additionally, the present invention provides methods for separating organic solvents from solvent-water mixtures or from multi-solvent mixtures. The method includes the following steps: (a) providing an organic solvent-absorbing element comprising an integral HA-derived foam; (b) contacting the urea with an organic solvent-water mixture or a multi-solvent mixture containing a first solvent and at least a second solvent; (c) enabling the element to absorb an organic solvent from the mixture or at least a first solvent from a second solvent; and (d) reprocessing the urea from the mixture and extracting the organic solvent or first solvent from the urea. Preferably, the method includes the additional step of (e) reusing the solvent-absorbing element.

1 is a schematic diagram illustrating a process for producing graphene sheets from natural graphite particles.
Figure 2 is a possible mechanism of chemical linkage and coalescence between humic acid molecules and between "linked HA molecules". Two or three original HA molecules can be chemically linked together to form a longer or wider HA molecule called a “linked HA molecule”. Multiple "linked HA molecules" can merge to form graphene-like hexagonal carbon atom planes.
Figure 3a is a thermal conductivity value versus specific gravity of HA-derived foam, mesophase pitch-derived graphite foam, and Ni foam-cast assisted CVD graphene foam produced by the process of the present invention.
Figure 3b is the thermal conductivity values of HA-derived foam, sacrificial plastic bead-templated GO foam, and hydrothermal reduced GO graphene foam.
4 is electrical conductivity data of HA-derived foam and hydrothermal reduced GO graphene foam produced by the process of the present invention.
5 graphically plots the thermal conductivity values of foam samples derived from HA and fluorinated HA as a function of specific gravity.
6 is the thermal conductivity values of foam samples derived from HA and pristine graphene as a function of final (maximum) heat treatment temperature.
Figure 7 plots the amount of oil absorbed per gram of HA-derived foam as a function of oxygen content in the foam at a porosity level of approximately 98% (separation of oil from oil-water mixture).
8 plots the amount of oil absorbed per gram of monolithic HA-derived foam as a function of porosity level (assuming equal oxygen content).
Figure 9 graphically plots the amount of chloroform absorbed from a chloroform-water mixture as a function of degree of fluorination.
10 is a schematic diagram of a heat sink structure (two embodiments).

The following examples are used to illustrate some specific details of the best mode of practicing the invention and should not be construed as limiting the scope of the invention.

Example 1: Humic acid from soft coal and reduced humic acid

Humic acid can be extracted from soft brown coal in very high yields (in the range of 75%) by dispersing the soft brown coal in a basic aqueous solution (pH 10). Subsequent acidification of this solution leads to precipitation of humic acid powder. In the experiment, 3 g of soft coal was dissolved in 300 ml of double deionized water solution containing 1 M KOH (or NH ₄ OH) under magnetic stirring. The pH value was adjusted to 10. The solution was then filtered to remove any large particles or any residual impurities. The resulting humic acid dispersion, containing HC alone or in the presence of a blowing agent, was cast onto a glass substrate to form a series of films for subsequent heat treatment.

In some samples, a chemical blowing agent (hydrazodicarbonamide) was added to the suspension just prior to casting. Then, the resulting suspension was cast on a glass surface using a doctor blade to exert shear stress to induce orientation of the HA molecules. The HA coating film obtained after removal of the liquid has a thickness that can vary from approximately 10 nm to 500 μm (preferably and typically 1 μm to 50 μm).

To prepare the HA foam specimens, the HA coated film was then subjected to heat treatment, which typically includes an initial thermal reduction temperature of 80 to 350 °C for 1 to 8 hours, followed by a heat treatment of 1,500 to 2,850 °C for 0.5 to 5 hours. followed by a heat-treatment at a second temperature. It may be noted that it was confirmed that it was necessary to apply compressive stress to the coated film sample during the first heat treatment. It is believed that this compressive stress helped to maintain good contact between the HA molecules or sheets, allowing chemical merging and linking between the HA molecules or sheets to occur while the pores were being formed. Without such compressive stress, heat-treated films are typically excessively porous, with the constituent hexagonal carbon atom planes in the pore walls being very poorly oriented/positioned and may be unable to chemically merge and link together. As a result, the thermal conductivity, electrical conductivity, and mechanical strength of the graphene foam are severely impaired.

Example 2: Various blowing agents and pore-forming (bubble-creating) processes

In the field of plastics processing, chemical blowing agents are mixed into plastic pellets in powder or pellet form and dissolved at higher temperatures. Above a certain temperature specific for dissolution of the blowing agent, gaseous reaction products (usually nitrogen or CO ₂ ) are evolved, which act as blowing agents. However, chemical blowing agents that are solid rather than liquid cannot be dissolved in the graphene material. This represents a problem in using chemical blowing agents to create pores or cells in graphene materials.

After extensive experimentation, the inventors found that virtually any chemical blowing agent (e.g., in powder or pellet form) can be used to create pores or bubbles in the dried layer of graphene when the temperature of the first heat treatment is sufficient to activate the blowing reaction. It was found that it can be used for A chemical blowing agent (powder or pellets) can be dispersed in a liquid medium to become a second component in the suspension, which can be deposited on a solid support substrate to form a wet layer. This wet layer of HA material can then be dried and heat treated to activate the chemical blowing agent. After the chemical blowing agent is activated and bubbles are generated, the resulting foamed HA structure is substantially maintained even when a higher heat treatment temperature is subsequently applied to the structure. This is actually very unexpected.

Chemical foaming agents (CFAs) can be organic or inorganic compounds that release gases upon thermal decomposition. CFAs are typically used to obtain medium- to high-density foams, and are often used in conjunction with physical blowing agents to obtain low-density foams. CFAs can be categorized as either endothermic or exothermic, which refers to the type of degradation that occurs in them. The endothermic type absorbs energy and typically releases carbon dioxide and moisture upon decomposition, while the exothermic type releases energy and usually releases nitrogen upon decomposition. The total gas yield and the pressure of the released gas with the exothermic foaming agent are often higher than with the endothermic type. Endothermic CFAs are known to decompose generally in the range of 130 to 230°C (266 to 446°F), and some of the more common exothermic foaming agents decompose at approximately 200°C (392°F). However, the extent of degradation of most pyrogenic CFAs can be reduced by the addition of certain compounds. The activation (decomposition) temperature of CFAs falls within this heat treatment temperature range. Examples of suitable chemical blowing agents are sodium bicarbonate (baking soda), hydrazine, hydrazide, azodicarbonamide (exothermic chemical blowing agent), nitroso compounds (e.g. N,N-dinitroso pentamethylene tetramine), hydrazine derivatives (eg 4,4'-oxybis(benzenesulfonyl hydrazide) and hydrazo dicarbonamide), and hydrogen carbonate (eg sodium hydrogen carbonate). All of these are commercially available in the plastics industry.

In the production of foamed plastics, physical blowing agents are metered into the plastic melt during foam extrusion or injection molding foaming, or supplied to one of the precursor materials during polyurethane foaming. Previously, it was not known that physical blowing agents could be used to create pores in solid state (not melt) HA materials. The inventors have surprisingly observed that a physical blowing agent (eg, CO ₂ or N ₂ ) can be injected into the stream of HA suspension before being coated or cast onto a supporting substrate. This will result in a foamed structure even when the liquid medium (eg water and/or alcohol) is removed. The dried layer of graphene material can retain a controlled amount of pores or bubbles during liquid removal and subsequent thermal treatment.

Technically viable blowing agents are carbon dioxide (CO ₂ ), nitrogen (N ₂ ), isobutane (C ₄ H ₁₀ ), cyclopentane (C ₅ H ₁₀ ), isopentane (C ₅ H ₁₂ ), CFC-11 (CFCI) ₃ ), HCFC-22 (CHF ₂ CI), HCFC-142b (CF ₂ CICH ₃ ), and HCFC-134a (CH ₂ FCF ₃ ). However, in selecting a blowing agent, environmental safety is an important factor to consider. Its impact on the Montreal Protocol and critical agreements poses a major challenge to the foam's producers. Despite the previously applied chlorofluorocarbons' effective properties and ease of handling, there is a worldwide consensus to ban them due to their ozone depletion potential (ODP). Some halogenated chlorofluorocarbons are also environmentally unsafe and, as such, have already been banned in many countries. Substitutes are hydrocarbons, such as isobutane and pentane, and gases such as CO ₂ and nitrogen.

Except for those regulated substances, all blowing agents cited above were tested in this experiment. For both physical and chemical blowing agents, the amount of blowing agent introduced into the suspension is typically defined as a blowing agent-to-HA material weight ratio, which is from 0/1.0 to 1.0/1.0.

Example 3: Preparation of humic acid from coal

In a typical procedure, 300 mg of coal was suspended in concentrated sulfuric acid (60 ml) and nitric acid (20 ml) followed by cup sonication for 2 hours. The reaction was then stirred and heated in an oil bath at 100 or 120° C. for 24 hours. The solution was cooled to room temperature, poured into a beaker with 100 ml ice, followed by adding NaOH (3M) until a pH value of 7 was reached.

In one experiment, the neutral mixture was then filtered through a 0.45 mm polytetrafluoroethylene membrane and the filtrate was dialyzed in a 1,000 Da dialysis bag for 5 days. For larger sheets of humic acid, times can be reduced to 1 to 2 hours using cross-flow ultrafiltration. After purification, the solution was concentrated using rotary evaporation to obtain a solid sheet of humic acid. These humic acid sheets alone and their mixtures with blowing agents were redispersed in solvents (ethylene glycol and alcohol, respectively) to obtain several dispersion samples for subsequent casting or coating.

A chemical blowing agent (N, N-dinitroso pentamethylene tetramine or 4,4'-oxybis (benzenesulfonyl hydrazide)) in varying amounts (1% to 30% by weight relative to the HA material) was added to the HA sheet. was added to the suspension containing The suspension was then cast onto a glass surface using a doctor blade to exert shear stress to induce orientation and proper positioning of the HA molecules or sheets. Several samples were cast, including one prepared using CO ₂ as a physical blowing agent introduced into the suspension immediately prior to casting. The resulting HA film, after removal of the liquid, has a thickness that can vary from approximately 1 to 100 μm.

The HA film was then subjected to a heat treatment comprising an initial (first) thermal reduction temperature of 80 to 1,500° C. for 1 to 5 hours. This first heat treatment gave rise to HA foam (for HTT less than 300°C) and foams of large sheet-like HA molecules or domains of hexagonal carbon atom planes in the pore walls (for HTT of 300 to 1,500°C). Some of the foam samples were then exposed to a second temperature of 1,500 to 2,850° C. to see if the graphene-like domains of the hexagonal carbon atom planes in the foam walls could be further perfected (graphitized to become more ordered or more ordered). whether it can have high crystallinity) was determined.

Comparative Example 3-a : CVD graphene foam on Ni foam mold

The procedure was adapted from that disclosed in the following published literature: Chen, Z. et al. "Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition," Nat. Mater. 10, 424-428 (2011). A nickel foam, i.e., a porous structure with nickel in an interconnected 3D scaffold, was chosen as a template for the growth of the graphene foam. Briefly, carbon was introduced into the nickel foam by decomposing CH ₄ at 1,000° C. under ambient pressure, and then a graphene film was deposited on the surface of the nickel foam. Due to the difference in thermal expansion coefficient between nickel and graphene, ripples and wrinkles were formed on the graphene film. To recover the (separate) graphene form, the Ni frame must be etched. Prior to etching the nickel backbone by a hot HCl (or FeCl ₃ ) solution, a thin layer of poly(methyl methacrylate) (PMMA) was applied to the surface of the graphene film as a support to protect the graphene network from collapse during nickel etching. deposited on it. After the PMMA layer was carefully removed by hot acetone, a brittle graphene foam sample was obtained. The use of a PMMA support layer is important for preparing free-standing films of graphene foam, and only severely distorted and deformed graphene foam samples were obtained in the absence of the PMMA support layer. This is a tedious process that is neither environmentally friendly nor scalable.

Comparative Example 3-b : Conventional Graphite Foam from Pitch-Based Carbon Foam

Pitch powder, granules, or pellets were placed in an aluminum mold with the desired final foam shape. Mitsubishi ARA-24 mesophase pitch was used. The sample was evacuated to less than 1 torr and then heated to a temperature of approximately 300°C. At this point, the vacuum was broken with a nitrogen blanket, after which a pressure of up to 1,000 psi was applied. Afterwards, the temperature of the system was raised to 800 °C. This was done at a rate of 2°C/min. The temperature was held for at least 15 minutes to achieve immersion, after which the furnace power was turned off and cooled to room temperature at a rate of approximately 1.5° C./minute while releasing the pressure at a rate of approximately 2 psi/minute. Final foam temperatures were 630°C and 800°C. During the cooling cycle, the pressure is gradually released to atmospheric conditions. The foam was then heat treated to 1050° C. under a nitrogen blanket and then to 2500° C. and 2800° C. in argon in separate runs in a graphite crucible.

Samples from the foam were machined into specimens to measure thermal conductivity. Bulk thermal conductivities ranged from 67 W/mK to 151 W/mK. The density of the samples ranged from 0.31 to 0.61 g/cm 3 . When weight is taken into account, the specific thermal conductivity of the pitch derived foam is approximately 67/0.31 = 216 and 151/0.61 = 247.5 W/mK per specific gravity (or per physical density).

The compressive strength of the sample having an average density of 0.51 g/cm 3 was measured to be 3.6 MPa, and the compressibility was measured to be 74 MPa. In contrast, the compressive strength and compressive modulus of HA-derived graphite foams with similar physical densities are 5.7 MPa and 103 MPa, respectively.

Figure 3a shows the thermal conductivity values for specific gravity of HA-derived foam, mesophase pitch-derived graphite foam, and Ni foam mold-assisted CVD graphene foam. These data clearly demonstrate the following unexpected results:

1) HA-derived foams produced by the process of the present invention have significantly higher CVD graphene compared to both mesophase pitch-derived graphite foams and Ni foam template-assisted CVD graphene, given the same physical density. Indicates thermal conductivity.

2) This is very surprising from the point of view of the concept that CVD graphene is essentially pristine graphene, which has never been exposed to oxidation, so that oxygen-containing functional groups can be used for conventional thermal or chemical reduction methods. Compared to HA-derived hexagonal carbon atom planes, which are highly defective (with high defect populations and thus low conductivity) after removal via These exceptionally high thermal conductivity values observed for the HA-derived graphite foam produced here are quite surprising.

3) Considering the same amount of solid material, the HA-derived foam of the present invention after heat treatment at HTT where the HTT exceeds 1,500 °C exhibits essentially the greatest conductivity, which is due to the high level of graphite crystalline integrity (larger crystalline dimensions, fewer grain boundaries and other defects, better crystal orientation, etc.). This is also unexpected.

4) the specific conductivity values of the HA-derived foam and the fluorinated HA-derived foam of the present invention (FIG. 5) show values of 250 to 490 W/mK per unit of specific gravity; Those of the other two foam materials are typically less than 250 W/mK per unit of specific gravity.

Comparative Example 3-c : Preparation of pristine graphene foam (0% oxygen)

Recognizing the potential for high defect populations in the HA sheet that act to reduce the conductivity of the individual graphene planes, the use of pristine graphene sheets (non-oxidized and oxygen-free, non-halogenated and halogen-free, etc.) leads to higher thermal conductivity. It was decided to investigate whether it could lead to a graphene form with Pristine graphene sheets were created by using direct ultrasonic processing (also known in the art as liquid phase exfoliation).

In a typical procedure, 5 g of graphite flakes ground to a size of approximately 20 μm or less were dispersed in 1,000 mL of deionized water (containing 0.1% by weight of DuPont's ^Zonyl® FSO as a dispersant) to obtain a suspension. An ultrasonic energy level of 85 W (Branson S450 Ultrasonicator) was used for exfoliation, separation, and size reduction of the graphene sheets for 15 minutes to 2 hours. The resulting graphene sheet is pristine graphene that has never been oxidized, is oxygen-free and relatively defect-free. There are no other non-carbon elements.

A chemical blowing agent (N, N-dinitroso pentamethylene tetramine or 4,4'-oxybis (benzenesulfonyl hydrazide)) in various amounts (from 1% to 30% by weight relative to the graphene material) was added to pristine. It was added to the suspension containing graphene sheets and surfactant. The suspension was then cast onto a glass surface. Several samples were cast, including one prepared using CO ₂ as a physical blowing agent introduced into the suspension immediately prior to casting. The resulting graphene film after removal of the liquid has a thickness that can vary from approximately 10 to 100 μm. Then, the graphene film was subjected to heat treatment at a temperature of 80 to 1,500 ° C. for 1 to 5 hours, which generated a graphene form.

Figure 6 summarizes the thermal conductivity data for a series of HA-derived foams and a series of pristine graphene-derived foams, both plotted against the same final (maximum) heat treatment temperature. These data indicate that the thermal conductivity of HA-derived foams is very sensitive to the final heat treatment temperature (HTT). Even when the HTT is very low, apparently some type of HA molecular concatenation and consolidation or crystal perfecting reactions are already activated. The thermal conductivity increases monolithically with the final HTT. In contrast, the thermal conductivity of the pristine graphene foam remains relatively constant until reaching a final HTT of approximately 2,500 °C, indicating the onset of recrystallization and perfecting of the graphite crystals. Pristine graphene lacks functional groups that enable chemical linkage of molecules at relatively low HTTs, such as -COOH and -OH in HA. For HTTs as low as 1,250 °C, the HA molecules and resulting hexagonal carbon atomic planes can coalesce to form significantly larger graphene-like hexagonal carbon sheets with reduced grain boundaries and fewer electron transport path interruptions. Although HA-derived sheets inherently exhibit more defects than pristine graphene, the process of the present invention allows HA molecules to form graphite foams that outperform pristine graphene foams. This is another unexpected result.

Comparative Example 3-d : Preparation of graphene oxide (GO) suspension from natural graphite and graphene foam from hydrothermally reduced graphene oxide

Graphite oxide was prepared by oxidizing graphite flakes at 30° C. in a ratio of 4:1:0.05 with an oxidizing agent liquid consisting of sulfuric acid, sodium nitrate, and potassium permanganate. When natural graphite flakes (particle size of 14 μm) are immersed and dispersed in an oxidizer mixture liquid for 48 hours, the suspension or slurry appears and remains optically opaque and thick. After 48 hours, the reaction mass was washed with water three times to adjust the pH value to at least 3.0. Afterwards, a series of GO-water suspensions were prepared by adding a final amount of water. We observed that GO sheets form a liquid crystalline phase when the GO sheets account for a weight fraction greater than 3%, and typically between 5% and 15%.

Self-assembled graphene hydrogel (SGH) samples were then prepared by hydrothermal method. In a conventional procedure, SGH can be readily prepared by heating a sealed 2 mg/mL homogenous graphene oxide (GO) aqueous dispersion in a Teflon-lined autoclave at 180° C. for 12 hours. SGH containing about 2.6% (by weight) graphene sheets and 97.4% water has an electrical conductivity of approximately 5 Х 10 ^-3 S/cm. Upon drying and heat treatment at 1,500 °C, the obtained graphene foam exhibits an electrical conductivity of approximately 1.5 Х 10 ^-1 S/cm, which is twice that of the HA-derived foam of the present invention produced by heat treatment at the same temperature. it is low

Comparative Example 3-e : Plastic Bead Mold-Assisted Formation of Reduced Graphene Oxide Foam

A rigid template-directed ordered assembly for macroporous bubbled graphene films (MGF) was fabricated. Mono-disperse polymethyl methacrylate (PMMA) latex spheres were used as hard templates. The GO liquid crystal prepared in Comparative Example 3-d was mixed with the PMMA sphere suspension. Subsequent vacuum filtration was then performed to produce an assembly of PMMA spheres and GO sheets, which were wrapped around PMMA beads. The composite film was peeled from the filter, air dried and fired at 800 °C to remove the PMMA mold and simultaneously thermally reduced GO to RGO. The gray free-standing PMMA/GO film turned black after firing, and the graphene film maintained its porosity.

Figure 3b shows the thermal conductivity values of the HA-derived foam of the present invention, the GO foam produced through the sacrificial plastic bead mold-assisted process, and the hydrothermally reduced GO graphene foam. Most surprisingly, given the same HTT, the HA-derived foam exhibits the highest thermal conductivity. The electrical conductivity data summarized in FIG. 4 are also consistent with these results. These data show that, given the same amount of solid material, the HA suspension deposition of the present invention (with stress-induced orientation) and subsequent heat treatment produces the HA-derived foam that is essentially the most conductive, resulting in the highest level of graphite. Further support is given to the notion that quality reflects perfect crystal perfection (larger crystal dimensions, fewer grain boundaries and other defects, better crystal orientation along the pore walls, etc.).

All prior art processes for producing graphite foams or graphene foams have physical densities in the range of approximately 0.2 to 0.6 g/cm3 with pore sizes typically too large (e.g., 20 to 300 μm) for most intended applications. It is important to note that it appears to provide a macroporous foam having In contrast, the present invention provides a process for producing HA-derived foams with densities that can be as low as 0.01 g/cm3 and as high as 1.7 g/cm3. The pore size can vary from mesoscale (2 to 50 nm) up to macroscale (1 to 500 μm) depending on the content of non-carbon elements and the amount/type of blowing agent used. This level of flexibility and versatility with which various types of graphite foam can be designed is unprecedented and unmatched by any prior art process.

Example 4: Preparation of Fluorinated HA Foam

In a typical procedure, sheets of HA-derived foam were fluorinated by vapor of chlorine trifluoride in a sealed autoclave reactor to obtain a fluorinated HA-carbon hybrid film. Different durations of fluorination time made it possible to achieve different degrees of fluorination. The sheets of fluorinated HA-derived foam were then individually immersed in containers each containing a chloroform-water mixture. It was observed that these foam sheets selectively absorbed chloroform from water, and the amount of absorbed chloroform increased with the degree of fluorination until the fluorine content reached 7.2% by weight, as shown in FIG. 9 .

Example 5: Preparation of Nitrogenated HA Foam

Several pieces of the HA-derived foam prepared in Example 3 were immersed in a 30% H ₂ O ₂ -water solution for a period of 2 to 48 hours to oxidize HA- with a controlled oxygen content of 2 to 25% by weight. An induction foam was obtained.

Some of the oxidized HA-derived foam samples were mixed with different proportions of urea and the mixture was heated in a microwave reactor (900 W) for 0.5 to 5 minutes. The product was washed several times with deionized water and dried under vacuum. The product obtained was a nitrogenated HA foam. The nitrogen content ranged from 3% to 17.5% by weight as determined by elemental analysis.

It can be mentioned that different functionalization treatments of HA-derived foams are for different purposes. For example, the oxidized HA foam structure is particularly effective as an absorbent of oil from an oil-water mixture (i.e., oil spilled into water and then mixed together) (FIGS. 7 and 8). In this case, the integral HA-derived foam structure (with 0-15 wt% oxygen) is both hydrophobic and lipophilic (FIG. 7). A surface or material is said to be hydrophobic if water is repelled from the material or surface and water droplets lying on the hydrophobic surface or material form a large contact angle. A surface or material is said to be lipophilic if it has a strong affinity for oil and otherwise for water.

Different amounts of O, F, and/or N also allow the HA-derived foam of the present invention to absorb different organic solvents from water, or to separate one organic solvent from a mixture of multiple solvents.

Example 6 : Characterization of various HA-derived foams and conventional graphite foams

The internal structure (crystal structure and orientation) of several series of HA-carbon foam materials was investigated using X-ray diffraction. X-ray diffraction curves of natural graphite typically show a peak at approximately 2θ = 26°, which corresponds to an intergraphene spacing (d ₀₀₂ ) of approximately 0.3345 nm. The RHA wall of the hybrid foam material exhibits a d ₀₀₂ spacing, typically between 0.3345 nm and 0.40 nm, but more typically up to 0.34 nm.

In the case of a heat treatment temperature of 2,750 °C for the foam structure under compression for 1 hour, the d ₀₀₂ spacing is reduced to approximately 0.3354 nm, which is the same value as the d ₀₀₂ spacing of graphite single crystal. Also, a second diffraction peak with high intensity appears at 2θ = 55°, which corresponds to X-ray diffraction from the (004) plane. The (004) peak intensity to (002) intensity, or I (004)/ I (002) ratio, on the same diffraction curve is a good indicator of the degree of crystal perfection and preferred orientation of the graphene-like plane. The (004) peak is absent or relatively weak, with an I (004)/ I (002) ratio of less than 0.1 for all graphitic materials heat treated at temperatures less than 2,800 °C. The I (004) / I (002) ratio for graphitic materials (eg, highly oriented pyrolytic graphite, HOPG) heat treated at 3,000 to 3,250 ° C ranges from 0.2 to 0.5. In contrast, the graphene foam prepared with a final HTT of 2,750 °C for 1 hour exhibits an I (004)/ I (002) ratio of 0.78 and a mosaic dispersion value of 0.21, indicating that the pore walls (when prepared under compressive force) It is shown to be a virtually perfect graphite monocrystal with excellent preferred orientation.

The "mosaic dispersion" value is obtained from the half maximum width of the (002) reflection in the X-ray diffraction intensity curve. This index of degree of alignment characterizes the graphite or graphene crystallite size (or grain size), the amount of grain boundaries and other defects, and the degree of preferred grain orientation. Almost perfect monocrystals of graphite are characterized by having mosaic dispersion values of 0.2 to 0.4. Some of the HA-derived foams of the present invention have mosaic dispersion values in this range of 0.3 to 0.6 when produced using a final heat treatment temperature of at least 2,500°C.

It is important to note that heat treatment temperatures as low as 500° C. are sufficient to bring the average interplanar spacing between hexagonal carbon atom planes along the pore walls to less than 0.4 nm, closer to natural graphite or graphite single crystals. The beauty of this approach is the concept that this HA suspension coating and thermal treatment strategy allows planar HA molecules to be organized, oriented/aligned, and chemically merged to form integrated structures, in the case of integrated structures, all graphene. -Pseudo-hexagonal carbon atom planes now have larger lateral dimensions (significantly larger than the original HA molecule's length and width). Potential chemical linking and merging mechanisms are illustrated in FIG. 3 . This resulted in exceptional thermal and electrical conductivity values.

In conclusion, the present inventors have successfully developed an absolutely new, novel, unexpected and distinct class of HA foam or HA-derived graphite foam materials and related production processes. Chemical composition (% of oxygen, fluorine, and other non-carbon elements), structure (crystal perfection, grain size, defect population, etc.), crystal orientation, morphology, production process, and properties of this new class of foam materials. is fundamentally different and distinct from mesophase pitch-derived graphite foams, CVD graphene-derived foams, and graphene foams from hydrothermal reduction of GO, and sacrificial bead mold-assisted RGO foams. The thermal conductivity, electrical conductivity, modulus of elasticity, and flexural strength exhibited by the foam materials of the present invention are much higher than prior art foam materials.

Claims (40)

As a humic acid-derived foam composed of a large number of pores and pore walls,
The pore walls contain single-layer or few-layer humic acid-derived hexagonal carbon atom planes or sheets, the multi-layer hexagonal carbon atom planes or sheets, as measured by X-ray diffraction, planar It has 2 to 10 layers of stacked hexagonal carbon atom planes with interspacing d ₀₀₂ of 0.3354 nm to 0.60 nm, wherein the single-layer or multi-layer hexagonal carbon atom planes contain 7% to 25% by weight of non-carbon elements. The humic acid is oxidized humic acid, reduced humic acid, fluorinated humic acid, chlorinated humic acid, brominated humic acid, iodinated humic acid, hydrogenated humic acid, nitrogenated humic acid, doped humic acid A humic acid-derived foam selected from the group consisting of chemically functionalized humic acids, and combinations thereof. The foam according to claim 1, wherein the foam has a density of 0.005 to 1.7 g/cm ³ , a specific surface area of 50 to 3,200 m ² /g, a thermal conductivity per unit of specific gravity of at least 100 W/mK, and an electrical conductivity per unit of specific gravity. A humic acid-derived foam having greater than 500 S/cm. The humic acid-derived foam of claim 1 , wherein the foam has a density of 0.01 to 1.5 g/cm ³ or an average pore size of 2 nm to 50 nm. The method of claim 1, wherein the foam has a content of non-carbon elements ranging from 10% to 20% by weight, wherein the non-carbon elements are selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. A humic acid-derived foam comprising elemental. The humic acid-derived foam of claim 1 , wherein the humic acid is a fluorinated humic acid and the foam has a fluorine content of 10% to 20% by weight. The humic acid-derived foam of claim 1 , wherein the humic acid is an oxidized humic acid and the foam has an oxygen content of 10% to 20% by weight. The humic acid-derived foam of claim 1, wherein the foam has a specific surface area of 200 to 3,000 m ² /g or a density of 0.1 to 1.2 g/cm ³ . The humic acid-derived method of claim 1 in the form of a continuous-length roll sheet having a thickness of 100 nm to 10 cm and a length of at least 2 meters, resulting from a roll-to-roll process. form. The method of claim 1 , wherein the foam comprises stacked hexagonal carbon atom planes having an interplanar spacing of less than 0.35 nm, a thermal conductivity per unit of specific gravity of at least 200 W/mK, and an electrical conductivity per unit of specific gravity of at least 1,000 S/cm. A humic acid-derived foam having a pore wall containing The method of claim 1 , wherein the foam comprises stacked hexagonal carbon atom planes having an interplanar spacing of less than 0.34 nm, a thermal conductivity per unit of specific gravity of at least 300 W/mK, and an electrical conductivity per unit of specific gravity of at least 1,500 S/cm. A humic acid-derived foam having a pore wall containing 2. The method of claim 1, wherein the foam comprises stacked hexagonal carbon atom planes having an interplanar spacing of less than 0.336 nm, a thermal conductivity per unit of specific gravity of at least 350 W/mK, and an electrical conductivity per unit of specific gravity of at least 2,000 S/cm. A humic acid-derived foam having a pore wall containing The foam according to claim 1 , wherein the foam has a plane-to-planar spacing of less than 0.336 nm, a thermal conductivity per unit of specific gravity of greater than 400 W/mK, and an electrical conductivity per unit of specific gravity of greater than 3,000 S/cm. A humic acid-derived foam having pore walls containing The humic acid-derived foam of claim 1 , wherein the pore walls contain stacked hexagonal carbon atom planes with an interplanar spacing of less than 0.337 nm and a mosaic spread value of less than 1.0. The humic acid-derived foam of claim 1 , wherein the pore walls contain a 3D network of interconnected hexagonal carbon atom planes. The humic acid-derived foam of claim 1 , wherein the foam contains mesoscale pores with a pore size of 2 nm to 50 nm. An oil-removing device or oil-separating device containing the humic acid-derived foam of claim 1 as an oil-absorbing element. A solvent-removing device or solvent-separating device containing the humic acid-derived foam of claim 1 as a solvent-absorbing or solvent-separating element. As a method for separating oil from water,
a. providing an oil-absorbing element comprising the humic acid-derived foam of claim 1;
b. contacting an oil-water mixture with the element to absorb oil from the mixture;
c. reprocessing urea from the mixture and extracting oil from the urea; and
d. Steps to Reuse Elements
Including, method. As a method for separating an organic solvent from a solvent-water mixture or from a multi-solvent mixture,
a. providing an organic solvent-absorbing or solvent-separating element comprising the humic acid-derived foam of claim 1;
b. contacting the component with an organic solvent-water mixture or multi-solvent mixture containing a first solvent and at least a second solvent;
c. enabling the component to absorb an organic solvent from the mixture or to separate the first solvent from the at least second solvent;
d. reprocessing the urea from the mixture and extracting the organic solvent or the first solvent from the urea; and
e. Steps to Reuse Elements
Including, method. A thermal management device containing the humic acid-derived foam of claim 1 as a heat spreading or heat dissipating element. 21. The heat exchanger, heat sink, heat pipe, high-conductivity insert, conductive plate between the heat sink and heat source, heat-spreading component, heat-dissipating component, thermal interface medium, and thermoelectric or a Peltier cooling device. As a process for producing humic acid-induced foam,
(a) preparing a humic acid dispersion having a plurality of humic acid molecules or sheets dispersed in a liquid medium, wherein the humic acid is oxidized humic acid, reduced humic acid, fluorinated humic acid, chlorinated humic acid, selected from the group consisting of brominated humic acids, iodinated humic acids, hydrogenated humic acids, nitrogenated humic acids, doped humic acids, chemically functionalized humic acids, and combinations thereof, wherein the dispersion is a blowing agent (blowing agent), and the foaming agent to humic acid weight ratio is 0/1.0 to 1.0/1.0, step;
(b) dispensing and depositing the humic acid dispersion onto the surface of a supporting substrate to form a wet layer of humic acid;
(c) partially or completely removing the liquid medium from the wet layer of humic acid to form a dry layer of humic acid; and
(d) a dry layer of humic acid at a first heat treatment temperature of from 80° C. to 3,200° C. at a desired heating rate sufficient to activate the blowing agent or induce volatile gas molecules from non-carbon elements to produce the humic acid-derived foam. heat-treating, wherein the humic acid-derived foam is composed of a plurality of pores and pore walls, wherein the pore walls contain single-layer or multi-layer humic acid-derived hexagonal carbon atom planes or sheets; The layered hexagonal carbon atom plane or sheet has from 2 to 10 layers of stacked hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.60 nm, as measured by X-ray diffraction, wherein the single layer or wherein the multi-layered hexagonal carbon atomic planes contain from 7% to 25% by weight of non-carbon elements. 23. The process of claim 22, wherein the dispensing and deposition procedure includes subjecting the humic acid dispersion to an orientation-induced stress. 23. The method of claim 22, further comprising heat-treating the humic acid-derived foam at a second heat treatment temperature higher than the first heat treatment temperature for a time sufficient to obtain a graphite foam, wherein the pore walls are: A process comprising layered hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.36 nm and a content of non-carbon elements of less than 2% by weight. 23. The process according to claim 22, wherein the blowing agent is a physical blowing agent, a chemical blowing agent, mixtures thereof, a dissolve-and-leach agent, or a mechanically introduced blowing agent. 23. The process of claim 22, wherein steps (b) and (c) are a roll-to-roll process, wherein steps (b) and (c) include feeding the supporting substrate from a supply roller to a deposition zone; Depositing continuously or intermittently on the surface of the humic acid to form a wet layer of humic acid thereon, drying the wet layer of humic acid to form a dry layer of humic acid, and depositing on the supporting substrate and collecting the dried layer of humic acid on a collecting roller. 23. The process of claim 22, wherein the first heat treatment temperature is from 100 °C to 1,500 °C. 25. The process of claim 24, wherein the second heat treatment temperature comprises at least a temperature selected from the group consisting of (A) 300 to 1,500 °C, (B) 1,500 to 2,100 °C, and (C) 2,100 to 3,200 °C. 25. The process of claim 24, wherein the second heat treatment temperature comprises a temperature in the range of 300 to 1,500°C for at least 1 hour followed by a temperature in the range of 1,500 to 3,200°C for at least 1 hour. 25. The process of claim 24, wherein the non-carbon element comprises an element selected from the group consisting of oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, and boron. 25. The process of claim 24, wherein step (d) of heat treating the dry layer of humic acid at the first heat treatment temperature is performed under compressive stress. 23. The process of claim 22, further comprising a compression step to reduce the thickness, pore size, or porosity level of the foam. 25. The method of claim 24, wherein the first and second heat treatment temperatures include temperatures in the range of 300 ° C to 1,500 ° C, the foam has an oxygen content or a non-carbon content of less than 1%, and the pore walls have an interplanar spacing of 0.35 nm, a thermal conductivity per unit of specific gravity of at least 250 W/mK, and an electrical conductivity per unit of specific gravity of at least 2,500 S/cm. 25. The method of claim 24, wherein the first and second heat treatment temperatures include a temperature in the range of 1,500 ° C to 2,100 ° C, the foam has an oxygen content or a specific carbon content of less than 0.01%, and the pore walls have an interplanar spacing of 0.34 nm, a thermal conductivity per unit of specific gravity of at least 300 W/mK, and an electrical conductivity per unit of specific gravity of at least 3,000 S/cm. 25. The method of claim 24, wherein the first and second heat treatment temperatures include a temperature greater than 2,100 ° C, the foam has an oxygen content or a specific carbon content of 0.001% or less, and the pore walls have an interplanar spacing of less than 0.336 nm , a mosaic dispersion value of 0.7 or less, a thermal conductivity per unit of specific gravity of at least 350 W/mK, and an electrical conductivity per unit of specific gravity of at least 3,500 S/cm. The method of claim 24, wherein the first and second heat treatment temperatures include a temperature of 2,500 ° C. or higher, the foam has an interplanar spacing of 0.336 nm, a mosaic dispersion value of 0.4 or less, and a thermal conductivity per unit of specific gravity of 400 W/ mK and having a pore wall containing layered hexagonal carbon planes having an electrical conductivity per unit of specific gravity greater than 4,000 S/cm. A roll-to-roll process for producing continuous-length sheets of humic acid-derived foam comprising:
(a) preparing a humic acid dispersion wherein humic acid molecules are dispersed in a liquid medium and contain a blowing agent;
(b) dispensing and depositing the humic acid dispersion continuously or intermittently on the surface of a support substrate to form a wet layer of humic acid, wherein the support substrate is supplied from a supply roller and collected on a collection roller. which is a continuous thin film;
(c) partially or completely removing the liquid medium from the wet layer of humic acid in one or more heating zones to form a dry layer of humic acid; and
(d) drying humic acid in one of the heating zones comprising a heating temperature of 80° C. to 500° C. at a desired heating rate sufficient to activate the blowing agent to produce the humic acid-derived foam. heat treating the layer, wherein the humic acid-derived foam is composed of a plurality of pores and pore walls, wherein the pore walls contain single-layer or multi-layer humic acid-derived hexagonal carbon atom planes or sheets; A multilayer hexagonal carbon atom plane or sheet has 2 to 10 layers of stacked hexagonal carbon atom planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.60 nm, as measured by X-ray diffraction, wherein the single layer or the multi-layered hexagonal carbon atom planes contain from 7% to 25% by weight of non-carbon elements. 23. The method of claim 22, wherein the humic acid-derived foam has a density of 0.005 to 1.7 g/cm ³ , a specific surface area of 50 to 3,200 m ² /g, a thermal conductivity per unit of specific gravity of at least 100 W/mK, and a specific gravity of claim 22 . wherein the electrical conductivity per unit of is greater than or equal to 500 S/cm. 25. The method of claim 24, wherein the humic acid-derived foam has a density of 0.005 to 1.7 g/cm ³ , a specific surface area of 50 to 3,200 m ² /g, and a thermal conductivity per unit of specific gravity of at least 100 W/mK, specific gravity wherein the electrical conductivity per unit of is greater than or equal to 500 S/cm. 38. The method of claim 37, wherein the humic acid-derived foam has a density of 0.005 to 1.7 g/cm ³ , a specific surface area of 50 to 3,200 m ² /g, and a thermal conductivity per unit of specific gravity of at least 100 W/mK, specific gravity wherein the electrical conductivity per unit of is greater than or equal to 500 S/cm.

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