CN109803820B - Humic acid derived conductive foams and devices - Google Patents

Abstract

A humic acid derived foam comprised of a plurality of pores and pore walls, wherein the pore walls contain a single or few layers of humic acid derived hexagonal carbon atom planes or platelets having from 2 to 10 stacked hexagonal carbon atom planes with an interplanar spacing d002#191 as measured by X-ray diffraction of from 0.3354nm to 0.40nm and the single or few layers of hexagonal carbon atom planes containing from 0.01% to 25% by weight of non-carbon elements, and wherein the humic acid is selected from 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, chemically functionalized humic acid, or combinations thereof.

Description

Humic acid derived conductive foams and devices

Cross Reference to Related Applications

This application claims priority from U.S. patent application No. 15/251,841 filed 2016, 8, 30 and U.S. patent application No. 15/251,849 filed 2016, 8, 30, which are incorporated herein by reference.

Technical Field

The present invention relates generally to the field of carbon/graphite foams, and more particularly to a novel form of humic acid-derived conductive foam, a device containing such humic acid-derived foam, and a method for producing the same.

Background

Carbon is known to have five unique crystal structures including diamond, fullerene (0-D nanographitic material), carbon nanotube or carbon nanofiber (1-D nanographitic material), graphene (2-D nanographitic material), and graphite (3-D graphitic material). All of these materials, except fullerenes, can be made into a foam structure.

Carbon Nanotubes (CNTs) refer to tubular structures grown with single or multiple walls. Carbon Nanotubes (CNTs) and Carbon Nanofibers (CNFs) have diameters of about several nanometers to several hundred nanometers. The longitudinal and hollow structure of the material endows the material with unique mechanical, electrical and chemical properties. CNT or CNF is a one-dimensional nanocarbon or 1-D nanographitic material. However, CNTs are difficult to produce and are extremely expensive. Furthermore, CNTs are known to be difficult to disperse in solvents or water and to mix with other materials. These characteristics have severely limited their range of applications.

A single layer graphene sheet consists of carbon atoms occupying a two-dimensional hexagonal lattice. Multi-layer graphene is a platelet composed of more than one graphene plane. Individual single-layer graphene sheets and multi-layer graphene platelets are collectively referred to herein as nano-graphene platelets (NGPs) or graphene materials. The NGP includes pristine graphene (substantially 99% carbon atoms), slightly oxidized graphene (< 5% oxygen by weight), and oxidized graphene ≧ 5% oxygen by weight.

NGPs have been found to possess a range of unusual physical, chemical and mechanical properties. Our research group first discovered Graphene [ b.z. jang and w.c. huang, "Nano-scaled Graphene Plates ]", U.S. patent application No. 10/274,473 filed 21/10/2002; now U.S. Pat. No. 7,071,258(07/04/2006) ]. Previously, we reviewed methods for producing NGP and NGP Nanocomposites [ Bor z. jang and a Zhamu, "Processing of Nano-Graphene plates (NGPs) and NGP Nanocomposites: a Review [ Processing of Nano-Graphene Platelets (NGP) and NGP Nanocomposites: review ] ", J.materials Sci. [ journal of Material science ]43(2008) 5092-5101. Four major prior art methods have been followed to produce NGP. Their advantages and disadvantages are briefly summarized as follows:

the method comprises the following steps: chemical formation and reduction of Graphene Oxide (GO)

The first method (fig. 1) entails treating natural graphite powder with an intercalant and an oxidant (e.g., concentrated sulfuric acid and nitric acid, respectively) to obtain a Graphite Intercalation Compound (GIC) or indeed Graphite Oxide (GO). Preparation of graphite Oxide [ William S.hummers, Jr. et al, Preparation of graphite Oxide]Journal of the American Chemical Society [ national Society of chemistry]1958, page 1339]. The graphite has an interplanar spacing (L) of graphene of about 0.335nm prior to intercalation or oxidation_d＝1/2d₀₀₂0.335 nm). In the case of intercalation and oxidation processes, the inter-graphene spacing increases to values typically greater than 0.6 nm. This is the first expansion stage that the graphite material undergoes during this chemical route. The resulting GIC or GO is then subjected to further expansion (often referred to as swelling) using a thermal shock exposure process or a solution-based sonication assisted graphene layer swelling (swelling) process.

In the thermal shock exposure process, the GIC or GO is exposed to an elevated temperature (typically 800 ℃ -1,050 ℃) for a short period of time (typically 15 to 60 seconds) to expand or expand the GIC or GO to form an expanded or further expanded graphite, typically in the form of "graphite worms" comprised of graphite flakes that are still interconnected with one another. This thermal shock procedure can produce some separate graphite flakes or graphene sheets, but typically most of the graphite flakes remain interconnected. Typically, the expanded graphite or graphite worms are then subjected to flake separation using air milling, mechanical shearing, or sonication in water. Thus, method 1 basically requires three different procedures: first expansion (oxidation or intercalation), further expansion (or "puffing"), and separation.

In a solution-based separation process, expanded or expanded GO powder is dispersed in water or an aqueous alcohol solution, which is subjected to sonication. It is important to note that in these processes, sonication is used after intercalation and oxidation of 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 powders dispersed in water are subjected to ion exchange or lengthy purification procedures in such a way that the repulsive forces between ions present in the inter-planar spaces prevail over the van der waals forces between graphene, resulting in graphene layer separation.

There are several major problems associated with this conventional chemical production process:

(1) this process requires the use of large amounts of several undesirable chemicals such as sulfuric acid, nitric acid and potassium permanganate or sodium chlorate.

(2) This chemical treatment process requires long intercalation and oxidation times, typically 5 hours to 5 days.

(3) During such prolonged intercalation or oxidation processes, the strong acid consumes a significant amount of graphite by "attacking its way into the graphite" (converting the graphite to carbon dioxide that is lost in the process). It is not uncommon for 20-50% by weight of the graphite material immersed in the strong acid and the oxidizing agent to be lost.

(4) Thermal expansion requires high temperatures (typically 800-1,200 ℃) and is therefore a highly energy intensive process.

(5) Both heat-and solution-induced bulking require very cumbersome washing and purification steps. For example, typically 2.5kg of water is used to wash and recover 1 gram of GIC, producing large amounts of waste water that needs to be properly treated.

(6) In both the heat-and solution-induced expansion processes, the resulting products are GO platelets, which must undergo further chemical reduction treatment to reduce the oxygen content. Typically, even after reduction, the conductivity of GO platelets is still much lower than that of pristine graphene. In addition, reduction procedures often involve the use of toxic chemicals, such as hydrazine.

(7) Further, the amount of intercalation solution that remains on the flakes after draining may range from 20 to 150 parts by weight solution per 100 parts by weight graphite flakes (pph), and more typically about 50 to 120 pph. During high temperature puffing, residual intercalated species retained by the flakes decompose to produce various undesirable sulfur-and nitrogen-containing compounds (e.g., NO)_xAnd SO_x). Effluent requires expensive remediation procedures in order not to have adverse environmental effects.

The method 2 comprises the following steps: direct formation of pristine nano-graphene platelets

In 2002, our research team successfully isolated single and multilayer Graphene sheets from partially carbonized or graphitized polymeric carbons obtained from polymer or pitch precursors [ b.z.jang and w.c. huang, "Nano-scaled Graphene Plates ]", U.S. patent application No. 10/274,473 filed 10/21/2002; now U.S. Pat. No. 7,071,258(07/04/2006) ]. Mack et al [ "Chemical manufacturing of nanostructured materials ]" U.S. Pat. No. 6,872,330 (3.29.2005) ] developed a process that involves intercalating graphite with a potassium melt and contacting the resulting K-intercalated graphite with an alcohol to produce severely expanded graphite containing NGP. The process must be carefully carried out in a vacuum or very dry glove box environment because soda metals such as potassium and sodium are extremely moisture sensitive and present an explosion hazard. This method is not suitable for mass production of NGP.

The method 3 comprises the following steps: epitaxial growth and chemical vapor deposition of nano-graphene sheets on inorganic crystal surfaces

Small-scale production of ultra-thin graphene sheets on a substrate can be achieved by epitaxial growth based on thermal decomposition and laser desorption-ionization techniques. [ wave a. deheer, Claire Berger, Phillip n.first, "Patterned thin film graphite devices and methods for making same ]" U.S. patent No. 7,327,000B2 (6/12/2003) ] have technical and scientific importance with only one or a few atomic layers of graphite epitaxial films due to their unique characteristics and great potential as substrates for devices. However, these methods are not suitable for the mass production of isolated graphene sheets for composite and energy storage applications.

For producing in the form of a film (typically of thickness)<2nm) is catalytic chemical vapor deposition. The catalytic CVD involves a hydrocarbon gas (e.g., C)₂H₄) Catalytic decomposition on Ni or Cu surfaces to form single or few layer graphene. In the case where Ni or Cu is a catalyst, carbon atoms obtained via decomposition of hydrocarbon gas molecules at a temperature of 800 ℃ to 1,000 ℃ are directly deposited on the Cu foil surface or precipitated from a Ni — C solid solution state onto the Ni foil surface to form a single-layer or few-layer graphene (less than 5-layer) sheet. Ni-or Cu-catalyzed CVD methods are not suitable for depositing more than 5 graphene planes (typically<2nm), over 5 graphene planes, the underlying Ni or Cu layer can no longer provide any catalytic effect. CVD graphene films are very expensive. The method 4 comprises the following steps: bottom-up method (Synthesis of graphene from Small molecule)

Yang et al [ "Two-dimensional Graphene Nano-ribs ]," J.Am.chem.Soc. [ Proc. Natl. Acad. USA chemical Association ]130(2008)4216-17] Synthesis of Nanoschragm sheets up to 12nm in length using the following method, which starts with the Suzuki-Miyaura coupling of 1, 4-diiodo-2, 3,5, 6-tetraphenyl-benzene with 4-bromobenzoic acid. The resulting hexaphenylbenzene derivatives were further derivatized and ring-fused into small graphene sheets. This is a slow method to date to produce very small graphene sheets.

Therefore, there is an urgent need for a new class of carbon nanomaterials that are comparable or superior to graphene in terms of properties, but that can be produced more cost-effectively, faster, more scaleable, and in a more environmentally friendly manner. The production process for this new carbon nanomaterial requires a reduced amount of undesirable chemicals (or elimination of these chemicals altogether), a shortened processing time, less energy consumption, reduced or eliminated entry of undesirable chemical species into the exhaust system (e.g., sulfuric acid) or into the air (e.g., SO)₂And NO₂) The outflow amount of (a). Furthermore, it should be possible to easily adapt the newThe nanomaterial of (a) is made into a relatively thermally and electrically conductive foam structure.

In general, foams or foam materials are composed of cells (or cells) and cell walls (solid material). The cells may be interconnected to form an open-cell foam. As an example, graphene foam is composed of cells and cell walls containing graphene material. There are three main methods of producing graphene foam, all of which are cumbersome, energy consuming, and slow:

the first method is hydrothermal reduction of graphene oxide hydrogels, which typically involves sealing an aqueous Graphene Oxide (GO) suspension in an autoclave and heating the GO suspension at high pressure (tens or hundreds of atm) at temperatures typically in the range of 180-300 ℃ for extended periods of time (typically 12-36 hours). Useful references to this method are given herein: xu et al, "Self-Assembled Graphene Hydrogel via One-Step Hydrothermal method", "ACS Nano [ ACS Nano ]2010,4, 4324-4330-. There are several major problems associated with this approach: (a) the high pressure requirements make it an impractical process for industrial scale production. First, this process cannot be performed on a continuous basis. (b) It is difficult, if not impossible, to perform control of the pore size and porosity level of the resulting porous structure. (c) There is no flexibility in changing the shape and size of the resulting Reduced Graphene Oxide (RGO) material (e.g., the material cannot be made into a film shape). (d) The method involves the use of ultra-low concentrations of GO suspended in water (e.g., 2 mg/mL-2 g/L-2 kg/kL). With the removal of non-carbon elements (up to 50%), only less than 2kg of graphene material (RGO) per 1000 liters of suspension can be produced. Furthermore, it is practically impossible to operate a 1000 liter reactor that must withstand high temperature and pressure conditions. Clearly, there is no scalable method for mass production of porous graphene structures.

The second method is a template-assisted catalytic CVD-based method that involves CVD deposition of graphene on a sacrificial template (e.g., Ni foam). The graphene material conforms to the shape and size of the Ni foam structure. The Ni foam is then etched away using an etchant, leaving a monolithic graphene skeleton that is essentially an open-cell foam. Useful references to this method are given herein: zongping Chen et al, "Three-dimensional flexible and connected interconnected graphene network growth by chemical vapor deposition" and Nature Materials [ Natural Materials ],10 (6.2011) 424-428. There are several problems associated with this approach: (a) catalytic CVD is inherently a very slow, highly energy intensive, and expensive process; (b) etchants are typically highly undesirable chemicals and the resulting Ni-containing etching solutions are a source of contamination. It is very difficult and expensive to recover or recycle the dissolved Ni metal from the etchant solution. (c) It is challenging to maintain the shape and size of the graphene foam without damaging the cell walls when the Ni foam is etched away. The resulting graphene foam is typically very brittle and friable. (d) Transporting CVD precursor gases (e.g., hydrocarbons) into the interior of the metal foam can be difficult, resulting in non-uniform structures, as certain points within the sacrificial metal foam may be inaccessible to the CVD precursor gases.

The third method of producing graphene foam also utilizes a sacrificial material (e.g., colloidal polystyrene particles, PS) that is coated with graphene oxide sheets using a self-assembly process. For example, Choi et al prepared Chemically Modified Graphene (CMG) paper in two steps: free-standing PS/CMG membranes were fabricated by vacuum filtration of a mixed hydrocolloid suspension of CMG and PS (2.0 μm PS spheres), followed by removal

The PS beads were grown into 3D macropores [ B.G.Choi et al, "3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities [ 3D Macroporous Graphene framework for Supercapacitors with High Energy and Power Densities ], ACS Nano [ ACS nm ],6(2012) 4020-. ]. Choi et al manufactured well-ordered free standing PS/CMG papers by filtration, starting with separately prepared negatively charged CMG colloids and positively charged PS suspensions. A mixture of CMG colloid and PS suspension is dispersed in a solution at a controlled pH (═ 2), where both compounds have the same surface charge (zeta potential value +13 ± 2.4mV for CMG and +68 ± 5.6mV for PS). When the pH was raised to 6, CMG (zeta potential-29 ± 3.7mV) and PS spheres (zeta potential +51 ± 2.5mV) were assembled due to electrostatic interactions and hydrophobic characteristics between them, and these were subsequently integrated into PS/CMG composite paper by filtration process. This approach also has several disadvantages: (a) this method requires very cumbersome chemical processing of both graphene oxide and PS particles. (b) Removal of the PS by toluene also results in a weakening of the macroporous structure. (c) Toluene is a highly regulated chemical and must be handled with extreme care. (d) The pore size is typically too large (e.g., several μm), too large for many useful applications.

The above discussion clearly indicates that each of the prior art methods or processes for producing graphene and graphene foam have major drawbacks.

Disclosure of Invention

It is an object of the present invention to provide a new class of thermally and electrically conductive and mechanically robust foam materials and to provide a cost-effective method of producing such foams.

Humic Acid (HA) is an organic substance that is commonly present in soil and can be extracted from soil using a base such as KOH. HA can also be extracted in high yield from a type of coal known as leonardite, which is a highly oxidized version of lignite. HA extracted from leonardite contains a large amount of SP located in graphene-like molecular center (hexagonal carbon structure)²Core) and oxygen-containing groups (e.g., carboxyl groups) around the periphery. This material is somewhat 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 (the other major elements are carbon and hydrogen). After chemical or thermal reduction, HA HAs an oxygen content of 0.01 to 5% by weight. For the purposes of the claims in this application, Humic Acid (HA) refers to the total oxygen content range 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 is directed to a new class of graphene-like 2D materials (i.e., humic acids) that can surprisingly be converted into foam structures with high structural integrity. It is therefore another object to provide a cost-effective process for the mass production of such nanocarbon foams (in particular humic acid derived foams). This method does not involve the use of environmentally unfriendly chemicals. This method enables flexible design and control of porosity levels and pore sizes.

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

It is a further object of the invention to provide products (e.g.plants) containing the humic acid derived foams of the invention and methods of operating these products.

The present invention provides a humic acid derived foam consisting of a plurality of pores and pore walls, wherein the pore walls contain a monolayer or few-layer of humic acid derived hexagonal carbon sheets and the few-layer hexagonal carbon sheets have 2 to 10 stacked planes of hexagonal carbon atoms with an interplanar spacing d from 0.3354nm to 0.60nm (preferably not more than 0.40nm) as measured by X-ray diffraction₀₀₂. The single or few layer hexagonal carbon sheet contains 0.01 to 25% by weight of non-carbon elements. The Humic Acid (HA) is selected from the group consisting of 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, chemically functionalized humic acid, and combinations thereof.

The humic acid derived foams of the invention herein may be divided into three types: (a) humic Acid (HA) foams containing at least 10% by weight (typically from 10% to 42% by weight, and most typically from 10% to 25%) of non-carbon elements that can be used for a wide range of applications (where the original humic acid molecules remain essentially unchanged, but some chemical linking between the HA molecules HAs occurred); (b) a chemically combined and reduced humic acid based foam, wherein extensive linking and merging between the original HA molecules HAs taken place to form initial graphene-like hexagonal carbon sheets constituting the pore walls, causing the release of chemical species containing non-carbon elements initially attached to the HA molecules (hence, the non-carbon element content is reduced to typically between 2 and 10% by weight); and (c) humic acid derived graphite foam containing essentially all only carbon (non-carbon content < 2% by weight, preferably < 1%, and further preferably < 0.1%), wherein the cell walls contain a monolayer or few layers (2-10) of graphene-like sheets that are hexagonal carbon atom planes.

Preferably and typically, the HA-derived foam HAs from 0.005g/cm³To 1.7g/cm³From 50m²G to 3,200m²A specific surface area per g, a thermal conductivity per specific gravity of at least 100W/mK, and/or an electrical conductivity per specific gravity of not less than 500S/cm. More typically, the humic acid derived foam has from 0.01g/cm³To 1.5g/cm³Or an average pore diameter from 2nm to 50 nm. In one embodiment, the foam has a thickness of from 200m²A/g to 2,000m²Specific surface area per gram or from 0.1g/cm³To 1.3g/cm³The density of (c).

Typically, if the HA-derived foam is produced by a process that does not contain a Heat Treatment Temperature (HTT) above 300 ℃, the foam HAs a non-carbon element content in the range of 10 to 42% by weight. These pore walls may still contain identifiable humic acid molecules in the form of lamellar hexagonal carbon structures. The non-carbon element may include an element selected from: oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. In a particular embodiment, the cell walls contain fluorinated humic acid and the foam contains a fluorine content of from 0.01% to 25% by weight. In another embodiment, the foam contains an oxygen content of from 0.01% to 25% by weight.

At HTTs above 300 ℃, closely packed and well aligned adjacent HA molecules can be chemically linked together to form a polycyclic aromatic structure similar to the original graphene-like hexagonal carbon structure. As the thermal 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, and at the same time, several hexagonal carbon planes can be stacked together to form a multi-layered carbon atom structure similar to the few-layered graphene structure. The interplanar spacing is typically reduced to < <0.60nm, more typically <0.40 nm. If the HTT is from 300 ℃ up to 1,500 ℃, foams based on chemically combined and reduced humic acid are typically produced, where extensive linking and combination between the original HA molecules HAs occurred to form the original graphene-like hexagonal carbon sheets that constitute the pore walls. The non-carbon elements in the foam are typically reduced to from 2% to 10%.

If the HTT is from 1,500 ℃ to 3,200 ℃, the foam can essentially become a graphite foam in which the cell walls contain single or few layers of graphene-like hexagonal carbon planes and the non-carbon content is reduced to less than 2% by weight.

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

In a preferred embodiment, the HA-derived foam HAs an oxygen content or non-carbon content of less than 1% by weight, and the cell walls have stacked graphene-like planes with an inter-plane spacing of less than 0.35nm, a thermal conductivity of at least 200W/mK per specific gravity, and/or an electrical conductivity of no less than 1,000S/cm per specific gravity.

In another preferred embodiment, the HA-derived foam HAs an oxygen content or non-carbon content of less than 0.1% by weight, and the cell walls contain stacked graphene-like hexagonal carbon atom planes having an interplanar spacing of less than 0.34nm, a thermal conductivity of at least 250W/mK per specific gravity, and/or an electrical conductivity of no less than 1,500S/cm per specific gravity.

In yet another preferred embodiment, the graphene foam has an oxygen content or non-carbon content of no greater than 0.01% by weight, and the cell walls contain stacked graphene-like planes having an inter-graphene spacing of less than 0.336nm, a mosaic spread value of no greater than 0.7, a thermal conductivity of at least 300W/mK per specific gravity, and/or an electrical conductivity of no less than 2,000S/cm per specific gravity.

In yet another preferred embodiment, the graphene foam has cell walls containing stacked graphene-like atomic planes having an inter-plane spacing of less than 0.336nm, a mosaic spread value of no greater than 0.4, a thermal conductivity of greater than 400W/mK per specific gravity, and/or an electrical conductivity of greater than 3,000S/cm per specific gravity.

In a preferred embodiment, the pore walls contain stacked graphene-like hexagonal carbon atom planes having an interplanar spacing of less than 0.337nm and a mosaic spread value of less than 1.0. In a preferred embodiment, the foam exhibits a graphitization degree not less than 80% (preferably not less than 90%) and/or a mosaic spread value less than 0.4. In a preferred embodiment, the pore walls contain a 3D network of interconnected graphene-like planes of hexagonal carbon atoms.

In a preferred embodiment, the solid foam contains mesoscale pores having a pore size of from 2nm to 50 nm. The solid foam can also be made to contain micron-sized pores (1-500 μm).

The HA-derived foams of the present invention may be produced by a process comprising: (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 selected from the group consisting of 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, chemically functionalized humic acid, or combinations thereof, and wherein the dispersion contains an optional blowing agent, has a blowing agent to humic acid weight ratio of from 0/1.0 to 1.0/1.0; (b) dispensing and depositing the graphene dispersion onto a surface of a support substrate (e.g., plastic film, rubber sheet, metal foil, glass sheet, paper sheet, etc.) to form a wet humic acid layer; (c) partially or completely removing the liquid medium from the wet humic acid layer to form a dried humic acid layer; and (d) heat treating the dried humic acid layer at a first heat treatment temperature of from 80 ℃ to 3,200 ℃ at a desired heating rate sufficient to initiate the formation and release of volatile gas molecules from non-carbon elements (e.g., O, H, N, B, F, Cl, Br, I, etc.) or to activate a foaming agent to produce a humic acid derived foam. Preferably, the distribution and deposition procedure comprises subjecting the humic acid dispersion to orientation-induced stress.

This optional blowing agent is not needed if the HA material HAs a non-carbon element (e.g. O, H, N, B, F, Cl, Br, I, etc.) content of not less than 5% (preferably not less than 10%, further preferably not less than 20%, even more preferably not less than 30%) by weight. This subsequent high temperature treatment serves to remove most of these non-carbon elements from the edges of the HA molecule, thereby generating volatile gaseous species that create pores or cells in the solid foam structure. In other words, quite unexpectedly, these non-carbon elements act as blowing agents. Thus, an externally added blowing agent is optional (not necessary). However, the use of a blowing agent may provide additional flexibility in adjusting the level of porosity and pore size for a desired application. If the non-carbon content of the humic acid is less than 5%, then typically a foaming agent is required.

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

The method may further comprise the step of heat treating the solid foam at a second heat treatment temperature higher than the first heat treatment temperature for a period of time sufficient to obtain a graphene-like foam in which the cell walls contain stacked hexagonal planes of carbon atoms having an interplanar spacing d from 0.3354nm to 0.40nm₀₀₂And a non-carbon element content of less than 5% by weight (typically from 0.001% to 2%). When the content of the non-carbon element obtained is from 0.1% to 2.0%, the inter-plane spacing d₀₀₂Typically from 0.337nm to 0.40 nm.

If the original HA molecules in the dispersion contain a non-carbon content higher than 5% by weight, the planes of hexagonal carbon atoms in the solid foam (after the heat treatment) 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 process is a roll-to-roll process, wherein steps (b) and (c) comprise feeding a support substrate from a feed roll to a deposition zone, continuously or intermittently depositing the HA dispersion onto the surface of the support substrate to form a wet layer of HA material thereon, drying the wet layer of HA material to form a dry layer of HA material, and collecting the dry layer of HA material deposited on the support substrate on a collection roll. This reel-to-reel or reel-to-reel approach is a truly industrial-scale, large-scale manufacturing process that can be automated.

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

The first and/or second heat treatment of the dried HA layer HAs several unexpected results, and different heat treatment temperature ranges enable us to achieve different objectives, such as (a) removal of non-carbon elements from HA material (e.g. thermal reduction of fluorinated humic acid to obtain reduced humic acid), this generates volatile gases to create pores or cells in the HA foam, (b) activates chemical or physical blowing agents to create pores or cells, (c) chemically links or merges humic acid molecules into highly aromatic molecules and edge-to-edge merges aromatic ring structures or hexagonal carbon planes to significantly increase the lateral dimensions (length and width) of graphene-like hexagonal carbon sheets in the foam walls (solid portion of the foam), (d) repairs defects naturally occurring in HA or created during fluorination, oxidation, or nitridation of humic acid molecules, and (e) reorganizes and perfects graphite domains or graphite crystals. These different purposes or functions are achieved to different degrees in different temperature ranges. Non-carbon elements typically include elements selected from: oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. Quite unexpectedly, even under low temperature foaming conditions, heat treatment often causes chemical bonding, coalescence, or chemical bonding between the plate-like HA molecules in an edge-to-edge manner (some in a face-to-face manner).

In one embodiment, the HA-derived foam HAs from 200m²A/g to 2,000m²Specific surface area in g. In one embodiment, the solid foam has from 0.1g/cm³To 1.5g/cm³The density of (c). In one embodiment, the step (d) of heat treating the layer of HA material at the first heat treatment temperature is performed under a compressive stress. In another embodiment, the method includes a compression step to reduce the thickness, pore size, or porosity level of the membrane of the HA-derived foam. In some applications, the foam has a thickness of no greater than 200 μm.

In one embodiment, the HA dispersion HAs at least 5% by weight of HA dispersed in a liquid medium to form a liquid crystal phase. In one embodiment, the first heat treatment temperature comprises a temperature in the range of 80 ℃ to 300 ℃, and as a result, the HA foam HAs an oxygen content or non-carbon element content of less than 5%, and the cell walls have an interplanar spacing of less than 0.40nm, a thermal conductivity of at least 150W/mK (more typically at least 200W/mK) per specific gravity, and/or an electrical conductivity of no less than 1,000S/cm per specific gravity.

In a preferred embodiment, the first and/or second heat treatment temperature comprises a temperature in the range of 300 ℃ to 1,500 ℃ and as a result the HA-derived foam HAs an oxygen content or non-carbon content of less than 2% and the cell walls have an inter-plane spacing of less than 0.35nm, a thermal conductivity of at least 250W/mK per specific gravity and/or an electrical conductivity of not less than 1,500S/cm per specific gravity.

When the first and/or second heat treatment temperatures comprise a temperature in the range of 1,500 ℃ to 2,100 ℃, the HA-derived foam HAs an oxygen content or non-carbon content of less than 1%, and the cell walls have an inter-graphene spacing of less than 0.34nm, a thermal conductivity of at least 300W/mK per specific gravity, and/or an electrical conductivity of not less than 3,000S/cm per specific gravity.

When the first and/or second heat treatment temperatures comprise a temperature greater than 2,100 ℃, the HA-derived foam HAs an oxygen content or non-carbon content of no greater than 0.1%, and the cell walls have an interplanar spacing of less than 0.336nm, a tesseral value of no greater than 0.7, a thermal conductivity of at least 350W/mK per specific gravity, and/or an electrical conductivity of no less than 3,500S/cm per specific gravity.

If the first and/or second heat treatment temperatures comprise a temperature of not less than 2,500 ℃, the HA-derived foam HAs cell walls comprising stacked graphene-like hexagonal carbon planes having an interplanar spacing of less than 0.336nm, a perplexity value of not greater than 0.4, and a thermal conductivity of greater than 400W/mK per specific gravity, and/or an electrical conductivity of greater than 4,000S/cm per specific gravity.

In one embodiment, the pore walls contain stacked graphene-like hexagonal carbon planes having an interplanar spacing of less than 0.337nm and a mosaic spread value of less than 1.0. In another embodiment, the solid wall portions of the HA-derived foam exhibit a degree of graphitization of not less than 80% and/or a mosaic spread value of less than 0.4. In yet another embodiment, the solid wall portions of the HA-derived foam exhibit a degree of graphitization of not less than 90% and/or a mosaic spread value of not greater than 0.4.

Typically, the pore walls in HA-derived graphite foams contain a 3D network of interconnected hexagonal carbon atom planes that are electron conduction pathways after heat treatment at HTT above 2,500 ℃. The cell walls contain graphitic domains or graphitic crystals having a transverse dimension (L)_aLength or width) of not less than 20nm, more typically and preferably not less than 40nm, still more typically and preferably not less than 100nm, still more typically and preferably not less than 500nm, often more than 1 μm, and sometimes more than 10 μm. The graphitic domains typically have a thickness from 1nm to 20nm, more typically from 1nm to 10nm, and even more typically from 1nm to 4 nm.

Preferably, the HA-derived foam contains mesoscale pores having a pore size of from 2nm to 50nm (preferably 2nm 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 comprised of a plurality of cells and cell walls. The method comprises 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 selected from the group consisting of 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, chemically functionalized humic acid, or combinations thereof, and wherein the dispersion contains an optional blowing agent, has a blowing agent to humic acid weight ratio of from 0/1.0 to 1.0/1.0; (b) continuously or intermittently dispensing and depositing the HA dispersion onto a surface of a support substrate to form a wet HA material layer, wherein the support substrate is a continuous film supplied from a feed roll and collected on a collection roll; (c) partially or completely removing the liquid medium from the wet humic acid layer to form a dried humic acid layer in a heating zone or zones; and (d) heat-treating the dried humic acid layer in one of the heating zones containing a heating temperature of from 80 ℃ to 500 ℃ at a desired heating rate sufficient to activate the foaming agent to produce a coating having from 0.01g/cm³To 1.7g/cm³Of from 50m²G to 3,000m²Humic acid derived foam per g of specific surface area. In this method, the heat treatment occurs in situ during the roll-to-roll procedure. This is a highly cost-effective process suitable for mass-producing HA-derived graphite foam sheets that are wound on rolls for ease of transport and handling and subsequently for ease of cutting and slitting.

The orientation-inducing stress may be a shear stress. As an example, shear stress can be encountered in a simple case like a "doctor blade" which directs the HA dispersion to spread at a sufficiently high shear rate on the plastic or glass surface during the hand casting process. As another example, effective orientation-induced stresses are generated in an automated roll-to-roll coating process, where a "knife-on-roll" configuration dispenses a graphene dispersion on a moving solid substrate (such as a plastic film). The relative motion between the moving film and the coating knife is used to achieve orientation of the graphene sheets in the direction of shear stress. Comma coating and slot die coating are particularly effective methods for this function.

Since it was surprisingly observed that shear stress enables alignment of HA molecules or sheets in a specific direction (e.g. X-direction or length direction) to create a preferred orientation and to promote contact between HA molecules or sheets along the foam walls, such orientation induced stress is a crucial step in the production of the HA-derived foams of the present invention. It is further surprising that these preferred orientations and improved HA-to-HA contact promote chemical merging or attachment between HA molecules or sheets during subsequent heat treatment of the dried HA layer. Such preferred orientation and improved contact are critical to ultimately achieve exceptionally high thermal conductivity, electrical conductivity, elastic modulus, and mechanical strength of the resulting HA-derived foam. In general, these excellent properties cannot be obtained without such shear stress induced orientation control.

The invention also provides an apparatus for removing oil or separating oil, which contains humic acid-derived foam as an element for absorbing oil. Also provided is an apparatus for removing or separating a solvent, which contains humic acid-derived foam as an element for absorbing or separating the solvent.

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

In addition, the present invention provides a process for separating an organic solvent from a solvent-water mixture or from a multi-solvent mixture. The method comprises the following steps: (a) providing an element for absorbing the organic solvent or separating the solvent, the element comprising integral humic acid derived foam; (b) contacting the element with an organic solvent-water mixture or a multi-solvent mixture comprising a first solvent and at least a second solvent; (c) allowing the element to absorb the organic solvent from the mixture or to separate the first solvent from the at least second solvent; (d) withdrawing the element from the mixture and extracting the organic solvent or first solvent from the element; and (e) reusing the element.

Also provided is a thermal management device containing humic acid derived foam as a heat spreading or dissipating element. The thermal management device may contain a device selected from the group consisting of: a heat exchanger, a heat sink, a heat pipe, a highly conductive insert, a conductive plate between the heat sink and a heat source, a heat spreading component, a heat dissipating component, a thermal interface medium, or a thermoelectric or Peltier cooling device.

Drawings

Fig. 1 shows a schematic diagram of a process for producing graphene sheets from natural graphite particles.

FIG. 2 possible mechanisms of chemical ligation and incorporation between humic acid molecules and between "linked HA molecules". Two or three original HA molecules may be chemically linked together to form a longer or wider HA molecule, which is referred to as a "linked HA molecule". Multiple "linked HA molecules" can be combined to form a graphene-like hexagonal carbon atom plane.

FIG. 3(A) thermal conductivity values versus specific gravity for HA-derived foams, mesophase pitch-derived graphite foams, and Ni foam template assisted CVD graphene foams produced by the method of the present invention;

fig. 3(B) thermal conductivity values for HA-derived foams, GO foams sacrificing plastic bead templates, and hydrothermally reduced GO graphene foams.

Figure 4 conductivity data for HA-derived foams and hydrothermally reduced GO graphene foams produced by the inventive process.

FIG. 5 thermal conductivity values plotted as a function of specific gravity for foam samples derived from HA and fluorinated HA.

Figure 6 thermal conductivity values as a function of final (maximum) heat treatment temperature for foam samples derived from HA and pristine graphene.

FIG. 7 plots the amount of oil absorbed per gram of HA-derived foam as a function of oxygen content in the foam having a porosity level of about 98% (oil separation from oil-water mixture).

FIG. 8 the amount of oil absorbed per gram of integral HA-derived foam is plotted as a function of porosity level (assuming the same oxygen content).

Figure 9 the amount of chloroform absorbed from a chloroform-water mixture is plotted as a function of the degree of fluorination.

Fig. 10 schematic view of a heat sink structure (2 examples).

Detailed Description

Humic Acid (HA) is an organic substance that is commonly present in soil and can be extracted from soil using a base such as KOH. HA can also be extracted from a type of coal known as leonardite, which is a highly oxidized version of lignite. HA extracted from leonardite contains a large amount of SP located in graphene-like molecular center (hexagonal carbon structure)²Core) oxygen-containing groups (e.g., carboxyl groups) around the periphery. This material is somewhat 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 (the other main elements are carbon, hydrogen, and nitrogen). Examples of the molecular structure of humic acids with various components including quinone, phenol, catechol and sugar moieties are given in scheme 1 below (source: Stevenson F.J. "Humus Chemistry: genetics, Composition, Reactions [ humic Chemistry: origin, Composition, reaction)]"John Wiley parent-child publishing company (John Wiley)&Sons), new york 1994).

The non-aqueous solvent of humic acid includes polyethylene glycol, ethylene glycol, propylene glycol, alcohol, sugar alcohol, polyglycerol, glycol ether, amine-based solvent, amide-based solvent, alkylene carbonate, organic acid, or inorganic acid.

The present invention provides a humic acid derived foam having a plurality of pores and pore walls and a method for producing the same. The pores in the foam are formed during or after the sheet-like humic acid molecules (1) are chemically linked/merged together (edge-to-edge and/or face-to-face) at temperatures typically from 100 ℃ to 1,500 ℃, and/or (2) are composed into larger graphite crystals or domains (referred to herein as graphitization) along the pore walls at elevated temperatures (typically >2,100 ℃ and more typically >2,500 ℃).

The invention also provides a production method, which comprises 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 selected from the group consisting of 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, chemically functionalized humic acid, or combinations thereof, and wherein the dispersion contains an optional blowing agent, has a blowing agent to humic acid weight ratio of from 0/1.0 to 1.0/1.0; (b) dispensing and depositing the graphene dispersion onto a surface of a support substrate (e.g., plastic film, rubber sheet, metal foil, glass sheet, paper sheet, etc.) to form a wet humic acid layer; (c) partially or completely removing the liquid medium from the wet humic acid layer to form a dried humic acid layer; and (d) heat treating the dried humic acid layer at a first heat treatment temperature of from 80 ℃ to 3,200 ℃ at a desired heating rate sufficient to initiate volatile gas molecules or activate blowing agents from non-carbon elements (e.g., O, H, N, B, F, Cl, Br, I, etc.) to produce a humic acid derived foam. Preferably, the distribution and deposition procedure comprises subjecting the humic acid dispersion to orientation-induced stress. When removed via thermally induced decomposition, these non-carbon elements produce volatile gases that act as blowing or foaming agents.

The resulting humic acid derived foam typically has from 0.005g/cm³To 1.7g/cm³(more typically from 0.01g/cm³To 1.5g/cm³And even more typically from 0.1g/cm³To 1.0g/cm³And most typically from 0.2g/cm³To 0.75g/cm³) Or from 50m²A/g to 3,000m²G (more typically from 200 m)²A/g to 2,000m²G, and most typically from 500m²G to 1,500m²Specific surface area of/g).

Blowing or foaming agents are substances that are capable of producing cells or foam structures in various materials that undergo hardening or phase transformation via a foaming process, such as polymers (plastics and rubbers), glass, and metals. They are typically applied when the foamed material is in a liquid state. It has not previously been known that blowing agents can be used to produce foams (when in the solid state). More significantly, it has not previously been taught or suggested that aggregates of humic acid molecules can be converted into graphene-like foams via a foaming agent. Cell structures in the matrix are typically created for the purpose of reducing density, increasing thermal resistance, and sound insulation while increasing the thickness and relative stiffness of the original polymer.

Blowing agents or related foaming mechanisms for producing cells or cells (bubbles) in a substrate to produce a foam or cellular material may be classified into the following groups:

(a) physical foaming agent: for example, hydrocarbons (e.g., pentane, isopentane, cyclopentane), chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), and liquid CO₂. The process of generating the bubbles/foam is endothermic, i.e., it requires heat (e.g., from a melting process or a chemical exotherm due to crosslinking) to volatilize the liquid blowing agent.

(b) Chemical foaming agent: for example, isocyanates, azo, hydrazine and other nitrogen based materials (for thermoplastic and elastomeric foams), sodium bicarbonate (e.g., baking soda, which is used for thermoplastic foams). Here, gaseous products and other by-products are formed by chemical reactions, promoted by the exothermic heat of the process or reacting polymer. Since the foaming reaction involves the formation of low molecular weight compounds which act as foaming gases, additional exothermic heat is also released. Powdered titanium hydride is used as a blowing agent in the production of metal foams because it decomposes at elevated temperatures to form titanium and hydrogen. Zirconium (II) hydride is used for the same purpose. Once formed, the low molecular weight compounds will never revert back to the original blowing agent or agents, i.e., the reaction is irreversible.

(c) Mixed physical/chemical blowing agents: for example for the production of flexible Polyurethane (PU) foams with very low densities. Both chemical and physical foaming can be used in tandemTo balance each other with respect to the thermal energy released/absorbed; thereby minimizing temperature rise. For example, isocyanate and water (which react to form CO)₂) With liquid CO₂(which boils to give a gaseous form) in combination with the use to produce a very low density flexible PU foam for use in mattresses.

(d) Mechanical injection: mechanically-made foams involve a process of introducing gas bubbles into a liquid polymerizable matrix, such as an uncured elastomer in the form of a liquid latex. The process involves stirring air or other gas or low boiling point volatile liquid in a low viscosity latex or injecting the gas into an extruder barrel or die or into an injection molding barrel or nozzle and allowing the shearing/mixing action of the screw to disperse the gas uniformly to form very fine bubbles or gas solutions in the melt. When the melt is molded or extruded and the part is at atmospheric pressure, gas comes out of solution, causing the polymer melt to expand immediately before solidification.

(e) Soluble and leachable agents: soluble fillers, such as solid sodium chloride crystals, are mixed into a liquid urethane system, which is then formed into a solid polymer part, which is later washed away by immersing the solid molded part in water for some time to leave small interconnected pores in the relatively high density polymer product.

(f) We have found that the above five mechanisms can be used to create pores in HA-derived materials when these materials are in the solid state. Another mechanism for creating pores in HA materials is by generating and evaporating volatile gases through the removal of those non-carbon elements in a high temperature environment. This is a unique self-foaming process that has not been previously taught or suggested.

The cell walls (cell walls) in the foam of the present invention contain planes of graphene-like hexagonal carbon atoms that are chemically bonded and coalesced. These planar aromatic molecules or carbon atoms of hexagonal structure are well interconnected physically and chemically. The lateral dimensions (length or width) of these planes are huge (from 20nm to >10 μm), typically several times or even orders of magnitude larger than the maximum length/width of the starting humic acid molecules. The hexagonal carbon atom planes are substantially interconnected to form a long electron conduction path with low resistance. This is a unique and new class of materials that have not previously been discovered, developed or suggested to be present.

In step (b), the HA suspension is formed as a wet layer on a solid substrate surface (e.g. PET film or glass), preferably under the influence of shear stress. One example of such a shearing procedure is the casting or coating of a film of HA suspension using a coater. This procedure is analogous to applying a layer of varnish, paint, coating or ink to a solid substrate. The roll, "doctor blade", or wiper may generate shear stress when the film is formed, or when there is relative motion between the roll/blade/wiper and the supporting substrate at a sufficiently high relative motion speed. Quite unexpectedly and significantly, this shearing action enables good alignment of planar HA molecules, for example, in the shearing direction. It was further surprising that this molecular alignment or preferred orientation was not disrupted when the liquid component of the HA suspension was subsequently removed to form a well-packed layer of at least partially dried, highly aligned, sheet-like HA molecules. The dried HA film HAs a high birefringence coefficient between the in-plane direction and the perpendicular-to-plane direction.

In one embodiment, this HA layer is then subjected to a heat treatment to activate the blowing agent and/or to remove non-carbon elements (e.g., F, O, etc.) from the HA molecules to generate volatile gases as a byproduct. These volatile gases create pores or bubbles within the solid HA material, pushing the plate-like HA molecules into the wall structure, thereby forming the HA foam. If no foaming agent is added, the non-carbon elements in the HA material preferably constitute at least 10% (preferably at least 20%, and further preferably at least 30%) by weight of the HA material. The first (initial) heat treatment temperature is typically greater than 80 ℃, preferably greater than 100 ℃, more preferably greater than 300 ℃, even more preferably greater than 500 ℃ and may be as high as 1,500 ℃. Blowing agents are typically activated at temperatures from 80 ℃ to 300 ℃ (but may be higher). The foaming procedure (formation of pores, cells, or bubbles) is typically accomplished at a temperature in the range of 80 c to 1,500 c. Quite unexpectedly, chemical attachment or incorporation between planes of hexagonal carbon atoms in an edge-to-edge and face-to-face manner (fig. 2) can occur at relatively low heat treatment temperatures (e.g., as low as from 150 ℃ to 300 ℃).

The HA-derived foam may be subjected to a further heat treatment involving at least a second temperature substantially higher than the first heat treatment temperature.

A suitably programmed thermal treatment program may involve only a single thermal treatment temperature (e.g., only a first thermal treatment temperature), at least two thermal treatment temperatures (a first temperature for a period of time and then raised to and held at a second temperature for another period of time), or any other combination of thermal treatment temperatures (HTTs) involving an initial treatment temperature (first temperature) and a final HTT (second) (higher than the first temperature). The highest or final HTT experienced by the dried HA layer can be divided into four different HTT schemes:

scheme 1(80 ℃ to 300 ℃): in this temperature range (chemical ligation and thermal reduction scheme, and also activation scheme of the foaming agent, if present), the HA layer undergoes mainly thermally induced chemical ligation of adjacent HA molecules, as schematically shown 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 in oxygen content from typically 20% -42% (O in HA) to about 10% -25%. This treatment results in a decrease in the interplanar spacing in the foam walls from about 0.6-1.2nm (as dried) to about 0.4-0.6nm and an increase in thermal conductivity to 100W/mK per specific gravity and/or an increase in electrical conductivity to 2,000S/cm per specific gravity. (since the porosity level, and thus the specific gravity of the graphene foam material, can be varied, and assuming the same graphene material, both thermal and electrical conductivity values vary with specific gravity, these property values must be divided by specific gravity to facilitate a fair comparison.) even at such low temperature ranges, some chemical bonding between the HA molecules occurs. The interplanar spacing remains relatively large (0.4nm or greater). Many functional groups containing O remain (e.g., -OH and-COOH).

Scheme 2(300 ℃ -1,500 ℃): in this chemical linking and merging scheme, extensive chemical combination, polymerization, and crosslinking between adjacent HA molecules or linked HA molecules occurs to form an initial graphene-like hexagonal carbon atom plane, as shown in the lower portion of fig. 2. The oxygen content is reduced to typically from 2% to 10% (e.g., after chemical joining and consolidation), thereby causing the inter-planar spacing to be reduced to about 0.345 nm. This means that some initial graphitization has already been started at such low temperatures, in sharp contrast to conventional graphitizable materials (such as carbonized polyimide films) which typically require temperatures as high as 2,500 ℃ to start graphitization. This is another different feature of the graphene foam of the present invention and the method for producing the same. These chemical linking reactions result in an increase in thermal conductivity to >250W/mK per specific gravity and/or an increase in electrical conductivity to 2,500-4,000S/cm per specific gravity.

Scheme 3(1,500 ℃ -2,500 ℃): in this ordered and graphitized approach, extensive graphitization or graphene-like planar coalescence occurs, resulting in a significant improvement in the degree of structural order in the foam walls. As a result, the oxygen content is reduced to typically 0.1% -2% and the inter-graphene spacing is reduced to about 0.337nm (depending on the actual HTT and duration, achieving a graphitization degree from 1% to about 80%). The improved degree of order is also reflected by an increase in thermal conductivity to >350W/mK per specific gravity, and/or an increase in electrical conductivity to >3,500S/cm per specific gravity.

Scheme 4 (above 2,500 ℃): in this recrystallization and perfection protocol, substantial movement and elimination of grain boundaries and other defects occurs, resulting in the formation of nearly perfect single or polycrystalline graphene-like crystals with large grains in the foam walls, which can be orders of magnitude larger than the original size of the HA molecules. Oxygen content is substantially eliminated, typically 0% to 0.01%. The interplanar spacing was reduced to about 0.3354nm (graphitization degree from 80% to nearly 100%), corresponding to that of a perfect graphite single crystal. The foam structure thus obtained exhibits a thermal conductivity of >400W/mK per specific gravity and an electrical conductivity of >4,000S/cm per specific gravity.

The HA-derived foam structure of the present invention may be obtained by heat treating the dried HA with a temperature program covering at least the first protocol (typically 1-4 hours are required in this temperature range if the temperature never exceeds 500 ℃), more typically the first two protocols (1-2 hours preferred), still more typically the first three protocols (preferably 0.5-2.0 hours in protocol 3), and possibly all 4 protocols (including protocol 4 for 0.2 to 1 hour, which may be carried out to achieve the highest conductivity).

X-ray diffraction patterns were obtained with an X-ray diffractometer equipped with CuKcv radiation. The shift and broadening of the diffraction peak were calibrated using silicon powder standards. Using the Mering equation, d₀₀₂0.3354g +0.344(1-g), degree of graphitization g calculated from X-ray diagram, where d is₀₀₂The spacing between graphite or graphene type crystal layers is in nm. Only when d₀₀₂Equal to or less than about 0.3440nm, this equation is valid. Having a d above 0.3440nm₀₀₂The HA-derived foam walls of (a) reflect oxygen-containing functional groups (such as-OH, on the planar surface or edges of graphene-like molecules, a-OH, a-group, a-containing group, a-hydroxyl group, a-containing group, a carboxyl group, a carboxyl group, a carboxyl group, a carboxyl group, a carboxyl group, a carboxyl group, a group,>O, and-COOH).

Another structural index that can be used to characterize the order of the HA-derived graphene-like foam walls and the planes of hexagonal carbon atoms stacked and bonded in conventional graphite crystals is the "mosaic spread", which is represented by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection. This degree of order characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the preferred degree of grain orientation. An almost perfect single crystal of graphite is characterized by a mosaic expansivity value of 0.2-0.4. Most of our graphene walls have mosaic spread values in this range of 0.2-0.4 (if produced with a Heat Treatment Temperature (HTT) of not less than 2,500 ℃). However, if the HTT is between 1,500 ℃ and 2,500 ℃, some values are in the range of 0.4-0.7; and some values are in the range of 0.7-1.0 if the HTT is between 300 ℃ and 1,500 ℃.

Illustrated in fig. 2 is a plausible chemical ligation and incorporation mechanism, where only 2 aligned HA molecule fragments are shown as an example, although a large number of HA molecules may be chemically ligated together and multiple "ligated HA molecules") may be chemically incorporated to form the foam wall. Furthermore, for HA molecules or sheets, chemical attachment can also occur face-to-face, rather than just edge-to-edge. 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 having essentially infinite molecular weight. All of the constituent hexagonal carbon planes are very large in lateral dimensions (length and width) and if the HTT is high enough (e.g., >1,500 ℃ or much higher), these planes are essentially bonded to each other.

In-depth studies using a combination of SEM, TEM, selective area diffraction, X-ray diffraction, AFM, raman spectroscopy and FTIR indicate that HA-derived foam walls are composed of several large planes of hexagonal carbon atoms (where length/width is typically the length/width>>20nm, more typically>>100nm, often>>1 μm, and in many cases>>10 μm, or even>>100 μm). If the final heat treatment temperature is below 2,500 ℃, these giant graphene-like planes are often stacked and bonded not only by van der waals forces (as in conventional graphite crystallites) but also by covalent bonds in the thickness direction (crystallographic c-axis direction). In these cases, without wishing to be bound by theory, raman and FTIR spectroscopy studies appear to indicate sp²(dominant) and sp³Coexistence of (weak but present) electronic configurations, not just conventional sp in graphite²。

(1) The HA-derived graphite foam wall is not made by gluing or bonding discrete flakes/platelets together with a resin binder, linking agent, or adhesive. In contrast, HA molecules are incorporated into an integrated graphene-like crystalline entity by interconnecting or forming covalent bonds, without the use of any externally added linking or binder molecules or polymers.

(2) The foam walls are typically polycrystalline, consisting of large grains with incomplete grain boundaries. This entity is derived from a plurality of HA molecules, and these aromatic HA molecules have lost their original properties. After removal of the liquid component from the suspension, the resulting HA molecules form a substantially amorphous structure. Upon heat treatment, these HA molecules chemically combine and join into a single or monolithic graphite entity that constitutes the foam wall. The foam walls are highly ordered.

(3) Due to these unique chemical compositions (including oxygen content or non-carbon content), morphology, crystal structure (including interplanar spacing), and structural features (e.g., high degree of orientation, few defects, incomplete grain boundaries, chemical bonding and absence of gaps between graphene sheets, and essentially no interruption in the hexagonal carbon plane), HA-derived foams have a unique combination of excellent thermal conductivity, electrical conductivity, mechanical strength, and stiffness (elastic modulus).

It may further be noted that if the non-carbon content (H and O) is from 2 to 20% by weight, a certain desired degree of hydrophilicity may be imparted to the cell walls of the humic acid-derived foam. These features enable the separation of oil from water by selective absorption of oil from the oil-water mixture. In other words, such HA-derived foams are capable of recovering oil from water, thereby facilitating the cleaning of oil spilled rivers, lakes, or oceans. The oil absorption capacity is typically from 50% to 500% of the foam's own weight. This is a very useful material for environmental protection purposes.

If high electrical or thermal conductivity is desired, the HA-carbon foam may be subjected to graphitization treatment at temperatures above 2,500 ℃. The resulting material is particularly useful for thermal management applications (e.g., for fabricating finned heat sinks, heat exchangers, or heat spreaders).

It may be noted that the HA-carbon foam may be subjected to compression during and/or after the graphitization treatment. This operation enables us to tune graphene sheet orientation and porosity.

To characterize the structure of the resulting graphitic material, X-ray diffraction patterns were obtained with an X-ray diffractometer equipped with CuKcv radiation. The shift and broadening of the diffraction peak were calibrated using silicon powder standards. Using the Mering equation, d₀₀₂0.3354g +0.344(1-g), degree of graphitization g calculated from X-ray diagram, where d is₀₀₂Is the spacing between graphite or graphene crystal layers in nm. Only when d₀₀₂Equal to or less than about 0.3440nm, this equation is valid. In the present study, the compounds haveD higher than 0.3440nm₀₀₂The graphene-like (HA or RHA) foam walls of (A) reflect oxygen-containing functional groups (such as-OH, on the planar surfaces or edges of graphene molecules, a-OH, a-H, and a-H, and a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier, and a salt thereof, and a pharmaceutically acceptable carrier, respectively, and a pharmaceutically acceptable carrier, in a base, in a pharmaceutically acceptable carrier, in a carrier, a base, in a carrier, in a,>O, and-COOH).

Another structural index that can be used to characterize the order of the stacked and bonded RHA planes in the foam walls of graphene and conventional graphite crystals is the "mosaic spread", which is represented by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection. This degree of order characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the preferred degree of grain orientation. An almost perfect single crystal of graphite is characterized by a mosaic expansivity value of 0.2-0.4. Most of our RHA walls have mosaic spread values in this range of 0.2-0.4 (if produced with a Heat Treatment Temperature (HTT) of not less than 2,500 ℃). However, if the HTT is between 1,500 ℃ and 2,500 ℃, some values are in the range of 0.4-0.7; and some values are in the range of 0.7-1.0 if the HTT is between 300 ℃ and 1,500 ℃.

In-depth studies using a combination of SEM, TEM, selective area diffraction, X-ray diffraction, AFM, raman spectroscopy, and FTIR indicate that humic acid-carbon foam walls are composed of several large graphene planes (where length/width is typically > >20nm, more typically > >100nm, often > >1 μm, and in many cases > >10 μm). This is quite unexpected, since the lateral dimensions (length and width) of the original humic acid pieces or molecules are typically <20nm, and more typically <10nm, before being subjected to the heat treatment. This suggests that multiple HA sheets or molecules can be combined edge-to-edge with each other into larger (longer or wider) sheets through covalent bonds.

These large graphene-like planes can also often be stacked and bonded along the thickness direction (crystallographic c-axis direction) not only by van der waals forces (as in conventional graphite crystallites) but also by covalent bonds if the final heat treatment temperature is below 2,500 ℃. In these cases, without wishing to be bound by theory, raman and FTIR spectroscopy studies appear to indicate sp²(dominant) and sp³(weak but not tooPresence) coexistence of electronic configurations, not just conventional sp in graphite²。

The unitary HA-derived foam is comprised of a plurality of pores and pore walls, wherein the pore walls comprise single or few-layered HA sheets chemically bonded together, wherein the few-layered HA sheets have 2-10 stacked graphene-like consolidated HA planes with an interplanar spacing d from 0.3354nm to 0.36nm as measured by X-ray diffraction₀₀₂And the single-or few-layer graphene-like HA sheet contains 0.01 to 25% by weight of non-carbon elements (more typically<15％)。

Integral HA derived foams typically have from 0.001g/cm³To 1.7g/cm³Density of from 50m²A/g to 3,000m²A specific surface area per g, a thermal conductivity per specific gravity of at least 200W/mK, and/or an electrical conductivity per specific gravity of not less than 2,000S/cm. In a preferred embodiment, the pore walls contain stacked graphene-like RHA planes with an inter-plane spacing d from 0.3354nm to 0.40nm as measured by X-ray diffraction₀₀₂。

The HA sheets may be covalently bonded to each other edge-to-edge to form a Reduced HA (RHA) entity. Due to these unique chemical compositions (including oxygen or hydrogen content, etc.), morphology, crystal structure (including interplanar spacing), and structural features (e.g., degree of orientation, few defects, chemical bonding and absence of gaps between graphene-like sheets, and substantially no interruption in the hexagonal plane direction), HA-derived foams have a unique combination of excellent thermal conductivity, electrical conductivity, mechanical strength, and stiffness (elastic modulus).

Thermal management applications

The above-described features and characteristics make unitary HA-derived foams ideal for a variety of engineering and biomedical applications. For example, for thermal management purposes only, the foam may be used in the following applications:

a) HA-derived foams that are compressible and have high thermal conductivity are ideally suited for use as Thermal Interface Materials (TIMs) that may be implemented between a heat source and a heat spreader or between a heat source and a heat sink.

b) HA-derived foams can be used as heat spreaders themselves due to their high thermal conductivity.

c) HA-derived foams can be used as heat sinks or heat dissipating materials due to their high heat spreading capacity (high thermal conductivity) and high heat dissipation capacity (large surface pores induce large air convection micro-or nano-channels).

d) Light weight (at 0.001 g/cm)³And 1.8g/cm³Adjustable low density), high thermal conductivity per unit specific gravity or per unit physical density, and high structural integrity (HA sheets are brought together to form long electron conducting pathways) make this HA-derived foam an ideal material for durable heat exchangers.

HA-derived foam based thermal management or dissipation devices include heat exchangers, heat spreaders (e.g., finned heat spreaders), heat pipes, highly conductive inserts, thin or thick conductive plates (between heat spreader and heat source), thermal interface media (or thermal interface material, TIM), thermoelectric or peltier cooling plates, and the like.

A heat exchanger is a device for transferring heat between one or more fluids; for example, gas and liquid flowing separately in different channels. These fluids are typically separated by solid walls to prevent mixing. The HA-derived foam material of the present invention is ideal for such walls, provided that the foam is not a fully open-cell foam that allows for fluid mixing. The process of the present invention enables the production of both open and closed cell foam structures. The high surface pore area allows for significantly faster heat exchange between two or more fluids.

Heat exchangers are widely used in refrigeration systems, air conditioning units, heaters, power plants, chemical plants, petrochemical plants, oil 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 through these coils, which cools the coolant and heats the incoming air. The solid walls (e.g., the solid walls that make up the radiator coil) are typically made of high thermal conductivity materials such as Cu and Al. The HA-derived foams of the present invention having higher thermal conductivity or higher specific surface area are excellent substitutes for, for example, Cu and Al.

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

The solid HA-derived foams of the present invention may 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, such as notebook computers, tablet computers, and smart phones, are well known heat sources. Typically, a metal or graphite object (e.g., a Cu or graphite foil) is brought into contact with the hot surface and this object helps to spread the heat to the outer surface or to the outside air (primarily by conduction and convection and to a lesser extent by radiation). In most cases, a thin Thermal Interface Material (TIM) mediates between the thermal surface of the heat source and the thermal diffusion surface of the heat spreader or heat spreader. (the HA-derived foams of the present invention may also be used as TIM.)

Heat sinks are typically composed of highly conductive material structures having one or more flat surfaces to ensure good thermal contact with the component to be cooled, and a series of comb or fin-like protrusions to increase surface contact with air and hence increase the rate of heat dissipation. The heat sink may be used in conjunction with a fan to increase the air flow rate over the heat sink. The heat sink may have a plurality of fins (elongated or protruding surfaces) to improve heat transfer. In electronic devices with a limited amount of space, the shape/arrangement of the fins must be optimized so that the heat transfer density is maximized. Alternatively or additionally, cavities (inverted fins) may be embedded in the areas formed between adjacent fins. These cavities are effective in extracting heat from the plurality of heat generating bodies to the heat sink.

Typically, an integral heat sink comprises a heat collecting member (core or base) and at least one heat dissipating member (e.g. one or more fins) integral with the heat collecting member (base) to form a finned heat sink. The fins and the core are naturally connected or integrated together as a single piece without the use of externally applied adhesives or mechanical fastening means to connect the fins to the core. The heat collecting base has a surface in thermal contact with a heat source (e.g., LED), collects heat from this heat source, and dissipates the heat into the air through the fins.

As an illustrative example, fig. 10 provides a schematic of two heat sinks: 300 and 302. The first contains a heat collecting member (or base member) 304 and a plurality of fins or heat dissipating members (e.g., fins 306) connected to the base member 304. The base member 304 is shown having a heat collecting surface 314 intended to be in thermal contact with a heat source. The 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 that includes a radial fin heat sink assembly comprising: (a) a base 308 including a heat collection surface 318; and (b) a plurality of spaced apart parallel planar fin members (e.g., 310, 312 as two examples) supported by or integral with the base 308, wherein the planar fin members (e.g., 310) include at least one heat dissipating surface 322. The plurality of parallel planar fin members are preferably equally spaced.

The highly elastic and resilient HA-derived foams of the present invention are themselves good thermal interface materials and are also highly effective thermal diffusion elements. In addition, this highly conductive foam may also be used as an insert for electronic device cooling and for enhancing heat removal from the chiplets to the heat sink. Since the space occupied by the highly conductive material is a major concern, a more efficient design is to utilize highly conductive paths that can be embedded into the heat generating body. The resilient 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 a good conductive slab to be placed as a heat transfer interface between a heat source and a cold flowing fluid (or any other heat sink) to improve cooling performance. In this arrangement, the heat source is cooled under the thick HA-derived foam sheet, rather than being cooled in direct contact with a cooling fluid. The slab of HA-derived foam can significantly improve heat transfer between the heat source and the cooling fluid by conducting the heat flow in an optimal manner. No additional pumping power and no additional heat transfer surface area are required.

HA-derived foams are also excellent materials for constructing heat pipes. Heat pipes are heat transfer devices that transfer large amounts of heat using evaporation and condensation of a two-phase working fluid or coolant, with very little temperature difference between the hot and cold interfaces. A conventional heat pipe consists of: a sealed hollow tube made of a heat conductive metal such as Cu or Al; and a wick (wick) that returns the working fluid from the evaporator to the condenser. The tubes contain both saturated liquid and vapor of a working fluid (such as water, methanol, or ammonia), all other gases being excluded. However, both Cu and Al are prone to oxidation or corrosion, and therefore their performance degrades relatively quickly over time. In contrast, HA-derived foams are chemically inert and do not have these oxidation or corrosion problems. Heat pipes for thermal management of electronic devices may have a foam envelope and a wick, using water as the working fluid. The HA-derived foam/methanol may be used if the heat pipe needs to operate below the freezing point of water, and the HA-derived foam/ammonia heat pipe may be used for electronics cooling in a space.

Peltier cooling plates act based on the peltier effect to generate a heat flux between the junction of two different electrical conductors by applying an electrical current. This effect is commonly used to cool electronic components and small instruments. In practice, a number of such junctions may be arranged in series to increase this effect to the amount of heating or cooling required. HA-derived foams may be used to improve heat transfer efficiency.

Filtration and fluid absorption applications

HA-derived foams can be made containing microscopic pores (<2nm) or mesoscale pores with pore sizes from 2nm to 50 nm. HA derived foams may also be made to contain micron-sized pores (1-500 μm). Based only on well-controlled pore size, the HA-derived foams of the present invention may be anomalous filter materials for air or water filtration.

Furthermore, Humic Acid (HA) pore wall chemistry can be controlled to impart varying amounts and/or types of functional groups to the pore walls (e.g., as reflected by the percentage of O, F, N, H, etc. in the foam). In other words, simultaneous or independent control of both pore size and chemical functionality at different sites of the internal structure provides unprecedented flexibility or the highest degree of freedom in designing and manufacturing HA-derived foams that exhibit some unique combination of many unexpected properties, synergistic effects, and properties that are generally considered mutually exclusive (e.g., some portion of the structure is hydrophobic and others are hydrophilic; or the foam structure is both hydrophobic and lipophilic). If water is repelled by a material or surface, such surface or material is considered hydrophobic and a drop of water placed on the hydrophobic surface or material will form a large contact angle. A surface or material is considered oleophilic if it has a strong affinity for oil and not for water. The method of the invention allows for precise control of hydrophobicity, hydrophilicity and lipophilicity.

The present invention also provides an apparatus for removing oil, separating oil, or recovering oil, which contains the HA-derived foam of the present invention as an element for absorbing oil or separating oil. Also provided is a desolventizing or solvent separating device comprising the HA-derived foam as a solvent absorbing element.

The main advantage of using the HA-derived foam of the present invention as an oil absorbing element is its structural integrity. Due to the idea that HA tablets are chemically combined and therefore have high structural integrity, the resulting foam will not disintegrate after repeated oil absorption operations. In contrast, we found that graphene-based oil-absorbing elements prepared by hydrothermal reduction, vacuum-assisted filtration, or freeze-drying disintegrate after absorbing the oil 2 or 3 times. Except that nothing (except for the weak van der waals forces present prior to first contact with the oil) holds these otherwise separated graphene sheets together. Once these graphene sheets are wetted by the oil, they are no longer able to return to the original shape of the oil-absorbing element.

Another major advantage of the present technology is the flexibility in designing and manufacturing an oil absorbing element capable of absorbing amounts of oil up to 400 times its own weight, yet maintaining its structural shape (without significant expansion). This amount depends on the specific pore volume of the foam, which can be controlled mainly by the ratio between the amount of the initial support polymer particles and the amount of HA molecules or sheets before the heat treatment.

The present invention also provides a method of separating/recovering oil from an oil-water mixture (e.g., spill oil water or wastewater from oil sands). The method comprises the following steps: (a) providing an oil absorbing element comprising an integral HA-derived foam; (b) contacting the oil-water mixture with the element, the element absorbing oil from the mixture; and (c) withdrawing the oil-absorbing element from the mixture and extracting the oil from the element. Preferably, the method comprises a further step (d): the element is reused.

In addition, the present invention provides a process for separating an organic solvent from a solvent-water mixture or from a multi-solvent mixture. The method comprises the following steps: (a) providing an organic solvent absorbing element comprising an integral HA-derived foam; (b) contacting the element with an organic solvent-water mixture or a multi-solvent mixture comprising a first solvent and at least a second solvent; (c) causing the element to absorb the organic solvent from the mixture or the first solvent from the at least second solvent; and (d) withdrawing the element from the mixture and extracting the organic solvent or first solvent from the element. Preferably, the method comprises a further step (e): the solvent-absorbing member is reused.

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

Example 1: humic acid and reduced humic acid from leonardite

Can be prepared by browning weatheringCoal is dispersed in an aqueous alkaline solution (pH 10) to extract humic acid from leonardite in very high yield (in the range of 75%). The solution was subsequently acidified so that humic acid powder precipitated. In one experiment, 300ml of a solution containing 1M KOH (or NH) was used with magnetic stirring₄OH) solution dissolved 3g of leonardite. The pH was adjusted to 10. The solution is then filtered to remove any large particles or any residual impurities. The resulting humic acid dispersion, containing only HC 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 (hydrazonodicarboxamide) was added to the suspension just prior to casting. The resulting suspension was then cast onto the glass surface using a doctor blade to apply shear stress, causing the HA molecules to orient. After the liquid is removed, the resulting HA coating film HAs a thickness that can vary from about 10nm to 500 μm (preferably and typically from 1 μm to 50 μm).

To make the HA foam samples, the HA coated film is then subjected to heat treatments typically involving an initial thermal reduction temperature of 80-350 ℃ for 1-8 hours, followed by a heat treatment at a second temperature of 1,500-2,850 ℃ for 0.5-5 hours. It may be noted that it is important to apply a compressive stress to the coated film sample while being subjected to the first heat treatment. This compressive stress appears to help maintain good contact between the HA molecules or sheets so that chemical incorporation and attachment between the HA molecules or sheets can occur while pores are formed. In the absence of such compressive stress, heat-treated films are typically overly porous, with the planes of constituent hexagonal carbon atoms in the pore walls being oriented/positioned very poorly and not chemically incorporated and bonded to each other. As a result, the thermal conductivity, electrical conductivity, and mechanical strength of the graphene foam are severely compromised.

Example 2: various blowing agents and methods for pore formation (bubble generation)

In the field of plastics processing, chemical blowing agents are mixed into plastics pellets in the form of powder or pellets and dissolved at higher temperatures. In particular for hairAbove a certain temperature at which the foaming agent dissolves, a gaseous reaction product (usually nitrogen or CO) is formed₂) Which acts as a blowing agent. However, chemical blowing agents cannot be dissolved in graphene materials, which are solids rather than liquids. This presents a challenge for creating pores or cells in graphene materials using chemical blowing agents.

After a number of experiments, we have found that almost any chemical blowing agent (e.g. in powder or pellet form) can be used to create pores or bubbles in the dried graphene layer when the first heat treatment temperature is sufficient to activate the foaming reaction. A chemical blowing agent (powder or pellet) may be dispersed in the liquid medium to become the second component in the suspension, which may be deposited onto the solid support substrate to form a wet layer. This wet layer of HA material may 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 largely maintained (even when a higher heat treatment temperature is subsequently applied to the structure). In fact, this is quite unexpected.

Chemical blowing agents (CFA) may be organic or inorganic compounds that release gas upon thermal decomposition. CFA is typically used to obtain medium to high density foams, and is often used with physical blowing agents to obtain low density foams. CFAs can be classified as either endothermic or exothermic, which refers to the type of decomposition they undergo. The endothermic type absorbs energy and typically releases carbon dioxide and moisture upon decomposition, while the exothermic type releases energy and typically generates nitrogen upon decomposition. The total gas yield and pressure of the gas released by the exothermic blowing agent is often higher than the endothermic type. Endothermic CFAs are generally known to decompose in the range of 130 ℃ to 230 ℃ (266 ° F-446 ° F), while some more common exothermic blowing agents decompose at about 200 ℃ (392 ° F). However, the decomposition range of most exothermic CFAs can be reduced by the addition of certain compounds. The activation (decomposition) temperature of the CFA falls within our heat treatment temperature range. Examples of suitable chemical blowing agents include sodium bicarbonate (baking soda), hydrazine, hydrazide, azodicarbonamide (exothermic chemical blowing agents), nitroso compounds (e.g., N-dinitrosopentamethylenetetramine), hydrazine derivatives (e.g., 4' -oxybis (benzenesulfonylhydrazide) and hydrazonodicarbonamide), and bicarbonate salts (e.g., sodium bicarbonate). These are all commercially available in the plastics industry.

In the production of foams, a physical blowing agent is metered into the plastic melt during foam extrusion or injection molding foaming, or is supplied to one of the precursor materials during polyurethane foaming. It was not previously known that physical blowing agents could be used to create pores in HA materials that are in a solid state (unmelted). We have surprisingly observed that physical blowing agents (e.g., CO)₂Or N₂) May be injected into the HA suspension stream prior to coating or casting onto the support substrate. This will produce a foam structure even when the liquid medium (e.g. water and/or alcohol) is removed. The layer of dry graphene material is capable of maintaining a controlled amount of pores or bubbles during liquid removal and subsequent thermal treatment.

Technically feasible blowing agents include carbon dioxide (CO)₂) Nitrogen (N)₂) Isobutane (C)₄H₁₀) Cyclopentane (C)₅H₁₀) Isopentane (C)₅H₁₂)、CFC-11(CFCI₃)、HCFC-22(CHF₂CI)、HCFC-142b(CF₂CICH₃) And HCFC-134a (CH)₂FCF₃). However, environmental safety is a major consideration in selecting blowing agents. The montreal protocol and its impact on the protocol accordingly poses a great challenge to foam producers. Despite the effective properties and ease of handling of chlorofluorocarbons previously used, worldwide agreement has been made to ban these due to their Ozone Depletion Potential (ODP). Partially halogenated chlorofluorocarbons are also not environmentally safe and have therefore been banned in many countries. Alternatives are hydrocarbons, such as isobutane and pentane, and gases, such as CO₂And nitrogen.

All of the blowing agents described above were tested in our experiments except for those that were controlled. For both physical and chemical blowing agents, the amount of blowing agent introduced into the suspension is defined as the weight ratio of blowing agent to HA material, which is typically from 0/1.0 to 1.0/1.0.

Example 3: preparation of humic acid from coal

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

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

Various amounts (1% -30% by weight relative to the HA material) of chemical blowing agents (N, N-dinitrosopentamethylenetetramine or 4.4' -oxybis (benzenesulfonylhydrazide) were added to the suspension containing the HA platelets₂Samples made as physical blowing agents. After the liquid is removed, the resulting HA film HAs a thickness that can vary from about 1 μm to 100 μm.

The HA film is then subjected to heat treatments involving an initial (first) thermal reduction temperature of 80-1,500 ℃ for 1-5 hours. This first heat treatment produces a foam of HA (if the HTT <300 ℃) and a foam of large, lamellar HA molecules or domains of hexagonal carbon atom planes in the pore walls (if the HTT is from 300 ℃ to 1,500 ℃). Some of the foam samples were then subjected to a second temperature of 1,500-2,850 ℃ to determine 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 have higher crystallinity).

Comparative example 3-a: CVD graphene foam on Ni foam template

This procedure was adapted from the procedures disclosed in the following publications: "Three-dimensional flexible and conductive interconnected graphene network by chemical vapor deposition" grown by chemical vapor deposition]"nat. mater. [ natural material ]]10,424-428(2011). Nickel foam (porous structure with interconnected 3D nickel scaffolds) was chosen as a template for graphene foam growth. Briefly, by decomposing CH at 1,000 ℃ under ambient pressure₄Carbon is introduced into the nickel foam, and then a graphene film is deposited on the surface of the nickel foam. Due to the difference in thermal expansion coefficient between nickel and graphene, ripples and wrinkles are formed on the graphene film. In order to recover (separate) the graphene foam, the Ni framework must be etched away. By hot HCl (or FeCl)₃) Before the solution etches away the nickel backbone, a thin layer of (methyl methacrylate) (PMMA) is deposited on the surface of the graphene film as a support to prevent the graphene network from collapsing during the nickel etch. After careful removal of the PMMA layer by hot acetone, a brittle graphene foam sample was obtained. The use of a PMMA support layer is critical to the preparation of free standing films of graphene foam; without the PMMA support layer, only severely distorted and deformed graphene foam samples were obtained. This is a cumbersome process that is not environmentally friendly and not scalable.

Comparative example 3-b: conventional graphite foam from pitch-based carbon foam

The pitch powder, granules, or pellets are placed in an aluminum mold having 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 about 300 ℃. At this point, the vacuum was released to a nitrogen blanket and then pressure was applied up to 1,000 psi. The temperature of the system was then raised to 800 ℃. This was done at a rate of 2 ℃/min. The temperature was held for at least 15 minutes to achieve soaking and then the furnace power was turned off and cooled to room temperature at a rate of about 1.5 deg.c/min, releasing the pressure at a rate of about 2 psi/min. The final foam temperatures were 630 ℃ and 800 ℃. During the cooling cycle, the pressure is gradually released to atmospheric conditions. The foam was then heat treated to 1050 ℃ under a nitrogen blanket and then heat treated to 2500 ℃ and 2800 ℃ in a separate operation in argon in a graphite crucible.

Samples from the foam were machined into samples for measuring thermal conductivity. The bulk thermal conductivity ranges from 67W/mK to 151W/mK. The density of the sample is from 0.31 to 0.61g/cm³. When considering weight, the specific heat conductivity of the bitumen-derived foam is approximately 67/0.31-216 and 151/0.61-247.5W/mK per specific gravity (or per physical density).

Having a density of 0.51g/cm³The compressive strength of the sample of average density of (a) was measured to be 3.6MPa and the compressive modulus was measured to be 74 MPa. In contrast, the compressive strength and compressive modulus of the inventive HA-derived graphite foam with comparable physical density were 5.7MPa and 103MPa, respectively.

Fig. 3(a) shows thermal conductivity values versus specific gravity for HA-derived foams, mesophase pitch-derived graphite foams, and Ni-foam template-assisted CVD graphene foams. These data clearly show the following unexpected results:

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

2) This is quite unexpected in view of the following: CVD graphene is primarily pristine graphene that HAs never been exposed to oxidation and should exhibit much higher thermal conductivity than HA-derived hexagonal carbon atom planes, which are highly deficient (have a high defect number and thus low conductivity) after removal of oxygen-containing functional groups via conventional thermal or chemical reduction methods. These exceptionally high thermal conductivity values observed with the HA-derived graphite foams produced herein are quite surprising.

3) Given the same amount of solid material, the HA-derived foams of the present invention are inherently the most conductive after heat treatment at HTT >1,500 ℃, reflecting a high level of graphite crystal integrity (larger crystal size, fewer grain boundaries and other defects, better crystal orientation, etc.). This is also unexpected.

4) The specific conductivity values of the HA-derived and fluorinated HA-derived foams of the invention (fig. 5) exhibit values from 250 to 490W/mK per specific gravity; but the specific conductivity values of the other two foams are typically below 250W/mK per specific gravity.

Comparative example 3-c: preparation of pristine graphene foam (0% oxygen)

Recognizing the possibility that a high defect number in HA sheets acts to reduce the conductivity of individual graphene planes, we decided to investigate whether the use of pristine graphene sheets (non-oxidized and oxygen-free, non-halogenated and halogen-free, etc.) could lead to graphene foams with higher thermal conductivity. Pristine graphene sheets are produced using a direct sonication process (also known in the art as liquid phase bulking).

In a typical procedure, 5 grams of graphite flakes milled to a size of about 20 μm or less are dispersed in 1,000mL of deionized water (containing 0.1% by weight of dispersant, from DuPont, Inc.; DuPont)

FSO) to obtain a suspension. An ultrasonic energy level of 85W (Branson S450 ultrasonicator) was used for puffing, separation and size reduction of graphene sheets for a period of 15 minutes to 2 hours. The resulting graphene sheets are pristine graphene that has never been oxidized and is oxygen-free and relatively defect-free. No other non-carbon elements are present.

Various amounts (1% -30% by weight relative to the graphene material) of chemical blowing agent (N, N-dinitrosopentamethylenetetramine or 4.4' -oxybis (benzenesulfonylhydrazide) were added to the suspension containing pristine graphene sheets and surfactant₂Samples made as physical blowing agents. After removal of the liquid, the graphite obtainedThe olefin film has a thickness that can vary from about 10 μm to 100 μm. These graphene films are then subjected to a heat treatment at a temperature of 80-1,500 ℃ for 1-5 hours, which generates a graphene foam.

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, are summarized in fig. 6. These data indicate that the thermal conductivity of HA-derived foams is highly sensitive to the final Heat Treatment Temperature (HTT). Even when the HTT is very low, it is clear that certain types of HA molecular attachment and incorporation or crystal integrity reactions have been activated. Thermal conductivity increases monotonically with the final HTT. In contrast, the thermal conductivity of pristine graphene foam remained relatively constant until a final HTT of about 2,500 ℃ was reached, indicating the onset of recrystallization and integrity of the graphite crystals. There are no functional groups in pristine graphene, such as-COOH and-OH in HA, which enable chemical attachment of molecules at relatively low HTT. At HTTs as low as 1,250 ℃, the HA molecules and resulting planes of hexagonal carbon atoms can combine to form significantly larger graphene-like hexagonal carbon sheets with reduced grain boundaries and fewer interruptions in electron transport paths. Although HA-derived sheets are inherently more deficient than pristine graphene, the method of the present invention enables HA molecules to form graphite foam that is superior to pristine graphene foam. This is another unexpected result.

Comparative example 3-d: preparation of Graphene Oxide (GO) suspensions from natural graphite and graphene foams from hydrothermally reduced graphene oxide

Graphite oxide was prepared by oxidizing graphite flakes with an oxidant liquid consisting of sulfuric acid, sodium nitrate and potassium permanganate in a ratio of 4:1:0.05 at 30 ℃. When natural graphite flakes (particle size of 14 μm) were immersed and dispersed in the oxidant mixture liquid for 48 hours, the suspension or slurry appeared and remained optically opaque and dark. After 48 hours, the reaction mass was washed 3 times with water to adjust the pH to at least 3.0. The final amount of water was then added to make a series of GO-water suspensions. It was observed that GO sheets form liquid crystalline phases when they represent > 3% and typically from 5 to 15% weight fraction.

Self-assembled graphene hydrogel (SGH) samples were then prepared by a hydrothermal method. In a typical procedure, SGH can be readily prepared by heating a 2mg/mL homogeneous Graphene Oxide (GO) aqueous dispersion sealed in a teflon-lined autoclave at 180 ℃ for 12 h. SGH containing about 2.6% (by weight) graphene sheets and 97.4% water has about 5x10^-3Conductivity of S/cm. After drying and heat treatment at 1,500 ℃, the resulting graphene foam exhibited about 1.5x10^-1S/cm, which is 2 times lower than the conductivity of the inventive HA-derived foam produced by heat treatment at the same temperature.

Comparative examples 3-e: plastic bead template-assisted formation of reduced graphene oxide foam

Preparation of hard template guide for macroporous graphene Membranes (MGF)

And (4) ordered assembly. Monodisperse Polymethylmethacrylate (PMMA) latex spheres were used as hard templates. The GO liquid crystals prepared in comparative example 3-d above were mixed with a PMMA sphere suspension. Subsequent vacuum filtration was then performed to prepare an assembly of PMMA spheres and GO sheets, wherein the GO sheets were wrapped around the PMMA beads. The composite membrane was stripped from the filter, air dried and calcined at 800 ℃ to remove the PMMA template and simultaneously thermally reduce GO to RGO. The off-white free standing PMMA/GO film darkened after calcination, while the graphene film remained porous.

Fig. 3(B) shows thermal conductivity values for HA-derived foams of the invention, GO foams produced via sacrificial plastic bead template-assisted methods, and hydrothermally reduced GO graphene foams. More unexpectedly, the HA-derived foams of the present invention exhibit the highest thermal conductivity, assuming the HTT is the same. The conductivity data summarized in fig. 4 also agreed with this conclusion. These data further support the following notions: given the same amount of solid material, the HA suspension deposition (with stress-induced orientation) and subsequent heat treatment of the present invention produces an HA-derived foam that is inherently the most conductive, reflecting the highest level of graphite crystal integrity (larger crystal size, fewer grain boundaries and other defects, better crystal orientation along the cell walls, etc.).

It is important to note that all prior art methods for producing graphite or graphene foam appear to provide foams having a density of only about 0.2g/cm³-0.6g/cm³Large pore foams with a physical density in the range of (a), the pore size is typically too large for most of the intended applications (e.g. from 20 to 300 μm). In contrast, the present invention provides that the production has a particle size that can be as low as 0.01g/cm³And up to 1.7g/cm³A HA-derived foam of a density of (1). The pore size may vary from the meso scale (2-50nm) to the macro scale (1-500 μm), depending on the content of non-carbon elements and the amount/type of blowing agent used. This level of flexibility and versatility in designing different types of graphite foam is unprecedented and no prior art approach is comparable.

Example 4: preparation of fluorinated HA foams

In a typical procedure, HA-derived foam sheets were fluorinated by chlorine trifluoride vapor in a sealed autoclave reactor to produce fluorinated HA-carbon hybrid films. Allowing different durations of fluorination time to achieve different degrees of fluorination. The fluorinated HA-derived foams were then individually immersed in containers each containing a chloroform-water mixture. We observed that the foam pieces selectively absorbed chloroform from water and the amount of chloroform absorbed increased with the degree of fluorination until the fluorine content reached 7.2% by weight, as indicated in figure 9.

Example 5: preparation of nitrided HA foams

Several pieces of HA-derived foam prepared in example 3 were immersed in 30% H₂O₂-in aqueous solution for a period of time comprised between 2 and 48 hours to obtain oxidized HA derived foams having a controlled oxygen content comprised between 2% and 25% by weight.

Some oxidized HA-derived foam samples were mixed with different proportions of urea and these mixtures were heated in a microwave reactor (900W) for 0.5 to 5 minutes. The product was washed several times with deionized water and dried in vacuo. The product obtained was a nitrided HA foam. The nitrogen content is from 3% to 17.5% by weight as measured by elemental analysis.

It may be noted that different functionalization treatments of HA-derived foams are used for different purposes. For example, the oxidized HA foam structure is particularly effective as an absorbent for oil from an oil-water mixture (i.e., oil sprinkled on water and then mixed together), fig. 7 and 8. In this case, the unitary HA-derived foam structure (with 0% -15% oxygen by weight) is both hydrophobic and oleophilic (fig. 7). If water is repelled by a material or surface, such surface or material is considered hydrophobic and a drop of water placed on the hydrophobic surface or material will form a large contact angle. A surface or material is considered oleophilic if it has a strong affinity for oil and not for water.

O, F, and/or N, also enable the HA-derived foams of the present invention to absorb different organic solvents from water or separate one organic solvent from a mixture of 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 foams was studied using X-ray diffraction. The X-ray diffraction curve of natural graphite typically exhibits a peak at about 2 θ ═ 26 °, corresponding to an inter-graphene spacing (d) of about 0.3345nm₀₀₂). The RHA wall of the hybrid foam exhibits a d typically from 0.3345nm to 0.40nm, but more typically up to 0.34nm₀₀₂And (4) spacing.

In the case of a heat treatment temperature of 2,750 ℃ for the foam structure under compression for 1 hour, d₀₀₂The pitch was reduced to about 0.3354nm, which is the same as that of the graphite single crystal. Further, the second diffraction peak having high intensity appears at 55 ° corresponding to the X-ray diffraction from the (004) plane. The intensity of the (004) peak on the same diffraction curve relative to the intensity of (002), or the I (004)/I (002) ratio, is a good indicator of the degree of crystal perfection and preferred orientation of the graphene-like planes. For all graphite materials heat treated at temperatures below 2,800C, the (004) peak is absent or relatively weak, the I (004)/I (002) ratio<0.1. Heat treatment at 3,000 deg.C to 3,250 deg.CThe I (004)/I (002) ratio of the graphite material (e.g., highly oriented pyrolytic graphite, HOPG) of (a) is in the range of 0.2-0.5. In contrast, graphene foams prepared with a final HTT of 2,750 ℃ for one hour exhibited an I (004)/I (002) ratio of 0.78 and a mosaic spread value of 0.21, indicating that the cell walls are virtually perfect graphite single crystals with a good degree of preferred orientation (if prepared under compressive force).

The "mosaic spread" value is obtained from the full width at half maximum of the (002) reflection in the X-ray diffraction intensity curve. This index of order characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the preferred degree of grain orientation. An almost perfect single crystal of graphite is characterized by a mosaic expansivity value of 0.2-0.4. Some of our HA-derived foams have a mosaic spread value in this range of 0.3-0.6 when produced using a final heat treatment temperature of not less than 2,500 ℃.

It is important to note that heat treatment temperatures as low as 500 c are sufficient to bring the average interplanar spacing between the planes of hexagonal carbon atoms along the pore walls below 0.4nm, closer and closer to the average interplanar spacing of natural graphite or graphite single crystals. The advantages of this method are the following: this HA suspension coating and heat treatment strategy enabled us to organize, orient/align, and chemically combine planar HA molecules into a unified structure, all graphene-like hexagonal carbon atom planes now being larger in lateral dimensions (significantly larger than the length and width of the original HA molecules). The potential chemical ligation and incorporation mechanism is shown in FIG. 3. This results in exceptional thermal and electrical conductivity values.

In summary, we have successfully developed an absolutely new, novel, unexpected, and distinctly different class of HA foam or HA-derived graphite foam materials and associated methods of production. The chemical composition (of oxygen, fluorine, and other non-carbon elements%), structure (crystal integrity, grain size, number of defects, etc.), crystal orientation, morphology, production method, and properties of such new foam materials are fundamentally different and distinctly different from mesophase pitch-derived graphite foam, CVD graphene-derived foam, and graphene foam from hydrothermal reduction of GO, and sacrificial bead-template assisted RGO foam. The thermal conductivity, electrical conductivity, modulus of elasticity and flexural strength exhibited by the foams of the present invention are much higher than those of the prior art foams.

Claims (41)

1. A humic acid derived foam consisting of a plurality of pores and pore walls, wherein the pore walls contain a monolayer or few-layered hexagonal carbon atom planes or platelets derived from humic acid, the few-layered hexagonal carbon atom planes or platelets having from 2 to 10 stacked hexagonal carbon atom planes with an interplanar spacing d from 0.3354nm to 0.60nm as measured by X-ray diffraction₀₀₂And the single or few-layer hexagonal carbon atom planes contain 0.01% to 25% by weight of elements other than carbon, and wherein the humic acid is selected from the group consisting of: 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, chemically functionalized humic acid, and combinations thereof.

2. The humic acid derived foam of claim 1, wherein the foam has from 0.005g/cm³To 1.7g/cm³From 50m²G to 3,200m²A specific surface area per g, a thermal conductivity per specific gravity of at least 100W/mK, and/or an electrical conductivity per specific gravity of not less than 500S/cm.

3. The humic acid derived foam of claim 1, wherein the foam has from 0.01g/cm³To 1.5g/cm³Or an average pore diameter from 2nm to 50 nm.

4. The humic acid-derived foam of claim 1, wherein the foam contains a non-carbon element content in the range of 0.01% to 20% by weight and the non-carbon element comprises an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron.

5. The humic acid derived foam of claim 1, wherein the cell walls contain fluorinated humic acid and the foam contains a fluorine content of from 0.01 to 25% by weight.

6. The humic acid derived foam of claim 1, wherein the cell walls contain oxidized humic acid and the foam contains an oxygen content of from 0.01 to 25% by weight.

7. Humic acid derived foam according to claim 1 wherein the foam has from 200m²A/g to 3,000m²Specific surface area per gram or from 0.1g/cm³To 1.2g/cm³The density of (c).

8. The humic acid derived foam of claim 1, which is in the form of a continuous length roll sheet having a thickness of from 100nm to 10cm and a length of at least 2 meters and is produced by a roll-to-roll process.

9. The humic acid-derived foam of claim 1, wherein the foam has an oxygen content or non-carbon content of less than 1% by weight and the cell walls have stacked hexagonal planes of carbon atoms having an interplanar spacing of less than 0.35nm, a thermal conductivity of at least 200W/mK per specific gravity, and/or an electrical conductivity of no less than 1,000S/cm per specific gravity.

10. The humic acid-derived foam of claim 1, wherein the foam has an oxygen content or non-carbon content of less than 0.01% by weight and the cell walls contain stacked hexagonal planes of carbon atoms having an interplanar spacing of less than 0.34nm, a thermal conductivity of at least 300W/mK per specific gravity, and/or an electrical conductivity of not less than 1,500S/cm per specific gravity.

11. The humic acid-derived foam of claim 1, wherein the foam has an oxygen content or non-carbon content of no more than 0.01% by weight and the cell walls contain stacked hexagonal carbon atom planes having an inter-plane spacing of less than 0.336nm, a thermal conductivity of at least 350W/mK per specific gravity, and/or an electrical conductivity of no less than 2,000S/cm per specific gravity.

12. The humic acid-derived foam of claim 1, wherein the foam has cell walls having stacked planes of hexagonal carbon atoms with an interplanar spacing of less than 0.336nm, a thermal conductivity per specific gravity of greater than 400W/mK, and/or an electrical conductivity per specific gravity of greater than 3,000S/cm.

13. The humic acid-derived foam of claim 1, wherein the cell walls comprise stacked hexagonal planes of carbon atoms having an interplanar spacing of less than 0.337nm and a mosaic spread value of less than 1.0.

14. The humic acid-derived foam of claim 1, wherein the cell walls comprise a 3D network of interconnected hexagonal planes of carbon atoms.

15. The humic acid-derived foam of claim 1, wherein the foam contains mesoscale pores having a pore size of from 2nm to 50 nm.

16. An apparatus for removing or separating oil, which contains the humic acid-derived foam as claimed in claim 1 as an element for absorbing oil.

17. An apparatus for removing a solvent or separating a solvent, which comprises the humic acid-derived foam as claimed in claim 1 as an element for absorbing a solvent or separating a solvent.

18. A method for separating oil from water, the method comprising the steps of:

a. providing an oil-absorbing element comprising the humic acid-derived foam of claim 1;

b. contacting an oil-water mixture with the element, the element absorbing oil from the mixture;

c. withdrawing the element from the mixture and extracting the oil from the element; and is

d. The element is reused.

19. A process for separating an organic solvent from a solvent-water mixture or from a multi-solvent mixture, the process comprising the steps of:

a. providing an element for absorbing an organic solvent or separating a solvent, the element comprising the humic acid-derived foam of claim 1;

b. contacting the element with an organic solvent-water mixture or a multi-solvent mixture comprising a first solvent and at least a second solvent;

c. allowing an element to absorb the organic solvent from the mixture or to separate the first solvent from the at least second solvent;

d. withdrawing the element from the mixture and extracting the organic solvent or first solvent from the element; and is

e. The element is reused.

20. A heat management device containing the humic acid derived foam of claim 1 as a heat spreading or dissipating element.

21. The thermal management device of claim 20 containing a device selected from the group consisting of: a heat exchanger, a highly conductive insert, a conductive plate between a heat sink and a heat source, a heat spreading member, a heat dissipating member, a thermal interface medium, and a thermoelectric cooling device.

22. The thermal management device of claim 21, wherein said heat exchanger is a heat sink or a heat pipe and said thermoelectric cooling device is a peltier cooling device.

23. A method for producing humic acid derived foam, the method comprising:

(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 selected from the group consisting of: 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, chemically functionalized humic acid, and combinations thereof, and wherein the dispersion contains an optional blowing agent, has a blowing agent to humic acid weight ratio of from 0/1.0 to 1.0/1.0;

(b) dispensing and depositing the humic acid dispersion onto a surface of a support substrate to form a wet humic acid layer;

(c) partially or completely removing the liquid medium from the wet humic acid layer to form a dry humic acid layer; and is

(d) Heat treating the dried humic acid layer at a first heat treatment temperature of from 80 ℃ to 3,200 ℃ at a desired heating rate sufficient to initiate volatile gas molecules from non-carbon elements or activate the foaming agent to produce the humic acid-derived foam comprised of a plurality of pores and pore walls, wherein the pore walls contain a single or few layers of humic acid-derived hexagonal carbon atom planes or platelets having from 2 to 10 stacked hexagonal carbon atom planes with an interplanar spacing, d, as measured by X-ray diffraction of from 0.3354nm to 0.60nm₀₀₂And the single or few-layered hexagonal carbon atom plane contains 0.01 to 25% by weight of a non-carbon element.

24. The method of claim 23, wherein the partitioning and depositing procedure comprises subjecting the humic acid dispersion to orientation-inducing stress.

25. The method of claim 23, further comprising the steps of: heat treating the humic acid-derived froth at a second heat treatment temperature higher than the first heat treatment temperature for a period of time sufficient to obtain a graphite froth in which the cell walls contain stacked hexagonal planes of carbon atoms having an interplanar spacing d from 0.3354nm to 0.36nm₀₀₂And a non-carbon element content of less than 2% by weight.

26. The method of claim 23, wherein the blowing agent is a physical blowing agent, a chemical blowing agent, mixtures thereof, a dissolution and leaching agent, or a mechanically introduced blowing agent.

27. The process of claim 23, which is a roll-to-roll process, wherein steps (b) and (c) comprise feeding the support substrate from a feed roll to a deposition zone, continuously or intermittently depositing the humic acid dispersion onto the surface of the support substrate to form the wet humic acid layer thereon, drying the wet humic acid layer to form the dry humic acid layer, and collecting the dry humic acid layer deposited on the support substrate on a collection roll.

28. The method of claim 23, wherein the first heat treatment temperature is from 100 ℃ to 1,500 ℃.

29. The method of claim 25, wherein said second heat treatment temperature comprises at least a temperature selected from the group consisting of: (A)300 ℃ to 1,500 ℃, (B)1,500 ℃ to 2,100 ℃, and (C)2,100 ℃ to 3,200 ℃.

30. The method of claim 25, wherein the heat treatment at the second heat treatment temperature comprises a temperature in the range of 300 ℃ -1,500 ℃ for at least 1 hour, and then a temperature in the range of 1,500 ℃ -3,200 ℃ for at least 1 hour.

31. The method of claim 25, wherein said non-carbon element comprises an element selected from the group consisting of: oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, and boron.

32. The method of claim 25, wherein the step (d) of heat treating the dried humic acid layer at the first heat treatment temperature is performed under compressive stress.

33. The method of claim 23, further comprising a compression step that reduces the thickness, pore size, or porosity level of the foam.

34. The method of claim 25, wherein the first and/or second heat treatment temperature comprises a temperature in the range of 300 ℃ to 1,500 ℃, and the foam has an oxygen content or non-carbon content of less than 1%, and cell walls having an inter-plane spacing of less than 0.35nm, a thermal conductivity of at least 250W/mK per specific gravity, and/or an electrical conductivity of not less than 2,500S/cm per specific gravity.

35. The method of claim 25, wherein the first and/or second heat treatment temperatures comprise a temperature in the range of 1,500 ℃ to 2,100 ℃, and the foam has an oxygen content or non-carbon content of less than 0.01%, cell walls having an inter-plane spacing of less than 0.34nm, a thermal conductivity of at least 300W/mK per specific gravity, and/or an electrical conductivity of not less than 3,000S/cm per specific gravity.

36. The method of claim 25, wherein the first and/or second heat treatment temperature comprises a temperature greater than 2,100 ℃ and the foam has an oxygen content or non-carbon content of no greater than 0.001%, cell walls having an inter-plane spacing of less than 0.336nm, a mosaicism value of no greater than 0.7, a thermal conductivity of at least 350W/mK per specific gravity, and/or an electrical conductivity of no less than 3,500S/cm per specific gravity.

37. The method of claim 25, wherein the first and/or second heat treatment temperatures comprise a temperature of no less than 2,500 ℃, and the foam has cell walls comprising stacked hexagonal carbon planes having an interplanar spacing of less than 0.336nm, a perplexity value of no greater than 0.4, a thermal conductivity greater than 400W/mK per specific gravity, and/or an electrical conductivity greater than 4,000S/cm per specific gravity.

38. The method of claim 23, wherein the humic acid derived foam has from 0.005g/cm³To 1.7g/cm³Density of from 50m²G to 3,200m²A specific surface area per g, a thermal conductivity per specific gravity of at least 100W/mK, and/or an electrical conductivity per specific gravity of not less than 500S/cm.

39. The method of claim 25, wherein the humic acid-derived foam has from 0.005g/cm³To 1.7g/cm³From 50m²G to 3,200m²A specific surface area per g, a thermal conductivity per specific gravity of at least 100W/mK, and/or an electrical conductivity per specific gravity of not less than 500S/cm.

40. A roll-to-roll process for producing continuous length sheets of humic acid derived foam, the process comprising:

(a) preparing a humic acid dispersion having humic acid molecules dispersed in a liquid medium, wherein the dispersion contains a foaming agent;

(b) continuously or intermittently dispensing and depositing the humic acid dispersion onto a surface of a support substrate to form a wet humic acid layer, wherein the support substrate is a continuous thin film supplied from a feed roll and collected on a collection roll;

(c) partially or completely removing the liquid medium from the wet humic acid layer to form a dry humic acid layer in the heating zone or zones; and is

(d) At a heating temperature of from 80 ℃ to 500 DEG CHeat treating the dried humic acid layer in one of the heating zones at a desired heating rate sufficient to activate the foaming agent to produce the humic acid-derived foam comprised of a plurality of cells and cell walls, wherein the cell walls contain a single or few layers of humic acid-derived hexagonal carbon atom planes or platelets having from 2 to 10 stacked hexagonal carbon atom planes with an interplanar spacing d from 0.3354nm to 0.60nm as measured by X-ray diffraction₀₀₂And the single or few-layered hexagonal carbon atom plane contains 0.01 to 25% by weight of a non-carbon element.

41. The method of claim 40, wherein the humic acid-derived foam has from 0.005g/cm³To 1.7g/cm³From 50m²G to 3,200m²A specific surface area per g, a thermal conductivity per specific gravity of at least 100W/mK, and/or an electrical conductivity per specific gravity of not less than 500S/cm.

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