CN108602046B - Graphene-carbon hybrid foam - Google Patents

Abstract

Provided is a unitary 3D graphene-carbon hybrid foam consisting of a plurality of cells and cell walls, wherein the cell walls contain single or few-layered graphene sheets chemically bonded by a carbon material, having a carbon material to graphene weight ratio of from 1/100 to 1/2, wherein the few-layered graphene sheets have 2-10 stacked graphene planar layers,these graphene planes have an interplanar spacing d from 0.3354nm to 0.40nm ₀₀₂ And these graphene sheets contain pristine graphene materials having substantially zero% non-carbon elements or non-pristine graphene materials having 0.01% to 25% non-carbon elements by weight, wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, fluorinated graphene, chlorinated graphene, brominated graphene, iodinated graphene, hydrogenated graphene, nitrogenated graphene, doped graphene, chemically functionalized graphene, or combinations thereof. Also provided are methods for producing the hybrid foam, products containing the hybrid foam, and uses thereof.

Description

Graphene-carbon hybrid foam

Cross Reference to Related Applications

This application claims priority to U.S. patent application nos. 14/998,356 and 14/998,357, each filed on 28/12/2015, 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 new form of porous graphite material, referred to herein as monolithic 3D graphene-carbon hybrid foams, methods of producing the same, products containing the same, and methods of operating the same.

Background

Carbon is known to have five unique crystal structures including diamond, fullerene (0-D nanographitic material), carbon nanotubes or carbon nanofibers (1-D nanographitic material), graphene (2-D nanographitic material), and graphite (3-D graphitic material). Carbon Nanotubes (CNTs) refer to tubular structures grown with single or multiple walls. Carbon Nanotubes (CNTs) and Carbon Nanofibers (CNFs) have diameters on the order of a few nanometers to a few 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.

As early as 2002, our research group developed the development of graphene materials and related production processes: (1) Jang and w.c. huang, "Nano-scaled Graphene Plates," U.S. Pat. No. 7,071,258 (07/04/2006), application filed 10/21/2002; (2) Jang et al, "Process for Producing Nano-scaled Graphene Plates [ method for Producing Nano-scaled Graphene Plates ]", U.S. patent application No. 10/858,814 (06/03/2004); and (3) b.z.jang, a.zhamu and j.guo, "Process for Producing Nano-scaled plates and Nanocomposites [ method for Producing Nano-sized Platelets and Nanocomposites ]", U.S. patent application No. 11/509,424 (08/25/2006).

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. NGPs include pristine graphene (substantially 99% carbon atoms), slightly oxidized graphene (< 5% oxygen by weight), oxidized graphene (5% oxygen by weight or more), slightly fluorinated graphene (5% fluorine by weight or more), other halogenated graphene, and chemically functionalized graphene.

NGPs have been found to possess a range of unusual physical, chemical and mechanical properties. For example, graphene was found to exhibit the highest intrinsic strength and highest thermal conductivity of all existing materials. Although practical electronic device applications of graphene (e.g., replacing Si as a backbone in transistors) are not expected to occur within the next 5-10 years, its application as a nanofiller in composite materials and as an electrode material in energy storage devices is imminent. The availability of large numbers of processable graphene sheets is crucial for the successful development of graphene composites, energy and other applications.

Our group first discovered Graphene [ 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. patent No. 7,071,258 (07/04/2006) ]. Recently, we reviewed methods of producing NGP and NGP Nanocomposites [ Bor Z. Jang and A Zhamu, "Processing of Nano Graphene Sheets (NGPs) and NGP Nanocomposites: A Review [ Processing of Nano Graphene Platelets (NGP) and NGP Nanocomposites: review ] ", j.materials Sci. [ journal of materials 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:

overview of the production of isolated nanographene plates or Sheets (NGPs)

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 about 0.335nm of graphene prior to intercalation or oxidation _d ＝1/2d ₀₀₂ =0.335 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 "swelling"), and separation.

In a solution-based separation process, expanded or puffed GO powder is dispersed in water or an aqueous alcohol solution and subjected to sonication. It is important to note that in these processes, sonication is used after intercalation and oxidation of the graphite (i.e. after the first expansion) and typically after thermal shock exposure of the resulting GIC or GO (after the second expansion). Alternatively, GO 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 method 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 120pph. During high temperature puffing, residual intercalated species retained by the flakes decompose to produce various undesirable sulfur-and nitrogen-containing compounds (e.g., NO) _x And SO _x ). Effluent requires expensive remediation procedures in order not to have adverse environmental effects.

The present invention has been made to overcome the limitations and problems outlined above.

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 the 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 present invention has been made to overcome the limitations outlined above.

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. Pat. No. 7,327,000B2 (6/12/2003) ]. Graphoepitaxy films with only one or a few atomic layers are of technical and scientific importance due to their characteristic features and great potential as device substrates. However, these methods are not suitable for the mass production of isolated graphene sheets for composite and energy storage applications. The present invention has been made to overcome the limitations outlined above.

For producing in the form of a film (typically of thickness)<2 nm) is catalytic chemical vapor deposition. The catalytic CVD involves a hydrocarbon gas (e.g., C) ₂ H ₄ ) 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<2 nm), 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 approach (synthesis of graphene from small molecules)

Yang et al [ "Two-dimensional Graphene Nano-ribs ]", J.Am.chem.Soc. [ Proc. Natl. Chem. Soc. [ J.S. Chem.Soc. ]130 (2008) 4216-17] Nanocontensine sheets up to 12nm in length were synthesized using the following method, starting with a Suzuki-Miyaura coupling of 1,4-diiodo-2,3,5,6-tetraphenyl-benzene with 4-bromophenylboronic acid. The resulting hexaphenyl benzene derivatives were further derivatized and ring fused into small graphene sheets. This is a slow method to date to produce very small graphene sheets. The present invention has been made to overcome the limitations outlined above.

Therefore, it is highly desirable to have a graphene production process that requires reduced amounts of undesirable chemicals (or elimination of these chemicals altogether), reduced processing times, reduced energy consumption, reduced graphene oxidation processesDegree, reduction or elimination of undesirable chemical species into exhaust systems (e.g., sulfuric acid) or into air (e.g., SO) ₂ And NO ₂ ) The outflow amount of (a). The method should be able to produce graphene sheets that are more pristine (less oxidized and damaged), more conductive, and larger/wider. Furthermore, these graphene sheets should be able to be easily made into a foam structure.

Our recent research has resulted in a method for the chemical-free production of isolated nano-graphene platelets that is novel in that it does not follow the established method of producing nano-graphene platelets outlined above. Furthermore, the method has enhanced utility because it is cost effective and provides novel graphene materials (with significantly reduced environmental impact). Furthermore, as disclosed herein, we have combined the chemical-free production of graphene with the formation of graphene-carbon hybrid foams into one single operation.

For the purposes of defining the claims of the present application, NGP or graphene materials include single and multiple layers (typically less than 10 layers) of discrete sheets/platelets of pristine graphene, graphene oxide, reduced Graphene Oxide (RGO), graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, doped graphene (e.g. doped with B or N). Pristine graphene has substantially 0% oxygen. RGO typically has an oxygen content of 0.001% to 5% by weight. Graphene oxide (including RGO) may have 0.001% -50% by weight oxygen. All graphene materials, except pristine graphene, have 0.001% -50% by weight of non-carbon elements (e.g., O, H, N, B, F, cl, br, I, etc.). These materials are referred to herein as non-native graphene materials. The graphene-carbon foam of the present invention may contain native or non-native graphene and the method of the present invention allows this flexibility.

Overview of the production of graphene foam

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. Graphene foam is composed of pores and pore walls containing graphene material. There are three main methods of producing graphene foam:

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., 2mg/mL =2g/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 based on a template-assisted catalytic CVD method, which 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 networks growth by chemical vapor deposition" 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 of the PS beads to generate 3D macropores. Choi et al, "3D Macroporous Graphene frames for Supercapacitors with High Energy and Power Densities [ 3D Macroporous Graphene framework for Supercapacitors with High Energy and Power density ], ACS Nano [ ACS Nano ],6 (2012) 4020-4028. Choi et al manufactured well-ordered free-standing PS/CMG paper by filtration, starting with separate preparation of 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 ± 3.7 mV) and PS spheres (zeta potential = +51 ± 2.5 mV) assembled due to electrostatic interaction 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 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 shows that each of the prior art methods or processes for producing graphene foam have major drawbacks. It is therefore an object of the present invention to provide a cost-effective method for mass production of highly conductive, mechanically robust graphene-based foams (in particular, monolithic 3D graphene-carbon hybrid 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 method for producing graphene-carbon hybrid foams that exhibit thermal conductivity, electrical conductivity, elastic modulus and/or strength comparable to or greater than those of conventional graphite or carbon foams.

It is yet another object of the present invention to provide (a) pristine graphene-based hybrid foam containing essentially all only carbon and preferably having a mesoscale pore size range (2-50 nm); and (b) non-pristine graphene foams (fluorinated graphene, chlorinated graphene, nitrogenated graphene, etc.) containing at least 0.001% by weight (typically from 0.01% to 25% by weight and most typically from 0.1% to 20%) of non-carbon elements, which foams may be used in a variety of applications.

It is another object of the invention to provide products (e.g., devices) containing the graphene-carbon foams of the invention and methods of operating these products.

Disclosure of Invention

The invention provides a method for producing an integrated 3D graphene-carbon hybrid foam directly from graphite material particles and polymer particles. This method is surprisingly simple. The method comprises the following steps:

(a) Mixing a plurality of particles of a graphite material and a plurality of particles of a solid polymeric carrier material in an impingement chamber of an energy impingement device to form a mixture;

(b) Operating the energy impingement device at a frequency and intensity for a time sufficient to exfoliate graphene sheets from the graphite material and transfer the graphene sheets to the surface of solid polymer carrier material particles to produce graphene-coated or graphene-embedded polymer particles inside the impingement chamber; ( For example, the impact device, when operated, imparts kinetic energy to the polymer particles, which in turn impact on the graphite particle surfaces/edges and strip the graphene sheets from the impacted graphite particles. The exfoliated graphene sheets adhere to the surface of the polymer particles. This is referred to herein as a "direct transfer" process, meaning that the graphene sheets are transferred from the graphite particles directly to the surface of the polymer particles without being mediated by any third party entity. )

(c) Recovering graphene-coated or graphene-embedded polymer particles from the impingement chamber and consolidating the graphene-coated or graphene-embedded polymer particles into the desired shape of the graphene-polymer hybrid structure (this consolidation step may be as simple as a compaction step that merely piles the graphene-coated or embedded particles into the desired shape); and is

(d) This shape of the graphene-polymer hybrid structure is pyrolyzed to thermally convert the polymer into pores and carbon or graphite that binds the graphene sheets to form a monolithic 3D graphene-carbon hybrid foam.

In certain alternative embodiments, multiple impacting balls or media are added to the impact chamber of the energy impact device. These impact balls accelerated by the impact device impact the surface/edge of the graphite particles and detach the graphene sheets therefrom. The graphene sheets are temporarily transferred to the surface of the impact balls. These graphene-bearing impacting balls then impact on the polymer particles and transfer the loaded graphene sheets to the surface of the polymer particles. This sequence of events is referred to herein as an "indirect transfer" process. In some embodiments of the indirect transfer process, step (c) comprises operating a magnet to separate the impact balls or media from the graphene-coated or graphene-embedded polymer particles.

The solid polymeric material particles may comprise plastic or rubber beads, pellets, spheres, threads, fibers, filaments, discs, ribbons or rods having a diameter or thickness of from 10nm to 10 mm. Preferably, the diameter or thickness is from 100nm to 1mm, and more preferably from 200nm to 200 μm. The solid polymer may be selected from solid particles of: thermoplastics, thermosetting resins, rubbers, semi-penetrating network polymers, natural polymers, or combinations thereof. In an embodiment, the solid polymer is partially removed by melting, etching or dissolving in a solvent prior to step (d).

In certain embodiments, the graphite material is selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fibers, graphite nanofibers, graphite fluoride, graphite oxide, chemically modified graphite, expanded graphite, recompressed expanded graphite, mesocarbon microbeads, or combinations thereof. Preferably, the graphite material comprises a non-intercalated and non-oxidized graphite material that has not been previously exposed to a chemical or oxidative treatment prior to the mixing step (a).

We have unexpectedly observed that a variety of percussion devices can be used to practice the present invention. For example, the energy impact apparatus may be a vibratory ball mill, a planetary ball mill, a high energy mill, a basket mill, a stirred ball mill (agitator ball mill), a cryogenic ball mill (cryo ball mill), a microsphere mill, a tumbling ball mill (tunbler ball mill), a continuous ball mill, a stirred ball mill (stirred ball mill), a pressurized ball mill, a freeze mill, a vibrating screen, a bead mill, a nanobead mill, an ultrasonic homogenizer mill (ultrasonic homogenerizer mill), a centrifugal planetary mixer, a vacuum ball mill, or a resonant acoustic mixer (resonant acoustic mixer).

To form the carbon component of the resulting graphene-carbon hybrid foam, polymer particles with high carbon yield or char yield (e.g., >30% by weight) may be selected. Carbon yield is the weight percentage of the polymer structure that is converted by heat into a solid carbon phase rather than becoming part of a volatile gas. The high carbon yield polymer may be selected from the group consisting of phenolic resins, polyfurfuryl alcohol, polyacrylonitrile, polyimides, polyamides, polyoxadiazoles, polybenzoxazoles, polybenzobisoxazoles, polythiazoles, polybenzothiazoles, polybenzobiothiazoles, poly (p-phenylene vinylenes), polybenzimidazoles, polybenzobisoxazoles, copolymers thereof, polymer blends thereof, or combinations thereof.

If a lower carbon content (higher graphene ratio) is desired in the graphene-carbon hybrid foam, the polymer may contain a low carbon-yield polymer selected from: polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile Butadiene (ABS), polyester, polyvinyl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethyl methacrylate (PMMA), copolymers thereof, polymer blends thereof, or combinations thereof.

It is noted that when heated at temperatures of 300 ℃ to 2,500 ℃, these polymers (high carbon yield and low carbon yield) convert to carbon materials that nucleate preferentially near the edges of the graphene sheets. Such carbon materials serve to bridge the gaps between graphene sheets, thereby forming an interconnected electron-conducting path. In other words, the resulting graphene-carbon hybrid foam is composed of an integral 3D network of carbon-bonded graphene sheets, allowing for the continuous transport of electrons and phonons (quantized lattice vibrations) between graphene sheets or domains without interruption. Upon further heating at a temperature above 2,500 ℃, the graphene-bound carbon phase may be graphitized, provided that the carbon phase is "soft carbon" or graphitizable. In this case, both the electrical conductivity and the thermal conductivity are further increased.

Thus, in certain embodiments, the step of pyrolyzing comprises carbonizing the polymer at a temperature of from 200 ℃ to 2,500 ℃ to obtain carbon-bonded graphene sheets. Optionally, the carbon-bonded graphene sheets may be subsequently graphitized at a temperature of from 2,500 ℃ to 3,200 ℃ to obtain graphite-bonded graphene sheets.

It may be noted that pyrolysis of the polymer is due to those volatile gas molecules such as CO ₂ And H ₂ The release of O tends to result in the formation of pores in the carbon phase of the resulting polymer. However, if the polymer is not subjected to carbonizationAnd limited, such pores also have a high tendency to become collapsed. We have unexpectedly found that graphene sheets surrounding polymer particles can limit carbon pore wall shrinkage and collapse, while some carbon species also penetrate into the interstices between the graphene sheets, where these species bind the graphene sheets together. The pore size and pore volume (porosity level) of the resulting 3D monolithic graphene foam depends on the starting polymer size and carbon yield of the polymer, and to a lesser extent on the pyrolysis temperature.

In certain preferred embodiments, the consolidating step comprises compacting a plurality of these graphene-coated polymer particles into a desired shape. For example, a compacted green body can be easily formed by extruding and compressing the plurality of graphene-coated particles into a mold cavity. The polymer may be rapidly heated and melted, the green body slightly compressed to slightly fuse the polymer particles together by heat, and rapidly cooled to solidify the green body. This consolidated green body is then subjected to a pyrolysis treatment (carbonization of the polymer and optionally graphitization).

In some alternative embodiments, the consolidating step comprises melting the polymer particles to form a polymer melt mixture having graphene sheets dispersed therein, forming the polymer melt mixture into a desired shape, and solidifying the shape into a graphene-polymer composite structure. The shape may be a rod, a film (thin or thick film, wide or narrow, single sheet or in roll form), a fiber (short or continuous length filament), a plate, an ingot, any regular shape or odd shape. This graphene-polymer composite shape is then pyrolyzed.

Alternatively, the consolidating step may include dissolving the polymer particles in a solvent to form a polymer solution mixture having graphene sheets dispersed therein, forming the polymer solution mixture into a desired shape, and removing the solvent to solidify the shape into a graphene-polymer composite structure. The composite structure is then pyrolyzed to form a porous structure.

The consolidating step can include melting the polymer particles to form a polymer melt mixture having graphene sheets dispersed therein, and extruding the mixture into rod or sheet form, spinning the mixture into fiber form, spraying the mixture into powder form, or casting the mixture into ingot form.

In some embodiments, the consolidating step comprises dissolving the polymer particles in a solvent to form a polymer solution mixture having graphene sheets dispersed therein, and extruding the solution mixture into a rod-like or sheet-like form, spinning the solution mixture into a fiber form, spraying the solution mixture into a powder form, or casting the solution mixture into an ingot form, and removing the solvent.

In particular embodiments, the polymer solution mixture is sprayed to produce a graphene-polymer composite coating or film, which is then pyrolyzed (carbonized or carbonized and graphitized).

Preferably, the consolidating step may comprise compacting the graphene-coated polymer particles into a porous green compact having macroscopic pores and then infiltrating or impregnating the pores with an additional carbon source material selected from: petroleum pitches, coal tar pitches, aromatic organic materials (e.g., naphthalene or other pitch derivatives), monomers, organic polymers, or combinations thereof. The organic polymer may contain a high carbon-yielding polymer selected from: phenolic resins, polyfurfuryl alcohol, polyacrylonitrile, polyimides, polyamides, polyoxadiazoles, polybenzoxazoles, polybenzdioxazoles, polythiazoles, polybenzothiazoles, poly (p-phenylene vinylene), polybenzimidazole, polybenzobimidazole, copolymers thereof, polymer blends thereof, or combinations thereof. When infiltrated green compacts of graphene-coated polymer particles are subjected to pyrolysis, these species become an additional carbon source if higher amounts of carbon in the hybrid foam are desired.

The present invention also provides a unitary 3D graphene-carbon hybrid foam comprised of a plurality of cells and cell walls, wherein the cell walls contain single or few layer graphene sheets chemically bonded by a carbon material, having a carbon material to graphene weight ratio of from 1/200 to 1/2, wherein the few layer graphene sheets have 2-10 stacked graphene planar layers, the graphene planes having, for example, graphene planesInterplanar spacing d from 0.3354nm to 0.36nm as measured by X-ray diffraction ₀₀₂ And the single-or few-layer graphene sheets contain pristine graphene materials having substantially zero% non-carbon elements or non-pristine graphene materials having 0.001% to 35% (preferably 0.01% to 25%) by weight non-carbon elements, wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, fluorinated graphene, chlorinated graphene, brominated graphene, iodinated graphene, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or combinations thereof. Multiple single or few layers of graphene surrounding the underlying polymer particle may overlap one another to form a stack of graphene sheets. The stack may have a thickness greater than 5nm, and in some cases greater than 10nm or even greater than 100 nm.

The monolithic 3D graphene-carbon hybrid foam typically has from 0.001g/cm ³ To 1.7g/cm ³ Of from 50m ² (ii) g to 3,000m ² Specific surface area in g. In a preferred embodiment, the pore walls contain stacked graphene planes having an inter-plane spacing d from 0.3354nm to 0.40nm as measured by X-ray diffraction ₀₀₂ 。

For oil recovery applications (e.g., separating oil from water), the graphene-carbon preferably has an oxygen content of from 1% to 25% (more preferably 1% -15% and most preferably 1% -10%) by weight. This can be achieved if the starting material is graphite oxide, or if the carbonization treatment is carried out in a slightly oxidizing environment at a temperature of 300 ℃ to 1,500 ℃ (preferably not more than 1,000 ℃) and without subsequent graphitization. We have unexpectedly found that highly porous graphene-carbon foams of this nature are capable of absorbing up to 500% of their own weight of oil from an oil-water mixture.

For thermal management applications, graphene-carbon hybrid foams are preferably made by subjecting carbon-bonded graphite sheets (after carbonization) to a graphitization treatment under compressive stress. This facilitates orientation and reorganization (merging, growth, etc.) of graphene sheets or domains. As a result, the graphene-carbon foam sheet or film exhibits a thermal conductivity of at least 200W/mK per specific gravity and/or an electrical conductivity of not less than 2,000S/cm per specific gravity.

In embodiments, the pore walls contain pristine graphene and the 3D solid graphene-carbon foam has from 0.001g/cm ³ To 1.7g/cm ³ Or an average pore diameter from 2nm to 50 nm. In embodiments, the pore walls contain a non-pristine graphene material selected from the group consisting of: graphene oxide, reduced graphene oxide, fluorinated graphene, chlorinated graphene, brominated graphene, iodinated graphene, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein the solid graphene foam contains a non-carbon element content in a range of 0.01% to 20% by weight. In other words, the non-carbon elements may include elements selected from: oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. In particular embodiments, the cell walls contain fluorinated graphene and the solid graphene foam contains from 0.01% to 20% fluorine content by weight. In another embodiment, the cell walls contain graphene oxide and the solid graphene foam contains an oxygen content of from 0.01 to 20% by weight. In an embodiment, the solid graphene-carbon hybrid foam has from 200m ² A ratio of/g to 2,000m ² Specific surface area per gram or from 0.01g/cm ³ To 1.5g/cm ³ The density of (c).

It may be noted that there is no limitation on the shape or size of the graphene-carbon hybrid foam of the present invention. In a preferred embodiment, the solid graphene-carbon hybrid foam is made in the form of a continuous length roll sheet (roll of continuous foam sheet) having a thickness of not less than 100nm and not more than 10cm 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. The sheet roll is produced by a roll-to-roll process. There is no prior art graphene-based foam made in the form of a sheet roll. It has not previously been found or suggested to have a possible roll-to-roll process for producing continuous lengths of graphene foam (based on virgin or non-virgin).

For applications based on thermal management or electrical conductivity, the graphene-carbon foam preferably has an oxygen content or non-carbon content of less than 1% by weight and the cell walls have stacked graphene planes with inter-graphene spacing of less than 0.35nm, a thermal conductivity of at least 250W/mK per specific gravity, and/or an electrical conductivity of no less than 2,500S/cm per specific gravity.

In another preferred embodiment, the graphene-carbon hybrid foam has an oxygen content or non-carbon content of less than 0.01% by weight and the cell walls contain stacked graphene planes having 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 no less than 3,000S/cm per specific gravity.

In yet another preferred embodiment, the graphene-carbon hybrid foam has an oxygen content or non-carbon content of no greater than 0.01% by weight, and the cell walls contain stacked graphene 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 350W/mK per specific gravity, and/or an electrical conductivity of no less than 3,500S/cm per specific gravity.

In yet another preferred embodiment, the graphene foam has cell walls containing stacked graphene planes with inter-graphene spacing less than 0.336nm, a mosaic spread value 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.

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

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

The present invention also provides an apparatus for removing or separating oil, which contains the 3D graphene-carbon hybrid foam of the present invention as an element absorbing oil. Also provided is an apparatus for removing or separating a solvent, which contains the 3D graphene-carbon hybrid foam as a solvent-absorbing member.

The present invention also provides a process for separating oil from an oil-water mixture, such as oil-spilled water or wastewater from oil sands. The method comprises the following steps: (a) Providing an oil-absorbing element comprising a monolithic graphene-carbon hybrid foam; (b) Contacting the oil-water mixture with the element, the element absorbing oil from the mixture; and (c) withdrawing the 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 imbibing element comprising a monolithic graphene-carbon hybrid 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 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 element is reused.

Drawings

Figure 1 shows a flow diagram of the most common prior art process for producing highly oxidized NGP, which requires cumbersome chemical oxidation/intercalation, washing and high temperature expansion procedures.

Fig. 2 (a) shows a flow diagram of a method of the present invention for producing a monolithic 3D graphene-carbon hybrid foam.

Fig. 2 (B) schematic representation of the thermally induced conversion of a polymer to carbon that binds graphene sheets together to form a 3D graphene-carbon hybrid foam. The compacted structure of the graphene-coated polymer particles is converted into a highly porous structure.

Fig. 3 (a) SEM image of the monolith structure of 3D graphene-carbon hybrid foam.

Fig. 3 (B) SEM image of the monolith structure of another 3D graphene-carbon hybrid foam.

Fig. 4 (a) thermal conductivity values relative to specific gravity for 3D monolithic graphene-carbon foam, mesophase pitch derived graphite foam, and Ni-foam template assisted CVD graphene foam produced by the method of the present invention.

Fig. 4 (B) thermal conductivity values for 3D graphene-carbon foam and hydrothermally reduced GO graphene foam.

Fig. 5 thermal conductivity values for 3d graphene-carbon hybrid foam and pristine graphene foam (prepared by casting with a blowing agent and then heat treating) are plotted as a function of final (maximum) heat treatment temperature.

Figure 6 conductivity values for 3d graphene-carbon foam and hydrothermally reduced GO graphene foam.

Fig. 7 plots the amount of oil absorbed per gram of integrated 3D graphene-carbon hybrid foam as a function of oxygen content in the foam with a porosity level of about 98% (separating oil from oil-water mixture).

Fig. 8 plots the amount of oil absorbed per gram of integrated 3D graphene-carbon hybrid foam 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

The invention provides a method for producing an integrated 3D graphene-carbon hybrid foam directly from graphite material particles and polymer particles.

As schematically shown in fig. 2 (a), the method begins with mixing a plurality of particles of a graphite material and a plurality of particles of a solid polymeric carrier material to form a mixture that is enclosed in an impingement chamber of an energy impingement device (e.g., a vibratory ball mill, a planetary ball mill, a high energy mill, a basket mill, an agitated ball mill, a cryogenic ball mill, a microsphere mill, a tumbling ball mill, a continuous ball mill, an agitated ball mill, a pressurized ball mill, a cryogenic mill, a vibrating screen, a bead mill, a nanobead mill, an ultrasonic homogenate mill, a centrifugal planetary mixer, a vacuum ball mill, or a resonant acoustic mixer). When operated, this energy impact device imparts kinetic energy to the solid particles contained therein, thereby allowing the polymer particles to impact on the graphite particles with high intensity and high frequency.

Under typical operating conditions, such impact events result in exfoliation of graphene sheets from the graphite material and transfer of the graphene sheets onto the surface of the solid polymer support particles. These graphene sheets wrap around the polymer particles to form graphene coated or graphene embedded polymer particles inside the impingement chamber. This is referred to herein as a "direct transfer" process, meaning that the graphene sheets are transferred from the graphite particles directly to the surface of the polymer particles without being mediated by any third party entity.

Alternatively, multiple impacting balls or media may be added to the impact chamber of the energy impact device. These impact balls accelerated by the impact device impact on the surface/edge of the graphite particles at a favorable angle with high kinetic energy to exfoliate the graphene sheets from the graphite particles. The graphene sheets are temporarily transferred to the surface of the impacting balls. These graphene-bearing impact balls then collide with the polymer pellets and transfer the loaded graphene sheets to the surface of the polymer particles. This sequence of events is referred to herein as an "indirect transfer" process. These events occur at very high frequencies and therefore most polymer particles are typically covered by graphene sheets in less than an hour. In some embodiments of the indirect transfer process, step (c) comprises operating a magnet to separate the impact balls or media from the graphene-coated or graphene-embedded polymer particles.

The method then includes recovering the graphene-coated or graphene-intercalated polymer particles from the impingement chamber and consolidating the graphene-coated or graphene-intercalated polymer particles into a graphene-polymer composite structure of a desired shape. This consolidation step can be as simple as a compaction step that merely mechanically stacks the graphene coated or embedded particles into the desired shape. Alternatively, this consolidation step may require melting the polymer particles to form a polymer matrix in which the graphene sheets are dispersed. Such graphene-polymer structures may be in any practical shape or size (fibers, rods, plates, cylinders, or any regular or odd shape).

The graphene-polymer compact or composite structure is then pyrolyzed to thermally convert the polymer into carbon or graphite, which combines graphene sheets to form a monolithic 3D graphene-carbon hybrid foam, as shown in fig. 3 (a) and 3 (B).

To form the carbon component of the resulting graphene-carbon hybrid foam, polymer particles can be selected that have a high carbon yield or char yield (e.g., >30% by weight of the polymer is converted to a solid carbon phase; rather than becoming part of the volatile gas). The high carbon yielding polymer may be selected from the group consisting of phenolic resins, polyfurfuryl alcohol, polyacrylonitrile, polyimides, polyamides, polyoxadiazoles, polybenzoxazoles, polybenzobisoxazoles, polythiazoles, polybenzothiazoles, polybenzobisoxazoles, poly (p-phenylene vinylenes), polybenzimidazoles, polybenzobisoxazoles, copolymers thereof, polymer blends thereof, or combinations thereof. Upon pyrolysis, the particles of these polymers become porous as shown in the bottom portion of fig. 2 (B).

If a lower carbon content (higher proportion of graphene relative to carbon) and lower foam density are desired in graphene-carbon hybrid foams, the polymer may contain a low carbon yield polymer selected from: polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile Butadiene (ABS), polyester, polyvinyl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethyl methacrylate (PMMA), copolymers thereof, polymer blends thereof, or combinations thereof. When pyrolyzed, the particles of these polymers become porous, as shown in the middle portion of fig. 2 (B).

When heated at temperatures between 300 ℃ and 2,500 ℃, these polymers (both high and low carbon yields) convert to carbon materials that nucleate preferentially near the edges of the graphene sheets. Such carbon materials naturally bridge the gaps between graphene sheets, thereby forming an interconnected electron conduction path. In fact, the resulting graphene-carbon hybrid foam consists of an integral 3D network of carbon-bonded graphene sheets, enabling continuous transport of electrons and phonons (quantized lattice vibrations) between graphene sheets or domains without interruption. Upon further heating at temperatures above 2,500 ℃, the carbon phase may become graphitized to further increase both electrical and thermal conductivity. If the graphitization time exceeds 1 hour, the amount of non-carbon elements is also reduced to typically less than 1% by weight.

It may be noted that organic polymers typically contain significant amounts of non-carbon elements, which may be reduced or eliminated via thermal treatment. Thus, pyrolysis of the polymer causes volatile gaseous molecules such as CO ₂ And H ₂ The formation and release of O, which results in the formation of pores in the carbon phase of the resulting polymer. However, if the polymer is not constrained when carbonized (the carbon structure may shrink when the non-carbon elements are released), such pores also have a high tendency to become collapsed. We have unexpectedly found that graphene sheets surrounding polymer particles can limit carbon pore wall collapse. At the same time, some of the carbon species also penetrate into the gaps between the graphene sheets, where they bind the graphene sheets together. The pore size and pore volume (porosity level) of the resulting 3D monolithic graphene foam depend primarily on the starting polymer size and the carbon yield of the polymer.

The graphite material from which the graphene sheets are derived may be selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fibers, graphite nanofibers, fluorinated graphite, graphite oxide, chemically modified graphite, expanded graphite, recompressed expanded graphite, mesocarbon microbeads, or combinations thereof. In this regard, there are several additional unexpected elements associated with the method of the present invention:

(1) Graphene sheets can be exfoliated from natural graphite by using individual polymer particles without the need to utilize heavier and harder impacting balls (such as, for example, zirconium dioxide or steel balls, which are commonly used in ball mills). The exfoliated graphene sheets are transferred directly to the surface of the polymer particles and firmly surround the polymer particles.

(2) It was also unexpected that the impact polymer particles were able to exfoliate graphene sheets from artificial graphite such as mesocarbon microbeads (MCMB), which are known to have an amorphous carbon surface layer.

(3) By means of harder impact balls, it is also possible to exfoliate graphene-like planes of carbon atoms constituting the internal structure of the carbon or graphite fibers and to transfer these planes to the surface of the polymer particles. This has never been taught or suggested in the prior art.

(4) The present invention provides a surprisingly simple, fast, scalable, environmentally friendly and cost-effective process that avoids substantially all of the disadvantages associated with prior art methods of producing graphene sheets. Graphene sheets are immediately transferred to and wrapped around polymer particles, which are then easily converted into monolithic 3D graphene-carbon hybrid foams.

It may be noted that if the starting graphite is intentionally oxidized to some extent (e.g., to contain 2-15% by weight oxygen), a certain desired degree of hydrophilicity may be imparted to the cell walls of the graphene-carbon hybrid foam. Alternatively, if the carbonization process is allowed to occur in a micro-oxidizing environment, oxygen-containing functional groups may be attached to the carbon phase. These features enable the separation of oil from water by selective absorption of oil from the oil-water mixture. In other words, such graphene-carbon hybrid foam is capable of recovering oil from water, thereby helping to clean up 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 graphite material may be selected from non-intercalated and non-oxidized graphite materials that have never been previously exposed to a chemical or oxidation treatment prior to placement in the impingement chamber. Alternatively or additionally, the graphene-carbon foam may be subjected to a graphitization treatment at a temperature higher than 2,500 ℃. The resulting material is particularly useful in thermal management applications (e.g., for making fin heat sinks, heat exchangers, or heat spreaders).

It may be noted that the graphene-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.

An X-ray diffraction pattern was 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 formula, d ₀₀₂ 0.3354g (= 0.344 g) and graphitization degree g calculated by X-ray pattern, where d is ₀₀₂ Is the interlayer spacing in nm of graphite or graphene crystals. Only when d ₀₀₂ This formula is effective at or below about 0.3440 nm. Having a d of greater than 0.3440nm ₀₀₂ The graphene foam wall(s) of (a) reflect oxygen-or fluorine-containing functional groups (e.g., -F, -OH, on planar surfaces or edges of graphene molecules) that act as spacers to increase the spacing between graphene molecules,>O and-COOH).

Another structural index that can be used to characterize the degree of order of the stacked and bonded graphene 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 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 ℃.

In-depth studies using a combination of SEM, TEM, selective zone diffraction, X-ray diffraction, AFM, raman spectroscopy and FTIR indicate that the graphene 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, or even>>100 μm). These giant fibers are formed if the final heat treatment temperature is less than 2,500 deg.CLarge graphene planes are often 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. In these cases, without wishing to be bound by theory, raman and FTIR spectroscopy studies appear to indicate sp ² (dominant) and sp ³ Coexistence of (weak but present) electronic configurations, not just conventional sp in graphite ² 。

The unitary 3D graphene-carbon hybrid foam is comprised of a plurality of pores and pore walls, wherein the pore walls contain single or few-layered graphene sheets chemically bonded by a carbon material, having a carbon material to graphene weight ratio of from 1/100 to 1/2, wherein the few-layered graphene sheets have 2-10 stacked graphene planar layers with an interplanar spacing D from 0.3354nm to 0.36nm as measured by X-ray diffraction ₀₀₂ And the single-or few-layer graphene sheets contain a pristine graphene material having substantially zero% non-carbon elements or have 0.01% to 25% non-carbon elements by weight (more typically<15%), wherein the non-native graphene is selected from graphene oxide, reduced graphene oxide, fluorinated graphene, chlorinated graphene, brominated graphene, iodinated graphene, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof. Multiple single or few layers of graphene surrounding the underlying polymer particle may overlap one another to form a stack of graphene sheets. The stack may have a thickness greater than 5nm, and in some cases greater than 10nm or even greater than 100 nm.

Monolithic 3D graphene-carbon hybrid foams typically have from 0.001g/cm ³ To 1.7g/cm ³ From 50m ² (ii) g to 3,000m ² A 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 planes having an inter-plane spacing d from 0.3354nm to 0.40nm as measured by X-ray diffraction ₀₀₂ 。

Many graphene sheets can be combined edge-to-edge with each other into a unitary graphene entity through covalent bonds. The gaps between the free ends of those un-merged sheets or shorter merged sheets are bound by the carbon phase converted by the polymer. Due to these unique chemical compositions (including oxygen or fluorine content, etc.), morphologies, crystal structures (including inter-graphene spacing), and structural features (e.g., degree of orientation, few defects, chemical bonding and lack of gaps between graphene sheets, and substantially no discontinuities along the graphene plane direction), graphene-carbon hybrid 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 monolithic 3D graphene-carbon hybrid foams ideal elements for a variety of engineering and biomedical applications. For example, graphene-carbon foams may be used in the following applications for thermal management purposes only:

a) Graphene-carbon hybrid 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) The hybrid foam itself can be used as a heat spreader due to its high thermal conductivity.

c) Hybrid 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) ³ And 1.8g/cm ³ Adjustable low density), high thermal conductivity per unit specific gravity or per unit physical density, and high structural integrity (graphene sheets bonded by carbon) make this hybrid foam an ideal material for durable heat exchangers.

Graphene-carbon hybrid foam based thermal management or heat 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 (Peltier) cooling plates, and the like.

Heat exchangers are devices used to transfer heat between one or more fluids; such as a gas and a liquid flowing separately in different channels. These fluids are typically separated by solid walls to prevent mixing. The graphene-carbon hybrid foam of the present invention is an ideal material 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., that make up the radiator coil) are typically made of high thermal conductivity materials such as Cu and Al. The graphene foam of the present invention having higher thermal conductivity or higher specific surface area is an excellent substitute 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 graphene foam of the present invention may also be used in a heat sink. 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.

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 may be embedded in the regions formed between adjacent fins (inverted fins). These cavities are effective to extract 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 whole 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 comprising 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 graphene-carbon hybrid foam of the present invention is itself a good thermal interface material and is also a highly effective thermal diffusion element. In addition, this highly conductive foam can also be used as an insert for electronic device cooling and for enhancing heat removal from the chiplets to the heat spreader. 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 graphene-carbon hybrid foam of the present invention a good conductive thick plate 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 such an arrangement, the heat source is cooled under the thick graphene foam sheet, rather than being cooled in direct contact with a cooling fluid. The slab of graphene foam can significantly improve the 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.

Solid graphene foam is also an excellent material 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, solid graphene foam is chemically inert and does not have these oxidation or corrosion problems. A heat pipe for electronic device thermal management may have a solid graphene foam envelope and a wick, using water as the working fluid. Graphene/methanol may be used if the heat pipe needs to operate below the freezing point of water, and graphene/ammonia heat pipes 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, many such junctions may be arranged in series to increase this effect to the amount of heating or cooling required. Solid graphene foam may be used to improve thermal transfer efficiency.

Filtration and fluid absorption applications

Solid graphene foams can be made to contain microscopic pores (< 2 nm) or mesoscale pores with pore sizes from 2nm to 50 nm. Solid graphene-carbon hybrid foams can also be made to contain micron-sized pores (1-500 μm). Based only on well-controlled pore size, the graphene-carbon foam of the present invention may be an exceptional filtration material for air or water filtration.

Further, graphene pore wall chemistry and carbon phase chemistry can be independently controlled to impart different amounts and/or types of functional groups to one or both of the graphene sheets and the carbon binder phase (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 graphene-carbon hybrid foams that exhibit some unique combination of many unexpected properties, synergistic effects, and properties that are generally considered to be 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, separating, or recovering oil, which contains the 3D graphene-carbon hybrid foam of the present invention as an element for absorbing or separating oil. Also provided is an apparatus for removing or separating a solvent, which contains the 3D graphene-carbon hybrid foam as a solvent-absorbing member.

A major advantage of using the graphene-carbon hybrid foam of the present invention as an oil absorbing element is its structural integrity. Due to the point that graphene sheets are chemically bonded by carbon materials, the resulting foam will not disintegrate after repeated oil absorption operations. In contrast, we found that graphene-based absorbing oil elements prepared by hydrothermal reduction, vacuum assisted filtration or freeze-drying disintegrate after absorbing the oil 2 or 3 times. Nothing else (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 volume can be controlled mainly by the ratio between the amount of initial support polymer particles and the amount of graphene sheets before the thermal 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 a monolithic graphene-carbon hybrid 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 imbibing element comprising a monolithic graphene-carbon hybrid 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 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: production of graphene-carbon foam from flake graphite via polypropylene powder-based solid polymer support

In the experiment, 1kg of polypropylene (PP) pellets, 50g of flake graphite, 50 mesh (average particle size 0.18mm; from Abury Carbons, asbury NJ, N.J.), and 250 g of magnetic steel balls were placed in a high energy ball mill vessel. The ball mill was operated at 300rpm for 2 hours. The container lid was removed and the stainless steel ball was removed via a magnet. The polymeric support material was found to be coated with a black graphene layer. The support material was placed on a 50 mesh screen and a small amount of unprocessed flake graphite was removed.

The coated support material sample was then immersed in tetrachloroethylene at 80 ℃ for 24 hours to dissolve the PP and allow the graphene sheets to disperse in the organic solvent. After removal of the solvent, isolated graphene flake powder (mostly few-layer graphene) is recovered. The remaining coated support material was then compacted in the mold cavity to form a green compact, which was then heat treated in a sealed crucible at 350 ℃ and then 600 ℃ for 2 hours to produce graphene-carbon foam.

In a separate experiment, the same batch of PP pellets and flake graphite particles (without impacting steel balls) was placed in the same high energy ball mill vessel and the mill was operated under the same conditions for the same period of time. The results are compared with those obtained by the striking ball assisting operation. Isolated graphene sheets isolated from PP particles after dissolution of PP are mostly single-layer graphene. The graphene-carbon foam produced by this method has a higher level of porosity (lower physical density).

Although polypropylene (PP) is used herein as an example, the support material for graphene-carbon hybrid foam production is not limited to PP. It may be any polymer (thermoplastic, thermoset, rubber, wax, adhesive, gum, organic resin, etc.), provided that the polymer may be made in particulate form. It is noted that uncured or partially cured thermoset resins, such as oligomers or rubbers based on epoxies and imides, can be made in particulate form at room temperature or lower (e.g., low temperatures). Thus, even partially cured thermoset resin particles can be used as a polymer carrier.

Example 2: graphene-carbon hybrid foam using expanded graphite (thickness >100 nm) as graphene source and ABS as polymeric solid support particles

In the experiment, 100 grams of ABS pellets as solid carrier material particles were placed in a 16 ounce plastic container along with 5 grams of expanded graphite. The vessel was placed in an Acoustic mixing unit (resodyne acoustics mixer) and processed for 30 minutes. After processing, the support material was found to be coated with a thin layer of carbon. A small sample of the carrier material was placed in acetone and subjected to ultrasonic energy to accelerate the dissolution of ABS. The solution was filtered using a suitable filter and washed four times with additional acetone. Following washing, the filtrate was dried in a vacuum oven set at 60 ℃ for 2 hours. The sample was examined by optical microscopy and found to be graphene. The remaining pellets were extruded to produce graphene-polymer sheets (1 mm thick) which were then carbonized to prepare graphene-carbon foam samples under different temperature and compression conditions.

Example 3: production of graphene-carbon hybrid foams from mesocarbon microbeads (MCMB as graphene source material) and Polyacrylonitrile (PAN) fibers (as solid support particles)

In one example, 100 grams of a PAN fiber segment (2 mm long, as a carrier particle), 5 grams of MCMB (China Steel Chemical co., taiwan), and 50 grams of zirconia beads were placed in a vibratory ball mill and processed for 2 hours. After the process was completed, the vibration mill was then opened and the support material was found to be coated with a black coating of graphene sheets. Zirconia particles having distinctly different sizes and colors were manually removed. The graphene coated PAN fibers are then compacted and melted together to form several composite membranes. These films were subjected to the following heat treatments: at 250 ℃ for 1 hour (in room air), at 350 ℃ for 2 hours, and at 1,000 ℃ for 2 hours (under an argon atmosphere) to obtain a graphene-carbon foam layer. The half carbonized foam layer was then heated to 2,850 ℃ and maintained at this temperature for 0.5 hours.

Example 4: curing phenolic resin particles as polymer carrier in a cryomill

In one experiment, 10 grams of phenolic particles were placed in a SPEX grinder Sample holder (SPEX Sample Prep, inc., methachen, N.J.) along with 0.25 grams of HOPG powder derived from graphitized polyimide and a magnetic stainless steel impactor. The same experiment was performed, but the sample holder did not contain any impactor balls. These processes are carried out in a "drying chamber" at 1% humidity to reduce condensation of water onto the finished product. The SPEX mill is operated for 10 to 120 minutes. After operation, the contents of the sample holder were sorted to recover graphene coated resin particles by removing residual HOPG powder and impactor balls (when used).

The resulting graphene-coated resin particles were examined in both cases (with or without impactor spheres) using both a digital optical microscope and a Scanning Electron Microscope (SEM). The thickness of the graphene sheet surrounding the resin particle was observed to increase with the milling operation time and the impactor assisted operation yielded thicker graphene coatings assuming the same operation duration.

A large amount of graphene-coated resin particles was compressed to form a green compact, which was then infiltrated with a small amount of petroleum pitch. Separately, another green compact of graphene-coated resin particles was prepared under comparable conditions, but without attempting pitch infiltration. The two compacts were then subjected to the same pyrolysis treatment.

Example 5: natural graphite particles as graphene source, polyethylene (PE) or nylon 6/6 beads as solid support particles, and ceramic or glass beads as added impact balls

In the experiment, 0.5kg of PE or nylon beads (as solid support material), 50g of natural graphite (graphene sheet source) and 250 g of zirconia powder (impact balls) were placed in the vessel of a planetary ball mill. The ball mill was operated at 300rpm for 4 hours. The vessel lid was removed and zirconia beads (different in size and weight than graphene coated PE beads) were removed by a vibrating screen. It was found that the particles of the polymeric support material were coated with a black graphene layer. The support material was placed on a 50 mesh screen and a small amount of unprocessed flake graphite was removed. In a separate experiment, glass beads were used as the impact balls; other ball milling operating conditions remained the same.

A quantity of graphene-coated PE pellets and a quantity of graphene-coated nylon beads were individually compacted in a die cavity and briefly heated above the melting point of PE or nylon and then rapidly cooled to form two green compacts. For comparison purposes, two corresponding compacts were prepared from a large number of uncoated PE pellets and a large number of uncoated nylon beads. These 4 compacts were then subjected to pyrolysis (by heating them in a chamber from 100 ℃ to 650 ℃). These results are highly unexpected. The compacts of the graphene-coated polymer particles were found to transform into graphene-carbon hybrid foam structures having dimensions comparable to those of the initial compacts (3 cm x 0.5 cm). SEM examination of these structures showed that carbon phases were present near the edges of the graphene sheets and that these carbon phases were used to bind the graphene sheets together. The carbon-bonded graphene sheets form a backbone of graphene-carbon hybrid pore walls with pores present therein for the space occupied by the initial polymer particles, as schematically shown in fig. 2 (a).

In contrast, two compacts from uncoated pellets or beads shrink to become essentially two carbon solid masses having a volume of about 15% -20% of the volume of the initial compact. These highly contracted solid blocks are virtually non-porous carbon materials; they are not foams.

Example 6: micron-sized rubber particles as solid polymer carrier particles

The experiment started with the preparation of micron-sized rubber particles. A mixture of methylhydrodimethyl-siloxane polymer (20 g) and polydimethylsiloxane (vinyldimethyl-terminated polymer) (30 g) was obtained by using a homogenizer for 1 minute at ambient conditions. Tween 80 (Tween 80) (4.6 g) was added and the mixture was homogenized for 20 seconds. Platinum-divinyltetramethyldisiloxane complex (0.5 g in 15g of methanol) was added and mixed for 10 seconds. This mixture was added to 350g of distilled water and a stable latex was obtained by homogenization for 15 minutes. The latex was heated to 60 ℃ for 15 hours. The latex was then demulsified with anhydrous sodium sulfate (20 g) and silicone rubber particles were obtained by vacuum filtration, washing with distilled water and vacuum drying at 25 ℃. The particle size distribution of the rubber particles obtained is 3 to 11 μm.

In one example, 10 grams of rubber particles, 2 grams of natural graphite, and 5 grams of zirconia beads were placed in a vibratory ball mill and processed for 2 hours. After the process was completed, the vibration mill was then opened and the rubber particles were found to be coated with a black coating of graphene sheets. The zirconia particles were removed manually. The graphene-coated rubber particles were then mixed with 5% by weight petroleum pitch (as binder) and mechanically compacted together to form several composite sheets. These compacts were then subjected to the following heat treatment in a tube furnace: 1 hour at 350 ℃,2 hours at 650 ℃, and 1 hour at 1,000 ℃ to obtain a graphene-carbon foam layer.

Example 7: preparation of fluorinated graphene foam

In a typical procedure, graphene-carbon hybrid sheets are fluorinated by chlorine trifluoride vapor in a sealed autoclave reactor to produce fluorinated graphene-carbon hybrid films. Allowing different durations of fluorination time to achieve different degrees of fluorination. The fluorinated graphene-carbon foam sheets were then individually immersed in containers each containing a chloroform-water mixture. We observed that these foam pieces selectively absorbed chloroform from water and the amount of chloroform absorbed increased with the degree of fluorination until the fluorine content reached 7.3% by weight (fig. 9).

Example 8: preparation of graphene oxide foam and graphene nitride foam

Immersing several pieces of graphene-carbon foam prepared in example 3 into 30% ₂ O ₂ -in aqueous solution for a period of 2-48 hours to obtain Graphene Oxide (GO) foams having an oxygen content of 2-25% by weight.

Some GO foam samples were mixed with different ratios 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 graphene 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 graphene-carbon hybrid foams are used for different purposes. For example, graphene oxide-carbon hybrid foam structures are particularly effective as absorbents from oil in oil-water mixtures (i.e., oil sprinkled over water and then mixed together). In this case, the unitary 3D graphene (0% -15% oxygen by weight) -carbon foam structure is both hydrophobic and oleophilic (fig. 7 and 8). 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 different amounts of N also enable the graphene-carbon hybrid foam of the present invention to absorb different organic solvents from water or separate one organic solvent from a mixture of solvents.

Comparative example 1: carbonization of graphene and graphene-polymer composites via Hummer method

Graphite oxide was prepared by oxidizing graphite flakes with sulfuric acid, nitrate salt and permanganate according to Hummers' method [ us patent No. 2,798,878, 7/9/1957 ]. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The graphite oxide was repeatedly washed in 5% HCl solution to remove most of the sulfate ions. The sample was then repeatedly washed with deionized water until the pH of the filtrate was neutral. The slurry was spray dried and stored in a vacuum oven at 60 ℃ for 24 hours. The interlayer spacing of the resulting layered graphite oxide was determined to be about 0.73nm (7.3A) by the Debey-Scherrer X-ray technique. A sample of this material was then transferred to a furnace preset at 650 ℃ for 4 minutes for puffing and heated in an inert atmosphere furnace at 1200 ℃ for 4 hours to produce a low density powder consisting of few layers of Reduced Graphene Oxide (RGO). Surface area was measured via nitrogen adsorption BET. The powder was then dry blended with ABS, PE, PP, and nylon pellets, respectively, at loading levels of 1% -25%, and compounded using a 25mm twin screw extruder to form composite sheets. These composite sheets are then pyrolyzed.

Comparative example 2: preparation of single layer Graphene Oxide (GO) sheets from mesocarbon microbeads (MCMB) and then generation of graphene foam layers from the GO sheets

Mesocarbon microbeads (MCMB) are supplied by China Steel Chemical co, a college of Taiwan hero (China Steel Chemical co., kaohsiung, taiwan). This material has a density of about 2.24g/cm ³ And a median particle diameter of about 16 μm. MCMB (10 g) was intercalated with an acid solution (4. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The intercalated MCMB was repeatedly washed in a 5% solution of HCl to remove most of the sulfate ions. The sample was then repeatedly washed with deionized water until the pH of the filtrate was not less than 4.5. The slurry is then subjected to ultrasonication for 10-100 minutes to produce the GO suspension. TEM and atomic force microscopy studies showed that when the oxidation treatment was over 72 hours, most of the GO sheets were single layer graphene, and when oxidizedFrom 48 hours to 72 hours, two or three layers of graphene.

For 48-96 hours of oxidation treatment, the GO sheet contains a proportion of oxygen of about 35% -47% by weight. GO sheets were suspended in water. Baking soda (5% -20% by weight) was added to the suspension as a chemical blowing agent just before casting. The suspension is then cast onto a glass surface. Several samples were cast, some containing blowing agent and some not. After liquid removal, the resulting GO film has a thickness that can vary from about 10 to 500 μm. Several GO membranes, with or without blowing agent, are then subjected to heat treatment involving heating temperatures of 80-500 ℃ for 1-5 hours, which results in graphene foam structure.

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

Recognizing the possibility that the high defect number in GO sheets works to reduce the conductivity of individual graphene planes, we decided to investigate whether using 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 flake milled to a size of about 20 μm or less is dispersed in 1,000ml of deionized water (containing 0.1% by weight of dispersant, from DuPont) containing

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.

Different 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 surfactant. Then theThe suspension was cast onto a glass surface. Casting several samples, including the use of CO introduced into the suspension just prior to casting ₂ Samples made as physical blowing agents. After the liquid is removed, the resulting graphene film has a thickness that can vary from about 10 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.

Comparative example 4: 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 pressure ₄ Carbon 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 poly (methyl methacrylate) (PMMA) is deposited on the surface of the graphene film as a support to prevent collapse of the graphene network 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 important for the preparation of free standing films of graphene foam; only severely distorted and deformed graphene foam samples were obtained without the PMMA support layer. This is a cumbersome process that is not environmentally friendly and not scalable.

Comparative example 5: 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 1,000psi. 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/minute, 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 ℃ (carbonized) under a nitrogen blanket and then heat treated to 2500 ℃ and 2800 ℃ (graphitized) in a separate operation in argon in a graphite crucible.

Comparative example 6: graphene foam from hydrothermally reduced graphene oxide

For comparison, self-assembled graphene hydrogel (SGH) samples were prepared by a one-step 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 (Teflon) -lined autoclave at 180 ℃ for 12 h. An SGH containing about 2.6% (by weight) graphene sheets and 97.4% water has a value of about 5X 10 ^-3 Conductivity of S/cm. After drying and heat treatment at 1,500 ℃, the resulting graphene foam exhibits about 1.5 × 10 ^-1 S/cm, which is 2 times lower than that of the graphene foam of the present invention produced by heat treatment at the same temperature.

Example 9: thermal and mechanical testing of various graphene foams and conventional graphite foams

Samples from various conventional carbon or graphene foams were machined into specimens for measuring thermal conductivity. The bulk thermal conductivity of mesophase pitch-derived foams ranges from 67W/mK to 151W/mK. The density of the sample is from 0.31 to 0.61g/cm ³ . When considering weight, the specific heat conductivity of the bitumen-derived foam is about 67/0.31=216 and 151/0.61=247.5w/mK per specific gravity (or per physical density).

Having a density of 0.51g/cm ³ The compressive strength of the sample of average density of (a) was measured as 3.6MPa and the compressive modulus was measured as 74MPa. Phase (C)In contrast, the compressive strength and compressive modulus of the inventive graphene-carbon foam samples with comparable physical densities were 6.2MPa and 113MPa, respectively.

Fig. 4 (a) shows thermal conductivity values relative to specific gravity for 3D graphene-carbon foam, mesophase pitch-derived graphite foam, and Ni-foam template-assisted CVD graphene foam. These data clearly show the following unexpected results:

1) Given the same physical density, the 3D monolithic graphene-carbon foam produced by the inventive method exhibits 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 essentially pristine graphene that has never been exposed to oxidation and should exhibit high thermal conductivity compared to our graphene-carbon hybrid foam. The carbon phase of the hybrid foam generally has low crystallinity (some is amorphous carbon) and therefore has much lower thermal or electrical conductivity than graphene alone. However, when a carbon phase is coupled with graphene sheets to form a unitary structure produced by the method of the present invention, the resulting hybrid foam exhibits thermal conductivity compared to a fully pristine graphene foam. These exceptionally high thermal conductivity values observed with the graphene-carbon hybrid foams produced herein are all surprising to us. This may be due to the following observations: the originally isolated graphene sheets are now bonded by carbon, providing a bridge for uninterrupted transport of electrons and phonons.

3) The specific conductivity values of the hybrid foam of the invention exhibit values from 250 to 500W/mK per specific gravity; but those of other types of foam materials are typically below 250W/mK per specific gravity.

4) Thermal conductivity data for a series of 3D graphene-carbon foams and a series of pristine graphene-derived foams, both plotted against the final (maximum) thermal treatment temperature, are summarized in fig. 5. In both types of materials, the thermal conductivity increases monotonically with the final HTT. However, the method of the present invention enables cost-effective and environmentally friendly production of graphene-carbon foams with properties exceeding pristine graphene foams. This is another unexpected result.

5) Fig. 4 (B) shows the thermal conductivity values of the hybrid foam of the invention and the hydrothermally reduced GO graphene foam. Fig. 6 shows conductivity values for 3D graphene-carbon foam and hydrothermally reduced GO graphene foam. These data further support the following notions: given the same amount of solid material, the graphene-carbon foam of the present invention is inherently largely conductive, reflecting the importance of continuity of the electron and phonon transport paths. The carbon phase bridges the gaps or breaks between the graphene sheets.

Example 10: characterization of various graphene foams and conventional graphite foams

The internal structure (crystal structure and orientation) of several series of graphene-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 0.3345nm ₀₀₂ ). The graphene walls of the hybrid foam material exhibit a d typically from 0.3345nm to 0.40nm, but more typically up to 0.34nm ₀₀₂ And (4) spacing.

In the case of a heat treatment temperature of 2,750 ℃ for the foam structure under compression for 1 hour, d ₀₀₂ The 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 2 θ =55 ° corresponding to the X-ray diffraction from the (004) plane. The intensity of the (004) peak over 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 planes. For all graphite materials heat treated at temperatures below 2,800 ℃, the (004) peak is absent or relatively weak, the I (004)/I (002) ratio<0.1. Graphite materials heat treated at 3,000 ℃ to 3,250 ℃ (e.g., highly oriented pyrolytic graphite, HOPG) have an I (004)/I (002) ratio in the range of 0.2 to 0.5. In contrast, graphene foam 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 graphene 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 graphene foams have mosaic spread values in this range of 0.3-0.6 when produced with a final heat treatment temperature of not less than 2,500 ℃.

The following is a summary of some of the more important results:

1) In general, the addition of the impact balls helps to accelerate the process of exfoliation of graphene sheets from graphite particles. However, this option requires separation of the impact balls after the graphene-coated polymer particles are produced.

2) When no impact balls (e.g., ceramic, glass, metal balls, etc.) are used, harder polymer particles (e.g., PE, PP, nylon, ABS, polystyrene, high impact polystyrene, etc., and filler-reinforced forms thereof) are more capable of exfoliating graphene sheets from graphite particles than softer polymer particles (e.g., rubber, PVC, polyvinyl alcohol, latex particles).

3) In the absence of externally added impact balls, softer polymer particles tend to produce graphene-coated or embedded particles having 0.001 to 5% by weight graphene (predominantly single-layer graphene sheets), and harder polymer balls tend to produce graphene-coated particles having 0.01 to 30% by weight graphene (predominantly single-layer and few-layer graphene sheets), assuming the same 1 hour operating time.

4) With the external addition of the impact balls, all polymer balls are capable of supporting from 0.001% to about 80% by weight of graphene sheets (mainly few-layer graphene, <10 layers if more than 30% graphene sheets by weight).

5) The graphene-carbon hybrid foam materials of the present invention typically exhibit significantly higher structural integrity (e.g., compressive strength, elasticity, and resilience) and higher thermal and electrical conductivity than their counterparts produced by conventional prior art methods.

6) It is important to note that all prior art methods for producing graphite or graphene foam appear to provide only foams having a density of about 0.2g/cm ³ -0.6g/cm ³ Large 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 for the production of a catalyst having a particle size as low as 0.001g/cm ³ And may be as high as 1.7g/cm ³ A method of producing a graphene foam of density (c). The pore size can be from micro: (<2 nm) via mesoscale (2-50 nm) and varies up to macroscale (e.g., from 1 to 500 μm). This level of flexibility and versatility in designing different types of graphene-carbon foams is unprecedented and none of the prior art approaches match.

7) The method of the present invention also allows for convenient and flexible control of chemical composition (e.g., F, O and N content, etc.) in response to various application needs (e.g., oil recovery from oil-contaminated water, separation of organic solvents from water or other solvents, heat dissipation, etc.).

In summary, we have successfully developed an absolutely new, novel, unexpected, and significantly different class of highly conductive graphene-carbon hybrid foams, devices, and related production methods. 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 foams are fundamentally different and distinctly different from mesophase pitch-derived graphite foams, CVD graphene-derived foams, and graphene foams from the hydrothermal reduction of GO.

Claims (29)

1. A method of producing a monolithic 3D graphene-carbon hybrid foam directly from a graphite material, the method comprising:

(a) Mixing a plurality of particles of a graphite material and a plurality of particles of a solid polymeric carrier material in an impingement chamber of an energy impingement device to form a mixture;

(b) Operating the energy impingement device at a frequency and intensity for a time sufficient to exfoliate graphene sheets from the graphite material and transfer the graphene sheets to the surface of the solid polymer support material particles to produce graphene-coated or graphene-embedded polymer particles inside the impingement chamber;

(c) Recovering the graphene-coated or graphene-intercalated polymer particles from the impingement chamber and consolidating the graphene-coated or graphene-intercalated polymer particles into a graphene-polymer composite structure of a desired shape; and is

(d) Pyrolyzing the shaped graphene-polymer composite structure to thermally convert the polymer into pores and carbon or graphite that binds the graphene sheets to form the monolithic 3D graphene-carbon hybrid foam.

2. The method of claim 1, wherein the solid polymer is selected from solid particles of: a thermoplastic, a thermoset, a rubber, a semi-penetrating network polymer, a natural polymer, or a combination thereof.

3. The method of claim 1, wherein the solid polymer is partially removed by melting, etching, or dissolving in a solvent prior to step (d).

4. The method of claim 1, wherein the solid polymer contains a high carbon-yielding polymer selected from the group consisting of: phenolic resins, polyfurfuryl alcohol, polyacrylonitrile, polyimides, polyamides, polyoxadiazoles, polybenzoxazoles, polybenzdioxazoles, polythiazoles, polybenzothiazoles, poly (p-phenylene vinylene), polybenzimidazole, polybenzobimidazole, copolymers thereof, polymer blends thereof, or combinations thereof.

5. The method of claim 1, wherein the solid polymer comprises a low carbon-yield polymer selected from the group consisting of: polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile Butadiene (ABS), polyester, polyvinyl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethyl methacrylate (PMMA), copolymers thereof, polymer blends thereof, or combinations thereof.

6. The method of claim 1, wherein the pyrolyzing step comprises carbonizing the polymer at a temperature from 200 ℃ to 2,500 ℃ to obtain graphene-carbon foam, or carbonizing the polymer at a temperature from 200 ℃ to 2,500 ℃ to obtain graphene-carbon foam and then graphitizing the graphene-carbon foam from 2,500 ℃ to 3,200 ℃ to obtain graphitized graphene-carbon foam.

7. The method of claim 1, wherein the consolidating step comprises melting the polymer particles to form a polymer melt mixture having graphene sheets dispersed therein, forming the polymer melt mixture into a desired shape, and solidifying the shape into a graphene-polymer composite structure.

8. The method of claim 1, wherein the consolidating step comprises shaping the graphene-coated polymer particles into a composite shape selected from: stick, sheet, film, fiber, powder, ingot or block form.

9. The method of claim 1, wherein the consolidating step comprises forming a plurality of the graphene-coated or graphene-embedded polymer particles into a compacted object.

10. A unitary 3D graphene-carbon hybrid foam obtained by the method of claim 1, said unitary 3D graphene-carbon hybrid foam consisting of a plurality of pores and pore walls, wherein said pore walls contain single or few layer graphene sheets chemically bonded by a carbon material, having a carbon material to graphene weight ratio of from 1/200 to 1/2, wherein said few layer graphene sheets have 2-10 stacked graphene planar layersThese graphene planes have an interplanar spacing d from 0.3354nm to 0.40nm as measured by X-ray diffraction ₀₀₂ And the single-or few-layer graphene sheets contain pristine graphene materials having essentially zero% non-carbon elements or non-pristine graphene materials having 0.001% to 25% non-carbon elements by weight, wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, fluorinated graphene, chlorinated graphene, brominated graphene, iodinated graphene, hydrogenated graphene, nitrogenated graphene, doped graphene, or combinations thereof.

11. A unitary 3D graphene-carbon hybrid foam obtained by the method of claim 1, said unitary 3D graphene-carbon hybrid foam consisting of a plurality of pores and pore walls, wherein said pore walls contain single or few layer graphene sheets chemically bonded by a carbon material, having a carbon material to graphene weight ratio of from 1/200 to 1/2, wherein said few layer graphene sheets have 2-10 stacked graphene planar layers with an inter-planar spacing D measured by X-ray diffraction of from 0.3354nm to 0.40nm ₀₀₂ And the single-or few-layer graphene sheets contain pristine graphene materials having substantially zero% non-carbon elements or non-pristine graphene materials having 0.001% to 25% non-carbon elements by weight, wherein the non-pristine graphene is chemically functionalized graphene.

12. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the monolithic 3D graphene-carbon hybrid foam has a density of from 0.005 g/cm ³ To 1.7g/cm ³ From 50m ² G to 3,200 m ² A 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.

13. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain pristine graphene and the monolithic 3D graphene-carbon hybrid foam has from 0.01g/cm ³ To 1.7g/cm ³ Or an average pore diameter from 2nm to 50 nm.

14. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain non-native graphene material and wherein the monolithic 3D graphene-carbon hybrid 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.

15. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain fluorinated graphene and the monolithic 3D graphene-carbon hybrid foam contains from 0.01 to 15% fluorine content by weight.

16. The unitary 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain graphene oxide and the unitary 3D graphene-carbon hybrid foam contains an oxygen content of from 0.01 to 20% by weight.

17. The unitary 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the unitary 3D graphene-carbon hybrid foam has from 200m ² G to 3,000m ² A specific surface area of 0.1 g/cm ³ To 1.2 g/cm ³ The density of (c).

18. The unitary 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the unitary 3D graphene-carbon hybrid foam has a non-carbon content of less than 1% by weight, and the cell walls have an inter-graphene 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.

19. The unitary 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the unitary 3D graphene-carbon hybrid foam has an oxygen content of less than 1% by weight, and the cell walls have an inter-graphene 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.

20. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain stacked graphene planes having an inter-graphene spacing of less than 0.337nm and a mosaic spread value of less than 1.0.

21. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the cell walls contain a 3D network of interconnected graphene planes.

22. The monolithic 3D graphene-carbon hybrid foam of claim 10 or 11, wherein the monolithic 3D graphene-carbon hybrid foam contains mesoscale pores having a pore size of from 2nm to 50 nm.

23. An apparatus for removing or separating oil, comprising the integrated 3D graphene-carbon hybrid foam according to claim 10 or 11 as an oil-absorbing member.

24. An apparatus for removing or separating a solvent, comprising the integrated 3D graphene-carbon hybrid foam according to claim 10 or 11 as an element for absorbing or separating a solvent.

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

a. providing an oil-absorbing element comprising the unitary 3D graphene-carbon hybrid foam of claim 10 or 11;

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 provided with

d. The element is reused.

26. 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 that absorbs an organic solvent or separates a solvent, the element comprising the monolithic 3D graphene-carbon hybrid foam of claim 10 or 11;

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 is

e. The element is reused.

27. A thermal management device containing the unitary 3D graphene-carbon hybrid foam of claim 10 or 11 as a heat spreading or dissipating element.

28. The thermal management device of claim 27, containing 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 cooling device.

29. The thermal management device of claim 27, comprising a peltier cooling device.

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