KR20180102557A - Graphene-carbon hybrid foams - Google Patents

Abstract

An integrated 3D graphene-carbon hybrid foam comprising multiple pores and pore walls, wherein the pore walls are chemically bonded by a carbon material having a carbon material-to-graphene weight ratio of 1/100 to 1/2, Wherein the minority layer graphene sheet has from 2 to 10 layers of superimposed graphene planes having an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm and wherein the graphene sheet comprises pure (0% pristine graphene material, or a non-pristine graphene material having from 0.01 wt% to 25 wt% non-carbon element, wherein the non-pure graphene is selected from the group consisting of graphene oxide, reduced graphene oxide, A 3D graphene-doped layer selected from graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrided graphene, doped graphene, chemically graphene graphene, Carbon Thereby providing a hybrid foam. Also provided are methods of making hybrid foams, products comprising such hybrid foams, and uses thereof.

Description

Graphene-carbon hybrid foams

Cross-reference to related application

This application claims priority to U.S. Patent Application Serial Nos. 14 / 998,356 and 14 / 998,357, filed December 28, 2015, each of which is incorporated herein by reference.

Technical field

The present invention relates generally to carbon / graphite foams and more particularly to novel porous graphite materials referred to herein as integral 3D graphene-carbon hybrid foams, methods of making the same, products containing them, and articles thereof And a method for operating the same.

Carbon can be a material selected from the group consisting of diamond, fullerene (0-D nano graphite material), carbon nanotube or carbon nanofiber (1-D nano graphite material), graphene (2-D nano graphite material) , It is known to have five unique crystal structures. Carbon nanotubes (CNTs) refer to a tube structure grown with a single wall or multiple walls. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have diameters of from about several nanometers to hundreds of nanometers. The hollow structure in its longitudinal direction imparts unique mechanical, electrical and chemical properties to the material. CNT or CNF is a one-dimensional nano-carbon or 1-D nano graphite material.

The research group has already pioneered the development of graphene materials and related manufacturing processes in 2002: (1) BZ Jang and WC Huang, "Nano-scaled Graphene Plates," US Patent 7,071,258 (July 4, 2006) Filed October 21, 2002; (2) B. Z. Jang, et al. "Process for Producing Nano-scaled Graphene Plates," U.S. Patent Application 10 / 858,814 (June 3, 2004); And (3) B. Z. Jang, A. Zhamu, and J. Guo, "Process for Producing Nano-scaled Platelets and Nanocomposites," U.S. Patent Application 11 / 509,424 (August 25, 2006).

Single-layer graphene sheets consist of carbon atoms occupying a two-dimensional hexagonal lattice. Multi-layer graphene is a plate consisting of more than one graphene surface. Individual single layer graphene sheets and multilayer graphene sheets are collectively referred to herein as nano graphene platelets (NGP) or graphen materials. NGP is a mixture of pristine graphene (essentially 99% carbon atoms), slightly oxidized graphene (less than 5 wt% oxygen), graphene oxide (more than 5 wt% oxygen), slightly fluorinated graphene %), Graphene fluoride (greater than 5 wt% fluorine), other halogenated graphene, and chemically functionalized graphene.

NGP has been found to have a variety of unique physical, chemical, and mechanical properties. For example, graphene has been found to have the highest intrinsic strength and highest thermal conductivity among all the materials present. Although it is not expected that the application of graphene to real electronic devices (for example, replacing Si as the backbone of transistors) will be realized within the next 5-10 years, The application of graphene as an electrode material is imminent. In order to successfully utilize graphene in composites, energy and other fields, it is essential that large amounts of machinable graphene sheets be available.

The study group was one of the first groups to detect graphene [B. Z. Jang and W. C. Huang, "Nano-scaled Graphene Plates," U.S. Patent Application 10 / 274,473 (filed October 21, 2002); Currently, U.S. Patent No. 7,071,258 (July 4, 2006)]. This study group recently reviewed the manufacturing process of NGP and NGP nanocomposites [Bor Z. Jang and A Zhamu, "Processing of Nano Graphene Platelets (NGPs) and NGP Nanocomposites: A Review," J. Materials Sci. 43 (2008) 5092-5101]. In the prior art, NGP was manufactured according to four main approaches. A summary of the advantages and disadvantages is as follows:

A review of the manufacture of an independent nano-graphene plate or sheet (NGP)

Approach 1: Chemical formation and reduction of graphene oxide (GO)

The first approach (FIG. 1) is to treat natural graphite powders with an intercalating agent and an oxidizing agent (for example, concentrated sulfuric acid and nitric acid, respectively) to obtain a Graphite Intercalation Compound (GIC) Followed by obtaining an oxide (GO) (William S. Hummers, Jr., et al., Preparation of Graphitic Oxide, Journal of the American Chemical Society, 1958, p. 1339]. The intergrain spacing of graphite before insertion or oxidation is about 0.335 nm ( L _d = ½ d ₀₀₂ = 0.335 nm). By the insertion and the oxidation treatment, the gap between the graphenes is usually increased to a value exceeding 0.6 nm. This is the first expansion step that the graphite material undergoes in the chemical pathway. The resulting GIC or GO then undergoes further expansion (often referred to as "peeling ") using either a thermal impact exposure approach or a solution based ultrasound assisted graft layer exfoliation approach.

In a thermal shock exposure approach, a GIC or GO is exposed to a high temperature (typically 800 to 1,050 ° C) for a short period of time (typically 15 seconds to 60 seconds) to peel or expand the GIC or GO to release or further expanded graphite Forming a "graphite worm" consisting of graphite flakes still interconnected with one another. This thermal shock method can produce some separated graphite flakes or graphene sheets, but usually most of the graphite flakes remain interconnected. Typically, the peeled graphite or graphite worm is then subjected to a flake separation process using air milling, mechanical shearing or underwater ultrasonication. Approach 1 therefore involves fundamentally three separate processes: primary expansion (oxidation or insertion), further expansion (or "exfoliation") and separation.

In the solution-based separation approach, the expanded or exfoliated GO powder is dispersed in water or an aqueous alcohol solution and sonicated. It is important to note that in these processes the ultrasonic treatment is used after the insertion and oxidation of the graphite (i.e. after the primary expansion) and usually after the thermal shock exposure of the resulting GIC or GO (after the secondary expansion) . Alternatively, the GO powder dispersed in water undergoes an ion exchange or long purification process in such a way that the repulsive forces between the ions in the spaces between the faces overwhelm the graphene van der Waals force, resulting in the separation of the graphene layer .

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

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

(2) The chemical treatment process requires a long time (typically 5 hours to 5 days) to insert and oxidize.

(3) During this long insertion or oxidation process, strong acid consumes a significant amount of graphite (ie, converts graphite to carbon dioxide, resulting in graphite loss) by "digging into the graphite". It is common that 20 to 50% by weight of the graphite material immersed in the strong acid and the oxidizing agent is lost.

(4) Heat peeling is a highly energy intensive process because it requires high temperature (typically 800-1,200 ° C).

(5) Both the thermal inductive detachment approach and the solution inductive detachment approach require a very demanding cleaning and purification step. For example, to clean and recover 1 g of GIC, typically 2.5 kg of water is used, resulting in a large amount of wastewater to be properly treated.

(6) In both the thermal inductive release approach and the solution inductive release approach, the resulting product is a GO plate which must undergo further chemical reduction treatment to reduce the oxygen content. Even after reduction, the electrical conductivity of the GO plate remains much lower than the electrical conductivity of the pure graphene. In addition, the reduction procedure often involves the use of toxic chemicals such as hydrazine.

(7) Furthermore, the amount of insoluble solution remaining in the flakes after draining may be 20 to 150 parts by weight (pph), more typically about 50 to 120 pph, based on 100 parts by weight of the graphite flake. During hot stripping, the remaining insert species left by the flake are decomposed to produce a variety of undesirable sulfur compounds and nitrogen compounds (e.g., NO _x and SO _x ). In order not to adversely affect the environment, emissions require costly restoration processes.

The present invention is intended to overcome the limitations or problems outlined above.

Approach 2: Direct formation of pure nano-graphen sheet

In 2002, the team succeeded in separating monolayer and multilayer graphene sheets from partially carbonized or graphitized polymeric carbons obtained from polymers or pitch precursors [B. Z. Jang and W. C. Huang, "Nano-scaled Graphene Plates," U.S. Patent Application 10 / 274,473 (filed October 21, 2002); U.S. Patent No. 7,071,258 (July 4, 2006)]. Mack et al., "Chemical manufacture of nanostructured materials" U.S. Patent No. 6,872,330 (Mar. 29, 2005) discloses a process for producing a graphite sheet by inserting a potassium melt into graphite, A process involving the step of producing graphite-containing NGP has been developed. Since pure alkali metals such as potassium and sodium are extremely sensitive to moisture and there is a risk of explosion, this process must be carried out carefully in a vacuum or an extremely dry glove box environment. This process is not suitable for mass production of NGP. The present invention is intended to overcome the limitations outlined above.

Approach 3: Epitaxial growth and chemical vapor deposition of nano-graphene sheet at the inorganic crystal surface

Small scale fabrication of ultra-thin graphene sheets on substrates can be achieved by thermal decomposition-based epitaxial growth and laser desorption-ionization techniques [Walt A. DeHeer, Claire Berger, Phillip N. First, "Patterned thin film graphite devices and method for making same "US Patent 7,327,000 B2 (June 12, 2003)]. Epitaxial films of graphite with only one or a few atomic layers are technically and scientifically important due to their unique characteristics and their great potential as device substrates. However, this process is not suitable for mass production of separate graphene sheets for composite materials and energy storage applications. The present invention is intended to overcome the limitations outlined above.

Another process for producing graphene in a thin film form (usually less than 2 nm thick) is the catalytic chemical vapor deposition process. This catalytic CVD involves catalytic cracking of a hydrocarbon gas (e.g., C ₂ H ₄ ) on a Ni or Cu surface to form a single layer or a few-layer graphene. When Ni or Cu is a catalyst, carbon atoms obtained through decomposition of hydrocarbon gas molecules at a temperature of 800-1,000 ° C are directly deposited on the surface of the Cu foil or precipitated from the Ni-C solid solution state onto the surface of the Ni foil, Layer or a minority layer graphene (less than five layers) sheet. Ni-catalyzed or Cu-catalyzed CVD processes are not suitable for depositing more than 5 graphene planes (typically less than 2 nm) because underlying Ni or Cu layers can no longer provide any catalytic effects. CVD graphene films are very expensive.

Approach 4: Bottom-up approach (graphene synthesis from small molecules)

Yang, "Two-dimensional Graphene Nano-ribbons," J. Am. Chem. Soc. 130 (2008) 4216-17) used a method starting with Suzuki-Miyaura coupling of 1,4-diiodo-2,3,5,6-tetraphenyl-benzene with 4-bromophenylboronic acid To synthesize a nano - graphene sheet with a maximum length of 12 nm. The resulting hexaphenylbenzene derivative was further derivatized and ring fused to a small graphene sheet. This is a slow process that has produced very small graphene sheets so far. The present invention is intended to overcome the limitations outlined above.

Therefore, there is a need to reduce the amount of undesirable chemicals (or the removal of all of these chemicals), shorten process times, less energy consumption, lower levels of graphene oxidation, the situation is a need for a graphene manufacturing process that requires the reduction or elimination of such as sulfuric acid), or discharge of air into (e.g., SO ₂ and NO ₂₎ urgent. The process should be purer (less oxidized and less damaging), more electrically conductive, and able to produce larger / wider graphene sheets. In addition, such a graphene sheet must be easily made into a foam structure.

Recent research in this group has resulted in the development of a new, independent, nano-graphene sheet without chemicals in that it does not follow the conventional methods for making nanograffin plates outlined above. In addition, the method is cost effective and has enhanced utility in providing novel graphene materials with significantly reduced environmental impact. In addition, as disclosed herein, the incorporation of chemical-free graphene production and graphene-carbon hybrid foam formation into a single process.

In order to define the claims of the present application, the NGP or graphene material may comprise a single layer and multiple layers (typically less than 10 layers) of pure graphene, graphene oxide, reduced graphene oxide (RGO), graphene fluoride, Graphene chloride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrided graphene, chemically graphene graphene, discrete sheets / layers of doped graphene (doped with B or N, And includes a platelet. Pure graphene has essentially 0% oxygen. The RGO typically has an oxygen content of from 0.001% to 5% by weight. The graphene oxide (including RGO) may have 0.001 wt% to 50 wt% oxygen. In addition to pure graphene, all graphene materials have 0.001 wt% to 50 wt% non-carbon elements (e.g., O, H, N, B, F, Cl, Br, These materials are referred to herein as non-pristine graphene materials. The graphene-carbon foam of the present invention may comprise pure or non-pure graphene and the process of the present invention allows this flexibility.

Review of manufacturing of graphene foams

Generally speaking, the foam or foam material consists of pores (or cells) and pore walls (solid materials). The pores may be interconnected to form an open-cell foam. The graphene foam consists of pore walls and pores containing graphene material. There are three main ways to make graphene foams:

The first method typically involves sealing the graphene oxide (GO) aqueous suspension in a high pressure autoclave and heating the GO suspension at high pressure (tens or hundreds of atmospheres) and typically at a temperature in the range of 180 to 300 DEG C for an extended period of time (usually 12 to 36 hours) And hydrothermal reduction of the graphene oxide hydrogel, including heating. A useful reference for this method is as follows: Y. Xu, et al. "Self-Assembled Graphene Hydrogel via a One-Step Hydrothermal Process," ACS Nano 2010, 4, 4324-4330. There are several major problems associated with this method. (a) It is an unrealistic method for industrial scale manufacture because it requires high pressure. First of all, this method can not be performed continuously. (b) It is not impossible, but difficult, to control the pore size and porosity level of the pore structure produced by this method. (c) is not flexible in terms of the variety and variety of shapes and sizes of reduced graphene oxide (RGO) materials produced by this process (e.g., can not be made into a film form). (d) This method involves the use of a very low concentration of GO suspended in water (for example, 2 mg / mL = 2 g / L = 2 kg / kL). It can only produce less than 2 kg of graphene material (RGO) per 1000 liters of suspension by removing non-carbon elements (up to 50%). It is also practically impossible to operate a 1000 liter reactor which must withstand high temperature and high pressure conditions. Obviously, this method is not a scalable method for mass production of porous graphene structures.

The second method is based on a template-assisted catalytic CVD process and involves CVD deposition of a graphene on a sacrificial template (e.g. Ni foil). This graphen material follows the shape and dimensions of the Ni foam structure. The Ni foams are then etched away using an etchant, leaving a monolith of graphene skeleton that is essentially an open cell foam. A useful reference for this method is as follows: Zongping Chen, et al., "Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition," Nature Materials, 10 (June 2011) 424-428. There are several problems associated with this method: (a) catalytic CVD is an inherently very slow, highly energy-intensive and costly process; (b) The etchant is typically a highly undesirable chemical and the resulting Ni-containing etch solution is a source of contaminants. It is very difficult and expensive to recover or recycle the dissolved Ni metal from the etching solution. (c) When the Ni foam is etched away, it is difficult to maintain the shape and dimensions of the graphene foam without damaging the cell walls. The resulting graphene foams are typically very brittle and fragile. (d) it may be difficult to transport CVD precursor gases (e.g., hydrocarbons) into the metal foam because certain points within the sacrificial metal foam may not be accessible to the CVD precursor gas, resulting in a non-uniform structure.

The third method of making graphene foams also uses a sacrificial metal (e. G., Colloidal polystyrene particles, PS) coated with a graphene oxide sheet using a self-assembly approach. For example, Choi et al. Prepared chemically modified graphene (CMG) paper in two stages: a mixed aqueous colloidal suspension of CMG and PS (2.0 占 퐉 PS spheres) was vacuum filtered to form free-standing PS / CMG films are prepared, and then the PS beads are removed to produce 3D macroscopic pores (B. Choi, et al., "3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities," ACS Nano, 6 (2012) 4020-4028. , Which began with the preparation of separately positively charged PS suspensions of negatively charged CMG colloids. The mixture of CMG colloid and PS suspension was dispersed in the solution under controlled pH (= 2) and both compounds had the same surface charge (+13 ± 2.4 mV for CMG and +68 ± 5.6 mV for PS) Respectively. When the pH is increased to 6, CMG (zeta potential = -29 ± 3.7 mV) and PS spheres (zeta potential = +5 ± 2.5 mV) are collected due to electrostatic interactions and hydrophobicity acting on each other, The process was integrated into PS / CMG composite paper. This method also has several disadvantages: (a) this method requires very severe chemical treatments for both graphene oxide and PS particles. (b) In addition, the removal of PS with toluene results in a weakening of the macroporous structure. (c) Toluene is a strictly regulated chemical and should be handled very carefully. (d) the pore size is usually too large (e.g., a few microns) and too large for many useful applications.

As noted above, it is clear that all prior art methods or processes for producing graphene foams have major deficiencies. It is therefore an object of the present invention to provide a cost-effective process for the mass production of graphene-based foams (specifically, integral 3D graphene-carbon hybrid foams) of high conductivity and mechanically strong properties. This method does not involve the use of chemicals that are not environmentally friendly. The method can flexibly design and control porosity level and pore size.

Another object of the present invention is to provide a process for producing a graphene-carbon hybrid foam exhibiting thermal conductivity, electrical conductivity, elastic modulus, and / or strength equal to or greater than conventional graphite or carbon foam.

Yet another object of the present invention is to provide a process for preparing a graft-based hybrid foam comprising: (a) a pure graphene-based hybrid foam comprising essentially only carbon and preferably having a meso-scaled pore size range (2 to 50 nm); And (b) a non-pure graphene foam comprising 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, , Graphene chloride, graphene nitride, etc.).

It is yet another object of the present invention to provide a product (e.g., a device) comprising the graphene-carbon foam of the present invention and a method of operating such a product.

The present invention provides a method for making integral 3D graphene-carbon hybrid foams directly from graphite material particles and polymer particles. This method is incredibly simple. In this method,

(a) mixing multiple particles of graphite material and multiple particles of a solid polymeric carrier material to form a mixture in an impacting chamber of an energy impacting apparatus;

(b) the energy impacting device is operated for a long time at a frequency and intensity sufficient to strip the graphene sheet from the graphite material and the graphene sheet is transferred to the surface of the solid polymeric carrier material particles to form graphene- - fabricating the insert polymer particles in the impact chamber; (For example, when the impact device is operating, it supplies kinetic energy to the polymer particles, and eventually collides with the surface / edge of the graphite particles and peels off the graphene sheet from the impacted graphite particles. This is referred to herein as a "direct transfer" process, which means that the graphene sheet is transferred directly from the graphite particles to the surface of the polymer particles without intermediation of any third party.)

(c) recovering the graphene-coated or graphene-inserted polymer particles from the impact chamber and incorporating the graphene-coated or graphene-embedded polymer particles into a graphene-polymer hybrid structure of the desired shape, The step may be as simple as just compressing the graphene-coated or intercalated particles into the desired shape); And

(d) pyrolyzing this type of graphene-polymer composite structure and thermally converting the polymer into carbon or graphite binding pores and graphene sheets to form an integral 3D graphene-carbon hybrid foam.

In certain alternative embodiments, a plurality of impact balls or media are added to the impact chamber of the energy impact device. This impact ball, which is accelerated by the impact device, impacts the surface / edges of the graphite particles and peels off the graphene sheet therefrom. This graphen sheet is temporarily moved to the surface of the impact ball. This graphene-supported impact ball then impinges on the polymer particles and moves the supported graphene sheet to the surface of the polymer particles. This series of events is referred to herein as the "indirect movement" process. In some embodiments of the indirect transfer process, step (c) comprises operating the magnet to separate the impact ball or medium from the graphene-coated or graphene-inserted polymer particles.

The solid polymeric material particles may include plastic or rubber beads, pellets, spheres, wires, fibers, filaments, discs, ribbons, or rods having diameters or thicknesses between 10 nm and 10 mm. Preferably, the diameter or thickness is 100 nm to 1 mm, more preferably 200 nm or 200 占 퐉. The solid polymer can be selected from solid particles of thermoplastic, thermosetting resin, rubber, semi-penetrating reticulated polymer, penetrating reticulated polymer, natural polymer, or a combination thereof. In one 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 the group consisting of natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fibers, graphite nanofibers, graphite fluoride, graphite oxide, chemically modified graphite, Graphite, expanded graphite, meso carbon microbeads, or combinations thereof. Preferably, the graphite material comprises non-intercalated and non-oxidized graphite materials which have not been exposed to chemical or oxidative treatment prior to the mixing step (a).

The present study group surprisingly observed that a wide range of impact devices could be used for the practice of the present invention. For example, the energy impacting device may be a vibrating ball mill, a planetary ball mill, a high energy mill, a basket mill, an agitator ball mill, a cryo ball mill, a microball mill, a tumbler ball mill, A free ball mill, a vibrator, a bead mill, a nano-bead mill, an ultrasonic homogenizer, a centrifugal oil mixer, a vacuum ball mill, or a resonant acoustic mixer mixer).

For the formation of the carbon component of the resulting graphene-carbon hybrid foam, polymer particles having a high carbon yield or a char yield (e.g., greater than 30 weight percent) can be selected. The carbon yield is the weight percent of the polymer structure that is converted to a solid carbon phase by heat rather than being part of the volatile gas. The polymer having a high carbon yield may be at least one selected from the group consisting of phenol resin, polyfurfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole, Poly (p-phenylenevinylene), polybenzimidazole, polybenzobisimidazole, copolymers thereof, polymer blends thereof, or combinations thereof.

When a lower carbon content (higher graphene content) is required in the graphene-carbon hybrid foam, the polymer may be selected from the group consisting of polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS) (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethyl methacrylate (PMMA), copolymers thereof, and polymers thereof Blends, or combinations thereof. ≪ / RTI >

It can be noted that when such polymers (both high carbon yields and low carbon yields) are heated at temperatures of 300-2,500 ° C, they are converted to carbon materials that preferentially nucleate near the edges of the graphene sheet. These carbon materials serve to bridge the gaps between the graphene sheets to form interconnected electronically conductive paths. That is, the resulting graphene-carbon hybrid foams consist of an integral 3D network of carbon-bonded graphene sheets, allowing continuous transfer of electrons and phonons (quantized lattice vibration) between graphene sheets or domains without interruption . Upon further heating at temperatures higher than 2,500 ° C, the carbon phase joining graphene can be graphitized if the carbon phase is "soft carbon" or graphitizable. In this situation, both the electronic conductivity and the thermal conductivity are further increased.

Thus, in certain embodiments, the pyrolysis step comprises carbonizing the polymer at a temperature of from 200 ° C to 2500 ° C to obtain a carbon-bonded graft sheet. Optionally, the carbon-bonded graphene sheet can then be graphitized at a temperature of from 2,500 ° C to 3,200 ° C to obtain a graphite-bound graphene sheet.

It is noted that the thermal decomposition of the polymer due to the generation of volatile gas molecules such as CO ₂ and H ₂ O tends to form pores in the resulting polymeric carbon phase. However, such pores tend to collapse unless the polymer is constrained when carbonized. The study group surprisingly found that a graphene sheet wrapping around polymer particles can prevent the pore wall from shrinking and collapsing while some carbon species also penetrate into the gaps between the graphene sheets to bond the graphene sheets together did. The pore size and pore volume (porosity level) of the resulting 3D monolithic graphene foam depends on the starting polymer size and the carbon yield of the polymer and, to a lesser extent, on the pyrolysis temperature.

In certain preferred embodiments, the step of incorporating comprises compressing this large amount of graphene-coated polymer particles into the desired shape. For example, a large amount of graphene-coated particles can be put into a mold cavity and compressed and compressed to easily form a hard molded body. The polymer is rapidly heated and melted, the molded body is slightly compressed, the polymer particles are slightly fused with each other by heat, and the formed body can be solidified by rapid cooling. The integrated compact is then subjected to pyrolysis treatment (polymer carbonization and, optionally, graphitization).

In some alternative embodiments, the step of integrating comprises melting the polymer particles to form a polymer melt mixture with the graphene sheet dispersed therein, shaping the polymer melt mixture into the desired shape, and solidifying the shape into a graphene-polymer composite structure . Such forms may be rods, films (thin or thick film, wide or narrow, in the form of a single sheet or roll), fibers (short filaments or continuous long filaments), plates, ingots, any ordinary or strange shape. This graphene-polymer composite form is then pyrolyzed.

Alternatively, the step of incorporating may include dissolving the polymer particles in a solvent to form a mixture of the polymer solution and the graphene sheet dispersed therein, shaping the polymer solution mixture into the desired shape, removing the solvent, ≪ / RTI > complex structure. This composite structure is then pyrolyzed to form a porous structure.

The step of incorporation comprises melting the polymer particles to form a polymer melt mixture with the graphene sheet dispersed therein, extruding the mixture into a rod or sheet form, spinning the mixture into a fiber form or spinning the mixture into a powder form Spraying, or casting the mixture into ingot form.

In some embodiments, the step of incorporating comprises dissolving the polymer particles in a solvent to form a mixture of the polymer solution and the graphene sheet dispersed therein, extruding the solution mixture into a rod form or a sheet form, Spinning, spraying the solution mixture in powder form, casting the solution mixture into an ingot form and removing the solvent.

In certain embodiments, the polymer solution mixture is sprayed to produce a graphene-polymer composite coating or film followed by pyrolysis (carbonization or carbonization and graphitization).

Preferably, the step of consolidating comprises compressing the graphene-coated polymer particles into a porous formed body having macropores and then compressing the graphene-coated polymer particles into a mixture of a petroleum pitch, a coal tar pitch, an aromatic organic material (e.g. naphthalene or other pitch derivative), a monomer, Or a combination thereof, into the pores. The organic polymer may be selected from the group consisting of phenolic resin, polyfurfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole, A high carbon yield polymer selected from azoles, poly (p-phenylenevinylene), polybenzimidazoles, polybenzobisimidazoles, copolymers thereof, polymer blends thereof, or combinations thereof . When the molded body of the impregnated graphene-coated polymer particle is pyrolyzed, when the amount of carbon in the hybrid foam is required, the species becomes an additional carbon source.

The present invention also provides an integral 3D graphene-carbon hybrid foam comprising multiple pores and pore walls, wherein the pore walls are chemically modified by a carbon material having a weight ratio of carbon material to graphene of 1/200 to 1/2 Wherein the hydrophobic graphene sheet has from 2 to 10 layers of superimposed graphene faces having an interplanar spacing d _{002 as} measured by X-ray diffraction of from 0.3354 nm to 0.36 nm, Layer or hydrophobic graphene sheet comprises a pure graphene material that is essentially 0% non-carbon element or a non-pure graphene material having 0.001 wt% to 35 wt% (preferably 0.01% to 25%) non-carbon elements Wherein the non-pure graphene is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrided graphene, chemically functionalized Graphene, or a combination thereof. A plurality of monolayer or hydrophobic graphenes containing polymer particles in the lower layer may overlap to form a graphene sheet stack. Such a stack may be more than 5 nm in thickness and, in some cases, more than 10 nm, or even more than 100 nm.

The integral 3D graphene-carbon hybrid foam typically has a density of 0.001 to 1.7 g / cm 3 and a specific surface area of 50 to 3,000 m 2 / g. In a preferred embodiment, the pore walls comprise superimposed graphene planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm as measured by X-ray diffraction.

(For example, separating oil from water), the graphene-carbon is preferably present in an amount of from 1% to 25% by weight (more preferably from 1 to 15% and most preferably from 1 to 10% %). ≪ / RTI > This can be achieved when the starting material is oxidized graphite or when the carbonization treatment is carried out in a weak oxidizing environment at a temperature of 300 to 1,500 ° C (preferably not more than 1,000 ° C) and thereafter no graphitization is carried out. The present study group surprisingly found that highly porous, graphene-carbon foams of this nature can absorb up to 500% of their weight of oil from the oil-water mixture.

For thermal management applications, graphene-carbon hybrid foams are preferably produced by graphitizing carbon bond graft sheets (after carbonization) under compressive stress. This facilitates the orientation and reorganization (merging, growth, etc.) of graphene sheets or graphene domains. As a result, the graphene-carbon foam sheet or film exhibits a thermal conductivity of at least 200 W / mK per unit specific gravity, and / or an electrical conductivity of 2,000 S / cm or more per unit gravity.

In one embodiment, the pore wall comprises pure graphene and the 3D solid graphene-carbon foam has a density of 0.001 to 1.7 g / cm3 or an average pore size of 2 nm to 50 nm. In one embodiment, the pore wall is formed of a material selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, Pin, and combinations thereof, wherein the solid graphene foam comprises a non-carbon element content in the range of 0.01 wt% to 20 wt%. That is, the non-carbon element may include an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron. In certain embodiments, the pore wall comprises graphene fluoride and the solid graphene foam comprises a fluorine content of from 0.01% to 20% by weight. In another embodiment, the pore wall comprises graphene oxide, and the solid graphene foam comprises an oxygen content of from 0.01% to 20% by weight. In one embodiment, the solid graphene-carbon hybrid foam has a specific surface area of 200 to 2,000 m < 2 > / g or a density of 0.01 to 1.5 g / cm < 3 >.

It is noted that the shape and dimensions of the graphene-carbon hybrid foam of the present invention are not limited. In a preferred embodiment, the solid graphene-carbon hybrid foam has a thickness of 100 nm or more and 10 cm or less and a length of at least 1 meter, preferably at least 2 meters, more preferably at least 10 meters, and most preferably 100 meters (Roll of continuous foam sheet). This sheet roll is produced by a roll-to-roll process. There have been no prior arts on graphene-based foams made in sheet roll form. It has not been found or suggested previously that a roll-to-roll process can produce a continuous or grained continuous length of graphene foam.

For thermal management or electrical conductivity-based applications, the graphene-carbon foam preferably has an oxygen content or a non-carbon content of less than 1 wt% and the pore wall has an intergranular spacing of less than 0.35 nm, at least 250 W / mK, and / or an electrical conductivity of at least 2,500 S / cm per unit specific gravity.

In a further preferred embodiment, the graphene-carbon hybrid foam has an oxygen content or a non-carbon content of less than 0.01% by weight, the pore wall has an intergranular spacing of less than 0.34 nm, a thermal conductivity of at least 300 W / And / or an overlapped graphene surface having an electrical conductivity of 3,000 S / cm or more per unit gravity.

In another preferred embodiment, the graphene-carbon hybrid foam has an oxygen content or a non-carbon content of 0.01% by weight or less, the pore wall has a graphene spacing of less than 0.336 nm, a mosaic spread value of less than 0.7, , Thermal conductivity of at least 350 W / mK per unit specific gravity, and / or overlapping graphene face having electrical conductivity of at least 3,500 S / cm per unit gravity.

In another preferred embodiment, the graphene foam has a graphene spacing of less than 0.336 nm, a mosaic dispersion value of less than 0.4, a thermal conductivity of greater than 400 W / mK per unit gravity, and / or a thermal conductivity of greater than 4,000 S / And has a pore wall containing superimposed graphene surfaces having electrical conductivity.

In a preferred embodiment, the pore walls comprise overlapping graphene surfaces with a graphene spacing of less than 0.337 nm and a mosaic dispersion value of less than 1.0. In a preferred embodiment, the graphene foam exhibits a degree of graphitization of 80% or more (preferably 90% or more) and / or a mosaic dispersion value of less than 0.4. In a preferred embodiment, the pore wall comprises a 3D network of interconnected graphene planes.

In a preferred embodiment, the solid graphene-carbon hybrid foam comprises medium-sized pores having a pore size between 2 nm and 50 nm. The solid graphene foam may be made to include micron-sized pores (1 to 500 mu m).

The present invention also provides an oil-removing or oil-separating apparatus, which comprises the 3D graphene-carbon hybrid foam of the present invention as an oil-absorbing element. In addition, there is provided a solvent-removing or solvent-separating apparatus comprising this 3D graphene-carbon hybrid foam as a solvent-absorbing element.

The present invention also provides a method of separating oil from an oil-water mixture (e.g., wastewater from oil spilled water or an oil sand). The method comprises the steps of: (a) providing an oil-absorbing element comprising an integral graphene-carbon hybrid foam; (b) contacting the oil-water mixture with the element to absorb oil from the mixture; (c) withdrawing said element from the mixture and extracting oil from said element. Preferably, the method further comprises the step of (d) reusing said element.

Additionally, the present invention provides a process for separating an organic solvent from a solvent-water mixture or a multiple-solvent mixture. The method comprises the steps of: (a) providing an organic solvent-absorbing element comprising an integral graphene-carbon hybrid foam; (b) contacting the element with an organic solvent-water mixture or 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 at least absorb the first solvent from the second solvent; And (d) withdrawing said element from the mixture and extracting an organic solvent or a first solvent from said element. Preferably, the method further comprises the step of (e) reusing said element.

Figure 1 is a flow chart illustrating the prior art of the most commonly used method of making highly oxidized NGPs involving severe chemical oxidation / insertion, cleaning, and hot stripping processes.
Figure 2a is a flow chart illustrating a method of making an integral 3D graphene-carbon hybrid foam of the present invention.
Figure 2b is a schematic diagram showing the polymer thermally-induced conversion of carbon into graphene sheets bonded together to form a 3D graphene-carbon hybrid foam. The compressed structure of graphene-coated polymer particles is converted to a highly porous structure.
Figure 3a is an SEM image of the internal structure of a 3D graphene-carbon hybrid foam.
Figure 3b is a SEM image of the internal structure of another 3D graphene-carbon hybrid foam.
FIG. 4A is a plot of the thermal conductivity values versus specific gravity of 3D integrated graphene-carbon foam, mesophase pitch induced graphite foam, and Ni foamed cell template assisted CVD graphene foam prepared by the method of the present invention.
Figure 4b is a plot of the thermal conductivity values of 3D graphene-carbon foam and hot reduced, GO graphene foam.
Figure 5 is a plot of the thermal conductivity values of 3D graphene-carbon hybrid foams and pure graphene foams (prepared by heat treatment after casting with blowing agent) as a function of final (maximum) heat treatment temperature.
Figure 6 is a plot showing the electrical conductivity values of 3D graphene-carbon foam and hot reduced, GO graphene foam.
Figure 7 shows the amount of oil absorbed per gram of the integral 3D graphene-carbon hybrid foam as a function of oxygen content in the foam with a porosity level of about 98% (separation of oil from the oil-water mixture).
Figure 8 shows the amount of oil absorbed per gram of integral 3D graphene-carbon hybrid foam as a function of porosity level (oxygen content is the same).
Figure 9 shows the amount of chloroform absorbed in the chloroform-water mixture as a function of fluorination.
10 is a schematic view of a heat sink structure (two examples).

The present invention provides a method for making integral 3D graphene-carbon hybrid foams directly from graphite material particles and polymer particles.

As shown schematically in Figure 2A, the method begins by mixing multiparticulates of graphite material and multiparticulates of solid polymeric carrier material to form a mixture and the mixture is introduced into an energy impacting device (e. G., A vibrating ball mill, Ball mill, high energy mill, basket mill, stirrer ball mill, cryogenic ball mill, micro ball mill, tumbler ball mill, continuous ball mill, agitated ball mill, pressurized ball mill, freezing mill, vibrator, Bead mill, ultrasonic homogenizer, centrifugal oil agitator, vacuum ball mill, or resonant acoustic mixer). When in operation, the energy impacting device imparts kinetic energy to the solid particles contained therein, causing polymer particles to collide with graphite particles at high intensity and high frequency.

Under normal operating conditions, this impact will strip the graphene sheet from the graphite material to move the graphene sheet to the surface of the solid polymeric carrier material. These graphene sheets wrap around the polymer particles to form graphene-coated or graphene-inserted polymer particles in the impact chamber. This is referred to herein as the "direct transfer" process, which means that the graphene sheet migrates directly from the graphite particles to the surface of the polymer particles without intermediation of any third party.

Alternatively, a plurality of impact balls or media may be added to the impact chamber of the energy impact device. Accelerated by the impact device, this impact ball has a high kinetic energy and collides with the surface / edge of the graphite particle at a good angle to peel off the graphene sheet from the graphite particle. This graphen sheet is temporarily moved to the surface of the impact ball. This graphen-supported impact ball then impinges on the polymer particles and moves the supported graphene sheet to the surface of the polymer particles. This series of events is referred to herein as the "indirect movement" process. Since this event occurs at a very high frequency, most polymer particles are usually covered by graphene sheets in less than one hour. In some embodiments of the indirect transfer process, step (c) comprises operating the magnet to separate the impact ball or medium from the graphene-coated or graphene-inserted polymer particles.

The method then involves recovering the graphene-coated or graphene-inserted polymer particles from the impact chamber and incorporating the graphene-coated or graphene-impregnated polymer particles into the desired form of graphene-polymer composite structure. This integration step may be as simple as compressing the graphene-coated or intercalated particles into a desired shape only mechanically. Alternatively, this integration step may involve melting the polymer particles to form a polymer matrix with the graphene sheet dispersed therein. This graphene-polymer structure may be of any practical form or dimension (fibers, rods, plates, cylinders, or any ordinary or strange shape).

The graphene-polymer compact or composite structure is then thermally cracked to thermally convert the polymer to carbon or graphite binding graphene sheets to form an integral 3D graphene-carbon hybrid foam, as shown in Figures 3a and 3b .

(E.g., greater than 30% by weight of the polymer converted to the solid carbon phase, instead of being part of the volatile gas) for the formation of the carbon component of the resulting graphene-carbon hybrid foam. Can be selected. The polymer having a high carbon yield may be at least one selected from the group consisting of phenol resin, polyfurfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole, Poly (p-phenylenevinylene), polybenzimidazole, polybenzobisimidazole, copolymers thereof, polymer blends thereof, or combinations thereof. When pyrolyzed, the particles of these polymers become porous, as shown at the bottom of Figure 2b.

When a lower carbon content (higher graphene ratio relative to the carbon ratio) and lower foam density are required in the graphene-carbon hybrid foam, the polymer may be a polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, Polyvinyl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethylmethacrylate (PMMA), polyacrylonitrile- , Copolymers thereof, polymer blends thereof, or combinations thereof. When pyrolyzed, the particles of these polymers become porous, as shown in the middle of Figure 2b.

When these polymers (both high carbon yields and low carbon yields) are heated at temperatures of 300-2,500 ° C, they are converted to carbon materials that preferentially nucleate near the edges of the graphene sheet. These carbon materials naturally bridge the gaps between the graphene sheets to form interconnected electronically conductive paths. In practice, the resulting graphene-carbon hybrid foam consists of an integral 3D network of carbon-bonded graphene sheets, allowing continuous transfer of electrons and phonons (quantized lattice vibration) between graphene sheets or domains without interruption . When further heated at a temperature higher than 2,500 ° C, the carbon phase can be graphitized to further improve both electrical and thermal conductivity. When the graphitization time exceeds 1 hour, the amount of the non-carbon element is usually reduced to less than 1% by weight.

It can be noted that the organic polymer typically contains a significant amount of non-carbon elements that can be reduced or eliminated through heat treatment. As such, pyrolysis of the polymer will form and release volatile gas molecules such as CO ₂ and H ₂ O and form pores on the resulting polymeric carbon. However, such pores tend to collapse if the polymer is not constrained when carbonized (the carbon structure can shrink as the non-carbon element is released). The research group surprisingly found that a graphene sheet wrapping around polymer particles could prevent the pore wall from collapsing. On the other hand, some carbon species also penetrate into the gaps between the graphene sheets to bond the graphene sheets together. The pore size and pore volume (porosity level) of the resulting 3D monolithic graphene foams largely depends on the starting polymer size and the carbon yield of the polymer.

As a raw material of a graphene sheet, graphite materials are natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphite nanofiber, graphite fluoride, graphite oxide, chemically modified graphite, peeled graphite, Graphite, meso carbon microbeads, or combinations thereof. In this regard, there are several additional surprising factors associated with the method of the present invention:

(1) Graphene sheets can be stripped from natural graphite using only polymer particles, without using heavier and harder impact balls (such as zirconium dioxide or steel balls commonly used in ball mills). The peeled graphene sheet is transferred directly to the polymer particle surface to tightly wrap around the polymer particles.

(2) It is also surprising that impact polymer particles can peel off graphene sheets from artificial graphite such as meso carbon microbeads (MCMB), which are known to have an outer layer of amorphous carbon.

(3) With the help of a stiffer impingement ball, the graphene-like surface of the carbon particles constituting the internal structure of the carbon or graphite fibers can also be peeled and moved to the polymer particle surface. 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 method, while fundamentally avoiding all deficiencies associated with conventional processes for producing graphene sheets. The graphene sheets are readily transferred to the polymer particles and wrapped around the polymer particles, after which they are readily converted into integral 3D graphene-carbon hybrid foams.

It can be noted that when the starting graphite is intentionally oxidized to some extent (for example, to contain 2 to 15% by weight of oxygen), a desired desirable degree of hydrophilicity may be imparted to the pore walls of the graphene-carbon hybrid foam have. Alternatively, if the carbonization treatment is allowed to take place in a weak oxidizing environment, the oxygen containing functionalities may be attached onto the carbon. This feature can separate oil from water by selectively absorbing oil from the oil-water mixture. That is, these graphene-carbon hybrid foam materials can recover oil from water, which can help to purify oil, runoff lakes, or oceans. The oil absorption capacity is typically 50% to 500% of the foam weight. This is a very useful material for environmental protection purposes.

If high electrical conductivity or thermal conductivity is desired, the graphite material may be selected from non-intercalated and non-oxidized graphite materials that have not been exposed to chemical or oxidative treatment prior to being placed in the impact chamber. Alternatively or additionally, the graphene-carbon foam may undergo a graphitization treatment at temperatures higher than 2,500 ° C. The resulting material is particularly useful for thermal management applications (e.g., for the manufacture of finned heat sinks, heat exchangers, or heat spreaders).

It can be noted that the graphene-carbon foam can be compressed during and / or after the graphitization treatment. This process makes it possible to adjust the orientation and porosity of the graphene sheet.

The X-ray diffraction pattern was obtained by an X-ray diffractometer equipped with CuKcv radiation. The shift and broadening of diffraction peaks were calibrated using a silicon powder standard. The graphitization degree g was calculated from the X-ray pattern using the Mering equation (Mering's Eq), d ₀₀₂ = 0.3354 g + 0.344 (1-g), where d ₀₀₂ is the interlayer spacing (in nanometers) of graphite or graphene crystals . This equation is valid only when d ₀₀₂ is approximately 0.3440 nm or less. A graphene foam wall with d ₀₀₂ greater than 0.3440 nm may be coated with an oxygen-containing or fluorine-containing functional group (e.g., a graphene particle surface or an edge -F, OH, > O, and -COOH).

Another structural index that can be used to characterize the degree of alignment of the graphene plane superimposed and bonded at the foam wall of graphene and of conventional graphite crystals is the "mosaic spread" Is expressed by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the (004) reflection. This alignment chart characterizes graphite or graphene crystal size (or grain size), grain size and other defects, and preferential crystal orientation. Almost complete single crystal of graphite is characterized by having a mosaic dispersion value of 0.2 to 0.4. Most of the graphene wall of the present invention has such a mosaic dispersion value in the range of 0.2 to 0.4 (when manufactured by setting the heat treatment temperature (HTT) at 2,500 DEG C or higher). However, some values range from 0.4 to 0.7 when HTT is from 1,500 to 2,500 ° C and from 0.7 to 1.0 when HTT is from 300 to 1,500 ° C.

Careful studies using a combination of SEM, TEM, limited field diffraction, X-ray diffraction, AFM, Raman spectroscopy and FTIR have shown that the graphene foam wall has some gigantic graphene surfaces (length / width typically &≫ 100 nm, often > 1 mu m, and in many cases > 10 mu m, or even > 100 mu m). Such a large graphene plane is superimposed and bonded along the thickness direction (c-crystal axis direction) when the final heat treatment temperature is less than 2,500 ° C, which is often combined with not only van der Waals force (as in conventional graphite microcrystals) . In this case, while not wishing to be bound by theory, Raman and FTIR spectroscopy studies show that not only sp ² in conventional graphite but sp ² (dominant) and sp ³ (weakly present) electron configurations coexist.

The integral 3D graphene-carbon hybrid foam is comprised of multiple pores and pore walls, and the pore walls comprise a single layer or a hydrophobic layer chemically bonded by a carbon material having a carbon material-to-graphene weight ratio of 1/100 to 1/2. And the minority layer graphene sheet has 2 to 10 layers of superimposed graphene planes having an interplanar spacing d ₀₀₂ measured by X-ray diffraction of 0.3354 nm to 0.36 nm, and the single layer or the minority layer graphene sheet Pure graphene material that is essentially 0% non-carbon, or a non-pure graphene material that has from 0.01% to 25% (more typically less than 15%) non-carbon elements, Is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrided graphene, chemically functionalized graphene, It is selected from. A plurality of monolayer or hydrophobic graphenes containing polymer particles in the lower layer may overlap to form a graphene sheet stack. Such a stack may be more than 5 nm in thickness and, in some cases, more than 10 nm, or even more than 100 nm.

The integral 3D graphene-carbon hybrid foams typically have a density of 0.001 to 1.7 g / cm3, a specific surface area of 50 to 3,000 m2 / g, a thermal conductivity of at least 200 W / mK per unit weight, and / / Cm. ≪ / RTI > In a preferred embodiment, the pore walls comprise superimposed graphene planes with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm as measured by X-ray diffraction.

A plurality of graphen sheets can be merged into one integrated graphene body through covalent bonding of the edges to each other. A gap between the free ends of the non-merged sheet or the shorter merged sheet is bonded by the carbon phase converted from the polymer. It is believed that these unique chemical compositions (including oxygen or fluorine content), morphology, crystal structure (including spacing between graphenes), and structural features (e.g., alignment, fewer defects, chemical bonds, Gravel-free, and substantially free from disconnection along the grain plane direction), the graphene-carbon hybrid foams have a unique combination of excellent thermal conductivity, electrical conductivity, mechanical strength and stiffness (modulus of elasticity).

Heat Management Purpose

The aforementioned features and characteristics make the integral 3D graphene-carbon hybrid foam ideal for a wide range of engineering and biomedical applications. For example, for thermal management purposes only, graphene-carbon foams can be used for:

a) The graphene-carbon hybrid foam with compressibility and high thermal conductivity is ideally suited for use as a thermal interface material (TIM) that can be implemented between a heat source and a heat spreader or between a heat source and a heat sink. Do.

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

c) Hybrid foams can be used as heat sinks or heat sinks due to their high thermal diffusivity (high thermal conductivity) and their high heat dissipation capability (a large number of surface pores inducing huge air convection micro- or nano channels).

d) high thermal conductivity per unit specific gravity or per unit physical density, and high structural integrity (graphene sheet bonded by carbon), lightweight (low density, adjustable from 0.001 to 1.8 g / cm3), makes this hybrid foam durable Making it the ideal material for a heat exchanger.

Graphene-carbon hybrid foam-based thermal management devices or heat dissipation devices include heat exchangers, heat sinks (eg, pin heat sinks), heatpipes, high conductivity inserts, thin or thick (between the heat sink and the heat source) A conductive plate, a heat transfer medium (or heat transfer material, TIM), or a thermoelectric cooling plate or a Peltier cooling plate.

Heat exchangers are devices that are used to transfer heat between one or more fluids (e.g., gases and liquids that flow individually into different channels). The fluid is typically separated by a solid wall that prevents mixing. The graphene-carbon hybrid foam material of the present invention is an ideal material for such a wall unless the foam is a fully open cell foam capable of mixing fluids. The method of the present invention can produce both open cell and closed cell foam structures. Due to the large surface area, heat exchange can be dramatically faster between two fluids or between multiple fluids.

Heat exchangers are widely used in refrigeration systems, air conditioning units, heaters, power plants, chemical plants, petrochemical plants, refineries, natural gas processing, and sewage treatment. A well-known example of a heat exchanger is found in an internal combustion engine where circulating engine coolant flows through the radiator coil while air flows through the coil to cool the coolant and heat the incoming air. Solid walls (e.g., constituting radiator coils) are usually made of a high thermal conductivity material such as Cu and Al. The graphene foams of the present invention with higher thermal conductivity or higher specific surface area are excellent substitutes for example Cu and Al.

There are many types of commercially available heat exchangers: shell and tube heat exchangers, plate heat exchangers, plate and shell heat exchangers, adiabatic wheel heat exchangers A plate heat exchanger, a pillow plate heat exchanger, a fluid heat exchanger, a waste heat recovery unit, a dynamic scraped surface heat exchanger, a phase change heat exchanger, Direct contact heat exchangers, and microchannel heat exchangers. All of these types of heat exchangers can utilize a very large thermal conductivity and specific surface area of the foam material of the present invention.

The solid graphene foams of the present invention may also be used in heat sinks. Heat sinks are widely used in electronic devices for heat dissipation purposes. In portable small electronic devices (eg, notebook computers, tablets and smart phones), the central processing unit (CPU) and battery are well known heat sources. Typically, a metal or graphite object (such as a Cu foil or graphite foil) is brought into contact with a hot surface which diffuses heat to the exterior surface or to the outside air (mainly by conduction and convection and to a lesser extent by radiation) . In most cases, a thin heat transfer material (TIM) transfers heat between the hot surface of a heat source and the heat spreader or the heat spreading surface of the heat sink.

The heat sink is usually constructed of a highly conductive material structure having one or more flat surfaces to ensure good thermal contact with the part to be cooled, and a comb or pin shaped protrusion to increase surface contact with air to increase the heat dissipation rate . The heat sink can be used with a fan to increase the air flow rate on the heat sink. The heat sink may have multiple fins (extended or protruded surfaces) to enhance heat transfer. In electronic devices with limited space, the pin shape / arrangement must be optimized to maximize the heat transfer density. Alternatively or additionally, a cavity (inverting pin) may be inserted in an area formed between adjacent fins. These cavities are effective for extracting heat from various heating elements to a heat sink.

Typically, the integral heat sink includes at least one heat dissipating member (e.g., a single pin or multiple pins) embedded in a heat collecting member (core or base) and a heat collecting member (base) . The pin and core are naturally connected or integrated together to form an integrated body, without external glue or mechanical fastening to connect the pin to the core. The heat collection base has a surface in thermal contact with a heat source (e.g., an LED), collecting heat from the heat source and dissipating heat into the air through the fin.

As an illustrative example, FIG. 10 provides a schematic view of two heat sinks 300 and 302 . The first heat sink includes a heat collecting member (or base member) 304 and a plurality of fins or heat dissipating members (e.g., pins 306 ) coupled to the base member 304 . The base member 304 is shown having a heat collecting surface 314 for thermal contact with a heat source. The heat dissipating member or fin 306 is shown having at least a heat dissipating surface 320 .

Particularly useful embodiments include (a) a base 308 comprising a heat collecting surface 318 ; And (b) the radial pin-shaped heat sink assembly including a base 308 and a one-piece or base 308, a plurality of spaced-apart parallel planes pin member supported by the (for example, as two examples 310 and 312) ( E.g. , 310 ) includes at least one heat dissipating surface 322. In one embodiment, Preferably, a plurality of parallel planar pin members are spaced at equal intervals.

The highly elastic and resilient graphene-carbon hybrid foams of the present invention are good heat transfer materials in themselves and also highly efficient heat diffusion elements. The high-conductivity foam can also be used as an insert for improving the heat removal from an electronic cooling insert and a small chip to a heat sink. Since the space occupied by the highly conductive material is an important part, it is a more efficient design to use a highly conductive pathway that can be inserted into the heating element. The elastic, highly conductive, solid graphene foams disclosed herein fully satisfy this need.

Because of its high elasticity and high thermal conductivity, the solid graphene-carbon hybrid foams of the present invention are a thick conductive sheet that is placed as a heat transfer interface between a heat source and a cooling flow fluid (or other heat sink), thereby improving cooling performance . In this arrangement, the heat source is cooled under thick graphene foam plates instead of being cooled in direct contact with the cooling fluid. The thick plates of the graphene foam can significantly improve the heat transfer between the heat source and the cooling fluid by delivering the heat flow in an optimal manner. No additional pumping power and no additional heat transfer surface area is required.

In addition, solid graphene foams are an excellent material for constructing heatpipes. A heat pipe is a heat transfer device that transfers a large amount of heat to a very small temperature difference between a hot interface and a cold interface by utilizing evaporation and condensation of fluid or cooling water operating in two phases. Conventional heat pipes consist of a sealed hollow tube made of a thermally conductive material such as Cu or Al, and a wick that returns the working fluid from the evaporator to the condenser. The pipe contains both the vapor and the saturated liquid of the working fluid (such as water, methanol, or ammonia) and blocks all other gases. However, both Cu and Al tend to be oxidized or corroded, so performance deteriorates relatively quickly over time. On the other hand, solid graphene foams are chemically inert and have no such problems of oxidation or corrosion. A heat pipe for electronic thermal management can have a shell and a wick of solid graphene foam together with water as a working fluid. Graphene / methanol can be used if the heat pipe needs to operate below the freezing point of water, and graphene / ammonia heat pipes can be used for electronic device cooling in space.

The Peltier cooling plate acts as a Peltier effect, which creates a heat flux between the junctions of two different electrical conductors by applying current. This effect is usually used to cool electronic components and small appliances. In practice, many such joints can be arranged in series to improve this effect up to the required amount of heat or cooling. This solid graphene foam can be used to improve heat transfer efficiency.

Filtration and fluid absorption applications

Solid graphene foams may be prepared to include micropores (less than 2 nm) or medium size pores having a pore size between 2 nm and 5 nm. Solid graphene-carbon hybrid foams may also be prepared to include micron-sized pores (1 to 500 mu m). Even with a well controlled pore size, the graphene-carbon foam of the present invention can be a very good filter material for air or water filtration.

In addition, the chemical nature of the graphene wall and the chemical properties on the carbon (e.g., as reflected in% O, F, N, H, etc. in the foam) May be independently controlled to impart different amounts of functional groups and / or different types of functional groups to the substrate. That is, it is possible to control both pore size and chemical functional groups simultaneously or individually at different locations of the internal structure, to obtain some unique combinations of properties that are often considered unexpected, synergistic, and usually mutually exclusive (e.g., And the other part is hydrophilic or the foam structure has both hydrophobic and lipophilic properties), it provides the highest degree of freedom or unprecedented flexibility in designing and manufacturing graphene-carbon hybrid foams. If water does not migrate to any material or surface, such surface or material is referred to as hydrophobic and water droplets placed on hydrophobic surfaces or materials will form a large contact angle. Some surfaces or substances are lipophilic, which means they have a strong affinity for oil, not water. The method of the present invention enables precise control over hydrophobicity, hydrophilicity, and lipophilicity.

The present invention also provides an oil-removing, oil-separating, or oil-recovering device, which comprises the 3D graphene-carbon hybrid foam of the present invention as an oil-absorbing element or oil-separating element. There is also provided a solvent-removing or solvent-separating apparatus comprising a 3D graphene-carbon hybrid foam as a solvent-absorbing element.

The main advantage of using the graphene-carbon hybrid foams of the present invention as an oil-absorbing element lies in its structural integrity. Due to the concept that the graphene sheet is chemically bonded by the carbon material, the resulting foam is not decomposed during repeated oil absorption operations. On the other hand, the group found that the graphene-based oil-absorbing element produced by hydrothermal reduction, vacuum-assisted filtration, or freeze-drying decomposes after two or three oil uptakes. Bonding these otherwise separated graphene sheets together (with the exception of the weak van der Waals forces that existed before the initial contact with oil) is nothing. Once this graphene sheet is oiled, it can no longer go back to its original form of oil-absorbing element.

Another major advantage of the present technology is that it can be used in the design and manufacture of oil-absorbing elements capable of absorbing oil up to 400 times its own weight while still retaining the structural form of the oil- It is flexible. The amount of oil absorption depends on the specific pore volume of the foam, which can be controlled primarily by the ratio between the amount of graphene sheet and the amount of original carrier polymer particles before heat treatment.

The present invention also provides a method for separating / recovering oil from an oil-water mixture (e.g., wastewater from oil spilled water or oil sand). The method comprises the steps of: (a) providing an oil-absorbing element comprising an integral graphene-carbon hybrid foam; (b) contacting the oil-water mixture with the element to absorb oil from the mixture; (c) withdrawing the oil-absorbing element from the mixture and extracting oil from the element. Preferably, the method further comprises the step of (d) reusing said element.

In addition, there is provided a process for separating an organic solvent from a solvent-water mixture or a multi-solvent mixture. The method comprises the steps of: (a) providing an organic solvent-absorbing element comprising an integral graphene-carbon hybrid foam; (b) contacting the element with an organic solvent-water mixture or 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 absorb at least the first solvent from the second solvent; And (d) withdrawing said element from the mixture and extracting an organic solvent or a first solvent from said element. Preferably, the method further comprises the step of (e) reusing the solvent-absorbing element.

The following examples are used to illustrate the best mode for carrying out the present invention and should not be construed as limiting the scope of the present invention.

Example 1 : Preparation of a graphene-carbon foam from flake graphite through a polypropylene powder-based solid polymer carrier

In the experiment, 1 kg of polypropylene (PP) pellets, 50 grams of flake graphite, 50 mesh (average particle size 0.18 mm; Asbury Carbons, Asbury NJ) and 250 grams of magnetic steel balls were placed in a high energy ball mill vessel. The ball mill was run at 300 rpm for 2 hours. The container lid was removed and the stainless steel ball was removed through a magnet. It was confirmed that the polymer carrier material was coated with a dark graphene layer. The carrier material was placed on a 50 mesh sieve and a small amount of untreated flake graphite was removed.

A sample of the coated carrier material was then immersed in tetrachlorethylene at 80 DEG C for 24 hours to dissolve the PP and allow the graphene sheet to disperse in the organic solvent. After removal of the solvent, the separate graphene sheet powder was recovered (mostly hydrophobic graphene). Thereafter, the remaining coated carrier material was compressed in a mold cavity to form a molded body. The molded body was heat-treated in a sealed crucible at 350 ° C and then heat-treated at 600 ° C for 2 hours to prepare a graphene-carbon foam .

In a separate experiment, the same batch of PP pellets and flake graphite particles (without impact steel balls) was placed in the same high energy ball mill vessel and the ball mill was run for the same time under the same conditions. The results were compared with those obtained from impact ball-assisted operation. In the case of PP dissolution, the graphene sheets independent of the PP particles 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 by way of example, the carrier material for the production of graphene-carbon hybrid foams is not limited to PP. Any polymers (thermoplastic resins, thermosetting resins, rubbers, waxes, mica resins, gums, organic resins, etc.) can be used as long as they can be produced in particulate form. It is noted that uncured or partially cured thermosetting resins (such as epoxide and imide oligomers or rubbers) may be prepared in particulate form at room temperature or below (e.g., cryogenic temperature). Therefore, partially cured thermoset resin particles can also be used as the polymer carrier.

Example 2 : A graphene-carbon hybrid foam with expanded graphite (thickness greater than 100 nm) as graphene feedstock and ABS as polymer solid carrier particles

In the experiment, 100 grams of ABS pellets as solid carrier material particles were loaded into a 16 ounce plastic container with 5 grams of expanded graphite. The container was placed in a Resodyn Acoustic mixer for 30 minutes. After the treatment, it was confirmed that the carrier material was coated with a thin carbon layer. A small sample of carrier material was placed in acetone and ultrasonic energy was applied to accelerate the dissolution of ABS. The solution was filtered through an appropriate filter and washed 4 more times with additional acetone. After washing, the filtrate was dried in a vacuum oven set at 60 DEG C for 2 hours. The sample was irradiated with an optical microscope to confirm that it was graphene. The remaining pellets were extruded to form a graphene-polymer sheet (1 mm thick) and carbonized to produce graphene-carbon foam samples under different temperature and compression conditions.

Example 3 : Preparation of graphene-carbon hybrid foams from meso carbon microbeads (MCMB, graphene raw material) and polyacrylonitrile (PAN) fibers (solid carrier particles)

In one embodiment, 100 grams of PAN fiber segments (2 mm in length as carrier particles), 5 grams of MCMB (China Steel Chemical Co., Taiwan) and 50 grams of zirconia beads were placed in a vibrating ball mill and treated for 2 hours Respectively. After the treatment was completed, the vibration mill was opened to confirm that the carrier material was coated with the dark coating of the graphene sheet. Zirconia particles with distinctly different sizes and colors were manually removed. The graphene-coated PAN fibers were then compressed and melted together to form various composite films. The film was heat treated at 250 占 폚 for 1 hour (in room air), 350 占 폚 for 2 hours, and 1,000 占 폚 for 2 hours (under argon gas atmosphere) to obtain a graphene-carbon foam layer. Next, half of the carbonized foam layer was heated to 2,850 占 폚 and held at this temperature for 0.5 hour.

Example 4 : Cured phenolic resin particles as a polymeric carrier material in a freeze mill

In one experiment, 10 grams of phenolic resin particles were placed in a SPEX mill sample holder (SPEX Sample Prep, Meter Chin, NJ) with 0.25 grams of HOPG powder derived from graphitized polyimide and a magnetic stainless steel impactor. Although the same experiment was carried out, no impact balls were contained in the sample holder. This process was performed in a "dry room " at 1% humidity to reduce the condensation of water on the finished product. The SPEX mill was run for 10 to 120 minutes. After operation, the contents of the sample holder were sorted and the HOPG powder residue and the impact ball (when used) were removed to recover the graphene-coated resin particles.

In both cases (with or without impact balls), the resulting graphene-coated resin particles were examined using both a digital optical microscope and a scanning electron microscope (SEM). The thickness of the graphene sheet wrapping around the resin particles increased with milling run time, and for the same given run time, impactor assisted movement was observed to make a thicker graphene coating.

A large amount of graphene-coated resin particles were compressed to form a compact, which was then impregnated with a small amount of petroleum pitch. Separately, although other shaped bodies of graphene-coated resin particles were produced under similar conditions, pitch penetration was not attempted. The two compacts were then subjected to the same pyrolysis treatment.

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

In the experiment, 0.5 kg of PE or nylon beads (as a solid carrier material), 50 grams of natural graphite (graphene sheet stock), and 250 grams of zirconia powder (impact balls) were placed in a planetary ball mill. The ball mill was operated at 300 rpm for 4 hours. The vessel lid was removed and zirconia beads (different size and weight from graphene-coated PE beads) were removed through a vibrating screen. It was confirmed that the polymer carrier material particles were coated with a dark graphene layer. The carrier material was placed on a 50 mesh sieve and a small amount of untreated flake graphite was removed. In a separate experiment, glass beads were used as impact balls; Other ball-milling operating conditions remained the same.

A large amount of graphene-coated PE pellets and a large amount of graphene-coated nylon beads were each pressed in a mold cavity, heated briefly above the melting point of PE or nylon, and quenched to form two shaped bodies. For comparison, two corresponding shaped bodies were prepared from a large amount of uncoated PE pellets and a large amount of uncoated nylon beads. Thereafter, these four formed bodies were pyrolyzed (by heating the molded body in a chamber from 100 캜 to 650 캜). The result was very surprising. It was confirmed that the molded body of graphene-coated polymer particles was converted into a graphene-carbon hybrid foam structure having dimensions similar to those of the original molded body (3 cm x 3 cm x 0.5 cm). As a result of SEM examination of this structure, it was found that the carbon phase was present near the edge of the graphene sheet, and this carbon phase serves to bond the graphene sheets to each other. As schematically depicted in FIG. 2A, the carbon-bonded graft sheet forms the framework of a graphene-carbon hybrid pore wall having pores present where it was the space occupied by the original polymer particles.

On the other hand, the two compacts obtained from uncoated pellets or beads contracted to essentially two solid lumps of carbon with a volume of approximately 15% to 20% of the original compact volume. This highly shrunk solid mass is a substantially pore-free carbon material; This is not a foam material.

Example 6 : Micron size rubber particles as solid polymer carrier particles

The experiment began with the production of micron sized rubber particles. A mixture of methylhydrodimethyl-siloxane polymer (20 g) and polydimethylsiloxane, vinyl dimethyl terminated polymer (30 g) was obtained using a homogenizer under atmospheric conditions for 1 minute. Tween 80 (4.6 g) was added and the mixture was homogenized for 20 seconds. A platinum-divinyltetramethyldisiloxane complex (0.5 g in 15 g methanol) was added and mixed for 10 seconds. This mixture was added to 350 g of distilled water and homogenized for 15 minutes to obtain a stable latex. The latex was heated to 60 占 폚 for 15 hours. The latex was then de-emulsified with anhydrous sodium sulfate (20 g), filtered under vacuum, washed with distilled water and dried under vacuum at 25 캜 to give silicone rubber particles. The particle size distribution of the produced rubber particles was 3 to 11 탆.

In one embodiment, 10 grams of rubber particles, 2 grams of natural graphite, and 5 grams of zirconia beads were placed in a vibrating ball mill and processed for 2 hours. After the treatment was completed, it was confirmed that the vibration mill was opened and the rubber particles were coated with the dark coating of the graphene sheet. The zirconia particles were removed manually. The graphene-coated rubber particles were then mixed with 5 wt% petroleum pitch (as binder) and mechanically compressed together to form various composite sheets. The composite sheet was then heat treated in a tubular furnace at 350 DEG C for 1 hour, 650 DEG C for 2 hours, and 1,000 DEG C for 1 hour to obtain a graphene-carbon foam layer.

Example 7 Preparation of Graphene Fluoride Foam

In a conventional method, a graphene-carbon hybrid sheet was fluorinated with steam of chlorine trifluoride in a sealed autoclave reactor to obtain a fluorinated graphene-carbon hybrid film. The duration of fluoridation was varied to achieve various degrees of fluoridation. The sheets of fluorinated graphene-carbon foam were then individually immersed in each vessel containing the chloroform-water mixture. This foam sheet selectively absorbed chloroform from water and observed that the amount of chloroform absorbed increased with fluorination until the fluorine content reached 7.3 wt% (FIG. 9).

Example 8 : Preparation of graphene oxide foams and nitrided graphene foams

Several graphene-carbon foams prepared in Example 3 were immersed in a 30% H ₂ O ₂ -water solution for 2 to 48 hours to obtain a graft oxide (GO) foam having an oxygen content of 2 to 25 wt% .

Some GO foam samples were mixed with different proportions of urea and the mixture was heated in a microwave reactor (900 W) for 0.5 to 5 minutes. The product was washed several times with deionized water and vacuum dried. The obtained product was a graphene nitride foam. The nitrogen content measured by elemental analysis was 3% to 17.5% by weight.

It can be noted that the different functionalization treatments of the graphene-carbon hybrid foams are for different purposes. For example, the oxidized graphene-carbon hybrid foam structure is particularly effective as an oil-absorbing agent from an oil-water mixture (i.e., pouring oil into water and mixing together). In this case, the integral 3D graphene (oxygen 0-15 wt%) -carbon foam structure has both hydrophobicity and oleophilicity (FIGS. 7 and 8). If water does not migrate to any material or surface, such surface or material is referred to as hydrophobic and water droplets placed on hydrophobic surfaces or materials will form a large contact angle. Some surfaces or substances are lipophilic, which means they have a strong affinity for oil, not water.

The different contents of O, F, and / or N also allow the graphene-carbon hybrid foams of the present invention to absorb various organic solvents in water or to separate one organic solvent from a mixture of multiple solvents .

Comparative Example 1 : Carbonization of graphene and graphene-polymer composites via Hummer's process

According to the method of Hummers, graphite flakes were oxidized with sulfuric acid, nitrate and permanganate to produce graphite oxides (U.S. Patent No. 2,798,878, July 9, 1957). As soon as the reaction was complete, the mixture was poured into deionized water and filtered. The graphite oxide was washed repeatedly in a 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 DEG C for 24 hours. The interlayer spacing of the resultant layered graphite oxide was measured at about 0.73 nm (7.3 A) by the Debey-Scherrer X-ray technique. A sample of this material was then transferred to a pre-set furnace, stripped at 650 ° C for 4 minutes and heated in an inert atmosphere oven at 1200 ° C for 4 hours to form a low density powder consisting of a reduced layer of reduced graphene oxide (RGO) Respectively. The surface area was measured by nitrogen absorption BET. The powder was then dry mixed with ABS, PE, PP and nylon pellets at 1% to 25% loading levels, respectively, and blended using a 25 mm twin screw extruder to form a composite sheet. Then, this composite sheet was pyrolyzed.

Comparative Example 2 : Preparation of single-layer graphene oxide (GO) sheet from meso carbon microbead (MCMB) followed by preparation of graphene foam layer from GO sheet

Meso carbon microbeads (MCMB) were supplied by China Steel Chemical Co., Kaohsiung, Taiwan. This material has a density of about 2.24 g / cm3 and a median particle size of about 16 microns. MCMB (10 grams) was inserted into the acid solution (4: 1: 0.05 ratio of sulfuric acid, nitric acid, and potassium permanganate) for 48 to 96 hours. When the reaction was complete, the mixture was poured into deionized water and filtered. The inserted MCMB was washed repeatedly 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 at least 4.5. The slurry was then sonicated for 10 to 100 minutes to prepare a GO suspension. TEM and atomic force microscopy studies suggest that most of the GO sheet was a single layer graphene when the oxidation treatment lasted more than 72 hours and that most of the GO sheet was graphene in two or three layers at oxidation times of 48 to 72 hours.

The GO sheet contains an oxygen ratio of approximately 35% to 47% by weight for an oxidation treatment time of 48 to 96 hours. The GO sheet was suspended in water. Baking soda (5-20% by weight) as a chemical blowing agent was added to the suspension just before casting. This suspension was then cast onto a glass surface. Several samples were cast, some containing blowing agent and some not. The resulting GO film may vary in thickness from approximately 10 to 500 mu m after removal of the liquid. Then, several GO films with or without a blowing agent were heat-treated at a heating temperature of 80 to 500 DEG C for 1 to 5 hours to form a graphene foam structure.

Comparative Example 3 : Preparation of pure graphene foam (0% oxygen)

Recognizing the possibility of many defect counts in GO sheets that act to reduce the conductivity of individual graphene faces, the use of pure graphene sheets (non-oxidized and oxygen-free, non-halogenated and halogen-free) It was decided to study whether this thermal conductivity could lead to higher graphene foams. A pure graphene sheet was prepared using direct sonication (known in the art as liquid-phase exfoliation) process.

In a conventional method, 5 g of graphite flakes milled to a size of about 20 탆 or less were dispersed in 1,000 mL of deionized water (containing 0.1 wt% of Zonyl® FSO dispersion formulation from DuPont) to obtain a suspension. The graphene sheet was stripped, separated, and size reduced using an ultrasonic energy level of 85 W (Branson S450 ultrasonic) for a period of 15 minutes to 2 hours. The resulting graphene sheet is pure graphene which is unoxidized, oxygen free and relatively defect free. Pure graphene contains no non-carbon elements.

(N, N-dinitrosopentamethylenetetramine or 4,4'-oxybis (benzenesulfonylhydrazide)) in various amounts (1% to 30% by weight with respect to the graphene material) And then added to the suspension containing the graphene sheet and the surfactant. This suspension was then cast onto a glass surface. Several samples were cast and one was prepared by injecting CO ₂ as a physical blowing agent into the suspension just before casting. The resulting graphene film may vary in thickness from approximately 10 to 100 mu m after removal of the liquid. Then, the graphene film was heat-treated at a temperature of 80 to 1,500 占 폚 for 1 to 5 hours to produce a graphene foam.

Comparative Example 4 : CVD Graphene foam on Ni foam template

This method is disclosed in Chen, Z. et al. "Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition," Nat. Mater. 10, 424-428 (2011). Nickel foam, a porous structure with nickel interconnected 3D scaffolds, was selected as the template for the growth of the graphene foam. In short, by decomposition it was at 1,000 ℃ for CH ₄ at atmospheric pressure introducing carbon into the nickel foam, and then depositing a pin Yes film on the surface of the nickel foam. Due to the difference in thermal expansion coefficient between nickel and graphene, ripples and wrinkles were formed on the graphene film. In order to recover (separate) the graphene foam, the Ni frame must be etched away. (Methyl methacrylate) (PMMA) on the surface of the graphene film as a support to prevent collapse of the graphene network structure during nickel etching, prior to etching away the nickel skeleton with hot HCl (or FeCl ₃ ) solution. Lt; / RTI > The PMMA layer was carefully removed with hot acetone and a weak graphene foam sample was obtained. The use of a PMMA support layer is important in making a stand-alone film of a graphene foam; Without the PMMA backing layer, only severely distorted and deformed graphene foam samples were obtained. This is a tricky process that is not environmentally friendly and scalable.

Comparative Example 5 : Conventional graphite foams from pitch-based carbon foams

The pitch powder, granules, or pellets are placed in an aluminum mold having the desired final shape of the foam. The Mitsubishi ARA-24 meso phase pitch was utilized. The sample was evacuated to less than 1 torr and then heated to a temperature of approximately 300 캜. At this point, the vacuum was released into a nitrogen blanket and then a pressure of 1,000 psi or less was applied. The temperature of the system was then raised to 800 占 폚. This was carried out at a rate of 2 [deg.] C / min. This temperature is maintained for at least 15 minutes to achieve a soak, then the furnace power is shut off and the furnace is cooled to room temperature at a rate of approximately 1.5 [deg.] C / min while relieving pressure at a rate of approximately 2 psi / . The final foam temperatures were 630 ° C and 800 ° C. During the cooling cycle, the pressure was gradually released to the atmospheric state. The foams were then heat-treated (carbonized) at 1050 ° C under a nitrogen blanket and subsequently heat-treated (graphitized) at 2500 ° C and 2800 ° C in a separate graphite crucible under argon.

Comparative Example 6 : Graphene foam from hydrothermal reduction graphene oxide

For comparison, samples of self-assembled graphene hydrogel (SGH) were prepared by a one-step hydrothermal method. In a conventional method, SGH can be easily prepared by heating 2 mg / mL of a homogeneous graphene oxide (GO) aqueous dispersion sealed in a Teflon-lined autoclave at 180 DEG C for 12 hours. SGH containing approximately 2.6 wt% graphene sheet and 97.4 wt% water has an electrical conductivity of approximately 5 x ^10-3 S / cm. Upon drying and heat treatment at 1,500 ° C., the resulting graphene foam exhibits an electrical conductivity of approximately 1.5 × 10 ^-1 S / cm 2, which is twice as low as the inventive graphene foam produced by heat treatment at the same temperature .

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

Samples of various conventional carbon or graphene foam materials were processed into specimens for thermal conductivity measurements. The bulk thermal conductivity of the mesophase pitch inducing foams ranged from 67 W / mK to 151 W / mK. The density of the sample was 0.31 to 0.61 g / cm3. Given the weight, the specific thermal conductivity of the pitch-induced foam is approximately 67 / 0.31 = 216 and 151 / 0.61 = 247.5 W / mK per specific gravity (or physical density).

The compressive strength of the sample with an average density of 0.51 g / cm3 was measured at 3.6 MPa and the compressive modulus at 74 MPa. In contrast, the compressive strength and compressive modulus of the graphene-carbon foam samples of the present invention having similar physical densities are 6.2 MPa and 113 MPa, respectively.

Figure 4a shows the thermal conductivity values versus specific gravity of 3D integrated graphene-carbon foam, mesophase pitch induced graphite foam, and Ni foam template assisted CVD graphene foam. This data clearly illustrates the following unexpected results:

1) The 3D monolithic graphene-carbon foams produced by the process of the present invention exhibit significantly higher thermal conductivities compared to mesophase pitch induction graphite foams and Ni foam template assisted CVD grains given the same physical density.

2) This is very surprising in the concept that CVD graphene is essentially pure graphene that has never been exposed to oxidation and should have exhibited a higher thermal conductivity than the graphene-carbon hybrid foams of the present invention. The carbon phase of the hybrid foam is generally lower in crystallinity (some amorphous carbon), so thermal conductivity or electrical conductivity is much lower than that of graphene alone. However, when the carbon phase is combined with a graphene sheet to form an integral structure made by the process of the present invention, the resulting hybrid foam exhibits thermal conductivity similar to that of a fully pure graphene foam. This very high thermal conductivity value observed in the graphene-carbon hybrid foams produced here is surprising. This may be due to the observation that the independent graphene sheet is now bound by the carbon phase and serves as a bridge for uninterrupted movement of electrons and phonons.

3) The non-conductivity value of the hybrid foam material of the present invention exhibits a value of 250 to 500 W / mK per unit weight; The nonconductivity values of other types of foam materials are typically less than 250 W / mK per unit weight.

4) The thermal conductivity data for a series of 3D graphene-carbon foams and a series of pure graphene-derived foams are summarized in FIG. 5 for the final (maximum) heat treatment temperature. In both types of materials, the thermal conductivity increases monotonically with the final HTT. However, the process of the present invention makes it possible to produce graphene-carbon foams that are superior to pure graphene foams in a cost effective and environmentally friendly manner. This is another unexpected result.

5) Figure 4b shows the thermal conductivity values of the hybrid foams of the present invention and the hot-reduced GO blend foams. The electrical conductivity values of 3D graphene-carbon foam and hot-reduced GO slabbing foam are shown in FIG. This data further supports the notion that given the same amount of solid material, the graphene-carbon foam of the present invention is inherently the most conductive and reflects the importance of continuity in electron and phonon migration paths. The carbon phase bridges gaps or breaks between graphene sheets.

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

The internal structure (crystal structure and orientation) of several series of graphene-carbon foam materials was investigated using X-ray diffraction. The X-ray diffraction curve of natural graphite typically shows a peak at about 2? = 26 °, corresponding to a graphene spacing (d ₀₀₂ ) of about 0.3345 nm. The graphene wall of the hybrid foam material typically exhibits a graphene spacing (d ₀₀₂ ) of 0.3345 nm to 0.40 nm, but more typically a maximum of 0.34 nm.

When the foam structure compression for one hour in a heat treatment temperature of 2,750 ℃, d ₀₀₂ spacing is reduced to the same as 0.3354 nm d ₀₀₂ spacing of graphite monocrystal. Further, the second diffraction peak appears at a high intensity at 2? = 55 corresponding to the X-ray diffraction from the (004) plane. The (004) peak intensity or the I (004) / I (002) ratio for the (002) intensity in the same diffraction curve is a good indicator of the degree of completeness of the crystal and the preferred orientation of the graphene plane. I (004) / I (002) ratio is less than 0.1 and (004) peak is absent or relatively weak for all graphite materials heat treated at a temperature lower than 2,800 ° C. I (004) / I (002) ratios for graphite materials heat treated at 3,000 to 3,250 ° C (for example, highly oriented pyrolytic graphite, HOPG) range from 0.2 to 0.5. In contrast, the graphene foam produced for 1 hour with a final HTT of 2,750 ° C exhibited a mosaic dispersion value of I (004) / I (002) ratio of 0.78 and a mosaic dispersion value of 0.21, indicating that the pore wall had a preferred orientation Indicating that it is a substantially complete graphene single crystal (when manufactured under compressive force).

The "mosaic dispersion" value is obtained from the full width at half maximum of the (002) reflection in the X-ray diffraction intensity curve. This index for the degree of alignment characterizes graphite or graphene crystal size (or grain size), grain size and other defects, and preference orientation degree. Almost complete single crystal of graphite is characterized by having a mosaic dispersion value of 0.2 to 0.4. Some of the graphene foams of the present invention have a mosaic dispersion value in the range of 0.3 to 0.6 when prepared using a final heat treatment temperature of at least 2,500 占 폚.

Here is a summary of some of the more important results:

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

2) In the case where impact balls (for example, ceramics, glass, metal balls, etc.) are not used, more rigid polymer particles (for example, PE, PP, nylon, ABS, polystyrene, high impact polystyrene, Reinforced form) can better delaminate the graphene sheet from the graphite particles as compared to the more flexible polymer particles (e.g., rubber, PVC, polyvinyl alcohol, latex particles).

3) If the impact ball is not added externally, given the same 1 hour of run time, the softer polymer particles will have a graphene-like structure with 0.001 wt% to 5 wt% graphene (predominantly monolayer graphene sheet) Coating or insert particles, and the harder polymer balls tend to produce graphene-coated particles with from 0.01% to 30% by weight of graphene (mainly monolayer and hydrophobic graphene sheets) .

4) By adding impact balls from the outside, all polymer balls will support from 0.001% to 80% by weight of graphene sheet (less than 10 layers of minority graphene in the case of more than 30% by weight graphene sheet) .

5) The graphene-carbon hybrid foam materials of the present invention typically exhibit significantly higher structural integrity (e.g., compressive strength, resilience, and resilience) and higher heat (as compared to the counterparts produced by conventional prior art processes) Conductivity and electrical conductivity.

6) All prior art processes for producing graphite foams or graphene foams appear to provide only macroscopically porous foams having physical densities in the range of about 0.2 to 0.6 g / cm < 3 >, and pore sizes for most intended applications (For example, 20 to 300 mu m). In contrast, the present invention provides a method of producing a graphene foam which can have a density as low as 0.001 g / cm < 3 > and a density as high as 1.7 g / cm < 3 >. The pore size can vary from fine (less than 2 nm) to medium (2 to 50 nm), macroscopic (eg, 1 to 500 μm). This level of flexibility and versatility in designing various types of graphene-carbon foam is unprecedented and not comparable to any prior art method.

7) The method of the present invention may also be used to determine the chemical composition (e. G., F < RTI ID = 0.0 > , O and N content, etc.).

In conclusion, we have successfully developed graphene-carbon hybrid foam materials, devices, and associated manufacturing processes that are entirely new, novel, and beyond expectations, apparently of a different kind of high conductivity. The chemical composition of this new type of foam material (oxygen, fluorine, and other non-carbon elements), structure (crystal integrity, crystal size, number of defects, etc.), crystal orientation, Which is fundamentally different from, and distinct from, graphene foams from leaded graphite foams, CVD graphene-derived foams, and GO hot water reductions.

Claims (41)

An integrated 3D graphene-carbon hybrid foam comprising multiple pores and pore walls, said pore wall having a carbon material-to-graphene weight ratio of 1/200 to 1/2 carbon material Wherein the minor grained graphene sheet comprises graphene planes 2 with an interplanar spacing d ₀₀₂ of 0.3354 nm to 0.40 nm as measured by X-ray diffraction To 10 layers, wherein the single layer or the hydrophobic graphene sheet comprises a pristine graphene material with essentially 0% non-carbon elements, or from 0.001 wt% to 25 wt% non-carbon elements Wherein the non-pure graphene material is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, Hydrogenated graphene, nitrided Graphene, doped graphene, chemically functionalized graphene, or a combination thereof. The 3D graphene foam of claim 1, wherein the 3D graphene foam has a density of 0.005 to 1.7 g / cm 3, a specific surface area of 50 to 3,200 m 2 / g, a thermal conductivity of at least 200 W / mK per unit weight, and / An integral 3D graphene-carbon hybrid foam having an electrical conductivity of S / cm or greater. The 3D graphene-carbon hybrid foam of claim 1 wherein said pore wall comprises pure graphene and said 3D graphene-carbon hybrid foam has a density of from 0.01 to 1.7 g / cm3, or an integral 3D Graphene-carbon hybrid foam. 2. The method of claim 1, wherein the pore wall comprises a non-pure graphene material, wherein the foam comprises a non-carbon element content in the range of 0.01 wt% to 20 wt% , Bromine, iodine, nitrogen, hydrogen, or boron. The integral 3D graphene-carbon hybrid foam of claim 1, wherein the pore wall comprises graphene fluoride and the solid graphene foam comprises a fluorine content of from 0.01% to 15% by weight. 2. The 3D graphene-carbon hybrid foam of claim 1, wherein the pore wall comprises graphene oxide, and wherein the solid graphene foam comprises an oxygen content of from about 0.01% to about 20% by weight. The 3D graphene-carbon hybrid foam of claim 1, wherein the foam has a specific surface area of 200 to 3,000 m 2 / g, or a density of 0.1 to 1.2 g / cm 3. The 3D graphene-carbon hybrid foam according to claim 1, in the form of a roll sheet of continuous length having a thickness of 100 nm to 10 cm and a length of at least 2 meters, and being produced by a roll-to-roll process. The foam of claim 1, wherein the foam has an oxygen content or a non-carbon content of less than 1 wt%, the pore walls have a graphene spacing of less than 0.35 nm, a thermal conductivity of at least 250 W / mK per unit weight, and / A 3D graphene-carbon hybrid foam having an electrical conductivity of at least 2,500 S / cm per unit specific gravity. 2. The method of claim 1, wherein the foam has an oxygen content or a non-carbon content of less than 0.01 wt%, the pore wall has a graphene spacing of less than 0.34 nm, a thermal conductivity of at least 300 W / mK per unit weight, and / A 3D graphene-carbon hybrid foam comprising an overlaid graphene face having an electrical conductivity of at least 3,000 S / cm per unit weight. The foam of claim 1, wherein the foam has an oxygen content or a non-carbon content of less than or equal to 0.01 percent by weight, the pore wall having a graphene spacing of less than 0.336 nm, a thermal conductivity of at least 350 W / mK per unit weight, and / And a superimposed graphene face having an electrical conductivity of at least 3,500 S / cm per unit gravity. The foam of claim 1, wherein the foam has a graphene spacing of less than 0.336 nm, a thermal conductivity of greater than 400 W / mK per unit weight, and / or an electrical conductivity of greater than 4,000 S / ≪ RTI ID = 0.0 > 3D < / RTI > graphene-carbon hybrid foam. 2. The 3D graphene-carbon hybrid foam of claim 1, wherein the pore wall comprises a superposed graphene surface having a graphene spacing of less than 0.337 nm and a mosaic dispersion value of less than 1.0. 2. The 3D graphene-carbon hybrid foam of claim 1, wherein the pore walls comprise a 3D network of interconnected graphene facets. The 3D graphene-carbon hybrid foam of claim 1, wherein the foam comprises meso-scaled pores having a pore size of 2 nm to 50 nm. An oil-removing or oil-separating device comprising the 3D graphene-carbon hybrid foam of claim 1 as an oil-absorbing element. A solvent-removing or solvent-separating device comprising the 3D graphene-carbon hybrid foam of claim 1 as a solvent-absorbing or solvent-separating element. As a method for separating oil from water,
a. Providing an oil-absorbing element comprising the integral 3D graphene-carbon hybrid foam of claim 1;
b. Contacting the oil-water mixture with the element to absorb oil from the mixture;
c. Withdrawing said element from the mixture and extracting oil from said element; And
d. The step of reusing the element
≪ / RTI > A method for separating an organic solvent from a solvent-water mixture or a multi-solvent mixture,
a. Providing an organic solvent-absorbing or solvent-separating element comprising the integral 3D graphene-carbon hybrid foam of claim 1;
b. Contacting said element with an organic solvent-water or 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; And
d. Withdrawing the element from the mixture and extracting an organic solvent or a first solvent from the element; And
e. The step of reusing the element
≪ / RTI > A thermal management device comprising the 3D monolithic graphene-carbon hybrid foam of claim 1 as a thermal diffusion or heat dissipation element. 21. The method of claim 20, further comprising the steps of: providing a heat exchanger, a heat sink, a heat pipe, a high conductive insert, a conductive plate between the heat sink and the heat source, a heat- A device selected from a cooling device or a Peltier cooling device. A method of making an integral 3D graphene-carbon hybrid foam directly from a graphite material,
(a) mixing multiple particles of graphite material with multiple particles of a solid polymeric carrier material to form a mixture in an impacting chamber of an energy impacting apparatus;
(b) moving said energy impacting device to a surface of said solid polymeric carrier material particle for a long period of time and at a frequency and intensity sufficient to release said graphene sheet from said graphite material and graphen- Producing graft-insertion polymer particles in the impact chamber;
(c) recovering the graphene-coated or graphene-inserted polymer particles from the impact chamber and integrating the graphene-coated or graphene-embedded polymer particles into a graphene-polymer composite structure of the desired type; And
(d) thermally decomposing the graphene-polymer composite structure of the above form to thermally convert the polymer into pores and carbon or graphite binding the graphene sheet to form the integral 3D graphene-carbon hybrid foam
≪ / RTI > 23. The method of claim 22, further comprising adding a plurality of impact balls or media to the impact chamber of the energy bombardment device. 24. The method of claim 23, wherein step (c) comprises operating the magnet to separate the impact ball or medium from the graphene-coated or graphene-inserted polymer particles. 23. The method of claim 22, wherein the solid polymeric material particles are plastic or rubber beads, pellets, spheres, wires, fibers, filaments, discs, ribbons, or rods having a diameter or thickness of from 10 nm to 10 mm. 26. The method of claim 25, wherein the diameter or thickness is 100 nm to 1 mm. 23. The method of claim 22, wherein the solid polymer is selected from solid particles of a thermoplastic, thermosetting resin, rubber, semi-penetrating reticulated polymer, penetrating reticulated polymer, natural polymer, or combinations thereof. 23. The method of claim 22, wherein the solid polymer is partially removed by melting, etching, or dissolving in a solvent prior to step (d). 23. The method of claim 22, wherein the graphite material is selected from the group consisting of natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphite nanofiber, graphite fluoride, graphite oxide, chemically modified graphite, Compressively exfoliated graphite, expanded graphite, meso carbon microbeads, or combinations thereof. 23. The method of claim 22, wherein the energy impacting device is selected from the group consisting of a vibrating ball mill, planetary ball mill, high energy mill, basket mill, agitator ball mill, cryo ball mill, micro ball mill, tumbler ball mill, A ball mill, a stirred ball mill, a pressurized ball mill, a freezer mill, a vibrating body, a bead mill, a nano-bead mill, an ultrasonic homogenizer, a centrifugal oil mixer, a vacuum ball mill or a resonance acoustic mixer resonant acoustic mixer. 23. The method of claim 22, wherein the graphite material comprises non-intercalated and non-oxidized graphite material that has not been exposed to a chemical or oxidation treatment prior to the mixing step. 23. The method of claim 22, wherein the solid polymer is selected from the group consisting of a phenolic resin, poly furfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, poly The carbon yields selected from benzothiazole, polybenzobisthiazole, poly (p-phenylenevinylene), polybenzimidazole, polybenzobisimidazole, copolymers thereof, polymer blends thereof, ≪ / RTI > high polymer. 23. The method of claim 22 wherein the solid polymer is selected from the group consisting of polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS), polyester, polyvinyl alcohol, polyvinylidene fluoride (PVDF) , A polymer having a low carbon yield selected from polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), polymethyl methacrylate (PMMA), copolymers thereof, polymer blends thereof, / RTI > 23. The method of claim 22, wherein the pyrolysis step comprises carbonizing the polymer at a temperature of from 200 DEG C to 2,500 DEG C to obtain a graphene-carbon foam, or carbonizing the polymer at a temperature of from 200 DEG C to 2,500 DEG C to form a graphene- And graphitizing said graphene-carbon foam at 2,500 ° C to 3,200 ° C to obtain graphitized graphene-carbon foam. 23. The method of claim 22, wherein said integrating step comprises melting said polymer particles to form a polymer melt mixture with a graphene sheet dispersed therein, shaping said polymer melt mixture into a desired shape, ≪ / RTI > The method of claim 22, wherein the step of integrating comprises the steps of: dissolving the polymer particles in a solvent to form a mixture of the polymer solution and the graphene sheet dispersed therein; molding the polymer solution mixture into a desired shape; Lt; RTI ID = 0.0 > graphen-polymer < / RTI > 23. The method of claim 22, wherein said integrating step comprises shaping said graphene-coated polymer particles into a composite form selected from a rod, sheet, film, fiber, powder, ingot, or block form. 23. The method of claim 22, wherein the step of consolidating comprises compressing the graphene-coated polymer particles in a porous molding having macropores and then selecting from petroleum pitch, coal tar pitch, aromatic organic material, monomer, organic polymer, Lt; RTI ID = 0.0 > pore < / RTI > into the pores. 39. The method of claim 38, wherein the organic polymer is selected from the group consisting of a phenolic resin, poly furfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, poly The carbon yields selected from benzothiazole, polybenzobisthiazole, poly (p-phenylenevinylene), polybenzimidazole, polybenzobisimidazole, copolymers thereof, polymer blends thereof, A method, comprising a high polymer 24. The method of claim 22, wherein said integrating step comprises shaping a large amount of said graphene-coated or graphene-inserted polymer particles into a compact. 41. The method of claim 40, wherein the compact is in a form selected from a rod, a sheet, a film, a fiber, a powder, an ingot, or a block.

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