Eco-friendly production of graphene

Abstract

Provided is method of producing graphene directly from a pulp, paper, or paper product, the method comprising a procedure of subjecting the pulp, paper, or paper product (preferably containing post-consumer, reclaimed, or recycled product) to a graphitization treatment at a graphitization temperature in the range of 1,500° C. to 3,400° C. (preferably >2,500° C.) in a substantially non-oxidizing environment for a length of time sufficient for converting the product to a graphene material product. Preferably and typically, the method does not involve the use of an externally added undesirable chemical (other than those paper chemicals already present in the paper product) or catalyst. The method is environmentally benign, ecologically friendly, and highly scalable.

Claims

1. A method of producing graphene from a pulp, said method comprising a procedure of subjecting said pulp to a graphitization treatment at a graphitization temperature in the range of 1,500° C. to 3,400° C. in a substantially non-oxidizing environment for a length of time sufficient for forming a graphene material product, wherein said pulp is selected from brown pulp, dissolving pulp, fluff pulp, market pulp, mechanical pulp, unbleached pulp, or a combination thereof, wherein said pulp is mixed with a carbonization promoter or flame retardant selected from the group consisting of nitrogenous salts of acids, acid salts, derivatives of phosphoric acid, chlorosilanes, and combinations thereof, prior to being heat treated.

2. The method of claim 1, wherein said pulp contains a post-consumer, reclaimed, or recycled product.

3. The method of claim 1, wherein said graphitization temperature is greater than 2,000° C.

4. The method of claim 1, wherein said graphitization temperature is greater than 2,500° C.

5. The method of claim 1, wherein said graphitization temperature is greater than 2,800° C.

6. The method of claim 1, wherein said procedure of subjecting said pulp to a graphitization treatment includes (a) positioning said pulp in a heat treatment chamber and exposing said product to a first treatment temperature selected from the range of 200° C. to 500° C. for a first period of time to form a first intermediate product; (b) further heat-treating the first intermediate product at a second temperature selected from the range of 700° C. to 1,500° C. for a second period of time to form a second intermediate product; and (c) subjecting said second intermediate product to a final graphitization treatment at a temperature selected from the range of 2,000° C. to 3,400° C.

7. The method of claim 1, wherein said heat treatment chamber has a structure being composed of a high-temperature refractory material selected from graphite, tungsten, tungsten carbide, zirconia, molybdenum oxide, niobium oxide, tantalum, tantalum oxide, or a combination thereof.

8. The method of claim 1, wherein said non-oxidizing environment includes nitrogen, hydrogen, a noble gas, or a combination thereof.

9. The method of claim 1, wherein said graphene material product is in a powder form containing at least 80% single-layer or few-layer graphene sheets, wherein few-layer graphene is defined as a graphene sheet having 2 to 10 graphene planes stacked together.

10. The method of claim 1, wherein said graphene material product contains at least 90% single-layer or few-layer graphene sheets.

11. The method of claim 1, further comprising a step of separating or recovering graphene from non-graphene carbon residue in said graphene material product.

12. The method of claim 1, wherein said graphene material contains at least 90% single-layer or few-layer graphene sheets.

13. The method of claim 1, wherein said procedure of subjecting said pulp to a graphitization treatment includes positioning said pulp in a heat treatment chamber and exposing said pulp to an initial temperature lower than 1,500° C., which is then increased to a temperature in the range of 1,500° C. to 3,400° C.

14. The method of claim 13, wherein said pulp is packed or compacted into a feedstock prior to being placed into said heat treatment chamber.

15. The method of claim 14, wherein said packed or compacted pulp has a bulk density in the range from 0.1 to 1.5 g/cm.sup.3.

16. The method of claim 14, wherein said packed or compacted pulp has a bulk density in the range from 0.2 to 1.2 g/cm.sup.3.

17. A method of producing graphene from a wood product or wood ingredient, not including a paper or paper product obtained from wood, said method comprising a procedure of subjecting said wood product or wood ingredient to a graphitization treatment at a graphitization temperature in the range of 1,500° C. to 3,400° C. in a substantially non-oxidizing environment for a length of time sufficient for converting said product to a graphene material product, wherein said wood ingredient is selected from purified cotton, an wood extractive, a cellulose derivative, rosin, alum, a combination thereof, or a combination thereof with wood pulp, wherein said cellulose derivative is selected from cellulose triacetate, cellulose propionate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), nitrocellulose (cellulose nitrate), cellulose sulfate, alkyl cellulose, hydroxyalkyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydroxyethyl cellulose, carboxyalkyl cellulose, or a combination thereof.

18. The method of claim 17, wherein said graphitization temperature is greater than 2,500° C.

19. The method of claim 17, wherein said graphitization temperature is greater than 2,800° C.

20. The method of claim 17, wherein said procedure of subjecting said wood product or wood ingredient to a graphitization treatment includes positioning said wood product or wood ingredient in a heat treatment chamber and exposing said wood product or wood ingredient to an initial temperature lower than 1,500° C., which is then increased to a temperature in the range of 1,500° C. to 3,400° C.

21. The method of claim 17, wherein said procedure of subjecting said wood product or wood ingredient to a graphitization treatment includes positioning said wood product or wood ingredient in a heat treatment chamber and exposing said wood product or wood ingredient to an initial temperature lower than 1,500° C., which is then increased to a temperature in the range of 1,500° C. to 3,200° C.

22. The method of claim 17, wherein said non-oxidizing environment includes nitrogen, hydrogen, a noble gas, or a combination thereof.

23. The method of claim 17, wherein said wood product or wood ingredient is mixed with a carbonization promoter or flame retardant selected from the group consisting of nitrogenous salts of acids, acids, acid salts, metal halides, derivatives of phosphoric acid, chlorosilanes, and combinations thereof, prior to being heat treated.

24. The method of claim 17, wherein said graphene material is in a powder form containing at least 80% single-layer or few-layer graphene sheets, wherein few-layer graphene is defined as a graphene sheet having 2 to 10 graphene planes stacked together.

25. The method of claim 17, wherein said procedure of subjecting said wood product or wood ingredient to a graphitization treatment includes (a) positioning said wood product or wood ingredient in a heat treatment chamber and exposing said product to a first treatment temperature selected from the range of 200° C. to 500° C. for a first period of time to form a first intermediate product; (b) further heat-treating the first intermediate product at a second temperature selected from the range of 700° C. to 1,500° C. for a second period of time to form a second intermediate product; and (c) subjecting said second intermediate product to a final graphitization treatment at a graphitization temperature selected from the range of 2,000° C. to 3,200° C.

26. The method of claim 25, wherein said first treatment at 200° C. to 500° C. is conducted in a reactive environment and said second treatment at 700° C. to 1,500° C. is conducted in an inert or non-oxidizing environment.

27. A method of producing graphene from a pulp, paper, or paper product, said method comprising a procedure of subjecting said pulp, paper, or paper product to a graphitization treatment at a graphitization temperature in the range of 1,500° C. to 3,400° C. in a substantially non-oxidizing environment for a length of time sufficient for forming a graphene material product, wherein the pulp, paper, or paper product is mixed with a carbonization promoter or flame retardant selected from the group consisting of nitrogenous salts of acids, acid salts, metal halides, derivatives of phosphoric acid, chlorosilanes, and combinations thereof, prior to being heat treated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A flow chart showing the most commonly used prior art process of producing highly oxidized NGPs that entails tedious chemical oxidation/intercalation, rinsing, and high-temperature exfoliation procedures.

(2) FIG. 2 A TEM image of graphene sheets produced from post-consumer paperboard.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(3) Carbon materials can assume an essentially amorphous structure (glassy carbon), a highly organized crystal (graphite), or a whole range of intermediate structures that are characterized in that various proportions and sizes of graphite crystallites and defects are dispersed in an amorphous matrix. Typically, a graphite crystallite is composed of a number of graphene sheets or basal planes that are bonded together through van der Waals forces in the c-axis direction, the direction perpendicular to the basal plane. These graphite crystallites are typically micron- or nanometer-sized. The graphite crystallites are dispersed in or connected by crystal defects or an amorphous phase in a graphite particle, which can be a graphite flake, carbon/graphite fiber segment, carbon/graphite whisker, or carbon/graphite nano-fiber, etc.

(4) One preferred specific embodiment of the present invention is a method of producing a graphene material (also referred to as nano graphene platelet, NGP) that is essentially composed of a sheet of graphene plane or multiple sheets of graphene plane stacked and bonded together (typically, on an average, up to five sheets per multi-layer platelet). Each graphene plane, also referred to as a graphene sheet, comprises a two-dimensional hexagonal structure of carbon atoms. Each platelet has a length and a width parallel to the graphene plane and a thickness orthogonal to the graphite plane. By definition, the thickness of an NGP is 100 nanometers (nm) or smaller, with a single-layer graphene being as thin as 0.34 nm. However, the presently invented method produces graphene sheets that are typically from 1 to 10 layers (or from 0.34 nm to 3.4 nm in thickness) and more typically from 1 to 5 layers. In many cases, the graphene materials produced are mostly single-layer graphene (typically >80% and more typically >90%). The length and width of a NGP are typically between 5 nm and more typically between 10 nm and 500 nm.

(5) The present invention provides a method of producing graphene directly from a pulp, paper, or paper product. The method comprises a procedure of subjecting the pulp, paper, or paper product (preferably containing post-consumer, reclaimed, or recycled products) to a graphitization treatment at a graphitization temperature selected from the range of 1,500° C. to 3,400° C. in a substantially non-oxidizing environment for a length of time sufficient for converting the product to a graphene material product, wherein the method does not involve the use of an externally added chemical (other than those paper chemicals already present in the paper product during manufacturing) or any catalyst. The substantially non-oxidizing environment contains an oxygen content in the atmosphere surrounding the product being less than 5%, preferably <1%, further preferably <0.1%, and most preferably <0.01%.

(6) Preferably, the pulp, paper, or paper product contains a post-consumer, reclaimed, or recycled product. This has a highly positive impact to the environment since paper and paper products constitute a significant proportion of post-consumer solid waste, which would otherwise get buried underground.

(7) The invented method is essentially a single-step process. The method is strikingly simple, scalable, environmentally benign, eco-friendly, and cost-effective. The method avoids essentially all of the drawbacks associated with prior art processes.

(8) In contrast, as shown in FIG. 1, the prior art chemical processes typically involve immersing graphite powder in a mixture of concentrated sulfuric acid, nitric acid, and an oxidizer, such as potassium permanganate or sodium perchlorate, forming a reacting mass that requires typically 5-120 hours to complete the chemical intercalation/oxidation reaction. Once the reaction is completed, the slurry is subjected to repeated steps of rinsing and washing with water and then subjected to drying treatments to remove water. The dried powder, referred to as graphite intercalation compound (GIC) or graphite oxide (GO), is then subjected to a thermal shock treatment. This is typically accomplished by exposing the GIC to a furnace pre-set at a temperature of typically 800-1100° C. (more typically 950-1050° C.). The prior art processes suffer from the seven (7) major problems described in the Background section.

(9) In certain embodiments of the present invention, the procedure of subjecting the pulp, paper, or paper product to a graphitization treatment may include positioning the pulp, paper, or paper product in a heat treatment chamber (e.g., a graphite crucible) and exposing the product to an initial temperature lower than 1,500° C. (e.g. ambient temperature), which is then increased to a temperature in the range of 1,500° C. to 3,400° C. Preferably, the graphitization temperature is greater than 2,000° C., more preferably greater than 2,500° C., and most preferably greater than 2,800° C.

(10) The feedstock (pulp, paper, or paper product) may be placed into a heat treatment chamber pre-set a temperature that is not too high so that loading of the feedstock would not become problematic. The temperature is then slowly ramped up to the desired final temperature (e.g. 2,500° C. to 3,200° C.), maintained at this temperature for 0.5 to 5 hours, and then cooled down to a temperature that enables easy removal of the graphene material product.

(11) In certain alternative embodiments, the feedstock (e.g. reclaimed pulp, paper, or paper product) is placed into a heat treatment chamber (e.g. graphite crucible), which is moved (e.g., conveyor-carried) into one end of a heating furnace and, after a desired length of heat treatment time, moves out of the furnace from an opposite end. Typically, the entry zone and the exit zone of the furnace have a lower temperature than the mid-section (graphitization zone) of the furnace. There should be a sufficient length of the graphitization zone to enable the product residence time in this zone for no less than 0.5 hours, preferably from 0.5 to 5 hours (can be longer, as deemed desired).

(12) In certain preferred embodiments, the procedure of subjecting the pulp, paper, or paper product to a graphitization treatment includes (a) positioning the pulp, paper, or paper product in a heat treatment chamber and exposing the product to a first treatment temperature selected from the range of 200° C. to 600° C. (also herein referred to as the first-stage treatment) for a first period of time to form a first intermediate product; (b) further heat-treating the first intermediate product at a second temperature selected from the range of 700° C. to 1,500° C. (also herein referred to as the second-stage treatment) for a second period of time to form a second intermediate product; and (c) subjecting the second intermediate product to a final graphitization treatment at a temperature selected from the range of 2,000° C. to 3,200° C. (more preferably from 2,500° C. to 3,000° C.).

(13) Preferably, the first period of time is from 0.5 hours to 6 hours, preferably in a reactive environment (e.g. with flowing air, oxygen, chlorine, or HCl gas). The second period of time is also preferably from 0.5 hours to 6 hours, but under an inert or non-oxidizing atmosphere. The graphitization must be conducted in an inert or non-oxidizing atmosphere.

(14) The two periods of pre-treatment of the pulp, paper, or paper product prior to the final graphitization treatment, although not required, can be beneficial in increasing the amount of graphene sheets that can be produced given the same amount of feedstock. The reasons for these improvements are not totally clear. However, the applicant believes that a first period of heat treatment at 200° C. to 600° C. at a relatively low heating rate can favor controlled decomposition of the cellulose structure in such a manner that it promotes aromatization and development of incipient graphene layers (graphene-like aromatic or fused-ring structures or domains). More aromatic fused rings or graphene-like layers will be nucleated and grow during the second period of heat treatment at 700° C. to 1,500° C. During graphitization, graphene planes from neighboring graphene-like domains are merged to form longer or wider graphene sheets.

(15) The heat treatment chamber may be constructed from a high-temperature refractory material selected from graphite, tungsten, tungsten carbide, zirconia, molybdenum oxide, niobium oxide, tantalum, tantalum oxide, or a combination thereof.

(16) Preferably, the provision of a non-oxidizing environment includes the introduction of nitrogen, hydrogen, a noble gas (e.g. Ar gas), or a combination thereof, into the heat treatment chamber. The substantially non-oxidizing environment implies an atmosphere containing less than 5% by weight oxygen, preferably <1%, further preferably <0.1%, and most preferably <0.01%.

(17) In certain preferred embodiments, the pulp, paper, or paper product is packed or compacted (with or without using a binder resin) into a feedstock prior to being placed into the heat treatment chamber. Preferably, the feedstock (packed or compacted mass of pulp, paper, or paper product) has a bulk density in the range from 0.1 to 1.5 g/cm.sup.3, more preferably in the range from 0.2 to 1.2 g/cm.sup.3, and most preferably greater than 0.4 g/cm.sup.3. This higher feedstock density is desirable not only for packing more feedstock materials into a given heat treatment chamber but also, surprisingly, enable the production of graphene at a much higher production yield (typically 15%-50% vs. 5%-15% yield rate for non-compacted feedstock). The resulting graphene sheets are also larger in lateral dimensions (length or width 50-500 nm vs. 5-50 nm for graphene sheets from non-compacted feedstock). This is truly unexpected and highly beneficial.

(18) The feedstock may contain a desired amount of a carbonization promoter (protecting against excessive evolution of volatile gas molecules from uncontrolled decomposition of the constituent cellulose molecules) and/or flame retardant that is mixed with the pulp, paper, or paper product. The carbon yield and graphene production yield can be significantly enhanced by impregnating or incorporating a carbonization promoter and/or flame retardant, which may be preferably selected from the group consisting of nitrogenous salts of acids, acids, acid salts, metal halides, derivatives of phosphoric acid, chlorosilanes, and combinations thereof.

(19) The method typically is capable of producing a graphene material product in a powder form containing at least 80% single-layer or few-layer graphene sheets, wherein few-layer graphene is commonly defined as a graphene sheet having 2 to 10 graphene planes stacked together. The method can lead to production of a graphene material product contains at least 90% single-layer or few-layer graphene sheets (in many cases, >90% of graphene sheets being single-layer). In certain embodiments of the invention, the method may further comprise a step of separating or recovering graphene from non-graphene carbon residue in the graphene material product. The carbon residue typically contains amorphous graphene and some minute graphite crystals.

(20) The paper or paper product in the feedstock may contain a material or product selected from a paper base, bond paper, construction paper, containerboard, corrugated container board, chipboard, cover paper, envelope paper, form bond paper, insulating board paper, Kraft bag paper, Kraft wrapping paper, mechanical paper, newsprint paper, napkin stock, offset paper, packaging paper, paperboard, printing-writing paper, fine paper, coarse paper, recycled paper, solid bleached bristols, specialty paper, tissue paper, or a combination thereof. The pulp may be selected from chemical pulp, brown pulp, dissolving pulp, fluff pulp, Kraft (sulfate) pulp, market pulp, mechanical pulp, sulfite pulp, unbleached pulp, or a combination thereof.

(21) The invention also provides a method of producing graphene directly from a wood product or wood ingredient (not including paper or paper product produced from wood). This environmentally benign method comprises a procedure of subjecting the wood product or wood ingredient to a graphitization treatment at a graphitization temperature in the range of 1,500° C. to 3,400° C. in a substantially non-oxidizing environment for a length of time sufficient for converting the product to a graphene material product, wherein the method does not involve the use of a catalyst. Preferably, the method also does not use any undesirable or hazardous chemical. The graphitization temperature is preferably greater than 2,000° C., further preferably greater than 2,500° C., most preferably greater than 2,800° C.

(22) The wood ingredient is selected from native cellulose, purified cotton, regenerated cellulose or Rayon, β-cellulose, γ-cellulose, nitro cellulose, hemicellulose, lignin, an wood extractive, a cellulose derivative, rosin, alum, starch, a combination thereof, or a combination thereof with wood pulp.

(23) The cellulose derivative is selected from cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), nitrocellulose (cellulose nitrate), cellulose sulfate, alkyl cellulose (e.g. methylcellulose, ethyl cellulose, ethyl methyl cellulose), hydroxyalkyl cellulose (e.g. hydroxyethyl cellulose, hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydroxyethyl cellulose), and carboxyalkyl cellulose (e.g. Carboxymethyl cellulose (CMC)).

(24) The procedure of subjecting the wood product or wood ingredient to a graphitization treatment includes positioning the wood product or wood ingredient in a heat treatment chamber and exposing the wood product or wood ingredient to an initial temperature lower than 1,500° C., which is then increased to a graphitization temperature in the range of 1,500° C. to 3,400° C. The non-oxidizing environment includes nitrogen, hydrogen, a noble gas, or a combination thereof.

(25) The procedure of subjecting the wood product or wood ingredient to a graphitization treatment may include positioning the wood product or wood ingredient in a heat treatment chamber and exposing the wood product or wood ingredient to an initial temperature lower than 1,500° C., which is then increased to a graphitization temperature in the range of 1,500° C. to 3,400° C.

(26) In certain preferred embodiments, the procedure of subjecting the wood product or wood ingredient to a graphitization treatment includes (a) positioning the wood product or wood ingredient in a heat treatment chamber and exposing the product to a first treatment temperature selected from the range of 200° C. to 600° C. for a first period of time to form a first intermediate product; (b) further heat-treating the intermediate product at a second temperature selected from the range of 700° C. to 1,500° C. for a second period of time to form a second intermediate product; and (c) subjecting the second intermediate product to a final graphitization treatment at a temperature selected from the range of 2,000° C. to 3,200° C. (more preferably from 2,500° C. to 3,000° C.).

(27) The first period of time is preferably from 0.5 hours to 6 hours. The second period of time is preferably from 0.5 hours to 6 hours. The first treatment at 200° C. to 500° C. is preferably conducted in a reactive environment and the second treatment at 700° C. to 1,500° C. is conducted in an inert or non-oxidizing environment. The two periods of pre-treatment of the wood product or wood ingredient prior to the final graphitization treatment, although not required, can be beneficial in increasing the amount of graphene sheets that can be produced given the same amount of feedstock.

(28) In certain preferred embodiments, the wood product or wood ingredient is mixed with a carbonization promoter or flame retardant selected from the group consisting of nitrogenous salts of acids, acids, acid salts, metal halides, derivatives of phosphoric acid, chlorosilanes, and combinations thereof, prior to being heat treated. These additives were found to increase the production yield of graphene.

(29) The graphene material product produced is typically in a powder form containing at least 80% single-layer or few-layer graphene sheets, wherein few-layer graphene is defined as a graphene sheet having 2 to 10 graphene planes stacked together. Typically, the graphene material product contains at least 90% single-layer or few-layer graphene sheets.

(30) The graphitization treatment products of pulp, paper, paper product, wood product, or wood ingredient can be in a powder form. In some cases, the products can mimic the original shape of the feedstock, but the products contain graphene sheets. In these cases, the graphitization treatment step may be followed by a step of subjecting the product to a mechanical shearing treatment to produce a graphene material product in a powder form. The mechanical shearing treatment comprises using air milling, air jet milling, ball milling, rotating-blade mechanical shearing, ultrasonication, cavitation, or a combination thereof.

(31) The following examples serve to provide the best modes of practice for the present invention and should not be construed as limiting the scope of the invention:

Example 1: Controlled Graphitization Treatments of Pulp, Paper and Paper Products

(32) A broad array of pulp, paper, and paper products were subjected to graphitization treatments, with or without the two-stage pre-treatments and with or without the incorporation of a carbonization promoter or flame-retardant additive. The compaction of products was conducted by using a hydraulic press, commonly known as a compression-molding machine. Other compaction procedures, well-known in the art, may also be used. The compressive force is implemented to compact the pulp, paper, or paper product to the extent that it has a bulk density in the range from 0.1 to 1.5 g/cm.sup.3, preferably density in the range from 0.2 to 1.2 g/cm.sup.3, and more preferably greater than 0.3 g/cm.sup.3. The processing conditions and the graphene production yield data (based on total feedstock weight) are summarized in Table 1 below:

(33) TABLE-US-00001 TABLE 1 Production of graphene materials different paper products. Sample 1.sup.st and 2.sup.nd stage Graphitization Graphene No. Feedstock material treatments treatment yield PS-1 Post-consumer shopping None Ramped to 2,800° C. in 21.5% bag paper, compacted 2 hrs, staying for 2 hrs PS-2 Post-consumer shopping None Ramped to 2,800° C. in  8.4% bag paper, loosely packed 2 hrs, staying for 2 hrs PS-3 Post-consumer shopping 200-300° C. for 2 hrs Staying at 2,800° C. for 28.4% bag paper, compacted in air; 1,200° C. 2 hrs for 2 hrs in argon PS-4 Post-consumer shopping 200-300° C. for 2 hrs Staying at 2,800° C. for 12.6% bag paper, loosely packed in air; 1,200° C. 2 hrs for 2 hrs in argon PS-5 Post-consumer shopping None Ramped to 2,800° C. in 31.4% bag paper, compacted, 2 hrs, staying for 2 hrs phosphoric acid added PWP-1 Wood pulp, dried and 300° C. for 2 hrs in Staying at 2,800° C. for 37.7% compacted, sodium air; 1,100° C. for 2 hrs 2 hrs acetate added in argon PB-1 Shipping box cardboard, None Ramped to 3,050° C. in 24.5% compacted 3 hrs, staying for 1 hr PB-2 Shipping box cardboard, None Ramped to 3,050° C. in 11.3% cut in pieces, loosely 3 hrs, staying for 1 hr packed PB-3 Shipping box cardboard, 250° C. for 2 hrs in Staying at 3,050° C. for   41% soaked in phosphoric HCl vapor; 900° C. 1 hr. sodium solution, for 2 hrs in argon compacted PB-4 Shipping box cardboard, 250° C. for 2 hrs in Staying at 3,050° C. for 32.3% compacted HCl vapor; 900° C. 1 hr. for 2 hrs in argon PC-1 Office copy paper, 250° C. for 2 hrs in Staying at 2,600° C. for 31.2% compacted, phosphoric air; 1,000° C. for 2 hrs 2 hrs acid added in argon PC-2 Office copy paper, None Ramped to 2,600° C. in 27.6% compacted, phosphoric 3 hrs, staying for 5 hr acid added PC-3 Office copy paper, None Ramped to 2,600° C. in 22.1% compacted 3 hrs, staying for 5 hr PN-1 Newspaper, compacted 250° C. for 2 hrs in Staying at 1,550° C. for 16.7% air; 900° C. for 2 hrs 10 hr. in argon PN-2 Newspaper, compacted, 250° C. for 2 hrs in Staying at 1,550° C. for 24.4% phosphoric acid added air; 900° C. for 2 hrs 10 hr. in argon

(34) The TEM image of a representative graphene material herein produced is shown in FIG. 2.

Comparative Example 1: Graphene Sheets (NGPs) from Oxidation/Intercalation of Graphite

(35) As an example, 20 mg of meso-phase pitch-derived artificial graphite of approximately 20 μm in size were used in the preparation of GO/GIC. Artificial graphite was dispersed in a mixture of sulfuric acid, nitric acid, and potassium permanganate at a weight ratio of 4:1:0.05 (graphite-to-intercalate ratio of 1:3) for 24 hours. Upon completion of the intercalation reaction, the mixture was poured into deionized water and filtered. The sample was then washed with 5% HCl solution to remove most of the sulfate ions and residual salt and then repeatedly rinsed with deionized water until the pH of the filtrate was approximately 5. The dried sample was then exfoliated in a tube furnace at 900° C. for 45 seconds.

(36) The graphene sheets obtained in each sample were examined using atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to determine their thickness (number of layers) and lateral dimensions (length and width). The graphene sheets suspended in water were cast onto a glass plate to form a thin film (2-5 μm thick) from each sample. The electrical conductivity of the thin film was measured using the four-point probe method. The experimental data indicate that the electrical conductivity of the graphene oxide film (after chemical reduction) is in the range of 30-300 S/cm. In contrast, the electrical conductivity of the graphene films produced according to the instant method is typically in the range of 500-4,500 S/cm.

(37) These data have clearly demonstrated the superiority of the presently invented direct graphitization method of producing graphene materials over conventional chemical methods of using oxidation/intercalation of graphite. Both methods are capable of producing single-layer graphene, but our presently invented method produces graphene sheets that are typically much more electrically conducting. The conventional Hummer's method and all other chemical oxidation/intercalation method necessarily involve highly oxidizing the graphitic material, creating damage (defects) to the resulting graphene sheets that could never be repaired or recovered. Even after heavy chemical reduction with hydrazine, the graphene material (a reduced graphene oxide) still exhibits an electrical conductivity one order of magnitude lower than that of the more pristine graphene produced by the present direct graphitization method.

(38) A wide variety of wood products and wood ingredients were also converted into graphene sheets using the presently invented method. The results are summarized in Table 2 below.

(39) TABLE-US-00002 TABLE 2 Production of graphene materials from different wood products or wood ingredients. Sample 1.sup.st and 2.sup.nd stage Graphitization Graphene No. Feedstock material treatments treatment yield WS-1 Wood saw dust, None Ramped to 2,800° C. in 20.4% compacted 2 hrs, staying for 2 hrs WS-2 Wood saw dust + 5% None Ramped to 2,800° C. in 34.6% phosphoric acid, 2 hrs, staying for 2 hrs compacted WS-3 Wood saw dust, 200-300° C. for 2 hrs in Staying at 2,800° C. for 24.5% compacted air; 1,200° C. for 2 hrs in 2 hrs argon WS-4 Wood saw dust + 5% 200-300° C., 2 hrs in air; Staying at 2,800° C. for 36.6% phosphoric acid, 1,200° C., 2 hrs in argon 2 hrs compacted WS-5 Wood saw dust + None Ramped to 2,800° C. in 38.7% phenolic resin binder 2 hrs, staying for 2 hrs WP-1 Wood pulp + wood 300° C. for 2 hrs in air; Staying at 2,800° C. for 36.2% saw dust, compacted, 1,100° C., 2 hrs in argon 2 hrs sodium acetate added WP-2 Wood pulp + wood 300° C. for 2 hrs in air; Staying at 2,800° C. for 28.5% saw dust, compacted 1,100° C., 2 hrs in argon 2 hrs CA-1 Cellulose acetate None Ramped to 3,050° C. in 34.4% 3 hrs, staying for 1 hr CA-2 Cellulose acetate + None Ramped to 3,050° C. in 41.3% polyimide binder 3 hrs, staying for 1 hr EC-1 Ethyl cellulose 250° C., 2 h HCl vapor; Staying at 3,050° C. for   41% 900° C., 2 hrs in argon 1 hr. RC-1 regenerated cellulose 250° C., 2 h HCl vapor; Staying at 3,050° C. for 52.3% 900° C., 2 hrs in argon 1 hr. HC-1 Hydroxyethyl 250° C., 2 hrs in air; Staying at 2,600° C. for 31.2% cellulose 1,000° C., 2 hrs in argon 2 hrs WH-1 Hemicellulose None Ramped to 2,600° C. in 24.6% 3 hrs, staying for 5 hr WH-2 Hemicellulose + None Ramped to 2,600° C. in 38.8% regenerated cellulose 3 hrs, staying for 5 hr WH-3 Hemicellulose 250° C., 2 hrs in air; Staying at 1,550° C. for 28.5% 900° C., 2 hrs in argon 10 hr. WL-1 Lignin 250° C. for 2 hrs in air; Staying at 2,550° C. for 18.4% 900° C., 2 hrs in argon 10 hr. WL-2 Lignin + regenerated 250° C. for 2 hrs in air; Staying at 2,550° C. for 29.3% cellulose + (50/50) 900° C., 2 hrs in argon 10 hr.

(40) In summary, the present invention provides an environmentally benign, eco-friendly, highly scalable, and potentially low cost method that can convert the discarded paper or wood products into highly value-added products—graphene. This method shall have a positive and significant impact to society and environment.