CARBON SOURCE

BACKGROUND OF INVENTION

Field of Invention

This disclosure relates generally to the field of carbon nanosheet structures with extremely high surface area and pore volume. Specifically, this disclosure relates to new eco-friendly and cost-effective methods of making carbon nanosheets and its related carbon network nanomaterials from a renewable resource.

Background Art

Carbon nanosheet is undoubtedly a critical raw material for emerging technologies because of its superior properties for a vast array of applications including printable electronics, catalysis, sensors, biomedical devices, and energy storage devices. A specialty two-dimensional (2D) layered carbon material called graphene comprises of hexagonal network of sp2 bonded carbon atoms in a crystalline form is the basic structure for fullerenes (OD), carbon nanotubes (ID), and graphite (3D). Graphene has

2 atoms per unit cell, hence two sub lattices [ 1]-[9] Graphene, the most preferred form of carbon nanostructure has extraordinary properties, which originates from its electronic configuration and sp2 bonding. This results in high carrier mobility, ambipolar electric field effect, high ballistic conduction of charge carriers, high surface area, ultra-high mechanical strength, excellent thermal conductivity, high elasticity, room temperature quantum Hall effect, unexpected high absorption of white light, gas adsorption, unusual magnetic properties, charge-transfer interactions with molecules, and tuneable electronic bad gap [5]-[30]

A major challenges with carbon nanosheet is how to produce high specific surface area material at commercial scale at low cost, and in reproducible manner. The common techniques for the production of graphene includes chemical vapor deposition, epitaxial growth on substrates, chemical reduction of exfoliated graphene oxide, and liquid phase exfoliation of graphite [31-32] All these method are remarkably expensive and utilized a non-renewable carbonaceous raw material as the starting material.

In 2004, Novoselov et al. used adhesive tape to peel off single-layer of graphene sheet

[14]-[15] These researchers subsequently demonstrated the superior electric field effect and room temperature quantum hall effect in exfoliated single layer graphene sheets, and received Nobel Prize in 2010 [1], [14]-[15] Although micromechanical exfoliation is not involve toxic chemicals, it is not ideal for commercial production of graphene, and as such several fundamental studies and prototype devices were obtained by using micromechanical cleavage graphene sheets [14] -[16].

Currently, liquid exfoliation of graphite is the most common process for making graphene based materials sold at the market place [31-40] Specifically, carbon nanosheet produced by Staudenmaier’s method and Hummer’s Staudenmaier’s as well as their modified methods have dominated the market place [38-40] Both methods use aggressive, expansive and utilize toxic chemicals to produce exfoliated carbon nanosheets with low specific surface area, about 600 m ² /g, which is a quarter of the theoretical surface of graphene (2630 m ² /g). Another concern is the toxic precursors used in these methods creates hazardous wastes [38]-[40]

In addition, current conventional manufacturing methods of graphene are complex with high cost of production, which results in expensive graphene products. This disclosure provides a cost effective and new method of making carbon nanosheets from a renewable carbon source, which unexpectedly resulted in nanomaterials with exceptional high specific surface area and pore volume.

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20 Oct. 2018. KTF-Split. 4 Nov. 2018

SUMMARY OF INVENTION

It is tiie object of this disclosure to provide a cheaper and eco-friendly method of producing carbon nanosheet from a renewable carbonaceous raw materials.

This disclosure provides a process that results in carbon nanosheet with undoubtedly superior combination of BET specific surface area (2956 m ² /g) and pore volume (5.0 cc/g) than ever reported previous; and also having an average pore diameter of 67.7

Angstroms, making its properties suitable for a vast array of applications including but not limited to catalysis, sensors, biomedical devices, and energy storage devices.

The intent of this summary is not to be a comprehensive description of the subject matter, but rather to provide a short overview of some of the subject matter's functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following figures and detailed claims. It is intended that all such additional systems, methods, features and advantages included within this description, be within the scope of the claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS)

FIG. 1 shows prior art of idealized structure of amylose and amylopectin (reference

41).

FIG. 2 depicts a schematic of removal of water molecules from glucose unit.

FIG. 3 shows a schematic of formation of a ring structure of carbon atoms with neighbouring unit.

FIG. 4 is a scanning electron micrograph of intermediate carbon produced after pretreatment of carbohydrate by this invention process.

FIG. 5 shows a scanning electron micrograph of carbon nanosheet prepared by exposing intermediate carbon product to microwave irradiation according to the inventive subject matter. FIG. 6 show's a scanning electron micrograph of carbon nanosheet obtained after thermal treatment at elevated temperature according to this invention.

FIG. 7 shows a scanning electron micrograph of carbon nanosheet prepared from com flour according to this invention.

FIG. 8 shows a scanning electron micrograph is carbon nanosheet prepared from com flour according to this invention.

FIG. 9 is an X-ray diffraction pattern of carbon nanosheet prepared from com flour according to this invention.

FIG. 10 shows an X-ray diffraction pattern of carbon nanosheet prepared from sucrose according to this inventive subject matter.

FIG. 11 shows scanning electron micrograph of carbon nanosheet prepared from sucrose according to this inventive subject matter.

FIG. 12 is a scanning electron micrograph showing carbon nanosheet prepared from cassava root extract by this invention.

FIG. 13 is a transmission electron micrograph showing detailed nanosheet prepared by tiiis invention from cassava root extract. FIG. 14 shows an X-ray diffraction pattern of carbon nanosheet prepared by this invention from cassava root extract.

FIG. 15 is an X-ray diffraction pattern of carbon nanosheet obtained from rice grain according to this inventive subject matter.

FIG. 16 shows a scanning electron micrograph of carbon nanosheet prepared by' this invention from rice grain.

FIG. 17 is a high resolution transmission electron micrograph showing carbon nanosheet prepared from rice grain according this embodiment.

FIG. 18 is a nitrogen gas adsorption isotherm of carbon nanosheet powder prepared by tins invention from rice grain.

FIG. 19 shows Brunauer, Emmett and Teller (BET) specific surface area data of carbon nanosheet produced from rice grain by this inventive subject matter.

FIG. 20 shows X-ray diffraction pattern of carbon nanosheet prepared by this invention from sucrose.

FIG. 21 shows a scanning electron micrograph of carbon nanosheet prepared by' tins invention from sucrose. FIG. 22 show's X-ray photoelectron survey spectrum of carbon nanosheet produced from cassava root extract according to this invention.

FIG. 23 shows high-resolution X-ray photoelectron spectrum of carbon nanosheet produced from cassava root extract according to this invention.

FIG. 24 display s high-resolution X-ray photoelectron spectrum of carbon nanosheet produced from cassava root extract according to this invention.

FIG. 25 shows Brunauer, Emmett and Teller (BET) specific surface area data of carbon nanosheet produced from cassava root extract by this inventive subject matter.

FIG. 26 is a nitrogen gas adsorption isotherm of carbon nanosheet powders produced from cassava root extract according to this inventive subject matter.

FIG. 27 shows a size distribution data of carbon nanosheet powders produced from cassava root extract according to this inventive subject matter.

FIG. 28 shows a micropore volume analysis data of carbon nanosheet powders produced from cassava root extract according to this inventive subject matter.

FIG. 29 is a high resolution transmission electron micrograph showing graphitic sheets of carbon produced from cassava root extract according to this inventive subject matter.

DETAILED DESCRIPTION OF INVENTION It has been discovered that carbon nanosheet with exceptional properties can be produced from a renewable carbonaceous raw materials such as cassava root extract, com flour, rice grain, wheat flour, yam root extract, potatoes root extract, sugar beet roots extract and sucrose (generally referred as carbohydrates). The process for making carbon nanosheet from these carbohydrates is described as follows:

First, said carbohydrate is placed in solvent containing water or ethylene glycol or ethanol to aid hydrolysis. This is followed by gradual removing of glycosidic linkages in the carbohydrate via chemical and thermal activation.

This pre-treatment step is critical for formation of intermediate fused carbon material which contains limited amount of glycosidic bonds, hydroxyl and carbonyl groups. Chemicals that were effective were chosen from a group consisting of sodium hydroxide, hydrochloric acid, phosphoric acid, phosphorous acid, and nitric add. In addition, catalyst such as yeast, aluminum-nickel alloy, cobalt, B ₂ H ₆ , zinc _, and copper were explored and tested for their effectiveness.

The mixture of carbonaceous material and chemical and/or catalyst were exposed to approximately 45 to 1050 degree C., in air or inert atmosphere to aid formation of fused carbon network with a sheet-like morphology, called intermediate carbon material.

The final major step will involve thermochemical activation of the intermediate carbon based material to initiate chemical bonding of carbon atoms to form hexagonal planar network of mainly sp2 hybridization carbons.

This occurs by at least switching oxygen atom and releasing hydroxyl portion of said intermediate carbon material to results in a short range or long range of aromatic ring structure or a or a mixture of both within the sheet is retained and other groups or molecules are released. This final step performed at temperature in the range of 500 to 1500 degree C., in an inert gas containing hydrogen gas. This results in a network of high surface area and pore volume sp2 bonded carbon nanosheet.

The resulting carbon nanosheet powders was typically washed with up to 10 volume % HC1 to remove any remaining precursors and catalyst in the final product; followed by heat treatment at 700 to 1500 degree C., in inert atmosphere.

Alternatively, die final steps in treating die intermediate carbon product to form mainly sp2 hybridization carbons can be accomplished via chemical process. Such as a process involves treating die intermediate carbon product with a chemical chosen from the group consisting of hydrazine, LiA1H ₄ , B ₂ H ₆ and NaBH ₄ ; preferably hydrazine and most preferably NaBH ₄ .

The process of producing carbon nanosheets in this disclosure start with a renewable carbonaceous raw materials such as cassava root extract, com flour, rice grain, wheat flour, and sucrose (generally referred as carbohydrates). These renewable carbonaceous materials contain high content of carbohydrates on water free basis, typically more than 70 % by weight. Each renewable carbonaceous material contains different percentage of glucose, and fructose bonded together by glycosidic linkages to form polymeric units such as amylose and amylopectin. Although the molecular formula for glucose and fructose are the same, thus (CeHnOe), they have different molecular structures. The structure of amylose and amylopectin, are well known and shown in FIG. 1.

In order to obtain a carbon nanosheet, each carbohydrate unit undergoes pre-treatment with a dehydration solution containing at least 1 % of acid or catalyst. The pretreatment results in an intermediate carbon material with dark-grey color made of up of fused sheet-like morphology. The mechanism unfolds in two stages. First, the treated carbohydrate via chemical and thermal activation results in hydrolysis and removal of the glycosidic linkages in the polymeric carbohydrate unit to form individual glucose and fructose units.

This is followed by a second mechanism to remove water molecules from each glucose or fructose unit by the dehydration solution as schematic described in FIG. 2.

This pretreatment is accomplished by gradually heating of the carbohydrate and hydration solution at 45 to 1050 degree C., preferably 80 degree C., for 36 hr. In the process, the carbon atoms rearrange to form a ring with neighbouring carbon atoms as illustrated in FIG. 3. The hydration solution intercalate the layers of carbon after ring formation giving rise to a layered structure. FIG. 4 shows scanning electron micrograph of this intermediate carbon product after pre-treatment.

The intermediate carbon product undergoes a second treatment to exfoliate the intercalated carbon layers. It was discovered that several thermal and chemical methods can be used to exfoliate the carbon sheet. Thermal methods involving direct heating of intermediate carbon material such as radiant heating in a resistive furnace, on top of hotplate, laser irradiation and microwave irradiation were effective for exfoliating carbon nanosheet and removing of water molecules to form mainly sp2 bonded carbon nanosheets.

FIG. 5 shows scanning electron micrograph of carbon nanosheet obtained after microwave irradiation of intermediate carbon materials. Thermal exfoliation via microwave heating removed substantial amount of H2O molecules from the intermediate carbon materials. Elemental analysis confirmed drastic reduction in oxygen content from in the intermediate carbon materials from 39.5 to 14.6 weight %.

Exfoliated carbon nanosheets were washed with 10 volume % HC1 to remove remaining hydration solution and catalyst compounds. Subsequently, the resulting product was washed with de-ionized water several times until the pH was about 7.

The resulting material was thermally treated at high temperatures in inert atmosphere to remove any groups attached to the nanosheet and terminate the ends with hydrogen.

FIG. 6 confirmed the carbon nanosheets retained its sheet-like morphology and carbon composition reached up to 94 weight %.

An alternate method of producing carbon nanosheets, the said carbohydrate was soaked in dehydration solution previously discussed. The mixture was directly exposed to rapid and uniform high temperature heating immediately after thorough and uniform mixing. This caused drastic removal of glycosidic bonds and release of water molecules, thereby forcing the resulting intermediate carbon materials to exfoliate in carbon nanosheet. Specifically, heating was accomplished by microwave irradiation or in oven preheated to at least 500 degree C. It was discovered this method yielded carbon nanosheet.

In another method in this invention, after thorough and uniform mixing of said carbohydrate and dehydration solution containing excess deionized water, this mixture was slowly heating to temperature below' 100 degree C. for held there for less than 24 hrs. The mixture formed a dark colored intermediate solution containing carbon. The dark intermediate solution was coated on a substrate to form thin films.

The resulting films was exposed to high temperatures in inert atmosphere containing at least 2 % by volume hydrogen gas. The films was slowly heating in the range of

700 - 1500 degree C., to form thin layer of conducting carbon nanosheet on substrate.

Several substrate were tested including copper foil, silicon wafer, glass slides and quartz substrate.

In a different aspect of this invention, the final carbon nanosheet powders were dried overnight in vacuum and compounded with polymer resins which resulted in composite having extraordinary properties. About 0.1 - 40.0 weight % of carbon nanosheet powder produced by this invention was used as filler in rubber and polymer resin such as high density polyethylene and polypropylene. The resulting nanocomposite exhibited improved strength and tolerance for chemical attack compared to the pure rubber or polymer resin.

The following examples are provided for the sake of concreteness, and only to illustrate selected aspects of the inventive subject matter herein and are not limiting the inventive concept presented herein, EXAMPLE 1

Preparation of Carbon Nanosheet from Com Flour

A total of 40.0 g of com flour was placed in a 500 mL Pyrex glass beaker. About

20.0 g of phosphorous acid was dissolved in 100 mL of deionized water and the resulting solution was added to the com flour. The mixture was stirred thoroughly and exposed to 80 °C for 36 hr., in a convection oven in air atmosphere. After heating, the sample formed an intermediate product, which was exposed to further heating on hotplate at 500 °C in air for 1 hr. The resulting product was washed thorough!}' in deionized to remove any unreacted precursors and followed by drying in an oven at 100

°C overnight.

The washed and dried sample was further heat treated in a tube furnace. About 10 g of sample was put in a porcelain combustion boat and placed inside quartz tube for thermal treatment. The reactor was connected with two mass flow meter/controller

(Alborg mass flow controllers) to monitor and control the flow rates of Ffe and Ar gases. All the mass flow controllers were turned on for 30 min to w'arm up and reach equilibrium temperature before flowing gases. The sample was ramped at 15 °C/min from 20 °C to 1050 °C and held at 1050 °C for 1 hr. The thermal treatment was carried out in a gas mixture containing 10 vol. % hydrogen gas in balance of argon, flowing at a total rate of 100 mL/rnin. Scanning electron micrograph of resulting nanosheet are presented in FIG. 7 and FIG. 8. X-ray diffraction pattern showed in FIG. 9 confirmed the final product is made-up of predominantly carbon nanosheets.

EXAMPLE 2

Preparation of Carbon Nanosheet from Sucrose A total of 100 g of sucrose was placed in a 500 mL Pyrex glass beaker. A 300 mL of solvent consisting 50 vol % of ethylene glycol and 50 vol. % deionized water was added to tire sucrose. The mixture was stirred thoroughly until all sucrose was dissolved in the solvent. About 25.0 g of phosphorous acid was added to the sucrose solution and exposed to 100 °C for 18 hr., in a convection oven in air atmosphere to form intermediate mixture.

The intermediate mixture was subjected to rapid and uniform heating for 10 minutes by using microwave irradiation (1000 W). The final solid product after microwave heating was washed thoroughly in 10 vol. % HC1 to remove any unreacted precursors and followed by drying in an oven at 100 °C overnight. X-ray diffraction pattern in

FIG. 10 and SEM image in FIG. 11 revealed the product is made of carbon sheets.

EXAMPLE 3

Preparation of Carbon Nanosheet from Cassava Extract

In this embodiment, about 50.0 g of phosphorous acid was dissolved in a 300 mL of solvent consisting 50 vol. % of ethanol and 50 vol. % deionized water. A total of 100 g of cassava extract was added to the solution and stirred thoroughly. The mixture was exposed to 100 °C for 24 hr., in a convection over in air atmosphere to form intermediate mixture.

After heating, the intermediate mixture was subjected to rapid and uniform heating for

10 minutes by using microwave irradiation (1000 W). The final solid product after microwave heating was washed thoroughly in 10 vol. % HC1 to remove any unreacted precursors and followed by drying in an oven at 100 °C overnight.

The washed and dried sample was further treated in a tube furnace to remove oxygen containing group from the sample. The sample was ramped at 15 °C/min from 20 °C to 1000 °C and held at 1000 °C for 1 hr. The thermal treatment was carried out in a gas mixture containing 50 vol. % argon and 50 vol. % hydrogen gas, flowing at a total rate of 1000 L/min. A typical sample size of 2 g was exposed to thermochemical treatment in the quartz reactor. FIG. 12 and FIG. 13 show scanning electron micrograph and transmission electron micrograph of carbon nanosheet prepared by this embodiment, respectively. Furthermore, X-ray diffraction data shows sample is made of carbon nanosheet due the low intensity of graphitic diffraction peaks in FIG.

14.

EXAMPLE 4

Preparation of Carbon Nanosheet from Rice Grain

In this embodiment, a total of 60 g of rice grain was washed thoroughly in 300 mL of deionized water. The rice grains were filtrated and added to 300 mL of phosphoric acid, and stirred thoroughly. The mixture was exposed to 100 °C for 24 hr in a convection oven in air atmosphere to form intermediate mixture.

A sample size of 40 g of intermediate mixture was put in a quartz combustion boat and placed inside quartz tube for heat treatment. The intermediate sample was ramped at 15 °C/min from 20 °C to 1000 °C and held at 1000 °C for 1 hr. The thermal treatment was carried out in a gas mixture containing 50 vol. % argon and 50 vol. % hydrogel gas, flowing at a total rate of 1000 L/min.

The final solid product after heating was washed thoroughly in 10 vol. % HC1 and rinsed with deionized water. This was followed by second heat treatment in inert atmosphere at 800 °C for 3 hr. FIG. 15 presents X-ray diffraction data of resulting carbon nanosheet. Scanning electron micrograph, FIG. 16, and transmission electron micrograph, FIG. 17, shows of carbon nanosheet prepared by this embodiment. Also, the gas adsorption data present in FIG. 18 and FIG. 19, show the final product has a specific surface area measurement of 2496 m ² /g and pore volume of 3.6 cc/g.

EXAMPLE S

Preparation of Carbon Nanosheet from Sucrose

A total of 100 g of sucrose was placed in a 500 mL Pyrex glass beaker. A 50 mL of deionized water was added to the sucrose and was stirred thoroughly until all sucrose was dissolved in the solvent. About 25.0 g of phosphoric acid was added to the sucrose solution and exposed to rapid and uniform heating for 10 minutes by using microwave irradiation (1000 W). The final solid product after microwave heating was w'ashed thoroughly in 10 vol. % HC1 to remove any unreacted precursors and followed by drying in an oven at 100 °C overnight. The presence of carbon nanosheet were confirmed by X-ray diffraction pattern, FIG. 20 and scanning electron micrograph, FIG. 21.

EXAMPLE 6

Preparation of Nanosheet from Cassava Root Extract

In this embodiment, a total of 60 g of cassava root extract was added to 200 mL of phosphoric acid, and stirred thoroughly. The mixture was exposed to 160 °C for 3 hr., in a convection oven in air atmosphere to form intermediate mixture.

A sample size of 40 g of intermediate mixture was put in a quartz combustion boat and placed inside quartz tube for heat treatment. The intermediate sample was ramped at 15 °C/min from 20 °C to 1000 °C and held at 1000 °C for 1 hr. The thermal treatment was carried out in a gas mixture containing 50 vol. % argon and 50 vol. % hydrogel gas, flowing at a total rate of 1000 L/min. The final solid product after heating was washed thoroughly in 10 vol. % HC1 and rinsed with deionized water. This was followed by second heat treatment in inert atmosphere at 800 °C for 3 hr. X-ray diffraction pattern of the resulting powder displayed in FIG. 21 shows extremely low diffraction peak intensities, confirming sample is made up of few layers of carbon nanosheets. In addition, X-ray photoelectron spectrum data presented in FIG. 22, FIG. 23 and FIG. 24 confirmed the resulting product has high carbon-carbon bonded content. The resulting product also has specific surface area of 2956 m ² /g and pore volume of 5.0 cc/g as validated by technical data presented in FIG. 25, FIG. 26, FIG. 27 and FIG. 28. Finally, FIG. 29 presents evidence of graphitic layers in the high resolution transmission electron micrograph of the resulting carbon nanomaterial prepared by this invention.