A thermochemical process for synthesizing a carbon nanomaterial

Abstract

A new process for synthesizing a carbon nanomaterial by thermochemically reducing an oxygenic carbon source under an ambient pressure, and an onset temperature in the range of 50 - 150 °C in the presence of a hydrogen abstractor, an ionic salt, and a solvent. Said carbon nanomaterial is selected from the group of a nanocrystalline carbon with a 1D, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof. The reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes.

Description

[0001] TITLE OF THE INVENTION

[0002] A THERMOCHEMICAL PROCESS FOR SYNTHESIZING A CARBON NANOMATERIAL

[0003] FIELD OF INVENTION

[0004] The present disclosure relates to the synthesis of a carbon nanomaterial, said carbon nanomaterial including a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof.

[0005] BACKGROUND OF THE INVENTION

[0006] Because of their excellent physical and electrical properties, carbon nanomaterials, including a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots (GQDs), N-doped graphene carbon dots (N-GQDs), and a combination thereof, are raw materials for a variety of specialized applications, especially in the electronic optoelectronic and electromagnetic industries. The demand for those carbon nanomaterials has been increasing and is unlikely to be satisfied by conventional production techniques.

[0007] Most conventional processes for synthesizing a carbon nanomaterial, particularly thermochemical processes, require considerably high-temperature conditions. The high thermal energy demand adversely affects the cost of synthesized carbon nanomaterial and the safety of the process. On the contrary, the processes conducted under mild conditions consume long processing time, which is not practical for industrial production.

[0008] US patent application No. US 2015 / 0284318 Al discloses a thermochemical process for preparing graphene quantum dots by pyrolyzing an organic starting material. This process requires a temperature within the range of 185 - 225 °C and thus consumes high energy.

[0009] US patent application No. US 2017 / 011396 Al presents a process that requires extremely high thermal energy to achieve a reaction temperature that is in the range of 500 - 1500 °C for converting biomass into carbon nanomaterials comprising a graphene and carbon nanotubes.

[0010] Additionally, Dong et al. (2014) reports the synthesis of N-doped carbon dots (N-CDs) by thermochemically reducing monoethanolamine at 250 °C, which requires high thermal energy. Although some other prior arts disclose processes for preparing carbon nanomaterials under mild conditions, the resulting synthesis of carbon nanomaterial may require as long as several days. Examples include Pang et al. (2018) which discloses a thermochemical reduction of citric acid for producing N-doped graphene quantum dots at 70 °C that takes 1,800 minutes to complete, and Dai et al. (2021) which provides a preparation of various nanocrystalline carbon allotropes at the room temperature, requiring the reaction time in the range of 7,200 - 20,160 minutes.

[0011] As such, achieving low energy consumption and high synthesis rate has been conventionally perceived as conflicting pursuits.

[0012] SUMMARY OF THE INVENTION

[0013] An object of the present invention is to provide a new process for preparing a carbon nanomaterial that addresses the problem of energy consumption while achieving the practical reaction time.

[0014] In the first aspect, the present invention provides a new process for synthesizing a carbon nanomaterial by thermochemically reducing an oxygenic carbon source. Said thermochemical reduction is carried out under an ambient pressure, and an onset temperature in the range of 50 - 150 °C, and in the presence of a hydrogen abstractor, an ionic salt, and a solvent. Said carbon nanomaterial is selected from the group of a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof. The reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes.

[0015] Said range of the onset temperature and ambient pressure are effects that distinguishes a process in accordance with the present invention from the previously available thermochemical reduction processes. Unlike the previously available processes, however, an embodiment’s substantially less energy-intensive operating conditions achieve excellent reaction times and yields.

[0016] In an embodiment, the yield of said carbon nanomaterial is in the range of 0.3 - 3 kg-L’ ^h .

[0017] The hydrogen abstractor is preferably a strong base or a compound that otherwise exhibits high affinity to a hydrogen atom or ion when dissolved in the respective solvent. In an embodiment, said hydrogen abstractor is selected from the group of a hydroxyl compound and a peroxide compound. Preferably, the concentration of the hydrogen abstractor is in the range of 1 - 10 M.

[0018] Preferably, the hydroxyl compound is potassium hydroxide. Also preferably, the peroxide compound is hydrogen peroxide.

[0019] In some embodiments, the thermochemical reduction occurs in presence of the hydrogen abstractor, the ionic salt, the solvent, and an acid. In such embodiments, the acid may be selected from the group of formic acid, acetic acid, and sulfuric acid. Preferably, the concentration of the acid is in the range of 0.1 - 1 M.

[0020] In an embodiment, said oxygenic carbon source is selected from the group of an oxygenic organic compound, a carbonate salt, and a bicarbonate salt.

[0021] Preferably, the concentration of the oxygenic carbon source is in the range of 0.001 - 10 M.

[0022] In an embodiment where the oxygenic carbon source is an oxygenic organic compound, it is preferable that such oxygenic organic compound is selected from the group of an amino acid, a sugar, a polypeptide, a phenolic compound, an amine, a carboxylic acid, an alcohol, a ketone, and an aldehyde.

[0023] More preferably, said amino acid is selected from the group of glycine, alanine, and aspartic acid. Also more preferably, said sugar is selected from the group of glucose and sucrose. Also more preferably, said polypeptide is gelatin. Also more preferably, said phenolic compound is tannic acid. Also more preferably, said amine is selected from the group of monoethanolamine and dimethylethanolamine. Also more preferably, said carboxylic acid is selected from the group of glycolic acid and citric acid. Also more preferably, said alcohol is glycerol. Also more preferably, said ketone is acetone. And also more preferably, said aldehyde is acetaldehyde.

[0024] In an embodiment where the oxygenic carbon source is a carbonate salt, it is preferable that such carbonate salt is sodium carbonate.

[0025] In an embodiment where the oxygenic carbon source is a bicarbonate salt, it is preferable that such bicarbonate salt is sodium bicarbonate.

[0026] In an embodiment, said ionic salt comprises an ammonium cation.

[0027] Preferably, the concentration of the ionic salt is in the range of 0.1 - 1 M.

[0028] Preferably, the ammonium cation is selected from the group of ammonium sulfate, choline chloride, and ammonium persulfate.

[0029] Preferably, the solvent is an inorganic solvent or a polar solvent. In the embodiments and Examples to be described below, water is preferred for its availability and low cost. In the second aspect, the present invention provides a new process for synthesizing a carbon nanomaterial by thermochemically reducing an oxygenic carbon source. Said thermochemical reduction is carried out under an ambient pressure, and an onset temperature in the range of 50 - 150 °C, and in the presence of a hydrogen abstractor, an ionic salt, a solvent, and a catalyst. Said carbon nanomaterial is selected from the group of a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof. The reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes.

[0030] Particularly, an embodiment according to the second aspect involves the presence of the catalyst.

[0031] In an embodiment, the yield of said carbon nanomaterial is in the range of 0.3 - 3 kg-L’ kh’1.

[0032] In an embodiment, said catalyst is a non-metallic catalyst. More preferably, the non- metallic catalyst is a carbon compound. Also more preferably, the non-metallic catalyst is graphene oxide.

[0033] Preferably, the non-metallic catalyst loading is in the range of 0.01 - 0.1 kg-L1.

[0034] The hydrogen abstractor is preferably a strong base or a compound that otherwise exhibits high affinity to a hydrogen atom or ion when dissolved in the respective solvent. In an embodiment, said hydrogen abstractor is selected from the group of a hydroxyl compound and a peroxide compound.

[0035] Preferably, the concentration of the hydrogen abstractor is in the range of 1 - 10 M.

[0036] Preferably, the hydroxyl compound is potassium hydroxide. Also preferably, the peroxide compound is hydrogen peroxide.

[0037] In some embodiments, the thermochemical reduction occurs in presence of the hydrogen abstractor, the ionic salt, the solvent, the catalyst, and an acid. In such embodiments, the acid may be selected from the group of formic acid, acetic acid, and sulfuric acid. Preferably, the concentration of the acid is in the range of 0.1 - 1 M.

[0038] In an embodiment, said oxygenic carbon source is selected from the group of an oxygenic organic compound, a carbonate salt, and a bicarbonate salt.

[0039] Preferably, the concentration of the oxygenic carbon source is in the range of 0.001 - 10 M.

[0040] In an embodiment where the oxygenic carbon source is an oxygenic organic compound, it is preferable that such oxygenic organic compound is selected from the group of an amino acid, a sugar, a polypeptide, a phenolic compound, an amine, a carboxylic acid, an alcohol, a ketone, and an aldehyde.

[0041] More preferably, said amino acid is selected from the group of glycine, alanine, and aspartic acid. Also more preferably, said sugar is selected from the group of glucose and sucrose. Also more preferably, said polypeptide is gelatin. Also more preferably, said phenolic compound is tannic acid. Also more preferably, said amine is selected from the group of monoethanolamine and dimethylethanolamine. Also more preferably, said carboxylic acid is selected from the group of glycolic acid and citric acid. Also more preferably, said alcohol is glycerol. Also more preferably, said ketone is acetone. And also more preferably, said aldehyde is acetaldehyde.

[0042] In an embodiment where the oxygenic carbon source is a carbonate salt, it is preferable that such carbonate salt is sodium carbonate.

[0043] In an embodiment where the oxygenic carbon source is a bicarbonate salt, it is preferable that such bicarbonate salt is sodium bicarbonate.

[0044] In an embodiment, said ionic salt comprises an ammonium cation.

[0045] Preferably, the concentration of the ionic salt is in the range of 0.1 - 1 M.

[0046] Preferably, the ammonium cation is selected from the group of ammonium sulfate, choline chloride, and ammonium persulfate.

[0047] Preferably, the solvent is an inorganic solvent or a polar solvent. In the embodiments and Examples to be described below, water is preferred for its availability and low cost.

[0048] In the third aspect, the present invention provides a new method for catalyzing a thermochemical reduction process for producing a carbon nanomaterial. Said carbon nanomaterial is selected from the group of a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof. Said method involves heating a solution comprising a hydrogen abstractor and a carbonaceous catalyst in order to form an active site upon the carbonaceous catalyst’s surface.

[0049] The present inventor has also discovered the foregoing application of the catalytic mechanism to the production of a carbon nanomaterial and found the results surprising and excellent. Said application is integrally related to the second aspect of the present invention. The particulars of said catalytic mechanism and confirmatory experiments will be further described in the Detailed Description.

[0050] Preferably, the hydrogen abstractor is selected from the group of a hydroxyl compound and a peroxide compound. Preferably, the solution further comprises an ionic salt.

[0051] Preferably, the ionic salt comprises an ammonium cation.

[0052] Preferably, the concentration of the ionic salt is in the range of 0.1 - 1 M.

[0053] More preferably, the ammonium cation is selected from the group of ammonium sulfate, choline chloride, and ammonium persulfate.

[0054] Accordingly, the present disclosure provides examples to illustrate the conditions of such processes and the characteristic properties of such products. The preferred embodiments will be described in detail later on.

[0055] BRIEF DESCRIPTION OF DRAWINGS

[0056] Fig. 1A shows a schematic diagram of a thermochemical reactor for thermochemically reducing an oxygenic carbon source in accordance with the first aspect of the present invention (not to scale).

[0057] Fig. IB shows a schematic diagram of a thermochemical reactor for thermochemically reducing an oxygenic carbon source in accordance with the second and third aspects of the present invention (not to scale).

[0058] Fig. 2A shows a Raman spectrum exhibiting merged peaks of a product of Example 1.

[0059] Fig. 2B shows a Transmission Electron Microscopy (TEM) image of the product of Example 1.

[0060] Fig. 2C shows Energy Dispersive X-ray (EDX) peaks of the product of Example 1.

[0061] Fig. 2D shows X-ray diffraction (XRD) peaks of the product of Example 1.

[0062] Fig. 3 shows a Raman spectrum exhibiting merged peaks of the product of Example 2.

[0063] Fig. 4 shows a Raman spectrum exhibiting merged peaks of the product of Example 3.

[0064] Fig. 5 shows a Raman spectrum exhibiting merged peaks of the product of Example 4.

[0065] Fig. 6 shows a Raman spectrum exhibiting merged peaks of the product of Example 5.

[0066] Fig. 7 shows a Raman spectrum exhibiting merged peaks of the product of Example 6.

[0067] Fig. 8 shows a Raman spectrum exhibiting merged peaks of the product of Example 7.

[0068] Fig. 9 shows a Raman spectrum exhibiting merged peaks of the product of Example 8.

[0069] Fig. 10A shows a Raman spectrum exhibiting merged peaks of the product of Example 9.

[0070] Fig. 10B shows a Transmission Electron Microscopy (TEM) image of the product of Example 9. Fig. IOC shows a Fourier Transform Infrared (FT-IR) Spectrum exhibiting peaks of chemical bonds in the product of Example 9.

[0071] Fig. 10D shows a Photoluminescence Spectrum exhibiting color spectrum of the product of Example 9.

[0072] Fig. 11 shows a Photoluminescence Spectrum exhibiting color spectrum of the product of Example 10.

[0073] Fig. 12 shows a Photoluminescence Spectrum exhibiting color spectrum of the product of Example 11.

[0074] Fig. 13 shows a Photoluminescence Spectrum exhibiting color spectrum of the product of Example 12.

[0075] Fig. 14A shows a Raman spectrum exhibiting merged peaks of the product of Example 13.

[0076] Fig. 14B shows a Transmission Electron Microscopy (TEM) image of the product of Example 13.

[0077] Fig. 14C shows Energy Dispersive X-ray (EDX) peaks of the product of Example 13.

[0078] Fig. 14D shows X-ray diffraction (XRD) peaks of the product of Example 13.

[0079] Fig. 15 shows a Raman spectrum exhibiting merged peaks of the product of Example 14.

[0080] Fig. 16 shows a Raman spectrum exhibiting merged peaks of the product of Example 15.

[0081] Fig. 17 shows a Raman spectrum exhibiting merged peaks of the product of Example 16.

[0082] Fig. 18 shows a Raman spectrum exhibiting merged peaks of the product of Example 17.

[0083] Fig. 19A shows a Raman spectrum exhibiting merged peaks of the product of Example 18.

[0084] Fig. 19B shows a Transmission Electron Microscopy (TEM) image of the product of Example 18.

[0085] Fig. 19C shows a Fourier Transform Infrared (FT-IR) Spectrum exhibiting peaks of chemical bonds in the product of Example 18.

[0086] Fig. 19D shows a Photoluminescence Spectrum exhibiting color spectrum of the product of Example 18.

[0087] Fig. 20 shows a Photoluminescence Spectrum exhibiting color spectrum of a product of Example 19.

[0088] Fig. 21 shows a Photoluminescence Spectrum exhibiting color spectrum of a product of Example 20. Fig. 22 shows a Photoluminescence Spectrum exhibiting color spectrum of a product of Example 21.

[0089] Fig. 23 shows a Photoluminescence Spectrum exhibiting color spectrum of a product of Comparative Example 1.

[0090] Fig. 24 shows a Photoluminescence Spectrum exhibiting color spectrum of a product of Comparative Example 2.

[0091] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0092] It is to be understood that the following detailed description will be directed to embodiments, provided as examples for illustrating the concept of the present invention only. The present invention is in fact not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of this invention will be limited only by the appended claims.

[0093] The detailed description of the invention is divided into various sections only for the reader’s convenience and disclosure found in any section may be combined with that in another section.

[0094] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0095] It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0096] The term “about” when used before a numerical designation, e.g., dimensions, time, amount, and such other, including a range, indicates approximations which may vary by ( + ) or ( - ) 10 %, 5 % or 1 %, or any sub-range or sub-value there between.

[0097] “Comprising” or “comprises” is intended to mean that the compositions and processes include the recited elements, but not excluding others. “Consisting essentially of’ when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination for the stated purpose. Thus, a process or product consisting essentially of the elements as defined herein would not exclude other materials or steps that do not materially affect the basic and novel characteristic(s) of the claimed invention. “Consisting of’ shall mean excluding more than trace elements of other ingredients and substantial steps. Embodiments defined by each of these transition terms are within the scope of this invention. “Oxygenic carbon source” is intended to mean a mono-molecular, polymeric or ionic compound containing both carbon and oxygen atoms.

[0098] “Oxygenic organic compound” is intended to mean a mono-molecular or polymeric organic compound having an oxygen atom.

[0099] “Hydrogen abstractor” is intended to mean a compound or an ion which can abstract (i.e., effectively compete for the chemical bonding with) a hydrogen atom or a hydrogen ion of another hydrogen-containing compound. In the below exemplary embodiments, a hydrogen abstractor is generally used to separate a hydrogen atom or ion from an oxygenic carbon source or its intermediate compound, and then to bind with said hydrogen atom or ion, whether temporarily or permanently.

[0100] Thermochemical reactor

[0101] Fig. 1A shows a schematic diagram of a thermochemical reactor in which a process for synthesizing a carbon nanomaterial is conducted in accordance with the first aspect of the present invention. The thermochemical reactor (10) comprises a receptacle (100), a heating element (200), a stirrer (300), and a vent (400). The receptacle (100) contains a solution (110). The solution (110) is a mixture of a hydrogen abstractor, an ionic salt, and a solvent in which an oxygenic carbon source is dissolved. The heating element (200), the source of thermal energy, is preferably connected to the lower part or the bottom of the receptacle (100) and configured to heat the solution (110). The stirrer (300) is preferably disposed so as to immerse in the solution (110). In the preferred embodiment, the stirrer (300) takes the form of a propeller having a shaft (310), an end of which is connected to multiple blades (320), and another end of which, to a motor (330). The shaft (310) is disposed substantially vertically so that the blades (320) are effectively immersed in the solution (110) and the motor (330) is located away from the solution (110). The vent (400), through which the gaseous byproducts leave the receptacle (100), is preferably located at the top of the receptacle (100).

[0102] Fig. IB shows a schematic diagram of a thermochemical reactor in which a process for synthesizing a carbon nanomaterial is conducted in accordance with the second and third aspects of the present invention. The thermochemical reactor (10) comprises a receptacle (100), a heating element (200), a stirrer (300), and a vent (400). The receptacle (100) contains a solution (110) in which non-metallic particles (120) are present and act as a heterogeneous catalyst. The solution (110) is a mixture of a hydrogen abstractor, an ionic salt, and a solvent in which an oxygenic carbon source is dissolved. In the preferred embodiment, the non-metallic particles (120) are a carbonaceous catalyst consisting essentially of a carbon compound, particularly graphene oxide. The heating element (200), the source of thermal energy, is preferably connected to the lower part or the bottom of the receptacle (100) and configured to heat the solution (110). The stirrer (300) is preferably disposed so as to immerse in the ionic solution (110) and configured to disperse non-metallic particles (120) in the solution (110). In this preferred embodiment, the stirrer (300) takes the form of a propeller having a shaft (310), an end of which is connected to multiple blades (320), and another end of which, to a motor (330). The shaft (310) is disposed substantially vertically so that the blades (320) are effectively immersed in the solution (110) and the motor (330) is located away from the solution (110). The vent (400), through which the gaseous byproducts leave the receptacle (100), is preferably located at the top of the receptacle (100).

[0103] Oxygenic carbon source

[0104] In an embodiment, an oxygenic carbon source is used as a carbon source for forming a carbon nanomaterial. The oxygenic carbon source is selected from the group of an oxygenic organic compound, a carbonate salt, and a bicarbonate salt. Preferably, the concentration of the oxygenic carbon source is in the range of 0.001 - 10 M. Preferably, the oxygenic organic compound is selected from the group of an amino acid, a sugar, a polypeptide, a phenolic compound, an amine, a carboxylic acid, an alcohol, a ketone, and an aldehyde. More preferably, the amino acid is selected from the group of glycine, alanine, and aspartic acid. Also more preferably, the sugar is selected from the group of glucose and sucrose. Also more preferably, the polypeptide is gelatin. Also more preferably, the phenolic compound is tannic acid. Also more preferably, the amine is selected from the group of monoethanolamine and dimethylethanolamine. Also more preferably, the carboxylic acid is selected from the group of glycolic acid and citric acid. Also more preferably, the alcohol is glycerol. Also more preferably, the ketone is acetone. And also more preferably, the aldehyde is acetaldehyde. Preferably, the carbonate salt is sodium carbonate. And preferably, the bicarbonate salt is sodium bicarbonate.

[0105] Hydrogen abstractor

[0106] In an embodiment, a hydrogen abstractor is used to separate a hydrogen atom or ion from the oxygenic carbon source or an intermediate compound during the formation of the carbon nanomaterial. The hydrogen abstractor is selected from the group of a hydroxyl compound and a peroxide compound. Preferably, the concentration of the hydrogen abstractor is in the range of 1 - 10 M. Preferably, the hydroxyl compound is potassium hydroxide. Also preferably, the peroxide compound is hydrogen peroxide.

[0107] Add as a protonation promoter In a preferred embodiment, an acid is added to and mixed with the solution to promote the protonation of an oxygenic functional group of the oxygenic carbon source. The acid may be selected from the group of formic acid, acetic acid, and sulfuric acid. Preferably, the concentration of the acid is in the range of 0.1 - 1 M.

[0108] Catalyst

[0109] In some embodiments, the oxygenic carbon source is thermochemically reduced in the presence of a catalyst. In those embodiments, the catalyst is preferably a non-metallic catalyst. More preferably, the non-metallic catalyst is a carbonaceous catalyst which most preferably consists essentially of a carbon compound or graphene oxide. Preferably, the non-metallic catalyst loading is in the range of 0.01 - 0.1 kg-L1. The present inventor theorizes that the present catalytic activities follow the below mechanism.

[0110] In embodiments involving a catalyst, heating the solution to the onset temperature (see further below for details) initiates the reaction between the catalyst and the hydrogen abstractor, thereby partially decomposing the catalyst’s surface. The decomposition causes the catalyst to release oxygen gas, and forms, upon the catalyst’s surface, the active sites which are favorable to the intended synthesis of carbon nanomaterial.

[0111] In such embodiments, the active sites act as catalytic sites at which the conversion of the oxygenic carbon source into elemental carbon is accelerated, as well as nucleation sites at which the nanocarbon material is formed from such elemental carbon. Most of the carbon nanomaterials of which nuclei have been sufficiently developed would naturally dissociate from their respective active sites. Both said roles contribute to the yield of carbon nanomaterial synthesis.

[0112] Depending on the reaction conditions, including the nature and concentration of the oxygenic carbon source, some embodiments require the catalyst to proceed, while others can proceed without the catalyst yet proceed more favorably in presence of the catalyst. The Examples further below will describe exemplary embodiments to illustrate these effects.

[0113] In particular embodiments where the catalyst is carbonaceous, carbon element and / or a carbon oxide compound is released along with the oxygen gas. In such embodiments, the release of oxygen gas or carbon oxide compound also frees the valence electrons of the carbon atoms at or nearby the active site. Those free valence electrons make the active sites, particularly the vacant ones, susceptible to the self-healing process whereby those carbon atoms bond with other carbon atoms of a similar electronic state, thereby closing some active sites and making them unavailable for catalytic activities. Said unfavorable self-healing process may be favorably retarded by the ionic salt, to be discussed in the next section.

[0114] After the thermochemical reduction, the catalyst is separated from the solution by a known separation process. Preferably, said separation process is filtration.

[0115] Ionic salt

[0116] Preferably, the ionic salt comprises an ammonium cation. And preferably, the ammonium cation is selected from the group of ammonium sulfate, choline chloride, and ammonium persulfate. Preferably, the concentration of the ionic salt is in the range of 0.1 - 1 M.

[0117] The advantages enabled by the ionic salt according to the concept of the present invention are twofold.

[0118] In an embodiment with or without a catalyst, the presence of the ionic salt stabilizes the nuclei of the carbon nanomaterial being synthesized, thereby promoting the yield of the carbon nanomaterial. The present inventor theorizes that the said stabilization is caused by the electrostatic interaction between the ionic salt’s cation and the carbon nuclei.

[0119] In an embodiment with a carbonaceous catalyst, exposing the catalyst to the ionic salt retards the unfavorable self-healing process on the catalyst’ s surface (see detail in the preceding section), thereby effectively promoting the active sites’ availability and the yield. The present inventor theorizes that the said retardation is caused by the electrostatic interaction between the ionic salt’s cation and the carbon atoms at or nearby the active site.

[0120] Pressure

[0121] A process according to the concept of the present invention may be carried out in various conditions which may be adjusted according to the circumstantial requirements.

[0122] The pressure in accordance with a preferred embodiment is an ambient pressure. The ambient pressure refers to a common or usual condition surrounding any person in a room. An ambient pressure for operating the process is preferably 1 atm. Because a process in accordance with a preferred embodiment allows the catalytic thermochemical reduction to occur effectively at such ambient pressure, it obviates the need to pressurize, depressurize, vacuumize or control the pressure at any part of the thermochemical reactor and thus substantially simplifies the production.

[0123] Onset temperature

[0124] Generally, the onset temperature of the thermochemical reactor is at least of the thermal energy sufficient to initiate the thermochemical reduction of the oxygenic carbon source. Preferably, the onset temperature of the solution is substantially constant during the thermochemical reduction.

[0125] The onset temperature of the thermochemical reactor depends on the oxygenic carbon source, the hydrogen abstractor and the ionic salt being selected. In an embodiment, the thermochemical reactor comprises a heating element to provide the onset temperature, which is preferably in the range of 50 - 150 °C.

[0126] Preferably, the heating element is adapted to monitor and control the onset temperature. In the following Examples, the thermochemical reduction occurred in an autoclave which was capable of both monitoring and regulating the onset temperature. An autoclave is commonly used as an industry-scale thermochemical reactor, which is applicable to the concept of the present invention.

[0127] Reaction time

[0128] In a preferred embodiment, the thermochemical reduction occurs in the thermochemical reactor as a batch operation. The structure and type of synthesized carbon nanomaterial depends on the oxygenic carbon source, the hydrogen abstractor and the ionic salt used, the thermal energy applied, and the reaction time.

[0129] Because the thermochemical reduction in accordance with an embodiment is an exothermic reaction, its effective termination may be observed through the cessation of heat release. Consequently, the reaction time of an embodiment may be determined by the duration from the time at which the onset temperature has been reached until the time at which the thermochemical reduction effectively terminates. Further, an embodiment’s yield may be determined based on said reaction time.

[0130] The preferred reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes, and the yield of said carbon nanomaterial is in the range of 0.3 - 3 kg-L^-h1.

[0131] Carbon nanomaterial

[0132] The carbon nanomaterial obtained from the process in accordance with a preferred embodiment is selected from the group of a nanocrystalline carbon with a ID, 2D, or 3D structure, a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N-doped graphene quantum dots, and a combination thereof.

[0133] In some embodiments, the carbon nanomaterial being produced is further separated from the solution by a known separation process. Preferably, said separation process comprising evaporation or filtration such as dialysis. After being separated from the solution, the carbon product may contain salt residues originating from the ionic salt, which can be further removed from the carbon nanomaterial by means of a conventional removal process, preferably washing with deionized water (DI water).

[0134] Examples of embodiments

[0135] In the twenty-one Examples and two Comparative Examples carried out for the preferred embodiment, the following applies:

[0136] The thermochemical reductions of oxygenic carbon sources took place in a batch thermochemical reactor (10). The thermochemical reactor (10) further contained the solution (110), said solution is mixture of the hydrogen abstractor, the ionic salt, and the solvent in which the oxygenic carbon source is dissolved. In all Examples, the solvent was DI water. In some Examples, an acid was added to the solution (110) along with the hydrogen abstractor to promote protonation. In some Examples, the non-metallic particles (120), consisting essentially of graphene oxide, was added to the solution (110) as a heterogeneous, carbonaceous catalyst. In those Examples, the non-metallic particles (120) were stirred by a stirrer (130) to promote their dispersion in the solvent (110). The onset temperature was generated, controlled, and measured by the heating element (200). The reaction was carried out under ambient pressure until its effective termination was observed. The resulting carbon nanomaterial was subsequently removed from the solution (110) and separated by evaporation or dialysis. The carbon nanomaterial synthesized and separated thus was subsequently washed with DI water.

[0137] In Examples 1 - 8 wherein the thermochemical reduction for producing graphitic carbon and amorphous carbon took place in the absence of the catalyst, the oxygenic carbon source, the hydrogen abstractor, the ionic salt, and the solvent were mixed and stirred by the stirrer at the room temperature and ambient pressure. Among those Examples, acids were added into the solutions of Examples 3, 4 and 8. After that, the solution was heated to the onset temperature while the solution was being stirred. Once the solution’s temperature reached the onset temperature, the reaction proceeded for no longer than 10 minutes until its effective termination was observed. Then, the graphitic carbon and amorphous carbon were separated from the solution by placing the solution in an oven at 270 °C for 1 - 4 hours to evaporate the solvent and decompose the ionic salt. Finally, the graphitic carbon and amorphous carbon were washed with DI water and subsequently dried at 110 °C for 1 - 4 hours to remove the remaining ionic salt residues.

[0138] In Examples 9 - 12 wherein the thermochemical reduction for producing graphene quantum dots took place in the absence of the catalyst, the oxygenic carbon source, the hydrogen abstractor, the ionic salt, and the solvent, were mixed and stirred by the stirrer at the room temperature and ambient pressure. Among those Examples, acids were added into the solutions of Examples 9 and 10. After that, the solution was heated to the onset temperature while the solution was being stirred. Once the solution’s temperature reached the onset temperature, the reaction proceeded for no longer than 10 minutes until its effective termination was observed. Then, the graphene quantum dots were separated from the solution by dialysis using a Spectra / Por cellulose membrane having the molecular weight cutoff (MWCO) rating of 1 kDa in DI water for 2 days, during which DI water was changed 4 times. Finally, the graphene quantum dots were heated at 110 °C for 1 - 4 hours to evaporate the solvent.

[0139] In Examples 13-17 wherein the thermochemical reduction for producing graphitic carbon and amorphous carbon took place in the presence of the catalyst, the oxygenic carbon source, the hydrogen abstractor, the ionic salt, the solvent, and the catalyst, were mixed and stirred by the stirrer at the room temperature and ambient pressure. After that, the solution was heated to the onset temperature while the solution was being stirred. Once the solution’s temperature reached the onset temperature, the reaction proceeded for no longer than 10 minutes until its effective termination was observed. After the reaction, the catalyst was filtered from the solution by a filter paper. Then, the graphitic carbon and amorphous carbon were separated from the solution by placing the solution in an oven at 270 °C for 1 - 4 hours to evaporate the solvent and decompose the ionic salt. Finally, the graphitic carbon and amorphous carbon were washed with DI water and subsequently dried at 110 °C for 1 - 4 hours to remove the remaining ionic salt residues.

[0140] In Examples 18-21 wherein the thermochemical reduction for producing graphene quantum dots took place in the presence of the catalyst, the oxygenic carbon source, the hydrogen abstractor, the ionic salt, and the solvent, were mixed and stirred by the stirrer at the room temperature and ambient pressure. Among those Examples, acids were added into the solutions of Examples 18 and 19. After that, the solution was heated to the onset temperature while the solution was being stirred. Once the solution’s temperature reached the onset temperature, the reaction proceeded for no longer than 10 minutes until its effective termination was observed. After the reaction, the catalyst was filtered from the solution by a filter paper. Then, the graphene quantum dots were separated from the solution by dialysis using a Spectra / Por cellulose membrane having the molecular weight cutoff (MWCO) rating of 1 kDa in DI water for 2 days, during which DI water was changed 4 times. Finally, the graphene quantum dots were heated at 110 °C for 1 - 4 hours to evaporate the solvent. Comparative Example 1 was DI water used for reference of product characterization.

[0141] Comparative Example 1 involved no other material or chemical reaction.

[0142] Comparative Example 2 followed the steps and reaction conditions as described in accordance with Example 18, except without the catalyst. Unless specified otherwise and except the DI water, the chemicals and materials used in the foregoing Examples and Comparative Examples were purchased from Sigma Aldrich.

[0143] Table 1 in the next sheet shows the particulars of Examples 1-21 and Comparative Examples 1 - 2. Description of the product obtained from each Example shall follow Table 1.

[0144]

[0145] Example 1 produced a carbon nanomaterial in the form of N-doped graphitic carbon and amorphous carbon. Fig. 2A shows the Raman spectrum of the product of Example 1. Moreover, the Transmission Electron Microscopy (TEM) is shown in Fig. 2B. Next, the peaks from the Energy Dispersive X-ray (EDX) analysis, shown in Fig. 2C, revealed the following atomic percentages of said product: 83.1 % carbon; 8.41 nitrogen; 5.25 % oxygen; and 3.24 % sulfur. Finally, the X-ray diffraction (XRD) analysis revealed the diffraction peak at around 29 = 27 degrees representing (002) plane of graphite, as shown in Fig. 2D. All the foregoing results confirmed that the product of Example 1 comprised N-doped graphitic carbon and amorphous carbon structures.

[0146] Example 2 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 3, as observed from the shown Raman spectrum, the carbon product obtained from Example 2 comprised graphitic carbon, and amorphous carbon structures.

[0147] Example 3 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 4, as observed from the shown Raman spectrum, the carbon product obtained from Example 3 comprised graphitic carbon, and amorphous carbon structures.

[0148] Example 4 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 5, as observed from the shown Raman spectrum, the carbon product obtained from Example 4 comprised graphitic carbon, and amorphous carbon structures.

[0149] Example 5 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 6, as observed from the shown Raman spectrum, the carbon product obtained from Example 5 comprised graphitic carbon, and amorphous carbon structures.

[0150] Example 6 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 7, as observed from the shown Raman spectrum, the carbon product obtained from Example 6 comprised graphitic carbon, and amorphous carbon structures.

[0151] Example 7 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 8, as observed from the shown Raman spectrum, the carbon product obtained from Example 7 comprised graphitic carbon, and amorphous carbon structures. Example 8 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 9, as observed from the shown Raman spectrum, the carbon product obtained from Example 8 comprised graphitic carbon, and amorphous carbon structures.

[0152] Example 9 produced a carbon nanomaterial in the form of N-doped graphene quantum dots. Fig. 10A shows the Raman spectrum of the product of Example 9. Moreover, the Transmission Electron Microscopy (TEM) is shown in Fig. 10B. Next, the Fourier Transform Infrared Spectrum (FT-IR), as shown in Fig. IOC, revealed the broad peak in the range of 2600 - 3400 cm1representing O-H and N-H bonds, the peak at 1700 cm1representing C=O bond in the carboxyl group, the peaks at 1341.5 and 1203.4 cm1representing C-N bond, and the peaks at 1287.2 and 1166.2 cm1representing C-0 bond. Finally, the Photoluminescence Spectrum revealed a broad and strong fluorescence spectrum having the center located at 475 nm, as shown in Fig. 10D, indicating emission of more than one color, including spectrums of blue, green, and yellow colors. The sum of said spectrums was visible to the human observer’s eyes in sea-green color. All the foregoing results confirmed that the product of Example 9 comprised N-doped graphene quantum dots comprising hydroxyl, carboxylic, and amine functional groups; and that the synthesized N-doped graphene quantum dots were blue, green, and yellow N-doped graphene quantum dots.

[0153] Example 10 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 11, the Photoluminescence Spectrum revealed a strong fluorescence spectrum having the center located at 463 nm, which matched the spectrum of blue color. Said spectrum was visible to the human observer’s eyes in blue color. The above result confirmed that the product of Example 10 comprised blue graphene quantum dots.

[0154] Example 11 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 12, the Photoluminescence Spectrum revealed a strong fluorescence spectrum having the center located at 418 nm, which matched the spectrum of blue color. Said spectrum was visible to the human observer’s eyes in blue color. The above result confirmed that the product of Example 11 comprised blue graphene quantum dots.

[0155] Example 12 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 13, the Photoluminescence Spectrum revealed a strong fluorescence spectrum having the center located at 439 nm, which matched the spectrum of blue color. Said spectrum was visible to the human observer’s eyes in blue color. The above result confirmed that the product of Example 12 comprised blue graphene quantum dots. Example 13 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. Fig. 14A shows the Raman spectrum of the product of Example 13. Moreover, the Transmission Electron Microscopy (TEM) is shown in Fig. 14B. Next, the peaks from the Energy Dispersive X-ray (EDX) analysis, shown in Fig. 14C, revealed the following atomic percentages of said product: 99.46 % carbon and 0.54 % oxygen. Finally, the X-ray diffraction (XRD) analysis revealed the diffraction peak at around 29 = 27 degrees representing (002) plane of graphite, as shown in Fig. 14D. All the foregoing results confirmed that the product of Example 13 comprised graphitic carbon and amorphous carbon structures.

[0156] Example 14 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 15, as observed from the shown Raman spectrum, the carbon product obtained from Example 14 comprised graphitic carbon and amorphous carbon structures.

[0157] Example 15 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 16, as observed from the shown Raman spectrum, the carbon product obtained from Example 15 comprised graphitic carbon and amorphous carbon structures.

[0158] Example 16 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 17, as observed from the shown Raman spectrum, the carbon product obtained from Example 16 comprised graphitic carbon and amorphous carbon structures.

[0159] Example 17 produced a carbon nanomaterial in the form of graphitic carbon and amorphous carbon. According to Fig. 18, as observed from the shown Raman spectrum, the carbon product obtained from Example 17 comprised graphitic carbon and amorphous carbon structures.

[0160] Example 18 produced a carbon nanomaterial in the form of N-doped graphene quantum dots. Fig. 19A shows the Raman spectrum of the product of Example 18. Moreover, the Transmission Electron Microscopy (TEM) is shown in Fig. 19B. Next, the Fourier Transform Infrared Spectrum (FT-IR), as shown in Fig 19C, revealed the broad peak in the range of 2600 - 3400 cm1representing O-H and N-H bonds, the peak at 1766 cm1representing C=O bond, the peak at 1578 cm1representing N-H bond, the peaks in the range of 1276 - 1425 cm1representing C-N and C-0 bonds, and the peak at 1081 cm1representing C-0 bond. Finally, the Photoluminescence Spectrum revealed a broad and strong fluorescence spectrum having the center located at 497 nm, as shown in Fig 19D, indicating emission of more than one color, including spectrums of blue, green, and yellow colors. The sum of said spectrums was visible to the human observer’s eyes in lemon-yellow color. All the foregoing results confirmed that the product of Example 18 comprised N-doped graphene quantum dots comprising hydroxyl, carboxylic and amine functional groups; and that the synthesized N-doped graphene quantum dots were blue, green, and yellow N-doped graphene quantum dots.

[0161] Example 19 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 20, the Photoluminescence Spectrum revealed a strong fluorescence spectrum having the center located at 453 nm, which matched the spectrum of blue color. Said spectrum was visible to the human observer’s eyes in blue color. The above result confirmed that the product of Example 19 comprised blue graphene quantum dots.

[0162] Example 20 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 21, the Photoluminescence Spectrum revealed a strong fluorescence spectrum having the center located at 469 nm, which matched the spectrum of blue color. Said spectrum was visible to the human observer’s eyes in blue color. The above result confirmed that the product of Example 20 comprised blue graphene quantum dots.

[0163] Example 21 produced a carbon nanomaterial in the form of graphene quantum dots. According to Fig. 22, the Photoluminescence Spectrum revealed a broad and strong fluorescence spectrum having the center located at 561 nm, indicating emission of more than one color, including spectrums of blue, green, and yellow colors. The sum of said spectrums was visible to the human observer’s eyes in green-yellow color. The above result confirmed that the product of Example 21 comprised graphene quantum dots having blue, green, and yellow colors.

[0164] Comparative Example 1 was DI water. The Photoluminescence Spectrum of DI water as shown in Fig. 23 was used as a reference for comparing the photoluminescence properties of the products obtained from Examples 9-12 and 18-21.

[0165] Comparative Example 2 did not produce a carbon nanomaterial, indicating that no thermochemical reduction of sodium bicarbonate took place in the absence of the catalyst. According to Fig. 24, the Photoluminescence Spectrum of the product obtained from Comparative Example 2 showed no obvious peak and was similar to the Photoluminescence Spectrum of Comparative Example 1, which confirmed that no carbon nanomaterial was synthesized in Comparative Example 2. The results of Comparative Example 2 were to be compared with Example 18 (see its respective description of Figs. 19A - 19D above) which also used sodium bicarbonate as the oxygenic carbon source and wherein the rest of the conditions and particulars were controlled so as to replicate those of Comparative Example 2, except without the catalyst.

[0166] List of Drawing References 10 thermochemical reactor

[0167] 100 receptacle

[0168] 110 solution

[0169] 120 non-metallic particle

[0170] 200 heating element 300 stirrer

[0171] 310 shaft

[0172] 320 blade

[0173] 330 motor

[0174] 400 vent

Claims

received by the International Bureau on 17 October 202427AMENDED CLAIMS1. A process for synthesizing a carbon nanomaterial by thermochemically reducing an oxygenic carbon source under an ambient pressure, and an onset temperature in the range of 50 - 150 °C in the presence of a hydrogen abstractor, an ionic salt, and a solvent, wherein — the carbon nanomaterial is selected from the group of a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N- doped graphene quantum dots, and a combination thereof, the reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes, the said oxygenic carbon source is selected from: an amino acid, a sugar, a polypeptide, a phenolic compound, an amine, a carboxylic acid, an alcohol, a ketone, an aldehyde, a carbonate salt, and a bicarbonate salt, the said hydrogen abstractor is selected from: a hydroxyl compound and hydrogen peroxide, and the said ionic salt is selected from: ammonium sulfate, choline chloride, and ammonium persulfate.

2. The process of claim 1, wherein the yield of said carbon nanomaterial is in the range of 0.3 - 3 kg-l h'1.

3. The process of claim 1, wherein the concentration of the hydrogen abstractor is in the range of 1 - 10 M.

4. The process of claim 1, wherein the hydroxyl compound is potassium hydroxide.

5. The process of claim 1, wherein the thermochemical reduction occurs in presence of the hydrogen abstractor, the ionic salt, the solvent, and an acid.

6. The process of claim 5, wherein the acid is selected from the group of formic acid, acetic acid, and sulfuric acid.

7. The process of claim 6, wherein the concentration of the acid is in the range of 0.1 - 1 M.

8. The process of claim 1, wherein the concentration of the oxygenic carbon source is in the range of 0.001 - 10 M.

9. The process of claim 1, wherein the amino acid is selected from the group of glycine, alanine, and aspartic acid.

10. The process of claim 1, wherein the sugar is selected from the group of glucose and sucrose.AMENDED SHEET (ARTICLE 19)11. The process of claim 1, wherein the polypeptide is gelatin.

12. The process of claim 1, wherein the phenolic compound is tannic acid.

13. The process of claim 1, wherein the amine is selected from the group of monoethanolamine and dimethylethanolamine.

14. The process of claim 1, wherein the carboxylic acid is selected from the group of glycolic acid and citric acid.

15. The process of claim 1, wherein the alcohol is glycerol.

16. The process of claim 1, wherein the ketone is acetone.

17. The process of claim 1, wherein the aldehyde is acetaldehyde.

18. The process of claim 1, wherein the carbonate salt is sodium carbonate.

19. The process of claim 1, wherein the bicarbonate salt is sodium bicarbonate.

20. The process of claim 1, wherein the concentration of the ionic salt is in the range of 0.1 - 1 M.

21. A process for synthesizing a carbon nanomaterial by thermochemically reducing an oxygenic carbon source under an ambient pressure, and an onset temperature in the range of 50 - 150 °C in the presence of a hydrogen abstractor, an ionic salt, a solvent, and a catalyst, wherein — the carbon nanomaterial is selected from the group of a graphitic nanocarbon, an N-doped graphitic nanocarbon, an amorphous carbon, graphene quantum dots, N- doped graphene quantum dots, and a combination thereof, the reaction time for synthesizing the carbon nanomaterial is no longer than 10 minutes, the said oxygenic carbon source is selected from: an amino acid, a sugar, a polypeptide, a phenolic compound, an amine, a carboxylic acid, an alcohol, a ketone, an aldehyde, a carbonate salt, and a bicarbonate salt, the said hydrogen abstractor is selected from: a hydroxyl compound and a peroxide compound, the said ionic salt is selected from: ammonium sulfate, choline chloride, and ammonium persulfate, and the said catalyst is graphene oxide.

22. The process of claim 21, wherein the yield of said carbon nanomaterial is in the range of 0.3 - 3 kg-l h'1.

23. The process of claim 21, wherein the catalyst’s loading is in the range of 0.01 - 0.1 kg-L1.AMENDED SHEET (ARTICLE 19)24. The process of claim 21, wherein the concentration of the hydrogen abstractor is in the range of 1 - 10 M.

25. The process of claim 21, wherein the hydroxyl compound is potassium hydroxide.

26. The process of claim 21, wherein the peroxide compound is hydrogen peroxide.

27. The process of claim 21, wherein the thermochemical reaction occurs in presence of the hydrogen abstractor, the ionic salt, the solvent, the catalyst, and an acid.

28. The process of claim 27, wherein the acid is selected from the group of formic acid, acetic acid, and sulfuric acid.

29. The process of claim 28, wherein the concentration of the acid is in the range of 0.1 - 1 M.

30. The process of claim 21, wherein the concentration of the oxygenic carbon source is in the range of 0.001 - 10 M.

31. The process of claim 21, wherein the amino acid is selected from the group of glycine, alanine, and aspartic acid.

32. The process of claim 21, wherein the sugar is selected from the group of glucose and sucrose.

33. The process of claim 21, wherein the polypeptide is gelatin.

34. The process of claim 21, wherein the phenolic compound is tannic acid.

35. The process of claim 21, wherein the amine is selected from the group of monoethanolamine and dimethylethanolamine.

36. The process of claim 21, wherein the carboxylic acid is selected from the group of glycolic acid and citric acid.

37. The process of claim 21, wherein the alcohol is glycerol.

38. The process of claim 21, wherein the ketone is acetone.

39. The process of claim 21, wherein the aldehyde is acetaldehyde.

40. The process of claim 21, wherein the carbonate salt is sodium carbonate.

41. The process of claim 21, wherein the bicarbonate salt is sodium bicarbonate.

42. The process of claim 21, wherein the concentration of the ionic salt is in the range of 0.1 - 1 M.AMENDED SHEET (ARTICLE 19)

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