REGEANT SOLUTION FOR PURIFICATION OF CARBON NANOMATERIALS AND A METHOD THEREOF

Abstract

The present invention relates to removal of catalytic metals from carbon nanomaterials bearing catalytic metals up to 15 wt % using an environmentally benign, non-mineral acid-based reagent solution. The reagent solution comprises a solid reagent selected from sodium persulphate or potassium persulphate or ammonium persulphate, wherein the solid reagent is dissolved in deionized water. The reagent solution enables removal of the metals present in the carbon nanomaterials without perturbing the structural integrity of carbon nanomaterials. The purification methodology disclosed in the present invention is suitable to use in energy storage, composite polymers, electromagnetic interference (EMI) shielding materials, conductive inks, conductive paints, field emission transistors, etc.

Claims

1. A non-mineral acid-based reagent solution for purification of a carbon nanomaterial, the solution comprising: (a) a solid reagent selected from the group consisting of sodium persulphate, potassium persulphate, ammonium persulphate and a mixture thereof; and (b) deionized water, wherein the solid reagent is dissolved in the deionized water in a molar ratio of 0.01 to 1; and wherein the carbon nanomaterial comprises catalytic metal impurities.

2. The solution as claimed in claim 1, wherein the solid reagent is a non-mineral acid compound.

3. The solution as claimed in claim 1, wherein the carbon nanomaterial has a bulk density in a range of 0.01 to 0.2 g/cc.

4. The solution as claimed in claim 1, wherein the carbon nanomaterial with or without heteroatoms is associated with a transitional metal in a form of a metal-carbide, wherein the catalytic metals with a carrier metal oxide are encapsulated or intercalated with the carbon nanomaterial.

5. The solution as claimed in claim 1, wherein the carbon nanomaterial is selected from the group consisting of a single walled carbon nanomaterial, a double walled carbon nanomaterial, a triple walled carbon nanomaterial, a thin walled carbon nanomaterial, a multi walled carbon nanomaterial, a carbon nanofiber, and a carbon nano ring.

6. A process for purifying a carbon nanomaterial using a non-mineral acid-based reagent solution, the process comprising: (a) mixing a solid reagent and deionized water in a molar ratio of 0.01 to 1 to form a reagent solution, wherein the solid reagent is selected from the group consisting of sodium persulphate, potassium persulphate, ammonium persulphate and a mixture thereof; (b) mixing the reagent solution with the carbon nanomaterial to make a carbon nanomaterial slurry, wherein the carbon nanomaterial comprises metal impurities; (c) heating the carbon nanomaterial slurry gradually from room temperature to a temperature of 40-100° C.; (d) filtering the carbon nanomaterial slurry under vacuum followed by washing with deionized water to obtain a purified carbon nanomaterial cake; and (e) drying the purified carbon nanomaterial cake to obtain a purified carbon nanomaterial with a purity of more than 99 wt. %.

7. The process as claimed in claim 6, wherein the carbon nanomaterial slurry is heated for a period of 4-12 hours with stirring.

8. The process as claimed in claim 6, wherein the carbon nanomaterial slurry is heated at temperature in a range of 70-100° C.

9. The process as claimed in claim 6, wherein the carbon nanomaterial slurry is heated at temperature in a range of 40 to 90° C.

10. The process as claimed in claim 6, wherein the carbon nanomaterial slurry is heated at a temperature of 70° C. for 12 hours.

11. The process as claimed in claim 6, wherein the purified carbon nanomaterial cake is dried in a hot air oven at 120° C. for 12 hours.

12. The process as claimed in claim 6, wherein the carbon nanomaterial with or without heteroatoms is associated with a transitional metal in a form of a metal-carbide, wherein the catalytic metals with a carrier metal oxide are encapsulated or intercalated with the carbon nanomaterial.

13. The process as claimed in claim 6, wherein the carbon nanomaterial is a pristine carbon nanomaterial.

14. The process as claimed in claim 13, wherein a concentration of the reagent solution is in a range from 1-50 wt. % with respect to a weight of the pristine carbon nanomaterial.

15. The process as claimed in claim 13, wherein the pristine carbon nanomaterial comprises metal impurities in a range of 1-15 wt. %.

16. The process as claimed in claim 15, wherein the metal impurities are in monometallic, bimetallic, trimetallic, or multimetallic form, and wherein the metal impurities comprise iron, cobalt, nickel, manganese, molybdenum, metals dispersed on carrier materials, whereas the carrier materials comprise magnesium oxide, alumina, silica, or combination thereof.

17. The process as claimed in claim 13, wherein the purity of the pristine carbon nanomaterial is in a range from 85 to 99 wt. %.

18. The process as claimed in claim 15, wherein a ratio of the reagent solution to the metal impurities in the pristine carbon nanomaterial is in a range from 0.1 to 1.

19. The process as claimed in claim 6, wherein the purified carbon nanomaterial has purity of more than 99-99.5 wt. %. The process as claimed in claim 6, wherein the reagent solution generates persulfate radical formed in-situ, and the generated persulphate radical reacts with the metal impurities that are embedded within the carbon nanomaterials.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] (A) TEM images

[0076] FIG. 1A discloses TEM image of CNT of example 2, unpurified;

[0077] FIG. 1B discloses TEM image CNT of example 3, purified.

[0078] FIG. 2A discloses TEM image of CNT of example 4, unpurified.

[0079] FIG. 2B discloses TEM image CNT of example 5, purified.

[0080] FIG. 3A discloses TEM image of CNT of example 6, unpurified.

[0081] FIG. 3B discloses TEM image CNT of example 7, purified.

[0082] (B) Raman Spectra images

[0083] FIG. 4A discloses Raman Spectrum of CNT of example 2, unpurified.

[0084] FIG. 4B discloses Raman Spectrum of CNT of example 3, purified.

[0085] FIG. 5A discloses Raman Spectrum of CNT of example 4, unpurified.

[0086] FIG. 5B discloses Raman Spectrum of CNT of example 5, purified.

[0087] FIG. 6A discloses Raman Spectrum of CNT of example 6, unpurified.

[0088] FIG. 6B discloses Raman Spectrum of CNT of example 7, purified.

[0089] (C) Thermogravimetric Analysis (TGA) images

[0090] FIG. 7A discloses TGA curve of CNT of example 2, unpurified.

[0091] FIG. 7B discloses TGA curve of CNT of example 3, purified.

[0092] FIG. 8A discloses TGA curve of CNT of sample 2, unpurified.

[0093] FIG. 8B discloses TGA curve of CNT of Sample 3, purified.

[0094] FIG. 9A discloses TGA curves of CNT sample of example 6, unpurified.

[0095] FIG. 9B discloses TGA curve of CNT sample of example 7, purified.

[0096] (D) XRD images

[0097] FIG. 10A discloses XRD images of CNT of sample 2, unpurified.

[0098] FIG. 10B discloses XRD images of CNT of sample 3, purified.

[0099] FIG. 11A discloses XRD images of CNT sample of example 4, unpurified.

[0100] FIG. 11B discloses XRD images of CNT sample of example 5, purified.

[0101] FIG. 12A discloses XRD images of CNT sample of example 4, unpurified.

[0102] FIG. 12B discloses XRD images of CNT sample of example 5, purified.

DETAILED DESCRIPTION OF THE INVENTION

[0103] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps of the process, features of the system, referred to or indicated in this specification, individually or collectively and all combinations of any or more of such steps or features.

Definitions

[0104] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are collected here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have their meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0105] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0106] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0107] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

[0108] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0109] 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 disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0110] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products and processes are clearly within the scope of the disclosure, as described herein.

[0111] The present invention discloses a reagent solution for purifying carbon nanomaterials at ambient to moderate process conditions. The disclosed reagent solution comprises a solid reagent selected from potassium persulphate or ammonium persulphate or sodium persulphate, which will be dissolved in deionized water in the desired molar concentrations. The reagent solution has been used in the appropriate mole ratios to the metal impurities present in carbon nanomaterials (CNMs), either equivalent or in fractional ratio of 0.1 to 1. The molar ratio of reagent solution selected is based on initial metal impurities present in carbon nanomaterials. The said carbon nanomaterials are characterized with a bulk density in a range of 0.01 to 0.2 g/cc. Also, the carbon nanomaterials, with or without heteroatoms, are associated with transitional metals in a form of metal-carbides, encapsulated or intercalated along with carrier metal oxides.

[0112] In another embodiment, the reagent solution for purification of carbon nanomaterials comprises—(a) a solid reagent selected from a group consisting of sodium persulphate, potassium persulphate, ammonium persulphate and mixture thereof; and (b) deionized water, wherein the solid reagent is dissolved in the deionized water in a molar ratio of 0.01 to 1. This molar ratio of reagents varies from 0.01 molar to 1 molar depending on initial purity of carbon nanomaterials. Also, the solid reagent is a non-mineral and acid-based solid reagent.

[0113] In another embodiment, the carbon nanomaterial derived from various supported catalysts consisting of iron, cobalt & nickel, manganese, magnesium has been chosen to purify using the aforementioned reagent solution under stipulated purification process conditions. The said reagent generates persulfate radical formed in-situ under the process condition, wherein the said generated persulphate radical reacts with metal impurities that are embedded within the carbon nanomaterials. After the purification treatment for stipulated time, carbon nanomaterial slurry is filtered under vacuum followed by washing with deionized water. The resulting purified carbon nanomaterial cake is dried in a hot air oven at 120° C. for 12 hours to remove the excess moisture from carbon nanomaterial. The oven dried carbon nanomaterial is further characterized using Thermogravimetric analysis (TGA) & Inductive coupled Plasma-Atomic emission spectroscopy (ICP-AES) techniques to monitor the residual metal content and metal concentrations in carbon nanomaterials.

[0114] In yet another embodiment, the process for purification of carbon nanomaterials comprises: [0115] (a) mixing a reagent solution with a pristine carbon nanomaterial which is produced by catalytic chemical vapour deposition process using hydrocarbon feedstock to make a carbon nanomaterial slurry; [0116] (b) heating the carbon nanomaterial slurry gradually from room temperature to a temperature of 70-100° C. for a period of 4-12 hours, while stirring; [0117] (c) filtering the carbon nanomaterial slurry under vacuum followed by washing with deionized water to obtain a purified carbon nanomaterial cake; and [0118] (d) drying the purified carbon nanomaterial cake in a hot air oven at 120° C. for 12 hours to obtain carbon nanomaterial with a purity of more than 99-99.5 wt. %.

[0119] In yet another embodiment, the disclosed purification method provides carbon nanomaterial with purity of >99-99.5 wt. % without compromising structural integrity of carbon nanomaterial. The structural integrity of carbon nanomaterials is evident by laser Raman Spectroscopy, wherein intensity of carbon bands corresponds to Sp.sup.3 to Sp.sup.2 akin to purified pristine carbon nanomaterial. The current method of purification of carbon nanomaterial eliminates the need of corrosive and concentrated acid solutions thereby structural damage of carbon nanomaterials does not take place.

[0120] One of the embodiments states that, reagent solution is either one or combination of the reagents such as ammonium persulfate (APS) or potassium persulfate (KPS) or sodium persulfate dissolved in deionized water.

[0121] In another embodiment, different molar concentrations of reagent solution are prepared in a vessel and stored in an airtight container. 1 to 100 wt. % of 0.01 molar to 1 molar reagent solution, preferably 1 to 50 wt. %, and more preferably 1 to 30 wt. % of 1 molar reagent solution has been used for treating pristine carbon nanomaterial to remove the encapsulated/embedded and excess metal impurities from the carbon nanomaterials.

[0122] In another embodiment, said carbon nanomaterials are derived from gaseous or liquid hydrocarbon feedstock bearing carbon number C1 to C30 in the presence of catalyst substrates at elevated temperatures in a suitable reactor configuration. The carbon nanomaterials are obtained by different process ranging from catalytic chemical vapor deposition in different type of reactors including horizontal, vertical tubular reactors with incipient fluidization, continuous fluidization, fixed bed or floating catalyst reactor, high-pressure carbon monoxide (HiPCO) process reactor.

[0123] In another embodiment, the said carbon nanomaterial comprises metal impurities, either in monometallic or bimetallic or trimetallic or multimetallic form, comprises iron, cobalt, nickel, manganese, molybdenum, metals dispersed on carrier materials such as magnesium oxide, alumina, silica, or combination thereof.

[0124] In another embodiment, carbon nanomaterials are produced from fluidization process, preferably using liquid or gaseous hydrocarbon feed stock in presence of catalyst, wherein catalyst is preferably selected from iron-manganese supported on magnesia, nickel-manganese supported on magnesia or cobalt-manganese supported on magnesia.

[0125] In another embodiment, the carbon nanomaterials comprise carbon nanotubes selected from a group consisting of single walled or double walled or triple walled carbon nanomaterials, multi walled carbon nanomaterials, carbon nanofibers, carbon nano rings, etc. The produced carbon nanomaterials having characteristics of tubular structures having variable diameter ranging from 1 to 100 nm, and tube length ranging from 1 to 50 μm, bulk density of 0.01 to 0.25 gram/cc and bearing metal content ranging from 0.1 to 15 wt. %, preferably 0.1 to 10 wt. %.

[0126] In another embodiment, thus produced carbon nanotubes (CNT) is ball-milled to homogenize to fine power. Further, the CNT slurry is prepared by mixing the thus formed CNT powder bearing metal concentration of 0.01 to 15 wt. % with a reagent solution in a continuous stirring temperature reactor (CSTR) or agitated nutsche filter/dryer reactor (ANFD). The CNT slurry mixed with reagent solution in ANFD, which is allowed to stir at temperature in the range of room temperature to 100° C., more preferably 40 to 70° C. for 4-12 hours. The treated CNT slurry is subjected to vacuum to remove the excess water solution followed by washing with de-ionized water. Thus, obtained filtrate cake is oven dried at 120° C. for 6 to 12 hours.

[0127] In another embodiment, purified CNT is analysed by inductively coupled plasma-Optical emission spectroscopy (ICP-OES), Thermogravimetric Analysis (TGA), Raman spectroscopy, Transmission Electron Microscopy (TEM), to monitor metal profiling, residual meal content, structural defects, and structural morphology, respectively.

[0128] In another embodiment, after purification treatment of CNT with reagent, resulted purified CNT bearing carbon purity of 99.5 wt. % or higher with retention of structural integrity.

EXAMPLES

[0129] Having described the basic aspects of the present invention, the following non-limiting examples illustrate specific embodiments thereof. Those skilled in the art will appreciate that many modifications may be made in the invention without changing the essence of invention.

Example 1: Preparation of Reagent Solution

[0130] 228 grams of ammonium persulphate dissolved in 10 liters of deionized water under stirring condition, which is denoted as solution A. The prepared solutions are kept in different sealed containers that can be used as purification agent for CNT purification process to remove the metals in an appropriate concentration.

Example 2: Process for Production of Carbon Nanotubes (CNTs) Using Fe—Mn Catalysts

[0131] 100 gm of 20 wt. % Iron and 22 wt. % Manganese supported on MgO catalyst is loaded into the vertical fluidized bed reactor, and the reactor is then heated up to the temperature of 650° C. under inert gas atmosphere. After achieving the desired temperature, hydrogen is passed over the catalyst along with nitrogen gas to reduce the metal oxide catalyst for 2 hours. After finishing the reduction step, hydrogen gas is turned off and nitrogen gas is being continuously passed over the catalyst. The petroleum hydrocarbon feed is fed into the reactor using a continuous high pressure dispensing pump at the flow rate of 400 gm per hour. The liquid feed is preheated up to 400° C. and the feed vapor is being carried into the reactor with help of nitrogen gas. The feed vapor and nitrogen gas enter the reactor wherein feed vapor passes over the catalyst surface, as a result feed starts to decompose and form the solid carbon product. After 8 hours of the process, feed is stopped, and the reactor is allowed to cool down in the nitrogen atmosphere. The solid carbon product is evacuated from the reactor, and the product weighs 1.5 kgs. The theoretical purity of CNT is approximately 93 wt. %

[0132] The carbon sample is analyzed by ICAP, XRD, TEM, Raman Spectroscopy, and TGA to get the physico-chemical characteristics of the produced carbon product.

Example 3: Process for Purification of Carbon Nanotubes (CNTs)

[0133] 1.5 kg of 93 wt. % carbon purity of CNT produced in Example 2 is charged into the 20-liter stainless steel vessel. The CNT bearing total metal impurities in the concentration range of 0.45 moles. The 100% reagent solution of 0.1M reagent solution is prepared in example 1 is added to 1.5 kg of CNT powder to make CNT slurry. Thus formed CNT slurry is kept under continuous stirring, while the vessel is heated at temperature of 70° C. for 12 hours. Thereafter, the vessel is cooled down under stirring by turning off heaters, and slurry solution is being allowed to rest for some time to settle the solid mass at the bottom, and the excess solution is decanted. The wet solid CNT sample is washed with water under vacuum and dried in the oven at 100° C. for 12 hours. The obtained CNT material is then crushed into powder and analyzed by ICAP, TGA, XRD, Raman, TEM characterization methods.

Example 4: Process for Production of Carbon Nanotubes (CNTs) Using Co—Mn Catalysts

[0134] 100 gm of 20 wt. % Cobalt and 22 wt. % Manganese supported on MgO catalyst is loaded into the vertical fluidized bed reactor, and reactor is then heated up to the temperature of 650° C. under inert atmosphere. After achieving the desired temperature, Hydrogen is passed over the catalyst along with nitrogen gas to reduce the metal oxide catalyst for 2 hours. After finishing the reduction step, hydrogen gas is turned off and nitrogen gas is being continuously passed over the catalyst. The petroleum hydrocarbon feed is fed into the reactor using a continuous high pressure dispensing pump at the flow rate of 400 gm per hour. The liquid feed is preheated up to 400° C. and the feed vapor is being carried into the reactor with help of nitrogen gas. The feed vapor and nitrogen gas enter the reactor wherein feed vapor passes over the catalyst surface, as a result feed starts to decompose and form the solid carbon product. After 8 hours of the process, feed is stopped, and the reactor is allowed to cool down in the nitrogen atmosphere. The solid carbon product is evacuated from the reactor, and the product weighs 2.5 kgs. The theoretical purity of CNT is approximately 96 wt. %.

[0135] The carbon sample is analyzed by ICAP, XRD, TEM, Raman Spectroscopy, and TGA to get the physico-chemical characteristics of the produced carbon product.

Example 5: Process for Purification of Carbon Nanotubes (CNTs)

[0136] 2.5 kg of 96 wt. % carbon purity of CNT produced in Example 4 is charged into the 20-liter stainless steel vessel. The CNT bearing total metal impurities in the concentration range of 0.45 moles. The 100% reagent solution of 0.1M reagent solution is prepared in example 1 is added to 2.5 kg of CNT powder to make CNT slurry. Thus formed CNT slurry is kept under continuous stirring, while the vessel is heated at temperature of 70° C. for 12 hours. Further, the vessel is cooled down by turning off the heaters, and slurry solution is being allowed to rest for some time to settle the solid mass at the bottom, and then excess solution is decanted. The wet solid CNT sample is washed with water under vacuum and dried in the oven at 100° C. for 12 hours. The obtained CNT material is then crushed into powder and analyzed by ICAP, TGA, XRD, Raman, TEM/SEM characterization methods.

Example 6: Process for Production of Carbon Nanotubes (CNTs) for Ni—Mn Catalyst

[0137] 100 gm of 20 wt. % Nickel and 22 wt. % Manganese oxide supported on MgO catalyst is loaded into the vertical fluidized bed reactor, and the reactor is then heated up to the temperature of 650° C. under inert atmosphere. After achieving the desired temperature, Hydrogen is passed over the catalyst along with nitrogen gas to reduce the metal oxide catalyst for 2 hours. After finishing the reduction step, hydrogen gas is turned off and nitrogen gas is being continuously passed over the catalyst. The petroleum hydrocarbon feed is fed into the reactor using a continuous high pressure dispensing pump at the flow rate of 400 gm per hour. The liquid feed is preheated up to 400° C. and the feed vapor is being carried into the reactor with help of nitrogen gas. The feed vapor and nitrogen gas enter the reactor wherein feed vapor passes over the catalyst surface, as a result feed starts to decompose and form the solid carbon product. After 8 hours of the process, feed is stopped, and the reactor is allowed to cool down in the nitrogen atmosphere. The solid carbon product is evacuated from the reactor, and the product is weighed as 2 kgs. The theoretical purity of CNT is approximately 95 wt. %. The resulted CNT is analyzed by ICAP, TGA, XRD, Raman, TEM/SEM characterization methods.

Example 7: Process for Purification of Carbon Nanotubes (CNTs)

[0138] 2 kg of 95 wt. % carbon purity of CNT produced in Example 6 is charged into the 20-liter stainless steel vessel. The CNT bearing total metal impurities in the concentration range of 0.45 moles. The 100% reagent solution of 0.1M reagent solution is prepared in example 1 is added to 2 kg of CNT powder to make CNT slurry. Thus formed CNT slurry is kept under continuous stirring, while the vessel is heated at temperature of 70° C. for 12 hours. After that, the vessel is cooled down by turn off heaters, and slurry solution is allowed to rest for some time to settle the solid mass at the bottom, and then excess solution is decanted. The decanted solution is analyzed by ICAP for metal analysis. The wet solid CNT sample is washed with water under vacuum and dried in the oven at 100° C. for 12 hours. The obtained CNT material is then crushed into powder and analyzed by ICAP, TGA, XRD, Raman, TEM/SEM characterization methods.

TABLE-US-00001 TABLE 1 Characterization of Carbon nanomaterial samples from Example 2, 3, 4, 5, 6 and 7 Tube Tube Metal Analysis Raman Diameter Length Surface Example by ICAP Spectroscopy (nm) by (μm) by Area Number (wt. %) (I.sub.D/I.sub.G) TEM SEM (m.sup.2/g) 2 Fe-1.8 wt. % <0.8 10-30 2-5 105 Mn-2 wt. % Mg-3.3 wt. % 3 Fe-0.2 wt. % <0.8 10-30 2-5 120 Mn-0.01 wt. % Mg-0.01 wt. % 4 Co-0.9 wt. % <0.7 10-25 5-8 117 Mn-1.3 wt. % Mg-1.8 wt. % 5 Co-0.1 wt. % <0.7 10-25 5-8 143 Mn-0.01 wt. % Mg-0.01 wt. % 6 Ni-1.5 wt. % <0.75 10-30 3-6 113 Mn-1.6 wt. % Mg-2.1 wt. % 7 Ni-0.15 wt. % <0.75 10-30 3-6 136 Mn-0.01 wt. % Mg-0.01 wt. %

[0139] Therefore, it can be seen from Table 1 that Examples 3, 5 and 7 pertaining to purification of CNTs have lower content of metals, when compared to their counter Examples 2, 4 and 6 which are pristine CNT and have higher content of metals.

Technical Advantages of the Invention

[0140] The advantages of the of the present invention are as follows: [0141] (a) The solid reagent used is environmentally benign, non-mineral acid-based reagent; [0142] (b) The process for purification of carbon nanomaterials operates at low temperature (40 to 90° C.), unlike vacuum annealing process, where process temperature is set in the range of 1400 to 2000° C. under vacuum which is nearly equivalent to boiling temperature of metals that are present in carbon nanomaterials. Further, vacuum annealing process is highly energy intensive due to requirement of very high temperature; [0143] (c) High purity carbon nanomaterial up to 99.5 wt. % can be achieved without damage to structural integrity of carbon nanomaterials; [0144] (d) No oxygen functional groups are introduced on the carbon nanomaterials; hence electrical properties of carbon nanomaterials are well preserved; [0145] (e) No side products formed unlike in the acid purification process, where part of carbon nanomaterial gets oxidized, hence some functional groups are introduced invariably on defective sites of carbon nanomaterials, along with formation of unwanted carbon soot thus caused the impairment of electrical properties of carbon nanomaterials. [0146] (f) The reagent solution is a water-based solution, hence there is no ecological effect on environment and human health. Furthermore, reagent is safe to handle as it doesn't cause any skin burning while get in contact with skin; [0147] (g) Non-corrosive reagent, so metallurgy of the reactor is protected, while in case of concentrated mineral acid-based purification process, it corrodes the metallurgy of the reactors. Alternatively, glass-based reactors are required to be used, however due to fragility these types of reactors are not suitable to use in industrial scale due to safety reasons; and [0148] (h) The method for removal process of metal impurities from CNMs using ammonium or potassium or sodium persulfate is a novel process without using any harsh acids.