Description:FIELD OF THE INVENTION
The present invention relates to carbon based materials. More specifically, the present invention relates to a hetero atom doped layered carbon sheet consisting of hetero atom boron (B), nitrogen (N), and sulfur (S) and a process for the preparation of the hetero atom doped layered carbon sheet from petroleum pitch. The hetero atom doped layered carbon sheet is further utilized in a grease composite.

BACKGROUND OF THE INVENTION
Petroleum pitch is a byproduct in petroleum and coal industries, is cheap and abundant, high polycyclic aromatic hydrocarbon content, and easily aromatized to form graphene-like nanosheets. This carbon sheets are considered as a promising candidate for lubricants, gas adsorption, anode materials for battery and electro and photocatalytic applications.

Hetero atom (B, N, O, S and P) doping is usually used to modify carbon materials, which can improve the electrochemical performance, catalytic performance, gas storage capacity and heavy metal ion removal efficiency from wastewater and so on.

Different type of carbon based materials like graphene, porous carbon, carbon Nano tube, carbon sphere, carbon dots are reported which are synthesized from pitch raw materials for different field of applications. CN105733573A discloses an electrochemical method for preparing petroleum coke-based carbon quantum dots and doping nitrogen in a one-step manner. Graphene are generally synthesis from pitch based product at high temperature (> 2000 °C). US11767221B2 discloses a method of producing isolated graphene sheets directly from a carbon/graphite precursor. However, the synthesis requires a temperature treatment of 3200 ? in the presence of a catalyst. Hao et al., discloses a porous carbon nanosheets with tunable microstructure, pore structure and chemical composition prepared from coal tar pitch through a two-step process involving NaCl template method and NH3 treatment [Fuel processing technology, 177 (2018), 328-335]. However, graphene like stack carbon sheet with hetero atom doping synthesized from pitch is not well reported.
OBJECTIVES OF THE INVENTION
The main objective of the present invention is to provide a hetero atom doped layered carbon sheet from petroleum pitch for the valorisation of petroleum pitch into useful products.

Another objective of the present invention is to provide a process for the preparation of a hetero atom doped layered carbon sheet from petroleum pitch.

Another objective of the present invention is to provide a grease composite comprising the hetero atom doped layered carbon nanosheet.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a hetero atom doped layered carbon nanosheet comprising carbon nanosheets doped with 1 to 2.5 weight % of a hetero atom, wherein the carbon nanosheets are arranged in layers having a distance of 0.340 nm to 0.349 nm between the carbon nanosheets.

The present invention provides a process for the preparation of hetero atom doped layered carbon nanosheet, the process comprises:
i. heating a hetero atom enriched pitch powder to obtain a carbonized black product; wherein the hetero atom enriched pitch powder comprise a hetero atom selected from a group comprising boron (B), nitrogen (N) and sulfur (S) and a combination thereof,
ii. grinding the carbonized black product to obtain a fine powder;
iii. dispersing the fine powder in a solvent to obtain a mixture;
iv. sonicating the mixture to obtain a product; and
v. separating the hetero atom doped layered carbon sheets the product from the product, followed by drying the hetero atom doped layered carbon nanosheet.

The present invention provides a grease composite comprising the hetero atom doped layered carbon nanosheet as defined above in a range of 1 to 3 weight % of the grease composite.

BRIEF DESCRIPTION OF THE DRAWINGS:
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 depicts FE-SEM images of (a) raw petroleum pitch, (b) SCN-1 (c) SCN-2 (d) SCN-3 (e) SCN-4 (f) SCN-5 (g) SCN-6 (h) EDX spectra of SCN.
Figure 2 depicts FE-SEM images of (a) NSCN, (b) BSCN, (c) BNSCN; TEM images of (d) SCN, (e) NSCN, (f) BNSCN.
Figure 3 depicts (a) RAMAN spectra of raw pitch and sulfur doped carbon sheets, (b) RAMAN spectra of all hetero atom doped carbon sheet, (c) XRD pattern of different heteroatom doped carbon sheet.
Figure 4 depicts (a) Co-efficient of friction vs. time plot for blank grease and all SCN sample, (b) Average of COF values with respect to different SCN sample, (c) average of wear scar diameter for different SCN sample, (d) Percentage reduction of COF with respect to different SCN sample.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

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.

The term “some” as used herein is defined as “none, or one, or more than one, or all”. Accordingly, the terms “none”, “one”, “more than one”, “more than one, but not all” or “all” would all fall under the definition of “some”. The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments”.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising”. The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element”. Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more” or “one or more element is REQUIRED”.

Use of the phrases and/or terms such as but not limited to “a first embodiment”, “a further embodiment”, “an alternate embodiment”, “one embodiment”, “an embodiment”, “multiple embodiments”, “some embodiments”, “other embodiments”, “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The present invention provides a hetero atom doped layered carbon nanosheet and a process for the preparation of hetero atom doped layered carbon sheets from less value petroleum pitch without using any template or activating agent. The hetero atoms like sulfur (S), nitrogen (N), and boron (B) are doped in carbon network in-situ during carbon nanosheet formation at a temperature in a range of 500-1300 °C in a single step carbonization method without using any template and activating agent. The hetero atom doped carbon nanosheets are stacked like in graphene. More than one hetero atoms (N, S, B) are doped in carbon nanosheets without changing morphology. The hetero atom doped stacked carbon nanosheets shows good performance as lubricating additives in grease. The hetero atom doped carbon sheet reduced by 26 % of coefficient of friction in grease composite.

The present invention provides a hetero atom doped layered carbon nanosheet comprising carbon nanosheets doped with 1 to 2.5 weight % of a hetero atom, wherein the carbon nanosheets are arranged in layers having a distance of 0.340 nm to 0.349 between the carbon nanosheets.

The hetero atom is selected from a group comprises boron (B), nitrogen (N) and sulfur (S) and a combination thereof.

The hetero atom doped layered carbon nanosheet has a particle size in a range of 1 µm to 6 µm, and a thickness in a range of 1 to 5 nm.

The present invention provides a process for the preparation of hetero atom doped layered carbon nanosheet, the process comprises:
i. heating a hetero atom enriched pitch powder to obtain a carbonized black product; wherein the hetero atom enriched pitch powder comprise a hetero atom selected from a group comprising boron (B), nitrogen (N) and sulfur (S) and a combination thereof,
ii. grinding the carbonized black product to obtain a fine powder;
iii. dispersing the fine powder in a solvent to obtain a mixture;
iv. sonicating the mixture to obtain a product; and
v. separating the hetero atom doped layered carbon sheets from the product, followed by drying the hetero atom doped layered carbon nanosheet.

The hetero atom enriched pitch powder is heated at a temperature in a range of 500 to 1300 ? for 3 to 5 hours. The hetero atom enriched pitch powder is heated in an alumina boat in a tube furnace.

The hetero atom enriched pitch powder is heated in nitrogen atmosphere at a heating rate of 2 to 6 °C/min and a nitrogen flow rate of 1.0 to 1.8 L/ min.

In an embodiment of the present invention, the hetero atom enriched pitch powder is heated in an alumina boat in a tube furnace at 900 °C for 3 h in nitrogen atmosphere with heating rate 5 °C/min and nitrogen flow rate 1.2 L/ min.

The solvent is selected from ethanol, a mixture of ethanol and tetrahydrofuran (THF), and hydrochloric acid (HCl).

The mixture is sonicated for 1 to 3 hours to obtain the product. The sonication is carried out at a frequency in a range of 20 to 40 kHz.

In an embodiment of the present invention, the hetero atom doped layered carbon sheets are separated from the product through sonicating the product for 1 to 3 hrs, followed by centrifugation.

The hetero atom doped layered carbon sheets are dried at a temperature in a range of 60 to 75 ?. In an exemplary embodiment the drying is performed in a hot air oven.

The hetero atom enriched pitch powder is prepared by a process comprising adding a hetero atom precursor to a petroleum pitch. The hetero atom precursor is added in a range of 10 to 30 weight % with respect to the petroleum pitch.

In an embodiment of the present invention, the hetero atom enriched pitch powder is prepared by grinding a hetero atom precursor with a petroleum pitch. In an exemplary embodiment, the grinding is performed through mortar and pestle.

In another embodiment of the present invention, the hetero atom enriched pitch powder is prepared by a process comprises:
i. mixing a hetero atom precursor and a petroleum pitch in a solvent to form a mixture;
ii. separating a supernatant from the mixture;
iii. removing the solvent from the supernatant to obtain a solid black product; and
iv. grinding the solid black product to obtain the hetero atom enriched pitch powder.

The solvent is selected from tetrahydrofuran (THF), toluene, xylene, and hexane.

In an exemplary embodiment, the supernatant is separated from the mixture through centrifuge. The mixture was centrifuged at 8000 rpm for 10 min.

In an exemplary embodiment, the solvent is evaporated from the supernatant using rotary evaporator.

In another embodiment of the present invention, the hetero atom enriched pitch powder is prepared by a process comprises:
i. grinding a hetero atom precursor to form a powder;
ii. adding the powder to a pitch solution to form a paste; wherein the pitch solution comprises the hetero atom precursor and a petroleum pitch in a solvent; and
iii. removing the solvent from the paste to obtain the hetero atom enriched pitch powder.

The hetero atom precursor is selected from a group comprising sulfur powder, boric acid, melamine and a combination thereof.

The solvent of the pitch solution is selected from tetrahydrofuran (THF) toluene, xylene and hexane.

The present invention provides a grease composite comprising the hetero atom doped layered carbon nanosheet as defined above in a range of 1 to 3 weight % of the grease composite.

In an embodiment of the present invention, the hetero atom doped layered carbon nanosheet materials have application in lubes, energy storage, rubber industry, polymer additives and so forth.

EXAMPLES:
The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

Example 1: Synthesis of Sulfur doped stack carbon nanosheet (SCN)
Graphene like stacked, sulfur doped layered carbon nanosheets were synthesized via carbonization method from petroleum pitch and sulfur powder at different temperature in the range of 500-1300 °C in nitrogen atmosphere. In this method, 10.0 g of petroleum pitch and 450 mg of sulfur powder was added in 200 mL tetrahydrofuran (THF) and stirred for 1 h. After that the mixture was centrifuged at 8000 rpm for 10 min. The supernatant was collected, and the solvent was removed using rotary evaporator. The solid black product was collected and grind to powder. This solid black product containing sulfur was used for synthesis of sulfur doped carbon sheet. In each set of synthesis, 1.0 g of sulfur mixed pitch powder was taken in an alumina boat and heated in a tube furnace at different temperature at 500 °C, 700 °C, 800 °C, 900 °C, 1100 °C, 1300 °C for 3 h in nitrogen atmosphere with heating rate 5 °C/min and nitrogen flow rate 1.2 L/ min. After the completion of carbonization, the black product was collected and grind into fine powder and dispersed in 30 mL ethanol/THF mixture. The mixture was then sonicated for 1 h and centrifuge to remove carbon nano particle. After the sonication the product was dried at 60 °C in hot air oven. The product synthesized at 500 °C, 700 °C, 800 °C, 900 °C, 1100 °C, 1300 °C are named as SCN-1, SCN-2, SCN-3, SCN-4, SCN-5, and SCN-6 respectively.

Example 2: Synthesis of Nitrogen, Sulfur co-doped carbon nanosheet (NSCN)
1.0 g of petroleum pitch was mixed with 350 mg of melamine and 50 mg of sulfur powder and grind in a mortar pestle. Next the powder was taken in an alumina boat and heated in a tube furnace at 900 °C for 3 h in nitrogen atmosphere with heating rate 5 °C/min and nitrogen flow rate 1.2 L/ min. after the completion of carbonization, the black product was collected and grind into fine powder and dispersed in 50 mL ethanol. The mixture was then sonicated for 1 h and centrifuge to remove carbon nano particle. After the sonication the product was dried at 60 °C in hot air oven. The nitrogen sulfur co-doped layered carbon sheet is named as NSCN.

Example 3: Synthesis of Boron, Sulfur co-doped carbon nanosheet (BSCN)
1.0 g of petroleum pitch was mixed with 300 mg of boric acid and 50 mg of sulfur powder and grind in a mortar pestle. Next the powder was taken in an alumina boat and heated in a tube furnace at 900 °C for 3 h in nitrogen atmosphere with heating rate 5 °C/min and nitrogen flow rate 1.2 L/min. after the completion of carbonization, the black product was collected and grind into fine powder and dispersed in 50 mL ethanol. The mixture was then sonicated for 1 h and centrifuge to remove carbon nano particle and boron oxide. After the sonication the product was dried at 60 °C in hot air oven. The nitrogen sulfur co-doped layered carbon sheet is named as BSCN.

Example 4: Synthesis of Boron, Nitrogen, and Sulfur co-doped carbon nanosheet (BNSCN)
300 mg of boric acid and 250 mg of melamine was mixed in a mortar pestle. 1.0 g of petroleum pitch and 60 mg of sulfur powder was dissolved in 20 mL of tetrahydrofuran (THF). Next the sulfur content pitch solution was added into the powder boric acid and melamine mixture and made a homogeneous thick paste after that the THF solvent was evaporated, and fine black powder was kept in an alumina boat and heated in a tube furnace at 900 °C for 3 h in nitrogen atmosphere with heating rate 5 °C/min and nitrogen flow rate 1.2 L/min. After the completion of reaction, the black product was collected and grind into fine powder. The powder was then dispersed in 100 mL 0.1 M HCl solution and sonicated for 3 h. After that the solution was washed with distilled water followed by ethanol and dried at 60 °C in hot air oven. The boron, nitrogen and sulfur co-doped layered carbon sheet is named as BNSCN.

Characterization: FESEM & TEM analysis
We have carried out FE-SEM analysis for pure petroleum pitch as well as all as-synthesized SCN sample. The Figure 1 shows the SEM images for all samples. It is seen that for pure petroleum pitch materials aggregated particle like morphology was visible. SCN-1 shows the particle like nature and SCN-6 shows sheet like structure was formed. With increasing temperature of synthesis more sheet like structure was formed. EDX spectra also shows the presence of sulfur along with carbon and oxygen which confirmed the doping of sulfur in the carbon sheet. For NSCN, BSCN and BNSCN all materials show sheet like structure in FE-SEM as shown in Figure 2.

In TEM analysis all hetero atom doped sample shows stacked carbon sheet. For sulfur doped and nitrogen, sulfur co-doped carbon nanosheet shows stacked sheets. In case of BNSCN shows it is shows very thin carbon nanosheet. Figure 2 shows the TEM images of hetero atom doped carbon sheets.

Raman analysis: The peak appeared in the Raman spectra for all sulfur doped carbon nanosheet are almost same position. The peak appeared in the range of 1365 cm-1 and 1597 cm-1 corresponds to D and G band of graphene. The ratio of intensities of D and G band (ID/IG ratio) of pure petroleum pitch materials was 0.597 and ID/IG ratio for sulfur doped carbon sheet was found high compared to pitch materials due to increase the defect in carbon sheet after sulfur doping. It is also noticed that at higher temperature synthesis condition the ID/IG ratio was higher compared to low temperature synthesis materials. At higher temperature, defect was more compared to low temperature synthesis. The Figure 3(a) and (b) shows the Raman spectra of all hetero atom doped carbon sheet sample. Table 1 shows the reaction condition with ID/IG ratio for all SCN sample.

XRD analysis: X-ray diffraction pattern of different heteroatom doped carbon sheet are shown in Figure 3(c). it is seen that for all sample a sharp peak appeared at 25.4° which corresponds to the (002) plane of graphite. And a small peak appeared at near 42.9° corresponds to the (100) plane of graphene. The d-spacing of as-synthesized carbon sheet is 0.349 nm.

Table 1: The reaction condition with ID/IG ratio for all SCN sample
Sample name Reaction condition ID/IG
Petroleum pitch -- 0.597
SCN-1 500 0.685
SCN-2 700 0.882
SCN-3 800 0.924
SCN-4 900 0.964
SCN-5 1100 0.943
SCN-6 1300 0.978
NSCN 900 0.929
BSCN 900 0.934
BNSCN 900 0.959

Example 5: Preparation of grease composite
The grease composite prepared by mixing of as-synthesized carbon sheet with lithium based grease. In this process, 1.0 weight % of as-synthesized hetero atom doped carbon sheet was mixed in a certain amount of lithium based grease and stirred by overhead stirrer at 800-1000 rpm. For uniform dispersion of carbon additives in grease, after mixing, the mixture was then put in three roller grinder and grind for some time. The grease composite was used for four ball testing to analysis the lubricating properties of carbon sheet.

Tribological application: Tribological performances for both the Coefficient of friction (COF) and wear scar diameter (WSD) for lithium based grease and heteroatom doped carbon sheet containing lithium based grease were performed as per ASTM 4172 (Test Conditions: Load = 147 N (15 Kg), Temperature = 75 °C, Speed (rpm) = 1200, Duration = 1 h) on DUCOM, India four-ball tester WO-1786. The SS balls having the diameter of 12.7 mm were used. The balls were cleaned with acetone before starting the experiments. The four ball testing was done by using 1% loading of SCN sample in grease.

After analysis the Co-efficient of friction (COF) and wear scar diameter for 1% SCN loaded grease. It is seen that SCN-6 shows the good result compared to other materials for coefficient of friction. The percentage reduction of COF for SCN-1 was 2.5% and it increases to 26.9% with respect to blank grease from SCN-1 to SCN-6. Due to more sheet like structure was formed at high temperature. This material shows good friction modifier or lubricating additive for grease materials. The Table -2 shows the corresponding COF and WSD values for all sample.

Table 2: The COF and WSD values for all sample
Sample COF
(1 % loading) Percentage reduction of COF WSD (µm)
(1 % loading)
Blank Grease 0.1775 -- 486.0
SCN-1 0.1730 2.5 430.0
SCN-2 0.1695 4.5 455.3
SCN-3 0.1592 10.3 411.5
SCN-4 0.1526 14.0 465.2
SCN-5 0.1437 19.0 456.0
SCN-6 0.1298 26.9 453.6

ADVANTAGES OF THE PRESENT INVENTION:
• Simple pyrolysis methods.
• Valuable materials synthesis from petroleum by-product pitch.
• Scalable synthesis with high percentage of yield.
• Heteroatom (N, S, B) are doped in carbon sheets by in-situ method.
• Single and more than single hetero atoms are doped in the carbon sheet at a time during synthesis.
• Tuning the doping percentage of heteroatom in carbon sheets.
• Graphitic layered stack carbon sheets are formed at lower temperature (500- 1300 °C).
• Layered carbon sheet are synthesized without using any template or any activating agent.
• Tribology study (anti-friction, and anti-wear) with respect to heteroatom doped carbon sheets shows the materials could be used as lubricating additive in grease.
• This carbon based materials could also have multiple field of applications like energy storage (battery and super capacitor), gas storage (CO2, CH4) and wastewater purifications.
, Claims:1. A hetero atom doped layered carbon nanosheet comprising carbon nanosheets doped with 1 to 2.5 weight % of a hetero atom, wherein the carbon nanosheets are arranged in layers having a distance of 0.340 nm to 0.349 nm between the carbon nanosheets.

2. The hetero atom doped layered carbon sheet as claimed in claim 1, wherein the hetero atom is selected from a group comprises boron (B), nitrogen (N) and sulfur (S) and a combination thereof.

3. The hetero atom doped layered carbon sheet as claimed in claim 1, wherein the hetero atom doped layered carbon nanosheets has a particle size in a range of 1 to 6 µm, and a thickness in a range of 1 to 5 nm.

4. A process for the preparation of hetero atom doped layered carbon nanosheet as claimed in claims 1-3, the process comprises:
i. heating a hetero atom enriched pitch powder to obtain a carbonized black product; wherein the hetero atom enriched pitch powder comprise a hetero atom selected from a group comprising boron (B), nitrogen (N) and sulfur (S) and a combination thereof,
ii. grinding the carbonized black product to obtain a fine powder;
iii. dispersing the fine powder in a solvent to obtain a mixture;
iv. sonicating the mixture to obtain a product; and
v. separating the hetero atom doped layered carbon sheets the product from the product, followed by drying the hetero atom doped layered carbon nanosheet.

5. The process as claimed in claim 4, wherein the hetero atom enriched pitch powder is heated at a temperature in a range of 500 to 1300 ? for 3 to 5 hours.

6. The process as claimed in claim 4, wherein the hetero atom enriched pitch powder is heated in nitrogen atmosphere at a heating rate of 2 to 6 °C/min and a nitrogen flow rate of 1.0 to 1.8 L/ min.

7. The process as claimed in claim 4, wherein the solvent is selected from ethanol, a mixture of ethanol and tetrahydrofuran (THF), and hydrochloric acid (HCl).

8. The process as claimed in claim 4, wherein the mixture is sonicated for 1 to 3 hours.

9. The process as claimed in claim 4, wherein the hetero atom doped layered carbon sheets are dried at a temperature in a range of 60 to 75?.

10. The process as claimed in claim 4, wherein the hetero atom enriched pitch powder is prepared by a process comprises adding a hetero atom precursor to a petroleum pitch, wherein the hetero atom precursor is added in a range of 10-30 weight % with respect to the petroleum pitch.

11. The process as claimed in claim 10, wherein the hetero atom enriched pitch powder is prepared by grinding a hetero atom precursor with a petroleum pitch.

12. The process as claimed in claim 10, wherein the hetero atom enriched pitch powder is prepared by a process comprises:
i. mixing a hetero atom precursor and a petroleum pitch in a solvent to form a mixture;
ii. separating a supernatant from the mixture;
iii. removing the solvent from the supernatant to obtain a solid black product; and
iv. grinding the solid black product to obtain the hetero atom enriched pitch powder.

13. The process as claimed in claim 10, wherein the hetero atom enriched pitch powder is prepared by a process comprises:
i. grinding a hetero atom precursor to form a powder;
ii. adding the powder to a pitch solution to form a paste; wherein the pitch solution comprises the hetero atom precursor and a petroleum pitch in a solvent; and
iii. removing the solvent from the paste to obtain the hetero atom enriched pitch powder.

14. The process as claimed in claims 10 to 13, wherein the hetero atom precursor is selected from a group comprising sulfur powder, boric acid, melamine and a combination thereof.

15. The process as claimed in claim 10 and 13, wherein the solvent is selected from tetrahydrofuran (THF), toluene, xylene, and hexane.

16. A grease composite comprising the hetero atom doped layered carbon nanosheet as claimed in claims 1-3, in a range of 1 to 3 weight % of the grease composite.