Process for synthesizing reduced graphene oxide on a substrate from seedlac

Abstract

The present invention relates to synthesizing reduced graphene oxide on the surface of a metal sheet and glass. The invention particularly relates to a process for coating a substrate with reduced graphene oxide using seedlac as a carbon source. As per the process of the current invention, a solution of seedlac is prepared in an alcohol and the substrate is dipped in to the solution for one or more time. The substrate is then dried in air for 1-10 minutes and thereafter, heated to a temperature range of 400 to 1200 C. under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at a different flow rate ranging from 100 to 500 seem for a period of 10 to 120 minutes.

Claims

1. A process for synthesizing reduced graphene oxide from seedlac on a substrate, the process comprising: preparing a seedlac solution in a C2-C4 alcohol; dipping the substrate into the seedlac solution one or more times; and heating the substrate in the temperature range of 400 C. to 1200 C. under a controlled atmosphere of Ar, N.sub.2, ArH.sub.2, and/or N.sub.2H.sub.2 at the flow rate of 100 to 500 sccm for a period of 10 to 120 minutes.

2. The process as claimed in claim 1, wherein the substrate is a metallic sheet.

3. The process as claimed in claim 2, wherein the metallic sheet is made of a material selected from the group consisting of steel, copper, zinc, nickel, aluminium and the alloys thereof.

4. The process as claimed in claim 1, wherein the substrate is a glass sheet.

5. The process as claimed in claim 1, wherein the C2-C4 alcohol is selected from the group consisting of ethanol, isopropanol and a mixture thereof.

6. The process as claimed in claim 1, wherein the substrate is an oxidized steel surface.

7. The process as claimed in claim 1 further comprising a step of drying the substrate after each dipping into the seedlac solution by keeping the substrate in an air atmosphere for a period of 1 to 10 minutes.

8. The process as claimed in claim 1, wherein the seedlac solution is prepared by heating seedlac in the C2-C4 alcohol at a temperature ranging between 60 C. to 90 C. for a period of 10 to 60 minutes.

9. The process as claimed in claim 1 further comprising the step of adding nickel chloride to the seedlac solution in the C2-C4 alcohol.

10. The process as claimed in claim 1, wherein the concentration of seedlac is in the range of 10-100 gram/liter of the C2-C4 alcohol.

11. The process as claimed in claim 1, wherein the substrate is heated using an electro-heating furnace.

12. A process for coating a substrate with reduced graphene oxide, the process comprising: preparing a seedlac solution in a C2-C4 alcohol; dipping the substrate in to the seedlac solution one or more times; and heating the substrate in the temperature range of 400 C. to 1200 C. under controlled atmosphere of Ar, N.sub.2, ArH.sub.2, and/or N.sub.2H.sub.2 at a flow rate of 100 to 500 sccm for a period of 10 to 120 minutes; wherein a coating thickness of the reduced graphene oxide is in the range of 2-100 nm.

13. The process as claimed in claim 12, wherein the substrate is a metallic sheet.

14. The process as claimed in claim 13, wherein the metallic sheet is made of a material selected from the group consisting of steel, copper, zinc, nickel, aluminium and the alloys thereof.

15. The process as claimed in claim 12, wherein the substrate is a glass sheet.

16. The process as claimed in claim 12, wherein the C2-C4 alcohol is selected from the group consisting of ethanol, isopropanol and a mixture thereof.

17. The process as claimed in claim 12, wherein the substrate is an oxidized steel surface.

18. The process as claimed in claim 12 further comprising a step of drying the substrate after each dipping into the seedlac solution by keeping the substrate in an air atmosphere for a period of 1 to 10 minutes.

19. The process as claimed in claim 12 further comprising the step of adding nickel chloride to the seedlac solution in the C2-C4 alcohol.

20. The process as claimed in claim 12, wherein the seedlac solution is prepared by heating seedlac in C2-C4 alcohol at a temperature ranging between 60 C. to 90 C. for a period of 10 to 60 minutes.

21. The process as claimed in claim 12, wherein the substrate is heated using an electro-heating furnace.

22. The process as claimed in claim 12, wherein the concentration of seedlac is in the range of 10-100 gram/liter of C2-C4 alcohol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts chemical structure of seedlac.

(2) FIG. 2 is a XPS spectrum of seedlac.

(3) FIG. 3 is a Raman spectrum of reduced graphene oxide coated steel.

(4) FIG. 4 XPS spectrum of reduced graphene oxide coated steel.

(5) FIG. 5 Backscattered image with EDX analysis of reduced graphene oxide coated steel.

(6) FIG. 6 Raman spectrum of reduced graphene oxide coated on oxidized steel.

(7) FIG. 7 Raman spectrum of reduced graphene oxide coated Cu.

(8) FIG. 8 XPS spectrum of reduced graphene oxide coated Cu.

(9) FIG. 9 Backscattered image of reduced graphene oxide coated Cu with EDX analysis.

(10) FIG. 10 Raman spectrum of reduced graphene oxide coated steel. The coating is developed using Seedlac and NiCl.sub.2 solution.

(11) FIG. 11 Backscattered and secondary images of reduced graphene oxide coated Nickel sheet with EDX analysis.

(12) FIG. 12, XPS data of reduced graphene oxide coated glass.

(13) FIG. 13 Backscattered image of reduced graphene oxide coated glass with EDX analysis.

(14) FIG. 14 TEM micrograph of the reduced graphene oxide sheet with SAED pattern.

SUMMARY OF THE INVENTION

(15) The present invention provides a process for developing a reduced graphene oxide coating on a metallic substrate such as steel, copper, zinc, nickel, aluminum and alloys thereof. The coating can be further developed on a glass substrate as well. The current process comprises dip coating of the substrate in seedlac or seedlac-Nickel chloride (NiCl.sub.2) solution followed by heating in the range under controlled atmosphere. The seedlac or seedlac-NiCl.sub.2 solution is prepared in a C1-C4 alcohol such as methanol, ethanol, isopropanol or tert-butyl alcohol. Preferably, a C2-C4 alcohol is used. The substrate is dipped in to the seedlac or seedlac-Nickel chloride (NiCl.sub.2) solution one or more times and then dried in air. The dried substrate is then heated under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at a different flow rate ranging from 100 to 500 sccm for a period of 10 to 120 minute.

DESCRIPTION OF THE INVENTION

(16) Graphene with some oxygen content was termed as reduced graphene oxide. Graphene variant as per the current invention also contains oxygen content and hence, has been termed reduced graphene oxide throughout the invention. Seedlac is a natural adhesive gum and is also known as natural varnish. Seedlac contains cyclic six and five membered carbon rings with a long aliphatic chain attached hydroxyl and acetate functional groups as depicted in FIGS. 1 & 2. Current invention makes use of seedlac as carbon source for synthesis of reduced graphene oxide. Seedlac can be transformed to reduced graphene oxide under optimized experimental conditions, as the bond rearrangement occurs through removal of hydroxyl functional groups on heating. This process overcomes some of the above problems associated with the large area coating of graphene on metal surface.

(17) In an embodiment of the present invention, the process for coating of reduced graphene oxide on a substrate comprises: (i) Preparation of seedlac solution in an alcohol. In an embodiment of the invention, alcohol is selected from ethanol, isopropanol, tert-butyl alcohol and a mixture thereof. Methanol can also be used however, it is toxic compared to C2-C4 alcohols. The concentration of seedlac solution varies in the range of 10-100 gram/liter of the alcohol. The seedlac solution is prepared by heating seedlac in the C2-C4 alcohal at a temperature ranging between 60 to 90 C. for a period of 10 to 60 minutes to prepare a homogeneous solution. (ii) Coating of the viscous seeldlac solution on the substrate. In an embodiment of the current invention, the substrate is selected from steel, copper, nickel and alloys thereof. In another embodiment of the invention, the substrate is glass. The coating thickness of seedlac solution on the substrate surface is controlled by varying the number of dipping of the substrate in the seedlac solution. In an embodiment of the current invention, the substrate is dipped in the seedlac solution in the range of 1 to 20 times. The substrate is dried in air atmosphere for a period of 1 to 10 minutes after each dipping. (iii) Heating the seedlac coated substrate in the temperature range of 400 to 1200 C. under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at a different flow rate ranging from 100 to 500 sccm for a period of 10 to 120 minutes. In an embodiment of the current invention, substrate can be heated using an electro-heating furnace.

(18) In an embodiment of the current invention, Nickel chloride (NiCl.sub.2) is added to the seedlac solution in the weight ranging from 0.001 g to 0.1 g per volume of 100 to 1000 ml seedlac solution. Coating thickness of reduced graphene oxide on the substrate was observed in the range of 2-100 nm.

(19) The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of the present invention.

Example-1

(20) Seedlac solution was made by adding 2 g of seedlac in isopropanol solvent of volume in the range of 100 to 500 ml at a temperature ranging between 60 to 90 C. The seedlac solution was coated over the surface of steel, copper, zinc, nickel, aluminum and their alloys by dip coating followed by air drying at room temperature. The thickness of coating layer was varied by the number of dippings. The coated metal sheets and glass were heated using an electro-heating furnace in the temperature range of 400 to 1200 C. under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at the flow rate of 100 to 500 sccm for a period of 10 to 120 minutes. The heated surface of steel, copper, zinc, nickel, aluminum and alloys was characterized using Raman spectroscopy, X-ray photoelectron spectroscopy and electron microscopy (FIG. 3-9).

Example 2

(21) Seedlac solution was prepared adding 2 g of seedlac in isopropanol solvent of volume in the range of 100 to 500 ml at a temperature ranging between 60 to 90 C. NiCl.sub.2-seedlac solution was made by adding NiCl.sub.2 of weight ranging from 0.001 g to 0.1 g in seedlac solution of a volume between 100 to 1000 ml. The resulting solution was coated over the surface of steel, copper, zinc, nickel, aluminum, alloys and glass by dip coating followed by air drying at room temperature. The coated metal sheets and glass were heated using an electro-heating furnace in the temperature range of 400 to 1200 C. under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at the flow rate of 100 to 500 sccm for a period of 10 to 120 minutes. The heated metal sheets and glass were characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (FIGS. 10 & 11).

Example 3

(22) Seedlac solution was made by adding 2 g of seedlac in isopropanol solvent of volume in the range of 100 to 500 ml at a temperature ranging between 60 to 90 C. The seedlac solution was coated over the glass surface by dip coating followed by air drying at room temperature. The thickness of coating layer was varied by the number of dipping. The coated metal sheets and glass were heated using an electro-heating furnace in the temperature range of 400 to 1200 C. under controlled atmosphere of Ar/N.sub.2/ArH.sub.2/N.sub.2H.sub.2 at the flow rate of 100 to 500 sccm for a period of 10 to 120 minutes. The heated surface of steel, copper, zinc, nickel, aluminum, alloys and glass was characterized using X-ray photoelectron spectroscopy and electron microscopy (FIG. 12-14). (i) The XPS data of the coated reduced graphene oxide exhibits the carbon to oxygen (C/O) ratio of better than 39:1 and the full width half maxima of C1s is less than 1.4 eV. (ii) The Raman data of the coated reduced graphene oxide exhibits the I.sub.D/I.sub.G value of less than 0.8. (iii) The observed number of layers in reduced graphene oxide is around 10 from TEM and Raman data (Nature Nanotech., 8, 235 (2013). (iv) The sheet resistance of the reduced graphene oxide over glass is less than 3 kOhm.

(23) The current process of synthesizing reduced graphene oxide coating on a substrate has a number of advantages. The process uses seedlac as a natural carbon source for direct coating of reduced graphene oxide on a metal surface. The process of coating is very simple and can be easily adapted to coat steel surfaces or any other metallic surface. Further, the process does not make use of any hazardous chemicals and hence, is an environmentally process. It was further tested and validated that currentin/ocess can be used to coat reduced graphene oxide even on oxidized steel surface.

(24) Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.