Process for the production of graphene sheets with tunable functionalities from seaweed promoted by deep eutectic solvents

Abstract

The present invention relates to the process for the scalable production of Fe.sub.3O.sub.4/Fe, Sn & Zn doped graphene nanosheets from a naturally abundant seaweed resources such as Sargassum tenerrimum, Sargassum wighti, Ulva faciata, Ulva lactuca and Kappaphycus alvarezii. The granules remained after the recovery of liquid juice from the fresh seaweeds were utilized as a raw material and a deep eutectic solvents (DESs) generated by the complexation of choline chloride and FeCl.sub.3, ZnCl.sub.2 and SnCl.sub.2 were employed as template as well as catalyst for the production graphene nanosheets functionalized with metals. Pyrolysis of the mixture of seaweed granules and DES at 700-900 C. under 95% N.sub.2 and 5% H.sub.2 atmosphere resulted formation of metal doped graphene sheets with high surface area (120-225 m.sup.2.Math.g.sup.1) and high electrical conductivity 2384 mS.Math.m.sup.1 to 2400 mS.Math.m.sup.1. The nanosheets thus obtained could remove substantial amount of fluoride from fluoride contaminated drinking water (95-98%).

Claims

1. A process for the preparation of facile production of functionalized graphene sheets using seaweed biomass as precursor and deep eutectic solvents (DESs) acting as both catalyst and template, comprising the steps of; (i) crushing the seaweeds mechanically to yield a liquid and residue in granular form; (ii) separating the liquid part from the residual part; (iii) obtaining the residual part in the granular form from step (ii); (iv) treating the granules obtained in step (iii) with deep eutectic solvents followed by pyrolysis under inert atmosphere and high temperature which produces functionalized graphene sheets.

2. The process as claimed in claim 1 wherein the seaweed biomass used is selected from brown seaweeds, green seaweeds, and red seaweeds.

3. The process as claimed in claim 1 wherein the obtained liquid consist of plant micro and macro nutrients and plant growth regulators.

4. The process as claimed in claim 1 wherein the granules obtained from Sargassum seaweed contains Na+ (1-1.5 wt %), K+ (0.5-1 wt %), Ca.sup.2+ (1.5-2 wt %), Mg.sup.2+ (1-1.5 wt %), Fe.sup.2+/3+ (0-0.5 ppm), Zn.sup.2+ (0.01-0.02 wt %), Cu.sup.2+ (2-3 ppm), Mn.sup.2+ (15-20 ppm), C (34-35%), H (4-5%), N (1.3-1.6%) and S (0.5-1%).

5. The process as claimed in claim 1 wherein the functionalized graphene either doped with Fe, Sn or Zn depending on the composition of the deep eutectic solvents used to prepare the composites of the seaweeds.

6. The process as claimed in claim 1 wherein the used deep eutectic solvents are obtained by the complexation of choline chloride with Lewis acids.

7. The process as claimed in claim 1 wherein semi-solid composite can also be prepared by mixing seaweed granules with ChoClFeCl.sub.3 (1:2), ChoClZnCl.sub.2 (1:2) and ChoClSnCl.sub.2 (1:2), respectively with 1:2 to 1:3 weight ratio of granule to deep eutectic solvent.

8. The process as claimed in claim 1 wherein the preparation of functionalized graphene sheets involves pyrolysis in 95% N.sub.2 and 5% H.sub.2 atmosphere for different durations.

9. The process as claimed in claim 1 wherein the semi-solid composites of Sargassum granule and ChoClFeCl.sub.3 1:2 is calcined at 700 C.-900 C. to give heteroatom doped magnetic graphene nanosheets containing various elements.

10. The process as claimed in claim 1 wherein the obtained functionalized graphene samples have reasonably good porosity of 2.7-4.1 nm characteristic of mesoporous material suitable for electrical double layer capacitors (EDLC).

11. The process as claimed in claim 1 wherein the obtained functionalized graphene samples have good electrical conductivity of 2384 mS.Math.m.sup.1 to 2400 mS.Math.m.sup.1.

12. The process as claimed in claim 1 wherein the obtained functionalized graphene samples have reasonably high BET surface area of 120-225 m.sup.2.Math.g.sup.1.

13. The process as claimed in claim 1 wherein the obtained functionalized graphene can remove 95-98% fluoride from drinking water collected from village of Govind Garh, Rajasthan, India (26 45 N, 74 38 E).

14. The process as claimed in claim 1 wherein the separation of graphene sheets after the adsorption of fluoride on the sheets can be done by using ordinary magnets in the case of magnetised graphene sheets.

15. The process as claimed in claim 2 wherein the seaweed biomass used includes a brown seaweed, and wherein said brown seaweed is selected from Sargassum tenerrimum and Sargassum wighti.

16. The process as claimed in claim 2 wherein the seaweed biomass used includes a green seaweed, and wherein said green seaweed is selected from Ulva faciata and Ulva lactuca.

17. The process as claimed in claim 2 wherein the seaweed biomass used includes a red seaweed, and wherein said red seaweed is Kappaphycus alvarezii.

18. The process as claimed in claim 6 wherein the Lewis acids are selected from FeCl.sub.3 (ChoClFeCl.sub.3 1:2), ZnCl.sub.2 (ChoClZnCl.sub.2 1:2), and SnCl.sub.2 (ChoClSnCl.sub.2 1:2).

19. The process as claimed in claim 9 wherein the various elements are selected from Nat, K.sup.+, Ca.sup.2+, Mg.sup.2+, Fe.sup.2+/3+, Zn.sup.2+, Cu.sup.2+, Mn.sup.2+, Sn.sup.2+, C, H, N and S.

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1: Schematic depiction of production of functionalized graphene nanosheets from seaweed promoted by deep eutectic solvents

(2) FIG. 2: Powder XRD spectra of graphene composites synthesized by the calcinations of Sargassum or Kappaphycus granules and DES semi-solid mixtures. (a) SAR-ChoCl:FeCl.sub.3, (b) SAR-ChoCl:ZnCl.sub.2, (c) SAR-ChoCl:SnCl.sub.2 and (d) KAP-ChoCl:FeCl.sub.3

(3) FIG. 3: (a-f) TEM images different graphene nanosheets having various functionalities and (g) Raman spectra of magnetic graphene nanosheets.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention provides a facile and scalable process for the synthesis of graphene nanosheets with tunable functionalities from seaweed biomass and deep eutectic solvents as shown in FIG. 1, which is a schematic depiction of the production of functionalized graphene nanosheets from seaweed promoted by deep eutectic solvents. The process comprises the following steps:

(5) crushing and centrifugation of freshly harvested seaweed to separate sap and solid residue (granular biomass)

(6) preparing deep eutectic solvents combing choline chloride (ChoCl) and metal salts in suitable ratio followed by heating at 80 C. for 1-2 h to get a homogenous solution

(7) preparing a semi-solid composite of granular biomass and deep eutectic solvent by heating at 80 C. for 30-60 minutes

(8) heating the above semi-solid composite as obtain in step (iii) at 700 C.-900 C. under 95% N.sub.2 and 5% H.sub.2 atmosphere

(9) collecting and washing the blackish product obtained after step (iv) and ensuring the formation of functionalized graphene nanosheets.

(10) Recognising that the fresh seaweed Sargassum tenerrimum is available abundantly and naturally in various seashores, its precious utilisation for direct production of functionalized graphene sheets is of considerable importance.

(11) Recognising that the fresh seaweed Sargassum tenerrimum contains more than 80% moisture, thus separation of liquid and solid residue led to its dual utilization i.e., for the production of functionalized graphene and as foliar sprays to increase grain yield of black gram in pot culture experiments.

(12) Recognising that deep eutectic solvents have wide range of solvation property and can be synthesized from low cost components such as choline chloride and metal salts and further recognizing that production of graphene directly from carbon source required template which mostly metal salts, thus metal salts based deep eutectic solvents were employed as both solvent and catalyst for the production of graphene nanosheets.

(13) Recognising that pyrolysis of only Sargassum granules under inert atmosphere led to the production of amorphous carbon composites, preparation of a semi-solid composite of granules and deep eutectic solvents in a suitable ration to soak the complete solvents was one of the inventive step which led to production of functionalized graphene nanosheets.

(14) Recognising huge oxygen functionalities present in the semi-solid composites due to high polysaccharides content mixed gas composition such as 95% N.sub.2 and 5% H.sub.2 was flowed thorough tubular furnace during pyrolysis.

(15) Optimizing suitable ratio of granules and deep eutectic solvent and suitable pyrolysis temperature led to production high quality graphene having high surface area and high conductivity.

EXAMPLES

(16) The following examples serve to provide the best mode of practice for the present invention, and should not be constructed as limiting the scope of the invention.

Example-1

(17) As taught in the prior art, the deep eutectic solvents (ChoCl:FeCl.sub.3, ChoCl:ZnCl.sub.2 and ChoCl:SnCl.sub.2) utilized in the present invention were prepared by heating choline chloride (ChoCl) with FeCl.sub.3, SnCl.sub.2 and ZnCl.sub.2, respectively, at 80 C. in optimized molar ratio of 1:2 (ChoCl:Metal salts) under stirring conditions for 30-60 minutes until homogenous liquid were formed.

(18) This example teaches the synthesis of deep eutectic solvents employed in the present invention.

Example-2

(19) In a typical experimental procedure, Sargassum tenerrimum was harvested from the west coast of India (2228 N, 694 E). The freshly harvested seaweed was mechanically crushed followed by centrifugation to obtain liquid sap as supernatant which were stored under refrigeration (1 Kg fresh Sargassum tenerrimum yielded 600 mL sap). The remaining solid residues (granules) were dried in oven (75 g of dry granules with 14.2 wt % moisture from 1 Kg fresh seaweed). This granular biomass was utilized as carbon source for the synthesis of graphene composites.

(20) This example teaches the simultaneous production of sap (a useful liquid fertilizer) and granular biomass (substrate for graphene synthesis) from fresh Sargassum tenerrimum seaweed.

Example-3

(21) The sap as obtained in Example 2 above was centrifuge to remove the suspended particles and analyzed for its inorganic constituents. It was found that the sap contained 574 ppm of Na.sup.+, 318 ppm of K.sup.+, 123 ppm of Ca.sup.2+, 122 ppm of Mg.sup.2+, 3.4 ppm of Fe.sup.2+, 550 ppb of Cu.sup.2+, 800 ppb of Mn.sup.2+ and 2.3 ppm of Zn.sup.2+. Thus the sap is rich in macro and micronutrient.

(22) This example teaches that instead of drying and using the whole seaweed, it would advantageous to separate liquid and solid residue as the liquid part is rich in useful elements which have utility as liquid fertilizer.

Example-4

(23) In a typical experimental procedure, 5 g of dried granules (14.2 wt % moisture) as obtained in Example 2 was added to ChoCl:FeCl.sub.3(1:2) in 1:2 weight ratio (optimized amount sufficient to soak the granules) followed by heating at 80 C. for 30 minutes until a semi-solid composites is formed.

(24) The above experiment was repeated with ChoCl:ZnCl.sub.2(1:2) and ChoCl:SnCl.sub.2 (1:2) as deep eutectic solvents to obtained semi-solid composites of granules with ChoClZnCl.sub.2 in 1:2 weight ratio and ChoClSnCl.sub.2 in 1:2.5 weight ratio, respectively. The other experimental conditions were same as above.

(25) This Example teaches the synthesis of composites with Sargassum granules and deep eutectic solvents and the optimization of ratio of deep eutectic solvent required to obtain a semi-solid composite.

Example-5

(26) In a typical experimental procedure, 2.44 g of the semi-solid composites composed of Sargassum granules and ChoClFeCl.sub.3 mixture (as obtained from Example 4) was calcined at 700 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.54 g of black flaky carbon powder was collected and washed with distilled water for several times followed by drying to yield magnetic graphene composites (SAR-Fe-700). The presence of Fe.sub.3O.sub.4 in the composites was confirmed by FTIR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis and CHNS analysis of SAR-Fe-700 revealed the presence of several inorganic constituents as shown in Table 1. Surface area analysis showed that the composites SAR-Fe-700 had BET surface area 220.7 m.sup.2/g and pore size 2.80 nm.

(27) This example teaches synthesis of Fe.sub.3O.sub.4 doped graphene composites having magnetic property. This example further teaches the Fe content in SAR-Fe-700 was found to be 6.62 wt %, whereas the concentration of other inorganic elements were in the range of 0.02-2.5% except Cu and Ni. Thus besides Fe.sub.3O.sub.4, the composite SAR-Fe-700 was found to be doped with other heteroatom.

(28) TABLE-US-00001 TABLE 1 Elemental composition of graphene-Fe composites SAR-Fe-700 SAR-Fe-800 SAR-Fe-900 Elements (%) (%) (%) Na 1.17 0.74 0.29 K 0.86 0.48 0.14 Ca 2.02 2.21 2.73 Mg 0.47 1.68 0.98 Fe 6.62 10.01 17.71 Zn 0.02 0.51 0.02 Ni 0.007 0.018 0.05 Cu 0.009 0.006 0.03 Mn 0.31 0.16 0.07 C 22.33 23.27 7.29 H 2.46 2.34 0.93 N 2.02 1.33 0.99 S 0.84 0.76 0.01

Example-6

(29) In a typical experimental procedure, 2.53 g of the semi-solid composites composed of Sargassum granules and ChoClFeCl.sub.3 mixture (as obtained from Example 4) was calcined at 800 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.48 g of black flaky carbon powder was collected and washed with distilled water for several times followed by drying to yield magnetic graphene composites (SAR-Fe-800). The presence of mainly Fe and nominal amounts of Fe.sub.3O.sub.4 in the composites was confirmed by FTIR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Fe-800 revealed the presence of several inorganic constituents as shown in Table 1. Surface area analysis showed that the composites SAR-Fe-800 had BET surface area 167.8 m.sup.2/g and pore size 2.79 nm.

(30) This example teaches synthesis of mixture of Fe and Fe.sub.3O.sub.4 doped graphene composites having magnetic property. This example further teaches the Fe content in SAR-Fe-800 was found to be 10.01 wt %, whereas the concentration of other inorganic elements were in the range of 0.01-2.4% except Cu. Thus besides Fe and Fe.sub.3O.sub.4, the composite SAR-Fe-800 was found to be doped with other heteroatom.

(31) FIG. 2 provides powder XRD spectra of graphene composites synthesized by the calcinations of Sargassum or Kappaphycus granules and DES semi-solid mixtures. (a) SAR-ChoCl:FeCl.sub.3, (b) SAR-ChoCl:ZnCl.sub.2, (c) SAR-ChoCl:SnCl.sub.2 and (d) KAP-ChoCl:FeCl.sub.3.

Example-7

(32) In a typical experimental procedure, 2.62 g of the semi-solid composites composed of Sargassum granules and ChoClFeCl.sub.3 mixture (as obtained from Example 4) was calcined at 900 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.46 g of black powder was collected and washed with distilled water for several times followed by drying to yield magnetic graphene composites (SAR-Fe-900). The presence of Fein major amount in the composite was confirmed by FTIR and powder XRD analysis, whereas the formation of graphene sheets was not shown by Raman spectra. ICP-OES and CHNS analysis of SAR-Fe-900 revealed the presence of several inorganic constituents as shown in Table 1. Surface area analysis showed that the composites SAR-Fe-900 had BET surface area 132.0 m.sup.2/g and pore size 4.18 nm.

(33) This example teaches synthesis of mainly Fe doped graphitic carbon composites having magnetic property. This example further teaches the Fe content in SAR-Fe-900 was found to be 17 wt %, whereas the concentration of other inorganic elements were in the range of 0.01-2.8%. Thus besides Fe, the composite SAR-Fe-900 was found to be doped with other heteroatom.

Example-8

(34) In a typical experimental procedure, 4.13 g of the semi-solid composites composed of Sargassum granules and ChoClZnCl.sub.2 mixture (as obtained from Example 4) was calcined at 700 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 1.01 g of black flaky and light weight powder was collected and washed with distilled water for several times followed by drying to yield Zn doped graphene composites (SAR-Zn-700). The presence of Zn and ZnO in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Zn-700 revealed the presence of several inorganic constituents as shown in Table 2.

(35) This example teaches the synthesis of ZnO and Zn doped graphene composites. This example further teaches the Zn content in SAR-Zn-700 composites was found to be 18.27 wt %. Besides Zn, the composite SAR-Zn-700 was also found to be doped with other heteroatom.

Example-9

(36) In a typical experimental procedure, 3.57 g of the semi-solid composites composed of Sargassum granules and ChoClZnCl.sub.2 mixture (as obtained from Example 4) was calcined at 800 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.798 g of black flaky and light weight powder was collected and washed with distilled water for several times followed by drying to yield Zn doped graphene composites (SAR-Zn-800). The presence of Zn and ZnO in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Zn-800 revealed the presence of several inorganic constituents as shown in Table 2.

(37) This example teaches the synthesis of Zn and ZnO doped graphene composites. This example further teaches the Zn content in SAR-Zn-800 composites was found to be 4.43 wt %. Besides Zn, the composite SAR-Zn-800 was also found to be doped with other heteroatom.

(38) TABLE-US-00002 TABLE 2 Elemental composition of graphene-Zn composites SAR-Zn-700 SAR-Zn-800 SAR-Zn-900 Elements (%) (%) (%) Ca 5.00 6.54 6.14 Fe 0.03 0.09 0.00 K 0.85 2.23 0.41 Mg 1.53 2.08 2.01 Mn 0.01 0.0005 0.00 Na 1.33 1.51 0.70 Ni 0.06 0.00 0.02 Zn 18.27 4.43 0.82 C 45.51 46.27 44.70 H 2.91 2.34 2.74 N 0.90 0.44 0.75 S 1.41 1.94 0.64

Example-10

(39) In a typical experimental procedure, 3.95 g of the semi-solid composites composed of Sargassum granules and ChoClZnCl.sub.2 mixture (as obtained from Example 4) was calcined at 900 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.838 g of black flaky and light weight powder was collected and washed with distilled water for several times followed by drying to yield Zn doped graphitic carbon composites (SAR-Zn-900). The presence of Zn in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphitic carbon was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Zn-900 revealed the presence of several inorganic constituents as shown in Table 2.

(40) This example teaches the synthesis of Zn doped graphene composites. This example further teaches the Zn content in SAR-Zn-900 composites was found to be 0.82 wt %. Besides Zn, the composite SAR-Zn-900 was also found to be doped with other heteroatom.

Example-11

(41) In a typical experimental procedure, 5.70 g of the semi-solid composites composed of Sargassum granules and ChoClSnCl.sub.2 mixture (as obtained from Example 4) was calcined at 700 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.986 g of black flaky powder was collected and washed with distilled water for several times followed by drying to yield Sn doped graphene composites (SAR-Sn-700). The presence of Sn, SnO and SnO.sub.2 in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Sn-700 revealed the presence of several inorganic constituents as shown in Table 3. Surface area analysis of SAR-Sn-700 composite showed that the composites had BET surface area 270.72 m.sup.2/g and pore size 3.07 nm.

(42) This example teaches the synthesis of Sn, SnO and SnO.sub.2 doped graphene composites. This example further teaches the Sn content in SAR-Sn-700 composites was found to be 17.12 wt %. Thus besides Sn, the composite SAR-Sn-700 was also found to be doped with other heteroatom.

Example-12

(43) In a typical experimental procedure, 6.13 g of the semi-solid composites composed of Sargassum granules and ChoClSnCl.sub.2 mixture (as obtained from Example 4) was calcined at 800 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.935 g of black flaky powder was collected and washed with distilled water for several times followed by drying to yield Sn doped graphene composites (SAR-Sn-800). The presence of Sn, SnO and SnO.sub.2 in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Sn-800 revealed the presence of several inorganic constituents as shown in Table 3. Surface area analysis of SAR-Sn-800 composite showed that the composites had BET surface area 98.39 m.sup.2/g and pore size 8.69 nm.

(44) This example teaches the synthesis of Sn, SnO and SnO.sub.2 doped graphene composites. This example further Leaches the Sn content in SAR-Sn-800 composites was found to be 14.76 wt %. Thus besides Sn, the composite SAR-Sn-800 was also found to be doped with other heteroatom.

(45) TABLE-US-00003 TABLE 3 Elemental composition of graphene-Sn composites SAR-Sn-700 SAR-Sn-800 SAR-Sn-900 Elements (%) (%) (%) Ca 4.68 5.25 5.23 Cu 0.00 0.00 0.00 Fe 0.17 0.00 0.00 K 0.75 0.94 0.67 Mg 1.55 1.75 1.64 Mn 0.00 0.00 0.00 Na 1.25 1.33 1.25 Ni 0.00 0.01 0.01 Zn 2.62 1.88 1.53 Sn 17.12 14.76 12.28 C 40.32 34.89 23.97 H 2.05 2.15 2.09 N 1.17 0.67 0.39 S 1.03 0.80 0.12

Example-13

(46) In a typical experimental procedure, 5.74 g of the semi-solid composites composed of Sargassum granules and ChoClSnCl.sub.2 mixture (as obtained from Example 4) was calcined at 900 C. in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture in a tubular furnace for 4 h at 3 C./min temperature ramp. After completing the pyrolysis, 0.856 g of black flaky powder was collected and washed with distilled water for several times followed by drying to yield Sn doped graphene composites (SAR-Sn-900). The presence of Sn in the composite was confirmed by FT-IR and powder XRD analysis, whereas the formation of graphene sheets was confirmed by XRD, Raman and TEM analysis. ICP-OES and CHNS analysis of SAR-Sn-900 revealed the presence of several inorganic constituents as shown in Table 3.

(47) This example teaches the synthesis of Sn doped graphene composites. This example further teaches the Sn content in SAR-Sn-900 composites was found to be 12.28 wt %. Thus besides Sn, the composite SAR-Sn-900 was also found to be doped with other heteroatom.

(48) FIG. 3 provides (a-f) TEM images of different graphene nanosheets having various functionalities and (g) Raman spectra of magnetic graphene nanosheets

Example-14

(49) In a typical experimental procedure, 5 g of dried Kappaphycus alvarezii granules (18 wt % moisture) was added to ChoCl:FeCl.sub.3 (1:2) in 1:2 weight ratio (optimized amount sufficient to soak the granules) followed by heating at 80 C. for 30 min. until a semi-solid composites is formed. 5.42 g of this semi-solid composite was calcined at 800 C. in a tubular furnace in the presence of 95% N.sub.2 and 5% H.sub.2 gas mixture for 4 h at 3 C./min. temperature ramp. After completing the pyrolysis, 1.64 g of brown powder was collected and washed with distilled water for several times followed by drying to yield doped graphene composites (KAP-Fe-800). The presence of Fe.sub.3O.sub.4 in major amount and a small fraction Fe in the composite was confirmed by powder XRD analysis and FTIR analysis, whereas the formation of graphene sheets was confirmed by Raman and TEM analysis. CHNS analysis of KAP-Fe-800 revealed the presence of C (9.31%), H (1.18%), N (0.10%), and S (1.28%) and the other elemental composition is shown in Table 4.

(50) The above experiment was repeated using ChoCl:ZnCl.sub.2 (1:2) and ChoCl:SnCl.sub.2 (1:2) as deep eutectic solvent and Kappaphycus granules. The other experimental conditions were similar.

(51) This example teaches the synthesis of functionalized graphene composites from Kappaphycus alvarezii granules. This example further teaches that the present invention not limited to Sargassum seaweed, other biomass can be converted to graphene composites through the procedure disclosed herein.

(52) TABLE-US-00004 TABLE 4 Elemental composition of graphene-Fe composites Elements Ca Cu Fe K Mg Mn Na Ni Zn C H N S % (w/w) KAP-Fe-800 1.14 0.01 3.83 5.57 0.28 0.36 1.17 0.04 1.05 40.32 2.05 1.17 1.03

Example-15

(53) In a typical experimental procedure, the metal doped graphene composite (as obtained from Example 5-14) were washed with 6N HCl aqueous solution followed by washed with distilled water for several times to neutralized the graphene sheets. After completed the neutralization process, the graphene samples were drying in an oven to obtained metal free graphene. The formation of metal free graphene sheets were confirmed by powder XRD.

(54) This example teaches the synthesis of graphene sheets without any doping of heteroatom.

Example-16

(55) In a control experimental procedure, 1 gm of sargassum granules was calcined at 700 C. under N.sub.2 atmosphere with 3 C./min ramp for 3 h. After completion of the pyrolysis, the black carbon materials was collected and washed with milli-Q water. The TEM, XRD and AFM analysis did not support for the production graphene nanosheets for this carbon material.

(56) This example teaches formation of amorphous carbon when only Sargassum granule was pyrolysed.

Example-17

(57) In another control experimental procedure, 1 gm of choline chloride was pyrolysed under similar condition as mention in Example 16 above. After pyrolysis very minor amount of mass left. This corresponds to amorphous carbon.

(58) This example teaches formation of amorphous carbon when only choline chloride was pyrolysed.

Example-18

(59) In a typical experimental procedure, 0.01 g of the SAR-Fe-700 (as obtained from the Example 5) was added to the 20 mL of fluoride contaminated drinking water (fluoride content were in the range of 2.72-6.71 ppm) which was collected from village of Govind Garh, Rajasthan, India (2645 N, 7438 E). After this, the solution was shaken at room temperature for 2 h (optimised condition) followed by filtration through Whalman filter paper No. 42. The filtrate was collected and analyzed for the fluoride ion concentration. After treating with SAR-Fe-700 the concentration of fluoride reduced to 0.85 ppm (below WHO standard) from initial concentration of 3.62 ppm i.e. 76% removal efficiency. The above experiment was repeated with SAR-Fe-800 and SAR-Fe-900, respectively.

(60) This Example teaches the metal doped graphene nanosheets were able to removes fluoride ion from drinking water. This example also teaches the SAR-Fe-700 graphene composites showed maximum fluoride removal efficiency in comparison to SAR-Fe-800 and SAR-Fe-900.

ADVANTAGE OF THE INVENTION

(61) The main advantage of the present invention is the use of inexpensive naturally abundant seaweed biomass as a precursor for the production of functionalized graphene sheets by the intervention of deep eutectic solvents (DESs) having tunable functionalities. The use of seaweeds as a source of materials is another advantage as they are cultivable which does not need fresh water irrigation unlike terrestrial plants making them abundant for large scale exploitation, the seaweeds are bestowed with very good growth rate and can be harvested multiple times unlike other terrestrial plants. The use of deep eutectic solvents obtained by the complexation between choline chloride and Lewis acids such as FeCl.sub.3, ZnCl.sub.2 and SnCl.sub.2 makes the process advantageous by producing the graphene sheets functionalized with metal functionalities present in the DESs.

(62) While the present invention has been illustrated by description of various embodiments and while those embodiments have been described in considerable detail, it is not the intention of Applicants to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. The present invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicant's invention.