Synthesis of GO, TRGO and CRGO

Graphene Oxide (GO): GO was prepared by modified Hummers method⁵¹. In this process, graphite powder (1 g) and sodium nitrate (NaNO_3, 1 g) were dissolved in H₂SO₄ (46 ml) in an ice bath. Thereafter, KMnO₄ (6 g) flakes was slowly added to the above mixture under stirring until this solution becomes dark green. The solution was then transferred to 35 ± 5 °C water bath and kept on vigorous stirring for about an hour till the consistency resembles a thick paste. Further, Milli-Q water (96 ml) was added, and the solution was stirred for 30 min at 90 ± 5 °C. To this solution, Milli-Q water (200 ml) was added followed by the slow addition of H₂O₂ (30%, 6 ml), turning the colour of the solution from dark brown to yellow. The warm solution was then filtered and washed with Milli-Q (200 ml) water. The filter cake was thereafter dispersed in Milli-Q water by mechanical agitation and centrifuged for 3–5 times at low (2000 rpm) & high (8000 rpm) speed for 2 min & 15 min respectively and repeated until the supernatant attains neutral pH. The final sediment was termed as GO.

Thermally reduced GO (TRGO): As prepared GO was subjected to thermal treatment at 1000 °C for 10 s to give TRGO.

Chemically reduced GO (CRGO): The chemical reduction of GO to make CRGO was done by mixing aqueous solution of GO and hydrazine hydrate in ratio 10:7 under stirring condition. The mixture was kept for 1 h at 95 °C to produce the CRGO.