Natural or synthetic graphite as precursors for the preparation of graphene oxide (GO) have constraints due to their limited availability, high reaction temperature for processing of synthetic graphite and higher generation cost. The use of oxidants, long reaction duration, the generation of toxic gases and residues of inorganic salts, the degree of hazard and low yield are some of the disadvantages of the oxidative-exfoliation methods. Under these circumstances, biomass waste usage as a precursor is a viable alternative. The conversion of biomass into GO by the pyrolysis method is ecofriendly with diverse applications, which partially overcomes the waste disposal problem encountered by the existing methods. In this study, graphene oxide (GO) is prepared from dry leaves of sugarcane plant through a two-step pyrolysis method using ferric (III) citrate as a catalyst, followed by treatment with conc. H₂SO₄. The synthesized GO is analyzed by UV-Vis., FTIR, XRD, SEM, TEM, EDS and Raman spectroscopy. The synthesized GO has many oxygen-containing functional groups (–OH, C–OH, COOH, C–O). It shows a sheet-like structure with a crystalline size of 10.08 nm. The GO has a graphitic structure due to the Raman shift of G (1339 cm⁻¹) and D (1591 cm⁻¹) bands. The prepared GO has multilayers due to the ratio of 0.92 between I_D and I_G. The weight ratios between carbon and oxygen are examined by SEM-EDS and TEM-EDS and found to be 3.35 and 38.11. This study reveals that the conversion of sugarcane dry leaves into the high-value-added material GO becomes realistic and feasible and thus reduces the production cost of GO.

Carbonaceous materials with large interlayer spacing and disordered structure are considered suitable as electrodes in sodium-ion batteries so as to overcome the problem encountered in conventional electrodes. In this study, carbon quantum dots (CQDs) decorated with SnO₂ and NaVO₃ are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs are prepared from dead leaves of the Samanea saman tree through alkaline-peroxide treatment and hydrothermal carbonization. As-prepared CQDs exhibit a quantum yield of 21.03% at an excitation wavelength of 360 nm. Various separators such as indium-doped tin oxide/polyoxyethylene tridecyl ether (ITO/PTE), rice paper (RP), silicone with three big holes (SIL BH), silicone with many small holes (SIL SH) and cellulose paper (CP) have been tried in flexible Na-ion batteries. SIL SH achieved higher specific capacitance (881 F g^–1) than other separators due to the function of many small holes on the surface of the silicone. The SIL SH separator delivered higher discharge capacities of 141 and 114 mC g^–1 at 1.5 and 2.5 V than SIL BH. The RP separator delivered specific discharge capacities of 1087 and 347 mC g^–1 in the 1st and 50th cycles, respectively, at 1 V. The RP separator delivered a high initial specific discharge capacity of 698 mC g^–1 at 2 V and maintained a good discharge capacity of 222 mC g^–1 in the 50th cycle. As compared to RP, SIL SH delivered high specific discharge capacity of 4246 in 1st cycle at 2 V but maintained a capacity of 71 mC g^–1 in the 50th cycle. This study reveals the scope of developing flexible Na-ion batteries with high capacity and cyclability using carbonaceous materials derived from the leaves of the S. saman tree. Carbon quantum dots (CQDs)-decorated with SnO2 and NaVO3 are used as electrodes in the fabrication of flexible Na-ion batteries. CQDs exhibit a quantum yield of 21% at the excitation wavelength of 360 nm. The electrochemical performances of fabricated batteries are investigated by cyclic voltammetry.