Mandhakini Mohandas

Carbon nanomaterials derived from agricultural waste streams present an exciting material platform that hits multiple sustainability targets by reducing waste entering landfill, and enabling clean energy and environmental remediation technologies. In this work, the energy and photocatalytic properties of reduced graphene oxide fabricated from coconut coir using a simple reduction method using ferrocene are substantially improved by introducing metallic oxides flakes. A series of cobalt ferrite rGO/CoFe₂O₄ nanocomposites were assembled using a simple soft bubble self-templating assembly, and their potential for clean energy applications confirmed. The transmission electron microscopy images revealed the uniform dispersion of the metal oxide on the rGO sheets. The functional group of the as synthesized metal oxide and the rGO nanocomposites, and its individual constituents, were identified through the FTIR and XPS studies, respectively. The composite materials showed higher specific capacitance then the pure materials, with rGO spinal metal oxide nanocomposites showing maximum specific capacitance of 396 F/g at 1 A/g. Furthermore, the hybrid super capacitor exhibits the excellent cyclic stability 2000 cycles with 95.6% retention. The photocatalytic properties of the synthesized rGO nanocomposites were analyzed with the help of malachite green dye. For pure metal oxide, the degradation rate was only around 65% within 120 min, while for rGO metal oxide nanocomposites, more than 80% of MG were degraded.

Scaling up the production of functional reduced graphene oxide (rGO) and its composites requires the use of low-cost, simple, and sustainable synthesis methods, and renewable feedstocks. In this study, silver oxide-decorated rGO (Ag_xO−rGO) composites were prepared by open-air combustion of mustard oil, essential oil-containing cooking oil commercially produced from the seeds of Brassica juncea. Silver oxide (Ag_xO) nanoparticles (NPs) were synthesized using Coleus aromaticus leaf extract as a reducing agent. Formation of mustard seed rGO and Ag_xO NPs was confirmed by UV-visible characteristic peaks at 258 nm and 444 nm, respectively. rGO had a flake-like morphology and a crystalline structure, with Raman spectra showing clear D and G bands with an I_D/I_G ratio of 0.992, confirming the fewer defects in the as-prepared mustard oil-derived rGO (M−rGO). The rGO-Ag_xO composite showed a degradation efficiency of 81.9% with a rate constant k⁻¹ of 0.9506 min⁻¹ for the sodium salt of benzidinediazo-bis-1-naphthylamine-4-sulfonic acid (known as the azo dye Congo Red) in an aqueous solution under visible light irradiation. The composite also showed some antimicrobial activity against Klebsilla pneomoniae, Escherichiacoli, and Staphylococcusaureus bacterial cells, with inhibition zones of ~15, 18, and 14 mm, respectively, for a concentration of 300 µg/mL. At 600 µg/mL concentration, the composite also showed moderate scavenging activity for 2,2-diphenyl-1-picrylhydrazyl of ~30.6%, with significantly lower activities measured for Ag_xO (at ~18.1%) and rGO (~8%) when compared to control.

Nitrogen-doped graphene-based aerogels with three levels of hierarchically organized pores were prepared via a simple environmentally friendly process, and successfully tested in supercapacitor applications. Mesopores and macropores were formed during the aerogel preparation followed by carbonization and its chemical activation by potassium hydroxide (KOH). These mesopores and macropores consist of amorphous carbon and a 3D graphene framework. Thermal treatment at 700 °C, 800 °C, 900 °C in N₂ atmosphere was done to etch out the amorphous carbon and obtain a stable N-doped 3D graphene. Specific capacitance values obtained from the electrochemical measurements are in the range of 232–170 F× g⁻¹. The thus fabricated structures showed excellent cyclic stability, suggesting that these materials have potential as electrodes for solid asymmetric supercapacitors.