Green synthesis of cobalt oxide nanoparticles (Co3O4NPs): Characterization and green light-driven photocatalytic aerobic oxidation of alkyl and aryl sulfides to the corresponding sulfoxides

In recent years, cobalt oxide nanoparticles (Co₃O₄NPs) have garnered significant attention due to their unique properties and wide range of applications, particularly in catalysis and environmental remediation. This study focuses on the green synthesis of Co₃O₄NPs using garlic extract as a bio-reducing and stabilizing agent, marking the first instance of employing this eco-friendly and cost-effective method. The synthesized nanoparticles were characterized using various techniques including SEM, EDX, FTIR, XRD, UV–Vis DRS, and BET analysis, revealing their spherical morphology, elemental composition, surface area, and optical properties. The primary application investigated was the photocatalytic aerobic oxidation of alkyl and aryl sulfides to sulfoxides under visible green light irradiation. The study meticulously optimized the reaction conditions, evaluating the effects of different solvents, light sources, and catalyst dosages. The optimal conditions were found to be a MeCN:H₂O (5:1) solvent system, green LED light (535 nm), and 10 mg of Co₃O₄NPs catalyst with the highest TON of 12.5. Under these conditions, the catalyst demonstrated high efficiency, achieving up to 95% yield of sulfoxides with various substrates. Furthermore, the reusability of the Co₃O₄NPs was assessed through multiple catalytic cycles, showing excellent stability and consistent performance. Mechanistic studies indicated that the photocatalytic activity involves the generation of reactive oxygen species (ROS) such as superoxide anion radicals (O₂^.-) and singlet oxygen (¹O₂), with both holes and electrons playing crucial roles in the oxidation process. This research highlights the potential of green synthesized Co₃O₄NPs as effective and sustainable photocatalysts for selective oxidation reactions, offering a promising approach for environmentally benign chemical processes. The findings pave the way for further exploration of bio-derived catalysts in various industrial applications, promoting greener and more sustainable practices in chemical synthesis.