Harnessing the Power of S/N Doped NiO Nanoparticles: Bandgap Tuning for Superior Photocatalytic and Antibacterial Performance

Abstract Nickel oxide (NiO) has gained attention as a promising photocatalyst, thanks to its high efficiency, photochemical stability, cost-effectiveness, and eco-friendly nature. However, a wide band gap and rapid electron-hole recombination hinder its practical application under visible light. This study synthesized pure NiO nanoparticles (NiO-NPs) and sulfur/nitrogen co-doped NiO nanoparticles (S/N-NiO-NPs) via the co-precipitation method. Comprehensive structural and optical analyses using UV-Vis, FT-IR, XRD, and SEM confirmed the successful formation of the desired materials. Notably, doping with 4% sulfur and 6% nitrogen significantly enhanced charge separation, extended light absorption, narrowed the band gap from 3.75 eV to 2.50 eV, and reduced crystalline size from 20.49 nm to 17.89 nm. Under optimal conditions (pH 10),40 mg of S/N-NiO-NPs achieved an impressive 98.9% degradation of 5 ppm methylene blue dye within just 60 min of sunlight irradiation, far outperforming pure NiO-NPs. Additionally, antibacterial evaluations demonstrated superior efficacy, with S/N-NiO-NPs exhibiting inhibition zones of13–17 mm against pathogens such as Bacillus cereus, Escherichia coli, Salmonella typhi, and Staphylococcus aureus, compared to the 5–10 mm zones observed for pure NiO-NPs. These results highlight the remarkable potential of S/N co-doping in transforming NiO into a highly efficient, multifunctional material for environmental remediation and biomedical applications.