Harnessing the power of S/N-doped NiO nanoparticles through bandgap tuning to achieve enhanced photocatalytic and antibacterial performances.

Nickel oxide (NiO) is a promising photocatalyst owing to its stability, cost-effectiveness, and eco-friendliness. However, its wide band gap and rapid electron-hole recombination limit its effectiveness under visible light. In this study, we introduce a novel approach by co-doping NiO nanoparticles with sulfur and nitrogen (S/N-NiO-NPs) to overcome these limitations. Using a co-precipitation method, we synthesized and thoroughly characterized the materials, confirming successful doping and significant modifications in their structural and optical properties. Notably, S/N co-doping reduced the band gap from 3.75 to 2.50 eV, enhanced charge separation, and improved visible-light absorption. Under optimal conditions (pH 10), only 40 mg of S/N-NiO-NPs achieved 98.9% degradation of methylene blue dye within 60 min of sunlight exposure; far surpassing the performance of pure NiO. The reusability of the catalyst was also tested, and the degradation efficiency was maintained at approximately 89.92% after three consecutive cycles. Furthermore, the doped nanoparticles exhibited enhanced antibacterial activity, with inhibition zones of 13-17 mm against common pathogens, compared to 5-10 mm for pure NiO. These findings demonstrate that S/N co-doping effectively transforms NiO into a highly efficient, multifunctional material with significant potential for environmental remediation and biomedical applications, marking a notable advancement in photocatalyst design.