Photocatalytic disinfection of bacteria using photosensitive nanomaterials is an efficient method for bacteria inactivation and is considered a beneficial alternative to chemical disinfectants that produce harmful by-products. However, due to the limited application scope of photocatalysts, the antibacterial efficiency remains unsatisfactory. To enhance the photocatalytic efficiency of the non-metal photosensitizer, graphitic carbon nitride (g-C3N4) nanosheets, they were composited with a metal-based photosensitizer, zinc peroxide (ZnO2) nanoparticles, with the aim of humic acid (HA). Besides the self-generating ability of H2O2 by ZnO2 in an aqueous medium, its deposition over g-C3N4 nanosheets enhances visible light harvesting and increases both surface area and active sites, thereby enhancing photocatalytic efficiency. The resulting composite, g-C3N4/ZnO2, produced more H2O2, •OH, and O2•- radicals than either component when exposed to visible light. Moreover, the photocatalyst demonstrated enhanced photocatalytic disinfection efficacy against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) under dark conditions compared to pure g-C3N4 nanosheets. However, a notably greater antibacterial activity was observed when the nanocomposites were subjected to light irradiation. FESEM images and live-dead assays revealed the physical contact of the nanocomposite with the surface of bacterial cells and the loss of cell membrane integrity. Furthermore, it was observed that there was greater cellular uptake of nanocomposites into cells and the generation of reactive oxygen species (ROS) under light irradiation compared to similar conditions in the dark, leading to an increased photoinactivation rate of bacteria. The enhanced photocatalytic and antibacterial activities of g-C3N4/ZnO2 nanocomposites make them attractive for a range of applications, including use in nanomedicine and environmental surface disinfection.

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