Enhanced visible-light-driven photocatalytic disinfection using AgBr-modified g-C₃N₄ composite and its mechanism

In this study, novel AgBr-modified g-C₃N₄ (AgBr/g-C₃N₄) photocatalysts were prepared by an adsorption-deposition method and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and ultraviolet-visible spectroscopy (UV-vis). Furthermore, the photocatalytic disinfection performance on Escherichia coli (ATCC 15597) was investigated. The as-prepared photocatalysts exhibited well crystalline structures and morphologies with C₃N₄ and exhibited a stronger bacterial inactivation than that of pristine g-C₃N₄. The disinfection efficiency reached up to 4.80 log under 150 min of visible light irradiation when AgBr-modified g-C₃N₄ was prepared at a molar ratio of 1:5 (AgBr: g-C₃N₄), which was a 4.2 log increase compared with that of pristine g-C₃N₄ under the same experimental conditions. The enhancement of the photocatalytic activity of AgBr/g-C₃N₄ was attributed to the effective production and transfer of the photo-induced electrons under visible light irradiation, since the AgBr modification reduced the bandgap energy and boarded the visible light area. Furthermore, h⁺ was found to be the dominant contributor for bacterial inactivation. The h⁺ and photo-generated reactive oxygen species (ROSs) damaged the cell membranes and destroyed metabolic processes, resulting in leakage of potassium ions and proteins, lipid peroxidation, degradation of intracellular protein, and a reduction of the ATP levels, which finally lead to bacterial death. These results provide a theoretical basis for the development of low-cost, high-efficiency photocatalysts for green/sustainable water disinfection.