AgBr/g-C3N4 nanocomposites for enhanced visible-light-driven photocatalytic inactivation of Escherichia coli

Abstract

Visible-light-driven photocatalytic disinfection is highly desired for water treatment due to its advantages such as wide applicability and being free of disinfection byproducts. In this study, AgBr/g-C₃N₄ hybrid nanocomposites were evaluated as photocatalysts under visible light irradiation for water disinfection using Escherichia coli as a model pathogen. The physicochemical and photo-electrochemical properties of the photocatalyst were systematically characterized using advanced techniques including scanning electron microscopy (SEM), transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), UV-visible diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and electron spin resonance (ESR) spectroscopy. The inactivation mechanism of E. coli was systematically investigated by monitoring the morphology change of the bacteria and analyzing the role of reactive species. The optimized AgBr/g-C₃N₄ hybrid photocatalyst exhibited remarkably enhanced visible-light-driven photocatalytic disinfection performance towards E. coli over that of pure g-C₃N₄ and AgBr under visible light, which could completely inactivate 10⁷ cfu mL⁻¹ E. coli in 90 min. Quenching studies indicated that h⁺ is the main reactive species responsible for inactivating E. coli. The mechanism study revealed a Z-scheme charge transfer mechanism between AgBr and g-C₃N₄. The g-C₃N₄ could effectively trap the photogenerated conduction band electrons of AgBr via a Z-scheme type of route, thus significantly promoting the electron–hole separation. The trapping of electrons by g-C₃N₄ could facilitate h⁺ accumulation, which accounts for the better disinfection performance of AgBr/g-C₃N₄ compared to AgBr and g-C₃N₄.