Magnetically recoverable Fe3O4/MoS2/BiOI microspheres for visible light water disinfection: Molecular mechanism and transcriptomic insights

Abstract

Photocatalysis driven by green energy is ideal for water purification. To gain a deeper understanding of the underlying mechanism behind the photocatalytic inactivation of bacteria, a novel visible-light-driven Fe3O4/MoS2/BiOI (FMB) photocatalyst was synthesized, and E. coli disinfection was demonstrated. Complete inactivation of E. coli was achieved in 100 min by FMB exposed to 30 mW/cm2 of > 400 nm light. FMB can also effectively reduce the total number of bacteria and heterotrophic bacteria in actual source water. The photochemical experiments revealed that h+, e-, H2O2, 1O2 and •O2– were responsible for inactivation reactions. The semipermeable membrane experiments provided further evidence that contact between the photocatalyst and the bacteria was necessary to achieve inactivation. During the disinfection process, the zeta potential of the cells first decreased and then increased, while the particle size first increased and then decreased, indicating the rupture of the cells. Scanning electron microscopy, potassium ion leakage, and changes in cell surface hydrophobicity and hydrophilicity all confirmed the destruction of the E. coli cell membrane at the molecular level. The β-GAL activity of E. coli decreased, and the activities of superoxide dismutase (SOD) and catalase (CAT) increased initially, but subsequently decreased, further demonstrating disruption of the cell membrane and the leakage of cell contents. Transcriptomics was employed to understand gene expression and confirm bacterial membrane damage followed by oxidative stress response. This work provides a demonstration of the FMB inactivation by visible light and a mechanistic understanding of inactivation of E. coli.