Mechanistic investigation of visible light driven photocatalytic inactivation of E. coli by Ag-AgCl/ZnFe2O4.

In this study, photocatalytic inactivation of Escherichia coli was investigated over magnetic nanocomposite Ag-AgCl/ZnFe2O4. The nanocomposite demonstrated efficient photocatalytic activity by complete inactivation of the bacteria within 60 min of visible light irradiation. The anions HPO42- and SO42- were found to play the most important role in the inhibition of photocatalytic inactivation of E. coli. A systematic investigation of mechanism of photocatalytic bacterial inactivation was carried out based on cell membrane injury test, scanning electron microscopy (SEM) of bacterial morphology changes, Fourier transform infrared (FTIR) spectroscopy of E. coli cells before and after treatment, superoxide dismutase (SOD) and catalase (CAT) activity assay, and role of various reactive oxygen species (ROS). The activities of SOD and CAT enzymes were found to decrease due to the ROSs attacks during photocatalytic inactivation. The ROS produced in the photocatalytic disinfection severely altered the bacterial permeability and led to protein fragmentation, release of ions, and generation of protein carbonyl derivatives. The leaked cytoplasmic substances and cell debris were further degraded and, ultimately, mineralized with prolonged photocatalytic treatment.