Visible-light-driven photocatalytic bacterial inactivation and the mechanism of zinc oxysulfide under LED light irradiation

Abstract

Zinc oxysulfide (ZnO_0.6S_0.4) nanoparticles, prepared via a coprecipitation–calcination method, were used as an effective visible-light-driven (VLD) photocatalyst for the inactivation of a typical Gram-negative bacterium, Escherichia coli K-12 for the first time. An energy-saving white light emitting diode (LED) lamp was employed as the visible light (VL) source. Compared to the only UV-responsive pure ZnO and ZnS, the light active region of ZnO_0.6S_0.4 was expanded as far as 550 nm in the VL region. Significantly, the obtained ZnO_0.6S_0.4 nanoparticles showed considerable VLD photocatalytic bacterial inactivation activity under white LED irradiation. The mechanism of inactivation was investigated in-depth. Photogenerated holes (h⁺) and hydrogen peroxide (H₂O₂) were predominantly responsible for the bacterial inactivation. Moreover, H₂O₂ was evidenced to be derived only from electrons in the conduction band of ZnO_0.6S_0.4 in the present photocatalytic system. The integrated damage from the direct oxidation effect of the h⁺ and continuous accumulation of H₂O₂ resulted in a high bacterial inactivation efficiency of ZnO_0.6S_0.4 nanoparticles under visible white LED lamp irradiation. The destruction process of bacterial cells by the ZnO_0.6S_0.4 photocatalyst was also monitored. This was shown to begin with an attack of the cell membrane and then end in the release of intracellular components.