CdIn2S4 microsphere as an efficient visible-light-driven photocatalyst for bacterial inactivation: Synthesis, characterizations and photocatalytic inactivation mechanisms

New types of visible-light-driven photocatalysts with high activity for bacterial inactivation are needed to address the problems caused by outbreak of harmful microorganisms. In this study, cadmium indium sulfide (CdIn2S4) microsphere, which can be synthesized continuously by a facile ultrasonic spray pyrolysis method, was used as an efficient photocatalyst in inactivation of Escherichia coli K-12 under visible light (VL) irradiation for the first time. The as-prepared CdIn2S4 showed a micro-spherical morphology with diameter of 0.5-1.0 mu m. It had an energy band gap of 2.02 eV and BET surface area of 34.8 m(2)/g. It was found that bacterial cells could also be effectively inactivated inside a partition system without the direct contact with the photocatalyst, which was attributed to the diffusible photon-generated hydrogen peroxide (H2O2) rather than hydroxyl radicals (center dot OH). Large amounts of H2O2 were produced from both conduction and valance bands with the involvement of superoxide (center dot O-2(-)). The used CdIn2S4 could be easily recycled by the partition system without loss of activity. The destruction process of bacterial cells was from the cell wall to the intracellular components as confirmed by TEM study. In addition, the center dot O-2(-) and center dot OH radicals were also detected in the CdIn2S4-VL system by ESR spin-trap with DMPO trapping technology. (c) 2012 Elsevier B.V. All rights reserved.