Visible-light-driven Photocatalytic Disinfection of Bacteria by the Natural Sphalerite.

摘要

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. In 1985, Matsunaga et al. first successfully reported that titanium dioxide (TiO2) photocatalyst could disinfect bacterial cells in water. Since then, photocatalytic technology was extensively studied and proved to be a cost-effective, safe and promising alternative for wastewater treatment. However, TiO2 can only be excited by light with wavelengths in the near ultraviolet (UV) region which is only 4% of the solar spectrum. Therefore, it is a crucial issue to develop new photocatalysts which can be excited by sunlight. Although synthetic photocatalysts show good disinfection efficiency under visible light (VL), however, the amounts of those synthetic visible-light-driven (VLD) photocatalysts are very limited so that they cannot satisfy with the large-scale application in the practical wastewater treatment. Obviously, a large quantity and low-cost VLD photo catalysts must be more popular than artificial semiconductors.;In this study, the photocatalytic disinfection capability of a natural semiconducting mineral, sphalerite, is studied for the first time. Natural sphalerite (NS), a ZnS containing metal ions such as Fe2+ and Cd2+, exhibits good photo activity under VL. Firstly, NS can inactivate Escherichia coli K-12 irradiated by fluorescent tubes (FTs). Moreover, it is the first time to experimentally prove that the photogenerated electron (e-) and hydrogen peroxide (H 2O2) play important roles in the bacterial disinfection of E. coli K-12 using multiple scavengers coupled with a partition system.;Secondly, the effect of different parameters of VL on photocatalytic disinfection efficiency of NS is explored. The "discreted peak spectrum" of FTs is much more effective than the "continuous spectrum" of white light emitting diode (LED) lamps and Xenon lamp to inactivate bacterial cells. Bacterial inactivation efficiency depends on the wavelength of VL. At equivalent intensity, blue and yellow LED lamps show the more disinfection efficiency than green and red LED lamps. Photocatalytic disinfection is also related to the VL intensity.;Finally, NS shows high photocatalytic activity to disinfect wastewater bacteria such as the Gram -ve bacterium, E. coli, and the Gram +ve bacterium, Microbacterium barkeri, under VL irradiation. The photocatalytic disinfection efficiencies at different pH are strongly influenced by the amount of H2O2. Moreover, different reactive species are involved in the photocatalytic disinfection of E. coli and M. barkeri. A possible cell damage mechanism by the photogenerated e- produced by NS is tentatively proposed.;In this study, NS is explored as a novel, cost-effective VLD photocatalyst. Due to its natural abundance and ease of procurement, NS can be used economically for the large-scale photocatalytic disinfection of bacterial cells.