Water disinfection using zinc phosphide nanowires under visible light conditions

Common methods of bacteria disinfection after water treatment include chlorination and ultraviolet irradiation. Although very effective, those methods require continual investment of energy or materials. Previous studies have shown that photocatalysis can enhance water disinfection. This study addressed the potential use of zinc phosphide nanowires to promote water disinfection under visible light conditions as a potentially economical alternative. Disinfection studies were conducted using boron nitride decorated zinc phosphide nanowires, unfunctionalized zinc phosphide nanowires, 1,4-benzenedithiol functionalized zinc phosphide nanowires, and bare zinc foil. Bioreactors inoculated with Escherichia coli isolates were exposed to the photocatalysts under visible light. E. coli was enumerated at five-min intervals during the disinfection period. At least a 5-log reduction in microbial load was achieved for all materials, with the unfunctionalized zinc phosphide nanowires consistently producing the highest log reduction. For each material, more than a 4-log reduction was observed after only 5 min of exposure. Minimal photoreactivation or dark repair (less than a 1.48-log increase) was observed. Disinfection efficacy did not differ significantly (p < 0.05) between the three isolates. Although the specific photocatalytic mechanism is not yet known, this study indicates that zinc phosphide nanowires can enhance disinfection of water using only visible light.