Effect of dissolved silica on photocatalytic water purification with a TiO2 ceramic catalyst

Abstract If photocatalytic water purification technologies will find practical applications, the impact of total dissolved solids in the source water on the activity of the photocatalyst must be evaluated. In this study, we evaluated the effects of SiO 3 2− in water on a TiO 2 ceramic photocatalyst; specifically, we determined the effects of SiO 3 2− on the rate of photocatalytic degradation of formic acid (as a model contaminant) and on the rate of photocatalytic inactivation of Escherichia coli in an aqueous solution. Both the rate of formic acid degradation and the sterilization rate decreased with increasing SiO 3 2− concentration. On the other hand, at a given SiO 3 2− concentration, the activity of the photocatalyst did not decrease over the course of 120 h, and the surface structure of the photocatalyst did not change (i.e., no precipitate formed on the surface). The decreases in photocatalytic activity due to the presence of SiO 3 2− could be recovered by flushing the experimental apparatus with distilled water. These results show that the reason for the lower photocatalytic activity in the presence of SiO 3 2− than in its absence was due to adsorption of SiO 3 2− onto the surface of the TiO 2 photocatalyst and that SiO 3 2− adsorption was an equilibrium process in water.