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

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 SiO32- in water on a TiO2 ceramic photocatalyst; specifically, we determined the effects of SiO32- 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 SiO32- concentration. On the other hand, at a given SiO32- 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 SiO32- 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 SiO32- than in its absence was due to adsorption of SiO32- onto the surface of the TiO2 photocatalyst and that SiO32- adsorption was an equilibrium process in water.