Nitrate reduction in water using commercial titanium dioxide photocatalysts (P25, P90, and Hombikat UV100)

Photocatalytic nitrate reduction was examined in a model water and in groundwater by using three commercially available titanium dioxide photocatalysts (Evonik P25, Evonik P90, and Sachtleben Hombikat UV100). The photocatalysts were characterized using uniform methods (TEM, XRD, surface area, UV-VIS, surface charge) and their photocatalytic activity was differentiated using these results. Under all experimental conditions, P25 and P90 were superior to UV100, and P90 outperformed P25 with nitrate reductions as high as 77% at the maximum irradiance level used (6.46×1022 photons/L). The photocatalytic nitrate reduction activity was found to be dependent on the rate of recombination, pH, and the total photocatalyst surface area, with the recombination rate being the limiting variable. Nitrate reduction was more efficient in model water than in groundwater that contained constituents capable of occupying photocatalyst surface sorption sites or scavenging conduction band electrons. The greater efficiencies of P25 and P90 compared with UV100 were attributed primarily to the mixed-phase nature of the photocatalysts, which allow for better charge separation, and the greater activity of P90 over P25 was attributed to a larger surface area. The results should be helpful in the selection of these commercially available photocatalysts to treat a wide range of pollutants other than nitrate.