Photocatalytic nitrate reduction under solar-simulated light using modified TiO2

The purpose of this project is to enhance the photocatalytic activity of TiO2 for the photocatalytic reduction of aqueous nitrates for application as a solar-catalytic treatment of polluted water. The aim is also to establish a better understanding of the mechanisms by which noble metals enhance the activity of TiO2. Mono-metallic and bi-metallic Au, Ag and other M-TiO2 catalysts were prepared with the aim of improving charge-carrier separation,these catalysts were then characterised by XRD, BET and TEM. Preparation method variables such as calcination temperature and metal loading were investigated and found to have a large effect on catalytic activity. Metal loadings of between 0.3 and 0.4% were found to give the highest activity and this was concluded to be due to an optimum amount of surface coverage by small metal nanoparticles. The catalysts were found to be very selective towards nitrogen with Au catalysts tending to form ammonia at high conversions and Ag catalysts forming nitrite at low conversions. Bimetallic AuAg catalysts were prepared that had higher activities than their mono-metallic equivalents with 100% selectivity to N2. These catalysts were found to be highly reusable. None of the prepared M-TiO2 catalysts were found to have any visible-only activity for nitrate photo-reduction and the enhancement of photo-activity with the deposition of metals was concluded to be due to increased charge-carrier separation effects. Attempts were made at visibly-active TiO2 by N-doping but although UV-visible DRS analysis showed a redshift in the adsorption band of these catalysts and XRD found the anatase to rutile ratio to be near ideal no reproducible visible-light activity was achieved