Photoreduction of nitrates from waste and drinking water

The photoreduction of nitrate ions was studied for the abatement of N-containing compounds from waste and drinking water. A new processwas developed in semibatch mode, aiming at maximum selectivity towards N2. Different photocatalysts have been prepared with two different methods and their photocatalytic performance has been compared with commercial nanostructured TiO2 (P25). TiO2 has been prepared in nanosized form by using an innovative flame pyrolysis (FP) approach, and mesoporous TiO2 was prepared by sol-gel method. Pd has been added to TiO2 by post synthesis impregnation. The physical/chemical properties of the photocatalysts were studied by means of XRD, BET and UV-Vis spectroscopy. The results show that the flame pyrolysis procedure is a viable technique for the preparation of nanosized TiO2 for this application, leading to ca. double conversion with respect to P25. Furthermore, the addition of a small amount of Pd (0.1 mol %), likely enhanced the lifetime of the photoproduced charges by electron trapping and resulted in higher conversion and selectivity toward N2. The best performance was obtained with Pd doped on TiO2 (FP), with 13% conversion and ca. 27% selectivity, only, toward ammonia formation.