Development of unconventional photocatalytic reactors and processes for the abatement of harmful N-containing pollutants

In the present work, innovative photocatalytic processes were developed for the abatement of harmful N-containing compounds, focusing on selectivity towards innocuous N2, to be applied for the treatment of waste waters to meet legislative specifications. The photocatalytic performance of the samples has been checked for the photoreduction of nitrate ions, the photooxidation of ammonia and of organic N-containing compounds. Catalytic performance was correlated with the properties of the nanomaterials. Two innovative semi-batch photoreactors were specifically designed and optimized for this application. Different photocatalysts have been compared. TiO2 has been prepared in nanosized form by using an innovative flame pyrolysis (FP) approach, able to synthesise in one step single or mixed oxide nanoparticles, characterized by homogeneous particle size and good phase purity. In some cases Pd has been added to TiO2 by post synthesis impregnation. The role of the metal nanoparticles was the enhancement of the lifetime of the photoproduced charges by electron trapping. The same materials formulations have been prepared starting from commercial nanostructured TiO2 supports for comparison purposes. The addition of Pd revealed the key to improve both the conversion and the selectivity to N2. The FP prepared materials were in general more active than the commercial TiO2 P25 sample.