Semi-Batch Photocatalytic Reduction of Nitrates : Role of Process Conditions and Co-Catalysts

Photocatalysis has been used to reduce nitrate ions from waste and drinking water. A semibatch photoreactor was developed for this process and commercial nanostructured TiO2 (P25) and TiO2 in nanosized form prepared by flame spray pyrolysis (FSP) were used as catalysts. Several noble metals were added as co-catalyst on both titania samples and the chemical physical properties of every sample were studied by XRD, BET and UV-Vis spectroscopy techniques. The optimum pH to reach the highest conversion of nitrates with lower selectivity toward ammonia was different for P25 and FSP samples, at basic pH and nearly neutral, respectively. The bare and doped FSP samples, with higher surface area, showed higher nitrates conversion with respect to P25-based samples. The photocatalytic rate of nitrate reduction over undoped TiO2 was higher than that of most noble metal loaded TiO2, except Ag. The highest activity for nitrate conversion has been obtained by adding Ag on P25 and FSP, increasing the conversion up to 3.5 and 1.5 times with respect to the bare semiconductor, respectively