Removal of alprazolam from aqueous solutions by heterogeneous photocatalysis: Influencing factors, intermediates, and products

Abstract

Efficiency of heterogeneous photocatalytic degradation of alprazolam was investigated. The structural and morphological properties of ZnO were investigated in detail. It was found that ZnO has wurtzite structure with crystallite size about 41nm, specific surface area about 6.5m2/g, and intraparticle system of pores (maximum pore width about 160nm). The efficiency of alprazolam photocatalytic degradation was examined as a function of the type of irradiation (UVA, visible, and simulated solar irradiation) and photocatalyst (ZnO, TiO2 Degussa P25), photocatalyst loading, pH, and the presence of hydroxyl radical, and positive hole scavengers. By examining the effect of types of irradiation and catalysts, it was found that the UVA/ZnO system is the most efficient for alprazolam removal. The optimum catalyst loading was 2.0mg/mL for TiO2 Degussa P25, while in presence of ZnO degradation rate increases in whole investigated range. In the case of ZnO, the pH 7 was selected as an optimal condition, while in aqueous suspension of TiO2 Degussa P25, degradation rate increases in whole investigated pH range (3.4–8.8), but increasing is not as pronounced as in case of ZnO. Also, it was found that ZnO photocatalysis takes place only via hydroxyl radicals, while using TiO2 Degussa P25 positive holes play significant role, too. The results of total organic carbon and ionic chromatography analysis showed that after 60min of irradiation using both catalysts alprazolam was completely mineralized. Here, for the first time, reaction intermediates formed using both catalysts were studied in detail, whereby the main intermediates were hydroxyl derivates. ZnO showed high stability in photodegradation after three successive runs.