In recent years, the use of pharmaceutical drugs has increased to high level. Their presences in wastewater have been considered as an emerging environmental problem due to their continuous input and persistence into the aquatic ecosystem even at low concentrations [1]. Diclofenac (DCF), a common analgesic, anti-arthritic and anti-rheumatic drug, is one of the most widely reported environmental pharmaceutical contaminants [2]. Its ecotoxicity is relatively low, but its combination with other drugs present in water increases the toxicity considerably and interferes with the biochemical functions of the fish [3]. Recent studies show that among the various AOPs, TiO2 photocatalysis seems to be a particularly attractive option for the treatment of pharmaceuticals such as DCF [4]. However, its photocatalytic performance is limited due to its wide band gap (3.03 eV for Rutile, 3.18 eV for Anatase) that strongly causes a limited use of the solar spectra as a source of irradiation. In order to overcome this limitation and enhance its catalytic properties, TiO2 can be doped with nitrogen (N) and produces new materials with high photocatalytic performance in the visible light [5]. In this study, a new sonochemical method was designed for the prepartion of N-TiO2 nano-particles to improve its optical efficiency and catalytic performance under solar light. The nanoparticles were characterized by XRD, TEM, FT-IR. The synthesized nano-particles showed a high catalytic activity under solar light in the degradation and mineralization of DCF. The degradation was conducted under different variables such as loading of catalyst, pH, temperature, time and initial concentrations. The perfect mineralization was achieved under optimum conditions. In addition, the results of degradation were fitted to the first-order kinetics model. Based on performed experiments to determine the mechanism of photocatalytic degradation of DCF, it was found that photogenerated electrons played an important role in the degradation process.

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