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BACKGROUND A typical approach for removing As from drinking water includes a pre-oxidation step to transform the more toxic As(III) to As(V) and a subsequent separation process for As(V) removal. Unfortunately, typical oxidants result in the formation of toxic oxidation by-products, so alternative options, such as TiO2 photocatalysis, have been investigated. But As(V) produced by oxidation of As (III) remains adsorbed on the catalyst surface, thus limiting process efficiency. In this work a new catalyst based on molybdenum oxide supported on titania (MoOx/TiO2) was investigated to overcome this drawback. RESULTS The complete photocatalytic oxidation of As(III) (5 mg L−1) to As(V) took place after 120 min exposure to UV-A light. Moreover, the removal of As(V) by adsorption treatment downstream of the photocatalytic process was more effective (90% by γ-Al2O3 after 10 min) compared with the combined photocatalysis–adsorption process. Finally, the experimental set-up with UV LED irradiation was found to be more effective (96% As(III) converted) than the UV-A light system (75% As(III) converted). CONCLUSION Photocatalytst did not adsorb As(V) which was completely released into the solution, thus preserving its surface activity and, consequently, drastically reducing operating costs related to catalyst reactivation. © 2014 Society of Chemical Industry

BACKGROUND Heterogeneous photocatalysis for the degradation of non-biodegradable organic contaminants in wastewater is an alternative to traditional treatment techniques. Since the applications developed employ photocatalysts in powder form, a main disadvantage remains related to the recovery of photocatalysts from the treated wastewater, resulting in damage and shorter lifetime for the recirculation pumps. Structured photocatalysts offer a valid solution to simplify the process; however, they have to guarantee light transmission, long-term stability under different operating conditions and under mechanical stress. RESULTS The photocatalytic performances of N-doped TiO2 nanocomposite syndiotactic polystyrene aerogels (Nt-sPS) were analyzed in the presence of visible light. A widely used model pollutant, methylene blue (MB), was chosen to verify the photocatalytic performance. After about 180 min of irradiation, on Nt-sPS, the conversion of MB reached 30%, higher than that obtained (16%) when the photocatalyst is suspended as powder in the liquid reaction medium. CONCLUSION N-doped TiO2, obtained by direct nitration during the hydrolysis of titanium tetraisopropoxide with ammonia solutions, was immobilized in s-PS aerogels, yielding high activity in the removal of methylene blue under visible light irradiation, in comparison with N-doped TiO2 dispersed as powder in solution. © 2014 Society of Chemical Industry