Photocatalytic degradation of atrazine by an N-doped TiO2/polymer composite: catalytic efficiency and toxicity evaluation

Monolithic composite aerogel based on N-doped TiO2 (NdT) photocatalyst dispersed into syndiotactic polystyrene (sPS) matrix was used for atrazine (ATZ) degradation under ultra-violet (UV) and visible light (Vis) irradiation. sPS/NdT composite aerogel, with a polymer/photocatalyst 90/10 wt ratio, was achieved by super critical CO2 extraction of chloroform from the relative sPS/NdT gel. Testing of the sPS/NdT photocatalytic activity was performed by using initial ATZ concentration of 0.1 mg/L and a sPS/NdT composite in monolithic aerogel form. ATZ removal was equal to 47% and 25% under UV or Vis light, respectively, after 180 min of irradiation. The efficiency of the photocatalytic process was also investigated by monitoring the ecotoxicity of the treated water to Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna. The results indicated that, for both UV and Vis irradiation, even for high ATZ removal efficiency (i.e., UV treatment), the toxicity of process effluent is greater than the initial one, most likely because of the generation of toxic by-products. The UV treatment was effective only after 72 h when the solution appeared not toxic to D. magna and presented a very low effect to R. subcapitata. On the other hand, under Vis light irradiation, a very high level of toxicity was still detected after 72 h of treatment time. Toxicity tests are confirmed as an indispensable tool for a correct assessment of the environmental impact of water treatment processes.