Photocatalytic degradation of sulfonamide and its human metabolite by immobilized ZnO nanorods/TiO2 nanoparticles

The heterojunction of zinc oxide (ZnO) and titanium dioxide (TiO2) over a glass substrate was investigated. The photocatalysts were applied to sulfamethoxazole (SMX) and N-acetyl sulfamethoxazole (AcSMX) photodegradation. ZnO/TiO2 exhibited a significant photocatalytic activity, visible light absorption and photo-stability. The best photocatalytic activity was achieved by coupling ZnO from zinc nitrate precursor with TiO2 (N-ZT). Degradation of 49% for SMX and 32% of AcSMX were observed after 240 min of irradiation. The degradation efficiency of SMX still reached 85% and 39% for AcSMX after 12 h under irradiation. For AcSMX metabolite, an interestingly photo-catalytic back-transformation to SMX was observed, indicating that this metabolite may serve as an environmental source of the sulfonamide antibiotic. The electrical energy required for SMX and AcSMX photocatalytic degradation was extremely high, although the results showed that application of ZnO/TiO2 was efficient in reducing the toxicity of the effluent. The main toxic effect was the inhibition of root growth for Lactuca sativa seeds, without inhibiting seed germination. Some byproducts generated by SMX degradation were responsible for cytotoxicity against Artemia sauna. At the same time, no toxicity were found on the treated sample after AcSMX degradation for both Artemia sauna and Lactuca sativa bioindicators.

Automated summary

The heterojunction of zinc oxide and titanium dioxide was investigated for the photodegradation of sulfamethoxazole and N-acetyl sulfamethoxazole. The results showed that ZnO/TiO2 exhibited significant photocatalytic activity, visible light absorption, and photo-stability. However, the electrical energy required for the photocatalytic degradation was high.