Chlorine dioxide radicals triggered by chlorite under visible-light irradiation for enhanced degradation and detoxification of norfloxacin antibiotic: Radical mechanism and toxicity evaluation

Abstract

A novel combined chlorine dioxide (ClO2)-photocatalysis technique was developed by dosing chlorite (ClO2−) in a visible light photocatalytic system. Active ClO2 radicals were produced through the activation of ClO2− by photoinduced ·OH radicals. It is for this reason that the degradation rate of norfloxacin (NOR) in the combined ClO2-photocatalysis system was promoted to 0.2672 min−1, approximately 6.6 times faster than the single photocatalytic system. The durable active ClO2 guaranteed the stability of the combined ClO2-photocatalysis system when facing external interferences, such as pH change, inorganic ions, and natural organic matter (NOM). Quantitative structure–activity relationship (QSAR) prediction and toxicity verification identified effective elimination of biological toxicity of NOR with the assistance of ClO2. Moreover, the residual ClO2− can be retransformed into ClO2 based on the ClO2−/ClO2 dynamic interchange mechanism, facilitating ClO2− residue elimination. ClO2− also served as the sacrificial agent of ·OH for promoting electron-hole separation and protecting photocatalysts from photo-erosion, which was responsible for the outstanding stability in multiple cycle tests. Results showed the novel combined technique can respond well to natural sunlight. This work provides a strategy for designing advanced oxidation processes (AOPs) by integrating ClO2 oxidation and photocatalytic oxidation to achieve degradation and detoxification of antibiotic wastewater under natural sunlight.