Solar photodegradation of the UV filter benzotriazole in the presence of persulfate

Benzotriazole (BT), which is used as a UV filter, an anti-corrosion agent and anti-icing fluid, has been frequently observed in various water bodies. In this study, a sunlight/persulfate system was used to investigate BT degradation for the first time. The BT degradation behavior in the sunlight/persulfate system was well fitted by pseudo first-order kinetics. Compared to direct photolysis and persulfate oxidation, BT was significantly photodegraded by 90% within two hours in the presence of persulfate. The BT degradation rate was fastest under acidic conditions and slightly decreased at neutral pH 7. However, the BT degradation rate dramatically decreased under alkaline conditions (pH 9 and 11) due to the lower persulfate activation rates and deprotonated form of BT. Sulfate radicals (SO4·–), hydroxyl radicals (·OH), singlet oxygen (1O2), and superoxide radicals (O2–·) were identified via an electron paramagnetic resonance (EPR) spectrometer in the sunlight/persulfate system. SO4·– and·OH were the dominant species under acidic and neutral pH; 1O2 and O2–·contributed to only partial BT degradation under alkaline conditions. In addition, BT degradation was inhibited in the presence of common water matrix components (Cl–, HCO3–, NO3–, and dissolved organic matter) due to the scavenger effect and formation of less reactive radicals. Only slight mineralization occurred within 15 h of operation in the sunlight/persulfate system. This study comprehensively evaluated the BT degradation mechanism in a sunlight/persulfate system, and the results provide promising insight into the application of sunlight/persulfate systems in advanced water polishing treatment.