Enhanced photocatalytic activity of TiO2 with acetylene black and persulfate for degradation of tetracycline hydrochloride under visible light

The photocatalysis and advanced oxidation processes were combined in the degradation of tetracycline hydrochloride (TH). The TiO2 doped with acetylene black (TiO2/AB) was employed with persulfate (PS) to generate reactive radicals. The TiO2/AB-2.5 wt% exhibited the best removal efficiency of TH, compared with TiO2/AB-1.25 wt%, TiO2/AB-5 wt% and TiO2/AB-10 wt%. The TiO2/AB/PS can significantly improve the TH degradation rate by 38.5% compared with the TiO2/AB. The operating conditions such as the PS dosage, TiO2/AB dosage, pH, and initial concentration of TH on the degradation of TH were investigated, and the optimal removal efficiency of TH was obtained when the concentration of PS was 3 mmol/L, TiO2/AB dosage was 0.5 g/L, pH = 4.1 and initial concentration of TH was 10 mg/L. The ethanol and tertiary butanol were used as the radical scavengers to identify the dominant reactive radical species in the TiO2/AB/PS system. The SO4− was demonstrated more important than OH in the degradation of TH. Then the intermediates and possible degradation pathways of TH were discussed. Finally, the stability of TiO2/AB and toxicity of TH were studied. The degradation efficiency was still above 85% after 5 cycles. The toxicity assessment results suggest that the aquatic toxicity of TH was effectively diminished.