Peroxydisulfate production in situ by blue titania nanotube array electrode for tetracycline degradation in groundwater: Performance and mechanism

Abstract

• PDS generation in situ by Blue-TNA was used to TC degradation in groundwater. • Coexisting anions inhibit the generation of PDS. • The hydroxyl radical is an important precursor of PDS generation. • TC is degraded through the combined action of PDS, ·OH and SO 4 ·- . In this study, a blue titania nanotube array (Blue-TNA) electrode was prepared and applied in oxidizing sulfate ions (SO 4 2- ) in groundwater to peroxydisulfate (PDS) for antibiotics degradation. Influencing factors, the mechanism of PDS formation and the efficiency of antibiotics degradation were studied. There was no PDS generation in both the PbO 2 and Pt electrolysis systems over the experimental time, but 2.8 mmol/L PDS was generated in the Blue-TNA electrolysis system in 90 min, which can be attributed to a higher oxygen evolution potential of Blue-TNA than that of PbO 2 and Pt. An increase in current density and Na 2 SO 4 concentration favored PDS generation and the current efficiency improvement. The coexisting anions (CO 3 2- 、HCO 3 - and PO 4 3- ) inhibited the PDS generation with the strength of inhibition following the sequence: CO 3 2- ＞ HCO 3 - > PO 4 3- . The effect of dissolved oxygen on PDS generation was negligible, but ·OH was an important precursor for PDS generation based on radical quenching experiments. The degradation efficiency of tetracycline (TC, 20 mg/L) by Blue-TNA was more than 90% in 30 min due to the synergy of ·OH and SO 4 ·- in the sulfate electrolysis system. This study proposed a novel and economic method for PDS generation by the oxidation of SO 4 2- in situ using Blue-TNA, which is an eco-friendly and efficient method in TC degradation.