Enhanced electrochemical oxidation of tetracycline and atrazine on SnO2 reactive electrochemical membranes by low-toxic bismuth, cerium doping

Abstract

SnO2-Sb electrodes are widely used in electrochemical advanced oxidation processes for water treatment; however, the release of highly toxic Sb3+/Sb5+ has aroused environmental concern. This study systematically investigated the potential of Bi and Ce elements as substitutes to fabricate doped-SnO2 reactive electrochemical membrane (REM) for water purification. Compared with the control (SnO2-Sb-REM), SnO2-Bi-REM showed a higher direct electron transfer (DET) rate and •OH yield due to its larger electroactive surface area. The higher oxygen evolution potential of SnO2-Ce-REM enhanced selectivity for •OH generation. Although both SnO2-Bi-REM and SnO2-Ce-REM exhibited higher electrooxidation of tetracycline hydrochloride (TCH) and atrazine (ATZ) than SnO2-Sb-REM, only the service lifespan of SnO2-Bi-REM can meet the requirements of practical applications. Mechanistic studies of the degradation pathways indicated that the rapid degradation of TCH on SnO2-Bi-REM was mainly contributed by the DET process, while the transformation of intermediates involved the reactions with •OH. In comparison, aqueous •OH played an important role in the degradation of refractory ATZ. Moreover, a SnO2-Bi-REM system demonstrated ∼99% removal of trace TCH and ATZ from wastewater effluent in single-pass operation at a low electrical efficiency per log order removal (EE/O, 0.71 kWh m−3). To this end, the SnO2-Bi-REM is demonstrated to be a promising electrode to replace SnO2-Sb-REM for efficient and sustainable water purification.