Electrochemical oxidation degradation of fungicide 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT) in brine of reverse osmosis by a novel Ti/CB@MXene anode

Abstract

The electrochemical oxidation purification of reverse osmosis concentrated brine was sustainable water purification technology; however, anode oxidation efficiency and capacity limit its development. According to MXene’s high surface area and structure characterization, a novel Ti/ carbon black (CB) @MXene anode was prepared for the first time for electrochemical oxidation degradation of 5-chloro-2-methyl-4-isothiazoline-3-one (CMIT) in reverse osmosis brine, even though MXene was studied more widely in sulfate radical based AOP and photocatalysis. This anode showed slippy surface and high oxygen evolution potential (2.84 V), suggesting it is hard to be fouled and eliminated the side reaction effect. According to the anode fabrication parameters optimization, the best mass ratio of Ti3C2Tx and CB was 1:1, showing the highest oxygen evolution potential. The reaction parameters including current density and plate spacing were optimized as 5.625 mA/cm2 and 1.0 cm, where the best CMIT degradation efficiency was 89.86 %. This performance was better than DSA and similar with BDD anode, however its stability needs to be improved. The indirect oxidation dominated CMIT degradation as 99.69 % and •OH formation rate was 13.81 L·mol−1·s−1, which was approximately 5.04 fold higher than that of traditional Ti anode. Three possible degradation pathways of CMIT were proposed, as below: electron rich sulfur in SN bond was oxidized to form sulfoxide structure, chlorine was replaced by •OH, olefin double bond was attacked by •OH. The formed intermediates showed less ecotoxicity. The Ti/CB@MXene anode showed better potential in electrochemical oxidation treatment of reverse osmosis brine.