Enhanced degradation of cefalexin using Co2SnO4@rGO as an effective peroxymonosulfate activator in hybrid ozonation system

Abstract

This study successfully developed a nanocomposite catalyst (Co2SnO4 @rGO) at optimal composite ratio of 2:1 between Co2SnO4 and GO for effectively activation of peroxymonosulfate (PMS) to degrade cefalexin (CFX) from water by hybrid ozonation system (O3/Co2SnO4 @rGO/PMS). The CFX removal efficiency was compared in three oxidation systems, including O3, Co2SnO4 @rGO/PMS and O3/Co2SnO4 @rGO/PMS under various operational conditions. The effect of co-existing anions and scavengers was studied to determine the CFX removal mechanisms. The characteristics of catalyst were analyzed using SBET, SEM, EDS and mapping, XRD, FTIR and pHPZC. The results illustrated that supplementation of O3 into Co2SnO4 @rGO/PMS system exhibited the highest degradation and mineralization efficiencies of CFX, reaching 99.93% and 67.03%, respectively under optimal operational conditions. At this condition, the CFX degradation and mineralization rates in O3/ Co2SnO4 @rGO/PMS system were higher than those in Co2SnO4 @rGO/PMS system by 2.8 and 1.32 times, respectively, thanks to synergistic effect of O3 and Co2SnO4 @rGO/PMS in the same reactor. The CFX removal mechanisms were proposed through both pathways: non-radical and radical pathway. The non-radical mechanism was through singlet oxygen (1O2) and radical pathway was via the free radicals of *OH, *SO4- and *O2. The scavenging experiments further confirmed CFX removal mechanism was through both non-radical and radical pathways. Among them, the 1O2 was predominately species in removal of CFX. Besides, the Co2SnO4 @rGO catalyst exhibited a high reusability over four consecutive catalytic cycles. These findings demonstrated the occurrence of O3 and Co2SnO4 @rGO in hybrid ozonation system effectively activated PMS to enhance CFX removal from wastewater.