Coexistence of free radical and nonradical mechanisms for triclosan degradation by CuO/HNTs

[Display omitted] •Nano-CuO was uniformly loaded on the HNTs.•Free radical and nonradical pathways coexisted in CuO/HNTs-PS-TCS system.•OH and O2•- were the main active substances in free radical pathway.•1O2 and surface electron transport played major roles in the nonradical pathway. In this study, CuO/HNTs were applied to activate persulfate (PS) to firstly degrade and mineralize TCS. The morphology, crystal structure, specific surface and surface composition were characterized by SEM, TEM, BET, XRD and XPS. The experimental parameters were optimized with 0.2 g/L CuO/HNTs and 2 mM PS. TCS was totally removed in 180 min under optimized conditions. The mechanism study using the quenching reaction, EPR, XPS and electrochemistry demonstrated that even radical reactions (•OH and O2•-) pathway existed; the nonradical mechanism (1O2 and surface electron transport) was dominant to the efficient TCS degradation. Using FT-ICR MS, the degradation intermediates were identified, and transformation pathways were proposed. The degradation intermediate studies indicated that TCS began to break from the aromatic ring containing monochlorine, and the Cl functional group was gradually substituted. CO2 and H2O were generated with breaking of ether bonds. The toxicity of the solution was also evaluated by the survival rate of the luminescent bacteria, and the toxicity of the solution decreased overall. A stability study showed that CuO/HNTs retained good crystal structure and degradation efficiency even after 5 cycles.