Determining the key factors of nonradical pathway in activation of persulfate by metal-biochar nanocomposites for bisphenol A degradation

In this study, three types of metal-biochar nanocomposites (CuO/BC, Fe3O4/BC and ZnO/BC) were synthesized as the catalysts to activate sodium persulfate (PS) for the degradation of bisphenol A (BPA). The results showed that nonradical pathway was the dominant reaction which was based on electron transfer intermediates in the CuO/BC-PS system (k(obs) ca. 0.0607 min(-1)) that consumed a small amount of PS (0.17 mM) for the mineralization of all BPA. Meanwhile, the higher k(obs) would be obtained when contained scavengers, verifying that the generation of intermediates were accompanied by the side reaction (CuO/BC reacted with PS and water to generate (OH)-O-center dot) in the CuO/BC-PS system. However, (OH)-O-center dot and SO4 center dot- were the dominant radicals in the Fe3O4/BC-PS system (without scavengers, k(obs) ca. 0.0037 min(-1)). Besides, (OH)-O-center dot was the main radical in the ZnO/BC-PS system (without scavengers, k(obs) ca. 0.0046 min(-1)). The mechanism was summarized below: PS effectively bond to unsaturated bonds (i.e., C=O lactones) and aromatic structures in the nanocomposites for the generation of the electron transfer intermediates, in which the stabilities of intermediates and the electron transfer capacities of nanocomposites themselves played the critical roles. In addition, nonradical degradation pathway of BPA was proposed, and could give a new insight into metal-carbon nanocomposites activating PS via nonradical pathway.