Built-in electric field mediated peroxymonosulfate activation over biochar supported-Co3O4 catalyst for tetracycline hydrochloride degradation

The strong electronic interaction between heterogeneous composite catalysts facilitates the charge separation and transfer, which is favorable for the enhancement of catalytic performance. Herein, the rape straw derived biochar (BC) supported ultrafine Co3O4 composites were synthesized for tetracycline hydrochloride (TC) degradation via activating peroxymonosulfate (PMS), and the built-in electric field (BIEF) driven catalytic degradation mechanism was proposed. The results indicated that 20 wt% Co3O4/BC catalyst could achieve 90% degradation efficiency of TC within 20 min, and demonstrated that BC not only served as a support to significantly inhibit the agglomeration of Co3O4 nanoparticles and improve the stability of catalyst, but also behaved as an activator of PMS to participate in the catalytic degradation reaction. Both radical pathway (SO4·-, ·OH and O2·-) and non-radical process (1O2 and direct electron transfer) were involved in the Co3O4/BC/PMS system, and the role of the latter is more prominent, in which Co2+/Co3+ redox cycle and C = O groups on the BC were the possible active sites. Furthermore, the density functional theory (DFT) calculations revealed that a BIEF pointing from BC to Co3O4 at the interface was formed, which could act as the internal driving force for electron transfer to accelerate the redox cycle of Co2+/Co3+ and induce the direct electron transfer, and thus resulting in the better degradation of TC. This work not only offered a mechanistic insight into synergistic effects of composite catalyst in PMS activation, but also provided a win–win strategy of realizing the resource utilization of agricultural waste and environmental remediation simultaneously.