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[Display omitted] • PMS activation by CoFe-LDH was improved by compounding with biochar. • Biochar acted as the catalyst carrier and electron mediator. • Reducing functional groups in biochar facilitated Co(III) and Fe(III) reduction. Efficient and low-cost catalysts for peroxymonosulfate (PMS) activation are needed for pollution prevention and environmental remediation. In this work, PMS activation by CoFe layered double hydroxide (CoFe-LDH) was promoted by compositing with biochar (BC). The characterization and catalytic performance of BC, CoFe-LDH, and BC@CoFe-LDH composite (BC-LDH) were investigated. The results indicated that BC could act as a catalyst carrier and electron mediator, which improved the physicochemical properties of CoFe-LDH and promoted the redox cycle of transition metals. The redox-active moieties (RAMs) of BC, especially the reduced functional groups (e.g., phenolic –OH), played an important role in the reduction of Co(III) and Fe(III). Remarkably, benefiting from the synergistic effect between BC and CoFe-LDH, the resulting BC-LDH exhibited excellent catalytic activity and stability for PMS activation. More reactive oxygen species (ROS) were produced in BC-LDH/PMS system. As a result, 100% of dimethyl phthalate (DMP, 10 mg L−1) degradation efficiency was achieved within 60 min in BC-LDH/PMS system, while only 62% in CoFe-LDH/PMS system. The intermediates of DMP degradation were identified and the degradation pathways were proposed. Our findings are expected to provide new insights into the rational design and application of BC materials and transition metals/PMS system for environmental remediation. [ABSTRACT FROM AUTHOR]