Display omitted •Bamboo biochar (BB) is an attractive material for environmental remediation.•Fe3O4–BB activated the accelerated formation of SO4− in persulfate oxidation.•Fe3O4–BB exhibited high polycyclic aromatic hydrocarbon (PAH) removal efficiency.•Fe3O4–BB-activated persulfate oxidation can treat PAH-contaminated sediment. This study developed a new and cost-effective method for the remediation of marine sediments contaminated with PAHs. Fe3O4 particles were synthesized as the active component, supported on bamboo biochar (BB) to form a composite catalyst (Fe3O4–BB). The effects of critical parameters, including the initial pH, sodium persulfate (PS) concentration, and dose of catalyst were investigated. The concentration of high-molecular-weight PAHs in sediments was much higher than that of low-molecular-weight PAHs; pyrene was an especially prominent marker of PAH contamination in sediments. Fe3O4–BB/PS exhibited a substantial improvement in PAH degradation efficiency (degradation rate: Fe3O4–BB/PS, 86%; PS, 14%) at a PS concentration of 1.7×10−5M, catalyst concentration of 3.33g/L, and pH of 3.0. The results of this study demonstrate that possible activation mechanisms include Fe2+–Fe3+ redox coupling and electron shuttling that mediates electron transfer of the BB oxygen functional groups, promoting the generation of SO4− in the Fe3O4–BB/PS system.