Recent progress of biochar for aquatic pollutant control: Modification, mechanism and application

Water pollution remains a serious global challenge, and biochar has become a sustainable and economically efficient adsorbent for removing various aquatic pollutants. Recent engineering advances, including physical/chemical activation, hetero-atom doping, template-assisted synthesis and O-functionalization, have substantially upgraded its textural and chemical attributes. State-of-the-art activations typically deliver surface areas of 1500-2600 m² g^-1 and Cd(II) uptake capacities in the 200-450 mg g^-1 range, whereas La or Mg-modified biochars frequently achieve over 80 % phosphate removal. Despite these advances, the current focus of biochar modification is still on the pore structure and functional groups, and the perspective of decontamination still only focuses on the single adsorption function of biochar. This review proposes a multi-pathway synergistic strategy integrating adsorption, oxidation, precipitation, and complexation, along with non-radical oxidation and metal-biochar collaborative systems for removing heavy metal ions, non-metallic ions, dyes, antibiotics, and pesticides. It systematically analyzes mechanistic coupling in multi-pollutant matrices and environmental influences, establishing a ternary design framework (pore-surface-electronic properties) and a mechanistic hierarchy from passive adsorption to active redox degradation, offering molecular-level guidance for next-generation biochar reactors.