Multifunctional biochar for water decontamination from adsorption to catalytic degradation

Biochar has emerged as a promising carbonaceous material for water remediation due to its high specific surface area, tunable pore structures, abundant surface functional groups, and cost-effectiveness derived from diverse biomass feedstocks. This review systematically summarizes recent progress in biochar-based water treatment technologies. The preparation methods including pyrolysis and hydrothermal carbonization are discussed alongside modification strategies such as acid or alkali treatment, metal oxide loading, heteroatom doping, and magnetic functionalization. The underlying pollutant removal mechanisms are comprehensively elucidated, covering physical adsorption, chemical adsorption, catalytic oxidation via persulfate and hydrogen peroxide activation, synergistic photocatalysis, filtration interception, ion exchange, precipitation, and microbial carrier effects. The applications of biochar for removing heavy metal ions, organic contaminants, microplastics, nitrogen and phosphorus nutrients, pathogenic microorganisms, and fluoride are critically evaluated with emphasis on removal performance, mechanistic pathways, and influencing factors. The practical implementation of biochar as adsorbents, catalytic materials, filtration media, and composite functional materials in water treatment systems is also reviewed. Key challenges including long-term stability under real water conditions, regeneration and reuse strategies, and large-scale production are identified. Future research directions are proposed to promote the engineering application of biochar for sustainable water pollution control.