Biochar-based composites have attracted growing attention because they combine biochar with minerals, metal oxides, and other functional components. Compared with pristine biochar, these composites generally provide more active surface sites, stronger ion-exchange capacity, improved electron-transfer behavior, and in some cases catalytic, photocatalytic, or magnetic properties. This review discusses four closely related aspects: feedstock and modification strategy, applications in wastewater treatment and soil remediation, the main variables governing remediation efficiency, and the constraints limiting large-scale use. Available evidence shows that lignocellulosic biomass is suitable for constructing stable porous matrices, while MgO-, ZnO-, and Fe-based modifications can introduce adsorption, co-precipitation, catalytic degradation, photocatalysis, and redox transformation functions. However, performance remains highly dependent on pyrolysis temperature, pH, contact time, pollutant concentration, coexisting species, and regeneration conditions. Wider practical use is still restricted by variability in material properties, limited knowledge of long-term stability, difficulties in spent material management, and economic barriers to scale-up. Future work should therefore emphasize standardized synthesis, mechanism-oriented characterization, life-cycle-aware design, and validation under realistic pilot- and field-scale conditions.
Yiping Ren (2026) studied this question.