Transforming waste into multifunctional biochar catalysts for pollution control: Synthesis strategies, catalytic mechanisms, and practical challenges

Converting waste feedstocks into multifunctional biochar catalysts provides a promising route for coupling solid‐waste valorization with pollution control. However, existing studies often emphasize individual removal performance, while the relationships among feedstock characteristics, synthesis strategies, active‐site evolution, catalytic pathways, and practical constraints remain insufficiently integrated. This review summarizes recent advances in waste‐derived multifunctional biochar catalysts, with emphasis on how pyrolysis, activation, metal loading, heteroatom doping, and composite construction regulate pore structure, surface chemistry, conductivity, and catalytic active sites. Adsorption–catalysis coupling, radical and non‐radical oxidation, electron‐transfer processes, and light‐, electricity‐, and heat‐assisted pathways are critically compared for different pollutant categories, including heavy metals, dyes, antibiotics, emerging contaminants, and gaseous pollutants. A literature‐based comparative assessment is further presented to summarize removal efficiency, reaction kinetics, stability, regeneration, and real‐matrix applicability across representative systems. Finally, key challenges, including active‐site stability, metal leaching, secondary pollution risks, cost‐related constraints, and scale‐up feasibility, are discussed to outline future directions for the design of safer, more efficient, and application‐oriented multifunctional biochar catalysts.