Engineered biochar for microplastic remediation in aquatic environments: Interfacial mechanisms, modification strategies, and future perspectives

Microplastics (MPs) are persistent pollutants in water, resulting from the degradation and improper disposal of both conventional and biodegradable plastics, posing risks to ecosystems and human health. Conventional wastewater treatment methods often remove only 40-78% of MPs from municipal and industrial effluents, consuming significant energy and potentially creating secondary pollutants. Biochar, a carbon-rich porous material made from biomass, has emerged as a low-cost, circular-economy-compatible solution for MP remediation. The effectiveness of biochars depends mainly on pore filling, hydrophobic interactions, electrostatic attraction, and π-π interactions. Adsorption capacities vary from 12.5 mg g⁻¹ for pristine biochars to 589 mg g⁻¹ for amine-functionalized biochars, while selected engineered biochars exhibit much higher Langmuir capacities under optimized conditions. Techniques such as hydrophobic functionalization, magnetic modification, and nanocomposite design can enhance recovery, reuse, and increase removal efficiency to as high as 99%, respectively. Multifunctional biochars may also help eliminate co-contaminants and promote broader environmental stabilization beyond simple adsorption. Future progress requires standardization, regeneration research, targeting nano-plastics, AI-assisted design, and integration into hybrid treatment systems.