Insights into enhancing microplastics adsorption of sludge-based biochar by APTES grafting: Combining individual...

Microplastics are now widespread in natural environments, creating adverse impacts on ecosystem that prompted growing efforts to address this challenging issue. Functionalized magnetic biochar (OBC-A) was prepared by pyrolyzing sludge under oxygen-limited conditions, followed by pre-oxidation treatment and APTES grafting modification of Fenton sludge-based biochar, which exhibited excellent adsorption capabilities toward both nano- and micro-scale plastics, with saturated adsorption amounts of 118.4 mg/g and 588.9 mg/g, respectively. Mechanistic investigations revealed that NH₂groups grafted onto OBC-A surface enabled electrostatic interactions and hydrogen bonding as dominant mechanisms in microplastics adsorption process. The cross-linked structure formed by self-polymerization of APTES on OBC-A surface induced aggregation confinement of microplastics through "net-catching". The adsorption process of microplastics by biochar was systematically evaluated under changing salinity gradient, and it verified different response behaviors of plastic particles with different sizes. OBC-A maintained high removal efficiency in real water matrices containing coexisting substances, confirming its robust performance under environmentally relevant conditions. Upon treatment with OBC-A, hypocotyl elongation in NP-exposed seedlings recovered to over 70 % of the blank control value, compared to only 20 % in untreated group. By elucidating the underlying mechanisms of magnetic biochar in microplastic removal, this work contributes to offering advanced technological strategies for environmental remediation.