Insights into enhancing microplastics adsorption of sludge-based biochar by APTES grafting: Combining individual binding and aggregation confinement

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 NHgroups 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.