Mechanism and performance modeling of sewage sludge-derived ZnAl-layered double oxides@biochar for high-performance nanoplastics remediation

Nanoplastics (NPs) pose severe environmental threats, while sewage sludge management remains a major hurdle for municipal wastewater treatment plants (WWTPs). This study addresses these critical concerns by developing a ZnAl-layered double oxides@biochar (ZnAl-LDO@biochar) composite from sewage sludge for effective NPs remediation. Such material demonstrated remarkable adsorption capacities for five representative NPs, achieving 716.3 mg g −1 for polyethylene terephthalate (PET), 615.8 mg g −1 for polystyrene (PS), 406.0 mg g −1 for polymethyl methacrylate (PMMA), 271.6 mg g −1 for polyvinyl chloride (PVC), and 178.6 mg g −1 for polylactic acid (PLA) at 25 °C. During the adsorption process, LDO in ZnAl-LDO@biochar regenerated a layered double hydroxide (LDH) structure via the “memory effect”, enabling NPs adsorption via electrostatic attraction, hydrogen bonding and π-π interactions. Biochar contributed to hydrogen bonding and π-π interactions, meanwhile its dispersive effect promoting the exposure of LDH’s adsorption sites. A quantitative structure–activity relationship (QSAR) model was established by correlating the adsorption behavior with molecular descriptors of NPs. Guided by the QSAR model, ZnAl-LDO@biochar achieved a treatment capacity of 5 m 3  g −1 for removing high-concentration PET NPs from a WWTP effluent. These findings highlighted the exceptional potential of the ZnAl-LDO@biochar composite for real-world NPs remediation in water treatment.