Coagulation-assisted removal of polystyrene microplastics from aqueous solution using amine-functionalized multi-walled carbon nanotubes with okra extract

Polystyrene microplastics (PS MPs) are widely distributed in aquatic environments and pose ecological and potential human-health risks. This study investigated the coagulation-assisted removal of PS MPs using MWCNTs@NH 2 in combination with okra extract as a natural coagulant aid. A Box–Behnken design was used to evaluate the effects of MWCNTs@NH 2 dose (0.2–1 g/L), initial PS concentration (50–400 mg/L), and pH (4–10), while maintaining the okra extract concentration at 0.5% (w/v). The maximum removal efficiency of 80.5% was achieved at 0.6 g/L MWCNTs@NH 2 , 400 mg/L PS, and pH 10. The removal mechanism involved partial charge neutralization, interparticle bridging by okra polysaccharides, hydrophobic interaction between PS and the graphitic CNT backbone, and floc enmeshment. The combined use of MWCNTs@NH 2 and okra extract reduced the required nanomaterial dose and improved floc formation. The proposed hybrid coagulation system offers a natural-coagulant-assisted strategy for PS MP removal, although further validation in real water matrices and assessment of residual nanotube release are required.