Biochar-facilitated remediation of nanoplastic contaminated water: Effect of pyrolysis temperature induced surface modifications

“Nanoplastics- the emerging contaminants” and “agricultural waste to resource conversion” both are currently at the scientific frontiers and require solutions. This study aims to utilize sugarcane bagasse-derived biochar for the removal of nanoplastics (NPs) from aqueous environment. Three types of biochar were synthesized at three different pyrolysis temperatures, i.e. 350, 550, and 750 ℃ and evaluated for their potential in removing NPs. Effect of various environmental parameters, i.e., competing ions, pH, humic acid and complex aqueous matrices on NPs sorption was also studied. Results showed that attributing to decreased carbonyl functional groups, increased surface area and pore abundance, biochar prepared at 750 ℃ showed drastically higher NPs removal (>99%), while BC-550 and BC-350 showed comparatively lower NPs sorption (<39% and <24%, respectively). Further sorption studies confirmed instantaneous NPs removal with equilibrium attainment within 5 min of interaction and efficient NPs sorption capacity, i.e. 44.9 mg/g for biochar prepared at 750 ℃. Non-linear-kinetic modeling suggested pseudo 1st order removal kinetics while isotherm and thermodynamic modeling confirmed- monolayer instantaneous sorption of NPs sorption. Enhanced electrostatic repulsion resulted in decrease in NPs sorption at alkaline conditions, whereas steric hindrance caused limited removal (<25%) at higher humic acid concentrations.