Eco-friendly magnetic biochar: An effective trap for nanoplastics of varying surface functionality and size in the aqueous environment

Abstract

• Nanoplastics (NPs) equilibrium was achieved in <10 min of interaction. • The size and functionality of NPs significantly influenced their elimination by composites. • The impact of different environmental conditions on composites affinity was minimal. • Complexation and electrostatic attraction were dominating adsorption processes. The surge in nano/microplastics (NPs/MPs) through myriad daily products released in the aqueous environment highlights the importance of the urgent development of mitigation techniques. The study has assessed the performance of iron-modified biochar pyrolyzed at two different temperatures, i.e., 550 °C (FB-550) and 850 °C (FB-850), with magnetic extractability for the easy and prompt removal of NPs of varying size and surface functionality. NP1 (1000 nm, carboxyl), NP2 (1000 nm, amine), and NP3 (30 nm, carboxyl) were subjected to batch experiments with the composites. Rapid elimination of all the NPs (<10 min) from the water system using robust magnetic-composites was observed. A higher-order of reaction kinetics (n > 2) was found through the general order model, and a good fit for Sips isotherm suggests ultrafast NPs removal and heterogeneous nature of the composite surface. Maximum removal capacities for NP1 (225.11 mg/g), and NP3 (206.46 mg/g) were obtained using FB-850, whereas FB-550 showed higher removal of NP2 (290.20 mg/g). The influence of solution pH on the sorption of NPs was limited with significant variation in zeta potential, suggesting the probability of surface complexation of NPs. The spectroscopic analysis of reaction mixture showed the disappearance of COO − peak, generation of FeOOH stretching, and shift in Fe-O band, confirming the involvement of surface complexation in the sorption process. Minimal impact of environmental parameters, reaction spontaneity, and efficient removal of NPs in complex aqueous matrices justify the composites' environmental applicability. No-iron release and excellent reusability of the utilized adsorbents support the large-scale applicability of the composites.