A turbidity-based study of removing polyvinyl chloride nanoplastics using magnetic biochar

Abstract

Magnetic biochars (MBCs) can quickly and efficiently remove polystyrene nanoplastics (NPs) from water. However, the removal efficiency of other types of NPs by different MBCs remains unknown. In this study, the removal performance of polyvinyl chloride NPs (PVC-NPs) by magnetic corncob biochar (MCCBC) and magnetic walnut shell biochar (MWSBC) was evaluated by measuring turbidity. The results indicate rapid adsorption of PVC-NPs onto MCCBC and MWSBC, reaching equilibrium within 1 h. The removal efficiencies of PVC-NPs by MCCBC and MWSBC were 94% and 92%, respectively. The relatively higher PVC-NPs removal capacity by MCCBC resulted from the greater amount of iron oxide on its surface, creating a rougher surface. The presence of monovalent ions (K+, Na+, Cl-, NO-3) promoted the removal of PVC-NPs by MWSBC, but caused a reduction in the adsorption of PVC-NPs on MCCBC. In contrast, divalent ions (Mg2+, Ca2+, and SO2-4) significantly inhibited the removal efficiency of PVC-NPs by competing for adsorption sites on MBCs (p < 0.01). Increasing the ionic strength inhibited the removal efficiency of PVC-NPs by MBCs. In addition, the highest removal efficiency of PVC-NPs was obtained at pH 5.0–7.0. Apart from adsorbing onto the surface of MBCs and becoming trapped within their pores, PVC-NPs can be magnetized by iron oxides. Moreover, PVC-NPs could aggregate with the small fragments of MBCs, thus allowing for easy removal by a magnet. The results provide new insight into the investigation of techniques to remove NPs other than PS from water.