Degradation of polyvinylpyrrolidone-coated iron oxide nanoparticles through ozonation: Steric to electrosteric repulsion and electrostatic interactions

Abstract

Surface degradation followed by aggregation of polyvinylpyrrolidone-coated iron oxide nanoparticles (PVP-IONPs) during ozonation make it possible to remove the toxic NPs from aqueous medium and reduce their environmental hazards. This study investigated the effect of concentration of NPs (50–150 mg/L), colloid pH (4−10), and ozonation time (10–30 min) on aggregates formation. The starting and ozonated NPs were characterized using DLS, XRD, VSM, UV-Vis, FTIR, XPS, SEM, and TEM. The optimal conditions (107.7 mg/L, pH 6.07, and 30 min ozonation) were determined by response surface method (RSM) to achieve maximum values of z-average (3.2 µm) and zeta potential (−6.64 mV). The steric repulsion changed to electrosteric and electrostatic interactions (van der Waals attraction) due to the degradation of the PVP coating, in which the clusters grew to form micrometer-sized aggregates. Irreversibility of NPs aggregation under optimal conditions of ozonation was confirmed by sonication of suspension; although the loose agglomerates formed at early periods were prone to breaking during sonication. A 77% reduction in COD of colloidal PVP-IONPs after ozonation under optimal conditions confirmed the significant degradation of PVP with ozone.