The role of available nitrogen in the adsorption of polystyrene nanoplastics on magnetic materials

Abstract

Several studies have been conducted on nanoplastics (NPs). However, few studies have investigated the complexity of the interactions between NPs and other aqueous pollutants in multi-solute media. In this study, the adsorption of polystyrene nanoplastics (PSNPs) on magnetic materials (MS) in the presence of available nitrogen (AN) was studied. The results demonstrated that the adsorbed amount of PSNPs increased in the presence of ammonium nitrogen (NH4+−N), whereas no significant difference was detected on the adsorbed amount of PSNPs using nitrate nitrogen (NO3−−N) as a cosolute. The increase in the adsorbed amount of PSNPs was attributed to the formation of an MS–PSNPs–NH4+−N complex. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential analyses indicated that the PSNPs with NH4+−N as a cosolute can be bound on the MS surfaces. Moreover, the change in the PSNPs amount adsorbed by MS depends on the valence state, electronegativity of the coexisting ions, and the surface properties and functional groups of PSNPs. Additionally, the ionic strength, dissolved organic matter, solution pH, metal cations and the subsequent release of MS-coated PSNPs and NH4+−N changed considerably in different aquatic systems and artificial nitrating fluids. Among different natural aquatic systems, the PSNPs adsorption on MS was excellent in lake water. The results indicate high potential for the attachment of PSNPs to MS in the presence of AN and further deepen the understanding of removing NPs using magnetic materials in aqueous systems with various coexisting contaminants.