Exploring the relation between aggregation and adsorption of microplastics in aquatic environment containing metal cations

Metal cations can be adsorbed on the surface of PSMPs which change the surface properties of PSMPs and lead to the aggregation of PSMPs in aqueous solution. However, previous studies have only examined the processes of aggregation and adsorption independently, without investigating the correlation of adsorption and aggregation. In this study, the adsorption and aggregation experiment were carried out simultaneously and monitored simultaneously. The results of this study reveal that, prior to charge reversal of polystyrene microplastic (PSMPs), both adsorption and aggregation increased gradually with increasing metal cations concentration, and were mutually reinforcing. However, following charge reversal, adsorption increased while aggregation decreased, indicating that adsorption inhibited aggregation. The Zeta potentials of PSMPs increase consistently with increasing metal cations concentrations suggested that electrostatic force was one of the primary mechanisms for the adsorption of metal cations by PSMPs. The FTIR analysis reveal that the peak corresponding to C--C stretching shifted from 1630 cm-1 to 1628 cm-1, 1621 cm-1, and 1615 cm-1 when Ag+, Cu2+ or Cr3+ metal cations were existed, and the results indicated that there might be interactions such as cations-pi between PSMPs and metal cations. This information is crucial in determining the environmental fate and impact of PSMPs that have adsorbed metal cations pollutants.