Aggregation kinetics of fragmental PET nanoplastics in aqueous environment: Complex roles of electrolytes, pH and humic acid.

Abstract

The aggregation kinetics of fragmental polyethylene glycol terephthalate (PET) nanoplastics under various chemistry conditions in aqueous environment were firstly investigated in this work. The aggregation of PET nanoplastics increased with increasing electrolyte concentrations and decreasing solution pH, which became stronger with the presence of divalent cations (e.g. Ca2+ and Mg2+) than that of monovalent cations (e.g. Na+ and K+). The effect of cations with the same valence on the aggregation of PET nanoplastics was similar. The measured critical coagulation concentrations (CCC) for PET nanoplastics at pH 6 were 55.0mM KCl, 54.2mM NaCl, 2.1mM CaCl2 and 2.0mM MgCl2, which increased to 110.4mM NaCl and 5.6mM CaCl2 at pH 10. In addition, the aggregation of PET nanoplastics was significantly inhibited with the presence of humic acid (HA), and the CCC values increased to 558.8mM NaCl and 12.3mM CaCl2 (1mgL-1 HA). Results from this study showed that the fragmental PET nanoplastics had the quite higher CCC values and stability in aqueous environment. In addition, the aggregation behaviors of PET nanoplastics can be successfully predicted by the Derjguin Landau Verwey Overbeek (DLVO) theory.