Interpreting the role of NO, SO, and extracellular polymeric substances on aggregation kinetics of CeO nanoparticles: Measurement and modeling.

The early stage of aggregation of cerium oxide nanoparticles (CeO NPs) in anion solutions was inspected in the absence and presence of extracellular polymeric substance (EPS) with a help of time-resolved dynamic light scattering (DLS). The aggregation kinetics and attachment efficiencies were calculated according to measured hydrodynamic diameter across a range of 1-500 mM NaNO and 0.01-100. mM NaSO. The aggregation of CeO NPs in both NaNO and NaSO solution conformed with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In NaNO solution, the critical coagulation concentrations (CCC) of CeO NPs was calculated to be about 47 mM; in NaSO solution, CeO NPs showed a re-stabilization process and thus there was no CCC value. SO had intenser effects on CeO NPs aggregation than NO might because of the distinction between their polarization, consisting in Hofmeister series. The presence of bound EPS (B-EPS), tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) in NaNO solutions all lead to significant decrease in CeO NPs aggregation. Steric repulsive force produced by absorbed EPS on CeO NPs might take main responsibility in stabilizing CeO NPs. Besides, Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) model successfully predicted the energy barrier between CeO NPs with B-EPS, TB-EPS and LB-EPS as a function of NaNO concentration. Furthermore, the difference in impeding the CeO NPs aggregation with B-EPS, TB-EPS and LB-EPS may be caused by the divergence in molecular weight and component mass fraction especially protein content. These results might subserve the assessment on the fate and transport behaviors of CeO NPs released in wastewater treatment plants.