Transport and long-term release behavior of polymer-coated silver nanoparticles in saturated quartz sand: The impacts of input concentration, grain size and flow rate

Abstract

This study investigated the transport and long-term release of stabilized poly vinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) in a quartz sand column with various sand grain sizes (0.3–0.5 μm, 0.5–1.0 μm, 1.0–2.0 μm), input concentrations of PVP-AgNP solution (1, 5, 15, 25 mg/L), and flow rates corresponding to a filter velocities (1.0, 1.5, 2.0, 2.5 mL/min–0.14, 0.21, 0.28, 0.35 cm/min) by determining breakthrough curves, retention profiles, and long-term release curves. Breakthrough curves and retention profiles were simulated by a mathematical model based on the advection dispersion equation coupled with second-order kinetics. The increased transport of PVP-AgNPs in quartz sand occurred with increased grain sizes and reduced input concentrations, and the transport can be predicted by the colloid filtration theory and DLVO theory.The long-term (one week) release amounts of retained PVP-AgNPs were 42.78%, 31.45%, and 10.95% in the fine, medium, and coarse sand columns, respectively, and were 34.70%, 40.79%, 47.24%, and 57.32% at flow rates of 0.0363, 0.0436, 0.0545, and 0.0726 mL/min, respectively. The released quantity of retained PVP-AgNPs decreased as the sand grain size increased. This phenomenon is opposite with the trend of increased transport of PVP-AgNPs with increased grain size in the transport test, which most likely because colloidal filtration regulates the transport process and adsorption (and desorption) dominates the release process. Increasing the flow rate increased the shear force on the particles, which improved the release of PVP-AgNPs. The results of the release tests further verified our previous published studies showing that the long-term release of retained PVP-AgNPs in the quartz sand was mostly in the form of released nanoparticles rather than ions. The results of this study indicated that sand grain size, input concentration, and flow rate have a prominent influence on the transport and long-term release behavior of PVP-AgNPs in saturated quartz sand.