Effect of different-sized colloids on the transport and deposition of titanium dioxide nanoparticles in quartz sand

摘要

Colloids (non-biological and biological) with different sizes are ubiquitous in natural environment. The investigations regarding the influence of different-sized colloids on the transport and deposition behaviors of engineered-nanoparticles in porous media yet are still largely lacking. This study investigated the effects of different-sized non-biological and biological colloids on the transport of titanium dioxide nanoparticles (nTiO(2)) in quartz sand under both electrostatically favorable and unfavorable conditions. Fluorescent carboxylate-modified polystyrene latex microspheres (CML) with sizes of 0.2-2 mu m were utilized as model non-biological colloids, while Gram-negative Escherichia coli (similar to 1 mu m) and Gram-positive Bacillus subtilis (similar to 2 mu m) were employed as model biological colloids. Under the examined solution conditions, both breakthrough curves and retained profiles of nTiO(2) with different-sized CML particles/bacteria were similar as those without colloids under favorable conditions, indicating that the copresence of model colloids in suspensions had negligible effects on the transport and deposition of nTiO(2) under favorable conditions. In contrast, higher breakthrough curves and lower retained profiles of nTiO(2) with CML particles/bacteria relative to those without copresent colloids were observed under unfavorable conditions. Clearly, the copresence of model colloids increased the transport and decreased the deposition of nTiO(2) in quartz sand under unfavorable conditions (solution conditions examined in present study). Both competition of deposition sites on quartz sand surfaces and the enhanced stability/dispersion of nTiO(2) induced by copresent colloids were found to be responsible for the increased nTiO(2) transport with colloids under unfavorable conditions. Moreover, the smallest colloids had the highest coverage on sand surface and most significant dispersion effect on nTiO(2), resulting in the greatest nTiO(2) transport. (C) 2015 Published by Elsevier Ltd.