Variation in porous media compositions influence the co-transport behavior of ZnO and FexOy mixed nanoparticles

The objective of this study is to evaluate the effect of porous media compositions on the co-transport behavior of nZnO-nFe(x)O(y)-mix suspension. To achieve this objective, porous media compositions are altered by coating the natural sediment granule with humic acid (HA), nFe(x)O(y), and kaolin-clay particles. The nZnO-nFe(x)O(y)-mix suspension is then injected through a series of a column packed with natural sediment and modified sand at pH 8 and in the presence of HA. The alteration in surface morphology after modification of sediment surface and deposition of ENPs is assessed using Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM). The results indicate that significant amount of nZnO and nFexOy get transported through natural sediment when injected as ENP-mix (C/C-0 = 0.57 and 0.66) or as individual entity (C/C-0 = 0.65 and 0.70). However, a decrease in the transport of nZnO and nFe(x)O(y) is observed when transported through HA-containing, nFe(x)O(y)-containing and clay-containing sand packed column. The high retention of nZnO and nFe(x)O(y) particles in those media is attributed to the combined effects of extensive straining and deposition. AFM and SEM image confirm more ENPs deposition on the collector surface when the sand is modified with HA-, nFe(x)O(y)- and clay-containing sand. Charge screening and occurrence of homo and hetero-aggregation are the major attributing factors for enhanced deposition. In all the cases, pore-blocking due to the formation of a cluster like aggregates on the sand surface has resulted in enhanced straining. Whereas, for the case of claycontaining sand, straining is further enhanced due to a reduction in porosity. Overall, it can be concluded that there is a risk of groundwater contamination by nZnO and nFe(x)O(y) when transported through natural sediment; however, the presence of natural organic matter, metal oxide nanoparticles, and clay in the natural soil can reduce the risk of contamination.