Cotransport of Titanium Dioxide and Fullerene Nanoparticles in Saturated Porous Media

Abstract

This study investigated the cotransport of titanium dioxide nanoparticles (nTiO2) and fullerene nanoparticles (nC60), two of the most widely utilized nanoparticles, in saturated quartz sand under a series of ionic strengths in NaCl solutions (0.1-10 mM) at both pH 5 and 7. Under all examined ionic strengths at pH 5, both breakthrough curves and retained profiles of nTiO2 in the copresence of nC60 were similar to those without nC60, indicating that nC60 nanoparticles copresent in suspensions did not significantly affect the transport and retention of nTiO2 in quartz sand at pH 5. In contrast, under all examined ionic strengths at pH 7, the breakthrough curves of nTiO2 in the copresence of nC60 in suspensions were higher and the retained profiles were lower than those without nC60, which demonstrated that the presence of nC60 in suspensions increased the rate of transport (decreased retention) of nTiO2 in quartz sand at pH 7. Competition of deposition sites on quartz sand surfaces by the copresence of nC60 was found to contribute to the increased nTiO2 transport at pH 7. Under all examined ionic strength conditions at both pH 5 and 7, the breakthrough curves of nC60 were reduced in the copresence of nTiO2, and the corresponding retained profiles were higher than those without nTiO2, indicating that the presence of nTiO2 decreased the transport of nC60 in quartz sand. Co-deposition of nC60 with nTiO2 in the form of nTiO2-nC60 clusters as well as the deposition of nC60 onto previously deposited nTiO2 were responsible for the increased nC60 deposition in the presence of nTiO2 at pH 5, whereas deposition of nC60 onto surfaces of predeposited nTiO2 was found to be responsible for the increased nC60 deposition at pH 7.

Highly Dynamic PVP-Coated Silver Nanoparticles in Aquatic Environments: Chemical and Morphology Change Induced by Oxidation of Ag0 and Reduction of Ag+

“…Furthermore, the formation of small NPs could also enhance the aggregation of large NPs by bridging flocculation, which was reported in a recent article. 39 Influence of Dissolved Organic Matter (DOM). It is well established that humic acid (HA) could easily adsorb on the surface of NPs, and the electrostatic and steric forces will prevent NPs from coalescence, which would help to stabilize NPs, and influence or even control the transport of NPs in natural aquatic systems.…”

Transport and retention behaviors of titanium dioxide nanoparticles in iron oxide-coated quartz sand: Effects of pH, ionic strength, and humic acid

“…However, the colloidal particles employed in the aforementioned studies were negatively charged due to their low IEP values, so that the above prediction (i.e., enhanced colloid retention) could be acknowledged over the pH range of natural environment. On the other hand, nanoparticles are very diverse and they have various IEP values depending on their surface properties [4,14,22,23,28,39,40]. For example, nTiO 2 particles used in our previous study had a neutral IEP value (∼6) [28], indicating that the surface charge of nTiO 2 particles could be positive or negative depending on surrounding pH conditions.…”

“…On the other hand, nanoparticles are very diverse and they have various IEP values depending on their surface properties [4,14,22,23,28,39,40]. For example, nTiO 2 particles used in our previous study had a neutral IEP value (∼6) [28], indicating that the surface charge of nTiO 2 particles could be positive or negative depending on surrounding pH conditions. Due to this, one could hypothesize that the transport behavior of nanoparticles with neutral IEP value would be sensitive to solution pH in the sand coated with iron oxide (i.e., enhanced retention of nTiO 2 particles is not always expected in iron oxide-coated sand).…”

“…Previous studies also revealed that nTiO 2 could facilitate the transport of coexisting pollutants in the natural environment due to the adsorption of the environmental contaminants onto nTiO 2 surfaces [10,11]. Hence, a great number of studies investigated the fate and transport of nTiO 2 in soils and groundwater [2,4,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

“…Physical, chemical, and biological factors such as fluid velocity [13][14][15][16], solution chemistry (pH, ionic strength, and ion valence) [2,4,14,[17][18][19], nanoparticle concentration [14,15], surfactant and polymer coating [16,18,20], natural organic matter [21][22][23][24][25][26], bacteria [24], biofilm [27], and the co-presence of other nanoparticles [28] have been found to affect the transport and deposition kinetics of nTiO 2 . Most of these previous studies were performed in model porous media (i.e.…”