Concurrent aggregation and transport of graphene oxide in saturated porous media: Roles of temperature, cation type, and electrolyte concentration

Mechanisms of graphene oxide aggregation, retention, and release in quartz sand

“…2 presents observed and simulated BTCs and RCs for GO when using 1090 μm quartz sand, C o = 10 mg L −1 , and the IS equal to 1, 20, and 100 mM NaCl during Phase I. An increase in the solution IS led to a significant decrease of GO mobility (the effluent mass balance, M eff , in Table 1) and enhanced retention (k sw in Table 2) due to the compression of the double layer thickness and charge screening (Dong et al, 2016;Liu et al, 2013;Wang et al, 2017a;Wang et al, 2018;Xia et al, 2015). Interaction energy parameters reveal that increasing the solution IS increases the depth of the secondary minimum (Table S2) and the frequency of primary minimum interactions that may sometimes occur depending on local scale variations in sand surface roughness and the GO orientation (Tables S4 and S5).…”

“…Commonly examined effects of solution chemistry on GO environmental fate include the ionic strength (IS) (Dong et al, 2016;Dong et al, 2017;Fan et al, 2015a;Lanphere et al, 2013;Lanphere et al, 2014;Liu et al, 2013;Qi et al, 2014;Wang et al, 2017a;Wang et al, 2018;Wu et al, 2013b;Xia et al, 2015) and cation type (Fan et al, 2015b;Wang et al, 2017a;Wang et al, 2018;Xia et al, 2015). An increase in solution IS has been reported to increase GO aggregation and retention in porous media due to the compression of the double layer thickness and charge screening which increases the depth of the secondary minimum (Dong et al, 2016;Lanphere et al, 2013;Liu et al, 2013;Wang et al, 2017a;Wang et al, 2018;Xia et al, 2015). Divalent cations have been reported to increase GO aggregation and retention due to cation bridging (Fan et al, 2015b;Wang et al, 2018;Wu et al, 2013a;Xia et al, 2015).…”

“…An increase in solution IS has been reported to increase GO aggregation and retention in porous media due to the compression of the double layer thickness and charge screening which increases the depth of the secondary minimum (Dong et al, 2016;Lanphere et al, 2013;Liu et al, 2013;Wang et al, 2017a;Wang et al, 2018;Xia et al, 2015). Divalent cations have been reported to increase GO aggregation and retention due to cation bridging (Fan et al, 2015b;Wang et al, 2018;Wu et al, 2013a;Xia et al, 2015).…”

“…Previous GO transport studies that have conducted interaction energy calculations assumed smooth and chemically homogeneous surfaces to interpret their results (Chowdhury et al, 2014;Dong et al, 2016;Feriancikova and Xu, 2012;Liu et al, 2013;Wang et al, 2017a;Wang et al, 2018;Wu et al, 2013b;Xia et al, 2015). In this case, GO interactions were mainly attributed to secondary minimum interactions (Dong et al, 2016;Liu et al, 2013;Wang et al, 2017a;Wang et al, 2018;Xia et al, 2015). A decrease in the solution IS to deionized (DI) water should eliminate the secondary minimum and induce disaggregation or release of retained particles (Shen et al, 2018;Torkzaban and Bradford, 2016;Wang et al, 2017a).…”

“…However, only a fraction of the retained GO particles was released when the IS was reduced to DI water, especially when GO particles were deposited in the presence of divalent cations (Dong et al, 2016;Wang et al, 2017a). Interaction energy calculations on smooth, chemically homogeneous surfaces also cannot explain the enhanced GO aggregation and retention in the presence of divalent cations at low IS (Fan et al, 2015b;Wang et al, 2018;Wu et al, 2013a;Xia et al, 2015), or complete recovery of retained GO following sand excavation (Lanphere et al, 2014;Sun et al, 2015;Wang et al, 2017a). These observations indicate that other factors were contributing to the GO retention and release besides the secondary minimum.…”