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The aim of this study was to quantify the interactions between graphene oxide (GO) and quartz sand by conducting experimental and modeling analyses. The results show that both GO and quartz sand were negatively charged in the presence of 0-50 mM NaCl and 5 mM CaCl (GO = -43.10 to -17.60 mV, quartz sand = -40.97 to -8.44 mV). In the Derjaguin-Landau-Verwey-Overbeek (DLVO) energy profiles, the adhesion of GO to quartz sand becomes more favorable with increasing NaCl concentration from 0 to 10 mM because the interaction energy profile was compressed and the primary maximum energy barrier was lowered. At 50 mM NaCl and 5 mM CaCl, the primary maximum energy barrier even disappeared, resulting in highly favorable conditions for GO retention to quartz sand. In the Maxwell model analysis, the probability of GO adhesion to quartz sand (α) increased from 2.46 × 10 to 9.98 × 10 at ionic strengths of 0-10 mM NaCl. In the column experiments (column length = 10 cm, inner diameter = 2.5 cm, flow rate = 0.5 mL min), the mass removal (Mr) of GO in quartz sand increased from 5.4% to 97.8% as the NaCl concentration was increased from 0 to 50 mM, indicating that the mobility of GO was high in low ionic strength solutions and decreased with increasing ionic strength. The Mr value of GO at 5 mM CaCl was 100%, demonstrating that Ca had a much stronger effect than Na on the mobility of GO. In addition, the mobility of GO was lower than that of chloride (Mr = 1.4%) but far higher than that of multi-walled carbon nanotubes (Mr = 87.0%) in deionized water. In aluminum oxide-coated sand, the Mr value of GO was 98.1% at 0 mM NaCl, revealing that the mobility of GO was reduced in the presence of metal oxides. The transport model analysis indicates that the value of the dimensionless attachment rate coefficient (D) increased from 0.11 to 4.47 as the NaCl concentration was increased from 0 to 50 mM. In the colloid filtration model analysis, the probability of GO sticking to quartz sand (α) increased from 6.23 × 10 to 2.52 × 10 as the NaCl concentration was increased from 0 to 50 mM.

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a b s t r a c tThe aim of this study was to investigate the adsorption characteristics of graphene oxide (GO) to remove Cu(II) from aqueous solutions. Batch experiments were performed to examine the effects of adsorbent dose, solution pH, competing Ni(II) ions, reaction time, initial Cu(II) concentration, and temperature on the adsorption of Cu(II) onto GO. Equilibrium, kinetic, and thermodynamic models were used to analyze the sorption data. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were also performed to characterize the adsorption of Cu(II) onto GO. Results showed that the Cu(II) sorption capacity remained relatively constant between pH 3 and 5 (12.26-12.88 mg/g), which was higher than that at pH 2 (5.43 mg/g). In a binary solution of Cu(II) and Ni(II), the Cu(II) sorption capacities (6.61-9.79 mg/g) were higher than those (5.17-7.88 mg/g) of Ni(II). The maximum Cu(II) sorption capacity of GO was determined from the Langmuir isotherm model to be 39.58 mg/g. Sorption model analyses demonstrated that the Langmuir isotherm was best fit to the equilibrium data, whereas the pseudo-first order model was most suitable at describing the kinetic data. Thermodynamic analysis showed that the adsorption of Cu(II) onto GO was endothermic and spontaneous (∆H° = 0.627 kJ/mol, ∆S° = 2.717 J/K/mol, ∆G° = -0.142 ~ -0.251 kJ/mol). FTIR spectra demonstrated that after the adsorption of Cu(II), the broad band (O=C-OH, carboxyl group) weakened and shifted to 3181 cm -1 , whereas the peak at 1164 cm -1 (C-OH, hydroxyl group) disappeared . XPS spectra showed that the Cu2p peak appeared in a wide scan of GO after the adsorption of Cu(II). Within a high-resolution scan of the Cu2p region, Cu2p 3/2 and Cu2p 1/2 peaks appeared at 932.8 and 953.1 eV, respectively.

Carbon nanomaterials such as fullerene, carbon nanotube and graphene are representative nanomaterials and widely used in various fields. Carbon nanomaterials can be exposed to environments during their production, usage and disposal, spreading to different systems and posing a great threat to various ecological receptors. Researches are conducted in order to determine the possibility of groundwater exposure to carbon nanomaterials due to their release and passage through soils. If soils can play a significant role in limiting the transport of carbon nanomaterials, the possibility of groundwater exposure to carbon nanomaterials can be reduced greatly. This review paper presented the research works performed for the mobility of carbon nanomaterials in soil media. Also, the paper provided the factors affecting the transport of carbon nanomaterials in soil media along with the DLVO theory/colloid filtration theory/transport model, which are used to describe the transport of carbon nanomaterials in soil media. Recently, production of carbon nanomaterials and their commercial and environmental applications increase rapidly in Korea. Therefore, researches regarding the fate and transport of domestic carbon nanomaterials in soil environments should be performed in various environmental conditions.