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ABSTRACT
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 CaCl2 (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 CaCl2, 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 (αm) increased from 2.46 × 10−4 to 9.98 × 10−1 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−1), 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 CaCl2 was 100%, demonstrating that Ca2+ 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 (Da) 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 (αf) increased from 6.23 × 10−3 to 2.52 × 10−1 as the NaCl concentration was increased from 0 to 50 mM.
Nomenclature
| A123 | = | combined Hamaker constant for microscopic bodies with compositions 1 and 3 in medium 2 ( = 9.85 × 10−21 J) |
| AS | = | porosity-dependent parameter |
| C | = | contaminant concentration in the effluent |
| Ce | = | collector efficiency |
| Ci | = | contaminant concentration in the aqueous phase |
| C0 | = | initial concentration of a contaminant |
| ci | = | concentration of molecules |
| D | = | hydrodynamic dispersion coefficient |
| Da | = | Damköhler number |
| dc | = | particle diameter of the collector grain |
| e | = | elementary charge |
| h | = | separation distance |
| Is | = | ionic strength |
| ka | = | removal rate coefficient |
| kB | = | Boltzmann constant |
| L | = | column length |
| n | = | porosity |
| NA | = | Avogadro's number |
| Na | = | attraction number |
| Ng | = | gravity number |
| Npe | = | Peclet number |
| Nr | = | aspect ratio |
| NvdW | = | van der Waals number |
| r | = | radius of graphene oxide |
| T | = | absolute temperature |
| t0 | = | injection time for the solute |
| v | = | pore water velocity |
| x | = | kinetic energy of graphene oxide |
| z | = | distance between the surface of the charged particle and the slipping plane (5 Å) |
| zi | = | charge number of ion species i |
| αf | = | sticking efficiency from the colloid filtration theory |
| αpri | = | fraction of deposition at the primary minimum |
| αsec | = | fraction of deposition at the secondary minimum |
| αm | = | sticking efficiency from the Maxwell model |
| ϵ | = | dielectric constant of water ( = 78.50) |
| ϵ0 | = | permittivity of free space ( = 8.854 × 10−12 C2 J−1 m−1) |
| ζ | = | zeta potential |
| κ | = | Debye-Hückel parameter |
| η | = | collision efficiency |
| λ | = | characteristic wavelength |
| λAB | = | characteristic wavelength of water |
| Ψi | = | surface potential of graphene oxide or porous media |
| Φdl | = | electrostatic double layer interaction energy |
| ΦDLVO | = | DLVO total interaction energy between two surfaces |
| Φmin1 | = | primary minimum energy |
| Φmin2 | = | secondary minimum energy |
| Φmax1 | = | primary maximum energy barrier |
| ΦvdW | = | van der Waals interaction energy |