| The toxicity and carcinogenicity of Arsenic(As) make it become one of the priority control elements in environmental pollutants, which have received wordwide attention of the researchers. The adsorption of As by nanoscale zero valent iron(NZVI) has drawn extensive research focus in recent years. However, NZVI tend to aggregate due to its small particle size and poor dispersion, which has limited its application greatly. In order to play a higher efficiency, NZVI is generally loaded on a carrier. Graphene has huge specific surface area and abundant oxygen containing groups, which make it become a kind of excellent adsorption material. And due to the strong interaction between layers, graphene is easily to aggregate during the preparation, which reduce its actual specific surface area greatly. Therefore, preventing the graphene layers from aggregation is one of the important problems need to be solved.In this study, the graphene/silica nanocomposites(GS) were prepared by sol-gel method, the stress of silica prevents the composites from aggregation, GS composites exhibited good properties as a carrier material. NZVI was loaded onto GS through a liquid phase reduction process, the NZVI/GS nanocomposites were obtained. X-ray diffraction(XRD), transmission electron microscopy(TEM), N2 adsorption-desorption isotherms(BET), X-ray photoelectron spectroscopy(XPS) and Zeta potential were used to analysis the properties of the materials. The NZVI/GS nanocomposites were used to the removal of As(III) and As(V), which provided a new kind of adsorption materials of As in waste water treatment. Discusses of the initial pH, initial concentration, reaction time and temperature on the adsorption performance, the experimental data were fitted for adsorption kinetics and isotherms to explain the adsorption process and mechanism. At the same time, GS and NZVI were compared with NZVI/GS under the same conditions for adsorption of As(III) and As(V).The results showed that NZVI has been loaded onto GS, NZVI/GS was successfully achivied. The adsorption mechanisms of As(III) and As(V) are different, the adsorption process of As(III) is divided into two stages, surface complexation(pH < 9.1) and electrostatic attraction(pH > 9.1), the adsorption effect of As(V) is electrostatic attraction. The As(III) removal efficiency could reach 99.81% after 60 min at the dosage adding of 0.4 g/L NZVI/GS at pH 7; the As(V) removal efficiency achieve 99.59% after 60 min at the dosage adding of 0.4 g/L NZVI/GS at pH 4. The experimental data fit better to the pseudo-second-order kinetics and Langmuir isotherm model. The maximum adsorption capacity of As(III) and As(V) were 55.93 and 45.58 mg/g, respectively, show that As(III) removal is superior to As(V). For the adsorption of As(III), the equilibrium concentration was found to meet the Standards for Drinking Water Quality after treated by 0.4 g/L NZVI/GS when the initial concentration of As(III) and As(V) were below 4 and 3 mg/L, within the concentration range of 20 and 14 mg/L, the equilibrium concentration was meet the Integrated Wastewater Discharge Standard.This study compared the adsorption experiments of As(III) and As(V) on GS and NZVI with NZVI/GS under the same condition. The results showed that the adsorption efficiency of NZVI is better than GS, and the adsorption isotherms are meet the Langmuir isotherm model, the maximum adsorption capacity of As(III) and As(V) on GS and NZVI were 8.55 and 6.88 mg/g, 40.73 and 32.83 mg/g, respectively. The maximum adsorption capacity of NZVI/GS is greater than the sum of GS and NZVI, showed that NZVI/GS is a promising adsorption material for arsenic removal. |
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