| In aqueous systems, Cr (VI) is mainly discharged from chemical industries such as electroplating, tanning, catalysis,etc. Exceed Cr(VI) is carcinogenic and mutagenic to living organisms and seriously threaten human heath. Various technologies such as ion exchange method, electrical degradation, adsorption, etc are available for Cr(VI) removal. Nowadays, adsorption has become the most versatile and widely used technology for its operation simplicity, availability, and the low price. But the traditional adsorbent materials are limited by some weaknesses, such as the poor repeatability, the field of application. MOFs, GO@MOFs as new adsorbents which have good hydrothermal stability and large specific surface area, are used in extensive areas such as catalysis, gas separation, and solid phase extraction.In this study, the composite adsorbents GO@MIL-101 synthesized by MIL-101 and graphene oxide were applied for the first time to removal Cr(VI) from the water. To explore the structures and the micro-morphologies of adsorbents, adsorbents were characterized by XRD, FT-IR, BET and SEM. The results showed that the crystal microstructure and functional group changed not obviously after adding the GO, but the particle size decreased with the increase of adding amount of GO. However, the formation of crystal nucleus would be affected when excess GO was added in MIL-101. It was indicated from the specific surface area results that surface area of composite adsorbents increased with increase of GO addition.2%GO@MIL-101 had the largest surface area.Batch experiments were carried out to investigate the effect of the kinds of adsorbent, the initial solution pH, and temperature, etc on Cr (VI) adsorption in aqueous solution by MIL-101 and GO@MIL-101. The result showed that the adsorbents adding of mass ratio of 2% GO removal of Cr (VI) had the best efficiency. When the initial concentration of K2CrO7 solution was 20 mg/L, the removal efficiency could reach 39.3%,10% higher than MIL-101.The adsorbent can always be achieved adsorption equilibrium under 60 minutes,and the best removal of pH was about 5. The adsorption process of removal of Cr(VI) from wastewater fited model of pseudo-second-order kinetic model and the Freundlich isotherm, The largest adsorption amount can reach maximum when temperature was 293 K, the maximum adsorption of MIL-101 and 2%GO@MIL-101, respectively was 115.26 mg/g and 143.09 mg/g.The regenerative experimental results showed that the morphology of MIL-101 changed a lot after many recycles, and skeleton collapsed. However, adsorbents that adding GO on morphology basically remain unchanged after many times regeneration, and removal performance-was still better. Therefore, GO@MIL-101 has good application prospect. The zero point, pH changes and ion exchange dose relationship results showed that, ion-exchange existed in the process of removal of Cr(VI) from waste water with MIL-101 and 2%GO@MIL-101 adsorbents.The exchange capacity of 2%GO@MIL-101was higher the MIL-101. when added graphene oxide in crystals, it can increase the oxygen-containing functional groups which easier to protonation, on the other hand, the pH of KaCrO7 solution was lower when adding 2%GO@MIL-101 and the form of the Cr (VI) in the solution was in the majority with HCrO4-, which increased the ion exchange between the adsorbents and solution.In conclusion, MIL-101, GO@MIL-101 could be effectively used as adsoebents for Cr (VI) removal from wastewater. Among them,2%GO@MIL-101 has the best performance and repeatability. So these adsorbents have favourable application prospect. |
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