Adsorption For Methylene Blue And Cr(Ⅵ) By Graphene Oxide Modified By Ionic Liquids From Aqueous Solutions

Inorganic heavy metal ions and organic dyes are two kinds of common water pollutants,which greatly harm the stability of ecological environment and the health of organisms.Adsorption method has become a research hotspot because of highly efficient,simple to operate,inexpensive,and the adsorbent can be recycled and reused by desorption.Therefore,to find an economic,efficient and environmentally friendly adsorbent to treat heavy metal and dye in water is one of the important ways to alleviate water pollution.Graphene oxide（GO）has a very high specific surface area and a large number of oxygen-containing groups on its surface and edge,providing adsorption sites for the adsorption of pollutants,and laying the foundation for the further modification of GO.In order to further improve the adsorption performance of GO,two composite adsorbents,GO-MIL and GO-DIL,were prepared by modifying GO with ionic liquids（ILs）,which can self-adjust structure to obtain the target physical and chemical properties,for the adsorption of the d ye methylene blue（MB）and heavy metal Cr（Ⅵ）in aqueous solutions,respectively.The main conclusions are as follows.（1）Monocationic ionic liquid（[BMIM]PF₆,MIL）and double-cationic ionic liquid（[C₄（MIM）₂]Cl₂,DIL）based on imidazole were synthesized,and their molecular structures were confirmed by NMR.GO was modified by these two ionic liquids to prepare novel composite adsorbents GO-MIL and GO-DIL.SEM,BET,FTIR and XPS were used to characterize the material before and after the modification,and a nalyze the interaction between MIL,DIL and GO.The results showed that the composite adsorbents GO-MIL and GO-DIL were successfully prepared,and the IL and GO in both adsorbents were combined by hydrogen bonding（O-H···N和C-H···O between imidazole N or imidazole H on IL and H or O on GO）.（2）In order to study the adsorption performance of GO-MIL and GO-DIL on MB and Cr（Ⅵ）in aqueous solutions,the effects of various factors（adsorbent dosage,contact time,solution p H,initial concentration of pollutants and reaction temperature）on the adsorption capacity were investigated.The results showed that:in aqueous solutions,the optimum conditions for adsorption of MB by GO-MIL were p H 8.0,and the adsorption reached equilibrium at 600 min,while the optimum conditions for adsorption of Cr（Ⅵ）by GO-DIL were p H 3.0,and the adsorption reached equilibrium at 40 min.The equilibrium adsorption capacities（q_e）were 493.62 mg/g and 260.92mg/g,respectively.（3）The adsorption data of GO-MIL/MB and GO-DIL/Cr（Ⅵ）adsorption systems were analyzed by adsorption kinetic model fitting,isothermal adsorption model fitting and adsorption thermodynamics analysis.The results showed that the adsorption behavior of the two adsorption systems conforms to the pseudo-second-order kinetic model and the pseudo-first-order kinetic model,respectively,and they were in accordance with Langmuir isothermal adsorption model.The maximum theoretical monolayer adsorption capacity(q_m,cal)was 531.82 mg/g and 263.77 mg/g,respectively,and the adsorption processes of GO-MIL/MB and GO-DIL/Cr（Ⅵ）were spontaneous endothermic reactions.（4）Regeneration experiments showed that the q_m of GO-MIL for MB and GO-DIL for Cr（Ⅵ）could still maintain 426.42 mg/g and 228.00 mg/g after 5 cycles of adsorption-desorption.（5）The materials before and after adsorption were characterized by FTIR and XPS,and the adsorption mechanism of the two adso rption systems was discussed.The adsorption mechanism in GO-MIL/MB system mainly involves electrostatic attraction（between GO-MIL anion PF₆^-and MB）,hydrogen bonding,pore filling andπ-πInteraction.GO-DIL/Cr（Ⅵ）system mainly involves electrostatic attraction（between GO-DIL protonated imidazole N and oxygen-containing functional group and Cr（Ⅵ））,reduction and pore filling.