Adsorption Separation-in-situ Synthesis Of ZIF(Co)/Graphene Composite And Its Adsorption Performance

As an indispensable trace element for human body,Co²⁺plays a vital role in human life activities.However,excessive Co²⁺can enter to the human body through bioaccumulation and bring hidden dangers to people’s health.Therefore,how to effectively remove Co²⁺from water has become an important research topic.Among them adsorption is an effective method to remove Co²⁺from aqueous solution,but the adsorbent after saturated adsorption needs to be regenerated or treated as hazardous waste,otherwise secondary pollution will be formed.Hence,it is important to treat the adsorbent after adsorption process.For this purpose numerous adsorbents have been used,among others Graphene due to its certain adsorption properties,which can adsorb and separate a variety of pollutants in aqueous solution,has been used in this study to adsorb and separate Co²⁺from water and wastewater.Accordingly,Co²⁺adsorbed on Graphene was used as metal ions in zeolite-like metal-organic framework material.The ZIF-67/Graphene composite was synthesized in situ to understand the adsorption separation and resource utilization of heavy metal Co²⁺.ZIF-67/Graphene composites prepared by adsorption separation-in-situ synthesis were characterized by XRD,FT-IR,BET and SEM.The composite material was used to adsorb methyl orange,Cr（Ⅵ）,PO₄^3-and other pollutants in water.The adsorption effect and various factors affecting the adsorption were investigated,and the adsorption performance and mechanism were analyzed.（1）The adsorption and separation experiments of Co²⁺by Graphene as well as the preparation conditions of the composite materials shows that the favorable adsorption conditions of Co²⁺by Graphene is at p H=3,with cobalt nitrate concentration between 15,25,35mg/L,and the adsorption time of 24h.The ZIF-67/Graphene composites were successfully fabricated at35℃for 24h.When the concentration of cobalt nitrate is 35mg/L,the prepared ZIF-67/Graphene composite had the best adsorption effect on Methyl orange,Cr（Ⅵ）and PO₄^3-.（2）The characterization results of ZIF-67/Graphene composites show that the ZIF-67 had a hexahedral crystal structure,and graphene has a lamellar structure,and ZIF-67 was not uniformly distributed on the surface of Graphene.The characteristic diffraction peaks of ZIF-67 appeared at 7.35°,10.35°and 12.45°,and those of Graphene appeared at 23.45°,38.15°,44.45°,64.85°and 77.9°.The special vibration peaks of Graphene and ZIF-67 were observed in the infrared spectra.The specific surface area,pore volume and pore size of ZIF-67/Graphene composites were 640.26m²/g,0.11187cm³/g and 8.48nm,respectively.（3）Experimental study on adsorption of Methyl orange,Cr（Ⅵ）and PO₄^3-by ZIF-67/Graphene material showed that the adsorption of PO₄^3-by ZIF-67/Graphene material basically reached at equilibrium point when the p H was 7,the temperature was 35℃and the adsorption time was 240min,and the adsorption capacity was 118.95mg/g.When the p H was adjusted to 4,the temperature was 35℃and the adsorption time was sited to 300min,the adsorption equilibrium of Methyl orange was reached to 87.93mg/g.When the p H was 2,the temperature was 25℃and the adsorption time was 300min,the adsorption capacity for Cr（Ⅵ）removal reached to 52.31mg/g.（4）The adsorption behaviors of ZIIF-67/Graphene on Methyl orange,Cr（Ⅵ）and PO₄^3-all conform to be fitted with the second-order kinetic model and Langmuir adsorption isotherm model,and the adsorption reaction was spontaneous exothermic reaction.After four adsorption-desorption,ZIF-67/Graphene composite still maintained good adsorption performance.