Study On The Preparation Of Graphene-based Composite Hydrogels And Adsorption Of Heavy Metal Ions In Water

In recent years,the water environment has been increasingly polluted by heavy metal ions.Therefore,how to effectively remove heavy metal ions from wastewater which has become a hot topic to research.The removal methods of heavy metal ions in wastewater include adsorption method,biological flocculation method,ion exchange method,precipitation method,solvent extraction method and so on,among which adsorption method is widely adopted due to its characteristics of no secondary pollution and simple process.However,most of the existing adsorption materials not only have poor adsorption effect,but also they are hard to be reused.Therefore,in this study,the graphene oxide and chitosan have good adsorption efficiency and high adsorption capacity on heavy metal ions,on the basis of that,using graphene oxide?GO?,chitosan?CS?and polyvinyl alcohol?PVA?as raw material was prepared by a new type GCP hydrogel of different proportion,the structure of GCP hydrogel was characterized,and then use it to adsorb divalent heavy metal ions in waste water.The specific research work is as follows:?1?A new type of GCP hydrogel with different GO,CS and PVA ratios was synthesized through a green,facile,and low-cost method of freeze-thaw physical cross-linking,and the GCP hydrogel was used to characterize the structure by XRD,FTIR,XPS,SEM and TEM.The result showed that GCP hydrogel with three-dimensional network structure had been successfully prepared.Through optimization,it was found that GCP_1:2:4 hydrogel prepared by GO,CS and PVA with a mass ratio of 1:4:16 had the best comprehensive performance.?2?The unit adsorption performance of GCP_1:2:4hydrogel on Cd²⁺and Ni²⁺in wastewater was studied.The results showed that,for the GCP_1:2:4hydrogel,the adsorption of Cd²⁺and Ni²⁺had been greatly influenced by the p H but was less impacted by the ionic strength.Also,the existence of soluble humic acid had a slight effect on Cd²⁺and Ni²⁺adsorption.The adsorption equilibrium data to the GCP_1:2:4 hydrogel toward Cd²⁺and Ni²⁺was commendably matched by the model of the Langmuir isotherm,and the largest values of the adsorption capacity of the GCP_1:2:4 hydrogel toward Cd²⁺and Ni²⁺were approximately 172.11 and 70.37 mg/g,respectively.The equilibrium of adsorption was reached after approximately 16 h,and the adsorption process obeyed the model of second-order adsorption kinetics.Furthermore,the GCP_1:2:4 hydrogel also has an excellent recycling and regeneration property.?3?The adsorption property of GCP_1:2:4 hydrogel on Cd²⁺and Ni²⁺in wastewater was studied.The results showed that:Ni²⁺had a synergistic effect on GCP_1:2:4 hydrogel adsorption of Cd²⁺,and Cd²⁺had a competitive effect on GCP_1:2:4 hydrogel adsorption of Ni²⁺.The synergistic and competitive effects of GCP_1:2:4hydrogel adsorption were explained.