Preparation Of Graphene Oxide-based Materials And Study Their Removal Performance For Cr（Ⅵ） And Cd（Ⅱ） In Water

Nowadays,the problem of water pollution is brought about by the rapid development of industrial technology.And Heavy metal pollution is the most harmful to the environment and human body in the water pollution system.There are many methods to deal with heavy metal pollution in water,among which adsorption method is one of the most popular methods because of its simple operation,low treatment cost and no secondary pollution.Therefore,in this paper,adsorption method is also used to treat Cr（VI）and Cd（II）in wastewater.Graphene oxide（GO）is widely used in the treatment of water pollution due to its high surface area,high functional groups,good hydrophilicity and easy dispersion,but it is not easy to separate from water after adsorption.Therefore,in this study,two new GO based adsorbents functionalized by amino（-NH₂）（TEPA:tetraethylenepentamine）and sulfhydryl（-SH）（MPTES:3-Mercaptopropyltriethoxysilane）were prepared by using GO as the matrix material,which were used to adsorb Cr（VI）and Cd（II）in wastewater,respectively.In this study,the matrix material GO was firstly prepared by the modified Hummers method,and then TGOM（TEPA-GO/Co Fe₂O₄）and SH-MGO（SH-Co Fe₂O₄/GO）,were successfully prepared by one-step hydrothermal method and continuous stirring method（constant temperature）,which were easy to separate from water and friendly to the environment.And the morphology and structure of the materials were characterized and analyzed.In this experiment,the effects of different factors（p H,time and temperature）on the adsorption process of Cr（VI）and Cd（II）in water by two materials were studied.On this basis,the kinetic and thermodynamic behaviors of the two materials in the adsorption process and the adsorption isotherm model were studied.At the same time,the XPS characterization analysis of the two materials was carried out to explore the possible mechanism of the adsorption process.（1）Preparation of TGOM and its adsorption of Cr（VI）in wastewater:Through the characterization analysis of the materials,it can be seen that both GO and TGOM exhibit a sheet-like structure with a large number of folds.The difference is that the TGOM material has a granular material distribution on the surface,which can effectively reduce the agglomeration of GO.The surface of TGOM contains many functional groups,and has the characteristics of high specific surface area,good thermal stability and high magnetism.In the process of adsorption,it achieves the purpose of removing Cr（VI）through a series of physical and chemical adsorption such as electrostatic action,complexation reaction and reduction reaction.The adsorption behavior of TGOM was studied in the range of p H 2 to 10.The results showed that the zero potential of Cr（VI）adsorption of TGOM appeared at p H_zpc=5.65,and the optimal adsorption at p H=2.The maximum adsorption capacity of TGOM for Cr（VI）in wastewater is 114.81 mg/g at p H=2 and temperature of 298 K,and its adsorption effect is better than that of MGO（Co Fe₂O₄/GO）.The effects of time and temperature on the adsorption were studied,and it was found that the adsorption process of Cr（VI）by TGOM was an exothermic process,and the adsorption process conformed to the pseudo-second-order kinetics and Langmuir isotherm model.The cycle experiments show that TGOM also has good cycle performance（the adsorption efficiency can reach 62%after four cycle experiments）.The overall results show that TGOM can effectively remove Cr（VI）from wastewater.（2）Preparation of SH-MGO and its adsorption of Cd（II）in wastewater:In this study,SH-MGO was prepared by a constant temperature continuous stirring method.Characterization analysis such as XRD proves that the magnetic material is loaded,and FT-IR analysis showed that the surface of SH-MGO contained a large number of groups.（-OH,-COOH,-SH,etc.）.At the same time,thermogravimetric and magnetic analysis of the material showed that SH-MGO had high thermal stability and magnetism.XPS characterization analysis proved that the adsorption of Cd（II）by SH-MGO was accomplished through electrostatic interaction and chelation（complexation）reaction.The results of adsorption experiments showed that the optimum p H for the adsorption of Cd（II）by SH-MGO is 5,and SH-MGO has the best adsorption effect on Cd（II）compared with Cr（VI）and Cu（II）in the experimental study of selective adsorption.The adsorption of Cd（II）on SH-MGO conforms to the pseudo-second-order kinetics and Freundlich isotherm model,and the reaction is a spontaneous endothermic process.The results of the recycling experiments of SH-MGO indicate that SH-MGO has good recycling performance and is an effective adsorbent for removing Cd（II）in wastewater.