Preparation Of Modified Three-dimensional Graphene Oxide Material And Its Adsorption On Uranium(VI)

Uranium is the main source of nuclear energy and the most toxic heavy metals.Therefore,it is necessary to remove and enrich uranium from wastewater.In recent years,graphene-based materials have attracted much attention due to their large specific surface area and excellent adsorption properties to contaminants in the environment.Among them,three-dimensional graphene-based materials have the advantages of porous and easy to recover,and show a potential application in the field of adsorption.In this paper,L-Arginine,4-Sulfocalix[4]arene and DTPA modified graphene oxide sponge(L-ArGOS,S-GOS,D-GOS)with three-dimensional structure were prepared by hydrothermal method and freeze-drying method using graphene oxide(GO)as precursors.The as-prepard materials were analyzed by SEM,EDS,XRD,FT-IR and XPS.Their adsorption properties to uranium(VI)were investigated.The specific research contents are as follows:(1)L-Ar-GOS has interconnected layered porous structure.In the process of hydrothermal,cross-linking reaction occured between GO and L-Ar.The adsorption of uranium(VI)on L-Ar-GOS is greatly affected by pH,but independ on ion strength.The optimum pH was 5.0.The adsorption equilibrium time was about 9 h.The adsorption process could be described by the pseudo-second-order model,and the adsorption of uranium(VI)was controlled by chemical action.The adsorption behavior was in accordance with Langmuir adsorption isotherm model,and the adsorption capacity of monomolecular layer was 238.66 mg·g-1.The adsorption thermodynamic parameters indicate that the adsorption of uranium(VI)was endothermic and spontaneous.The experimental results of adsorption/desorption cycle show that L-Ar-GOS has good reproducibility and reproducibility.In addition,the selectivity for U(IV)was improved after modification with L-Arginine.(2)S-GOS also has a three-dimensional interconnected layered porous structure,the 4-Sulfocalix[4]arene play a role of cross-linking agent in the process of forming three-dimensional graphene structure.The adsorption of uranium(VI)by S-GOS is affected by the initial pH,adsorption time,initial concentration of uranium and ionic strength.The optimum pH was 6.0.The adsorption process is completed within 180 min.The adsorption of uranium(VI)is more suitable for the pseudo-second-order model and Langmuir isothermal model.The adsorption process is dominated by chemical action,and the adsorption capacity of uranium(VI)is 257.07 mg·g-1.In addition,the adsorption thermodynamics results show that the adsorption of uranium(VI)by S-GOS is an endothermic and spontaneous process.S-GOS has a good regeneration-reusability.Most of the uranium(VI)can be desorbed by 1.0 mol·L-1 HCl solution,and the adsorption capacity of uranium is only decreased by 13% after adsorption/desorption cycles.(3)The structure of D-GOS is different from L-Ar-GOS and S-GOS,and it has a relatively ordered three-dimensional layered structure.This may be due to the fact that the hydrothermal reaction is carried out under alkaline conditions when preparing D-GOS.The adsorption performance of D-GOS on uranium(VI)is affected by the initial pH value,adsorption time,initial concentration of uranium and temperature,and is not affected by ionic strength.At pH 6,the adsorption capacity of uranium(VI)reached the highest value of 312.1 mg·g-1.The adsorption equilibrium time was 240 min.The results of adsorption kinetics show that the pseudo-second-order model can describe the adsorption process of uranium(VI)more accurately.The monolayer adsorption capacity of D-GOS on uranium(VI)was 418.4 mg·g-1,which was much higher than that of GO(192.6 mg·g-1).Thermodynamics studies have shown that the adsorption of uranium(VI)by D-GOS is an endothermic and spontaneous process.In addition,D-GOS shows good regeneration and reusability.