The Removal Of Uranyl Ions And Heavy Metal Ions From Environment By Graphene-based Materials:A Theoretical Study

With the development of nuclear energy,the treatment of radioactive wastewater had become one of the environmental problems that need to be solved urgently.Radionuclide uranium has intensified chemical toxicity and radioactivity.Excess exposure to U may cause various diseases such as thyroiditis and renal failure,and increase the incidence of cancer enormously.The treatment of radioactive wastewater was one of the environmental problems to be solved urgently.In addition,with the development of industry,a large number of industrial wastewater containing heavy metal ion was discharged into natural water,which led to serious environmental pollution and threatened the health of humans.Therefore,the removal of uranium from radioactive wastewater and heavy metal ion from industrial wastewater is of great significance to environmental protection.In recent years,graphene-based materials have been widely used in the treatment and disposal of radioactive and heavy metal elements due to their excellent properties.In this work,the interaction mechanism of graphene-based materials with uranium and heavy metal ions had been studied at molecular level based on density functional theory.Firstly,we simulated the adsorption of uranyl ions on graphene oxide surface.In this process,we investigated the effects of different oxygen-containing functional groups(including epoxy,carboxyl,mono-hydroxyl and bi-hydroxyl)and the pH value of the solution on the adsorption process.The results showed that bi-hydroxy graphene oxide had the strongest adsorption capacity for uranyl ions and the highest adsorption energy was 105.56 kcal/mol.Moreover,the adsorption of uranyl on graphene oxide mainly depended on the electrostatic interaction between them,and alkaline environment was more conducive to the adsorption reaction.Secondly,we studied the adsorption beheavior of uranyl ions on N,P and S doped graphene materials.The results showed that the action site of uranyl ion was mainly its axial oxygen atom(Oax)when it interacted with doped graphene.In addition,the P and S atoms of doped-graphene played an important role in the adsorption process.Thirdly,the adsorption properties of cobalt ions on graphene oxide modified by two different functional groups were also studied theoretically in order to elucidate the contribution of different oxygen functional groups in the adsorption process,and to explore the interaction mechanism between graphene oxide and cobalt dioxide ions.The results showed that carboxyl graphene oxide adsorbed cobalt ion more efficiently than hydroxyl graphene oxide.The adsorption of cobalt ion on graphene oxide depended mainly on the electrostatic interaction between them.Finally,we studied the adsorption properties of graphene oxide and nickel-aluminium hydrotalcite compounds(GO@LDH)towards two heavy metal ions(Cu(?)and Cr(?)).The results show that the adsorption properties of GO@LDH towards Cr(?)are stronger than that of Cu(?).This study can provide new ideas and theoretical basis for the design of new materials for removing radioactive nuclide uranium and heavy metal ions form the environment.