Preparation And Properties Of Uranium Adsorbsents Based On Graphene

With the increasingly severe environmental pollution and energy shortage,nuclear power has aroused considerable attention as a sustainable and low-carbon energy.Uranium resource is a bundant in the seawater,which is about one thousand times of that in the terrestrial mineral reserve.Therefore,the uranium resource in the seawater,which can provide adequate nuclear fuel and ease energy crisis currently,is an important potential reserve for the ongoing nuclear fuel demands.Nevertheless,uranium contamination in nuclear waste,produced by the nuclear industries,poses a significant environmental problem and is high toxic to human health.In addition,it is of great importance to adsorb uranium effectively and efficiently,which is the heaviest naturally occurring radionuclide.Thus it is desirable to develop novel adsorbents for the extraction of uranium from seawaters and radioactive wastes.Hence graphene nanocomposites are thoroughly studied for their large specific surface areaand typical mesoporous characterisitics,and have been an attractive candidate to adsorb uranium for adsorption of uranium in seawater and waste waters in the near future.A series of inorganic functional materials with adsorption properties of uranium,such as NiAl_LDH@rGO,NiCo2O4@rGO,MnO2@Fe3O4@rGO and CoFe2O4@rGO were prepared successfully.The adsorption properties of as-prepared products with different experimental conditions were investigated and the best condition was chosen.The adsorption thermodynamics,kinetics and influence of.simulated seawater on the adsorption properties of as-prepared products were also discussed.The three-dimensional hierarchical structured NiAl-LDH@rGO was synthesized by in situ growth method.The compositewas characterized by XRD,SEM,TEM,FT-IR and N2 absorption-desorption.The analysis shows nickel-aluminum hydrotalcite vertically grows on both sides of the grapheme,which has large specific surface area and unique pore structure,specific surface area is 256.8m2/g,and the average pore size is 4.52 nm.The influence of different experimental conditions on the adsorption properties of NiAl-LDH@rGO was investigated.The results show that the NiAl-LDH@rGO has excellent adsorption performance,when the pH value equals to 4.0,the maximum adsorption capacity of NiAl-LDH@rGO is 242.8mg/g.The experimental data are fitted well by a pseudo-second-order equation and Langmuir model.The thermodynamic parameters of uranium(VI)adsorption onto NiAl-LDH@rGO further display the adsorption is an endothermic and spontaneous process.The NiCo2P4@rGP composites,namely,the growth of NiCo2P4 nanoparticles on the surface of graphene,were prepared successfully by the solvent thermal method.The results of uranium adsorption experiment showed that the adsorption capacity with pH value increased at first increased and then decreased.The adsorption effect is best at pH 5.0 and the adsorption capacity reach 342.4mg/g.The results of thermodynamic analysis show that the adsorption process of NiCo2P4@rGP on uranium is a spontaneous and endothermic process.The adsorption kinetics of NiCo2P4@rGO for uranium conforms to a pseudo-second-order equation.The adsorption of uranium at different temperatures of NiCo2P4@rGO is in accordance with the Langmuir model.With 0.5mol/L HCl as desorption agent,after 3 times adsorption desorption cycles,the adsorption efficiency reached 80%.The functionalized ternary composite material MnO2@Fe3O4@rGO was prepared by the two-steps method.The dispersion of graphene in water was improved,and its adsorption property was increased.The experimental results show that the adsorption performance for uranium is best when pH is 6.0.The adsorption of MnO2@Fe3O4@rGO for uranium ion is accorded with the Langmuir isotherm model,and the maximum adsorption capacity of MnO2@Fe3O4@rGO is 108.7mg/g at 55?.The experimental data are fitted well by a pseudo-second-order equation and Langmuir model.The thermodynamic data shows that MnO2@Fe3O4@rGO adsorbed uranium(VI)is a spontaneous and endothermic process.With 0.4mol/L HCl solution can be carried out effectively,after four times adsorption desorption cycles,the adsorbent can still maintain a high adsorption efficiency 85.46%.The magnetic adsorption material CoFe2O4@rGO of hierarchical structure was synthesized by solvent thermal method and the product was characterized by using different testing methods(such as XRD,SEM,TEM and VSM).The results show that the saturation magnetization of CoFe2O4@rGO is 37.56emu/g.With a strong response to external fields,the CoFe2O4@rGO could be recovered readily from aqueous solution by magnetic separation method.The adsorption property is dramatically influenced by pH value,and the best adsorption pH is 6.0.The experimental data are fitted well by a pseudo-second-order equation and Langmuir model.The thermodynamic parameters of uranium(VI)adsorption onto CoFe2O4@rGO show the process is endothermic and spontaneous in nature.With 0.1mol/L NaHCO3 as desorption agent,after 3 times adsorption desorption cycles,the adsorption capacity reached 118.5mg/g.