The Preparation And Adsorption Properties On Uranium Of Graphitic Carbon Nitride Complexes

With the rapid development of the global economy,the availability of limited resources has motivated people to pursuit new energy.Nuclear energy,as a clean energy,has attracted researchers'eyes from all over the world.Uranium is the major nuclear fuel.The proven reserves of uranium in the ocean are 4.5 billion tons,which can be used as a source for the sustainable and stable development of nuclear energy.Therefore,we seek for the effective enrichment methods to extract uranium from seawater.At present,adsorption method has been widely used for extraction uranium.It is great significant to design adsorbent materials with high adsorption capacity,high selectivity and rapid adsorption kinetics for uranium extraction from seawater.In this paper,three kinds of composite materials?IIP-g-C3N4/?-CD,Fe₇S₈/CNNS-1 and MFCN-DETA?were synthesized by physicochemical modification with graphite carbon nitride as the base material to realize the efficient extraction and enrichment of uranium.A high selectivity U?VI?-imprinted graphitic carbon nitride/?-cyclodextrin composite sorbent was synthesized through ion-imprinting technique with?-cyclodextrin??-CD?as the functional ligand.The results of adsorption experiments show that the optimal adsorption pH of IIP-g-C₃N₄/?-CD?7.0-9.0?is close to the seawater pH?7.9-8.3?.The saturated adsorption capacity at 25°C can reach 808.6 mg g^-1,which is much larger than the value of non-imprinted composite material NIP-g-C₃N₄/?-CD(646.28 mg g^-1).The surface of IIP-g-C₃N₄/?-CD contains amount of selective adsorption sites to specific coordination of uranium.The selective experiment shows that all selectivity factors of IIP-g-C3N4/?-CD are larger than 1,showing the excellent selectivity for uranium.IIP-g-C3N4/?-CD can maintain rapid adsorption kinetics and high removal rates at different initial uranium concentrations in the simulating seawater adsorption experiments.The adsorption mechanism is that the nitrogen-containing functional groups and oxygen-containing functional groups on the surface of IIP-g-C₃N₄/?-CD could selectively coordinate to uranium.In order to achieve rapid separation of adsorbent materials from solution,magnetic nanocomposites Fe7S8/CNNS were prepared by in-situ hydrothermal method using graphite phase carbon nitride nanosheet CNNS as substrate.The effect of the proportion of loaded nanoparticles on the adsorption performance was also explored.The structure characterization shows that CNNS can effectively avoid the agglomeration of Fe7S8 magnetic nanoparticles and expose more active sites,which is beneficial to the adsorption and immobilization of U?VI?.The saturation magnetization of Fe₇S₈/CNNS-1 is 4.69 emu g^-1,which could promote the separation of adsorbent materials.The adsorption experiments show that the ionic strength have little effect on the adsorption process of Fe7S8/CNNS-1,belong to the inner layer complexation.The adsorption process conforms to the Langmuir model,and the calculated adsorption capacity is 572.78 mg g^-1.Based on the XPS results,the main mechanism of Fe7S8/CNNS-1 is the adsorption coordination of nitrogen-containing functional groups on the surface of CNNS and the reduction of Fe₇S₈ nanoparticles.As a result,Fe₇S₈/CNNS-1 can achieve the purpose of effective immobilization of uranium.The macroscopic three-dimensional porous sponge material MFCN was prepared using melamine sponge as template and urea as the source material.Different amino functionalized sponge composites MFCN-DETA,MFCN-TETA and MFCN-TEPA were synthesized by Schiff base reaction and the adsorption properties were also studied.The MFCN-DETA material has a macroscopic three-dimensional network structure and able to bear the 20 g weight with certain mechanical properties.The adsorption experiments suggest that the MFCN-DETA display the excellent adsorption efficiency,and reach the adsorption equilibrium in the first 30 min.The three-dimensional structure ensures that the MFCN-DETA material is easy to separate from solution,and it exhibits excellent adsorption selectivity and cycle stability.Therefore,the MFCN-DETA material is the adsorbent material that is easy to separate.