Synthesis And Property Of Anti-fouling Zeolitic Imidazolate Framework-based Composites For Uranium Adsorption

In the context of economic globalization,energy is the basis for the development of human society and the realization of national modernization.As the main fuel of nuclear energy,uranium is an important strategic resource to ensure global energy consumption demand and sustainable economic development.The ocean has abundant potential uranium resource reserves.It is of great significance for the sustainable development of nuclear energy to promote the development of technologies for extracting uranium from seawater.Zeolitic imidazolate frameworks(ZIFs)are widely used in the field of uranium adsorption,due to its adjustable structure,large specific surface area,high porosity,chemical and thermal stability.However,there are many marine microorganisms in seawater,and biofouling is easy to occur on the surface of the adsorbent,which seriously reduce the adsorption performance of the adsorbent.Moreover,marine environment is high salinity and weak alkalinity,which greatly reduce the adsorption amount of ZIFs and limit the application of materials in the field of uranium extraction in seawater.Therefore,the development of ZIFs materials with excellent biofouling resistance and suitable for marine environments still faces great challenges.Combining the edge effect of two-dimensional graphene oxide sheet structure with outstanding antimicrobial property of silver ions,a silver ion-doped zeolitic imidazolate frameworks/graphene oxide composite(GZA)was prepared by in-situ growth method.The basic structure characterization of GZA was also studied.The effects of graphene oxide and silver ions on the properties of ZIF-67 materials were explored by a series of seaweed resistance and adsorption experiments.The GZA composite showed more than 20% of algae cells death rate;and the adsorption capacity of the ZIF-67 material under weakly alkaline conditions can be significantly enhanced when the molar ratio of silver ions to cobalt ions is1:2.At p H 8.0,the adsorption capacity of GZA composites was 1.77 times that of the ZIF-67,which can reach 158.06 mg/g.The adsorption capacity and removal rate of GZA composites were 4.974 ?g/g and 73.27% at seawater condition,respectively.These results proved that graphene oxide and silver ions can effectively enhance the biofouling resistance and adsorption properties of GZA,making it more suitable for seawater environments.Aiming at the problem of poor cyclic adsorption performance of the above materials,a magnetic ZIF-8-silver ion nanocomposite(FCZ8A)was prepared by solvothermal and in-situ growth methods.The relationship between the structure and properties of magnetic core,silver ions and ZIF-8 shell were studied.The saturation magnetization of FCZ8 A was 33.5emu/g;the algae cell death rate was 41%;and the adsorption capacity was 120.15 mg/g at p H8.0.Moreover,the adsorption capacity of FCZ8 A was 72.53 mg/g during the fifth cycle adsorption and much higher than that of GZA composites(22.63 mg/g),which confirmed its potential for recycling.These results showed that the magnetic core only provided superior magnetic properties,and silver ions were used as the main ingredient for the improvement of antibiofouling and adsorption performances of the ZIF-8 material.The pre-crosslinking reaction of zinc ions and chitosan was used to overcome the chemical inertness of the melamine sponge matrix.The ZIF-8/chitosan sponge adsorbent(CFZ8)with three-dimensional porous structure was prepared by in-situ growth method.A series of characterization and performance tests were performed on CFZ8 sponge and ZIF-8powder.CFZ8 sponge has excellent mechanical properties with 0.565 MPa of compressive stress;its seaweed cell death rate is 35%;and adsorption capacity is 129.90mg/g at p H 8.0.At the fifth adsorption-desorption cycle,the U(VI)adsorption capacity of CFZ8 sponge was still95.47 mg/g,which was higher than the initial adsorption capacity of ZIF-8 powder adsorbent(91.45 mg/g).In order to further improve the adsorption capacity of ZIFs composites,a graphene oxide-chitosan/ZIF-8-silver ion foam adsorbent(GCZ8A)with three-dimensional porous structure was prepared by covalent cross-linking,in-situ growth and freeze-drying technology,using GO as nanofiller.The effects of added components on the performance of ZIF-8 were discussed.The compressive stress of GCZ8 A can reach 352.41 k Pa,and the mass loss rate is3.26% in seawater,indicating that it has good mechanical property and hydrolysis stability.The algae cell death rate of GCZ8 A materials was 70%,and only a small amount of seaweed adhered on its surface;besides,the adsorption capacity of GCZ8 A is 1.73 times that of the ZIF-8 powder at p H 8.0 and reach 162.60mg/g.At the fifth cycle of adsorption,the adsorption amount can still reach 121.70 mg/g;moreover,the adsorption capacity and removal rate of the GCZ8 A composites are 12.24 ?g/g and 66.31% at seawater condition,respectively.