Effective Removal Of U(Ⅵ) From Water By Functionalized Calix[6]arene Of Composite Hollow Mesoporous Silica Spheres As A Novel Sorbent

This thesis is devoted to the synthesis of calix[6]arene hydroxime derivatives of composite hollow mesoporous silica spheres and their adsorption mechanism of U（Ⅵ）ions in water.Firstly,using the soft template method,the hexadecyl trimethyl ammonium bromide（CTAB）as a soft template agent,ethyl orthosilicate（TEOS）as a silica source,hollow mesoporous silica spheres（HMSS）were synthesized.Then the amino-functionalized hollow mesoporous silica spheres（NH₂-HMSS）were synthesized by grafting amino groups on the inner and outer surfaces of HMSS.On this basis,the calix[6]arene hydroxime derivatives（HCHMHC6）were combined with NH₂-HMSS by an amide reaction to synthesize calix[6]arene hydroxime derivatives of composite hollow mesoporous silica spheres（HC6-HMSS）.Finally,HC6-HMSS sorbent was applied to the adsorption treatment of low-concentration U（Ⅵ）from water.SEM,TEM,FTIR,XRD,TG,BET,EDS,DSC,EA,NMR and laser particle analysis have been utilized to characterize and analyze samples during synthesis and adsorption.The effects of p H,contact time,sorbent dosage,initial concentration and coexisting ions on the U（Ⅵ）removal by three mesoporous silica materials were compared and studied.Combined with the Visual MINTEQ simulation of U（Ⅵ）type content distribution,adsorption thermodynamics,adsorption kinetics and isotherm model,the adsorption mechanism of HC6-HMSS for U（Ⅵ）removal was revealed.The research findings were as follows:1)The particle size distributions of HMSS,NH₂-HMSS and HC6-HMSS were in the 200-350 nm range and their pore size distributions peak remained at 2.15-2.42 nm.Three materials possessed the characteristics of monodispersity and uniformity.Compared with HMSS,the specific surface area,the order degree of worm-like mesopores channels and the characteristic parameters of pore structure decreased with the increase of the complexity of grafted groups.2)²⁹Si SSNMR indicated that mesoporous Si-OH of HMSS existed a high degree of condensation.FTIR,EDS,XRD,TG and EA analysis showed that the grafted aminoalkyl chain and calix[6]arene hydroxime derivatives were grafted onto the surface of HMSS effectively.The effective silanol groups amount of HMSS was 7.11%,the grafting amount of the aminoalkyl chain of NH₂-HMSS and the calix[6]arene hydroxime derivatives of HC6-HMSS reached 7.06%and 4.40%,respectively.3)Under the optimized adsorption condition(p H 6,V=20 m L,T=298 K,Sorbent dose=0.5 g L^-1,t=60 min),HC6-HMSS,NH₂-HMSS and HMSS could all remove more than 98%U（Ⅵ）in water at low-concentration(10 mg L^-1).For medium and high concentration U（Ⅵ）(>50 mg L^-1),the residual concentration of U（Ⅵ）in aqueous solution was above 6.25 mg L^-1 after physical adsorption dominated HMSS could complete adsorption,while chemical adsorption dominated NH₂-HMSS and HC6-HMSS could still adsorb more than 98%U（Ⅵ）in water.In the multi-ion(Al³⁺,Ca²⁺,Cd²⁺,Cu²⁺,Mg²⁺,Zn²⁺,K⁺,Na⁺,PO₄^3-,SO₄^2-,CO₃^2-,C₂O₄^2-and Cl^-)and U（Ⅵ）bi-component adsorption experiments,Al³⁺,K⁺and C₂O₄^2-had the significant impact on U（Ⅵ）adoption onto HMSS,the adsorption rate decreased to 77.24%,87.23%,54.68%,but the above ions had little effect on U（Ⅵ）adsorption onto NH₂-HMSS and HC6-HMSS.And HC6-HMSS had a stronger selectivity to U（Ⅵ）than NH₂-HMSS4)The kinetics of U（Ⅵ）adsorption onto NH₂-HMSS and HC6-HMSS conformed to the pseudo-second-order kinetics model.The adsorption thermodynamics of both materials showed that the adsorption process was a spontaneous endothermic process.The adsorption isotherm model followed the Langmuir isotherm model,and the calculated saturated adsorption capacities of NH₂-HMSS and HC6-HMSS were 746.40 mg g^-1and 790.07 mg g^-1,respectively.The cavity conformation of calix[6]arene matched the size of U（Ⅵ）,conjugated pi bond and coordination of hydroxime groups made the secondary grafted HC6-HMSS further improve the chemical adsorption performance of NH₂-HMSS for U（Ⅵ）.5)After five successive adsorption-desorption cycles,HC6-HMSS could still maintain a U（Ⅵ）removal rate of more than 93%,which indicated a significant economic value.