Preparation Of Modified Lanthanum-based Metal Organic Frameworks And Their Adsorption Properties For Gd³⁺

Rare earth elements are known as"treasures of new materials and industrial condiments",among which gadolinium（Gd）stands out from many rare earth elements because of its excellent conductivity and irreplaceable magnetism,and has been widely used in the fields of medicine,industry,nuclear energy and so on,which leads to the increasing demand for high-purity gadolinium.In addition,the hasty treatment of gadolinium-containing wastes accelerates the harm of gadolinium to the ecosystem.Therefore,based on the protection of the environment and the secondary utilization of rare resources,two new lanthanum-based MOF materials modified by polyethyleneimine（PEI）and 4,6-Diamino-2-mercaptopyrimidine（DMP）were successfully prepared in this paper,and they were used for the adsorption of rare earth ion Gd³⁺.The main work of this paper is as follows:（1）La BDC was effectively synthesized in N,N-dimethylformamide（DMF）environment by solvothermal method,using hexahydrate and lanthanum nitrate（La（NO3）3 6H2O）as intermediate coordination metals and terephthalic acid as organic ligand.SEM,FTIR and XRD showed that the material conforms to the structural characteristics of La BDC.Subsequently,two modifiers,PEI and DMP,were added to modify the surface and pore channels,and the amino-and sulfhydryl-functionalized La BDC@PEI and La BDC@DMP composites were prepared respectively.The characterization by SEM-EDS,FTIR and XPS showed that the two composites contained N and S elements or functional groups in different degrees,which indicated that the modifier was successfully integrated with La BDC,and the surface and pores of La BDC were modified.（2）On the basis of previous work,with La BDC,La BDC@PEI and La BDC@DMP as adsorbents and rare earth ion Gd³⁺as adsorbents,the concentration of modifier,adsorption kinetics,p H,adsorption isotherm,thermodynamics,ion interference,cycle performance and adsorption mechanism were explored.The experimental results showed that the maximum adsorption capacities of La BDC,La BDC@PEI and La BDC@DMP for Gd³⁺were 37.04 mg/g,181.77 mg/g and 241.40mg/g respectively.The adsorption process of Gd³⁺on these three materials is combined with Langmuir isotherm model,and the kinetics can be described by quasi-second-order rate equation.In the interference experiment of Na⁺,NH₄⁺,Ca²⁺,Mg²⁺and Al³⁺on the adsorption capacity of rare earth ions,it was found that the interference effect of univalent and bivalent ions was negligible,and the interference of trivalent ions was obvious,but the adsorption capacity of Gd³⁺remained above80%.Using 0.1M hydrochloric acid solution as the solution for 2 h,the desorption efficiency of Gd³⁺by La BDC@PEI and La BDC@DMP is above 92%,and the adsorption capacity can be maintained at about 80%after repeated analysis for three times,which showed that the synthesized composite material has good stability,can be reused,reduces the production cost,increases its application prospect for rare earth element recovery,and provides certain reference for actual industry.（3）Finally,by comparing the SEM-EDS,FTIR,XRD,XPS and DFT calculation of the materials before and after adsorption,it was found that the functional groups containing oxygen,nitrogen and sulfur in the composites participated in the adsorption reaction,and it was inferred that the possible adsorption mechanisms were surface complexation,ion exchange,hydrogen bonding and electrostatic attraction.The strong chemical interaction between these molecules provides a stable and efficient adsorption capacity for the adsorbent.