Enhanced Adsorption Of Rubidium Ions With Water-resistant Metal Organic Frameworks

Adsorption aggregation of high valuable rubidium ions from salt lake is a hot topic at present research.Due to high specific surface area,high porosity,and adjustable structure,etc.,the metal organic frameworks?MOFs?has a promising application in the fields of liquid adsorption and separation.However,the adsorption ability could be invalid in water because the hydrolysis effect of the MOFs in water could cause its structure collapses.Therefore,three different types of MOFs were innovatively designed and synthesized in this paper.The water-resistant and adsorption performances were greatly enhanced by the surface modification of materials.The results of this paper provided a support of theory and data for industrial application of MOFs.The research detail are following as:1.The PDMS@Cu-BTC with water-resistant shielding performance was prepared by coated with polydimethylsiloxane?PDMS?through a chemical vapor deposition technique.The results of Brunauer-Emmett-Teller?BET?,diffraction of X-rays?XRD?,scanning electron microscope?SEM?,Fourier transform infrared spectroscopy?FT-IR?,contact angle and the coated amount of PDMS proved that PDMS coating on the Cu-BTC maintained the features of its structural morphology and water-resistant.The results of batch tests indicated that the PDMS@Cu-BTC with a intact structure exhibited a remarkable adsorption capacity?83mg/g?of Rb⁺and the regeneration efficiency reached more than 99%after the fifth cycle.2.The spherical nanoscale Fe₃O₄ as the core,carboxymethylcellulose sodium?CMC?as the link agent,ZIF-8 as the shell and the phenol as the surface modifier,a Fe3O4@CMC@ZIF-8-OH core-shell material was designed and synthesized by the hydrothermal synthesis and impregnation method.The properties and structural features of the material were systematic characterized by SEM,FT-IR,BET surface area,XRD and Zeta-potential,etc.The results of characterizations and bath tests showed that Fe₃O₄@CMC@ZIF-8-OH has a good water-resistant ability and its Rb⁺uptake capacity was enhanced due to existence of the negatively charged carbonyl carboxyl,and hydroxyl groups in its structure.In comparison with ZIF-8,the uptake capacity has a increase of 45%and reached 109mg/g.3.The AMP@PCN-224 composite was designed and synthesized by encapsulating the ammonium phosphomolybdate trihydrate?AMP?into the PCN-224structural cavity through in-situ hydrothermal method.The materials before and after coated with AMP was proved by BET,XRD,SEM,and FT-IR,etc.As a result,the structure morphology of AMP@PCN-224 has no significant change compared with PCN-224.Because the partial pore volume was occupied by AMP,the BET specific surface area reduced from 1013m²/g to 516m²/g,a decrease of 49%The introduction of AMP is favorable for improving the Rb⁺adsorption performance,and the adsorption capacity increased from 69mg/g to 102mg/g increased by 48%.The Freundlich and pseudo-second-order model could better describe the Rb⁺adsorption process over the surface of AMP@PCN-224.