Carboxylated UiO-66 Tailored for U(VI) and Eu(III) Trapping: From Batch Adsorption to Dynamic Column Separation

Abstract

U­(VI) and Eu­(III), as representative elements of the hexavalent actinide and trivalent lanthanides (always as a chemical analogue for trivalent actinide), respectively, have attracted more and more attentions due to the widespread use of nuclear energy. Much effort has been focused on developing versatile materials for their uptake from aqueous solution. For the first time, we report here UiO-66 and its mono- (UiO-66-COOH) and di-carboxyl (UiO-66-2COOH) functional derivatives as robust adsorbents for efficient U­(VI) and Eu­(III) removal. It is found that the introduction of carboxyl groups greatly reduces the surface charge of UiO-66, thus guaranteeing excellent adsorption capacity at low pH. At pH = 3, for example, the adsorption capacity of UiO-66-2COOH for U­(VI) and Eu­(III) is more than 100 and 60 mg/g, respectively, while almost no adsorption occurs for pristine UiO-66. At pH = 4, both UiO-66-COOH and UiO-66-2COOH show high performance on U­(VI) and Eu­(III) removal. UiO-66-COOH has adsorption capacities of 80 and 43 mg/g for U­(VI) and Eu­(III), respectively, while the values for UiO-66-2COOH reach 150 and 80 mg/g, respectively. Also, all these materials achieve adsorption equilibrium within 100 min. More importantly, combining the needs of practical applications and the characteristics of high stability, high porosity, and excellent adsorption performance of UiO-66-2COOH, dynamic adsorption column experiments were successfully conducted; ∼99% U­(VI)/Eu­(III) can be efficiently adsorbed, and >90% adsorbed U­(VI)/Eu­(III) can be re-collected with dilute nitric acid solution, even after four adsorption–desorption cycles. The findings of this work demonstrate the application potential of metal–organic framework materials to remove radionuclides from environmental samples or nuclear waste liquids.

The Carboxyl Functionalized UiO-66-(COOH)2 for Selective Adsorption of Sr2+

“…The sorption amount reached a plateau in 2 h for Sr 2+ with the value of approximately 40 mg g −1 . It is known that the presence of carboxyl groups increases the defect concentration of the UiO-66 structure, producing a negative charge in acidic conditions, [28,37,38] therefore electrostatic attractions exist and contribute to a fast equilibrium adsorption process. While the zeta-potential value before and after adsorption were −31.7 and −33 mV, respectively (see Table S2), indicating the absence of the electronic interaction with cationic at room temperature.…”

“…It is noteworthy that two carboxylate arms of H 4 btec play the role of linkers, while the two remaining are non-bonded. These free carboxylic acid groups are uniformly distributed throughout the MOF making them readily accessible for binding with cations without structure collapse [28]. UiO-66-(COOH) 2 , its features of gas sorption, dyes elimination, conductivity, and good water stability, have been respectively assessed [27,[29][30][31][32].…”

High Sorption and Selective Extraction of Actinides from Aqueous Solutions

“…The sorption of uranium from water is not only important environmental, but also for nuclear fuel extraction. Zhao et al [ 21 ] synthesized UiO-66 and functionalized the UiO-66 with carboxyl functional groups to achieve its mono-carboxyl (UiO-66-COOH) and di-carboxyl (UiO-66-2COOH) derivatives. The -COOH groups can efficiently reduce the surface charge and thereby increase the sorption capacity of UiO-66 at low pH values.…”

Amyloid-like assembly converting commercial proteins to water-insoluble adsorbents with ultrahigh adsorption capacity and excellent antifouling property for uranium extraction

“…However, the adsorption rates of these amidoxime-based adsorbents are not highly desirable as they might take several weeks to attain adsorption equilibrium in natural seawater, leading to low extraction efficiency and high economic cost. Very recently, advanced porous materials, including metal/ covalent-organic frameworks [21][22][23][24] and porous aromatic frameworks, [25][26][27] have also been utilized for capturing uranium from seawater. Indeed, their extraction efficiency has been greatly improved, beneting from their abundant porous channels and large specic surface areas.…”