UiO-66-NH-(AO) MOFs with a New Ligand BDC-NH-(CN) for Efficient Extraction of Uranium from Seawater

Abstract

Metal–organic frameworks (MOFs) with a high surface area and excellent stability are potential candidates for uranium (U) adsorption. Amidoxime (AO) is the most widely used functional group to extract U, which is usually introduced into MOFs by two-step post-synthetic methods (PSMs). Herein, MOF UiO-66-NH-(AO) was obtained by a one-step PSM with amidoximation from UiO-66-NH-(CN), which was synthesized by a new organic ligand of 2-cyano-terephthalic acid and whose morphology was octahedron and could be well controlled with the new ligand. The one-step PSM can greatly maintain the octahedron of the MOFs. What is more, UiO-66-NH-(AO) showed good adsorption performance for U, the adsorption equilibrium was obtained within 1500 min, and the adsorption capacity of U was calculated to be 134.1 mg/g according to the Langmuir model. It also had excellent selectivity for U in the presence of high concentrations of vanadium (V), ferrum (Fe), magnesium (Mg), calcium (Ca), and zirconium (Zr). The adsorption capacity of U in natural seawater was determined to be 5.2 mg/g within 8 days. The recyclability of UiO-66-NH-(AO) in simulated seawater was demonstrated for at least four adsorption/desorption cycles. The binding mechanism was investigated by the extended X-ray absorption fine structure spectroscopy, revealing that U binding occurs in a fashion η2 motif. This study provides a reliable idea for the modification of MOFs and the potential for MOF-based materials to extract U from seawater.

Uranium extraction from seawater: material design, emerging technologies and marine engineering

“…In addition to developing AO-functionalized polyolefin polymers, scientists have also made considerable efforts to exploit the expanding family of porous organic frameworks, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs) and porous aromatic frameworks (PAFs), to be potential uranium adsorbents in recent years. 37,[82][83][84][85][86][87][88][89][90][91][92] The flexible molecular design, programmable pore structures, broad chemical and reticular/ topological variety, and especially ultrahigh surface area of these porous organic materials provide excellent opportunities to introduce a high density of chelating groups to promote the ligand-uranyl interaction. 30 Typically, Wang and colleagues performed the first use of AO as a functional ligand of classical UiO-66 MOF material for UES.…”

Functional metal–organic frameworks as adsorbents used for water decontamination: design strategies and applications

“…Modifying MOFs with Lewis base groups has been proven to be an effective approach. Ma et al 155 synthesized UiO-66-NH-(CN) with a new organic ligand of 2-cyano-terephthalic acid. Then, they introduced amidoxime groups by postsynthetic methods to obtain UiO-66-NH-(AO).…”

Highly Selective Extraction of U(VI) from Solutions by Metal Organic Framework-Based Nanomaterials through Sorption, Photochemistry, and Electrochemistry Strategies

“…This study provided the valuable references for extraction of U(VI) from natural seawater by MOF-based nanomaterials. 51 The amidoxime-functionalized TFTPN-crosslinked phloroglucinol polymers reached the high capacity of 579 mg/g for U(VI) at pH = 6 with high stability, selectivity, and reusability. It also had excellent ability in the selective detection of U(VI) with the limitation of 24.2 nmol/L in natural lake water.…”

“…The extended X-ray absorption fine structure (XAFS) analysis revealed the binding of U(VI) through η 2 -bound fashion. This study provided the valuable references for extraction of U(VI) from natural seawater by MOF-based nanomaterials . The amidoxime-functionalized TFTPN-cross-linked phloroglucinol polymers reached the high capacity of 579 mg/g for U(VI) at pH = 6 with high stability, selectivity, and reusability.…”