Fabrication of Carboxylate‐Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution

Abstract

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal–organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra‐low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50–500 µg L−1 within 5 min. Moreover, the 2D nano‐material exhibits ultra‐high anti‐interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT‐IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

MIL-53(Fe) Nanosheet Arrays with Coordinatively Unsaturated Metal Sites as an Electrocatalyst for Oxygen Evolution Reaction

“…The OER polarization curves and overpotential histograms are shown in Figure S3, where MIL-53­(Fe)/NF-2 presents relatively good OER performance. Previous research indicates that 2D MOFs with large specific surface areas are more likely to expose abundant unsaturated metal sites or structural defects, conducive to efficient OER. − Although MIL-53­(Fe)/NF-2 with a nanosheet structure exhibits a relatively good OER performance, it also exhibits noticeable stacking phenomena. Converting MOFs with a stacked structure into 2D ultrathin nanosheets can greatly improve the electrocatalytic activity .…”

Decorating Cage-Shaped Cavities with Carboxyl Groups on Two-Dimensional MOF Nanosheet for Trace Uranium(VI) Trapping

“…43−45 By rational modification for the top and bottom rims, cavity structures with predesigned adsorption sites can be purposefully introduced into MOFs, and the assynthesized MOFs tend to produce a layered structure. 46 Moreover, the large molecular skeleton of the calix[n]arene would enable the layered structures with large layer separations, facilitating further exfoliation. 36 As a consequence, the ligand calix [4]arene 5,11,17,23t e t r a k i s [ ( p -c a r b o x y p h e n y l ) a z o ] -2 5 , 2 6 , 2 7 , 2 8tetrahydroxycalix [4]arene (H 4 L) was elaborately selected for MOF fabrication (Scheme 1).…”

“…Functionalizing pores or cavities onto the surfaces of 2D MOF nanosheets could be an efficient tactic to fully utilize their unique structural advantages in uranium removal. Calix[n]arenes (n = 4, 6, and 8), with a special cup-shaped structure and facilely modified rims, can be an ideal ligand for the construction of MOF nanosheets with cavity structures. − By rational modification for the top and bottom rims, cavity structures with predesigned adsorption sites can be purposefully introduced into MOFs, and the as-synthesized MOFs tend to produce a layered structure . Moreover, the large molecular skeleton of the calix[n]arene would enable the layered structures with large layer separations, facilitating further exfoliation …”