Ultrathin Mesoporous Metal-Organic Framework Nanosheets

Abstract

Designing 2D mesoporous metal-organic framework (MOF) nanosheets to overcome the limitations of bulk MOF counterparts, with a focus on enabling smooth mass transport, presents an attractive yet challenging endeavor. Here, a novel bottom-up interface-directed co-assembly method is presented for the synthesis of ultrathin 2D mesoporous UiO-66(Ce) nanosheets. The method utilizes an interface-directed co-assembly of amphiphilic perfluorooctanoic acid-induced lipid bilayers and spherical micelles from PS-b-PEO block copolymers to form unique 2D sandwich-like assemblies that guide the creation of 2D mesoporous UiO-66(Ce). The resultant 2D mesoporous UiO-66(Ce), with ≈23 nm pore diameters and a thickness that can be tuned from 3 to 150 nm, represents a substantial advancement in the application of MOFs for environmental remediation. As a model reaction, the U(VI) photoreduction benefits from the through-mesopores of its 2D morphology, which are absent in previously reported UiO-66(Ce), as they shorten the diffusion path, thereby improving mass transport and accessibility to active sites. This report demonstrates the significant role of existing mesopores in MOFs and the shape control of MOFs.

Keywords: 2D nanosheets; double soft‐template method; mesoporous structures; metal‐organic frameworks.

Figure 1

Schematic of the synthesis of the 2D mesoporous UiO‐66(Ce) nanosheets (2D‐mUiO‐66(Ce)).

Figure 2

Morphological and structural characterizations of 2D ‐mUiO‐66(Ce). a,b) SEM images, c–e) TEM images, f) elemental mapping, and g) AFM image and its corresponding height information.

Figure 3

a) XRD patterns, b) N₂ adsorption‐desorption isotherms, c) Ce 3d XPS patterns, d) O 1s XPS patterns, e) percentage of Ce (III)/ Ce (III)+Ce (IV), f) percentage of Ce‐OH/oxygen‐containing groups, g) X‐ray absorption near‐edge spectra (XANES), h) Fourier transforms of EXAFS spectra, i) k²‐weighted Ce K‐edge EXAFS of 2D‐mUiO‐66(Ce), Ce₃PO₄, and CeO₂.

Figure 4

a) U(VI) (50 ppm) removal ratio in the dark and upon irradiation, b) UV–vis adsorption spectra, c) Tauc plot for band gap calculation, d) Mott–Schottky plots, e) transient current density, and f) band structure alignments.

Figure 5

a) Top view of the models investigated with DFT: 3D‐UiO‐66(Ce), 3D‐spUiO‐66(Ce), 2D‐UiO‐66(Ce), 2D‐spUiO‐66(Ce), and 2D‐lpUiO‐66(Ce), where “sp” denotes small‐pore and “lp” denotes large‐pore. Green, red, and white spheres represent Ce, O, and C atoms, respectively. The calculated band gap (in eV) for each model is also shown. b) Snapshots from MD simulations at 30 ns, showing both side and top views. Pink and yellow spheres represent Na⁺ and Cl⁻ ions, respectively, while MOF atoms are shown in white for clarity. The percentage values indicate the proportion of ions in the bottom, MOF, and top layers.