Exact Stoichiometry of Ce_xZr_6–x Cornerstones in Mixed-Metal UiO-66 Metal–Organic Frameworks Revealed by Extended X-ray Absorption Fine Structure Spectroscopy

Abstract

Bimetallic Ce/Zr-UiO-66 metal–organic frameworks (MOFs) proved to be promising materials for various catalytic redox applications, representing, together with other bimetallic MOFs, a new generation of porous structures. However, no direct proof for the presence of both metals in a single cornerstone of UiO-type MOFs was reported so far. Employing element-selective X-ray absorption spectroscopy techniques herein, we demonstrate, for the first time, that our synthesis route allows obtaining Ce/Zr-UiO-66 MOFs with desired Ce content and bimetallic CeZr5 cornerstones. Performing multiple-edge extended X-ray absorption fine structure analysis, we determine the exact stoichiometry of the cornerstones, which explains the dependence of thermal and chemical stability of the materials on Ce content.

Mixed-metal metal–organic frameworks

“…Quantitative analysis of EXAFS though fitting provides information on the distance of neighboring atoms, their number and chemical identity. 58 Figure 13 illustrates the power of EXAFS in resolving the tiny shifts in the nearest O-shell distance around Fe in MIL-53(Fe) upon Li + insertion. 56 Corresponding changes in the nearest neighboring metal shells proved more difficult to resolve, though.…”

Bimetallic metal–organic frameworks and their derivatives

“…39 Extended X-ray absorption ne structure spectroscopy (EXAFS), neutron powder diffraction (NPD) and XPS can determine the spatial arrangements of metals in the SBUs of bimetallic MOFs. [40][41][42] Different techniques should be combined for the accurate characterization of the synthesized bimetallic MOFs.…”

A Hybrid Artificial Photocatalysis System Splits Atmospheric Water for Simultaneous Dehumidification and Power Generation

“…Recently, metal-organic frameworks such as microporous MOF-74 (UiO-66), mesoporous MIL-100/-101, and porous silica gel have been found for harvesting water directly from air. [22][23][24][25] But, the inadequacies of these materials are poor humidity absorption rate and low quantity of saturated value. According to a recent report on zinc-based hydrogel exhibiting the humidity harvested behavior, [26,27] a new cobalt-based hygroscopic hydrogel has been developed and deployed to fetch atmospheric humidity for water splitting.…”

“…Although many systems have been reported on collecting water from ambient environment, materials or devices to harvest humidity and use it for energy‐related applications are sparse. Recently, metal–organic frameworks such as microporous MOF‐74 (UiO‐66), mesoporous MIL‐100/‐101, and porous silica gel have been found for harvesting water directly from air . But, the inadequacies of these materials are poor humidity absorption rate and low quantity of saturated value.…”