Gel-Based Morphological Design of Zirconium Metal-organic Frameworks

The ability of metal–organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero- or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+-based MOFs: UiO-66-X (X = H, NH2, NO2, (OH)2), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 μm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Bart Bueken (ORCID) identifier: Tom Willhammar (ORCID) identifier: Timothée Stassin (ResearcherID) identifier: Ivo Stassen (ORCID) identifier: Joeri F. M. Denayer (ResearcherID) identifier: Rob Ameloot (ORCID) identifier: Thomas D. Bennett (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported Licence (CC BY-NC 3.0) history: Received 21 December 2016; Accepted 20 March 2017; Accepted Manuscript published 23 March 2017; Advance Article published 29 March 2017; Version of Record published 3 May 2017status: publishe