Enhanced Stability of the Metal-Organic Framework MIL-101(Cr) by Embedding Pd Nanoparticles for Densification through Compression

Metal-organic frameworks (MOFs) are ideal platforms for new and original functionalization, as the confinement of metallic nanoparticles (NPs) within their pores. However, the insertion of NPs could impact the framework's mechanical stability, thus affecting their performances in applications. Indeed, MOFs are usually loose powders that need to be compressed to increase the volumetric density before being employed as gas adsorbers. Here, we investigate the high-pressure behavior of the mesoporous MOF MIL-101 loaded with Pd NPs (20, 35 wt %) by synchrotron X-ray diffraction and infrared spectroscopy. The control of the metal content allows us to demonstrate that Pd NPs enhance the mechanical stability of MIL-101, with the bulk modulus and the crystalline-amorphous transition pressure increasing with the Pd loading. This is attributed to the NP steric hindrance, whereas the presence of host-guest chemical interactions is ruled out by infrared spectroscopy. We also define a spectroscopic quantity highlighting the framework amorphization that can be exploited from now on to characterize these materials when densified. Our results demonstrate that the incorporation of NPs makes MOFs not only more functional but also more mechanically stable and thus suitable for densification.