(263b) Encapsulation of Gold Nanoparticles in Uio-66 for CO Oxidation

Gold nanoparticles (AuNPs) are incorporated in the zirconium-based metal-organic framework, UiO-66, via encapsulation, or the formation of crystals around pre-formed nanoparticles. Encapsulation is advantageous over conventional impregnation techniques because (1) the nanoparticles can be designed for specific target applications, (2) the spatial location can be controlled, (3) there is limited pore blockage, and (4) the complete MOF database can be used as supports. The greatest limitation of encapsulation is nanoparticle stability; they cannot react adversely with any of the precursors, intermediates, or products. The conventional UiO-66 synthesis generates hydrochloric acid during the reaction which often reacts with or dissolves nanoparticles, including AuNPs. Therefore, the HCl-sensitive AuNPs require an alternative UiO-66 synthesis that does not generate HCl. The use of zirconium propoxide (Zr(OnPr)) in place of zirconium chloride (ZrCl₄) leads to an alternative synthesis route for producing high-quality crystals of UiO-66 with no generation of HCl. This new method enables the inclusion of HCl-sensitive AuNPs into the mother solution for encapsulation by UiO-66, yielding a composite with 8nm AuNPs randomly distributed throughout high-quality UiO-66 crystals. The resulting Au@UiO-66 exhibits enhanced catalytic activity for carbon monoxide oxidation compared to the parent material. It also demonstrates improved catalytic activity over physical mixtures of AuNPs and UiO-66, suggesting a synergistic effect that developed during encapsulation. This alternative synthesis lays the ground-work for the encapsulation of a broad base of HCl-sensitive nanoparticles in chemically, mechanically, and thermally stable UiO-66 for designed applications.