Confined growth of MOF nanocrystals using a “locked” metal ion source

Abstract

The controlled growth of MOF crystals in a confined space has long been a challenge. In this contribution, we present a facile strategy for the confined growth of MOF crystals in a mesoporous silica shell by pre-installing a metal stock inside the cavity while transporting organic linkers through the permeable shell. Remarkably, the size and shape of the confined MOF crystals could be controlled effectively by adjusting the synthesis parameters. The obtained MOF@mSiO₂ composites could further be functionalized with a range of surfactant-free metal nanoparticles (MNPs, e.g., Au, Pd, and Ag) via galvanic replacement reactions on the encapsulated Cu₂O surface during a one-pot preparation. This led to ultrafine MNPs embedded within the MOF matrix. The construction of the MOF and the galvanic replacement reaction occurred on similar time scales, and the Cu₂O cores are believed to play dual roles in the synthesis: (i) providing a source of copper ions for building MOFs, and (ii) serving as a reductant to form noble MNPs which in turn significantly accelerated the formation kinetics of MOF crystals (to within 1 minute). Furthermore, it was also demonstrated that the encapsulated MOFs/MNPs within the mSiO₂ shells were highly accessible to the general gas/liquid molecules and exhibited excellent catalytic activity for several oxidation reactions.