Modulated formation of metal-organic frameworks by oriented growth over mesoporous silica

Abstract

Engineering the structure of metal-organic frameworks at the molecular level is of major interest for taking MOFs beyond their uses as bulk materials and creating multifunctional features with advanced applications. The notion involves directing MOF structure and controlling crystallization in terms of phase and orientation through interactions with directing agents. We have successfully used different concentrations of SBA-15 mesoporous silica for directed growth of the archetypal MOF-5 microcrystals along preferred crystallographic orientations, resulting in the production of interesting flower-like and nanorod frameworks instead of the conventional cubic structure. The results point to the possibility of using mesoporous silicas for designation of a wide range of MOF structural motifs with expedient performance and applications via selective interactions of MOF crystal building blocks with active functionalities on mesoporous surface, allowing heterogeneous seeding and controlled expansion of the framework along a preferred direction. The modifications in MOF structure have proven to improve the catalytic performance of MOF–silica nanocomposites up to 50% for Friedel–Crafts alkylation, compared to pure MOF-5. By discussing the effect of MOF texture on catalytic performance, this research aims to take MOF-5 beyond its bulk applications and opens up a new paradigm to design highly active and selective green heterogeneous catalysts based on MOFs.