Morphology and size controlled synthesis of metal-organic framework crystals for catalytic oxidation of toluene

In this paper, an efficient approach based on an ionic liquid-modified microemulsion system is presented to prepare Co-MOF-74 crystals with a controllable morphology and size. It is found that Co-MOF-74 crystallization in the interface region between the alkyl chain of the ionic liquid cation and water can not only generate uniform microcrystals with olive-like, lamellae and hexagonal column geometries but can also enable tailoring of the crystal size and pore texture during the growth process. All samples were tested by multiple characterization methods, and the formation mechanism was studied by controlled preparation experiments and MD simulations. Catalytic evaluation was performed through the oxidation of toluene as a model reaction. The hexagonal column geometry crystal was found to exhibit the best catalytic activity due to the abundance of exposed catalytic active sites and special micro-meso pore structure. It is noteworthy that this strategy utilizes a green, simple construction of a microemulsion system to tune the morphology and size of MOFs, affording a way to prepare functional materials with outstanding performance for heterogeneous catalysis.