The controlled microfluidic formation of stable mixed phase HCP/FCC-UiO-67(Zr)-benzoic acid through modification of water concentration

This work reports the synthesis of a mixed crystal phase mesoporous metal–organic framework (MOF) through a new synthesis route. The Hexagonal Centred Planar/Face Centred Cubic mixed phase UiO-67(Zr) product was microfluidically synthesised using benzoic acid as the acid modulator. This phase ratio can be altered through changing the concentration of water present in the reaction solution. This product shows increased mesoporosity and uptake of N2 at 77 K and 1 bar of 1083 cm3/g, as compared to 615 cm3/g for the product made via the traditional batch approach. This leads to an increase working capacity due to the change in isotherm type, from type I to type IV, with the uptake occurring more gradually overall as pressure increases. An increased working capacity allows for a greater range of control for the volume of N2 stored in/released from the material. This product has only been successful in microfluidic conditions, highlighting the potential importance of this method for future synthesis of this MOF.