Hierarchically Porous Metal–Organic Framework Monoliths Synthesized from Sacrificial Zirconium-Based Templates

Metal–organic frameworks (MOFs) are typically synthesized as microcrystalline powders, a form not always suitable for applications in adsorption and catalysis. The structuring of MOFs into macroscopic architectures is one way to overcome this limitation. Here, we report a versatile strategy for synthesizing hierarchically porous Zr-based MOF monoliths from zirconium oxy/hydroxide gel sacrificial templates using the coordination replication method. This simple, two-step approach is applicable to a range of 12-connected Zr-based MOFs, including MOFs exhibiting the UiO-66 and -67 topology, and is sufficiently robust to accommodate various linker functionalities and lengths. The factors influencing conversion of the sacrificial template into the MOF were explored by systematic investigation of the reaction conditions (e.g., temperature, time, and modulator concentration). This approach afforded hierarchically porous Zr-based MOF monoliths with tunable pore size distributions that could be controlled via the reaction conditions and the structural features of the parent monolith. Furthermore, we show that through a model Knoevenagel reaction and kinetic adsorption studies, the catalytic activity and active site accessibility of UiO-66 can be preserved following structuralization using the optimized reaction conditions, which demonstrates full accessibility of the hierarchically arranged MOF particles.