Temperature-Controlled Synthesis of Trimodal Hierarchically Porous MOFs with Variable Core–Shell Configurations

Abstract

Despite that multi-modal hierarchically porous metal–organic frameworks (MOFs) are highly desirable due to their capability for the spatial organization of different host reaction, their facile synthesis templated by a single surfactant system is still challenging. Herein, we developed a temperature-controlled strategy to synthesize trimodal hierarchically porous Ce-based UiO-66-type MOFs (THPUiO­(Ce)) with tailorable core–shell configurations by using nanoemulsions as soft templates. The hierarchical pore sizes and structures of cores and shells are controllable by facilely manipulating two-step temperatures and the components of the nanoemulsion. For a given nanoemulsion system, when the initial synthetic temperature is higher than the second one, the resultant THPUiO­(Ce) is composed of dendritic channels (30–50 nm) in cores and smaller cage-like mesopores (15–20 nm) in shells. Reversely, when the initial synthetic temperature is lower than the second one, the smaller mesopores (around 15 nm) are located in cores surrounded by large pore channels. Similarly, trimodal hierarchically porous bimetallic THPUiO­(Ce/Zr) can also be constructed upon extending this temperature-controlled approach, in which the molar ratio of the Zr content could be tuned up to 48%. In virtue of the inhomogeneous nature of THPUiO­(Ce), the hollow Ce-based MOFs with mesopores distributed on 60 nm thickness shells can be achieved after the acid treatment of THPUiO­(Ce). This facile assembly approach is expected to set a guideline for the construction of hierarchically porous MOFs for potential multicompartmental related applications.