Microfluidic synthesis of uniform single-crystalline MOF microcubes with a hierarchical porous structure.

Creating hierarchical porosity in MOFs and controlling their size and morphology have emerged as efficient means for achieving significant improvement of MOF properties, and are crucial for facilitating the practical implementation of their various applications. Although important advances in this respect have been made, the realization of a hierarchical pore structure in a single crystalline MOF particle with controlled size and shape is still a challenge, and highly desirable. In this work, based on droplet-based microfluidics in conjunction with evaporative crystallization, an efficient approach to large-scale synthesis of uniform single-crystalline HKUST-1 particles with a hierarchical pore structure is presented. It is found that the MOF crystallization in confined droplets could generate not only monodisperse single-crystalline microcubes with an engraved rich porous texture including bimodal or trimodal pore structures, but also the size and porosity of the resulting cubes as well as the introduced meso- or macropore size could be widely tailored by varying the preparation conditions. Importantly, through the simple addition of an active species into the formed droplets, the functionalization of the resulting pore structured HKUST-1 cubes could be facilely realized, affording a series of high-performance functional nanomaterials.