Downsizing metal–organic frameworks by bottom-up and top-down methods

Downsizing metal–organic framework (MOF) crystals into the nanoregime offers a promising approach to further benefit from their inherent versatile pore structures and surface reactivity. In this article, downsizing is referred to as the deliberate production of typical large MOF crystals into their nanosized versions. Here, we discuss various strategies towards the formation of crystals below 100 nm and their impact on the nano-MOF crystal properties. Strategies include an adjustment of the synthesis parameters (e.g., time, temperature, and heating rate), surface modification, ligand modulation, control of solvation during crystal growth and physical grinding methods. These approaches, which are categorized into bottom-up and top-down methods, are also critically discussed and linked to the kinetics of MOF formation as well as to the homogeneity of their size distribution and crystallinity. This collection of downsizing routes allows one to tailor features of MOFs, such as the morphology, size distribution, and pore accessibility, for a particular application. This review provides an outlook on the enhanced performance of downsized MOFs along with their potential use for both existing and novel applications in a variety of disciplines, such as medical, energy, and agricultural research.