Sol–Gel Processing of Metal–Organic Frameworks

Sol–gel processing represents a powerful and versatile strategy for the preparation of functional inorganic and hybrid materials that facilitate control over the molecular composition, as well as organization of the materials at the various length scales relevant to fundamental and applied research. Recent advances have enabled its use for the processing of an emerging class of functional porous materials called metal–organic frameworks (MOFs). Here, sol–gel approaches can be employed for the direct manipulation of MOFs, or as a route to the construction of composite materials where the properties of the MOF are synergistically combined with those of a carefully chosen inorganic phase. In this review, we present the most significant progress made in this emerging area, according to four main synthetic strategies, with a particular focus on describing how sol–gel processing enhances the functionalities of the MOF. These strategies include (1) molecular scale manipulations of the pore surfaces of MOFs with sol–gel precursors; (2) the controlled positioning or growth of MOF crystals on inorganic surfaces; (3) the use of MOF crystals as templates for sol–gel processes (either within the pores, or at the external surfaces); and (4) the use of sol–gel-derived sacrificial inorganic templates for the structuring of MOF-based architectures. Each of these processing methods imparts unique properties to the systems and provides a route to higher-order architectures and material compositions not accessible through conventional approaches to MOF synthesis. Sol–gel processing provides promising routes toward new functional materials that display enhanced properties and are expected to play an important role in allowing MOFs to be optimized for specific applications.