Porous materials are abundant in nature in the forms of soils, minerals, and biological tissues. Conventional synthetic porous materials include activated carbons, polymeric foams, and synthetic zeolites. The past two decades have witnessed significant progress in the development and applications of a new generation of porous materials named open framework materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), and their derivatives obtained by various post-synthetic treatments.
This themed collection of studies highlights the unique common features of these novel porous materials that distinguish them from conventional porous materials. The first unique feature is their intrinsic tunable porosity. Many of these porous materials have ultrahigh porosities that could benefit a variety of energy-related applications. The second unique feature is their modular framework structures. These porous materials are typically constructed from molecular blocks (monomers) with specific functional groups that can interconnect these monomers into extended frameworks via chemical reactions or even supramolecular interactions. This feature allows judicious selection of monomers with predesigned geometry and functional groups to endow the ultimate frameworks with desired topologies and physical/chemical properties. Moreover, the modular nature allows post-synthetic modification approaches to introduce additional modules/functional groups or alter existing moieties to further tailor the framework properties without compromising the framework integrity and porosity.
The applications of novel porous materials, as showcased in this special topic featuring Open Framework Materials for Energy Applications, are established on the basis of the employment of the aforementioned two unique features. For instance, the pores of these materials can accommodate guest molecules to introduce extra properties, such as electrochromic properties, to the composites.1 Integrating internal porosity and the possibility to tune framework functional groups make these porous materials promising adsorbents for cost-effective gas separation applications such as CO2 capture and natural gas upgrading.2,3 In addition, open framework materials have widespread applications in heterogeneous catalysis, because it is facile to incorporate catalytic active sites into the modular frameworks, and the high specific surface area guarantees the exposure of these sites to target reactants. The catalytic active centers can be embedded in the monomers before framework formation if the active sites are robust enough to sustain the chemical environment where the frameworks are synthesized.4 Otherwise, the liable active sites such as noble metal complexes or photosensitizers for photocatalysis can be grafted to reactive moieties on the porous frameworks or integrated with the frameworks via self-assembly afterward.5–7 Finally, open framework materials bearing precursors of functional sites can be transformed to porous carbon or metal oxides/selenides/phosphides via thermal treatment to improve their material conductivity for electrocatalytic applications.8,9
We hope that this special topic issue will be inspirational to researchers who are interested in the development of open framework materials and their applications in energy and environmental sustainability. We appreciate all the authors and reviewers for their valuable contributions and the editorial team of APL Materials, without whom this issue would not be possible, for their obliging support.
