Abstract
To date, only several microporous, and even fewer nanoporous, glasses have been produced, always via post synthesis acid treatment of phase separated dense materials, e.g. Vycor glass. In contrast, high internal surface areas are readily achieved in crystalline materials, such as metal-organic frameworks (MOFs). It has recently been discovered that a new family of melt quenched glasses can be produced from MOFs, though they have thus far lacked the accessible and intrinsic porosity of their crystalline precursors. Here, we report the first glasses that are permanently and reversibly porous toward incoming gases, without post-synthetic treatment. We characterize the structure of these glasses using a range of experimental techniques, and demonstrate pores in the range of 4 – 8 Å. The discovery of MOF glasses with permanent accessible porosity reveals a new category of porous glass materials that are elevated beyond conventional inorganic and organic porous glasses by their diversity and tunability.
Highlights
To date, only several microporous, and even fewer nanoporous, glasses have been produced, always via post synthesis acid treatment of phase separated dense materials, e.g. Vycor glass
The free energy requirement for breaking the zinc-imidazolate bond has been calculated to be ca. 95 kJ mol−1 at 567 °C11. This relatively low bond strength led us to consider zeolitic imidazolate framework (ZIF) containing this ligand as primary candidates for melting, followed by quenching of the liquid to produce porous glasses
Limitations exist to the exclusive use of imidazolate since close association of the Zn and Im components in the liquid and glass states leads to dense materials[16]
Summary
Only several microporous, and even fewer nanoporous, glasses have been produced, always via post synthesis acid treatment of phase separated dense materials, e.g. Vycor glass. Conventional porous glasses are silica-rich materials derived by acid treatment of phase-separated borosilicate glass precursors They have found widespread applications in electrodes, chromatography and medical devices, and as desiccants, coatings and membranes[1]. Surface areas verging on 1000 m2 g−1 arising from pore sizes of up to 1 nm have been reported While these organic materials present fewer chemical restrictions on their functionality than their inorganic counterparts, their thermal stability is limited and their susceptibility to densification over time (physical aging) is well documented[5]. We report the successful realization of this goal, in the form of glasses derived from ZIFs that reversibly adsorb gas molecules These materials can be considered prototypical new porous glasses, given that there is no requirement for post-processing treatment. We anticipate that the stability, processability and chemical diversity of these glasses will underpin their applications in separations, and as components of membranes, catalysts, functional coatings and thin films
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