A new route to porous metal–organic framework crystal–glass composites

Abstract

A lower temperature route to metal–organic framework crystal–glass composites is presented. Specifically, the annealing pre-formed ZIF-62 glass with a crystalline MOF above Tg will enable formation of a greatly expanded range of materials.

Thermal Expansion of Metal–Organic Framework Crystal–Glass Composites

“…A pure sample of agZIF-62 is observed to exhibit the largest thermal expansivity (⍺L = 32.11 × 10 -6 K -1 ) of the measured materials, following previously reported data (35 × 10 -6 K -1 ). 21 Predictably, the sample of (UL-MOF-1)0.5(agZIF-62)0.5 with the largest volumetric expansion also exhibits the largest thermal expansion of the measured composites (⍺L = 27.59 × 10 -6 K -1 , 143-306 °C). A smaller expansion of (MIL-53)0.25(agZIF-62)0.75 (⍺L = 14.22 × 10 -6 K -1 , 111-177 °C) is likely due to the very small expansion of the MIL-53-lp phase inside the composite, and a larger contributing volume of ZIF-62 compared to that in (UL-MOF-1)0.5(agZIF-62)0.5.…”

“…Accordingly, several composite materials have been formed by mixing crystalline ZIF-62 with a crystalline MOF powder and heating the mixture to bring the ZIF-62 into the liquid state. 20,21 After quenching, the resultant self-supporting bulk material comprises a well-dispersed crystalline MOF within the agZIF-62 matrix. These materials are referred to as metal-organic framework crystal-glass composites (MOF CGCs) and are denoted as (crystal)x(glass)1-x where x is the weight fraction of the crystalline material in the composite, consistent with prior nomenclature.…”

“…Whilst the expansion behavior of agZIF-62, MIL-53, Na2NDC (a sodium analogue of UL-MOF-1), and MIL-118 have all been probed separately, there exists no study detailing the unit cell expansion of any crystalline material within a MOF glass. 21,23,28,29 Motivated by the absence of prior studies, here we compare and contrast the change in thermal expansivity of three crystalline MOFs upon encapsulation within a MOF CGC.…”

Guest size limitation in metal–organic framework crystal–glass composites

“…17 To date, the MOF CGC formed from MIL-53 and a g ZIF-62 is the first of only three known examples of this class of materials. [16][17][18] The extension of this approach to other crystalline MOFs is dependent upon their structural integrity at the temperatures required for the fabrication of the MOF CGC (e.g. T m , ZIF-62 = 437 °C).…”

The reactivity of an inorganic glass melt with ZIF-8

“…16,17 Further problems arise when considering stability during com-posite formation, such as reported correlations between incorporated ZIF amount, and mechanical failure in MMMs. 18,19 Motivated by the promising results obtained when using a ZIF glass matrix to embed a variety of different crystalline MOFs into composite materials, 11,12,20 this work examines the possibility of expanding the MOF CGC concept, to incorporate structures in which the glass matrix is an inorganic glass. This would greatly expand the range of different matrices available, as the number of glass forming MOFs is extremely limited compared to the vast amount of known inorganic glasses.…”