(456d) Controlled Demolition and Reconstruction of Metal-Organic Frameworks By Acid Gas Treatment and Linker Insertion

The metal ion-organic linker coordination bond of Metal-Organic Frameworks (MOFs) is often unstable in acid gas environments (such as dry or humid CO₂, SO₂, NO₂). The associated bond cleavage leads to loss of crystallinity and porosity due to the formation of defects consisting of acid-linker complexes. Recently, a method called “Solvent-Assisted Crystal Redemption” (SACRed) has demonstrated the controlled degradation of an existing ‘template’ MOF (such as ZIF-8) with humid SO₂, followed by treatment with a native or non-native fresh linker solution to yield a reconstructed ZIF-8 or hybrid ZIF-8 containing non-native linkers respectively. In the present talk, we discuss how to expand and generalize the controlled demolition and reconstruction concept to a broader range of ZIF/MOF materials, thereby allowing a more general technique to synthesize MOFs that are otherwise difficult to obtain by conventional de novo synthesis or linker exchange methods.

In particular, we have investigated the use of several MOF templates of different classes (several ZIF and UiO materials), and the effects of controlled demolition with different kinds of acid gases (SO₂ and NO_2­ in dry and humid conditions). The extent of room temperature exposure for each MOF-acid gas pair is chosen to cause significant degradation as characterized by the reduction of pore volume, BET surface area, and crystallinity. SACRed recovery protocols designed for each degraded MOF display significant recovery of crystallinity and porosity in all cases. The distinctive physical and chemical modifications occurring in the degraded and recovered MOFs are studied by spectroscopic, crystallographic, and pore texture analysis techniques. The findings can enable us to construct a more general set of guidelines for applying this technique for reconstructing damaged MOFs and for synthesizing new MOFs that are otherwise difficult to synthesize conventionally (e.g., due to kinetic or thermodynamic barriers). Potential practical uses of this approach include the regeneration of MOFs after prolonged use, and insertion of functional new linkers into template structures of known topology and stability in order to obtain improved adsorption and diffusion properties.