Souryadeep Bhattacharyya

Engineering Porous Organic Cage Crystals with Increased Acid Gas Resistance.

Both known and new CC3-based porous organic cages are prepared and exposed to acidic SO2 in vapor and liquid conditions. Distinct differences in the stability of the CC3 cages exist depending on the chirality of the diamine linkers used. The acid catalyzed CC3 degradation mechanism is probed via in situ IR and a degradation pathway is proposed and supported with computational results. CC3 crystals synthesized with racemic mixtures of diaminocyclohexane exhibited enhanced stability compared to CC3-R and CC3-S. Confocal fluorescent microscope images reveal that the stability difference in CC3 species originates from an abundance of mesoporous grain boundaries in CC3-R and CC3-S, allowing facile access of aqueous SO2 throughout the crystal, promoting decomposition. These grain boundaries are absent from CC3 crystals made with racemic linkers.

Recovery of Acid-Gas-Degraded Zeolitic Imidazolate Frameworks by Solvent-Assisted Crystal Redemption (SACRed)

The acid stability of zeolitic imidazolate frameworks (ZIFs) is an important issue hindering their application. Acid-gas damage of ZIFs has been considered irreversible. However, we demonstrate a methodology called solvent-assisted crystal redemption (SACRed) to reverse acid-gas damage to ZIFs with a high degree of structural and functional recovery. For example, post-SACRed ZIF-8 is shown to be structurally and chemically near-identical with the original pristine ZIF-8 that suffered a large loss of surface area, porosity, and crystallinity during acid-gas exposure. We also provide mechanistic insight into the recovery process using deuterium-labeled linkers and 2H NMR spectroscopy. SACRed treatments could allow large extensions in the lifetime of ZIF-based membranes and adsorbents that degrade over time.