Thermal Structural Transitions and Carbon Dioxide Adsorption Properties of Zeolitic Imidazolate Framework‑7 (ZIF-7)

As a subset of the metal–organic frameworks, zeolitic imidazolate frameworks (ZIFs) have potential use in practical separations as a result of flexible yet reliable control over their pore sizes along with their chemical and thermal stabilities. Among many ZIF materials, we explored the effect of thermal treatments on the ZIF-7 structure, known for its promising characteristics toward H₂ separations; the pore sizes of ZIF-7 (0.29 nm) are desirable for molecular sieving, favoring H₂ (0.289 nm) over CO₂ (0.33 nm). Although thermogravimetric analysis indicated that ZIF-7 is thermally stabile up to ∼400 °C, the structural transition of ZIF-7 to an intermediate phase (as indicated by X-ray analysis) was observed under air as guest molecules were removed. The transition was further continued at higher temperatures, eventually leading toward the zinc oxide phase. Three types of ZIF-7 with differing shapes and sizes (∼100 nm spherical, ∼400 nm rhombic-dodecahedral, and ∼1300 nm rod-shaped) were employed to elucidate (1) thermal structural transitions while considering kinetically relevant processes and (2) discrepancies in the N₂ physisorption and CO₂ adsorption isotherms. The largest rod-shaped ZIF-7 particles showed a delayed thermal structural transition toward the stable zinc oxide phase. The CO₂ adsorption behaviors of the three ZIF-7s, despite their identical crystal structures, suggested minute differences in the pore structures; in particular, the smaller spherical ZIF-7 particles provided reversible CO₂ adsorption isotherms at ∼30–75 °C, a typical temperature range of flue gases from coal-fired power plants, in contrast to the larger rhombic-dodecahedral and rod-shaped ZIF-7 particles, which exhibited hysteretic CO₂ adsorption/desorption behavior

Healing of Microdefects in SSZ-13 Membranes via Filling with Dye Molecules and Its Effect on Dry and Wet CO₂ Separations

It is quite challenging to avoid microdefect formation during hydrothermal growths and/or calcination processes, while manufacturing high-quality zeolite membranes in a reproducible manner. Even less than 1% of defects, which generally provide nonselective pathways, will considerably worsen the intrinsic, high molecular sieving-based separation performance of a continuous zeolite membrane. Herein, we propose a simple and reliable method for blocking defects using water-soluble dye molecules, which were originally used for the visualization of nonzeolitic, defective structures in a zeolite membrane. Because the dye molecules are ∼1 nm in size, they cannot diffuse into the zeolitic pores and selectively access the defects. For the demonstration of dye-based defect healing, we chose a siliceous chabazite type SSZ-13 zeolite membrane (pore size = 0.37 × 0.42 nm²) with some degree of defects and investigated the effect of defect healing on the final CO₂ separation performance. Because the defects were gradually filled by the dye molecules, both CO₂/N₂ and CO₂/CH₄ separation performances were concomitantly increased. Intriguingly, the CO₂ perm-selectivity test with ternary mixtures including H₂O vapor (the third largest component in the flue and natural/shale/bio gas streams) in the feed diminished CO₂ separation performance. This could be ascribed to inhibited transport of the fast permeating species, here CO₂, from the adsorbed H₂O molecules on the dye-treated and water-friendly (relatively hydrophilic) membrane surface. On the contrary, the intact, siliceous (water-repelling or hydrophobic) SSZ-13 membranes showed improved CO₂ perm-selectivities in the presence of H₂O vapor, seemingly due to defect blocking by the physisorbed H₂O molecules

Thermosensitive Structural Changes and Adsorption Properties of Zeolitic Imidazolate Framework‑8 (ZIF-8)

We compared four types of ZIF-8 with varying sizes and shapes to determine their thermal-structural stability and derive appropriate thermal activation conditions and correlation between structural characteristics and adsorption properties. Under air, the ZIF-8 phase for all the samples was converted completely into the zinc oxide phase above ∼300 °C, though thermalgravimetric analysis (TGA) indicated that the original structure was stable to ∼300–350 °C. Longer exposures (∼30 d) suggested that thermal activation at ∼200 °C was appropriate for the removal of guest and/or solvent molecules under air without structural damage. Despite no noticeable change in X-ray diffraction (XRD) patterns after activation at 250 °C under air, the resulting BET surface areas and CO₂ adsorption amounts (at 1 bar and 30 °C) of ZIF-8s were reduced to ∼44–54 and ∼72–87%, respectively, as compared to those of appropriately activated ZIF-8s. It appears that after the activation at 250 °C under air, some Zn and N atoms were dissociated and converted to ZnOH and NOH, respectively, causing the partial structural damage of ZIF-8s

Multiplexed Detection of Epigenetic Markers Using Quantum Dot (QD)-Encoded Hydrogel Microparticles

Epigenetic alterations in gene expression are influenced by experiences and environment, resulting in significant variation of epigenetic markers from individual to individual. Therefore, it is imperative to measure various epigenetic markers simultaneously from samples of individual subjects to accurately analyze the epigenetic markers in biological samples. Moreover, the individualized genome-wide analysis has become a critical technology for recent trends in clinical applications such as early diagnosis and personalized medicine screening of numerous diseases. The array-based detection of modified histones, conventionally used for multiplexed analysis of epigenetic changes, requires pooling of samples from many subjects to analyze population-wise differences in the expression of histone markers and does not permit individualized analysis. Here, we report multiplexed detection of genome-wide changes in various histone modifications at a single-residue resolution using quantum dot (QD)-encoded polyethylene glycol diacrylate (PEGDA) hydrogel microparticles. To demonstrate the potential of our methodology, we present the simultaneous detection of (1) acetylation of lysine 9 of histone 3 (Ac–H3K9), (2) dimethylation of H3K9 (2Me-H3K9), and (3) trimethylation of H3K9 (3Me-H3K9) from three distinct regions in the brain [nucleus accumbens (NAc), dorsal striatum (DSt), and cerebellum (Cbl)] of cocaine-exposed mice. Our hydrogel-based epigenetic assay enabled relative quantification of the three histone variants from only 10 μL of each brain lysate (protein content = ∼ 1 μg/μL) per mouse. We verified that the exposure to cocaine induced a significant increase of acetylation while a notable decrease in methylation in NAc