One-dimensional metal-organic framework photonic crystals used as platforms for vapor sorption.

We present the fabrication of one-dimensional photonic crystals (Bragg stacks) based on a microporous metal–organic framework material and mesoporous titanium dioxide. The Bragg stack heterostructures were obtained using two complementary synthesis approaches utilizing the bottom-up assembly of heterogeneous, i.e. two-component photonic crystal multilayer structures. Zeolitic imidazolate framework ZIF-8 and mesoporous titanium dioxide were chosen as functional components with different refractive indices. While ZIF-8 is intended to impart molecular selectivity, mesoporous TiO2 is used to ensure high refractive index contrast and to guarantee molecular diffusion within the Bragg stack. The combination of micro- and mesoporosity within one scaffold endows the 1D-MOF PC with characteristic adsorption properties upon exposure to various organic vapors. In this context, the sorption behavior of the photonic material was studied as a function of partial pressure of organic vapors. The results show that the multilayered photonic heterostructures are sensitive and selective towards a series of chemically similar solvent vapors. It is thus anticipated that the concept of multilayer heterogeneous photonic structures will provide a versatile platform for future selective, label-free optical sensors

Adsorption and Diffusion Phenomena in Crystal Size Engineered ZIF‑8 MOF

ZIF-8 is a flexible zeolitic imidazole-based metal−organic framework whose narrow pore apertures swing open by reorientation of imidazolate linkers and expand when probed with guest molecules. This work reports on the crystal size dependency of both structural transitions induced by N2 and Ar adsorption and dynamic adsorption behavior of n-butanol using well-engineered ZIF-8 crystals with identical surface area and micropore volume. It is found that the crystal downsizing of ZIF-8 regulates the structural flexibility in equilibrium adsorption and desorption of N2 and Ar. Adsorption kinetics of n-butanol in ZIF-8 are strongly affected by the crystal size, however, not according to a classical intracrystalline diffusion mechanism. Our results suggest that structural transitions and transport properties are dominated by crystal surface effects. Crystal downsizing increases the importance of such surface barriers

Intensified biobutanol recovery using zeolites with complementary selectivity

[EN] A vapor phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanolethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape selective all-silica zeolites CHA and LTA were prepared and evaluated via single component isotherms and breakthrough experiments. These zeolites show an opposite selectivity; adsorption of ethanol was favorable on all-silica CHA, while the LTA topology had clear preference for butanol. The molecular sieving properties of both zeolites allowed to easily eliminate acetone from the mixture. The molecular interaction mechanisms were studied by density functional theory (DFT) simulations. Effect of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior was investigated. Desorption profiles were studied to maximize butanol purity and recovery. The combination of LTA with CHA type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows to obtain butanol in unpreceded purity and recovery. A butanol purity of 99.7 mole% could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.S.V.D.P. and J.F.M.D. are grateful to FWO Vlaanderen for financial support (G025614N). M.P., L.Y.S., S.V. and F.R. gratefully acknowledge financial support of Spanish Government (MAT2015-71842P and Severo Ochoa SEV-2012-0267). The authors thank to A. Vidal and T. Blasco for performing NMR measurements and discussion.Van Der Perre, S.; Gelin, P.; Claessens, B.; Martin-Calvo, A.; Saint Remi, JC.; Duerinck, T.; Baron, GV.... (2017). Intensified biobutanol recovery using zeolites with complementary selectivity. ChemSusChem. 10(14):2968-2977. https://doi.org/10.1002/cssc.201700667S29682977101

Nonuniform Chain-Length-Dependent Diffusion of Short 1‑Alcohols in SAPO-34 in Liquid Phase

Liquid-phase diffusion of 1-alcohols in SAPO-34 was explored by batch experimentation. The uptake of pure and binary mixtures of 1-alcohols, dissolved in <i>tert</i>-butanol, was obtained for C1–C8 1-alcohols at temperatures between 25 and 80 °C, concentrations varying between 0.5 and 10 wt %, and crystal sizes between 7.5 and 20 μm. The experimental uptake data were fitted with an intracrystalline diffusion model and a linear driving force model. The intracrystalline diffusion coefficient showed a nonuniform stepwise decrease with chain length, ranging from 10^–12 m²/s for methanol to 10^–20 m²/s for 1-pentanol. No effect of the external concentration on the intracrystalline diffusion coefficient was observed. Variation of the crystal size showed that the intracrystalline diffusion is the rate-limiting step. On the basis of the Arrhenius equation, the activation energies of diffusion of ethanol, 1-propanol, and 1-butanol were determined, being, respectively, 27.8, 47.8, and 47.2 kJ/mol. Co-diffusion occurred in the uptake of binary mixtures of methanol/ethanol, methanol/1-propanol, and ethanol/1-propanol, where mutual effects could be noticed. From this experimental work, it could be concluded that the small dimensions of the SAPO-34 framework generate a very sterically hindered diffusion of 1-alcohols into the crystals, resulting in a chain-length-dependent behavior, interesting to obtain efficient kinetic-based separations

3D-printed SAPO-34 monoliths for gas separation

ISSN:1387-1811ISSN:1873-309