Understanding the breathing phenomena in nano-ZIF-7 upon gas adsorption

Journal Article · Mon Sep 11 00:00:00 EDT 2017 · Journal of Materials Chemistry. A

DOI:https://doi.org/10.1039/C7TA05922A· OSTI ID:1422567

Cuadrado-Collados, Carlos ^[1]; Fernández-Català, Javier ^[1]; Fauth, François  ^[2]; Cheng, Yongqiang Q.  ^[3]; Daemen, Luke L. ^[3]; Ramirez-Cuesta, Anibal J.  ^[3]; Silvestre-Albero, Joaquín  ^[1]

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1. Universidad de Alicante (Spain). Laboratorio de Materiales Avanzados, Departamento de Quimica Inorganica, Instituto Universitario de Materiales
2. CELLS-ALBA Synchrotron, Barcelona (Spain)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division

For this research, synchrotron X-ray diffraction and inelastic neutron scattering measurements have been applied to evaluate the breathing phenomena in small nanocrystals of ZIF-7 upon gas adsorption. The experimental results show that an extended solvent exchange process with methanol is crucial to get a solvent-free narrow pore structure. Under these conditions, nano-ZIF-7 is indeed able to adsorb N₂ with a total BET surface area of around 380 m² g^-1, in close agreement with theoretical predictions. The breathing phenomenon upon nitrogen adsorption is accompanied by a phase-to-phase transition, from a narrow-pore (phase II) to a large-pore (phase I) structure and a suppression of the cooperative deformation of the framework involving mainly the flapping motion of the benzimidazolate (bIm) ligand with the 4- and 6-membered rings. Whereas nitrogen requires temperature and pressure conditions close to condensation (close to 1 bar and 77 K) to induce the breathing in ZIF-7, CO₂ can do it under milder conditions (at room temperature and low relative pressures). These results reflect that the nature of the adsorptive probe and the gas–framework interactions, rather than the molecular diameter and/or shape, play a crucial role in defining the pressure and temperature conditions required to induce the breathing. Lastly, the presence of two different cavities in ZIF-7 as suggested by theoretical predictions, one with a window diameter of below 0.4 nm (cavity A) and the other with a pore size of around 0.6 nm (cavity B), has been confirmed experimentally using immersion calorimetry.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1422567
• Journal Information: Journal of Materials Chemistry. A, Vol. 5, Issue 39; ISSN 2050-7488
• Publisher: Royal Society of Chemistry
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY