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

Carlos Cuadrado-Collados, Javier Fernández-Català, François Fauth, Yongqiang Q. Cheng, Luke L. Daemen, Anibal J. Ramirez-Cuesta, Joaquín Silvestre-Albero

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Abstract

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. 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.

Original languageEnglish
Pages (from-to)20938-20946
Number of pages9
JournalJournal of Materials Chemistry A
Volume5
Issue number39
DOIs
StatePublished - 2017

Funding

J. S. A. and C. C. C. acknowledge nancial support from the University of Alicante (ACIE16-04) to cover all the expenses for the INS measurements at ORNL. J. S. A. gratefully acknowledges nancial support from MINECO (MAT2016-80285-p), European Union H2020 (MSCA-RISE-2016/NanoMed Project) and Generalitat Valenciana (PROMETEOII/2014/004), Spanish ALBA synchrotron for beam time availability (Project ID: 2016021724) and Oak Ridge beam time availability (Project ID: IPTS-16291.1). The research at the VISION beamline at ORNL's Spallation Neutron Source was supported by the Scientic User Facilities Division, Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE), under Contract No. DE-AC0500OR22725 with UT Battelle, LLC. The computing resources were made available through the VirtuES and the ICE-MAN projects, funded by the Laboratory Directed Research and Development program at ORNL.

FundersFunder number
European Union H2020MSCA-RISE-2016
Office of Basic Energy Sciences
Scientic User Facilities Division
U.S. Department of EnergyDE-AC0500OR22725
Oak Ridge National Laboratory
Laboratory Directed Research and Development
British Ecological Society
Ministerio de Economía y Competitividad
Generalitat ValencianaIPTS-16291.1, PROMETEOII/2014/004, 2016021724

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