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 language | English |
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Pages (from-to) | 20938-20946 |
Number of pages | 9 |
Journal | Journal of Materials Chemistry A |
Volume | 5 |
Issue number | 39 |
DOIs | |
State | Published - 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 Scientic 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.
Funders | Funder number |
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European Union H2020 | MSCA-RISE-2016 |
Office of Basic Energy Sciences | |
Scientic User Facilities Division | |
U.S. Department of Energy | DE-AC0500OR22725 |
Oak Ridge National Laboratory | |
Laboratory Directed Research and Development | |
British Ecological Society | |
Ministerio de Economía y Competitividad | |
Generalitat Valenciana | IPTS-16291.1, PROMETEOII/2014/004, 2016021724 |