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


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. 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 around 380 m2/g, in close agreement with theoretical predictions. The breathing phenomenon upon nitrogen adsorption is accompanied by a phase-to-phase transition, from 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 77K) to induce the breathing in ZIF-7, CO2 can do it under milder conditions (room temperature and at extremely low relative pressures). These results reflect that the nature of the probe adsorptive rather than the molecular diameter and/or shape, and the gas-framework interactions play a crucial role defining the pressure and temperature conditions to induce the breathing. The presence of two different cavities in ZIF-7 as suggested by theoretical predictions, one with a window diameter below 0.4 nm (cavity A) and a second one with a pore size around 0.6 nm (cavity B), have been confirmed experimentally using immersion calorimetry.

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Publication details

The article was received on 07 Jul 2017, accepted on 11 Sep 2017 and first published on 11 Sep 2017

Article type: Paper
DOI: 10.1039/C7TA05922A
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    Understanding the breathing phenomena in nano-ZIF-7 upon gas adsorption

    C. Cuadrado Collados, J. Fernandez-Catalá, F. Fauth, Y. Cheng, L. L. Daemen, A. J. Ramirez-Cuesta and J. Silvestre-Albero, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA05922A

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