Understanding the breathing phenomena in nano-ZIF-7 upon gas adsorptionElectronic supplementary information (ESI) available: Characterization of the different MOFs synthesized (FTIR, XRD and SEM), and synchrotron and conventional X-ray powder diffraction measurements of samples ZIF-7-M4-130 and ZIF-7-M4-60 upon gas adsorption. See DOI: 10.1039/c7ta05922a

• Main Authors: Cuadrado-Collados, Carlos, Fernández-Català, Javier, Fauth, François, Cheng, Yongqiang Q, Daemen, Luke L, Ramirez-Cuesta, Anibal J, Silvestre-Albero, Joaquín
• Format: Journal Article
• Language: English
• Published: 10.10.2017
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c7ta05922a

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 N 2 with a total BET surface area of around 380 m 2 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, CO 2 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. 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.