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This work constitutes a guide towards the preparation of metal-organic framework materials (MOF) supported and/or confined in activated carbon monoliths (ACM). The resulting hybrid porous materials exhibit improved physico-chemical properties as compared with their parent constituents. The different hybrids were obtained exploring several experimental approaches, which were thoroughly discussed. All hybrids were characterized by N2 adsorption isotherms, SEM, TGA and XRD techniques. The characterization studies pointed out that the preparation conditions are of paramount importance in defining the nucleation and growth of HKUST-1, either outside of the carbon grains (surface coating), and/or in the internal pores (bulk confinement). While the surface coating was achieved by directly synthesizing the MOF in presence of the ACM (i.e. in-situ synthesis), bulk confinement is favored after applying an additional step that involves a pre-nucleation at low temperatures (5 °C). The hybrid material with the best performance, sample A5(1), shows enhanced mechanical properties compared to its parent counterparts, combined with high apparent surface area (up to 1300 m2/g), an improved crushing strength (about 8 times superior to ACM) and a geometrical density of around 0.45 cm3/g, which almost duplicates that of ACM. Last but not least, the adsorption behavior of the hybrid was tested for CO2 and CH4 adsorption. Application of IAST equation to the single component adsorption isotherms at room temperature gives rise to a CO2/CH4 selectivity factor of 5.5 in the hybrid material, larger than that on ACM (S = 3.5). ; This work was supported by MINECO projects: MAT2013-45008-p. MEC wants to thank the Spanish Government for the fellowship FPU AP2010-4920.

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. ; J. S. A. and C. C. C. acknowledge financial support from the University of Alicante (ACIE16-04) to cover all the expenses for the INS measurements at ORNL. J. S. A. gratefully acknowledges financial 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).