Differences between the isostructural IRMOF-1 and MOCP-L porous adsorbents

Abstract

Several discrepancies have emerged about the preparation methods of MOF-5 material, one of the adsorbents more studied for hydrogen storage, because different synthesis procedures give rise to apparently isostructural materials but actually having very different textural properties and also showing different hydrogen adsorption capacities. In this work, MOF-5 material has been successfully synthesized according to the two most extended methods, and the respective resulting materials, IRMOF-1 and MOCP-L, have been widely characterized. Powder X-ray diffraction confirmed that MOF-5 is the main crystallized phase obtained in both cases, and that the MOCP-L product contains some ZnO impurities, mainly in the form of segregated crystals that appear preferentially outside the micropores. The presence of ZnO in the MOCP-L material has been also confirmed by other characterization techniques. On the other hand, interpenetrated networks in the MOCP-L material are not significant, appearing in any case at a similar extent than in IRMOF-1; consequently it cannot be considered for explaining the differences observed in the adsorption capacity of both materials. These differences cannot be completely explained simply by the segregated ZnO impurities, so the presence of some ZnO nanocrystals partially blocking the micropores of MOCP-L must be admitted.