HKUST-1@ACM hybrids for adsorption applications: A systematic study of the synthesis conditions

Abstract

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).