Template-directed fabrication of MIL-101(Cr)/mesoporous silica composite: Layer-packed structure and enhanced performance for CO 2 capture.

A novel hybrid material constituted of MIL-101(Cr) and mesoporous silica was successfully assembled through an in-situ hydrothermal method. The MCM-41 with well-ordered mesopores acted as the structure-directing agent, which regulated the growth of MIL-101(Cr) crystals along a certain direction and restricted the expansion of framework. Meanwhile, the hydroxyl groups existed in MCM-41 preferentially coordinated with the Cr3+ centers in MOF, followed by the layer-packed arrangement of MIL-101(Cr) nanocrystals on the surface of matrix. The structural characterizations further revealed that the introduction of MCM-41 could increase the micropore volume and specific surface area. The MIL-101(Cr)@MCM-41 exhibited higher CO2 uptake capacity and adsorption rate compared with the original MIL-101(Cr) at 298 K and 1 bar. Via ideal adsorbed solution theory (IAST), it could be further predicted that the composite was more inclined to adsorb CO2 than N2 . The calculated isosteric heats of CO2 adsorption and desorption activation energy demonstrated that the interaction between CO2 molecules and the composite was also enhanced. The as-prepared MIL-101(Cr)@MCM-41 showed good reusability and could be easily regenerated without any reduction in its CO2 adsorption capacity. Hence, this study opened up a new pathway for designing hierarchical porous structured MOF-based materials with advanced gas separation performance.