Template-directed fabrication of MIL-101(Cr)/mesoporous silica composite: Layer-packed structure and enhanced performance for CO₂ 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.