CO2 mediated fabrication of hierarchically porous metal-organic frameworks

Hierarchically porous metal-organic frameworks with micropores, mesopores, and macropores have been successfully fabricated by using compressed CO2. Not any acid or addition but compressed CO2 was added into the synthesis system for achieving hierarchically porous materials. TEM, SEM, N-2 adsorption, XRD, TG, FTIR, and EDX were employed to character structural and component of the obtained materials. The mesopores size of resultant MOFs prepared by this approach can be expanded as large as 28 nm, which is rather difficult to obtain by conventional syntheses method. In addition, the amount and proportion of micropores, mesopores, and macropores distributed in the obtained samples can be controlled by adjusting CO2 pressure. Furthermore, the resulting hierarchically porous MOFs (HP-MOFs) can be utilized to absorb selectively on CO2 and CH4, which demonstrate the enhanced adsorption behavior. The liquid phase adsorption performances of the as-prepared HP-MOFs samples are evaluated by using methylene blue as a model adsorbate. The possible mechanism of formation of HP-MOFs by using compressed CO2 was proposed according to results of the experiments. Compared with traditional synthetic methods, the compressed CO2 plays many roles in the synthesis of HP-MOFs. Notably, this versatile approach can be applied to prepare other hierarchically porous materials in the organic solvent-water miscible system.