Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in MOF-74 Thin Films

Thin films of Co-MOF-74 and Ni-MOF-74 were synthesized on Au-coated quartz crystal microbalance substrates by a vapor-assisted conversion (VAC) method that precludes the need for activation via postsynthetic solvent exchange. All thin films were structurally characterized by powder X-ray diffraction, reflection- absorption infrared spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images reveal that the NiMOF-74 films exists as a dense base layer with hemispherical protrusions on the surface. In contrast, the scanning electron microscopy images of the Co-MOF-74 thin films show a rough surface with spherical deposits. The thin film morphologies were different than the powders resulting from the bulk synthesis. Gravimetric vapor-phase adsorption measurements for xylene isomers and ethylbenzene within Co-MOF-74 and Ni-MOF-74 thin films were conducted, and the results were compared with those reported for the corresponding bulk powders. Despite different morphologies, the saturation capacities of Ni-MOF-74 and CoMOF-74 thin films were found to be nearly equivalent to those reported for the bulk powders. The results demonstrate that the VAC method can produce MOF-74 thin films that retain the intrinsic properties that are observed in bulk powders.

Automated summary

Thin films of Co-MOF-74 and Ni-MOF-74 were successfully synthesized using the VAC method on Au-coated quartz crystal microbalance substrates. The thin film morphologies were found to be different from the bulk synthesis powders. However, the saturation capacities of the thin films were nearly equivalent to those of the bulk powders, indicating that the VAC method can produce MOF-74 thin films with retained intrinsic properties observed in bulk powders.