The Interaction of Guest Molecules with Co-MOF-74: A Vis/NIR and Raman Approach

Co-MOF-74 rod like crystals with a length of several hundred micrometers are synthesized by a solvothermal procedure and their interaction with different gases is evaluated for selective gas sensing. We show strongly anisotropic absorption behavior of the Co-MOF-74 crystals when illuminated with polarized light. The interactions of guests (CO2, propane, propene, Ar, MeOH, H2O) with Co-MOF-74, is studied by various spectroscopic techniques. Vis/NIR shows peak shifts of Co-MOF-74 depending on the interaction with the guest. In the visible and the NIR the maximum absorbance is shifted selectively corresponding to the intensity of the Co-II-guest interaction. Even propene and propane could be distinguished at room temperature by their different interactions with Co-MOF-74. Raman spectroscopy was used to detect a modified vibrational behavior of Co-MOF-74 upon gas adsorption. We show that the adsorption of H2O leads to a characteristic shift of the peak maxima in the Raman spectra.