Adsorption of CO2 on CoII3[CoIII(CN)6]2 using DRIFTS

Adsorption of CO2 on dehydrated Prussian blue analogue CoII3[CoIII(CN)6]2 was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). An infrared peak at 2340 cm−1 assigned to adsorbed CO2 was identified and used semi-quantitatively to construct an isotherm at 298 K that followed the Langmuir–Freundlich equation in the low-coverage Henry's law limit with CO2 pressure below about 25 kPa. Temperature-dependence at 6.8 kPa CO2 was used to determine ΔHad = −23 ± 3 kJ mol−1, in this limit as well. Deviation from the Langmuir–Freundlich model was significant at temperatures above 298 K and attributed primarily to a loss of reliability of the DRIFT spectra at higher CO2 pressures, particularly at higher temperatures, and the accompanying uncertainties in the difference spectra when correcting for the presence of gaseous CO2. Based on this work, the application of DRIFTS to study CO2 adsorption on Prussian blue analogues and other adsorbents is promising, although the range of conditions over which it can be applied appears to be more limited than with other techniques.