| Abstract
| - Attenuated total reflection Fourier transform infrared spectroscopy was used to correlate the band shiftof the ν2 vibrational band of carbon dioxide with the density of the fluid. Upon adsorption of CO2 onmesoporous silica and a nonporous SiO2 film, additional bands were detected due to interactions of CO2with SiO2. Near the saturation pressure for the porous samples, the absorbance of the ν2 band increasedstrongly, which was concluded to be caused by liquidlike CO2 inside the pores. Integration of single-beam-sample-reference spectra between bulk CO2 and CO2 adsorbing on the mesoporous silica coated onone part of the internal reflection element revealed excess adsorption type isotherms with sharp maximaat 21 °C. A flatter curve shape could be observed at 25 °C, which allowed estimating the pore criticaltemperature. Moreover, the density of the fluid inside and outside the pores could be compared. Over theinvestigated ranges of pressure, temperature, and pore size, the results evidenced that the CO2 densitywas always higher in the silica pores than in the bulk, even under supercritical conditions. This hasimportant consequences on the pressure dependence of dissolution power and diffusivity of fluids inmesoporous solids. An overview is given on the influences of fluid phase behavior in the bulk and in thepores at various conditions on solubility and diffusivity.
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