2017-Sustainable Industrial Processing Summit
SIPS 2017 Volume 5. Marquis Intl. Symp. / New and Advanced Materials and Technologies
| Editors: | Kongoli F, Marquis F, Chikhradze N |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2017 |
| Pages: | 590 pages |
| ISBN: | 978-1-987820-69-0 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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FTIR Spectroscopy of Strongly Absorbing Molecules Adsorbed on Highly Scattering Disperse Materials
Alexey Tsyganenko1; Roman Novikov2; Oleg Pestsov3;1ST.PETERSBURG STATE UNIVERSITY, St. Petersburg, Russian Federation; 2ST.PETERSBURG STATE UNIVERSITY, St.Petersbur, Russian Federation; 3ST.PETERSBURG STATE UNIVERSITY, St.Petersburg, Russian Federation;
Type of Paper: Regular
Id Paper: 379
Topic: 43
Abstract:
Most disperse solids are highly scattering objects. Here we analyze the difficulties in spectral studies of such materials, and suggest ways on how to work with them.
To see the spectra of adsorbed species, the background spectrum of the sample before adsorption has to be subtracted. However, for very intense bands of gases adsorbed on strongly scattering media, the scattering coefficient changes near the absorption bands, following the variations of refraction index. The problem is illustrated by the spectrum of CO2 adsorbed on a thin layer of NaX zeolite. In order to reduce the effect of scattering it is possible to register the spectrum of "diffuse transmittance" when only the light deviated due to scattering reaches the detector. Combining the usual spectrum with such one, it is possible to reconstruct the pure absorption spectrum.
Another way to lower the effect of scattering is to immerse the sample in a liquid, such as liquid oxygen. Spectrum of NaX with adsorbed CO2 submerged in O2 displays a complex structure of the band, more visible after subtraction of the initial spectrum. The structure is not seen at lower coverages, nor in the region of admixed 13CO2 molecules. From this we have concluded that it is not the presence of different sites, but the resonance dipole-dipole interaction between the adsorbed molecules. This effect was shown to determine the band shape of adsorbed SF6, so that the spectra of interacting molecules provide information about the geometry of adsorbed layer. Due to low frequencies the effect of scattering here is negligible, but weak distortions of band contours can be caused by the reflection that also depends on the refraction index.
The presented results show that FTIR spectroscopy still remains a promising method for the studies of surface properties of dispersed solid materials.