Surface hydroxyl groups spectroscopic measurements

TPRS experiments for this reaction step. The two hydrogens released in the methanol adsorption and the surface methoxy decomposition steps are eventually converted to water. Spectroscopic details about the formation of water are presently not available, but the formation of water most likely proceeds via the condensation of two surface hydroxyl groups. The reduced surface vanadia site is readily reoxidized back to vanadium (+5) by gas phase oxygen as shown by in situ Raman measurements.42... 

It is to be noted that the adsorption isotherm on the freely vibrating group is of the simple Langmuir type and that there is excellent agreement between the volumetric and spectroscopic data showing that the volumetric adsorption isotherm which is commonly measured is indeed the summation of the adsorption on the hydroxyl group plus the adsorption on the remainder of the surface (19). 

Among spectroscopic methods, X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA), has been used for the analysis of enzyme-treated PET substrates [11, 27, 31, 102]. With XPS, the elemental composition of the top 10 nm of the PET surface is measured, and the presence of specific functional groups can be identified. XPS analysis of PET treated with a lipase from Thermomyces lanuginosus and a cutinase from Ther-mobifida fusca indicated increased amounts of hydroxyl and free acid groups, while the amount of carbon-carbon bonds decreased [11, 27], XPS has been shown to be very sensitive to contamination by residual enzyme protein strongly adsorbed to the polymer surface [31, 102]. 

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