Methodology for the identification of carbonyl absorption maxima of carbon surface oxides in DRIFT spectra

Carbon surface oxides have been demonstrated to be crucial for high performing carbon materials in various applications. Diffuse reflectance infrared Fourier transform spectroscopy represents a powerful time-resolved method to study the surfaces of functional materials under process conditions. Due to the severe overlap of the contributions of individual surface groups in combination with compared to organic molecules shifted absorption maxima meaningful analysis remains challenging. Especially due to the unknown maxima, deconvolution of the superimposed bands is strongly hindered. In this study, we developed a procedure based on hydrolysis, thermal annealing or a combination thereof, which allows to disentangle carbonyl absorption maxima of carboxylic acids, anhydrides and lactones on carbon surfaces. In order to verify the proposed transformations, thorough characterization by temperature programmed desorption, X-ray photoelectron spectroscopy, potentiometric titration and Boehm titration was carried out. Applying this procedure for a polymer derived reference material, the carbonyl absorption maximum could be deduced, which are positioned for lactones at 1771 cm⁻¹, for carboxylic acids between 1753 cm⁻¹ and 1760 cm⁻¹, and for carboxylic anhydrides at 1792 cm⁻¹ and 1852 cm⁻¹. This allowed deconvolution of the carbonyl band, paving the way for in situ time-resolved analyses.