Valence band structure of cellulose and lignin studied by XPS and DFT

In this report, X-ray induced photoelectron spectroscopy (XPS) measurements of the valence band structure of cellulose and lignin are combined with a theoretical reconstruction of the spectra based on density functional theory (DFT) calculations. These calculations involve an analysis of the valence band structures and their respective orbitals in which basic units of cellulose and lignin are considered. In addition, photoionization cross sections are incorporated for reconstruction of the XPS spectra. This combination of theoretical calculations and experimental measurements revealed that an emission present up to 10 eV in the valence band structure is dominated by oxygen rather than by carbon, as reported in literature. Furthermore, a quantitative elemental analysis shows significant carbon contributions at binding energies above 13 eV. The valence band analysis supported by DFT provides a powerful basis for a detailed interpretation of spectroscopic data and enables a profound insight into application relevant processes in future.