The composition-and chemical changes induced in the films by the photocatalytic reduction were further characterized via XPS analysis. Figure ) shows XPS spectra of the C 1s core levels of GO/TNP thin films (one LbL-SC cycle) before (0 h) and after 0.5 h and 4 h DUV exposure. The peak centered around 284.5 eV corresponds to sp 2 -hybridized C=C-bonds. Peaks corresponding to oxidized carbon species are located at higher binding energies, and are usually assigned to C-O bonds in hydroxy/epoxy groups, C=O bonds, as well as C-C bonds. With increasing DUV exposure time, the intensity of the peaks corre-sponding to oxidized carbon groups significantly decreases, while the peak of the C=C bonds increases, confirming the formation of rGO and the removal of oxygen-containing functional groups. Bell et al. reported the selective removal of epoxy-and hydroxy groups in photocatalytically reduced GO. Figure ) shows the O 1s core level spectra of the same films. The peaks at 532-533 eV can be assigned to O-C/O=C bonds present in functional groups in GO, while peaks at lower energies are assigned to the metal oxide Ti-O bonds and hydroxyls.