Graphite (Gr) and carbon nanomaterials such as graphene oxide (GO) and reduced graphene oxide (RGO) and those decorated with Pd nanoparticles were investigated by photoelectron spectroscopy (XPS) aided with Quantitative Analysis of Surfaces by Electron Spectroscopy (QUASES) and reflected electron energy loss spectroscopy (REELS). Oxidation of Gr decreased the C/O ratio from 10 (Gr) to 2.2 (GO), whereas reduction of GO by N2H4 increased this ratio to 6.6 (RGO) due to decreasing number of oxygen groups (hydroxyl, epoxy, carbonyl and hydroxyl). Graphene materials and those after Pd decoration had 6-11 average number of layers in stacked nanostructures. Pd decoration using NaBH4-reducing agents formed nanoparticles of size 6.9 nm (Pd/Gr) > 5.3 nm (Pd/RGO) > 4.25 nm (Pd/GO), with PdOx overlayer thickness of 2.20 nm (Pd/GO) > 1.42 nm (Pd/Gr)> 1.20 nm (Pd/RGO), decreased number of oxygen groups and average number of layers. Smaller Pd nanoparticles of larger PdOx overlayer thickness were observed on highly hydrophilic substrates (functional oxygen groups content). Decoration accompanied by reduction using NaBH4 led to the removal of water attached by hydrogen bonding to graphene interplanes and the formation of PdOx overlayer from oxygen functional groups. Nanoparticle size obtained from QUASES was confirmed by Pd (3)d(5/2) spectra binding energy and full-width at half maximum. Various chemistry and mechanisms of graphene reduction using N2H4 and NaBH4 were observed, where NaBH4 was more efficient to remove water bonded by hydrogen bonding to oxygen groups and thus further graphene exfoliation. A substantial influence of substrate, functional group content on nanoparticle coverage, size and Pd oxide overlayer thickness was observed. (C) 2017 Elsevier B.V. All rights reserved.