Fig. 9 shows XPS spectra of various graphene and graphene/TiO2 composite materials. After deconvolution, 5 different peaks can be designated. These are those representing the sp2 of C=C/C-C (of the basal plane) at 284.97 eV, C-OH (of the hydroxyl group) at 285.88 eV, C-O-C (of the epoxide group) at 286.86 eV, >C=O (of the carbonyl group) at 287.84 eV, and C(O)OH (of the carboxyl group) at 288.94 eV. From the above results, it can be seen that intensity of the peaks representing the carbonyl and the epoxide groups decreased after thermal reduction. Intensity of the peaks representing carbon-carbon bonds in the annealed GO (Fig. 9b) is also greater than those of the annealed rGO (Fig. 9d). This suggests that electrical properties of former should be better than that of the latter. The above results also implies that the thermal reduction method is more effective than the chemical reduction approach, taking into account the relative intensity of the C-C peaks from the two systems. For the composite materials, it is also of noteworthy that an intensity of the peaks relating to the carboxylic group of Ti@rGO-01 (Fig. 9e) increased after annealing. This suggests that TiO2 might induce the oxidation of rGO phase in the composite during the heat treatment