The relatively weak peak at 288.3 eV
was contributed by carboxyl carbon (O–CO), indicating the
esterification reaction ofOH on TiO2 withCOOH on the
graphene oxide surface and the formation of O–COTi bonds
(Xiang et al., 2011b). The peak located at 287.0 eV, which
corresponded to the oxygen-containing carbonaceous bands,
disappeared in the C 1s XPS spectra of GT. Therefore, graphene
oxide was effectively reduced to graphene during the hydro-thermal treatment. Moreover, the sp
2
carbon network was
retained in graphene, as indicated by the CCpeakat 284.2 eV
(Murugan et al., 2009).