In this work, the hydrothermal method was used for synthesizing Pt-TiO2/graphene nanocomposites. Obtained Pt-TiO2/graphene photocatalysts were characterized by Raman spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, photoluminescence spectroscopy, and UV-vis spectroscopy. The photocatalytic activity of the Pt-TiO2/graphene nanocomposite catalyst was assessed by examining the degradation of acid orange 7 (AO7) dye from aqueous solutions as a probe reaction under solar light irradiations. X-ray photoelectron spectroscopy analyses showed that the Pt ions substituted in the TiO2 lattice were present mainly in the Pt(II) state. Pt-TiO2/graphene exhibited higher photocatalytic activities than TiO2/graphene under visible light irradiation. The visible light activity of Pt-TiO2/graphene was strongly affected by the calcination temperature and the amounts of H2PtCl6, which were optimal at 500 degrees C and 10% H2PtCl6, respectively. The degradation efficiency of the Pt-TiO2/graphene nanocomposite was 99% after 6 h of visible light irradiation. The enhanced photodegradation activity might be mainly attributed to the role of Pt-TiO2 as a charge generating center and graphene played as electron acceptor and transporter in the nanocomposite, which effectively suppressed the charge recombination and promoted the charge transfer within the composite. (C) 2015 Elsevier B.V. All rights reserved.