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Mixed-phase TiO2photocatalysts with small particle size of anatase and rutile (~5 nm) have been successfully synthesized using hydrothermal method. The effects of curing temperature and curing time before the hydrothermal treatment on the crystalline phase, the phase composition, and the particle size of TiO2were investigated by the X-ray diffraction spectroscopy (XRD) and the transmission electron microscopy (TEM), respectively. It was found that the anatase and rutile phase contents in the TiO2particles were successfully controlled by simply adjusting the curing temperature and the curing time. More importantly, the particle size of both anatase and rutile is small in the mixed-phase TiO2particles. The photocatalytic activity of TiO2was evaluated by the degradation of Rhodamine B (RhB) in aqueous solution. The TiO2with phase junction formed by anatase and rutile exhibited higher separation rate between the photo-induced electrons and holes, which was confirmed by the surface photovoltage (SPV) spectra, and at the same time exhibited the higher photocatalytic degradation on RhB than pure anatase-phase TiO2. Moreover, it was found that TiO2with 83% of anatase and 17% of rutile showed a highest photocatalytic activity among the mixed-phase TiO2samples.