Si-doped and un-doped nanocrystalline TiO2 samples have been synthesized by simple one-pot water-organic two-phase separated hydrolysis-solvothermal (HST) processes, and characterized by XRD, BET, TEM, FT-IR, DRS and surface photovoltage techniques. The effects of the solvothermal temperature and Si doping on the anatase thermal stability, and on the photocatalytic activity for degrading rhodamine B were investigated in detail. The results show that, as the solvothermal temperature rises, the crystallinity and thermal stability of the resulting nano-sized anatase TiO2 gradually increase. Noticeably, the as prepared TiO2 obtained at appropriate solvothermal temperature (160 degrees C) exhibits high photocatalytic activity. Moreover, although Si doping does not improve the photocatalytic activity of the as-prepared anatase TiO2, it greatly enhances the anatase thermal stability and inhibits crystallite growth during the process of post-thermal treatment. Interestingly, the Si-doped TiO2 post-treated at high temperature displays much higher photocatalytic activity than commercial P25 TiO2. It is clearly demonstrated that the joint effects of high anatase crystallinity and large surface area lead to high photocatalytic activity. This work provides a simple and effective strategy for the synthesis of high-performance TiO2-based functional nanomaterials. (C) 2009 Published by Elsevier B.V.