Synthesis of TiO2@C core-shell nanostructures with various crystal structures by hydrothermal and postheat treatments

TiO2@C core-shell nanostructures with various crystal structures of TiO2-B, anatase, and rutile were successfully synthesized by a simple hydrothermal process and postheat treatments. As-synthesized precursor hydrogen titanate@carbonaceous nanoribbons transformed into TiO2-B@C nanoribbons at 400 degrees C and further transformed into anatase and rutile TiO2@C nanoribbons at 700 and 800 degrees C, respectively. The morphology of nanoribbons can be retained up to 800 degrees C. The transformation temperature (800 degrees C) from anatase to rutile phase is lower than that of TiO2 nanofibers without carbon layers and anatase TiO2@C nanoparticles. These results show that the carbon shell plays important roles in promoting the phase transition from anatase to rutile phase and protecting the nanoribbon-like morphology. The formation mechanism of the TiO2@C core-shell nanostructures with various crystal structures was discussed.