Alternative approaches to fabrication of gold-modified TiO2 nanotubes

Three approaches, impregnation–reduction, deposition and direct assembly, are used to fabricate gold-modified TiO2 nanotubes. Prepared materials are characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV–visible absorption spectroscopy and BET, etc. The gold-modified TiO2 nanotubes prepared via various procedures exhibit distinct difference in structure. By impregnation–reduction approach, gold-modified TiO2 nanotubes with large gold particles are fabricated. The gold particles are either deposited on or encapsulated in TiO2 nanotubes. However, by using gold hydrophilic colloidal dispersion as gold precursor, gold particles in the modified TiO2 nanotubes are very small. Gold particles only adhere to the outer surface of TiO2 nanotubes after deposition process, whereas adhere to not only the outer but also the inner walls of TiO2 nanotubes after direct assembly process. A possible mechanism is proposed to illustrate the formation of gold-modified nanotubes that are prepared by direct assembly process.