Low-temperature synthesis of heterogeneous crystalline TiO ₂-halloysite nanotubes and their visible light photocatalytic activity

One-dimensional heterogeneous crystalline TiO₂-halloysite nanotubes with high visible-light photocatalytic activity have been successfully obtained by employing the low-temperature synthesis of crystalline TiO ₂ on halloysite nanotubes. The halloysite nanotubes can adsorb the TiO₂ precursor and induce the growth of TiO₂ nanocrystals on the support in situ. By simply adjusting the acidity of the TiO₂ sol, crystalline TiO₂ composite halloysite nanotubes with tunable crystalline phases of anatase or anatase/rutile mixed phases were achieved. The traditional thermal treatment for crystallite transformation was not required, thus an intact halloysite structure could be guaranteed. The as-obtained products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption, UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalysis test results revealed that the obtained heterogeneous TiO₂-halloysite showed enhanced visible-light photocatalytic activity for the degradation of rhodamine B and gentian violet compared with the pure halloysite nanotubes and Degussa-P25 owing to the heterogeneous TiO ₂ structure.