Low-temperature synthesis of heterogeneous crystalline TiO2-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 TiO2 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 TiO2 structure.