Heterojunction of SrTiO3/TiO2 nanotubes with dominant (001) facets: Synthesis, formation mechanism and photoelectrochemical properties

Abstract Controllable growth of anatase TiO 2 with dominant high reactive crystal facets has attracted intense interest in the past few years due to their unique structure-dependent properties. In this work, SrTiO 3 /TiO 2 heterostructure nanotubes (SrT) arrays films with high reactive dominant (001) facets of anatase TiO 2 were successfully prepared through the part conversion of TiO 2 by a hydrothermal method. Various characterizations were used to investigate the morphologies, crystal phases and chemical compositions of the prepared samples. Structure analyses using X-ray diffraction and a high-resolution transmission electron microscope revealed that, the treatment sequence of hydrothermal reaction and annealing was a crucial influence factor on controlling the growth of preferred orientation of (001) facets of TiO 2 in SrTiO 3 /TiO 2 heterojunction, whereas the inverse treatment sequence yielded randomly oriented facets. The formation mechanism of dominant (001) facets of TiO 2 in the heterojunction was related to crystal structures of TiO 2 and SrTiO 3 . The heteroepitaxial growth on (001) plane of SrTiO 3 led to dominant (001) facets of anatase TiO 2 attributing to their excellent surface lattices match. The photoelectric performances of pure TiO 2 nanotubes and SrT were investigated by photoluminescence, UV–visible diffuse reflectance, photocurrent and current–voltage response. The semiconductor characteristics of them were studied by electrochemical impedance spectroscopy and Mott–Schottky analysis in detail. The results demonstrated that the heterostructure of SrT not only increased light absorption, but also effectively shifted the Fermi level and promoted charge transfer. Among all the samples, the SrTiO 3 /TiO 2 heterojunction prepared by 1 h hydrothermal treatment (1SrT) exhibited the best photoelectrochemical performances due to the synergetic contributions of the high active (001) facets of anatase TiO 2 and the charge transport properties of the heterostructure.