Controllable Synthesis And Photocatalytic Properties Of Visible Light Response TiO₂ Hetero Structure

TiO₂ nanotube arrays（TiO₂ NTAS） because of its unique chemical and physical properties, such as highly ordered structure, good chemical stability, high specific surface area and excellent corrosion resistance, has become one of the extensively studied in the field of environmental energy photocatalytic materials. However, TiO₂ low utilization rate of visible light and high photogenerated electron hole recombination rate still limits its practical application. In order to improve the utilization of visible light, the surface modification of TiO₂ nanotube catalyst has become the focus of the study. In this study, the SrTiO₃ and TiO₂ composite nanotubes were synthesized by a simple hydrothermal method, which effectively improved the separation and transport rate of the photo induced electron-hole. Then through high temperature melting aluminum reduction means in SrTiO₃/TiO₂ composite nanotubes into Ti³⁺ doping, the success of the TiO₂ NTAs light response to expand the scope of the visible region, improves the utilization efficiency of sunlight. In addition, by changing the hydrothermal reaction conditions, prepared by the uniform morphology of the nanocubic SrTiO₃ and TiO₂ heterostructured nanotube arrays, formed by SrTiO₃ cube and TiO₂ heterojunction structure effectively improve and reduce the photoinduced electron-hole recombination rate, through the introduction of Ti³⁺ ions doped in further expanding the TiO₂ light absorption range, and improve the utilization efficiency of sunlight, the main contents of the paper are showed as following:（1） SrTiO₃/TiO₂ nano-composite materials, the TiO₂ NTAs reacted with Sr（OH）2in Na OH solution under hydrothermal treatment, in which TNTAs were utilized as both substrate and reactant for the subsequent top-graft of SrTiO₃ nanospheres. By controlling the hydrothermal reaction time successfully, the SrTiO₃/TiO₂ composite nanotubes with the best composition were obtained, and the hydrothermal reaction was 1.0 h. By comparing the photocurrent response and photocatalytic properties of pure TiO₂ NTAs and Sr TiO3 composite, the special SrTiO₃/TiO₂ composite nanotubes have improved photoelectric conversion and photocatalytic performance. It is worth noting that, when SrTiO₃/TiO₂ after high temperature molten aluminum reduction to get the SrTiO₃-x/TiO₂-x with a strong visible absorption.（2） In summary, SrTiO₃-x/TiO₂-x with a unique heterostructured arrays wereprepared via the hydrothermal reaction of TiO₂ nanotube arrays, followed by a facile aluminium reduction technique. By controlling the time of hydrothermal reaction, the optimal composition and morphology of SrTiO₃-x/TiO₂-x were obtained, and the hydrothermal reaction was 35 min. The photocurrent density of the SrTiO₃-x/TiO₂-x heterostructures irradiated with 350–600 nm monochromatic light was much higher than those of TiO₂, TiO₂-x, SrTiO₃, Sr TiO3-x and SrTiO₃/TiO₂, which is consistent with the above UV-Vis absorption spectra. The SrTiO₃-x/TiO₂-x photoanode exhibited substantially enhanced photocurrent densities of 1.38 mA?cm-2 at 0.6 V vs SCE, and greatly improved hydrogen evolution rate of 21.01 μmol?h-1 under visible light. The synergistic effect between TiO₂-x and SrTiO₃-x with modified the electronic band structure significantly enhances the efficient charge transition can reduce the recombination of charge carriers and prolong the charge lifetime under visible light.Furthermore, the vectorial electron transfer rapidly through aligned TiO₂-x nanotube arrays, which facilitates charge transport and thus enhances the photoconversion efficiency and H2 evolution rate.