A heterogeneous Li2TiO3/TiO2 nanocomposite was successfully prepared from anodized amorphous TiO2 nanotube arrays in CH3COOLi solution by using a facile hydrothermal method. Morphology transformation from nanotubes into diamond-shaped nanoparticles can be attributed to the water-induced dissolution and recrystallization processes of the nanotube arrays in a weak acid salt solution. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction results showed that a large amount of Li2TiO3/TiO2 diamond-shaped nanoparticles were formed on the surface of the TiO2 nanotube arrays. UV-vis diffuse reflectance spectra indicated improved visible light absorbance. The enhanced photoelectrochemical water splitting was demonstrated under UV-vis light illumination, and the photocurrent density of the electrode prepared in 0.1 M CH3COOLi was greater than that of other electrodes. The semiconductor characteristics were studied using electrochemical impedance spectroscopy in detail. This work is expected to guide next studies to design and fabricate photocatalysts for efficient photoelectrochemical water splitting.

TiO2 thin films were fabricated by RF magnetron sputtering on titanium substrates and then implanted with different amounts of carbon. The microstructure, valence states and optical characteristics of each sample were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis diffuse reflection spectroscopy. Photoelectric property was evaluated under visible light using a xenon lamp as illuminant. The experimental results indicate that the implanting carbon concentration has a significant influence on film’s micro structure and element valence states. The dominant valence states of carbon vary as carbon content increases. Carbon ion implantation remarkably enhances the current density and photocatalytic capability of TiO2 thin films. The optimized implanting content is 9.83×1017 ion/cm2, which gives rise to a 150% increased photocurrent and degradation rate.

A novel bilayer structure of TiO2 film was found capable of yielding fairly strong photocurrent under visible light. The base layer was lightly doped with Mo and then etched by reactive ion beam, and was finally covered by an undoped TiO2 surface layer. Because of Fermi level drop at the interface of the trenches, such a deposition–etching–redeposition process implanted an array of depletion layer into TiO2 film successfully. Microstructures, crystallite parameters, and the absorption property were investigated with scanning electron microscope, atomic force microscopy, X-ray diffraction, and ultraviolet–visible spectroscopy in order. Photocurrent density was collected on an electrochemical workstation under visible light. The results indicate that carrier collection probability near depletion layer was enhanced significantly owing to high parallel diffusivity. Under visible light, current density demonstrates a marked increase as etching depth grows. At an etching depth around 660 nm, photocurrent density achieved is 56 times larger than TiO2 film. Depletion layer at vertical trench edges may have a much bigger universal value than anticipated for various doping cases of wide-bandgap films.Keywords: anisotropic transport; depletion layer array; magnetron sputtering; Mo doping; reactive ion beam etching; TiO2 film;

•Propose a novel approach to implant internal electric fields in multilayer films.•Optimized film structure with an ultrathin, heavy doped bottom layer.•Investigate effects of various layer-assemble modes on internal carrier transfer.•Confirm the effectiveness of electric field as carrier separation accelerator.Multilayer Mo-doped TiO2 thin films were prepared by In-situ RF magnetron co-sputtering. Surface morphology, crystallite parameters, valence states and absorption band were investigated with atomic force microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy and ultraviolet–visible spectroscopy. AC impedance spectroscopy and photocatalytic capability of different layer-assemble modes were examined on an electrochemical workstation under visible light. The result indicates the electric fields resulted from Fermi level drops could remarkably accelerate the separation of photogenerated carriers. The double-layer film, which was prepared by covering the uniformly Mo doped layer with an undoped surface layer, has the smallest impedance. The strongest catalytic capability is demonstrated by the three-layer film, which has an undoped surface layer, a uniformly doped middle layer and an ultrathin, heavy doped bottom layer. Although different layer modes have little influence on absorption edge, our observations suggest that by manipulating doping content in each layer, we can implant upward electric field arrays, which has considerable potential to enhance the photocatalytic property, into multilayer Mo-doped TiO2 films.

TiO2 thin films doped with different contents of Mo were deposited by DC reactive magnetron sputtering. Surface morphology, crystal structure, elements' valence states and absorption edge of each sample were characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet–visible spectrometer. Cyclic voltammetry was utilized to study the photoelectric properties while the photocatalytic activity was evaluated by the degradation rate of methylene blue. The result indicates that an appropriate concentration of Mo could extend the absorption edge of TiO2 film to visible range remarkably. When the content reached 0.9 at.%, with a xenon lamp we observed the strongest photocurrent as well as the best photocatalytic property while under the illumination of strong visible light, a photocurrent 10 times the undoped sample appeared. The electrochemical impedance spectroscopy observed the fastest speed of carrier transfer as doping content increased to 0.9 at.%, while higher doping amount would precipitate carrier recombination due to a large number of lattice defects.Highlights► Mo-doped TiO2 thin films were deposited by DC reactive magnetron sputtering. ► Doped films present high specific area and well-grown crystals. ► Proper content of Mo accelerates charge separation and inhibits the recombination. ► Enhanced photocatalytic activity under ultraviolet light is attained by doping. ► Under visible light, the strongest photocurrent after doping increases tenfold!