Enhanced Photoelectrochemical Properties of Cu_2O-loaded Short TiO_2 Nanotube Array Electrode Prepared by Sonoelectrochemical Deposition

Copper and titanium remain relatively plentiful in earth crust.Therefore,using them in solar energy conversion technologies are of significant interest.In this work,cuprous oxide（Cu2O）-modified short TiO2 nanotube array electrode was prepared based on the following two design ideas:first,the short titania nanotubes obtained from sonoelectrochemical anodization possess excellent charge separation and transportation properties as well as desirable mechanical stability;second,the sonoelectrochemical deposition technique favours the improvement in the combination between Cu2O and TiO2 nanotubes,and favours the dispersion of Cu2O particles.UV-Vis absorption and photo-electronchemical measurements proved that the Cu2O coating extended the visible spectrum absorption and the solar spectrum-induced photocurrent response.Under AM1.5 irradiation,the photocurrent density of the composite electrode（i.e.sonoelectrochemical deposition for 5 min） was more than 4.75 times as high as the pure nanotube electrode.Comparing the photoactivity of the Cu2O/TiO2 electrode obtained using sonoelectrochemical deposition with others that synthesized using plain electrochemical deposition,the photocurrent density of the former electrode was 2.2 times higher than that of the latter when biased at 1.0 V（vs.Ag/AgCl）.The reproducible photocurrent response under intermittent illumination demonstrated the excellent stability of the composite electrode.Such kind of composite electrode material will have many potential applications in solar cell and other fields.

Transient competition between photocatalysis and carrier recombination in TiO_2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array （TNA） films are fabricated by using an anodic oxidation method. Au nanoparticles （NPs） films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C （UVC, 266 nm） light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence （PL） spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence （NTRT-PL） spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au-TNA composite are evaluated through photo-degradation of methyl orange （MO） in an aqueous solution with ultraviolet-visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

Phosphomolybdic acid-modified highly organized TiO2 nanotube arrays with rapid photochromic performance

TiO2 nanotube arrays were prepared by means of an electrochemical anodization technique in an organic electrolyte solution doped with polyvinyl pyrrolidone (PVP) and were subsequently modified with phosphomolybdic acid (PMoA) to obtain PMoA/TiO2 nanotube arrays. The microstructure and photochromic properties were investigated via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), and X-ray photoelectron spectroscopy (XPS). The results indicated that the Keggin structure of PMoA and the nanotube structure of TiO2 were not destroyed, and there was a strong degree of interaction between PMoA and TiO2 at the biphasic interface with lattice interlacing during the compositing process. The XPS results further indicated that there was a change in the chemical microenvironment during the formation process of the composite, and a new charge transfer bridge was formed through the Mo-O-Ti bond. Under visible light irradiation, the colorless PMoA/TiO2 nanotube array quickly turned blue and exhibited a photochromic response together with reversible photochromism in the presence of H2O2. After visible light irradiation for 60s, the appearance of Mo^5+ species in the XPS spectra indicated a photoreduction process in accordance with a photoinduced electron transfer mechanism.

Unveiling the controversial mechanism of reversible Na storage in TiO2 nanotube arrays： Amorphous versus anatase TiO2

Due to their inherent safety, low cost, and structural stability, TiO2 nanostructures represent a suitable choice as anode materials in sodiumion batteries. In the recent years, various hypotheses have been proposed regarding the actual mechanism of the reversible insertion of sodium ions in the TiO2 structure, and previous reports are often controversial in this respect. Interestingly, when tested as binder- and conducting additive-free electrodes in laboratory-scale sodium cells, amorphous and crystalline （anatase） TiO2 nanotubular arrays obtained by simple anodic oxidation exhibit peculiar and intrinsically different electrochemical responses. In particular, after the initial electrochemical activation, anatase TiO2 shows excellent rate capability and very stable long-term cycling performance with larger specific capacities, and thus a clearly superior response compared with the amorphous counterpart. To obtain deeper insight, the present materials are thoroughly characterized by scanning electron microscopy and ex situ X-ray diffraction, and the insertion of sodium ions in the TiO2 bulk phases is systematically modeled by density functional theory calculations. The present results may contribute to the development of more systematic screening approaches to identify suitable active materials for highly efficient sodium-based energy storage systems.

An Energy-Efficient Electrochemical Method for CuO-TiO_2 Nanotube Array Preparation with Visible-Light Responses

A rapid and energy-efficient method was presented for preparing CuO-TiO2 nanotube arrays. TiO2 nanotube arrays were first prepared by anodic oxidation using titanium anode and platinum cathode. Then, the formed TiO2 nanotube arrays and Pt were used as cathode and anode, respectively, for subsequent formation of CuO-TiO2 nanotube arrays, through an electro- chemical process in a solution of 0.1 mol/L CuSO4. The morphology and composition of the CuO-TiO2 nanotube arrays were characterized using field-emission scanning electron microscopy, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and UV-Vis diffusion reflection spectroscopy （UV-Vis DRS）. XPS and XRD analyses suggested that the Cu element in the nanotubes existed in CuO form, and its content changed along with the voltage during the second electrochemical process. The photocatalytic activities of the CuO-TiO2 nanotube arrays were evaluated by the degradation of a model dye, rhodamine B. The results showed that Cu incorporation aroused wide visible-light adsorption and improved the photocatalytic efficiency of TiO2 nanotube arrays significantly under visible-light irradiation. The stability of the CuO-TiO2 nanotube arrays was also detected.

Fabrication, Characterization and Optical Properties of TiO2 Nanotube Arrays on Boron-doped Diamond Film Through Liquid Phase Deposition

TiO2 nanotube（TiNT） arrays were deposited on boron-doped diamond films by a liquid-phase deposition method with ZnO nanorod arrays as the template.The different morphologies of TiNTs have been obtained by controlling the morphology of ZnO template.The X-ray diffraction and energy-dispersive X-ray analysis show that the ZnO nanorod array template has been removed in the TiNTs formation process.The crystalline quality of the TiNTs is improved by increasing the annealing temperature.The band gap of the TiNTs is about 3.25 eV estimated by the UV-Vis absorption spectroscopy,which is close to the value of bulk TiO2.In the photoluminescence spectrum,a broad visible emission in a range of ca.550-750 nm appears due to the surface oxygen vacancies and defects.

Enhanced Efficiency of Dye-sensitized Solar Cells Using rGO@TiO2 Nanotube Hybrids

We established a novel strategy for the synthesis of reduced graphene oxide（rGO）@TiO2 nanotube hybrids using an 18 W UV-assisted photo-catalytic reduction method for utilization as photo-anode of dye-sensitized solar cells（DSSCs）. The photo-conversion efficiency of DSSCs was significantly enhanced after the addition of rGO, and in addition, the photo-anode showed decreased internal resistance. Analysis of rGO@TiO2 hybrids by transmissions scanning electron microscopy（TEM）, X-ray diffraction（XRD）, Raman spectra, N2 adsorption and desorption, atomic force microscopy（AFM） and X-ray photoelectron speetroscopy（XPS） demonstrates that the rGO modified TiO2 nanotubes can increase the short-circuit current and the conversion efficiency of dye-sensitized solar cells. The efficiency is improved by almost two folds as much compared to those of the bare TiO2 nanotubes.