钛基TiO2纳米管阵列电极的光电催化性能

应用电化学阳极氧化法在纯Ti基底上制备高度有序的TiO2纳米管阵列,考察了Ti/TiO2光阳极的光电化学响应.以苯酚溶液为目标污染物,研究Ti/TiO2电极的光电催化性能,并与光催化性能进行比较.结果表明,该电极光电催化性能优于光催化性能.施加0.6 V电压时,光电催化性能最好.电化学阻抗谱分析显示,光电催化和光催化降解过程的速控步骤均为表面反应步骤,外加偏压减小了界面电荷转移阻抗,提高了光生载流子的分离效率.     

Some critical factors for photocatalysis on self-organized TiO2 nanotubes

In the present work, different intrinsic and extrinsic parameters are investigated that affect the photocatalytic activity of self-organized TiO₂ nanotube layers. Particularly, the influence of annealing temperature and annealing atmosphere, the influence of different gas purging in the electrolyte, and the effect of applied voltage on the photocatalytic degradation rates of acid orange (AO7) are discussed. We find that the effect of the reducing gas atmosphere dominates over the anatase/rutile ratio in activating the nanotube layers. Moreover, we show that the effect of different gas purging (Ar and O₂) of the electrolyte affects the reaction rate twofold: (1) by providing electron acceptor states and also by (2) a different change in the red–ox potential, i.e., the band bending in TiO₂. By an external anodic voltage, the reaction rates can be increased drastically due to increased band bending. Nevertheless, the magnitude of the effect is also affected by the presence or absence of O₂ in the electrolyte.     

Fabrication of self-organized TiO2 nanotube arrays for photocatalytic reduction of CO2

The photocatalytic conversion of CO₂ and H₂O to alcohols was achieved using self-organized TiO₂ nanotube arrays (TNAs), which were prepared by electrochemical anodization of Ti foils in 1 M (NH₄)₂SO₄ electrolyte containing 0.5 wt% NH₄F. Experimental results revealed that the morphology and structure of self-organized TNAs could be strongly influenced by the applied voltage and anodization temperature, and the optimized TNAs were prepared by electrochemical anodization of Ti foils under optimal conditions (i.e., at 20 V for 2 h at 30 °C). The as-prepared TNAs were amorphous and could be transformed to anatase phase during the thermal treatment at 450 °C in air for 3 h. By using the annealed TNAs as a photocatalyst, the photocatalytic reduction of CO₂ to alcohol, predominately methanol and ethanol, was demonstrated under Xenon lamp illumination. Based on the photocatalytic measurements, the production rates of methanol and ethanol were calculated to be ～10 and ～9 nmol cm^?2 h^?1, respectively. In addition, the formation mechanism of methanol and ethanol was also tentatively proposed.     

TiO2 nanotubes in dye-sensitized solar cells: Higher efficiencies by well-defined tube tops

Aligned self-organized TiO₂ nanotubes of 15–20 µm length proved to be very promising for application in dye-sensitized solar cells. Conventional anodic nanotube layers usually show an irregular structure (nanograss) or a thin nucleation layer at the top of the nanotube array. In the present paper, we demonstrate that by a simple photoresist based method, well-defined and open TiO₂ nanotube tops can be obtained which significantly enhances their performance when used in DSSCs. In fact, the layers show the highest reported solar energy conversion efficiency up to now for a pristine (particle-free) nanotube layer.     

Preparation and characterization of Zr doped TiO2 nanotube arrays on the titanium sheet and their enhanced photocatalytic activity

This paper described a new method for the preparation of Zr doped TiO₂ nanotube arrays by electrochemical method. TiO₂ nanotube arrays were prepared by anodization with titanium anode and platinum cathode. Afterwards, the formed TiO₂ nanotube arrays and Pt were used as cathode and anode, respectively, for preparation of Zr/TiO₂ nanotube arrays in the electrolyte of 0.1 M Zr(NO₃)₄ with different voltage and post-calcination process. The nanotube arrays were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV-Vis diffusion reflection spectra (DRS). The photocatalytic activities of these nanotubes were investigated with Rhodamine B as the model pollutant and the results demonstrated that the photocatalytic efficiency of Zr doped TiO₂ nanotubes was much better than that of TiO₂ nanotubes under UV irradiation. Zr/TiO₂ nanotube arrays doped at 7 V and calcined at 600 °C (denoted as TiO₂-7 V-600) achieved the best photocatalytic efficiency and the most optimal doping ratio was 0.047 (Zr/Ti). TiO₂-7 V-600 could be reused for more than 20 times and maintained good photocatalytic activities.     

Transition of TiO2 nanotubes to nanopores for electrolytes with very low water contents

Over the past decade, the electrochemical formation of self-organized nanotube layers in dilute fluoride containing electrolytes has been studied intensively. In the present work, we show that by anodization of Ti in similar electrolytes but containing only very low water contents, the formation of ordered TiO₂ nanoporous structures can be observed. I.e., the water content in the electrolyte is the critical factor that decides whether self-ordered oxide tubes or pores are formed. This supports the concept that tube formation originates from ordered porous oxide by a “pore-wall-splitting” mechanism.     

Tailoring the wettability of TiO2 nanotube layers

Self-organized TiO₂ nanotube layers were grown on Ti by electrochemical anodization. As prepared, these layers showed a super-hydrophilic wetting behaviour. When modified with organic molecules, octadecylsilane (C₁₈H₃₇SiH₃) or octadecylphosphonic acid (C₁₈H₃₇PO(OH)₂), the layers show a super-hydrophobic behaviour. We demonstrate how the tubular geometry of the TiO₂ layers combined with UV induced decomposition of the organic monolayers (SAM) can be used to adjust the surface wetting properties to any desired degree from super-hydrophobic to super-hydrophilic.     

Robust free standing flow-through TiO2 nanotube membranes of pure anatase

We report the fabrication of defect-free crystalline TiO₂ nanotube (NT) membranes that maintain a full anatase phase composition up to an annealing temperature of 950 °C. Key is the use of a lactic acid electrolyte for the growth of the anodic nanotube layers. These nanotube layers are mechanically sufficiently robust to fabricate, by chemical etching, lift-off and annealing, both-end-open membranes that feature no morphological damage over their entire surface area and thickness. We illustrate the beneficial use of the pure anatase membranes for a flow-through photocatalytic application, i.e., the photodegradation of Acid Orange 7. However, it is anticipated that these pure anatase membranes will also have a wide range of uses in photo(electrochemical) applications of TiO₂.     

铋掺杂二氧化钛纳米颗粒的制备及其可见光催化性能

采用水热法,以纳米管钛酸为前驱物制备了Bi掺杂的TiO₂,并利用X射线衍射、透射电子显微镜、X射线光电子能谱、紫外-可见漫反射光谱等手段对样品进行了表征. 以甲基橙的光催化降解为模型反应评价了样品的可见光催化性能. 结果表明,Bi离子并没有进入TiO₂的晶格中,而是以BiOCl的形式存在. 所制得的BiOCl/TiO₂复合物对甲基橙降解表现出较优越的可见光催化活性;当Bi/Ti摩尔比为1%,水热温度为130℃时,所制催化剂的光催化性能最佳,并对光催化活性提高的机理进行了讨论. 同时,该催化剂对4-氯苯酚降解也表现出较高的光催化性能.     

高度有序的二氧化钛纳米管阵列的制备及其光催化活性的研究

采用电化学阳极氧化法在钛表面构筑了一种结构有序、微米级的TiO₂纳米管阵列膜层. 考察了制备电压、氧化时间、溶液搅拌等实验参数对TiO₂纳米管阵列形貌和尺寸的影响. 应用SEM和XRD对膜层的形貌和晶型进行了分析和表征, 并通过TiO₂纳米管阵列膜对甲基橙的光催化降解, 研究了TiO₂纳米管阵列膜层结构与光催化活性的关系. 结果表明: 阳极电压和溶液搅拌对制备TiO₂纳米管阵列的结构起到关键的作用. 控制20 V电压制备的TiO₂纳米管阵列膜, 管长达2.6～3.3 μm, 经500 ℃热处理后具有最高的光催化活性, 其光催化性能明显优于一般的TiO₂纳米颗粒膜.     

Nitrogen doped anodic TiO2 nanotubes grown from nitrogen-containing Ti alloys

N-doped TiO₂ nanotubes were produced by anodization of a TiN alloy. The alloy was prepared to contain approximately 5 at.% of N from high-purity Ti and TiN powders using an arc-melting and consisted of a two-phase structure with different N-contents. Anodization of the alloy in fluoride-containing electrolyte results, under optimized conditions, in the growth of an ordered TiO₂ nanotube layer on both phases. On the N-rich phase significantly smaller nanotubes are grown while on the low N-concentration phase nanotubes with larger diameter were formed. However, XPS and photoelectrochemical measurements demonstrate successful nitrogen doping of the resulting nanotube layers, which leads to a significant visible photoresponse from this material.     

A self-cleaning nonenzymatic glucose detection system based on titania nanotube arrays modified with platinum nanoparticles

In the present work, we show how TiO₂ nanotube layers that are decorated with a Pt-nanoparticle coating can be fabricated and operated as a reusable glucose sensing system. A critical amount of Pt coating is essential not only to provide an effective catalyst for glucose oxidation but also to establish a sufficient conductivity along TiO₂ nanotube walls to allow an efficient amperometric operation of the electrode. On such an electrode the self-cleaning photocatalytic features of TiO₂ can be maintained and used to re-establish poisoned activity of the Pt particles.     

Preparation of highly ordered TiO2 nanotubes on Ti-foil for dye-sensitized solar cells

TiO₂ nanotube arrays were grown on Ti foil in mixed electrolyte by the anodizing process. TiO₂ nanotube arrays were immersed in the TiCl₄ solution to improve the photocurrent by enhanced charge transfer between TiO₂ and dye molecules on the activity surface. Internal resistance of dye-sensitized solar cells (DSSC) was measured by impedance spectroscopy measurements. Backside illuminated DSSC with TiCl₄-treated TiO₂ nanotubes exhibited a conversion efficiency of 1.45% and showed improved electron transfer.     

TiO2–carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

TiO₂–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO₂ layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO₂ layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO₂ layer proved to be best for efficient charge separation among the tested samples. The optimized TiO₂–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO₂ nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO₂–CNT heterojunctions and TiO₂ nanotubes were 0.75 h⁻¹ (R² = 0.983) and 0.39 h⁻¹ (R² = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO₂–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO₂ nanotubes. These results demonstrate the super capability of the TiO₂–CNT heterojunction arrays in photocatalysis with comparison to TiO₂-only nanomaterial.     

Synthesis of Bi-doped TiO2 Nanotubes and Enhanced Photocatalytic Activity for Hydrogen Evolution from Glycerol Solution

Bi‐doped TiO₂ nanotubes with variable Bi/Ti ratios were synthesized by hydrothermal treatment in 10 mol·L^?1 NaOH (aq.) through using Bi‐doped TiO₂ particles derived from conventional sol‐gel method as starting materials. The effects of Bi content on the morphology, textural properties, photo absorption and photocatalytic activity of TiO₂ nanotubes were investigated. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) observations of the obtained samples revealed the formation of titanate nanotube structure doped with Bi, which exists as a higher oxidation state than Bi³⁺. Bi‐doping TiO₂ nanotubes exhibited an extension of light absorption into the visible region and improved photocatalytic activities for hydrogen production from a glycerol/water mixed solution as compared with pure TiO₂ nanotubes. There was an optimal Bi‐doped content for the photocatalytic hydrogen production, and high content of Bi would retard the phase transition of titanate to anatase and result in morphology change from nanotube to nanobelt, which in turn decreases the photocatlytic activity for hydrogen evolution.     

Ellipsometric and mechanical characterization of nanostructured anodic oxide film formed on Ti-6Al-7Nb alloy

In this work, we grow TiO₂ nanotube layers by using the single-step direct anodization of Ti-6Al-7Nb alloy in aqueous electrolytes containing F^? ions. Nanotube layers are characterized by spectroscopic ellipsometry (SE) and field-emission gun scanning electron microscopy (FEG-SEM). We also use SE to monitor the anodization process for TiO₂ nanotube layers on biocompatible Ti-6Al-7Nb alloy. In addition, we study mechanical properties by nanoindentation.     

Effect of the anodization voltage on the dimensions and photoactivity of titania nanotubes arrays

This work compares the behaviors of TiO₂ nanotube (TNTs) array obtained by anodization of Ti foils in an ethylene glycol/NH₄F/water electrolyte with different applied voltages during a constant anodization time, and for the same electrolyte composition. The crystal structure and surface morphology of the annealed anodic films are investigated by X‐Ray diffraction system, Raman spectroscopy and scanning electron microscopy, respectively. The TiO₂ nanotubes obtained at potentials of 20–40–60 V show different inner diameters (42–89–124 nm), tube length (1.2–3.3–12.7 µm) and wall thicknesses (12–15–18 nm). The influence of these geometric parameters on the photoelectrochemical properties and the photocatalytic activity were investigated in detail. The results showed that the photocatalytic performances of TNT films are improved when the specific surface, the tube length and the solid fraction are increased, but the increase is slowed down when a limiting thickness of the layer is reached. The surface states which usually show high density in nanostructured layers do not seem to influence significantly the photocatalytic activity of the layers. Copyright © 2013 John Wiley & Sons, Ltd.     

Design of highly ordered Ag-SrTiO3 nanotube arrays for photocatalytic degradation of methyl orange

Ag-SrTiO₃ nanotube arrays were successfully prepared for the degradation of methyl orange (MO) under ultraviolet irradiation. In order to form highly ordered SrTiO₃ nanotube arrays, the preparation of TiO₂ nanotube arrays by anodic oxidation of titanium foil in different electrolytes was investigated. The selected organic solvents in electrolytes include glycerol, dimethyl sulfoxide and glycol. The results indicate that the morphology of TiO₂ nanotube arrays prepared in glycol containing ammonium fluoride electrolyte is more regular. Then SrTiO₃ nanotube arrays were synthesized by a hydrothermal method using TiO₂ nanotube arrays as the precursor. In order to further improve the photocatalytic activity of SrTiO₃ nanotube arrays, Ag nanoparticles were loaded on SrTiO₃ nanotube arrays by two sets of experiments. The loaded Ag results in an enhancement of photocatalytic activity of SrTiO₃ nanotube arrays. Moreover, the effect of pH on the photocatalytic degradation of MO was also studied.     

Fe2O3/TiO2纳米管阵列的制备及其光催化性能

在钛基体上采用阳极氧化法制备了TiO₂纳米管阵列,采用化学浴方法在TiO₂纳米管阵列上修饰了Fe₂O₃纳米颗粒.利用扫描电镜、X射线衍射和紫外可见漫反射光谱等手段对材料进行了表征,同时测试了材料的光电化学性能及其光催化降解亚甲基蓝染料废水的性能.结果表明,Fe₂O₃纳米颗粒的修饰将TiO₂纳米管阵列的光响应拓宽至可见光区域,提高了光电流,Fe₂O₃/TiO₂纳米管阵列的光电流是未修饰的TiO₂纳米管阵列的9倍.而在光催化反应中,亚甲基蓝最高降解率可达80%,比未修饰的TiO₂纳米管阵列高出30%.