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.     

Synthesis,Characterization, and Photocatalytic Activity of N‐Doped TiO2 Nanotubes

N‐doped TiO₂ nanotubes with high photocatalytic activity were prepared by the combination of sol‐gel process with hydrothermal treatment. The prepared materials are characterized with transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), x‐ray diffraction (XRD), x‐ray photoelectron spectra (XPS), and UV‐vis spectra. Photocatalytic performance of the N‐doped TiO₂ nanotubes is studied by testing the degradation rate of methyl orange under UV irradiation. Obtained results indicate that N‐doped TiO₂ nanotubes have high catalytic activity for photocatalytic oxidation.     

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.     

Hierarchical TiO2 nanosheet‐assembled nanotubes with dual electron sink functional sites for efficient photocatalytic degradation of rhodamine B

A novel Pt–TiO₂/Ag nanotube photocatalyst has been synthesized successfully via a facile method. TiO₂ nanotubes are assembled with numerous ultrathin TiO₂ nanosheets and show a highly open structure. The gaps between adjacent TiO₂ nanosheets can serve as channels for the access of reactants, accelerating the mass transfer process. During the fabrication process of the Pt–TiO₂/Ag nanotube photocatalyst, high‐quality Pt–SiO₂ nanotubes are synthesized first with the structure‐directing effect of polyvinylpyrrolidone. Then a TiO₂ layer is coated on the outside surface of the silica nanotubes. The introduced titanium species can be converted into TiO₂ nanosheet structure during the subsequent hydrothermal treatment, gradually constructing nanosheet‐assembled nanotubes. Lastly, after the introduction of another electron sink function site of Ag through UV irradiation, the Pt–TiO₂/Ag nanotube photocatalyst with dual electron sink functional sites is obtained. The specially doped Pt and Ag NPs can simultaneously inhibit the recombination process of photogenerated charge carriers and increase light utilization efficiency. Therefore, the as‐synthesized Pt–TiO₂/Ag nanotube catalyst exhibits a high photocatalytic degradation performance for rhodamine B of 0.2 min^?1, which is about 3.2 and 5.3 times as high as that of Pt–TiO₂ and TiO₂ nanotubes because of the enhanced charge carrier separation efficiency. Furthermore, in the unique nanoarchitecture, the nanotubes are assembled with numerous ultrathin TiO₂ nanosheets, which can absorb abundant active species and dye molecules for photocatalytic reaction. On the basis of experimental results, a possible rhodamine B degradation mechanism is proposed to explain the excellent photocatalytic efficiency of the Pt–TiO₂/Ag nanotube photocatalyst.     

脉冲沉积制备Cu2O/TiO2纳米管异质结的可见光光催化性能

在用阳极氧化法制备有序排列TiO₂纳米管阵列薄膜的基础上,引入脉冲沉积工艺,成功实现了均匀、弥散分布的Cu₂O纳米颗粒修饰改性TiO₂纳米管阵列,形成Cu₂O/TiO₂ 纳米管异质结复合材料. 利用场发射扫描电镜（FESEM）、场发射透射电镜（FETEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）和紫外-可见漫反射光谱（UV-Vis DRS）对样品进行表征,重点研究了Cu₂O/TiO₂ 纳米管异质结的光电化学特性和对甲基橙（MO）的可见光催化降解性能. 结果表明,Cu₂O纳米颗粒均匀附着在TiO₂纳米管阵列的管口和中部位置,所制备的Cu₂O/TiO₂ 纳米管异质结具有高效的可见光光催化性能;在浓度为0.01 mol·L^-1的CuSO₄溶液中制得的Cu₂O/TiO₂纳米管异质结表现出最好的电化学特性和光催化性能;另外,对Cu₂O纳米颗粒影响光催化活性的机理进行了讨论.     

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.     

Controllable synthesis of well-ordered TiO2 nanotubes in a mixed organic electrolyte for high-efficiency photocatalysis

Well-ordered TiO 2 nanotube arrays (TNAs) were fabricated by electrochemical anodization in a mixed organic electrolyte consisting of ethylene glycol and glycerol. The morphology, structure, crystalline phase, and photocatalytic properties of TNAs were characterized by using TEM, SEM, XRD and photodegradation of methylene blue. It was found that the morphology and structure of TNAs could be significantly influenced by the anodization time and applied voltage. The obtained tube length was found to be proportional to anodization time, and the calculated growth rate of nanotubes was 0.6 m/h. The microstructure analysis demonstrated that the diameter and thickness of the nanotubes increased with the increase of anodization voltage. The growth mechanism of TNAs was also proposed according to the observed relationship between current density and time during anodization. As expected, the obtained TNAs showed a higher photocatalytic activity than the commercial TiO 2 P25 nanoparticles.     

阳极氧化法制备二氧化钛纳米管及其荧光性质

室温下采用电化学阳极氧化法在NaF、Na₂SO₄和H₂SO₄的混合溶液中用化学处理后的纯Ti片表面组装了一层结构高度有序的高密度TiO₂纳米管阵列。考察了几种主要的实验参数(阳极氧化电压、温度、电解液浓度)对TiO₂纳米管阵列形貌和尺寸的影响，探讨了二次阳极氧化对纳米管形貌的改善。对TiO₂纳米管阵列进行扫描电子显微镜(SEM)和荧光(PL)分析，探讨其生长机理。结果表明，孔径随阳极氧化电压的升高而变大，温度、电解液浓度影响反应过程中电流密度的大小；二次阳极氧化得到的纳米管的有序性有所改善，孔径大小更为均一，并且发现TiO₂纳米管的荧光具有量子效应。     

Improvement the wastewater purification by TiO2 nanotube arrays: The effect of etching-step on the photo-generated charge carriers and photocatalytic activity of anodic TiO2 nanotubes

The current study demonstrates how the etching step in anodization process effects on the photocatalytic activity of TiO₂ nanotubes. In this regard, the TiO₂ nanotubes were made by one-step and two-step anodization process on two different substrates Ti and etched-Ti foils, respectively. The results revealed that two-step anodization process is a beneficial way to prepare highly well-organized structure and regular surface. The two-step anodization by an enhancement in the fluoride ions diffusion led to a decrease in nanotubes' porosity and an increment in the nanotubes’ surface area, a factor of roughness, and the ratio of length to diameter, respectively. As a consequence of the improvement in geometrical properties, the two-step TiO₂ nanotubes led to the intensification of photocurrent density (from 0.383 to 0.677 mA cm⁻²⁾ and photoconversion efficiency (from 0.18% to 0.29%) in comparison with the one-step nanotubes, respectively. Further, a synergetic impact of the photoelectrochemical measurement and photocatalytic process was observed. The degradation efficiencies of 2,4-dichlorophenol by two-step nanotubes increased from 47 to 55% under visible light, and from 58 to72% under UV irradiation, which it was attributed to more light harvesting, more photo-generated electrons, higher separation efficiency and improvement in geometrical properties. Furthermore, the kinetic study showed that the reactions follow first-order kinetics and the reaction rate constants by two-step nanotubes are 1.25 and 1.44 times as great as those of one-step nanotubes under visible and UV irradiation, respectively. Moreover, the reusability tests showed that 2-step TiO₂ nanotubes has good stability and is active even up to the Fifth run.     

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.     

Morphological,electrochemical and photoelectrochemical characterization of nanotubular TiO2 synthetized electrochemically from different electrolytes

The electrochemical synthesis of auto-organized TiO₂ arrays generated by Ti anodization in different non-aqueous electrolytes was analyzed. Propylene carbonate-based electrolytes seem to be good electrolytic media for the controlled growth of titania nanotube structures. Scanning electron microscopy (SEM) analysis indicated that, depending on the media employed in the synthesis of the TiO₂ nanotubes, different aspect ratios (length/diameter) could be obtained. Impedance analysis using the passive pit model gave the electrical properties of the layers during the different stages of nanotubes formation. Mott–Schottky analysis and the impedance results showed that the TiO₂ nanotubes layers were n-type semiconductors with highly defective walls on top of a resistive barrier layer. Photoelectrochemical measurements showed that tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbed onto the TiO₂ nanotube arrays, which could be employed as an efficient photosensitizer for solar-energy conversion by TCPP-sensitized nanotubular TiO₂ electrodes.     

Electrochemically assisted photocatalysis on self-organized TiO2 nanotubes

In this work we investigate influence of an externally applied bias on the photocatalytic performance of self-organized TiO₂ nanotube layers. These layers were grown by anodization of titanium in fluoride containing electrolytes and have different geometric dimensions. Since the layers are grown directly on the Ti substrate, a very good electrical backside contact is directly provided. Therefore, we use the nanotube layers/Ti structures as photo-anodes for the UV light induced photocatalytic decomposition of acid orange 7. For comparison, we use TiO₂ nanopowder (Degussa P25) compacted also on a Ti sheet. The present results demonstrate that the photocatalytic activity of self-organized TiO₂ nanotube layers can significantly be increased by electrochemical bias.     

Preparation of TiO2/ZnS core/sheath heterostructure nanotubes via a wet chemical method and their photocatalytic activity

TiO₂/ZnS core/sheath heterostructure nanotubes are prepared via a simple wet chemical method at room temperature. The samples are characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectrum. Their photocatalytic activity for degradation of methyl orange under UV illumination is valuated. It is found that the ZnS layer changes with the concentration of precursors. The photocatalytic activity of the TiO₂/ZnS depends not only on the structure of the support (TiO₂ nanotubes) but also on the specific interaction between ZnS and support.     

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.     

Characterization of TiO2 nanotube arrays prepared via anodization of titanium films deposited by DC magnetron sputtering

Highly ordered TiO₂ nanotube arrays were fabricated on a conducting glass substrate in NH₄HF₂/glycol electrolyte via anodization of titanium film which was deposited by direct current magnetron sputtering (DCMS) at different temperatures. The results showed that Ti films with good homogeneity and high denseness could be formed under the conditions Ar pressure 0.35 Pa, direct current 3.5 A, and 2 h at 300 °C. Characterization of the TiO₂ nanotube arrays was investigated comparatively, by altering anodization time. The surface morphology of the samples changed as the anodization time was prolonged from 10 to 150 min at 30 V. The TiO₂ thin film was amorphous and could be transformed into anatase by annealing at 450 °C. On the basis of UV?Cvisible transmission spectra the bandgap of the thin film was calculated to be 3.12 eV, and its tail extended to 2.6 eV.     

Enhanced electron collection in photoanode based on ultrafine TiO2 nanotubes by a rapid anodization process

The separated and ultrafine TiO₂ nanotubes are fabricated by a modified rapid anodization method, which cannot be achieved through conventional anodization. Then, model dye-sensitized solar cells based on the prepared TiO₂ nanotubes and commercial TiO₂ nanoparticles (P25) are investigated, and a discrepancy is discovered between the light-harvesting capability and the power conversion efficiency. The charge transport and recombination are studied by the electrochemical impedance spectroscopy and the open-circuit voltage decay technique. Results show that the nanotube photoanode owns a longer electron diffusion length and a larger electron lifetime than the nanoparticle one, which can compensate for the loss of light absorption. The enhanced electron collection efficiency observed is attributed to the facilitated charge carrier pathways in the photoanode composed by the separated TiO₂ nanotubes fabricated in this work. Therefore, the TiO₂ nanotubes synthesized by this method are verified to have good electronic properties, which might find applications not only in photovoltaic, but also in catalysis, sensors, and other areas.     

Microwave‐Hydrothermal Preparation and Visible‐Light Photoactivity of Plasmonic Photocatalyst Ag‐TiO2 Nanocomposite Hollow Spheres

Visible‐light‐driven plasmonic photocatalyst Ag‐TiO₂ nanocomposite hollow spheres are prepared by a template‐free chemically‐induced self‐transformation strategy under microwave‐hydrothermal conditions, followed by a photochemical reduction process under xenon lamp irradiation. The prepared samples are characterized by using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N₂ adsorption‐desorption isotherms, X‐ray photoelectron spectroscopy, UV/Vis and Raman spectroscopy. Production of ?OH radicals on the surface of visible‐light illuminated TiO₂ was detected by using a photoluminescence method with terephthalic acid as the probe molecule. The photocatalytic activity of as‐prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under visible‐light irradiation. The results show that the surface plasmon absorption band of the silver nanoparticles supported on the TiO₂ hollow spheres was red shifted, and a strong surface enhanced Raman scattering effect for the Ag‐TiO₂ nanocomposite sample was observed. The prepared nanocomposite hollow spheres exhibits a highly visible‐light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of pure TiO₂ and commercial Degussa P25 (P25) powders. Especially, the as‐prepared Ag‐TiO₂ nanocomposite hollow spheres at the nominal atomic ratio of silver to titanium ( R ) of 2 showed the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2.     

TiO2一维纳米材料及其纳米结构的合成

本文对合成TiO₂一维纳米材料及其有序纳米阵列的阳极氧化法、模板法以及水热法进行了全面而系统的评述，着重介绍了它们的最新研究进展。阳极氧化法能制备牢固负载于基体上的TiO₂纳米管阵列，这有助于构筑TiO₂纳米结构及其在纳米器件上的应用；与多种制备技术如溶胶－凝胶工艺、电化学沉积以及原子层沉积等相结合，模板法可以合成出多种形貌的TiO₂纳米材料如纳米管、纳米线和纳米棒，并可以通过改变所用模板的微观尺寸来调控TiO₂一维纳米材料及其有序阵列的微结构参数；水热合成法可以制备出直径小且比表面积大的TiO2纳米管粉末。但从目前看来，该法还不能制备出牢固负载于基体上的有序纳米阵列。文章最后指出了TiO₂一维纳米材料及其有序纳米阵列合成中存在的问题及今后发展方向。     

电镀法制备Pt/TiO2纳米管电极及其电催化析氢性能

采用阳极氧化法制备得到锐钛矿型二氧化钛(TiO₂)纳米管阵列,在其表面通过电镀法沉积Pt,得到了低铂的Pt/TiO₂纳米管电极(Pt/TiO₂?NTs)。通过扫描电子显微镜和透射电子显微镜对其进行形貌表征后发现,Pt较为均匀地分布于TiO₂纳米管阵列中。进一步的电催化析氢结果表明,Pb/TiO₂?NTs在10 mA·cm^-2时,过电位为0.079 V,塔菲尔斜率为42.7 mV·dec-1,较Pt/TiO₂致密膜电极(Pt/TiO₂?F)以及商业Pt/C催化剂显示了更为优异的催化活性。同时,在长循环稳定性测试(3000个周期)中,Pb/TiO₂?NTs相较于上述2种对比电极显示了更为优异的稳定性。