Dye‐Sensitized TiO2 Nanotube Solar Cells: Rational Structural and Surface Engineering on TiO2 Nanotubes

Owing to well‐defined structural parameters and enhanced electronic properties, highly ordered TiO₂ nanotube arrays have been employed to substitute TiO₂ nanoparticles for use in dye‐sensitized solar cells. To further improve the performance of dye‐sensitized TiO₂ nanotube solar cells, efforts have been directed toward the optimization of TiO₂ photoanodes, dyes, electrolytes, and counter electrodes. Herein, we highlight recent progress in rational structural and surface engineering on anodic TiO₂ nanotube arrays and their effects on improving the power conversion efficiency of dye‐sensitized TiO₂ nanotube solar cells.     

CdS/TiO2–SrTiO3 heterostructure nanotube arrays for improved solar energy conversion efficiency

TiO₂–SrTiO₃ heterostructure nanotube arrays have been utilized as a novel oxide substrate for CdS quantum dot sensitized solar cells (QDSCs). SrTiO₃ on TiO₂ surface passivates surface states of TiO₂ and builds cascade-structured band alignment, which significantly reduces charge recombination at electrode surface. CdS/TiO₂–SrTiO₃ electrode exhibits a superior photoelectrochemical performance than CdS/TiO₂ electrode with ～ 70% increase in external quantum efficiency. This study suggests that the suppression of charge recombination at electrode surface is critical to efficient solar energy conversion.     

微含水量电解液中高管径比TiO_2纳米管阵列的制备

通过阳极氧化法在微含水量为0.5wt%的NH4F/乙二醇/H2O酸性电解质体系中制备了管径大、高管径比的二氧化钛(TiO2)纳米管阵列。采用SEM、XRD等测试手段对TiO2纳米管阵列形貌及晶相进行表征,探讨了不同氧化时间、电压对纳米管阵列形貌的影响,微含水量下氧化电压可以适当增加,更容易得到规整的长纳米管阵列;通过测定样品的光电流和紫外-可见光漫反射吸收光谱,研究分析了含水量以及超声工艺对纳米管光吸收及光电流特性,微含水量下得到的纳米管阵列可见光吸收边红移至420nm,对480~700nm可见光有明显的光吸收,光电流显著增大;丙酮作为超声介质可有效去除纳米管阵列表面的集束,能进一步提高纳米管阵列的光电性能。     

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.     

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%.     

微含水量电解液中高管径比TiO2纳米管阵列的制备

通过阳极氧化法在微含水量为0.5wt%的NH₄F/乙二醇/H₂O酸性电解质体系中制备了管径大、高管径比的二氧化钛（TiO₂）纳米管阵列。采用SEM、XRD等测试手段对TiO₂纳米管阵列形貌及晶相进行表征,探讨了不同氧化时间、电压对纳米管阵列形貌的影响,微含水量下氧化电压可以适当增加,更容易得到规整的长纳米管阵列;通过测定样品的光电流和紫外-可见光漫反射吸收光谱,研究分析了含水量以及超声工艺对纳米管光吸收及光电流特性,微含水量下得到的纳米管阵列可见光吸收边红移至420nm,对480~700nm可见光有明显的光吸收,光电流显著增大;丙酮作为超声介质可有效去除纳米管阵列表面的集束,能进一步提高纳米管阵列的光电性能。     

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.     

Fe_2O_3/TiO_2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%。     

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.     

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.     

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.     

阴离子改性甘油溶液中TiO2纳米管阵列的制备和表征

本文采用电化学阳极氧化法以含氟的甘油和水混合溶液为电解液在纯钛表面制备了一层排列规整的TiO2纳米管阵列,研究了电解液中额外添加3种2价阴离子、不同的电解时间及不同的添加物浓度等因素对所获得的TiO2纳米管阵列形貌的影响。结果表明,在改性电解液中制备的TiO2纳米管阵列的长度均超过了未改性的电解液中制备的,并随着氧化时间的增长,纳米管管口直径增大,管壁变薄;同时添加的(NH4)2TiF6浓度在0.025~0.1 mol.L-1范围内均可获得管长更长且形貌较好的TiO2纳米管阵列。     

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.     

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.     

Water oxidation on N‐Doped TiO2 nanotube arrays

Photocatalytic splitting water into hydrogen and oxygen by utilizing solar energy is regarded as an effective strategy to solve oil crisis. By utilizing density functional calculations, we herein present the systemic studies with respect to water splitting mechanism on N‐doped TiO₂ nanotube arrays (NTAs), and focus on activation energy, thermodynamic properties, and effects of N‐doping on reaction process. Our results reveal that the impurity 2p states of doped nitrogen effectively change electronic structure of TiO₂ NTAs, which act as an electron acceptor and facilitate weakly bound electrons of valence band to be easily excited to acceptor level, as well as enhance the first H₂O adsorption and dissociation on the inside wall of N‐doped TiO₂ NTAs. Therefore, it is found that the rate‐determining step of water splitting is the formation reaction of HOO* on N‐doped TiO₂ NTAs rather than the formation of HO* from the first H₂O. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

TiO2 nanotube arrays fabricated by anodization in different electrolytes for biosensing

Titania nanotube arrays were fabricated by anodic oxidation of titanium foil in different electrolytes. The morphology, crystallinity and composition of the as-prepared nanotube arrays were studied by XRD, SEM and EDX. Electrochemical impedance spectroscopy (EIS) was employed to investigate their electrical conductivity and capacitance. Titania nanotube arrays co-adsorbed with horseradish peroxidase (HRP) and thionine chloride (Th) were studied for their sensitivity to hydrogen peroxide by means of cyclic voltammetric and galvanostatic measurements. The experiments showed that TiO₂ nanotube arrays possessed appreciably different sensitivities to H₂O₂ due to their different conductivity. Further experiments revealed that TiO₂ nanotubes have noticeably different ability of adsorbing HRP and Th, and the best sensitivity was achieved when the density of HRP is the highest. The TiO₂ nanotube arrays fabricated in potassium fluoride solution demonstrated the best sensitivity on hydrogen peroxide in the range of 10⁻⁵–3 × 10⁻³ M at pH 6.7 and at a potential of −600 mV (vs. Ag/AgCl).     

TiO2纳米管阵列光电催化氧化处理氨氮废水

用电化学阳极氧化法制备了高度有序的钛基二氧化钛纳米管阵列薄膜。用场发射扫描电镜(FE-SEM)、X射线衍射(XRD)表征样品的形貌与晶型特征。以二氧化钛纳米管阵列为光阳极,石墨为对电极,测试了不同pH值和外加偏压条件下的光电流响应和光电催化氧化降解NH4Cl水溶液(以N计,100 mg·L-1)的效率。结果表明:所制备的TiO2纳米管阵列具有锐钛矿和金红石的混晶结构,且主要晶型为锐钛矿。光电流响应的强弱与光电催化氧化效率的高低相对应,降解氨氮废水的最佳条件为pH=11,偏压为1.0 V。     

Biocompatibility and <Emphasis Type="Italic">in vitro</Emphasis> antineoplastic drug-loaded trial of titania nanotubes prepared by anodic oxidation of a pure titanium

TiO₂ nanotube (NT) arrays have been prepared by anodic oxidation of a Ti sheet, and carbon-deposited TiO₂ NT arrays have been prepared by annealing TiO₂ NT arrays in carbon atmosphere. The biocompatibility of the as-prepared NT arrays was investigated by observing the growth of osteosarcoma (MG-63) cells on the NT arrays. The application of the TiO₂ NT arrays as a drug delivery vehicle was investigated. Both the TiO₂ NTs and the carbon-modified TiO₂ NTs have good biocompatibility supporting the normal growth and adhesion of MG-63 cells with no need of extracellular matrix protein coating. The one end-opened TiO₂ NTs can be easily filled with drugs, working as an efficient drug delivery vehicle.     

自掺杂TiO2纳米管：液相制备及光催化性能

采用水合肼（N₂H₄·H₂O）作为还原剂,在液相环境中制备了自掺杂TiO₂纳米管阵列（NTs）。利用FE-SEM、EDS、XPS、XRD、Raman、UV-Vis/NIR分光光度法以及半导体特性分析系统（Keithley 4200 SCS）分别对样品的形貌,晶体结构,光学特性以及电学性能进行了表征。结果表明：通过这种方法制备的自掺杂TiO₂NTs在带隙中引入了大量的氧空位,创造了氧空位能级,从而提高了样品的电导率,有效提高光生电子-空穴对的产生、分离和传输。此外,由于氧空位的作用,使得TiO₂NTs的带隙变窄,增强了可见光吸收能力,致使样品具有较高的光催化活性,并通过降解甲基橙溶液对样品的光催化活性进行评估。结果显示当光照150min后,自掺杂TiO₂NTs对甲基橙溶液的降解率达73%,并且这种催化剂便于回收和重复使用。     

TiO2 Nanotube Arrays Modified with Cr‐Doped SrTiO3 Nanocubes for Highly Efficient Hydrogen Evolution under Visible Light

In recent decades, solar‐driven hydrogen production over semiconductors has attracted tremendous interest owing to the global energy and environmental crisis. Among various semiconductor materials, TiO₂ exhibits outstanding photocatalytic properties and has been extensively applied in diverse photocatalytic and photoelectric systems. However, two major drawbacks limit practical applications, namely, high charge‐recombination rate and poor visible‐light utilization. In this work, heterostructured TiO₂ nanotube arrays grafted with Cr‐doped SrTiO₃ nanocubes were fabricated by simply controlling the kinetics of hydrothermal reactions. It was found that coupling TiO₂ nanotube arrays with regular SrTiO₃ nanocubes can significantly improve the charge separation. Meanwhile, doping Cr cations into SrTiO₃ nanocubes proved to be an effective and feasible approach to enhance remarkably the visible‐light response, which was also confirmed by theoretical calculations. As a result, the rate of photoelectrochemical hydrogen evolution of these novel heteronanostructures is an order of magnitude larger than those of TiO₂ nanotube arrays and other previously reported SrTiO₃/TiO₂ nanocomposites under visible‐light irradiation. Furthermore, the as‐prepared Cr‐doped SrTiO₃/TiO₂ heterostructures exhibit excellent durability and stability, which are favorable for practical hydrogen production and photoelectric nanodevices.