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.     

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.     

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.     

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.     

A Dewetted‐Dealloyed Nanoporous Pt Co‐Catalyst Formed on TiO2 Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H2 Production

Pt nanoparticles are typically decorated as co‐catalyst on semiconductors to enhance the photocatalytic performance. Due to the low abundance and high cost of Pt, reaching a high activity with minimized co‐catalyst loadings is a key challenge in the field. We explore a dewetting‐dealloying strategy to fabricate on TiO₂ nanotubes nanoporous Pt nanoparticles, aiming at improving the co‐catalyst mass activity for H₂ generation. For this, we sputter first Pt‐Ni bi‐layers of controllable thickness (nm range) on highly ordered TiO₂ nanotube arrays, and then induce dewetting‐alloying of the Pt‐Ni bi‐layers by a suitable annealing step in a reducing atmosphere: the thermal treatment causes the Pt and Ni films to agglomerate and at the same time mix with each other, forming on the TiO₂ nanotube surface metal islands of a mixed PtNi composition. In a subsequent step we perform chemical dealloying of Ni that is selectively etched out from the bimetallic dewetted islands, leaving behind nanoporous Pt decorations. Under optimized conditions, the nanoporous Pt‐decorated TiO₂ structures show a>6 times higher photocatalytic H₂ generation activity compared to structures modified with a comparable loading of dewetted, non‐porous Pt. We ascribe this beneficial effect to the nanoporous nature of the dealloyed Pt co‐catalyst, which provides an increased surface‐to‐volume ratio and thus a more efficient electron transfer and a higher density of active sites at the co‐catalyst surface for H₂ evolution.     

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%。     

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%.     

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.     

Sulfur and Ti3+ co‐Doping of TiO2 Nanotubes Enhance Photocatalytic H2 Evolution Without the Use of Any co‐catalyst

TiO₂ nanotubes were successfully co‐doped with sulfur and Ti³⁺ states using a facile annealing treatment in H₂/H₂S gas mixture. The obtained nanotubes were investigated for their photocatalytic performance and characterized by SEM, XRD, XPS, EPR, IPCE, IMPS and Mott‐Schottky measurements. The synthesized co‐doped TiO₂ nanotubes show an enhanced photocatalytic hydrogen production rate compared to tubes that were treated only in pure H₂ or H₂S atmosphere—this without the presence of any co‐catalyst. It was found that sulfur in co‐doped TiO₂ exists in the form of S^2? and a small quantity of S⁴⁺/S⁶⁺, which leads to a narrowing of the band gap. However, the enhanced absorption of light in the visible range is not the key reason for the improved photocatalytic performance. We ascribe the enhanced photocatalytic activity to a synergetic effect of S mid‐gap states and disordered Ti³⁺ defects that facilitate photo generated electron transfer.     

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.     

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。     

Entrapment of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in TiO<Subscript>2</Subscript> nanotubes for visible light-driven photocatalysis

In this study, we prepared nanoparticles of the visible light-responsive photocatalyst, Bi₂O₃ entrapped in anatase TiO₂ nanotubes (Bi₂O₃-in-TNTs) via a vacuum-assisted precursor-filling process followed by annealing. Owing to the unique tubular electronic structure of TiO₂ nanotubes, the interior of the nanotube is in an electron-deficient state, which was confirmed by XPS spectra and H₂-TPR. Electrochemical impedance studies showed that the Bi₂O₃-in-TNTs demonstrated a more efficient separation of photogenerated carriers than when Bi₂O₃ nanoparticles were deposited on the outer wall of TiO₂ nanotubes (Bi₂O₃-out-TNTs). Due to the confinement effect of TiO₂ nanotubes, which inhibits photogenerated carriers’ recombination, the Bi₂O₃-in-TNTs exhibited a better photocatalytic performance for the photo-degradation of methyl orange under visible light compared to Bi₂O₃-out-TNTs.     

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.     

Effect of electrolysis conditions on photocatalytic activities of the anodized TiO2 films

Photocatalytic activities of anodized TiO₂ films for decomposition of gaseous acetaldehyde were investigated. The anodized TiO₂ films were fabricated by galvanostatic anodization in a mixed electrolyte composed of H₂SO₄, H₃PO₄, and H₂O₂. Pre-nitridation treatment effectively enhanced the photocatalytic activity of the anodized TiO₂ films. The electrolysis parameters such as anodization time, current density, electrolyte temperature, and electrolyte composition significantly affected the photocatalytic activity of the anodized TiO₂ films. The improvement of photocatalytic activity of the anodized films is attributed to increase in surface areas of the anodized specimens.     

Preparation of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO<Subscript>2</Subscript> and acquirement of efficient photocatalyst

ZnFe₂O₄ nanoparticles sensitized by C-modified TiO₂ hybrids (ZnFe₂O₄–TiO₂/C) were successfully prepared by a feasible method. The ZnFe₂O₄ nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO₂ were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N₂ adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO₂ lattice but adhered to the surface of TiO₂. The photocatalytic activity of the as-prepared C-modified TiO₂ (TiO₂/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe₂O₄ into the TiO₂/C could enhance the absorption spectrum range. The ZnFe₂O₄–TiO₂/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO₂ and TiO₂/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe₂O₄–TiO₂/C composites. The optimum photocatalytic performance was obtained from the ZnFe₂O₄(0.8 wt%)–TiO₂/C sample.     

Branched core-shell a-TiO2@N-TiO2 nanospheres with gradient-doped N for highly efficient photocatalytic applications

A branched core-shell nanosphere composed of an anatase TiO₂ (a-TiO₂) core and a TiO₂ nanobranch shell with gradient-doped N (a-TiO₂@N-TiO₂) is synthesized by a simple in situ doping method, in which mixed crystal anatase-rutile TiO₂ (ar-TiO₂) nanosphere is first prepared by oxidizing Ti using H₂O₂, and then is etched by NH₃·H₂O to form (NH₄)₂TiO₃ nanobranches, which is converted into a-TiO₂@N-TiO₂ following an ambient annealing process. The diameter of a-TiO₂ core is ～500 nm, and the thickness of N-TiO₂ branched shell is ～100 nm with gradually increased N concentration from the bottom to the edge. Ultra-thin amorphous coating layers on the branches are also observed. The morphology of the composites could be further tuned by the amount of NH₃·H₂O, and its effect on the photocatalytic performance is also investigated. The optimized a-TiO₂@N-TiO₂ shows an outstanding hydrogen evolution rate of 308.1 μmol g^?1 h^?1 under air mass (AM) 1.5 illumination, and also exhibits highly active in photocatalytic degradation of various refractory organic pollutants, including organic dyes, phenols, antibiotics, and personal care products, with removal ratios higher than 96% after 2 h operation. This can be due to the gradient-doped N-TiO₂ nanobranches, which not only provide bending band structure and defect level derived from the N impurities and O vacancies, resulting the formation of n-n⁺ heterojunctions to improve the charge separation, but also enhance the charge transfer at the liquid-solid interface due to the numerous nanobranches and amorphous coating layers.     

Decoration of TiO2 nanotube layers with WO3 nanocrystals for high-electrochromic activity

We report a simple approach to decorate ordered TiO₂ nanotube (TiNT) layers with tungsten trioxide nanocrystallites by the controlled hydrolysis of a WCl₆ precursor. These WO₃ nanocrystallites, when formed, are amorphous, but can be annealed to a monoclinic crystal structure. The WO₃ crystallites on the TiO₂ nanotube skeleton are electrochemically active, and hence ion insertion reactions are possible. As a result, the decorated nanotube layers show remarkable enhancement of the electrochromic properties. In particular, a significantly lower threshold voltage and an increased electrochromic contrast can be achieved compared with unloaded (neat) TiO₂ nanotube layers.     

Efficient Decomposition of Organic Pollutants Over In2O3/TiO2 Nanocomposite Photocatalyst Under Visible Light Irradiation

The heterojunction structures of In₂O₃/TiO₂, exhibiting visible light photocatalytic efficiency, has been synthesized by utilizing maleic acid as an organic linker to combine In₂O₃ and Degussa P25 (TiO₂) nanoparticles. The prepared nanocomposite has been characterized by FESEM, TEM, XRD and UV?CVisible reflectance spectra. The photocatalytic efficiency of the composite photocatalyst has been investigated based on the decomposition of 2-propanol (IP) in gas phase and 1,4-dichlorobenzene (DCB) in aqueous phase under visible light (??????420?nm) irradiation. The results reveal that the In₂O₃/TiO₂ composite photocatalyst with 7?wt% In₂O₃ demonstrated 6.3 times of efficiency in evolving CO₂ from gaseous IP and 8.7 times of efficiency in removing aqueous DCB in compare with Degussa P25. In this In₂O₃/TiO₂ composite system, TiO₂ seems to be the principal photocatalyst whereas the function of In₂O₃ is to sensitize TiO₂ by absorbing visible light (??????420?nm). The extraordinary high photocatalytic efficiency of this composite In₂O₃/TiO₂ under visible light has been explained on the basis of relative energy band positions of the component semiconductors.     

TiO2纳米管阵列覆盖Si薄膜光催化还原CO2性能的研究

本工作采用CVD法在阳极氧化TiO2纳米管阵列膜表面沉积一层非晶Si膜,通过退火后得到晶化了的Si膜/TiO2纳米管阵列的复合结构,并初步就其光催化还原CO2制备碳氢化合物的活性进行研究。拉曼光谱(Raman)、X射线衍射(XRD)、场发射扫描电镜(FE-SEM)、高分辨透射电子显微镜(TEM)等微结构表征结果表明所制备的TiO2纳米管阵列的厚度为270 nm左右,管直径约为70 nm,管壁厚度约为16 nm。覆盖的Si膜已晶化,其厚度约为300 nm。通过高效液相色谱(HPLC)及总有机碳(TOC)来检测光催化还原液相产物中的甲酸及总有机碳含量,发现负载Si膜后的TiO2纳米管阵列光催化性能有所提高,在装有400cut滤光片氙灯照射2 h下TOC含量从21.2 mg.L-1增长到29.5 mg.L-1,表明Si与TiO2的复合可有效的提高光催化还原CO2的活性,这可能与该异质结结构可增加对光的吸收并且可降低光生空穴-电子对复合有关。光催化循环实验表明所制得的催化剂在循环5次后仍可保持91.6%的催化活性。     

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.