二氧化钛纳米管的研究进展

二氧化钛纳米管由于其新奇的光电、催化、气敏等性能引起了广泛的关注,在太阳能电池、光催化、环境净化、气体传感器等领域有潜在的应用价值.本文概述了近年来在制备方法、反应机理和组成、晶型和形貌及掺杂和应用方面的进展,并讨论了今后可能的研究发展方向.     

Catalysis by Using TiO2 Nanoparticles and Nanotubes

TiO2 has attracted considerable attention due to its stability, non-toxicity, low cost, and great potential for use as a photocatalyst in environmental applications. Since strong metal-support interaction (SMSI) of titania-supported noble metals was first reported in 1978, titania supported catalyst has been intensively studied in heterogeneous catalysis. However, the effective catalytic activity was restricted due to the low surface area of TiO2. Recently, TiO2-based nanotubes were extensively investigated because of their potentials in many areas such as highly efficient photocatalysis and hydrogen sensor.In the present study, formation of titanium oxide (TiO2) nanotubes was carried out by hydrothermal method, with TiO2 nanoparticle-powders immersed in concentrated NaOH solution in an autoclave at 110 ℃. Preparation of nano-size Pt on TiO2-nanoparticles or TiO2-nanotubes was performed by photochemical deposition method with UV irradiation on an aqueous solution containing TiO2 and hexachloroplatinic acid or tetrachloroauric acid. The TEM micrographs show that TiO2-nanotubes exhibit ～300 nm in length with an inner diameter of ～ 6 nm and the wall thickness of ～ 2 nm, and homogeneous nanosize Pt particles (～ 2 nm) were well-dispersed on both nanoparticle- and nanotube- titania supports. It also shows the nanotube morphology was retained up2o n Pt-immobilization. Nitrogen adsorption isotherm at 77K resulted a high surface area (～ 200m/g) of TiO2-nanotubes, which is about 40 times greater than that of "mother" TiO2 nanoparticles (～5 m/g). All the spectroscopic results exhibited that the nanotube structure was not significantly affected by the immobilized Pt particles. Ti K-edge XANES spectra of TiO2 nanotube and Pt/TiO2-nanotube represent that most titanium are in a tetrahedral coordination with few retained in the octahedral structure.In the in-situ FT-IR experiments, an IR cell was evacuated to a pressure of 10-5 torr at room temperature as soon as the catalyst-pellet, Pt/TiO2 or Pt/TiO2-nanotube, was placed inside the cell.Then, 60 torr of hydrogen was introduced into the cell and subsequently the temperature was programmed to increase from room temperature to 300℃ at a constant heating rate of 5℃/min.For Pt/TiO2, an IR peak at 2083 em-1 started to appear at 200℃ with a maximum intensity at 250℃ and then decreasing as temperature increased. The 2083 em-1 IR peak corresponds to the linearly adsorption of CO on the well-dispersed Pt sites. Simultaneously, the IR bands of gaseous methane at 3016 em-1 started to appear at 225℃ and the peak intensity increased with temperature. The results reveal that Pt/TiO2 can adsorb gaseous CO2 and further catalyzes the reduction of CO2 by H2 through the intermediate CO, which further produces gaseous methane. While for the Pt/TiO2-nanotube catalyst, methane was produced at relatively low temperature, 100℃, and it catalyzed the direct conversion of CO2 to CH4. The absence of intermediate CO-adsorption signals durinng the temperature programmed process indicates that the prepared TiO2 nanotube-supported nanosize Pt possesses a potent capability for CO2 adsorption and highly catalytic activity in the hydrogenation of CO2, and was superior to the conventional Pt/TiO2 catalyst. The catalytic activity of Pt/TiO2-nanotube was indeed significantly enhanced by the high surface area of TiO2-nanotubes.Details will be discussed.     

TEM Study on the Formation Process of TiO2 Nanotubes

The process,that the polycrystalline TiO2 powders were converted into TiO2 nanotubes,was observed with transmission electron microscope.The results obtained indicated that in concentrated NaOH aqueous solution,anisotroplc swelling appears on the polycrystalline TiO2 granula at first,and then the nanotubes are formed.     

碳掺杂的二氧化钛纳米管的制备及其可见光催化性能

以尿素作为碳元素前驱体对TiO2纳米管进行掺杂,采用比表面积测定、X射线衍射、透射电子显微镜、能量色散X射线荧光光谱、X射线光电子能谱、固体漫反射紫外-可见吸收光谱和荧光光谱对产物进行了表征。 结果表明,以尿素作为前驱体可制备C掺杂的TiO2纳米管,C掺杂后,TiO2纳米管的可见光催化活性明显提高。 此外,研究了C掺杂量、煅烧温度、催化剂用量和pH值对TiO2纳米管光催化降解活性的影响,发现当C的掺杂量为5.3%、催化剂用量为1.5 g/L、溶液的pH值为5时,在其催化作用下,可见光光照3 h后罗丹明B的降解率可达到91%。     

TiO2纳米管电极金属离子掺杂的表征

采用浸渍法对TiO₂纳米管电极进行Zn²⁺、Fe³⁺、Cu²⁺离子的掺杂改性,并进行了各种性能表征.扫描电镜(SEM)及X射线衍射光谱(XRD)结果表明,金属离子掺杂后的TiO₂纳米管电极依然保持了良好的表面形态及锐钛矿晶型,纳米管的直径为60-100 nm,其晶面主要为101面;可见紫外漫反射光谱(DRS)分析表明,进行掺杂的TiO₂纳米管电极的光学性质有不同程度的改变,Zn²⁺、Fe³⁺和Cu²⁺掺杂的TiO₂纳米管电极的禁带宽度分别为3.37 eV3、.14 eV、2.86 eV.这表明掺Cu²⁺的TiO₂纳米管电极的吸收边带发生了明显的红移.     

Free‐Standing Membranes to Study the Optical Properties of Anodic TiO2 Nanotube Layers

In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO₂ nanotube layers directly transferred as self‐standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thickness varying from 1.8 to 50 μm, and the layers were investigated in their amorphous and crystalline forms. A series of wavelength‐dependent light attenuation coefficients are extrapolated and found to match the photocurrent versus irradiation wavelength behavior. A feature specific to anodic nanotubes is that their intrinsic carbon contamination content causes a proportional sub‐bandgap response. Overall, the extracted data provide a valuable basis and understanding for the design of photo‐electrochemical devices based on TiO₂ nanotubes.     

纳米二氧化钛/碳纳米管复合催化剂光催化性能及碳纳米管组分的作用

运用溶胶-凝胶及低温水热法合成纳米TiO₂/碳纳米管复合催化剂, 以甲基橙为目标降解物考察复合物的光催化活性. 运用X光衍射、透射电镜、Brunauer-Emmett-Teller低温氮气吸附、差热-热重分析及紫外-可见漫反射吸收光谱等表征催化剂. 结果表明, 与单纯纳米TiO₂相比, 溶胶-凝胶法制备的复合催化剂的光催化活性显著提高, 实验条件下复合的碳纳米管最适含量为3%(碳纳米管/TiO₂, 重量百分比), 复合催化剂经在缓和氧化气氛中焙烧处理可在保持碳纳米管热稳定前提下获得纳米TiO₂的充分晶化. 观察到了低温水热合成的复合催化剂的甲基橙降解活性的进一步提升, 复合催化剂中纳米TiO₂在碳纳米管表面分散均匀, TiO₂和碳纳米管组分间的紧密和充分键合及低温水热条件下催化剂的大比表面积、超细粒径以及碳纳米管的热稳定等有利于复合催化剂的光催化活性. 进一步地, 探讨了复合催化剂中适量碳纳米管组分的光活性促活机制.     

Direct Electrochemistry of Hemoglobin on Vertically Aligned Carbon Hybrid TiO2 Nanotubes and Its Highly Sensitive Biosensor Performance

The present work is focused on developing a novel biomaterial platform to achieve enhanced direct electron transfer (DET) of hemoprotein and higher biosensor performance on vertically aligned carbon hybrid TiO₂ nanotubes (C‐TiO₂ NTs). Using a simple surfactant‐assisted method, controllable hybridization of TiO₂ NTs with conductive amorphous carbon species is realized. The obtained C‐TiO₂ NTs is ingeniously chosen to serve as an ideal "vessel" for protein immobilization and biosensor applications. Results show that the appropriate hybridization of C into TiO₂ NTs leads to a much better conductivity of TiO₂ NTs without destroying their preponderant tubular structures or damaging their excellent biocompatibility and hydrophilicity. When used in loading proteins, the C‐TiO₂ NTs can be used as a super vessel for rapid and substantive immobilization of hemoglobin (Hb), with a large surface electroactive Hb coverage ( Γ ??) of 3.3×10^?9 mol·cm^?2. Enhanced DET of Hb is commendably observed on the constructed Hb/C‐TiO₂ NTs biosensor with a couple of well‐defined redox peaks in a fast electron transfer process. The biosensor further exhibits fast response, high sensitivity and stability for the amperometric biosensing of H₂O₂ with the detection limit as low as 3.1×10^?8 mol/L.     

Preparation of High-Orderly TiO2 Nanotubes in Organic Solution and Characterization of C-doped TiO2

"High-orderly TiO2 nanotube arrays were fabricated by anodic oxidation of pure titanium substrate in organic electrolyte containing fluoride. Different morphological nanotubes of titania were obtained through controlling the different anodization voltages and durations. The length of the longest nanotubes was approximately 60 1m and the length-to-width aspect ratio was about 600. The nanotube layers were then annealed at different temperatures (450, 550, and 650 oC) in air for 2 h. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD), energy dispersive X-Ray (EDS) and UV-Vis spectrometer. The XRD results demonstrated that the as-anodized samples were amorphous and the structure changed to antanse and rutile when the samples were annealed at higher temperature. The EDS microanalysis indicated the presence of carbon in the TiO2 nanotubes. The result of degradation of methylene blue showed clearly that the photocatalytic activity of C-doped TiO2 nanotubes increased by 10%."     

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.     

TiO2纳米管的光催化作用

光催化降解;十二烷基苯磺酸钠;紫外可见光谱;TiO2纳米管的光催化作用     

STS study of TiO2 film and Pt-deposited TiO2 film in air

Direct investigation of the electronic structure of catalyst surfaces on the near-atomic scale in general has not been impossible in the past. However, with the advent of the scanning tunneling microscope (STM), the opportunity arises for incorporating the scanning tunneling spectroscopy (STS) for correlation in-situ surface electronic structure with topography on a sub-nanometer scale. In this paper, we report the STS results of thin film TiO2 and Pt-deposited TiO2 annealed at 450℃. It was found that the TiO2 semiconductor changes from n-type to p-type after Pt deposition.Fig. 1 shows the surface electronic property (Ⅰ-Ⅴ curve) of thin TiO2 film measured in air by STS. A steep descent of the anodic tunneling current at ca.- 1.0 Ⅴ and a rapid ascent of cathodic tunneling current at ca. +2.0V. The zero bias represents the Fermi level (Ef). Ef is situated at the Ecb side indicating that the thin TiO2 film possesses the same band gap as that of bulk TiO2 phase ( Egs =3.0 to 3.2 eV). For the sample of Pt-deposited TiO2 film, Pt/(Pt+Ti+O) atomic ratio≈0.2, which indicates that the surface of TiO2 film is partly covered by Pt particles, and there are two types of Ⅰ-Ⅴ curves to be detected. One of them (Fig.2a)is attributed to the electronic property of TiO2, which has same Egs as that shown in Fig. 1. However, the Ef is transferred to valence side (△≈1eV). This phenomenon hints that TiO2 is doped by an impurity which can introduce h+ into TiO2 lattice.Such a type of defects may be described by Ti1-xPtxO2(h )2x, here Pt+2 as a substitutional site of Ti+4. Fig.2b is the Ⅰ-Ⅴ curve of a Pt particle situated on a TiO2 particle contained Ti1-xPtxO2(h )2x.     

TiO2与碳纳米管的复合及光催化协同作用*

TiO₂与碳纳米管均是近15年来最受关注的功能材料。将TiO₂与碳纳米管复合构建的TiO₂/碳纳米管兼有两种材料的特点及优点,在许多领域得到广泛研究。本文基于国内外最新研究进展,系统综述了近年来逐步建立起来的制备TiO₂/碳纳米管的方法,着重介绍了混合法、化学气相沉积法、静电纺丝法、溶胶-凝胶法、水热溶剂热法等几种比较主要的方法。并且以TiO₂ /碳纳米管在光催化领域的应用研究为侧重点,详细分析了碳纳米管在促进TiO₂光生电子-空穴分离、增强可见光吸收等方面的协同作用。文章最后指出相关研究中有待解决的问题,并对此类材料的发展趋势做了展望。     

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes

Attaching π-conjugated molecules onto TiO₂ can form surface complexes that could capture visible light. However, to make these TiO₂ surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (−SO₃⁻Na⁺). The DHNS−TiO₂ showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS−TiO₂ photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O₂ by cooperative photocatalysis of DHNS−TiO₂ with 4-amino-TEMPO. Notably, superoxide (O₂^•−) is crucial in coupling the photocatalytic cycle of DHNS−TiO₂ and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.     

Single‐Walled TiO2 Nanotubes: Enhanced Carrier‐Transport Properties by TiCl4 Treatment

In the present work we report significant enhancement of the photoelectrochemical properties of self‐ organized TiO₂ nanotubes by a combined “de‐coring” of classic nanotubes followed by an appropiate TiCl4 treatment. We show that, except for the expected particle decoration, a key effect of the TiCl4 treatment is that the electron transport characteristics in TiO₂ nanotubes can be drastically improved, for example, we observe an enhancement of up to 70 % in electron‐transport times.     

ATO包覆TiO2的导电性能研究

采用化学共沉淀法制备了Sb掺杂SnO_2包覆TiO_2的微纳米导电粉体。考察了不同Sb量对粉体的导电性能影响,通过XRD、SEM对粉体进行了表征。将导电粉体制成复合电极片,利用电化学工作站对其进行循环伏安和交流阻抗分析。结果表明,随着扫描速率的增加,氧化峰和还原峰分别向阴极和阳极移动,而且氧化还原峰的形状没有随着扫描速率的增加发生明显的变化;当m(SnCl_4·5H_2O)/m(SbCl_3)=10∶1时,容抗弧半径最小,且斜率最大,电阻最小,导电性最好。此结果与用电阻率测定仪测得电阻率的结果一致,说明利用交流阻抗法和循环伏安法考察导电粉体的导电性是可行的。     

TiO2 Nanotubes: Nitrogen‐Ion Implantation at Low Dose Provides Noble‐Metal‐Free Photocatalytic H2‐Evolution Activity

Low‐dose nitrogen implantation induces an ion and damage profile in TiO₂ nanotubes that leads to “co‐catalytic” activity for photocatalytic H₂‐evolution (without the use of any noble metal). Ion implantation with adequate parameters creates this active zone limited to the top part of the tubes. The coupling of this top layer and the underlying non‐implanted part of the nanotubes additionally contributes to an efficient carrier separation and thus to a significantly enhanced H₂ generation.     

Antimony Doped Tin Oxide Nanoparticles Deposited onto Nb−TiO2 Nanotubes for Electrochemical Degradation of Bio‐refractory Pollutions

To improve the service life of SnO₂?Sb electrodes in degradation of refractory wastewater, we report anodic information of tin oxide antimony on top of Nb?TiO₂ nanotubes (Nb?Ti/Nb?TiO₂?NTs/ATONPs) prepared through screen‐printing. It was found that the Nb?Ti/Nb?TiO₂?NTs/ATONPs anodes presented a significantly enhanced in electro‐catalytic oxidation performance (in Acid Red 73) compared to titanium‐based tin antimony electrodes (Ti/ATONPs). Additionally, the electrochemical properties and the stability were further studied by the electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA) measurements and accelerated life test, respectively. These results indicated that Nb?TiO₂?NTs/ATONPs anode possessed Nb?TiO₂ nanotubes which exhibited a higher oxygen evolution potential (2.24 V vs. Ag/AgCl), as well as a better wettability, a larger current at constant potential and 2.1 times longer lifetime than the conventional Ti/ATONPs anode.