A review on TiO2 nanotube arrays: Fabrication, properties, and sensing applications

Fabrication, properties, and sensing applications of TiO₂ nanotubes have been reviewed, and the highly ordered TiO₂ nanotube arrays made by anodic oxidation in fluoride-contained electrolytes highlighted. The effect of anodization parameters (electrolyte, pH, and voltage) on the titania nanotube size and shape were discussed. The excellent biocompatibility of TiO₂, the high orientation, the large surface area with tunable pore sizes, as well as the high electron transfer rate along with the nanotubes make TiO₂ nanotube array an ideal substrate for the sensor’s fabrication and application. The sensors based on the TiO₂ nanotube arrays for sensing hydrogen, oxygen, humidity, glucose and hydrogen peroxide all exhibited low detection limit, high stability, very good reproducibility and high sensitivity.     

Preparation of Zn-doped TiO2 nanotubes electrode and its application in pentachlorophenol photoelectrocatalytic degradation

Zn-doped titanium oxide （TiO2） nanotubes electrode was prepared on a titanium plate by direct anodic oxidation and immersing method in sequence. Field emission scanning electron microscopy （FESEM） showed that the Zn-doped TiO2 nanotubes were well aligned and organized into high density uniform arrays with diameter ranging from 50 to 90 nm. The length and the thickness were about 200 and 15 nm respectively. TiO2 anatase phase was identified by X-ray diffraction （XRD）. X-ray photoelectronspectroscopy （XPS） indicated that Zn ions were mainly located on the surface of TiO2 nanotubes in form of ZnO clusters. Compared with TiO2 nanotubes electrode, about 20 nm red shift in the spectrum of UV-vis absorption was observed. The degradation of pentachlorophenol （PCP） in aqueous solution under the same condition （initial concentration of PCP： 20 mg/L; concentration of Na2SO4：0.01 mol/L and pH： 7.03） was carried out using Zn-doped TiO2 nanotubes electrode and TiO2 nanotubes electrode. The degradation rates of PCP using Zn-doped TiO2 nanotubes electrode were found to be twice and 5.8 times as high as that using TiO2 nanotubes electrode by UV radiation （400 μw/cm^2） and visible light radiation （4500 μw/cm^2）, respectively. 73.5% of PCP was removed using Zn-doped TiO2 nanotubes electrode against 45.5% removed using TiO2 nanotubes electrode in 120 min under UV radiation. While under visible light radiation, the degradation efficiency of PCP was 18.4% using Zn-doped TiO2 nanotubes electrode against 3.2% using TiO2 nanotubes electrode in 120 min. The optimum concentration of Zn doping was found to be 0.909%. The PCP degradation efficiencies of the 10 repeated experiments by Zn-doped TiO2 nanotubes electrode were rather stable with the deviation within 3.0%.     

Performances improvement of eosin Y sensitized solar cells by modifying TiO2 electrode with silane-coupling reagent

Chemical fixing of xanthene dye （eosin Y） on the surface of TiO2 electrode was carried out by modifying the electrode with silane-coupling reagent to obtain stable dye-sensitized TiO2 electrode. Such silane modification can not only evidently enhance the stability of dye-sensitized TiO2 electrode but also improve the energy conversion efficiency of the assembled cells by increasing short-circuit photocurrent （Jsc） and open-circuit photovoltage （Voc）. It was found that the improvements of cell performances differ depending on the composition of the electrolyte. The optimum cell of the cell performance was achieved in the electrolyte with 0.5 mol/L TBAI/0.05 mol/L 12/EC：PC（3：1 w/w）, yielding Jsc of 4.69 mA. cm-2, Voc of 0,595 V, fill factor （FF） of 0.64 and ηof 1,78%, Different spectroscopic techniques including UV-Vis spectra, fluorescence spectra, EIS and dark current measurements were employed to derive reasonable analysis and explanations.     

Synthesis and characterization of BiFeO3 nanotube arrays and Y-junction BiFeO3 nanotubes

Multiferroic BiFeO₃ (BFO) nanotube arrays (∼100 nm in diameter and ∼50 μm in length) were synthesized by the sol-gel method utilizing the anodic aluminum oxide (AAO) membrane technique. The microstructure and chemical components of the BFO nanotubes were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectrometer (XPS). The BFO nanotubes exhibited polycrystalline microstructures. The novel Y-junction BFO nanotubes were simultaneously fabricated. Supported by the National Natural Science Foundation of China (Grant No. 90306010), Program for New Century Excellent Talents in University (Grant No. NCET-04-0653) and National Basic Research Program of China (Grant No. 2007CB616911)     

Photovoltaic properties of MEH-PPV/TiO2 nanocomposites

Photovoltaic properties of photodiodes based on nano-TiO2 and poly[2-methoxy,5-（2＇-ethlhexyloxy）-p-phenylenevinylene] （MEH-PPV） composites are investigated. By comparing composite devices with the same weight of TiO2 （nanoparticles and nanotubes）：MEH-PPV, it was found that the device with TiO2 nanotubes exhibited better performance. By further optimizing the weight radio of TiO2 nanotubes： MEH-PPV, we gained the device with a short circuit current density of 9.27μA/cm^2 with a light intensity of 16.7mW/cm^2 at the 500 nm wavelength, the highest open-circuit voltage of 1.1V, and a photosensitivity of 332 at reverse bias of -0.6V. The photosensitivity is improved by a factor of 33 compared with the undoped MEH-PPV device.     

Fabrication of visible-light responsive S-F-codoped TiO<Subscript>2</Subscript> nanotubes

Fabrication and S-F-codoping of TiO2 nanotubes were carried out by a one-step electrochemical anodization process to extend the photoresponse of TiO2 to the visible-light region. The prepared samples were annealed in air and detected by SEM, XRD, XPS and UV-vis DRS spectrophotometer. The results showed that the average tube diameter of the nanotubes was 150 nm and the average tube length was 400 nm. The doped TiO2 nanotubes exhibited strong absorption in visible-light region. Photoelectrocatalytic degradation efficiency of 4-CP over S-F-codoped TiO2 nanotubes was 39.7% higher than that of only-F-doped sample. Moreover, sulfur and fluorine codoped into substitutional sites of TiO2 had been proven to be indispensable for strong response and high photocatalytic activity under visible light, as assessed by XPS.     

Effect of Cl- on photosynthetic bicarbonate uptake in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803

Photosynthetic inorganic carbon utilization was investigated in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803 grown in standing culture. Photosynthetic rates for the two algae reached about 10 times the theoretical CO₂ supply rate at low dissolved inorganic carbon (DIC) of 100 μmol/L, and the rates were unaffected by the addition of 20 mmol/L Na⁺, indicating that the two algae possessed Na+-independent HCO^-₃ utilization for photosynthesis under low DIC. Their photo- synthetic rates at low DIC were inhibited by higher Cl^- and the degrees of inhibition were increased with the rise of CI^- concentration, and in the presence of Diphenylamine-2-carboxylate (DPC), a reported Cl^- channel inhibitor, the rates decreased by 74%－82%, implying that putative DPC-sensitive Cl^- channels participate in Na+-independent HCO₃^- uptake for photosynthesis. The experiment of intracellular 14C-DIC accumulation for photosynthesis showed that internal DIC pools decreased by about 80% with 200 μmol/L DPC and by 64%－70% with 100 mmol/L Cl^-. The experiment of chlorophyll a fluorescence quenching showed that initial rates and extents of fluorescence quenching obviously decreased with 200 μmol/L DPC or 100 mmol/L Cl^-. The two experiments gave further evidence that putative DPC-sen- sitive Cl^- channels participate in Na+-independent HCO^-₃ uptake for photosynthesis in the two algae grown in standing culture.     

Solvothermal synthesis of CdS nanorods and photovoltaic characteristics of CdS/PVK composite system

Large quantities of CdS nanorods are successfully synthesized through Cd（CH3COO）2·2H2o reacting with Na2S·9H2O and EDA in aqueous solution. XRD result shows that the sample is of hexagonal structure. And TEM result shows that the morphologies of the resulting CdS are mainly in three-armed rod-like structure with a diameter of 10--15 nm and a length of 100 nm. The nanocomposites of CdS/PVK with different molar ratios are prepared by spin coating method on tin-doped indium oxide （ITO） substrate. A notable decrease of photoluminescence （PL） efficiency and a significant enhancement of surface photovoltage signal have been observed in CdS/PVK composites when the molar fraction of CdS increases. We interpret these results as the energy level matching between CdS and PVK in nanocomposites. This energy level matching facilitates fast interfacial charge transfer then increases the separation efficiency of electron-hole pairs and the carrier generation efficiency. The detailed charge transfer process has also been demonstrated.     

Effect of TiO2 nanotubes lateral spacing on photovoltaic properties of dye-sensitized solar cells

Vertically aligned TiO2 nanotube arrays （-8 μm long, -110nm wide） have been fabricated through anodic oxidation of Ti-metal sheet in fluoride- containing electrolyte. By changing the volume ratio of ethylene glycol and diethylene glycol in the electrolyte, TiO2 nanotube arrays with different tube-to-tube lateral spacing, i.e., closely packed, just separated, and fully separated, have been synthesized and applied as photoanodes for dye-sensitized solar cells （DSSCs）. Photovoltaic efficiency of 2.99 %, 3.34 %, and 3.44 % has been obtained for DSSCs based on the closely packed, just separated, and fully separated TiO2 nanotube arrays, respectively, illustrating the effect of tube-to-tube lateral spacing of TiO2 nanotube arrays on the performances of DSSCs. It is suggested that fully separated TiO2 nanotube arrays are beneficial to the conversion efficiency of DSSCs due to higher dye loading and faster electron transfer.     

CdS光化学修饰介孔TiO2及其增强的可见光催化活性

[目的]提高介孔TiO₂材料的光催化活性。[方法]采用蒸发诱导自组装法(EISA),以四氯化钛和钛酸丁酯为钛源,嵌段共聚物P123(EO₂₀PO₇₀EO₂₀)为模板剂,制备介孔TiO₂。用光化学修饰法将CdS掺进介孔TiO₂中,合成对可见光有较好响应的复合材料,并利用X射线衍射(XRD)、透射电镜(TEM)、原子吸收分光光度法(AAS)和光催化等手段对样品进行表征。[结果]XRD和TEM结果表明成功合成有序的六方介孔材料;AAS确定复合材料中Cd的含量为0.96mg/g;光催化于500 W氙灯下以2×10^-5mol/L次甲基蓝(MB)为模型污染物,结果显示CdS/TiO₂复合材料的可见光催化活性明显提高。[结论]光化学修饰法制备的介孔CdS/TiO₂复合材料可增强其可见光催化活性。     

TiO2-based building materials: Above and beyond traditional applications

In the 1910s, TiO₂ began to be used in building materials as pigments and opacifier due to its excellent optical property. Since the photocatalytic property of TiO₂ was observed in 1972, its application field was expanded to air cleaning and sterilization. Thereafter, people added TiO₂ into building materials to develop novel and facile building materials. These materials were widely used for air cleaning, sterilization, self-cleaning, anti-fogging, decoration, and building cooling. The combination of building and other functions can serve simultaneously. Although TiO₂-based building materials have bright prospects, some aspects such as improving the stability and enhancing photoactive performance of the materials are of importance for future research. Supported by the National High Technology Research and Development Program (“863” Program) of China (Grant No. 2007AA061402), Chinese Key Technology Research and Development Program of the Eleventh Five-year Plan (Grant No. 2006BAJ02A08), Hangzhou Science & Technology Development Program (Grant No. 20061133B27) and Research Fund for the Doctoral Program of Higher Education (Grant No. 20070335197)     

CdS修饰低密度TiO2纳米棒阵列复合膜的制备及光电性能

为了提高CdS光敏层在TiO₂一维纳米棒阵列中的填充率,在TiO₂种子层的基础上,采用水热法于FTO导电玻璃表面生长了棒长较短、棒间距较大的低密度TiO₂一维纳米棒阵列膜,通过化学浴沉积在TiO₂纳米棒表面包覆CdS种子层,以此为基底采用水热法于TiO₂一维纳米阵列中生长CdS光敏层。采用SEM,XRD及紫外-可见吸收光谱对不同CdS水热生长时间的TiO₂/CdS复合膜结构进行了表征,并对其光电性能进行了研究。结果表明,低密度TiO₂纳米棒阵列有利于CdS生长液在阵列中渗入形成完全包覆的CdS种子层,CdS光敏层通过水热过程在整个TiO₂纳米棒表面均匀生长,逐渐形成CdS对TiO₂纳米棒阵列的完全填充和包覆,并在阵列顶端形成由CdS纳米短棒组成的花状修饰层;CdS的修饰将TiO₂一维纳米阵列膜的光吸收拓展至可见光区,水热生长7 h所得到的TiO₂/CdS复合膜具有最高光电流。所制备的CdS修饰低密度TiO₂纳米棒复合膜在太阳电池器件中具有很好的应用前景。     

Fluorescence and sensitization performance of phenylene-vinylene-substituted polythiophene

A new kind of polythiophene derivative, Poly(3-{2-[4-(2-ethylhexyloxy)-phenyl]-vinyl}-2,2′-bithiophene) (PTh), was applied in dye-sensitized solar cell to extend the light response of nanocrystalline TiO2 electrode. UV-vis absorption and fluorescence spectra were employed to investigate the interaction of PTh with nanocrystalline TiO2. The absorption coefficient of the PTh was high in visible part of spec- trum, and the fluorescence emission of the PTh can be efficiently quenched by TiO2 nanoparticles ow- i...     

硫化镉/石墨烯/TiO_2纳米棒阵列的光电化学性能

采用水热法在掺氟导电玻璃(FTO)上生长TiO_2纳米棒阵列。通过电化学伏安法将氧化石墨烯还原并沉积在TiO_2纳米棒阵列上,再经过化学水浴沉积硫化镉,形成Cd S/石墨烯/TiO_2阵列复合材料。用X射线衍射仪、扫描电子显微镜及X射线能量色散仪对样品的晶型、形貌以及成分进行分析。通过电化学工作站表征样品交流阻抗、开路电位、光电流响应及光化学能转换效率。结果表明,复合材料的电荷转移电阻约是未修饰的TiO_2纳米棒阵列的1/17,光电流比未修饰的TiO_2纳米棒阵列提高约2.5倍,在外加电压为-0.6 V时可达到2.2%。     

The comparison of Cu（ll） adsorption capability of baker＇s yeast,nano-titania and their composite adsorbent

The anatase nano-TiO2 powder, with crystal size between 40 and 80 nm, was prepared by the liquid phase hydrolysis of TiCI4. At the same time, the nano-TiO2 was utilized with the baker＇s yeast biomass as a composite adsorbent to adsorb the Cu ions in the artificial aqueous solution. The investigation showed that the composite adsorbent had a fine adsorption efficiency. The TiO2 in the composite adsorbent could cooperate well with baker＇s yeast to improve the adsorbing capability of Cu^2＋ under the following experimental conditions as well： a quantity of composite adsorbent of 5 g·L^-1, pH≥4.0, an adsorption time of 40 min and an initial concentration of Cu ions of 10 mg·L^-1. In addition, the results of measurements, obtained with a scanning electron microscope, an infrared spectrophotometer and a Zeta potential analyzer, revealed that the baker＇s yeast and nano-TiO2 produced the composite adsorbent through coordination and hydrogen bonds in particular, etc. The stability of the composite adsorbent and the amount of titania loaded were largely dependent on the concentration of hydrogen ion in the solution.     

Direct electrochemistry and electrocatalysis of horseradish peroxidase in MnO2 nanosheet film

A novel material MnO2 nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase （HRP）. HRP entrapped in MnO2 nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s^-1. The HRP/MnO2 nanosheet film gives a reversible redox couple with the apparent formal peak potential （E^0＇） of -0.315 V （vs. Ag/AgCl） in pH 6.5 phosphate buffer solution （PBS）. The formal potential E^0＇ of HRP shifts linearly with pH with a slope of -53.75 mV.pH^-1, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatslytic activity to the reduction of H2O2. The response time of the biosensor for H2O2 is less than 3 s, and the detection limit is 0.21 μmol · L^-1 based on signal/noise = 3.     

Effect of Nano red elemental selenium on GPx activity of broiler chick kidney cells<Emphasis Type="Italic">in vitro</Emphasis>

A new selenium source, Nano red elemental selenium (Nano-Se) was used to study the effect on the GPx activity of broiler chick kidney cells (BCKC)in vitro, Sodium selenite (Na₂SeO₃) and seleno-1-methionine (Se-Met) were used as the controls. The results showed that the effects of three kinds of Se forms on the GPx activity of BCKC were accordant (p>0.05) compared with each other at 0.01. 0.05 and 0.10 μmol/L Se concentrations treatments. In the range of 0.00–0.10 μmol/L Se concentrations, the GPx activity increased with elevation of Se concentrations in medium. For the three kinds of Se forms, the GPx activity reached the climax at 0.10 μmol/L Se concentration. At 0.20 and 0.30 μmol/L Se concentrations, the influnces of three kinds of Se forms were not accordant with one another. For Nano-Se, the GPx activity at 0.20 and 0.30 μmoi/L Se concentrations remained the same as that at 0.10 μmol/L Se concentration treatment. For Se-Met, the GPx activity at 0.20 μmol/L Se concentration treatment remained the same with 0.10 μmol/L treatment; the GPx activity at 0.30 μmol/L Se concentration treatment was declined significantly (p<0.05) compared with 0.10 or 0.20 μmol/L treatment. For Na₂SeO₃, the GPx activity falled gradually with Se concentration increasing from 0.10 μmol/L to 0.30 μmol/L, and at 0.30 μmol/L Se concentration treatment, the GPx activity was less than the original of BCKC. The results implicated, on the GPx activity of BCKCin vitro, the ranking of width range of the most suitable Se concentration for nutrition curve of the three Se formes is Nano-Se>Se-Met>Na₂SeO₃. Foundation item: Supported by the Key Item of the Science and Technology Bureau of Zhejiang Province (021122680) Biography: Xu Bao-hua (1966-), male, Associate professor, Ph. D. research direction: nanobiology and animal nutrition.     

Fabrication and structural characterization of large-scale uniform SnO<Subscript>2</Subscript> nanotube arrays by sol-gel method

Semiconductor SnO2 nanotube arrays were fabricated by sol-gel method based on highly ordered nanoporous anodic alumina membrane. Their microstructures were characterized by scanning electron microscopy,transmission electron microscopy, selective electron diffraction spectroscopy and X-ray diffraction. Results indicated that SnO2 nanotubes have a thickness of about 20-30 nm,and a diameter of about 100-200 nm. The length of the nanotubes is about 1 μn, XRD and SEDS indicated that these SnO2 nanotubes are polycrystalline.     

A novel advanced oxidation process――wet electro-catalytic oxidation for high concentrated organic wastewater treatment

A novel advanced oxidation process——wet electrocatalytic oxidation (WEO) was studied with p-nitrophenol as model pollutant and β-PbO2 electrode as the anode. Compared with the effect of the individual wet air oxidation (WAO) and electrochemical oxidation (EO), the effect of WEO showed syn- ergistic effect on COD removal under the conditions of temperature 160℃, C=1000 mg·L-1, PN2=0.50 MPa, PO2=0.9 MPa, current density = 3 mA·cm-2, Na2SO4 3 g·L-1. And the synergistic factor got the best value of 0.98 within 120 min after 180 min treatment. The synergistic factor was studied after 120 min treatment at 100℃, 120℃, 140℃ and 160℃, and the effect of 120℃ was the best with the value of 1.26. Possible mechanism for the synergistic effect was discussed based on the analysis of free-radical generation and intermediates detected by HPLC and GC/MS.     

碳纳米管/纳米TiO2-聚苯胺复合膜电极的电化学制备及表征

在含有0.2 mol/L苯胺的0.5 mol/L　H₂SO₄溶液中， 采用循环伏安法(CV)， 以扫描速度50 mV/s, 扫描电位-0.1~0.9 V，在碳纳米管/纳米TiO₂(CNT/nanoTiO₂)膜电极上实现了苯胺的电化学聚合， 用电化学阻抗谱（EIS）和CV法对制备的碳纳米管/纳米TiO₂聚苯胺(CNT/nanoTiO₂ PAn)复合膜电极的电化学性质进行了表征， 从扫描电镜对膜层的微观形貌观察发现， 这种在纳米基体上聚合得到的聚苯胺膜层呈疏松、 多孔的纳米纤维网状结构， 同时具有良好的导电性， 不同于在普通金属基体上聚合得到的颗粒状聚苯胺膜.