Pulsed laser deposition of titania on rutile nanorod arrays

Oriented rutile nanorod arrays are precipitated on metallic Ti plates from a precursor derived by interactions between Ti and aqueous hydrogen peroxide. Pulsed laser deposition (PLD) is then carried out to deposit titania on the nanorod arrays, in comparison with bare Ti substrates, utilizing a high-temperature sintered rutile target in oxygen atmosphere. It is found that dense and homogeneous titania thin films are obtained on Ti substrates; while growth on the rutile nanorod arrays is epitaxial, resulting in enlarged nanorods conformally covered with titania. Titania grown on both Ti substrates and rutile nanorod arrays is either pure rutile or a mixture of anatase and rutile, with the formation of anatase favored by an increasing oxygen pressure during the PLD procedure. The surface roughness and the particle size of the dense titania films on Ti substrates increase as a result of increasing oxygen pressure and prolonged deposition time. The PLD-induced epitaxial growth of titania is inhibited by increasing substrate temperatures. The photocatalytic experiments reveal a significantly enhanced activity for the rutile nanorod arrays after a subsequent PLD treatment.     

Study on photocatalysis of TiO 2 nanotubes prepared by methanol-thermal synthesis at low temperature

TiO₂ nanotubes were synthesized by the solvothermal process at low temperature in a highly alkaline water–methanol mixed solution. Their characteristics were identified by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), specific surface area (BET), Fourier transform infrared spectroscopy (FTIR) and UV–Vis absorption spectroscopy. The as-prepared samples were tested by the photodegradation reaction of methylene blue (MB) dye under visible-light irradiation. The ratios of methanol and water, as well as calcination temperature, affected the morphology, nanostructure and photocatalytic performance. The methanol solvent plays an important role in improving crystallization of the anatase phase, which affects the photocatalytic reaction. Titanate nanotubes were synthesized in methanol–water volume ratios of 10:90, 20:80 and 30:70 which still had high absorbability. Titania nanotubes formed at a calcination temperature of 300 °C using methanol–water volume ratio of 30:70 showed highest photocatalytic performance, much higher than that using water solvent and TiO₂–P25 powder.     

制备条件对TiO2纳米管晶型影响研究

用不同TiO2作原料,在一般水热法和微波法条件下,制备TiO2纳米管,通过TEM、XRD等表征手段,研究了影响合成TiO2纳米管晶型的因素,提出了影响纳米管晶型结构的机理.结果表明,利用不同的原料在一定制备条件下可制得单一晶型的TiO2纳米管.     

Structural engineering of thin films of vertically aligned TiO2 nanorods

Self-assembled and vertically aligned rutile titania nanorods and thin films with a preferred [002] axial orientation were grown on substrates of fluorine-doped tin dioxide, using a hydrothermal method. Each nanorod was made of a bundle of densely packed and ultra fine nano-fibers growing along the [002] direction. The results show that ethanol substitution of water as solvent is highly effective in promoting the one-dimensional growth of the rutile nanorods and increasing their packing density in the thin films, which offers a simple-but-effectual leverage to monitor the nanorod structures for varied applications.     

Comparative in vitro cytotoxicity study of carbon nanotubes and titania nanostructures on human lung epithelial cells

The aim of this study is to assess in vitro cytotoxic effects of titania nanostructures and carbon nanotubes (CNTs) by exposing A549 lung epithelial cell line to these materials. Titania nanotubes (TiNTs) were grown by hydrothermal treatment of TiO(2) nanoparticles, followed by annealing them at 400°C. The titania nanostructures obtained on annealing (mixture of nanotubes and nanorods) were hollow and open ended, containing 3-5 layers of titania sheets, with an internal diameter ～3-5 nm and external diameter ～8-10 nm, and a specific surface area of 265 m(2)/g. As-supplied single walled (SWCNTs) and microwave plasma enhanced chemical vapour deposition (MPCVD) grown multi walled carbon nanotubes (MWCNTs) were used in this study. The lengths and diameters of the SWCNTs were 5-10nm and 0.5-3 nm respectively. The lengths and diameters of the MWCNTs were 25-30 μm and 10-30 nm respectively. The cell viability was evaluated using the MTT (3-(4,-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium) assay. No significant cytotoxic effects of titania nanostructures were observed over a period of a week of testing time, while the presence of CNTs in some cases demonstrated significant cytotoxic effects. Finally, possible reason of cytotoxicity is discussed in the light of microstructures of materials.     

Influence of copper on the microstructure of sol–gel titanium oxide nanotubes array

The effect of copper addition in the microstructure of sol–gel titanium oxide (TiO₂) supported on anodic aluminum oxide (AAO) membranes is reported. Two deposition methods based on immersion and flow techniques were used for the coating of the porous AAO membrane. Copper-free membranes were studied as a function of different ratios of H⁺/Ti, H₂O/Ti, selecting the most appropriate for the sensitization with copper. For copper-doped TiO₂ arrays, the presence of copper causes the reduction of grain size and enhances titania deposition inside the AAO pores, although no clear tendency with copper content was found. The formation of copper-doped titania nanotubes was validated after dissolving the AAO membranes, finding a deposition-dependent stability in the Cu-doped materials. Titania and Cu-doped titania nanotubes analyzed as colloidal solutions show band gaps substantially shifted to the red in comparison to the direct band gap of near-spherical colloidal materials. These arrays are important for photocatalysis and for the development of third generation photovoltaic devices.     

射频磁控共溅射制备光催化Ag-TiO2薄膜

采用射频磁控共溅射法制备Ag-TiO2复合薄膜,通过控制Ag靶的溅射时间可调节Ag与TiO2的比例.所制备的Ag-TiO2薄膜为锐钛矿结构.通过紫外光照降解亚甲基蓝溶液和循环伏安法研究Ag-TiO2薄膜光催化及光电化学特性.实验结果表明:掺1.5% Ag的Ag-TiO2薄膜在紫外光照射下能增强亚甲基蓝溶液的降解并得到更大的光生电流.这种光催化的增强主要是由于光生电子-空穴对的复合被抑制的结果.     

Combination of photocatalytic and antibacterial effects of silver oxide loaded on titania nanotubes

Silver nanoparticles were photodeposited on titania nanotubes and their antibacterial activity was tested. Investigation of the structure and morphology of the nanostructures showed nanometer size silver oxide particles homogeneously distributed on titania nanotubes. Furthermore the modified titania nanotubes were spin-coated as thin films and their antibacterial activity was examined under visible light irradiation and in complete darkness. Although silver oxide loaded titania nanotubes (TiNT-AgO) has a potential for antibacterial activity in both conditions with and without light irradiation, enhanced activity was observed in visible light irradiation condition.     

高长径比TiO_2纳米管的制备及表征

用钛粉为原料,在强碱性条件下,用简单的水热方法制备出了大量高长径比的TiO2纳米管。讨论了对前驱物钛粉进行热处理对TiO2纳米管结构的影响。在热处理温度为800℃的条件下制备出了外径约为10nm,内径约为5nm,平均长度为3μm的TiO2纳米管。用扫描电子显微镜、X-射线衍射,透射电镜分别表征了TiO2纳米管的微观形貌,成分与结构。     

Photochemical performance and electrochemical capacitance of titania nanocomplexes

Titania nanocomplexes, comprising the disordered nanoribbons or nanowires on the top surface and highly ordered nanotube array on the underlaying layer, has been fabricated by longitudinally splitting off nanotubes in a controlled anodization process. Anatase titania nanocomplexes show higher photovoltage and photocurrent responses and photocatalysis activity than titania nanotube array due to the enhanced light harvesting caused by nanoribbons and nanowires. Furthermore, titania nanowire-nanotube demonstrates a higher photoelectrical performance than nanoribbon-nanotube due to its thicker space charge layer caused by long nanotubes and more effective surface area contributed by nanowires. Cyclic charge-discharge measurements show that titania nanotube array exhibits a much higher electric double layer capacitance than titania nanocomplexes because the surface nanoribbons or nanowires inhibit the free diffusion and transportation of electrolyte ions into the underlaying nanotubes. Therefore, titania nanocomplexes can act as a photoactive material for photocatalysis applications and titania nanotube array can act as an electrode substrate for electrochemical supercapacitor applications.     

Effects of mineral tourmaline particles on the photocatalytic activity of TiO2 thin films

Titania composite thin films (T/TiO2) containing tourmaline particles were prepared by a sol-gel method, using alkoxide solutions as precursor. The tourmaline particles and thin films were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and so on. The effects of tourmaline on the photocatalytic activity of TiO2 were measured with methyl orange as an objective photodegradation substance. The results showed that the photocatalytic degradation of methyl orange conformed to the first-order kinetic equation and the composite thin films had better photocatalytic activity due to the cooperation of polarity and the far infrared emission of tourmaline. The T/TiO2 thin films including 0.5 wt% tourmaline exhibited better photocatalytic activity when heat-treated at 250 degrees C for 3 h, than pure TiO2 thin films under the ultraviolet irradiation.     

原位合成TiO2纳米管阵列及其光催化性能研究

采用液相沉积法(LPD), 以阳极氧化铝(AAO)为模板, 原位合成高度有序的TiO₂纳米管薄膜材料. 实验结果表明, 经过400℃热处理后, 制备的TiO₂纳米管为锐钛矿相, 长度达5μm, 管外径为150nm左右, 管壁厚为25nm左右. 热处理后的TiO₂薄膜具有良好的光催化降解甲基蓝的性能, 即经过120min卤灯照射后, 甲基蓝被完全降解.     

Porous Titania Thin Films Grown by Anodic Oxidation for Hydrogen Sensors

Porous titanium dioxide (Titania) thin films were grown by anodic oxidation using high purity (99.7%) titanium foil in a dilute sulphuric acid (1 M) medium. The anodization process was carried out for 30 minutes with 20 mA/cm² and 50 mA/cm² current densities. The samples were characterized by XRD, SEM, and AFM techniques. It was found that the grown porous titania films were less sensitive to 500 ppm hydrogen in air ambient below 300°C; however, the sensitivity and response behavior of the film at 300°C are very much dependent on the growth conditions. Particularly, the films grown at current density 50 mA/cm² and 1 M acid concentration exhibited the lowest response time of 151 sec at 300°C.     

Preparation of regularly structured nanotubular TiO2 thin films on ITO and their modification with thin ALD-grown layers

Nanotubular titanium dioxide thin films were prepared by anodization of titanium metal films evaporated on indium tin oxide (ITO) coated glass. A facile method to enhance the adhesion of the titanium film to the ITO glass was developed. An optimum thickness of 550 nm for the evaporated titanium was found to keep the film adhered to ITO during the anodization. The films were further modified by growing amorphous titania, alumina and tantala thin films conformally in the nanotubes by atomic layer deposition (ALD). The optical, electrical and physical properties of the different structures were compared. It was shown that even 5 nm thin layers can modify the properties of the nanotubular titanium dioxide films.     

Strain analysis of photocatalytic TiO2 thin films on polymer substrates

Titania (TiO₂) thin films have been deposited on polymer sheets by magnetron sputtering at room temperature. Previous X-ray diffraction experiments revealed, for a wide range of deposition parameters, that the as-deposited titania thin films are predominantly amorphous; however, Raman scattering experiments revealed small traces of crystalline phases. The photocatalytic behaviour of the titania coatings was determined by combined ultra-violet (UV) irradiation and absorption measurements of a chosen dye (pollutants) in the presence of this catalyst. In order to assess the mechanical behaviour of the as-sputtered films, the film/substrate composite system was loaded unidirectionally using a tensile testing machine. As the system was stretched, cracks transverse to the loading direction developed in the film. The number of cracks increased as the applied strain increased, thus the relation between the measured crack density and the applied strain has been used to characterize the film strength and has also been correlated with the film photocatalytic efficiency. As a result of moderate fissuring on the titania film, it was found that for strain deformations up to 5% the photocatalytic activity is enhanced due to the exposure of more catalyst surface area for the pollutant to be adsorbed and subsequently dissociated upon UV illumination.     

Shifting mechanisms in the initial stage of dye photodegradation by hollow TiO2 nanospheres

Hollow TiO₂ (HT) sphere aggregates were prepared using carbon spheres as templates. The photocatalytic activity of HT was determined by degradation of two nitrogen-containing dyes, methylene blue (MB) and methyl orange (MO). The adsorption isotherms and the photocatalytic degradation kinetics of the two dyes were studied and compared using different concentrations of dyes for the pure, isopropanol-added, and KI-added systems. Isopropanol was used as a OH^? radical scavenger, while KI was added as a valance band hole scavenger. The results showed that the reaction mechanism of the photocatalytic process of MB was first governed by OH^? radicals, and then by valence band holes, whereas holes played a major role in the whole photodegradation process of MO. The photocatalytic adsorption constant K _V has a positive correlation with the reaction constant k _ov in all systems. The photodegradation efficiencies of the dyes were discussed considering the surface characteristics of HT and the structure of the dyes with different catalyst loads (0.25–2 g L^?1) and under different pH (3–10) conditions. Compared with solid TiO₂, HT exhibited enhanced performance in photocatalytic degradation of both MB and MO.     

Synthesis of mesoporous titania thin films by a simple route at low-temperature via plasma treatment

A new combination of techniques named evaporation-induced self-assembly–plasma etching (EISA–PE) method for mesoporous titania thin films preparation has been developed. The main advantage of this method is that the organic templates can be removed by plasma etching method thus the inorganic frameworks shrinkage or collapse induced by calcination can be avoided. Titania films prepared by this method have been characterized by Fourier transform infrared spectroscopy, thermogravimetric analyses, small and wide-angle X-ray diffraction, and field emission scanning electron microscope. The results show that titania thin film with well-resolved mesostructure can be created by EISA–PE method. The results also prove that plasma parameters have a great influence on the mesoporous property of the film and it is a good kind of catalyst support for methanol catalytic combustion.     

Detection of phosphopeptides by localized surface plasma resonance of titania-coated gold nanoparticles immobilized on glass substrates

We herein demonstrate a new sensing method for phosphopeptides by localized surface plasmon resonance (LSPR) using titania-coated gold nanoparticles immobilized on the surface of a glass slide as the sensing substrate and using UV-visible spectrophotometry as the detection tool. Titania has been known to be an effective substrate for binding with phosphorylated species. The detection principle is the shift of wavelength of optical absorption due to SPR of the gold nanoparticles induced by binding of phosphorylated species with titania on the surface of the gold nanoparticles. The feasibility of the approach is demonstrated by detection of tryptic digest products of beta-casein and milk. Gold nanoparticles coated with thin films of titania, immobilized on a glass slide, can selectively bind traces of phosphopeptides from complex samples, resulting in a wavelength shift of the absorption band in the SPR spectrum with good reproducibility. The LSPR results are confirmed by matrix-assisted laser desorption/ionization mass spectrometry. The detection limit for the tryptic digest product of beta-casein is 50 nM.     

Liquid phase processing and thin film deposition of titania nanocrystallites for photocatalytic applications on thermally sensitive substrates

Titania films were deposited from sols peptized in acidic conditions and subsequently autoclaved. The microstructural, morphological, optical, and photocatalytic properties of titania films were studied with respect to sol-gel processing parameters. It is shown that films deposited at room temperature are well-crystallized and exhibit good optical quality. Their photocatalytic activity was verified through malic acid decomposition tests. From comparisons with a previous work, processing the sol in acidic conditions is found to be more advantageous than in basic conditions. Using this low temperature approach, titania films could be deposited on thermally sensitive polymer substrates for new photocatalytic applications.     

Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.