Effect of Substrate Pretreatment on Controllable Growthof TiO2 Nanorod Arrays

Well-aligned TiO2 nanorod arrays(TNAs) were prepared on the pretreated quartz substrates.The effect of the pretreatment conditions on the growth of TNAs was systematically investigated by X-ray diffraction(XRD),field-emission scanning electron microscopy(FE-SEM) and high-resolution transmission electron microscopy(HRTEM).It is demonstrated that the pre-coating TiO2 crystal seeds on the substrates can greatly improve the growth orientation of TNAs.Rutile TiO2 crystal seeds induce the nucleation and growth of TNAs more preferably than the anatase TiO2 seeds.The growth density and diameter distribution of TNAs strongly depend on the TiO2 crystal seeds density.It is proved that TNAs with different morphologies can be controllably synthesized by using hydrothermal approach by pretreating substrates.The photocatalytic activity of TNAs was investigated by measuring the photodegradation rate of methyl blue aqueous solution under UV irradiation(254 nm).And the results show that TNAs with large growth density and small diameter size exhibit relatively higher photocatalytic activity.     

Thermal optical properties of TiO2 films

A fibre optic experimental arrangement was used to determine the thermo-optic coefficient (dn/dT) of electron beam deposited titanium dioxide coatings on the cleaved end faces of multimode optical fibres for a wavelength range between 600 and 1050 nm. The temperature-induced change in the index of refraction (n) and extinction coefficient (k) were successfully determined from reflection spectra. Measurements of n and k at various wavelengths for different temperatures enabled the determination of dn/dT and dk/dT. It was found that dn/dT takes different values at different temperature ranges. For example, at 800 nm, dn/dT was (−1.77±0.7)×10⁻⁴ K⁻¹, between 18°C and 120°C, and took a value of (−3.04±0.7)×10⁻⁴ K⁻¹ between 220°C and 325°C.     

Preparation and photocatalytic study of fibrous K0.3Ti4O7.3(OH)1.7–anatase TiO2 nanocomposite photocatalyst

Nanocomposite of K_0.3Ti₄O_7.3(OH)_1.7 fiber and anatase TiO₂ nanoparticle was prepared by hydrothermal treatment of the K_0.3Ti₄O_7.3(OH)_1.7 which was synthesized by calcination of K₂CO₃ and TiO₂ at 1250 °C followed by refluxing in nitric acid. Effects of hydrothermal treatment conditions such as temperature and time on morphology, phase composition and crystal structure of the nanocomposites were extensively studied. Photocatalytic activities of the catalysts prepared at various hydrothermal conditions were evaluated by means of methylene blue decomposition under blacklight irradiation.     

Influence of growth time and annealing on rutile TiO2 single-crystal nanorod arrays synthesized by hydrothermal method in dye-sensitized solar cells

Vertically aligned TiO₂ nanorod (NR) arrays have been grown on the fluorine doped tin oxide (FTO) substrates by hydrothermal methods and the structures were employed to fabricate the dye-sensitized solar cells (DSSCs). The charge transport properties were investigated by the current to voltage curves and the electrochemical impedance spectroscopy. It was found that DSSCs containing the as-prepared and 500 °C annealed TiO₂ NRs exhibit different trends with the growth time (t). The DSSCs assembled with the un-sintered NR arrays showed the highest power conversion efficiency (η) of 1.87%. When DSSCs were assembled with the sintered NR arrays, nearly 400% enhanced efficiency were obtained, and the values (η) showed a positive correlation with t. This behavior may be attributed to the improved adhesion and electric contact between TiO₂ and FTO, as well as the reduced number of recombination sites.     

Synthesis of carbon-doped TiO2 nanoparticles using CO2 decomposition by thermal plasma

This study examined the synthesis of carbon-doped titanium dioxide using TiCl₄ and CO₂ as titanium and carbon sources, respectively, by thermal plasma at atmospheric pressure. The effect of the CO₂ gas flow rate on the preparation of TiO₂ was investigated. The results showed that the decomposition rate of CO₂ was 90% at a CO₂ gas flow rate of 1 L/min. When TiCl₄ was added to produce TiO₂, the decomposition rate of CO₂ reached 95% at a CO₂ gas flow rate of 1 L/min. The resulting powders contained mixed anatase and rutile phases with particle sizes ranging from 20 to 50 nm. The carbon in the CO₂ acted as a dopant to produce the carbon-doped TiO₂. The prepared samples were mainly characterized by X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area measurements and ultraviolet-visible spectroscopy.     

Effect of SnO2 on the photocatalytical properties of TiO2 films

TiO₂/SnO₂ thin films with different tin atomic percentages were successfully prepared on glass substrates by the spray pyrolysis method from an alcoholic solution of TiO[C₅H₇O₂]₂ with different concentrations of SnCl₄. The TiO₂/SnO₂ thin films prepared at 450 °C presented the anatase phase in polycrystalline configuration from %Sn = 0 in the starting solution up to %Sn = 20, at higher tin content the films present an amorphous configuration. The resulting thin films have a homogeneous surface structure with some porosity. The photocatalytical properties of the films were evaluated with the degradation of methylene blue. The products of the degradation reaction were identified by ¹H nuclear magnetic resonance and the film properties were studied by atomic force microscopy, scanning electron microscopy, UV–Vis spectroscopy, and X-ray diffraction.     

One step room temperature photodeposition of Cu/TiO2 composite films and its conversion to CuO/TiO2

Cu/TiO₂ composite films were prepared at low temperature on glass substrates by a photodeposition method. Films were deposited by irradiating the substrate while in contact with an aqueous TiO₂ suspension containing copper(II) nitrate and ethanol. Cu/TiO₂ composite films of 500 nm in thickness were deposited at room temperature after a short irradiation time (15 min) with a 125 W mercury vapour lamp. According to scanning electron microscopy observations, the obtained films were homogeneous and porous. Energy dispersive X-ray spectroscopy analysis revealed a 3:1 Cu:Ti atomic ratio. Grazing angle X-ray diffraction analysis showed that the films contained Cu and TiO₂ as major components and Cu₂O as a minor component. Heat treatment at 400 °C in air for a period of 3 h transformed the initial material into a CuO/TiO₂ composite, improved the adhesion to the substrate and favoured a more regular distribution of copper oxide according to backscattering micrographs.     

TiO2 deposition on the surface of activated fluoropolymer substrate

Anatase-structured TiO₂ films were deposited on a commercial fluorinated polymer (FEP) with a treated surface, by means of a sol-gel dip-coating technique. Two different curing temperatures were investigated and the film microstructures were characterized by X-ray diffraction, atomic force microscopy and scanning electron microscopy analyses. The prepared samples presented very high performances in terms of photocatalytic activities, analyzed by the degradation of an organic dye in a liquid medium, and of bactericidal activities, tested on Staphylococcus aureus (S. aureus, a Gram positive bacterium) and Escherichia coli (E. coli, a Gram negative bacterium).     

Substrate and Fe-doping effects on the hydrophilic properties of TiO2 thin films

Titanium dioxide films are known for their hydrophilic and photocatalytic characteristics. Increasing specific surface area and doping can enhance their photocatalytic activity and hydrophilicity. We report here results regarding the enhancement of the photocatalytic properties of titania by both controlling surface morphology and the anatase/rutile ratio. The samples were deposited on glass, indium tin oxide covered glass, and SrTiO₃ by sputtering and laser ablation techniques. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. Film hydrophilicity was assessed from contact angle measurements during- and post-irradiation with UV light. The contact angle data are discussed in terms of the synergic effects of surface morphology, structure and composition of the films.     

Novel electrochromic devices based on complementary nanocrystalline TiO2 and WO3 thin films

Electrochromic devices were elaborated based on two complementary electrodes made of a nanocrystalline metal oxide thin film deposited on conducting glass. The first electrode holds a 5 μm thick nanocrystalline TiO₂ film derivatized by a monolayer of a phosphonated triarylamine which can be rapidly oxidized by electron transfer to the conducting support followed by charge percolation inside the monolayer. The oxidation in accompanied by a blue coloration due to the absorption band at 730 nm of the stable triarylamminum radical cation. The second electrode bears a 0.2 μm thick nanocrystalline WO₃ film which turns from colorless to blue by reduction and lithium ion insertion. The former electrode reaches an absorbance of at least 3 between 700 and 730 nm after full oxidation (16 mC/cm²) at 1.0 V vs. NHE while for the second, complete reduction at −1.3 V (74 mC/cm²) leads to A=2.4 at 774 nm. An electrochromic device comprising both electrodes separated by an electrolytic solution of 0.1 Li⁺ in 4,7-dioxaoctanitrile reaches an absorbance of 2.2 at 700 nm, 4 s after a voltage step to 1.5 V. The system was shown to sustain at least 14400 coloration-discoloration cycles without degradation.     

Photoactive and self-cleaning TiO2-SiO2 thin films on 316L stainless steel

In this study, TiO₂-SiO₂ nanocomposite films with different amounts of SiO₂ were prepared by sol-gel process and were coated onto stainless steel 316L. The effect of addition of various amount of SiO₂ in the precursor solution on the photocatalysis, photo-generated hydrophilicity and self-cleaning property of TiO₂ thin films was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, water contact angle measurements and UV spectroscopy. In the tested ranges of SiO₂ content and sintering temperature, the highest photocatalytic activity and self-cleaning property were observed in the 15 mol% SiO₂ sample sintered at 750 °C. Addition of less than 30 mol% SiO₂ had a suppressive effect on the transformation of anatase to rutile and on the crystal growth of anatase in the sintering heat treatment. Phase separation occurred in the composite films for SiO₂ content of 30 mol% or more.     

Hydrothermal growth of double-layer TiO2 nanostructure film for quantum dot sensitized solar cells

A double-layer (DL) film with a TiO₂ nanosheet-layer on a layer of TiO₂ nanorod-array, was synthesized on a transparent conductive fluorine-doped tin oxide substrate by a two-step hydrothermal method. Starting from the precursors of NaSeSO₃, CdSO₄ and the complex of N(CH₂COOK)₃, CdSe quantum dots (QDs) were grown on the DL-TiO₂ substrate by chemical bath deposition method. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Energy dispersion spectroscopy, and their optical scattering property was measured by light reflection spectrometry. Some CdSe QDs sensitized DL-TiO₂ films serve as the photoanodes, were assembled into solar cell devices and their photovoltaic performance were also characterized. The short circuit current and open-circuit voltage of the solar cells range from 0.75 to 4.05 mA/cm² and 0.20 − 0.42 V under the illumination of one sun (AM1.5, 100 mW/cm²), respectively. The photocurrent density of the DL-TiO₂ film is five times higher than that of a bare TiO₂ nanorod array photoelectrode cell.     

Photocatalysis and characterization of the gel-derived TiO2 and P-TiO2 transparent thin films

The gel-derived TiO₂ and P-TiO₂ transparent films coated on fused-SiO₂ substrates were prepared using a spin-coating technique. Effects of phosphorus dopants and calcination temperature on crystal structure, crystallite size, microstructure, light transmittance and photocatalytic activity of the films were investigated. By introducing P atoms to Ti-O framework, the growth of anatase crystallites was hindered and the crystal structure of anatase-TiO₂ could withstand temperature up to 900 °C. The photocatalytic activities of the prepared films were characterized using the characteristic time constant (τ) for the photocatalytic reaction. The titania film with a smaller τ value possesses a higher photocatalytic ability. After exposing to 365-nm UV light for 12 h, the P-TiO₂ films calcined between 600 °C and 900 °C can photocatalytically decomposed ≥ 84 mol% of the methylene blue in water with corresponding τ ≤ 7.1 h, which were better than the pure TiO₂ films prepared at the same calcination temperature.     

Photoreduction of CO2 by TiO2 nanocomposites synthesized through reactive direct current magnetron sputter deposition

The photoreduction of CO₂ into methane provides a carbon-neutral energy alternative to fossil fuels, but its feasibility requires improvements in the photo-efficiency of materials tailored to this reaction. We hypothesize that mixed phase TiO₂ nano-materials with high interfacial densities are extremely active photocatalysts well suited to solar fuel production by reducing CO₂ to methane and shifting to visible light response. Mixed phase TiO₂ films were synthesized by direct current (DC) magnetron sputtering and characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Bundles of anatase-rutile nano-columns having high densities of two kinds of interfaces (those among the bundles and those between the columns) are fabricated. Films sputtered at a low deposition angle showed the highest methane yield, compared to TiO₂ fabricated under other sputtering conditions and commercial standard Degussa P25 under UV irradiation. The yield of methane could be significantly increased (~ 12% CO₂ conversion) by increasing the CO₂ to water ratio and temperature (< 100 °C) as a combined effect. These films also displayed a light response strongly shifted into the visible range. This is explained by the creation of non-stoichiometric titania films having unique features that we can potentially tailor to the solar energy applications.     

真空钙热还原法制备金属钛粉的研究

在真空炉中(30~40 Pa)1273 K下,将物料放入螺纹密封的石墨坩埚中进行不同时间下的还原反应。本文采用热力学分析及X射线衍射、扫描电子显微镜及能量弥散X射线谱等方法与手段,系统研究了金属钙(Ca)与反应器中的氧气(O2)、氮气(N2)、二氧化钛(TiO2)的反应和还原时间及还原产物的预处理对得到金属钛粉(Ti)的影响。通过热力学研究,在温度低于钙的熔点(1115 K)时,密封容器内的O2与Ca的反应及N2与Ca的反应满足反应发生的热力学条件。当温度达到1273K时,Ca的饱和蒸气压p*≈p系,有利于整个气固反应进行。实验研究表明,在还原反应发生前,反应器内的O2,N2与Ca反应完全。将在1273 K下还原时间为4 h得到的还原产物在酸洗前真空挥发处理还原产物表面大量的Ca时,金属单质Ti再次被氧化成低价氧化物,最终得不到金属Ti粉。将反应时间延长至6 h时,酸洗过滤后得到形状不规则、纯度达到98.64%的Ti粉。     

Synthesis and characterization of P-doped TiO2 nanotubes

Titanium dioxide (TiO₂) doped with phosphorus (P) was synthesized by anodization of Ti in the mixed acid electrolyte of H₃PO₄ and HF and characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrum. The morphology greatly depends on the applied voltage. The as-formed nanotubes under the optimized condition, at 20 V for 2 h, are highly ordered with ~ 200 nm in length and the average tube diameter is about 100 nm. By annealing the initial samples at different temperatures, the importance of the crystalline nature is confirmed. Significantly, the peak positions of anatase in XRD patterns shifts to lower diffraction angles with an increase in the amount of H₃PO₄ ion. A remarkable red shift of the absorption edge has been observed for the sample formed in the electrolyte of HF and H₃PO₄, which is related to the introduction of P⁵⁺ into TiO₂ crystallization and the possible impurity energy level formed in the TiO₂ band gap. The presence of P 2p state in XPS spectrum can further confirm the P⁵⁺ which can replace a part of Ti⁴⁺ has been introduced into TiO₂ crystallization. The present convenient synthesis technique can be considered to the composition of other doped oxide materials.     

Conductivity of nanometer TiO2 thin films by magnetron sputtering

The conductivity of nanometer TiO₂ thin films was presented in this paper. The dependence of the conductivity of TiO₂ thin films on the thickness of the film and the substrate material were educed. The TiO₂ films were deposited by reactive magnetron sputtering of a Ti targets in an Ar+O₂ mixture in a conventional sputtering reactor. The thickness of the films deposited on Ti varied in the range from 15 to 225 nm. The resistivity of the films was measured at room temperature in the air. It was found that the conductivity of TiO₂ thin films varies in the range from conductor, semiconductor to nonconductor. This was attributed to electrons transfer at the interface between the TiO₂ and substrates, and the depth of electrons transfer was determined by the difference of work function.     

Hydrothermal synthesis of 1D TiO2 nanostructures for dye sensitized solar cells

Mono-dimensional titanium oxide nanostructures (multi-walled nanotubes and nanorods) were synthesized by the hydrothermal method and applied to the construction of dye sensitized solar cells (DSCs). First, nanotubes (TiNTs) and nanotubes loaded with titanium oxide nanoparticles (TiNT/NPs) were synthesized with specific surface areas of 253 m²/g and 304 m²/g, respectively. After that, thermal treatment of the nanotubes at 500 °C resulted in their transformation into the corresponding anatase nanorods (TiNT-Δ and TiNT/NPs-Δ samples). X-ray diffraction and Raman spectroscopy data indicated that titanium oxide in the pristine TiNT and TiNT/NP samples was converted into anatase phase TiO₂ during the heating. Additionally, specific surface areas and water adsorption capacities decreased after the heat treatment due to the sample agglomeration and the collapse of the inner nanotube channels. DSCs were fabricated with the nanotube TiNT and TiNT/NP samples and with the anatase nanorod TiNT-Δ and TiNT/NPs-Δ samples as well. The highest power conversion efficiency of η = 3.12% was obtained for the TiNT sample, despite its lower specific surface compared with the corresponding nanoparticle-loaded sample (TiNT/NP).     

Effect of crystallization on humidity sensing properties of sol-gel derived nanocrystalline TiO2 thin films

In the present work, we describe the effect of crystallization on humidity sensing properties of nanocrystalline TiO₂ thin films prepared by sol-gel techniques. Here, we report an enhancement in the relative humidity (RH) sensitivity just after the crystallization at 375 °C, which is attributed to increased surface activity near crystallization and lower crystallite size. After crystallization, the RH sensitivity was found to decrease with increasing grain size. The complex impedance of the sensor, measured using impedance spectroscopy, fits well with an equivalent circuit consisting of inter-granular resistance and capacitance in parallel. It was found that with the change in RH, only resistance changes significantly, when compared with the capacitance.     

The effects of morphological changes on the vibrational properties of self-organized TiO2 nanotubes

This paper reports the synthesis of TiO₂ nanotubes by anodic process. The effects of different electrolyte concentrations on the morphological, structural and vibrational properties of TiO₂ nanotubes were studied. Scanning electron microscopy images showed that nanotube inner diameter ranging from 15 to 115 nm could be obtained. At lower concentration, nanotubes were homogenous, and highly ordered. As concentration increased, nanotubes experienced dissolution process, and led to formation of pore-like structure. X-ray diffraction measurements revealed that anatase phase and Ti were present in the samples upon annealing at 500 °C for one hour. The intensity of Raman E_g(1) peak was electrolyte concentration dependent. Full width half maximum value derived from E_g(1) peak was associated with the intensity which was related to the change of TiO₂ nanotubes morphological quality.