A facile method to grow V-doped TiO2 hydrophilic layers with nano-sheet morphology

V-doped titania layers with a novel morphology and a rough surface were grown the via micro arc oxidation process in the electrolytes consisting of sodium vanadate under various voltages. Morphological investigations, performed by SEM, revealed that the layers had a sheet-like structure whose average thickness was less than 100 nm depending on the applied voltage. Our XRD and XPS results showed that the layers consisted of anatase, rutile, and vanadia phases with a varying fraction depending on the voltage. Hydrophilicity of the layers was also studied by measuring the water contact angle on their surfaces under ultraviolet and visible illuminations. The layer synthesized under the voltage of 450 V exhibited the highest hydrophilicity.     

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.     

Fabrication of ZrO2-Al2O3 hybrid nano-porous layers through micro arc oxidation process

Zirconia-alumina layers, with a pores size of 40-300 nm, were fabricated via micro arc oxidation method for the first time. The layers were grown under alternative current in the electrolytes of ZrOCl₂ salt. They consisted of α-Al₂O₃, γ-Al₂O₃, monoclinic ZrO₂, tetragonal ZrO₂. Increasing the voltage resulted in higher zirconium concentrations in the layers. A porous structure was obtained when the layers were grown under intermediate voltages. Microcracks were observed to appear when the applied voltage increased. Finally, a formation mechanism was proposed with emphasis on the chemical and the electrochemical foundations.     

Electron field emission from the carbon-doped TiO2 nanotube arrays

The field-emission characteristics of the carbon-doped TiO₂ nanotube arrays (TNAs), which can be obtained by a heat treatment of the as-fabricated TNAs under a continuous argon and acetylene flux, were investigated. The morphology, crystalline structure, and composition of the as-grown specimens were characterized by the use of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the samples' turn-on electric field is reduced from 21.9 to 5.0 V/μm and the field-emission current density rapidly reaches about 9.0 mA/cm² at 11.8 V/μm after carbon doping. The dramatically improved field-emission characteristics would be mainly attributed to the reduced work function and the enhanced conductivity due to the carbon doping into TNAs.     

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.     

Silver loaded WO3 − x/TiO2 composite multifunctional thin films

Multifunctional WO_3 − x-TiO₂ composite thin films have been prepared by sol-gel synthesis and shown to be good visible light photocatalysts whilst retaining a desirable underlying blue colouration. The WO_3 − x-TiO₂ composite thin films were further enhanced using silver nanoparticles synthesised in-situ on the surface from the photo-degradation of silver nitrate solution. Thin films were characterised using X-ray diffraction, Raman, Scanning electron microscopy and UV-visible spectroscopy and shown to photo degrade stearic acid, using white light λ = 420-800 nm.     

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.     

Preparation and antibacterial behavior of Fe-doped nanostructured TiO2 thin films

Fe³⁺-doped nanostructured TiO₂ thin films with antibacterial activity were prepared on soda–lime–silica glass slides by using sol–gel technology. Water containing Escherichia coli K-12 with TiO₂ thin films in was exposed to low intensity fluorescent light and antibacterial efficiency was evaluated with spread plate techniques. The films are porous and have anatase phase. Iron ions increased luminous energy utilization as the absorption edge of the Fe³⁺-doped film has a red shift compared to that of the pure TiO₂ film in the UV–VIS absorption spectrum. The bacterial removal efficiency reached 95% at the optimum concentration of iron ion (about 0.5% (mol)) after 120 min irradiation. The antibacterial behavior of the doped TiO₂ films was explicitly observed using scanning electron microscopy and cell wall damage was found.     

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.     

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。     

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.     

Preparation and photocatalytic activity of WO3/TiO2 nanocomposite particles

A novel photocatalyst WO₃/TiO₂ nanocomposite was prepared through a hydrothermal method by using cetyltrimethylammonium bromide (CTAB) as surfactant. The obtained WO₃/TiO₂ was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and diffused reflectance spectroscopy (DRS). Photocatalytic experiments indicate that the nanocomposites show much higher photoactivity than that of pure TiO₂ in the photodegradation reaction of Rhodamine B (RhB). The increased photoactivity of WO₃/TO₂ may be attributed to the improvement of the light absorption properties and the slow down of the recombination between the photoexcited electrons and holes during the photoreaction.     

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.     

Preparation and characterization of doped TiO2 nanodandelion

Doped dandelion-like TiO₂ microspheres assembled nanorods were synthesized from rutile powders using either urea or thiourea leading to N- or S-doped TiO₂. The rutile particles reacted in concentrated NaOH and urea (or thiourea) solution under hydrothermal conditions (200 °C for 24 h), yielding N- and S-doped TiO₂ nanodandelions with diameters ranging from 0.7 to 1.3 μm. SEM, HRTEM, X-ray diffraction (XRD) and IR spectra were used to characterize the synthesis of powders. The results show that concentrated urea (or thiourea) and NaOH are used as additives that help in the construction of the dandelion-like structures. The fabricated nanostructures exhibit high photocatalytic activity in the photodegradation of aqueous Methylene Blue solution.     

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.     

Low-temperature and ambient-pressure synthesis of TiO2(B)

Nanocrystalline TiO₂(B) powder was obtained by the hydrolysis of an ionic liquid like titania precursor (the triethylammonium salt of hexafluorotitanate) induced by the addition of boric acid in the presence of dopamine. The entire synthetic procedure was carried out at ambient pressure and low temperature (85 °C). X-ray diffraction, high resolution transmission electron microscopy and selected area electron diffraction characterization techniques confirmed the formation of the TiO₂(B) phase. Moreover, Raman spectroscopy indicated that TiO₂(B) was the major component, although it also revealed the presence of anatase as a minor component (< 10%). The as-prepared material has a mesoporous architecture with high specific surface area (235 m² g^− 1).     

低温等离子体射流制备二氧化钛薄膜及其光催化活性的研究

利用大气压低温等离子体射流技术,以空气为放电气体,四氯化钛为钛源,在玻璃载玻片基底上制备了二氧化钛薄膜。利用扫描电镜及椭圆偏振仪分析测量了薄膜的表面形貌与沉积速率。利用紫外光照射硬脂酸分解速率评价所制备薄膜的光催化活性,结果显示在同一放电输入功率及气体流量条件下,四氯化钛前驱体引入位置距射流枪枪口越近,所制备的二氧化钛薄膜光催化性能越高。在同一反应位置时,放电输入功率的增加有助于提高二氧化钛薄膜的光催化活性。     

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).