Selective synthesis of brookite,anatase and rutile nanoparticles: thermolysis of TiCl<Subscript>4</Subscript> in aqueous nitric acid

The three polymorphs of titania (anatase, rutile and brookite) have been obtained as nanoparticles selectively and with well definite morphologies (platelets of brookite, rods of rutile) by thermohydrolysis of TiCl₄ in concentrated aqueous nitric acid. The selectivity of the synthesis depends strongly on the acidity of the medium. The presence of concentrated nitrate ions seems to be the determining factor for the formation of brookite and its stabilization against recrystallization.     

XPS and biocompatibility studies of titania film on anodized NiTi shape memory alloy

A dense titania film is fabricated in situ on NiTi shape memory alloy (SMA) by anodic oxidation in a Na₂SO₄ electrolyte. The microstructure of the titania film and its influence on the biocompatibility of NiTi SMA are investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), hemolysis analysis, and platelet adhesion test. The results indicate that the titania film has a Ni-free zone near the surface and can effectively block the release of harmful Ni ions from the NiTi substrate in simulated body fluids. Moreover, the wettability, hemolysis resistance, and thromboresistance of the NiTi sample are improved by this anodic oxidation method.     

Microstructures and Photocatalytic Properties of S Doped Nanocrystalline TiO2 Films

The nanocrystalline S doped titanium dioxide films were successfully prepared by the improved sol-gel process. Here TiO(C₄H₉O)₄ and CS(NH₂)₂ were used as precursors of titania and sulfur, respectively. The as-prepared specimens were characterized using x-ray diffraction (XRD), x-ray energy dispersive spectroscopy (EDS), high-resolution field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solution. The results of XRD, FE-SEM, and BET analyses indicated that the TiO₂ films were composed of nanoparticles. S doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO₂ film, S doped TiO₂ film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the modified films is responsible for improving the photocatalytic activity.     

Effect of crystal structure on photoinduced superhydrophilicity of copper grafted TiO2 nanostructure thin film

In this work, copper grafted titanium dioxide (rutile and brookite) thin films were deposited on glass substrates using the dip-coating method. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to evaluate the surface morphology and properties of the film surfaces. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyser. The results indicate that copper grafted titanium dioxide brookite thin film showed higher hydrophilicity than copper grafted titania rutile thin film.     

Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods

Nanocrystalline particles of pure anatase titania were prepared by two different methods. One is the sol-gel method at ambient temperature using ultrasonication (TiO₂-SG-US) and conventional stirring method (TiO₂-SG-S) and the other by surfactant assisted hydrothermal synthesis (TiO₂-HT). More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability and phase purity are some of the advantages of preparation of nanocrystalline titania by sol gel ultrasonication method and hydrothermal synthesis method. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of TiO₂-SG-US is attributed to the more uniform size of the particles as compared to TiO₂-SG-S samples. Both TEM and XRD data on TiO₂-HT samples reveal a uniform and nanocrystalline TiO₂ particles, which showed photocatalytic activity in both UV and visible region although brookite phase was also present.     

Modified thermoelectric figure of merit estimated from enhanced mobility of [100] oriented beta-FeSi<Subscript>2</Subscript> thin film

The modification of thermoelectric figure of merit was estimated from enhanced mobility of [100] oriented beta-FeSi₂ film. beta-FeSi₂ on Si(001) substrate was prepared by molecular beam epitaxy method using an Fe source. The crystallographic orientation of beta-FeSi₂ film on Si(001) substrate was characterized by using X-ray diffraction. Using scanning electron microscopy, surface morphology and film thickness of samples were observed and estimated, respectively. The mobility of beta-FeS₂ film on Si(001) substrate were also characterized by Hall measurement at room temperature. A part of the enhancement of figure of merit was evaluated as the functions of mobility and crystallographic orientation of samples.     

The crystalline phase stability of titania particles prepared at room temperature by the sol-gel method

Titania particles having anatase, brookite and rutile phase were prepared at various H⁺/TTIP (Titaniumtetraisopropoxide) mole ratios and room temperature by the sol-gel method. The crystalline phases according to the variation of the post heat treatment temperature were observed. The crystalline phase and the phase transformation, morphology, and crystallite size were identified by using XRD, TG/DTA, Raman spectroscopy and TEM. The brookite phase of titania particles prepared at the H⁺/TTIP mole ratio of 0.02 and room temperature was not transformed into anatase or rutile even with the heat treatment at 750°C, and also the anatase phase was stable at the temperature as high as 850°C. However, the titania particles prepared at the H⁺/TTIP mole ratio of 0.67, which contained the mixed phases of anatase, brookite, and rutile at room temperature, showed only rutile phase at temperature of 750°C. It was thus shown that the initial crystalline phase of the primary particles prepared at room temperature had an important effect on the phase transformation behavior upon post heating. Phase transformation from brookite to anatase and subsequently to rutile occurred with heating.     

Layer-by-layer assembly of titanate nanosheets/poly- (ethylenimine) on PEN films

Alternating layers of TiO₂ nanosheets and poly(ethylenimine) were sequentially dip coated onto a polyethylene naphthalate substrate (PEN) using layer-by-layer assembly. UV-vis spectroscopy shows a linear growth of the PEI/nanosheets bilayer on the PEN substrate. The cross-section microstructure of the LBL film was studied using scanning electron microscopy (SEM). Helium permeability measurement showed that the titania nanosheet/PEI bilayers reduced the permeation rate of He through the coated PEN film.     

不同晶型纳米TiO2的溶剂热合成及其光催化活性研究

采用不同的醇溶剂,以六亚甲基四胺为沉淀剂,以TICl3为前驱体,通过溶剂热的方法控制合成出纳米级的锐钛矿型、金红石型和板钛矿型的二氧化钛.通过XRD、TEM、UV-Vis光谱和XPS能谱对其进行了表征,研究了醇的种类、六亚甲基四胺的量对二氧化钛相组成及光催化性能的影响.结果发现,以甲醇为溶剂,酸性条件有利于生成锐钛矿相,碱性条件有利于生成金红石相和板钛矿相.溶剂热条件下可以得到氮掺杂的TiO2-xNx.光催化降解甲基橙活性结果表明锐钛矿和板钛矿混晶具有最好的光催化活性.     

Nitrogen and europium doped TiO2 anodized films with applications in photocatalysis

Micro-arc oxidation method is a useful process for mesoporous titanium dioxide films. In order to improve the photocatalytic activity of the TiO₂ film, N-Eu co-doped titania catalyst was synthesized by micro-arc oxidation in the H₂SO₄/Eu(NO₃)₃ mixture solution.The specific surface area and the roughness of the anodic titania film fabricated in the H₂SO₄/Eu(NO₃)₃ electrolyte, were increased compared to that of the anodic TiO₂ film prepared in H₂SO₄ solution. The absorbance response of N-Eu titania film shows a higher adsorption onset toward visible light region, and the incorporated N and Eu ions during anodization as a dopant in the anodic TiO₂ film significantly enhanced the photocatalytic activity for dye degradation. After dye decomposition test for 3 h, dye removal rates for the anodic TiO₂ film were 60.7% and 90.1% for the N-Eu doped titania film. The improvement of the photocatalytic activity was ascribed to the synergistic effects of the surface enlargement and the new electronic state of the TiO₂ band gap by N and Eu co-doping.     

Percolation threshold for electrical resistivity of Ag-nanoparticle/titania composite thin films fabricated using molecular precursor method

To find the percolation threshold for the electrical resistivity of metallic Ag-nanoparticle/titania composite thin films, Ag-NP/titania composite thin films, with different volumetric fractions of silver (0.26 ≤ φ_Ag ≤ 0.68) to titania, were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. The resistivity of the films was of the order of 10⁻² to 10⁻⁵ Ω cm with film thicknesses in the range 100–260 nm. The percolation threshold was identified at a φ_Ag value of 0.30. The lowest electrical resistivity of 10⁻⁵ Ω cm at 25 °C was recorded for the composite with the Ag fraction, φ_Ag, of 0.55. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopic (TEM) evaluation of the effect of the morphology and the nanostructures of the Ag nanoparticles in the composite thin films on the electrical resistivity of the film revealed that the films consist of rutile, anatase, and metallic Ag nanoparticles homogeneously distributed in the titania matrix. It could be deduced that the electrical resistivity of the thin films formed at 600 °C was unaffected by the anatase/rutile content within the thin film, whereas the shape, size, and separation distance of the Ag nanoparticles strongly influenced the electrical resistivity of the Ag-nanoparticle/titania composite thin films.     

Preparation and apatite layer formation of plasma electrolytic oxidation film on titanium for biomedical application

Porous and rough titania film containing Ca and P on titanium was prepared by plasma electrolytic oxidation. The film was composed of titania and a little CaTiO₃. Apatite layer was formed on the titania film when the film was immersed in the simulated body fluid, indicating the potencial capability for formation of the plasma electrolytic oxidation film on titanium.     

Hydrothermal growth of titania nanostructures with tunable phase and shape

In this paper, we report hydrothermal synthesis of titania nanostructure with tunable phase and shape in the presence of methylcellulose (MC) and NaCl. As determined by X-ray diffraction, and scanning electron microscopy, nanosized flower-like rutile titania (nanorod aggregates) was obtained without the presence of MC. While MC was added, the assembled spheres of bicrystalline (brookite and rutile) titania nanoparticles was produced, and the bicrystalline titania with a brookite fraction in the range of 0–49.2% was prepared by changing the MC concentration. The mechanisms of bicrystalline phase formation were also briefly discussed.     

Sol-gel derived TiO2 coating on plasma nitrided 316L stainless steel

Titania film is coated on plasma nitrided 316L stainless steel by sol-gel method. Crystallization of titania as well as N loss and formation of Fe₂O₃ occurs during the annealing heat treatment. The titania film has short cracks within the grooves of plasma etched grain boundaries. With the increase of annealing temperature and duration, surface hardness of the samples is increased, but the toughness is decreased due to oxidization of the surface layer. The coating sample heat treated at 350 °C for 10 min and 450 °C for 10 min has better corrosion resistance than the nitrided stainless steel tested by the potentiodynamic polarization in 0.9% NaCl solution. Water contact angle of the titania film on the rough nitrided steel substrate decreases with UV irradiation treatment, reaching 17° after 3 h treatment.     

Investigation of superhydrophilic mechanism of titania nano layer thin film—Silica and indium oxide dopant effect

In this paper, TiO₂?CSiO₂?CIn₂O₃ nano layer thin films were deposited on glass substrate using sol?Cgel dip coating method. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements were used to evaluate chemical structure, surface composition, hydroxyl group contents and superhydrophilicity of titania films. FTIR result indicated that Si?CO?CSi, Si?CO?CTi and Ti?CO?CTi bands formed in TiO₂?CSiO₂?CIn₂O₃ sample. According to XPS, the hydroxyl content for TiO₂, TiO₂?CSiO₂ and TiO₂?CSiO₂?CIn₂O₃ films was calculated as 11·6, 17·1 and 20·7%, respectively. The water contact angle measurements indicated that silica and indium oxide dopant improved the superhydrophilicity of titania nano film surface especially in a dark place. The enhanced superhydrophilicity can be related to the generation of surface acidity on the titania nano film surfaces. In the present state, superhydrophilicity is induced by the simultaneous presence of both Lewis and Bronsted sites.     

Preparation of RF sputtered AZO/Au thin film hydrogen peroxide sensitive electrode for utilization as a biosensor

In this study, hydrogen peroxide (H₂O₂) sensitive Al doped ZO(AZO)/Au thin film electrode has been developed for the utilization as a biosensor. A preferred c-axis oriented AZO/Au thin film was deposited on quartz substrate by RF magnetron sputtering at room temperature. Structural, morphological and optical properties of the AZO film were analyzed by X-ray diffraction, atomic force microscopy and photoluminescence. The sensor performance was characterized by electrochemical analysis device. The sensibility of prepared thin film electrodes to H₂O₂ was studied. The dependence of amperometric response current on the glucose and cholesterol concentrations was also investigated.     

Low temperature synthesis of crystalline mesoporous titania with high photocatalytic activity by post-treatment in nitric acid ethanol solution

Mesoporous titania powder with a bicrystalline (anatase and brookite) framework was prepared by modified sol-gel method using dodecylamine as template. The template could be easily removed by refluxing the powder in nitric acid ethanol solution. The effects of the acid treatment on the stability of inorganic framework were investigated. The samples were characterized by FT-IR, XRD, N₂ adsorption-desorption isotherms and HRTEM. The result showed that all of the as-prepared samples were wormhole-like mesoporous structure. The as-prepared sample showed a high photocatalytic activity to degrade Rhodamine B under UV-light irradiation, which was attributed to the porous structure, large BET surface area, bicrystalline, and small crystallite size.     

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.     

Photocatalytic activity of vanadium-doped titania-activated carbon composite film under visible light

A V-doped titania-activated carbon composite film was prepared by a modified sol-gel method under mild condition. X-ray diffraction analysis revealed that the titania was a pure anatase phase. From scanning electron microscopy and N₂ adsorption-desorption measurements, we found that the composite film was porous since it formed a micro-nano structure. The photocatalytic activity of such film was evaluated through degradation of azo-dye Reactive Brilliant Red under visible light, and was compared to commercially available TiO₂, pure titania and vanadium-doped titania films. Results showed that the photocatalytic activity was enhanced a lot. It was due to expansion of the absorption edge by vanadium doping, and the synergistic effect of activated carbon with titania. Furthermore, the hydrophilic property of the as-prepared composite film was superior to other samples.     

Porous titania films fabricated via sol gel rout – Optical and AFM characterization

Mesoporous titania films of low refractive index ∼1.72 and thickness within the range of 57–96 nm were fabricated via sol–gel rout and dip-coating technique on a soda–lime glass substrate. Tetrabutylorthotitanate Ti(OBu)₄ was used as a titania precursor. High porosity and consequently low refractive index were achieved using the polyethylene glycol (PEG 1100) as a template. Based on transmittance, using Tauc’s relations, the optical energy band gaps and the Urbach energy were determined. The research shows that in the fabricated titania films there are two types of optical energy band gaps, connected with direct and indirect electron transitions and brought about by the presence of amorphous and crystalline phase respectively. Based on the quantum size effect, the diameters of nanocrystals versus film thickness were determined. AFM studies of the titania films have demonstrated that there are changes of surface morphology taking place with the change of thickness. We have demonstrated that the surface morphology of titania films has influence on wettability.