Anatase-rutile Transformation Research Articles

Hydrothermal synthesis of anatase nanoleaves and size dependence of anatase–rutile transformation upon heating

Amorphous TiO2 obtained by adding TiCl4 to an alkaline medium crystallizes slowly and upon 3 years ageing transforms to nanosized anatase containing an admixture of brookite. The hydrothermal treatment of this sample in solutions of lithium hydroxide leads to anatase nanoleaves, and the more concentrated LiOH solution, the greater the nanoleaves and the smaller their specific surface area. The thermal treatment of nanoleaves leads to the bulk rutile, and the greater the specific surface area of anatase nanoleaves, the lower the anatase–rutile transition temperature. This is in line with conclusions based on the thermodynamic stability of nanosized anatase over the bulk rutile.

Nanophase Changes in Nickel Doped Titania Composites by Thermal Treatment and Photocatalytic Destruction of NO(x).

This study investigated the influence of Ni doping and thermal treatment (600, 800 degrees and 1000 degrees C) on the physiochemical properties of a commercially available low cost KA100 TiO2. Ni containing KA100 samples were prepared with different loading of Ni (3%, 6% and 9% wt to KA100) and subjected to heat treatement at 600 degrees, 800 degrees and 1000 degrees C. The as-prepared samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Diffuse reflection UV-Visible spectroscopy and Raman spectroscopy and nitrogen-adsorption-desorption measurements to observe the nanophase changes in the particle characteristics following Ni modification and thermal treatment. The results show that the Ni atom entered the TiO2 lattice structure upon heat treatment at 800 degrees C and 1000 degrees C influencing the anatase-rutile phase transformation. The TiO2 powders after heat treatment had a bimodal pore-size distribution as the temperature of the heat treatment increased. In addition, the anatase crystallite size and average pore sizes increased. Photodegradation of NO(x) was investigated using the Ni doped KA100 as a photocatalyst. Modification of KA100 with nickel and heat treatment up to 1000 degrees C enhanced the photocatalysis for the degradation of NO(x). Typically, KA100 modified with 6% Ni and heat treated to 1000 degrees C exhibited excellent NO(x) removal activity.

Role of aluminum doping on phase transformations in nanoporous titania anodic oxides

The role of aluminium doping on anatase to rutile phase transformation of nanoporous titanium oxide films were investigated. For this purpose pure and aluminum doped metal films were deposited on alumina substrates by cathodic arc physical deposition. The nanoporous anodic oxides were prepared by porous anodizing of pure and aluminum doped titanium metallic films in an ethylene glycol + NH4F based electrolyte. Nanoporous amorphous structures with 60–80 nm diameter and 2–4 μm length were formed on the surfaces of alumina substrates. The amorphous undoped and Al-doped TiO2 anodic oxides were heat-treated at different temperatures in the range of 280–720 °C for the investigation of their crystallization behavior. The combined effects of nanoporous structure and Al doping on crystallization behavior of titania were investigated using X-ray diffraction (XRD) and micro Raman analysis. The results indicated that both Al ions incorporated into the TiO2 structure and the nanoporous structure retarded the rutile formation. It was also revealed that presence or absence of metallic film underneath the nanopores has a major contribution to anatase-rutile transformation.

Hg-doped TiO2 nanostructures thin film prepared by sol–gel method for gas sensing applications: Correlation between the structural and electrical properties

Hg-doped TiO2 and undoped thin films have been synthesized from mercury acetate and titanium tetrabutyl-orthotitanate precursors deposited on silicon substrates using a sol–gel dip-coating technique. Annealing temperatures and layer thickness were found crucial for thin films nanostructures morphology which was characterized by X-ray diffraction (XRD), Raman and FTIR spectroscopy, Scanning electron microscopy (SEM) and Atomic force microscopy (AFM). XRD, Raman and FTIR results show that the 5% Hg doping shows crystallization at lower annealing temperatures. After heat treatments of thin films at 450°C, the anatase–rutile transformation takes place with annealing temperature. The average crystallite size of the doped TiO2 films was increased with annealing temperature and was about 20nm. SEM and AFM reveal nanostructures surface agglomerates of TiO2 doped Hg nanoparticles arranged with preferred orientation. The electrical properties of TiO2 doped thin films were investigated by current–voltage (I–V) characteristics. These nanostructures arrays exhibit excellent sensitivities with the increase of CO2 concentration at room temperature. Current–voltage analysis indicated that the enhanced gas sensitivity is probably due to the high surface/volume ratio of this nanostructure material in combination with the remarkable effect of Hg doping in TiO2.

Anatase–rutile transformation of TiO2 sol–gel coatings deposited on different substrates

Titanium dioxide is widely used in a lot of applications. The properties of TiO2 strongly depend on its phase composition. The transformation temperature between phases is influenced by a lot of factors. One of them is a type of substrate under the TiO2 film. In presented work, thin films of TiO2 were deposited by the sol–gel method on silicon, stainless steel (304L) and Co–Cr–Mo alloy (Vitallium). The process of anatase–rutile phase transformation was investigated by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) studies of deposited coatings. The results were compared with anatase–rutile transformations temperature of TiO2 powders obtained by analogous sol–gel process. The temperature of anatase–rutile phase transformation changed in the range of 700–1000°C and strongly depends on a kind of substrate. It was found that anatase–rutile transformation of TiO2 coating proceeded at a higher temperature than rutilization of titania powders.

Effects of Fe doping on the optical and magnetic properties of TiO2 films deposited on Si substrates by a sol–gel route

Fe-doped TiO2 films were deposited on Si(100) substrates by a sol–gel technique. X-ray diffraction measurements show that all the films contain both anatase and rutile phases, and Fe doping promotes the anatase–rutile transformation of TiO2 films. The optical constants of the films were attained by tackling spectroscopic ellipsometry data. With increasing Fe content, the refractive indices n values at 2 eV photon energy first increases, then decreases, and finally increases again, and the optical band gap of the films sharply reduces from 3.60 to 3.30 eV. These results may be not only related to Fe contents but also to the phase composition changed by Fe doping. In addition, the undoped TiO2 film showed feeble ferromagnetic character. Ferromagnetic behaviors were clearly observed for x = 0.01 Fe-doped TiO2 film. When x > 0.01, the magnetizations of the samples, firstly decrease and then increase with the increment Fe content, which may be due to an anatase-to-rutile junction destroying an F-center bound magnetic polaron. The n values at 2 eV photon energy first increases, then decreases, and finally increases again with the increase of Fe composition, which suggested the complicated polarity mechanism of the present samples. The abnormal changes of refractive indices may be related to not only Fe doping but also the outcome of the anatase/rutile junctions

Crystalline Mixed Phase (Anatase/Rutile) Mesoporous Titanium Dioxides for Visible Light Photocatalytic Activity

The high photocatalytic activity of mixed phase (80% anatase and 20% rutile) titanium dioxide (Degussa P25) has attracted a great deal of interest in recent years. However, its low efficiency in visible light and nonporous nature limits the potential use and capabilities. Here, we report a novel preparation method for crystalline, thermally stable (up to 800 °C) TiO2 materials with tunable anatase/rutile phase compositions (0–100%) and monomodal mesoporosity. The control of the phase compositions was achieved by framework vanadium doping and various applied heat treatments. Vanadium (0% to 10% doping) decreased the anatase–rutile transformation temperature (from 1000 to 600 °C) and shifted the absorption band to the visible light region (narrowed the band gap). The mesopore structure was preserved in mixed phase TiO2. These materials are members of the recently discovered University of Connecticut (UCT) mesoporous materials family. The UCT materials are randomly packed nanoparticle aggregates and mesopores that are formed by connected intraparticle voids. The synthesis of UCT materials relies on controlling the sol–gel chemistry of inorganic sols in inverse surfactant micelles and NOx (nitric oxides) chemistry. The visible light (>400 nm) photocatalytic activity of mixed phase mesoporous titania samples was studied. The highest photocatalytic activity was obtained by mesoporous titania with 61% anatase and 39% rutile composition. The catalyst can totally remove (100% conversion) methylene blue dye (MB) under visible light irradiation in 2 h, whereas commercial P25 was only able to remove 28% under the same reaction conditions. The mixed phase mesoporous material also shows high photocatalytic activity for degrading phenol and 4-chlorophenol under visible light irradiation. Moreover, the good crystallinity, high surface area (94 m2/g), and monomodal mesoporosity (around 5 nm) can be preserved even after three cycles of photocatalytic reactions.

Enhanced photocatalytic performance of TiO2 particles via effect of anatase–rutile ratio

In the present work anatase–rutile transformation temperature and its effect on physical/chemical properties as well as photocatalytic activity of TiO2 particles were investigated. The characterisation of the synthesised and annealed TiO2 particles were determined by X-Ray Powder Diffraction (XRD), scanning electron microscope (SEM), dynamic light scattering (DLS) and Brunauer–Emmett–Teller surface area analysis (BET). The refraction in the ultraviolet–visible (UV–vis) range was assessed using a dual-beam spectrophotometer. The photocatalytic performance of the particles was tested on methylene blue solution. The XRD data indicated that the percentage of rutile increased with the annealing temperature and almost 100% of anatase transformed to rutile at 1000°C. In addition, the phase transformation was a linear function of annealing temperature so phase composition of TiO2 can be controlled by changing the annealing temperature. The SEM and BET results presented the increase of agglomerate size and the decrease of specific surface area with the increasing annealing temperature. This proved that anatase has smaller particle size and higher surface area than rutile. The photocatalytic activity of the annealed TiO2 powders reduced with the increase of annealing temperature. The samples annealed at 900°C and 925°C with anatase: rutile ratio of 92:8 and 77:23, respectively, showed the best activity. These results suggested that the photocatalytic activity of TiO2 particles is a function of phase composition. Thus it can be enhanced by changing its phase composition which can be controlled by annealing temperature.

Sol–gel derived Ag-containing TiO2 films on surface roughened biomedical NiTi alloy

Ag-containing TiO2 films (Ag/Ti=3.3, 9.1 at%) were sol–gel coated on NiTi alloy that had been surface roughened by the NaOH–HCl treatment for antibacterial application. Thermal analyses of the dried gels reveal that the addition of 9.1 at% Ag lowers the anatase-rutile transformation temperature from 618 to 586°C. Morphological observation shows that surface roughening and silver addition improve structural integrity of the TiO2 films. X-ray diffraction reveals that the addition of Ag does not obviously change crystallinity of the anatase films. X-ray photoelectron spectroscopy results indicate metallic nature of Ag in the film and complete coverage of the films on the roughened alloy substrate. Microindentation test exhibits that the Ag–TiO2 film on the roughened substrate has higher cohesive strength than that on the polished substrate. The potentiodynamic polarization test in a Ca-free Hank׳s balanced salt solution demonstrates good protection of the TiO2 and Ag–TiO2 films for the alloy substrate. Ultraviolet light illumination for 3h can increase surface hydrophilicity of the coated NiTi samples by reducing contact angles from >65° to <20°.

High energy ball milling of titania and titania–ceria powder mixtures

Titania alone and several titania–ceria blends of powders were milled by high energy ball milling for different periods of time. Phases, crystal size, particle size and morphology were evaluated. The research has demonstrated that milling reduces the mean crystallite size to less than 30nm for any time whereas powder particles coalesce into coarse agglomerates. At the same time anatase titania transforms to rutile after 3hour milling, but a thermal treatment at 700°C for 1h partially recovers the original crystal structure. The behaviour of ceria–titania blends is similar to that of titania alone, but the reversibility of the anatase–rutile transformation does not occur when the quantity of ceria is greater than a critical level which we have set between the composition with Ce/Ce+Ti ratios of 5 and 10wt.%.

Nanostructuring anatase through the addition of acetic acid by the sol–gel low temperature aqueous processing

Extremely small, thermostable and highly crystalline anatase nanopowder was produced by increasing additions of acetic acid. The chemistry of the acetate carboxilate group formed by the addition of acetic acid during the sol–gel aqueous acidic process, is investigated by IR spectroscopy. An excess of the acetic acid brings about a higher concentration of the bidentate complex, leading to a higher crystallinity of the anatase, limiting the particle size and retarding the anatase–rutile transformation temperature. Anatase nanostructural characterization is achieved through X Ray diffraction, TEM, HRTEM and electron diffraction techniques.

The influence of concentration of doping elements on anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their pigmentary properties

An analysis of the effects of dopants concentration and different starting titanium compounds on the anatase to rutile phase transformation at the synthesis of rutile pigments Ti1−3xCrxNb2xO2±δ is presented in this study. The main goal was to analyze reaction mixtures for x = 0.05 (previous study) and 0.30 by simultaneous TG–DTA analysis and to determine the temperature of anatase–rutile transition. For x = 0.05, initial temperatures 760–830 °C are needful for a formation of rutile structure. The temperature is the lowest for the hydrated Na2Ti4O9 paste (760 °C) and similar for other starting compounds of titanium. But for x = 0.30, the anatase–rutile transition begins at higher temperatures 910–1,030 °C because of high-Nb content, which is the inhibitor of this modification change. In addition, we found the influence of calcination temperatures (850, 900, 950, 1000, 1050, 1100, and 1150 °C) on color properties and particle size distribution of these materials prepared from anatase TiO2 and with x = 0.30. Selected pigments were also analyzed by X-ray powder diffraction.

Dielectric Properties and Characterisation of Titanium Dioxide Obtained by Different Chemistry Methods

We made comparison of titanium dioxide powders obtained from three syntheses including sol‐gel and precipitation methods as well as using layered (tetramethyl)ammonium titanate as a source of TiO2. The obtained precursors were subjected to step annealing at elevated temperatures to transform into rutile form. The transformation was determined by Raman measurements in each case. The resulting products were characterised using Raman spectroscopy and dynamic light scattering. The main goal of the studies performed was to compare the temperature of the transformation in three titania precursors obtained by different methods of soft chemistry routes and to evaluate dielectric properties of rutile products by means of broadband dielectric spectroscopy. Different factors affecting the electrical properties of calcinated products were discussed. It was found that sol‐gel synthesis provided rutile form after annealing at 850°C with the smallest particles size about 20 nm, the highest value of dielectric permittivity equal to 63.7, and loss tangent equal to 0.051 at MHz frequencies. The other powders transformed to rutile at higher temperature, that is, 900°C, exhibit lower value of dielectric permittivity and had a higher value of particles size. The correlation between the anatase‐rutile transformation temperature and the size of annealed particles was proposed.

Influence of transition metal doping on the structural, optical, and magnetic properties of TiO2 films deposited on Si substrates by a sol-gel process.

Transition metal (TM)-doped TiO2 films (TM = Co, Ni, and Fe) were deposited on Si(100) substrates by a sol–gel method. With the same dopant content, Co dopants catalyze the anatase-to-rutile transformation (ART) more obviously than Ni and Fe doping. This is attributed to the different strain energy induced by the different dopants. The optical properties of TM-doped TiO2 films were studied with spectroscopic ellipsometry data. With increasing dopant content, the optical band gap (EOBG) shifts to lower energy. With the same dopant content, the EOBG of Co-doped TiO2 film is the smallest and that of Fe-doped TiO2 film is the largest. The results are related to electric disorder due to the ART. Ferromagnetic behaviors were clearly observed for TM-doped TiO2 films except the undoped TiO2 film which is weakly magnetic. Additionally, it is found that the magnetizations of the TM-doped TiO2 films decrease with increasing dopant content.

Structural, magnetic and optical properties of Ni-doped TiO2 thin films deposited on silicon(1 0 0) substrates by sol–gel process

Ni-doped TiO2 films were deposited on Si(100) substrates by sol–gel technique. X-ray photoelectron spectroscopy analysis suggests that the valence of Ni ion is in +2 and oxygen vacancies increase with increasing Ni content. X-ray diffraction measurements indicate that Ni doping catalyzes the anatase-to-rutile transformation (ART) of TiO2 films, which is due to the decrease of the ART activation energy. The reversible ferromagnetism of the samples with Ni fraction is found, which is due to an anatase-to-rutile junction destroying an F-center bound magnetic polaron. Optical properties of Ni-doped TiO2 films were studied by the ellipsometric spectra. With increasing Ni content, the optical band gap of TiO2 films is decreased from 3.56 to 3.34eV, which may be related to phase composition and impurity band.

The effects of magnesium and aluminium ions’ additions on the kinetics of titanium dioxide structural transformation

Knowledge of kinetics structural transformation of titanium dioxide is very important for the calcination process in titanium white production. Some impurities of titanium raw could have the influence in the crystalline structure of products and the kinetics of transitions. Sulphate salts of aluminium or magnesium were added into samples of TiO2 suspension. After drying, the samples were studied by thermogravimetry at a heating rate of 10 K min−1 to temperature at 1,000 °C. Results of thermogravimetric investigations of dry titanium dioxide suspension show two-stage decreases of sample mass: the first stage is associated with the removal of water, and the second stage is related to the emission of sulphur oxides. A method of X-ray diffraction (XRD) was used in the investigation of the kinetics of anatase–rutile transformation. The samples after drying were heated at 750, 800, 850 or 900 °C in a muffle furnace for 70 min, and then the phase composition was analysed using the XRD method. The results of XRD measurements show that at a temperature of 800 °C after 60 min, the complete transformation of titanium dioxide into rutile occurs. The addition of Al ions to the suspension of TiO2 has a negative influence on (increases) the time it takes for the complete transformation of the anatase into rutile. Analysis of these phase-transformation diffractograms led to an activation energy in the Avrami–Erofeev model with n = 8/3 of 178 kJ mol−1. The influence of the Mg ion’s addition on the kinetics of the phase transformation is negligible.

Anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their color properties

Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti1−3xCrxNb2xO2+x/2 by conventional solid state method from titanium dioxide TiO2 (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO2·nH2O, titanyl sulfate dihydrate TiOSO4·2H2O (VKR 611), hydrated sodium titanium oxide paste Na2Ti4O9·nH2O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na2Ti4O9 paste (760 °C) and similar for other starting compounds of titanium.

Pigmentary properties of rutile TiO2 modified with cerium, phosphorus, potassium, and aluminium

AbstractThe influence of different modifiers, phosphorus, potassium, aluminium, and cerium on the pigmentary properties of TiO2 was studied. The phase composition and distribution of modifiers in prepared TiO2 products was investigated using XRD analysis, the selective leaching method, and ICP-AES technique. The optical properties, photoactivity, morphology, and surface area of modified TiO2 were determined by spectrophotometric, fluorescent, SEM, and BET measurements. The research was directed towards obtaining a pigmentary TiO2 with the highest possible photostability. It was found that the final calcination temperature, at which the anatase-rutile transformation rate was &gt; 97 %, depended on the kind and amount of the modifiers introduced into hydrated titanium dioxide. In comparing the colour of TiO2 products modified with Ce, it was found that the addition of K to the TiO2 series caused an increase in all the optical properties examined. The presence of K and Al in TiO2 modified with Ce resulted in decreased photocatalytic activity. The photostability of TiO2 modified with Ce and K improved with an increase in P2O5 content. The highest photostability was measured for the TiO2-CePKAl series. It was concluded that the differences in both the optical properties and photoactivity of TiO2 depended on its phase composition and the distribution of modifiers in the products obtained.

Photocatalytic degradation of methylene blue dye using Fe2O3/TiO2 nanoparticles prepared by sol–gel method

The photocatalytic degradation of methylene blue dye was successfully carried under UV irradiation over Fe2O3/TiO2 nanoparticles embedded various composition of Fe2O3 (0–20)wt.% synthesized by sol–gel process. Structural and textural features of the mixed oxide samples were investigated by X-ray diffraction [XRD], Fourier transformer infra-red [FTIR], Energy dispersive X-ray [EDX], Field emission electron microscope [FESEM] and transmission electron microscope [TEM]. However, the optical features were estimated using UV–Vis spectrophotometer. The results reveal that the incorporation of various Fe2O3 up to 7% is associated by remarkable increase in surface area, reduction of particle size, stabilization of anatase phase, shifting the photoexcitation response of the sample to visible region and exceptional degradation of methylene blue dye. On the other hand, increasing Fe2O3 contents up to 20wt.% is associated by anatase–rutile transformation, increasing in particle size and remarkable decrease in surface area which are prime factors in reducing the degradation process. The experimental results indicate that Fe2O3/TiO2 nanoparticles having both the advantages of photodegradation–adsorption process which considered a promising new photocatalysts that involve in the abatement of various organic pollutants.

Nanoparticulate TiO2–Al2O3 Photocatalytic Media: Effect of Particle Size and Polymorphism on Photocatalytic Activity

Impregnation of size-selected titanium-oxo-alkoxy nanoparticles into monolithic ultraporous alumina (UPA) permits nanoparticulate photocatalytic media with an extended activity into the high-temperature range up to 1000 °C, which is explained by anatase TiO2 phase stability due to the inhibited nanoparticles aggregation. In this Article we report on the effect of the nanoparticle polymorphism and size on the photocatalytic ethylene gas decomposition. Use of UPA supports of γ, θ, and α polymorphs, covered with silica or not, and thermal treatment at different temperatures allow modification of the nanoparticles size and crystalline composition. In all cases, the interaction between titania and UPA support is found to affect the polymorph stability. In particular, a separating layer of silica increases the temperature of the anatase-rutile transformation. The main conclusion is that anatase nanoparticles exhibit the higher activity compared to rutile and composite anatase/rutile nanoparticles. The rutile activity strongly decreases with size 2R ≥ 5 nm, while that of anatase nanoparticles does not appreciably change for sizes 5 nm ≤ 2R ≤ 10 nm. The material activity strongly decreases when rutile phase is nucleated onto the anatase one.