Anatase-rutile Phase Research Articles

DSC investigation of nanocrystalline TiO2 powder

The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25–100 atm) and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured TiO2 was compared with three commercial TiO2 samples. The sequence of brookite–anatase–rutile phase transformation in TiO2 samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported.

Synthesis and characterization of TiO 2 membrane with palladium impregnation for hydrogen separation

This paper reports the synthesis and characterization of TiO 2 membranes impregnated with elemental palladium (Pd–TiO 2) for hydrogen separation at elevated temperatures and pressures. The membranes were prepared by sol–gel method where the elemental Pd was introduced through sol-mixing of titania sol and Pd precursor solution. The Pd–TiO 2 membranes were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TG/DTA), N 2 adsorb/desorption analysis, and single permeation test of H 2 and N 2. The XRD analysis revealed that the presence of Pd nanoparticles has retarded the crystallization and anatase-rutile phase transition. The TEM images indicated that the Pd–TiO 2 membranes are composed of non-uniform particle size as compared to that of TiO 2 membranes alone. For four times dip-coating, the membrane thickness was measured to be approximately 634 nm. By impregnating small concentration of Pd, it significantly enlarged the pore size of the original TiO 2 membrane structure besides increasing its surface area and pore volume. However, a reverse trend was observed when the Pd concentration was increased further. Single permeance of H 2 and N 2 for both TiO 2 and Pd–TiO 2 membranes showed that the transport mechanism to be dominated by Knudsen diffusion and Poiseuille flow. The ideal selectivity of H 2/N 2 crossing through the Pd–TiO 2 membrane was calculated and found to be less than the theoretical value of Knudsen diffusion based separation. The selectivity of Pd–TiO 2 membrane increased with the temperature increment, whereas the same trend was not observed for TiO 2 membrane. These results show that, there were other transport mechanisms involved apart from Knudsen diffusion and Poiseuille flow.

The Effects of Organic Binders on Palladium Impregnated in TiO2Membrane Synthesis: X‐Ray Diffraction Analysis

This paper reports the effects of organic binders on the crystal microstructure of unsupported, Pd2+‐impregnated TiO2membranes. The organic binders used in this study were polyvinyl alcohol and hydroxypropyl cellulose. The use of the binders is important in the production of crack‐free membranes. However, the use of the binders influenced the microstructure of the unsupported TiO2membranes. X‐ray diffraction analysis utilized showed that the addition of binders has caused aggregation of palladium oxide (PdO) during its formation in the TiO2network. This phenomenon directly affects the effectiveness of PdO presence in the suppression of anatase–rutile phase transition. N2adsorb/desorption analysis was conducted to investigate the Pd2+–TiO2membrane morphology at different Pd2+loading. Based on the observation, the presence of 2 wt% Pd2+in the TiO2microstructure has significant impacts on the increment of surface area, pore volume, and average pore width from the original TiO2. However, the surface area shows decrement after the Pd2+loading was further increased from 2 to 6 and 10 wt%.

Synthesis and characterization of TiO2 doping with rare earths by sol–gel method: photocatalytic activity for phenol degradation

The enhancement of TiO2 photocatalyst activity will lead to more practical applications of this technology. In this work we studied the effect of rare earth doping of sol–gel synthesized TiO2 for phenol degradation and we compared the performance with commercial catalyst. Photocatalysts were characterized by nitrogen adsorption to determine textural properties, ultraviolet visible light diffuse reflectance spectrometry (UV-Vis DRS), X-ray diffraction, STEM-EDS (scanning transmission electronic microscopy-energy dispersive X-ray spectroscopy) and XPS (X-ray photoelectron spectroscopy). Main phase for materials calcined at 500 °C was anatase. Residual nitrogen from NH4OH used in the sol–gel synthesis was identified by XPS analysis. Ti3+/Ti4+ ratio increased when TiO2 was doped with 0.5 wt% of Ce. Anatase phase was stabilized in photocatalysts doped with La even after calcination at 800 °C, for Pr and Nd a mixture of anatase-rutile phases was obtained, whereas for Ce doping only rutile phase was found. For the photocatalytic oxidation of phenol, the best results were obtained for Ce doped TiO2, which could be related to the ability of CeIV/CeIII oxidation/reduction cycle.

Effect of thermal spray processes on anatase–rutile phase transformation in nano-structured TiO2 photo-catalyst coatings

TiO2 photo-catalytic coatings were deposited using three different thermal spray techniques, namely, flame, plasma and high velocity oxy-fuel (HVOF). TiO2 nanopowders were used as feedstock. X-ray diffraction analysis and scanning electron microscopy were used to study the deposited TiO2 coating. It was concluded that a high anatase content of 80 vol.% can be achieved for the coating deposited by HVOF if kerosene is used as fuel. On the contrary, the anatase contents in the coating deposited by the flame and plasma spray processes were reduced to 29 and 5 vol.% respectively due to their structural transformation of anatase to rutile. Microstructure shows that the as sprayed HVOF TiO2 coating had nanostructure characteristics with smaller grain size than feedstock powder. It was found that the structural transformation of anatase to rutile is significantly influenced by the thermal spray processes. Liquid fuelled HVOF technique can prevent this transformation.

Synthesis of Nanoparticles of Mixed Oxides Containing Titanium Cerium Silver and Silicon: Phase Transformation

Problem statement: Titanium dioxide is a well known material using with self-cleaning application. This is due to its properties after exposed to UV light: Superhydrophilicity and photocatalysis. The addition of other oxides could prolong these properties without continuing exposed to UV. However, titanium dioxide phase is essential. In order to obtain these properties, titanium dioxide needs to be in anatase phase. Approach: In this Research, phase transformation temperatures of mixed oxide of titanium dioxide and other oxides were determined. Samples of different mixed oxides were prepared by sol gel method. The first sample contained 30%TiO2 and 70%SiO2. The second sample contained 30%TiO2, 15%CeO2 and 55%SiO2. The last sample contained 30%TiO2, 15%CeO2 and 55%SiO2. Each sample was separately calcined at various temperatures from 350-850°C stepping by 50°C and followed by grinding and sieving to obtain in the form of powders. Then, each powder was characterized for its microstructure and phases of titanium dioxide, crystallite size by X-Ray diffraction. Results: The results from XRD showed that for a 30%TiO2/SiO2, an increase in calcined temperatures from 350-850°C (increasing by 50°C) increased average crystallite sizes of titanium dioxide (from 5.1-11.8 nm). Also, titanium dioxide phase found in the samples was only anatase. For a 30%TiO2/15%CeO2/SiO2, an increase in calcined temperatures was not affect to the structure of the samples and XRD patterns seemed to be in an amorphous structure. Finally, for a 30%TiO2/15%AgO/SiO2, titanium dioxide was found in an anatase phase at 350°C until 650°C. Then, at calcined temperatures greater than 700°C, rutile phase started appearing in the structure while anatase phase peaks slowly declined with an increasing in calcined temperatures. This result showed that using these mixed oxides to coat over glass slides or mirrors for self-cleaning purposes, the films should be treated at certain temperatures to obtain an anatase phase. Conclusion: Phase transformation of titanium dioxide depends on calcined temperatures. The addition of other oxides such as silica, cerium or silver can effectively suppress the anatase-rutile phase transformation and resulted in an increase of anatase-rutile phase transformation temperatures.

Photocatalytic Activity of N-doped TiO2 Photocatalysts Prepared from the Molecular Precursor (NH4)2TiO(C2O4)2

We developed a novel approach for the preparation of N-doped TiO2 photocatalysts by calcining ammonium titanium oxalate at different temperatures. The structures of N-TiO2 were characterized by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, diffuse reflectance UV-Vis spectroscopy, and scanning electron microscope. The N-doped TiO2 photocatalysts calcined below 700 °C are the pure anatase phase but that calcined at 700 °C is a mixture of anatase and rutile phases. The doped N locates at the interstitial site of TiO2 which leads to the narrowing of bad gap of pure anatase N-TiO2. Among all photocatalysts, N-TiO2 photocatalysts calcined at 600 and 400 °C exhibit the best performance in the photodegradation of methyl orange under the UV light and all-wavelength light illuminations, respectively; however, because of the perfect crystallinity and the existence of anatase-rutile phase junctions, N-TiO2 photocatalyst calcined at 700 °C exhibits the highest specific photodegradation rate, i.e., the highest quantum yield, under both the UV light and all-wavelength light illuminations.

Influence of Sodium Chloride and Dibasic Sodium Phosphate Salt Matrices on the Anatase–Rutile Phase Transformation and Particle Size of Titanium Dioxide Powder

The influence of sodium chloride (NaCl) and dibasic sodium phosphate (Na2HPO4·2H2O, DSP) on the phase transformation and particle size of titanium dioxide powder had been investigated. The salt matrix was shown to suppress both the amorphous to anatase transition and the anatase to rutile transition. DSP was particularly effective. Irrespective of the additives, transformation versus time curves of the anatase to rutile conversion were observed to be sigmoidal, and were interpreted in terms of a first order, nucleation‐growth controlled phenomenon. Analysis of these curves using appropriate rate laws yielded activation energies for nucleation of ∼4.3 eV for NaCl salt matrix and ∼8.6 eV for DSP salt matrix, compared with ∼3.2 eV for a sample with no salt. Activation energies for the growth or propagation stage were ∼5 and ∼8.9 eV for NaCl and DSP powders, respectively, compared with ∼3.8 eV for no salt. In the solid state, salt matrices suppressed the particle growth as well. These behaviors, in general are thought to be governed by the presence of salt impurities, especially anions chemisorbed at the surface.

Phase transformation of anatase–rutile crystals in doped and undoped TiO 2 particles obtained by the oxidation of polycrystalline sulfide

The anatase–rutile phase transformation of doped and undoped TiO 2 is discussed on the basis of crystal chemistry and the photoelectric oxidation properties of the mixture phase using different parameters. The X-ray diffraction (XRD) results confirm that temperature and time affect the anatase–rutile transformation, whereas the Fe-dopant concentrations had no effect on the anatase–rutile transformation. Field Emission Scanning Electron Microscope (FE-SEM) studies also indicate the presence of single anatase and anatase–rutile mixed phase structures on the surface of TiO 2. X-ray photoelectron spectroscopy (XPS) was used to investigate the Ti state in the final product. The coexistence of the anatase–rutile mixture in TiO 2 particles caused significant light absorption and higher degradation efficiency by the synergism between rutile and anatase particles.

Thermogravimetric and UV–vis spectroscopic studies of chromium redox reactions in rutile pigments

In this study undoped and Cr, Sb or Mo doped TiO 2 were synthesized by polymeric precursor method and characterized by X-ray diffraction, UV-VIS spectroscopy, infrared spectroscopy and thermogravimetry (TG). The TG curves showed a continuous mass loss assigned to the hydroxyl elimination and Cr 6+ reduction. Doped TiO 2 samples showed a higher mass loss assigned to water and gas elimination at lower temperatures. In these doped materials a decrease in the anatase-rutile phase transition temperature was observed. After calcination at 1,000 °C, rutile was obtained as a single phase material without the presence of Cr 6+ .

Hydrothermal synthesis of mesostructured nanocrystalline TiO 2 in an ionic liquid–water mixture and its photocatalytic performance

Anatase mesostructured TiO 2 nanocrystalline was prepared in a mixture of 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIM +BF 4 −) ionic liquid and water by a low temperature hydrothermal method. The obtained materials were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and N 2 adsorption–desorption. The existence of BMIM +BF 4 − enhanced the polycondensation and crystallization rate, which encouraged the formation of anatase crystal. The TiO 2 particles were thermally very stable and thus resistant to anatase-rutile phase transformation during calcination at high temperatures. The anatase TiO 2 showed high photocatalytic activity in the degradation of p-chlorophenol than that of the commercially available TiO 2, Degussa P25. After 2 h reaction under the UV-irradiation of 250 W, the removing rate of p-chlorophenol was up to 96.3%.

Highly stable re-dispersibility of nanocrystalline TiO2 observed during anatase-rutile phase transformation

TiO2 nanoparticles were prepared employing forced hydrolysis of titanium tetrachloride in an acid aqueous solution. We observed the highly stable dispersibility of TiO2 nanoparticles calcined at 600 °C and 700 °C in water. X-ray diffraction (XRD) showed that the phase transformation from anatase (A) to rutile (R) occurred when the nanoparticles were calcined over 600 °C. Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FT-IR) and Thermo-gravimetric analysis (TGA) showed that the phase transformation led to the formation of the better spherical particlesis, which were in favour of water adsorption onto the surface of the TiO2. The Brunauer–Emmett–Teller (BET) data of particles calcined at different temperatures showed that the surface hydration forces impeded TiO2 particles aggregation and resulted in the high structural stability during A–R phases transformation. Zeta potentials of TiO2 nanoparticles calcined at different temperature showed the electrostatic forces were not crucial factors in the stable dispersibility. A model illustrated that the spherical particles of TiO2 allowed maintaining the high density of water on the surface of TiO2 nanoparticles. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study of phase transformations in the surface layer of titanium dioxide

The capabilities of the diffuse reflectance spectroscopy in a study of the state of the surface layer of anatase in anatase-rutile phase transformations in successive thermal treatments of anatase in the temperature range 200–900°C and in analysis of titanium dioxide of P25 brand (Degussa) containing anatase and rutile in a 80: 20 ratio, respectively, are demonstrated for the example of dispersed titanium oxide.

Direct continuous hydrothermal synthesis of high surface area nanosized titania

Nanosized TiO 2 powder of high surface area was prepared from an aqueous solution of titanium(IV) bis(ammonium lactato) dihydroxide using a continuous hydrothermal flow synthesis (CHFS) reactor which uses superheated water at 400 °C and 24.1 MPa as a crystallizing medium. Freeze-dried nano-TiO 2 was heat-treated in air over a range of temperatures and then the resulting powders were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), BET surface area measurement, and Raman spectroscopy. The particle size of the ‘as-prepared’ TiO 2 made using CHFS was ca. 4.8 nm (by HR-TEM), and grew with increasing heat-treatment temperature. It was found that the onset of the anatase–rutile transition of heat-treated nano-TiO 2 in air occurred at 500 °C and reached 100% rutile at 900 °C. The Raman band ( E g) at ∼150 cm −1 of anatase (nano-TiO 2) softens as the particle size increases with heat-treatment temperature (up to 600 °C). The photocatalytic activity of the TiO 2 powders for the decolourisation of methylene blue dye was assessed. The effects of nano-TiO 2 anatase-rutile phase composition, crystallinity, and crystallite size on the catalytic activity were investigated.

The influence of temperature on the color of TiO 2:Cr pigments

TiO 2:Cr brown pigments were prepared via a polymeric precursor derived from the Pechini method. The pigments were analyzed by infrared spectroscopy, X-ray diffraction, ultraviolet–vis spectroscopy, and colorimetry. The increase of the calcination temperature from 700 to 1000 °C led to a decrease in the L* values, corresponding to darkening of the pigments. The pigments obtained in this work are darker than those produced by a solid-state reaction method reported before. The change in the pigment color is due to the anatase–rutile phase transition, which leads to a shift in the charge transfer bond (Ti 4+ ↔ O 2−) due to a change in the crystal field around the chromophore ions. Moreover, the oxidation state of chromium was observed to change, and this also alters the color of the pigments.

Structure tailoring of fluorine-doped TiO 2 nanostructured powders

Fluorine-doped nanocrystalline TiO 2 powders with controlled anatase–rutile phase content are synthesized by a sol–gel route using NH 4F and CF 3COOH as fluorine sources. The X-ray diffraction (XRD) study reveals that fluorine-doping through NH 4F leads to the formation of anatase crystalline phase, whereas F-doping through CF 3COOH favors the formation of rutile along with anatase phase. These results are connected to the influence of the fluorine precursor on the pH of the starting solutions. The presence of the fluorine in the powders is confirmed using X-ray photoelectron spectroscopy (XPS). The dopant in concentrations between 11 and 16 at.% is found mainly in the form of metal fluoride. The measured UV–vis diffuse reflectance spectra and the calculated band gap widths using Kubelka–Munk phenomenological theory are in good agreement with the crystallographic results. The calculations reveal no change in the band gap values due to fluorine doping. The enhanced absorbance in the vis region and the red shift of the absorption edge are attributed to the presence of fluorine and the anatase/rutile phase composition of the TiO 2 powders.

Effect of manganese ions concentration on the anatase–rutile phase transformation of TiO 2 films

The phase structures of Ti 1− x Mn x O 2 (0⩽ x<0.08) films synthesized by sol–gel spin coating have been investigated. The effect of Mn dopants on the stability of titanium dioxide (TiO 2) was studied by X-ray diffraction and Raman spectra for isochronally annealed samples. The increased Mn dopant concentration decreased the onset temperature of anatase–rutile (A–R) phase transformation. The calculated activation energy for the phase transformation decreased from 173.6 to 89.4 kJ/mol with Mn dopants concentration increasing from 0% to 7.51%. The Mn ions incorporated into the TiO 2 lattice reduce the rutile nucleation barrier and promote the nucleation rate.

Preparation and visible-light-driven photoelectrocatalytic properties of boron-doped TiO 2 nanotubes

In the present study, chemical vapour deposition (CVD) was applied to dope boron into TiO 2 nanotubes anodized Ti in C 2H 2O 4·2H 2O + NH 4F electrolyte with the goal of improving the photocatalytic (PC) activity under visible light. The undoped TiO 2 nanotubes had a highly self-organized structure. However, after doping through CVD, TiO 2 nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results confirmed that annealing temperature had an influence on the phase structure and boron impurities could retard anatase–rutile phase transition. Diffuse reflectance absorption spectra (DRS) analysis indicated that B-doped samples displayed stronger absorption in both UV and visible range. B-doped TiO 2 nanotubes electrode annealed at 700 °C through CVD showed higher photoelectrocatalytic (PEC) efficiency in methyl orange (MO) degradation than that annealed at 400 °C and 550 °C. MO degradation was substantially enhanced with the increasing applied bias potential. Moreover, there was a synergetic effect between the electrochemical and photocatalytic processes, and the synergetic factor R reached 1.45. B-doped TiO 2 nanotubes electrode showed good stability after 10 times by repeating photoelectrocatalysis of MO.

Formation of solid solutions in the TiO2-Cr2O3 system

The phase formation and reaction kinetics in the TiO2-Cr2O3 system have been studied by x-ray diffraction and electron microscopy. The Cr2O3 solubility in TiO2 has been accurately determined, and the rate parameters of the formation of solid solutions in this system have been evaluated. The results demonstrate that Cr2O3 dissolves in rutile and not in anatase. Cr2O3 markedly reduces the temperature of the anatase-rutile phase transition.

Photocatalytic property of colloidal TiO2 nanoparticles prepared by sparking process

Titanium oxide nanoparticles (NPs) were successfully prepared by sparking off two titanium tips into water for 1–5 h. The nanoparticle-dispersed water was obtained for further characterization. The transmission electron microscopy result shows that the particle size is in the range of 1–5 nm. The electron diffraction patterns and Raman spectra reveal that the as-prepared and the annealed samples at 250 °C are the anatase phase. However, the anatase–rutile phase transformation was observed from the samples at annealing temperature as low as 500 °C. The result of methylene blue-decoloration testing under sunbath suggests that the NPs have good photocatalytic property.