Structural and dielectric properties of Li2O-doped TiO2

The dielectric properties of the system Li–Ti–O have been exploited in the frequency range 20 Hz–1 MHz in order to obtain permittivity data of materials having high-κ′ and low loss. Doping of titanium dioxide with lithium oxide acts as a strong promoter of the anatase to rutile phase transition and it may reduce the phase transition temperature (915 °C) by more than 100 °C, possibly due to induced oxygen concentration disorders in the ternary Li–Ti–O system. For TiO₂:Li₂O molar ratios of 98.92:1.08 and calcination temperature of 950 °C the resulting material exhibits high-κ′ and low-loss permittivity properties with lack of interfacial polarization effects. Its dielectric response is superior compared to pure (undoped) rutile as obtained by calcination at much higher temperatures (1180 °C).     

Raman spectroscopy study of the phase transformation on nanocrystalline titania films prepared via metal organic vapour deposition

Raman spectroscopy (RS) was used to study the phase transformations of nanocrytalline TiO₂ thin films. The films were grown by a vertical-flow cold-wall metal organic chemical vapour deposition system, using Ti(C₁₀H₁₄O₅) as the source reagent, at different substrate temperatures. The results indicate that the anatase phase is present at around 550 °C and the rutile phase starts to form at 620 °C. The anatase phase completely transforms into the rutile phase at 680 °C. We have demonstrated that RS can be used as a powerful nondestructive technique for a quick and efficient determination of the phase of TiO₂ thin films.     

Development of the fumed TiO2 having high content of rutile structure and dispesibility using the dry-type of surface modification and the thermal treatment

The effect of dry-type surface modification of a fumed TiO₂ and the thermal treatment were studied to synthesize the new fumed TiO₂ having a high content of rutile structure and high dispersibility. The fumed TiO₂ was modified with various metallic alkoxides to prepare precursors and next the resulted precursors were thermally-treated by the novel natural dropping method with a very short heating time, less than 1 s. The focus of this investigation was on the metallic alkoxide species as a surface modification agent and morphologies of both the precursor and thermally-treated fumed TiO₂. The morphologies and nanostructures of the obtained fumed TiO₂ were characterized. The carbon content and agglomerate of the precursor influenced on the transformation ratio from anatase to rutile structure. It was confirmed that the dry-type surface modification with tetraethoxysilane (TEOS) and titanium tetra-isopropoxide (TTIP) at room temperature is very effective method to prepare precursors for the next thermal treatment. The thermally-treated fumed TiO₂ modified with TTIP showed 100% rutile structure with pure TiO₂ composition at 1400 °C. The thermally-treated fumed TiO₂ modified with small quantities of TEOS exhibited both 100% rutile structure and excellent dispersibility. This high dispersibility caused from a sponge-like structural characteristic of the agglomerate and static electricity repellence by coated SiO₂ layer. The thermally-treated fumed TiO₂ modified with TEOS and TTIP showed the color tone shift can be attributed to rutile structure. It was revealed that the combination of dry-type surface modification and natural dropping thermal treatment is an attractive method to prepare the new fumed TiO₂ with 100% rutile structure maintaining the high dispersiblity.     

Preparation and photocatalytic activity of highly ordered mesoporous TiO2–SBA-15

TiO₂–SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO₂₀PO₇₀EO₂₀) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N₂ adsorption–desorption experiments. The resulting TiO₂–SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S_BET of 689 m² g^? 1 and 347 m² g^? 1 at different hydrothermal temperatures (100 °C and 130 °C). The photocatalytic activity of these TiO₂–SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO₂–SBA-15 mesoporous materials prepared at the TiO₂:SiO₂ mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO₂:SiO₂ mass ratio of 75:25.     

Adsorption and photocatalysis of nanocrystalline TiO2 particles prepared by sol–gel method for methylene blue degradation

Titanium dioxide (TiO₂) powders were synthesized by using TiO₂ colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol–gel method. The effect of aging times and temperatures on physical and chemical properties of TiO₂ sol particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO₂ can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO₂ powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO₂ powders was evaluated by studying the degradation of 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO₂ powders. The highest photocatalytic activity was observed in TiO₂ powder synthesized at 90 °C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio.     

Structure and luminescence properties of TiO2:Er3+ nanocrystals annealed at different temperatures

Erbium doped TiO₂ nanocrystals with the structures of anatase, pyrochlore Er₂Ti₂O₇, and rutile, characterized by X-ray diffraction, have been obtained at different annealing temperatures from 300 °C to 900 °C. The nanocrystalline size for anatase TiO₂ is reduced with increasing doped erbium concentration. Following ultraviolet 325 nm irradiation, the intensity of the green emission is the most intense for the TiO₂:Er³⁺ nanocrystals with a structure of pyrochlore Er₂Ti₂O₇, which evolves from the structure of anatase annealed at 800 °C. Moreover, following ultraviolet 325 nm and infrared 980 nm irradiation, the visible emission spectra for the nanocrystals annealed at 900 °C change drastically. Correspondingly, the structure of anatase disappears, while that of rutile becomes dominant, which indicates that phase transformation occurs.     

Photocatalytic degradation mechanisms of dimethyl phthalate esters by MWCNTs-anatase TiO2 nanocomposites using the UHPLC/Orbitrap/MS technique

Dimethyl phthalate esters (DMPEs) have been identified as endocrine disrupting plastisizers and emerging contaminants which can be released readily upon exposure to the environment. In this study, MWCNTs/TiO₂ nanocomposites, which possess the potential application for the photocatalytic degradation of DMPEs under UV irradiation, were prepared via simple one-pot sol-gel reaction using titanium isopropoxide (TTIP) as titania precursor and multiwalled carbon nanotubes (MWCNTs). The MWCNTs/TiO₂ nanocomposites was calcined in air for 2 h at the temperatures ranging from 350 to 750 °C. As a result, the MWCNTs/TiO₂ nanocomposites synthesized at calcination temperature of 450 °C demonstrated the highest photodegradation efficiency of 97% after 180 min UV irradiation and its degraded products were evaluated using the ultra high performance liquid chromatography (UHPLC) coupled with a high resolution (HR) Orbitrap mass spectrometry (MS). A primary degradation mechanism was proposed and it was noteworthy that some new intermediates were discovered and reported. This work has developed a simple method for qualitative determination of DMPEs based on HPLC with UV detection.     

Nanoporous,bioactive and cytocompatible TiO2 encapsulated Ti particles as bone augmentation material

Bone impaction grafting is a surgical technique used for the restoration of bone stock loss with impaction of autograft or allograft bone particles. Porous Ti particles are deformable, like bone particles, and offer better primary stability. In this study, spherical Ti particles were subjected to H₂O₂ solution treatment at 70 °C for 3 h and heat treated at different temperatures in the range of 400–800 °C. FE-SEM observation showed that Ti particle form highly porous network structure and these porous network structures were confirmed to be hydrogen titanate by Raman analysis. Subsequent heat treatment at temperature ranges of 400–800 °C showed the gradual transformation of hydrogen titanate network to anatase and finally rutile phase of TiO₂. The network structure appeared to be compacted by the heat treatment due to water removal and ultimately take the particulate morphology above 800 °C. Thus formed TiO₂ encapsulated Ti particles showed bioactivity in terms of deposition of apatite layer from simulated body fluid in the range of 400–600 °C. The cytocompatibility studies using osteoblast-like cells, MG63 showed good cell viability as well as adhesion for all Ti particles. Present results indicates that bioactive TiO₂ encapsulated Ti particles could be a candidate material to be useful as bone or dental cavity filler or bone cement for total hip replacement materials.     

Synthesis of TiO2 thin films using single molecular precursors by MOCVD method for dye-sensitized solar cells application and study on film growth mechanism

For dye-sensitized solar cells application, in this study, we have synthesized TiO₂ thin films at deposition temperature in the range of 300–750 °C by metalorganic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, {TIP, Ti(OⁱPr)₄} and Bis(dimethylamido)titanium diisopropoxide, {BTDIP, (Me₂N)₂Ti(OⁱPr)₂} were used as single source precursors that contain Ti and O atoms in the same molecule, respectively. Crack-free, highly oriented TiO₂ polycrystalline thin films with anatase phase were deposited on Si(1 0 0) with TIP at temperature as low as 450 °C. XRD and TED data showed that below 500 °C, the TiO₂ thin films were dominantly grown in the [2 1 1] direction on Si(1 0 0), whereas with increasing the deposition temperature to 700 °C, the main film growth direction was changed to [2 0 0]. Above 700 °C, however, rutile phase TiO₂ thin films have only been obtained. In the case of BTDIP, on the other hand, only amorphous film was grown on Si(1 0 0) below 450 °C while a highly oriented anatase TiO₂ film in the [2 0 0] direction was obtained at 500 °C. With further increasing deposition temperatures over 600 °C, the main film growth direction shows a sequential change from rutile [1 0 1] to rutile [4 0 0], indicating a possibility of getting single crystalline TiO₂ film with rutile phase. This means that the precursor together with deposition temperature can be one of important parameters to influence film growth direction, crystallinity as well as crystal structure. To investigate the CVD mechanism of both precursors in detail, temperature dependence of growth rate was also carried out, and we then obtained different activation energy of deposition to be 77.9 and 55.4 kJ/mol for TIP and BTDIP, respectively. Also, we are tested some TiO₂ film synthesized with BTDIP precursor to apply dye-sensitized solar cell.     

Effect of HNO<Subscript>3</Subscript> on crystalline phase evolution in lithium silicate powders prepared by sol–gel processes

An interesting observation is reported on the dramatic effect of HNO₃ on crystalline phase evolution in the 33.3 mol% Li₂O–SiO₂ glass–ceramic (stoichiometric composition of lithium disilicate Li₂Si₂O₅, LS₂) prepared by sol–gel processes from tetraethylorthosilicate (TEOS) and lithium ethoxide precursors. Nitric acid (65%), in molar ratio HNO₃/TEOS = 0.1, was added either to the precursor sol or to 95 °C dried gel. The product, which is amorphous at temperatures below 450 °C, transforms into crystalline lithium metasilicate (Li₂SiO₃, LS) at around 550 °C (starting temperature ∼450 °C), instead of forming crystalline LS₂. Phase separation in the glassy phase may be responsible for the formation of lithium metasilicate. XRD, ²⁹Si MAS, and ⁷Li static NMR were used to follow the crystallization evolution and network structures of the materials heat-treated at various temperatures.     

Photovoltaic performance of dye sensitized solar cell based on rutile TiO2 scaffold electrode prepared by a 2 step bi-layer process using molten salt matrices

Dye sensitized solar cells were made on TiO₂ scaffold anodes of rutile particles. These TiO₂ scaffold anodes were grown from rutile seeds by using a molten salt synthesis technique. Different thickness coatings of mixed amorphous titanium hydroxide and NaCl–KCl eutectic salt mixture on the rutile seeds were heat treated at different temperatures. The rutile whiskers of different aspect ratios were grown depending on the growth temperature. The best photovoltaic performances were obtained for the device made from the scaffold of 20–50 nm diameter and 0.5–1 μm length nanowhiskers obtained at 700 °C for 5 h of treatment.     

Comparison of nano-particulate TiO2 prepared from titanium tetrachloride and titanium tetraisopropoxide

Nanocrystalline titanium dioxides (TiO₂) prepared from (a) titanium tetrachloride (TiCl₄) and (b) titanium tetraisopropoxide (TTIP) have been compared. The effect of the reaction parameters on the phase formation of TiO₂ was investigated systematically. For TiO₂ prepared by hydrolysis of TiCl₄, the crystal phase changed with the speed of TiCl₄ addition and slow addition favoured the formation of rutile. For TiO₂ prepared by hydrolysis of Ti(OC₃H₇)₄, the reduction in hydrolysis rate associated with lower reaction temperatures promoted rutile formation. For both TiCl₄ and TTIP derived samples, increasing the anatase content decreased the measured rate of photocatalytic oxidation of isopropanol to acetone.     

无模板法可控合成多层次结构二氧化钛微球

以1,4-二氧六环为溶剂,采用溶剂热法成功实现无模板法可控合成二氧化钛多层次结构微球。通过系统改变反应体系中浓盐酸与四异丙醇钛(TTIP)相对物质的量比能够有效调控二氧化钛形貌。当浓盐酸与TTIP物质的量比控制在0(或0.7或0.9)、1.8、3.6与5.7时,所得产物分别为纳米颗粒构建二氧化钛微球、纳米棒修饰二氧化钛微球、纳米棒花菜结构以及纳米棒海胆结构。在成功进行形貌调控的基础上,进一步探讨了二氧化钛多种结构的形成机理,并对其光催化产氢性能进行了表征。研究发现,在这4种结构中,纳米棒修饰二氧化钛微球具有最佳的光催化性能,这可能是由于同时存在金红石和锐钛矿两种晶型而形成异质结结构所导致。     

The effects of different acids on the preparation of TiO2 nanostructure in liquid media at low temperature

Titania of different crystalline structures and morphology was prepared by the low temperature dissolution–reprecipitation process (LTDRP) of amorphous precursors in various acidic mediums at 70 °C for 8 h. The effects of different acids on the crystalline and morphology of titania nanostructures were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results showed that HCl, HNO₃ and their mixture favored the formation of rod-like rutile TiO₂, while H₂SO₄ and its mixture with HCl or HNO₃ retarded the formation of rutile but favored the formation of the anatase phase of with an irregular shape. The mechanism of the formation of various titania nanostructures was also discussed.     

Effect of heat treatment on structure evolution and properties of nano zinc titanate ceramics

Nano zinc titanate ceramics are prepared using a conventional solid state method. The obtained compacts are sintered at 800, 900, 1000 and 1100 °C for 3 h. The prepared compacts are analyzed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM) for structural and microstructural studies. Based on the X‐ray diffraction (XRD) data, it is observed the coexistence of ZnTiO₃ and α‐Zn₂TiO₄ phases together at low temperature (800 °C) without the presence of TiO₂ (rutile) contradicting the general mechanism stating the transformation of ZnTiO₃ to α‐Zn₂TiO₄ and TiO₂ at higher temperatures. A new mechanism is proposed to explain the formation of nano ZnTiO₃ and α‐Zn₂TiO₄ structures depending on the role of TiO₂ in achieving this mission. According to this mechanism, we propose a partial diffusion of TiO₂ in the ZnO lattice forming the ZnTiO₃ phase. The second part of TiO₂ acts as a catalyst that facilitates the transformation of nano ZnTiO₃ to nano α‐Zn₂TiO₄. The catalytic power of rutile is achieved from its enhanced tensile stress that induces the phase transition from nano ZnTiO₃ to nano α‐Zn₂TiO₄.     

Titanium and iron oxides produced by sol–gel processing of [FeCl{Ti2(OPri)9}]: structural,spectroscopic and morphological features

The first structurally characterised titanium and iron isopropoxide, [FeCl{Ti₂(OPrⁱ)₉}] (1), has been used as a single-source precursor for TiO₂/Fe₂TiO₅ composites prepared by the sol–gel route. Two distinct hydrolysis and condensation conditions were employed, followed by drying and thermal treatment up to 1000 °C. Product composition and oxide phase transitions were characterised by powder X-ray diffractometry and Raman, electron paramagnetic resonance, Mössbauer and Fourier-transformed infrared spectroscopies. A mixture of nanometric-size TiO₂ (anatase, 3.6–5.8 nm) and amorphous iron(III) oxide was obtained up to 500 °C, while TiO₂ (rutile), α-Fe₂O₃ (hematite) and Fe₂TiO₅ (pseudobrookite) were found at 700 °C. At 1000 °C, only rutile and pseudobrookite were observed. These results suggest that 1 behaves as a type III single-source precursor. Powders calcined at 1000 °C were analysed for surface morphology, microstructure and elemental composition by scanning electron microscopy/energy dispersive X-ray spectroscopy. Results suggest no phase segregation on a sub-micrometer level. Different morphologies were observed for the materials produced by the N₂ route, and this could relate to early crystal growth in an oxygen-deficient environment.     

TEM microstructure characterization of nano TiO2 coated on nano ZrO2 powders and their photocatalytic activity

Nano TiO₂ coated commercial nano ZrO₂ powders (20 and 80 wt.%) were synthesized by a sol–gel process. Their microstructure and crystal structure depending on the calcination temperatures were investigated using XRD and HRTEM techniques. In the as-received powders, the nano TiO₂ particles attached to the ZrO₂ particles existed in an amorphous phase. After calcination at 450 and 600 °C, most of the TiO₂ powders were crystallized to an anatase type, whereas at 750 °C, they were changed to a rutile phase.From the comparison of photocatalytic activity, the nano TiO₂ coated ZrO₂ powders calcined at 450 and 600 °C showed excellent efficiency for the removal of methyl orange (MO). However, in the powders calcined at 750 °C, the photocatalytic activity was decreased due to the appearance of a rutile phase.     

The preparation of the anatase and rutile forms of Ag-TiO2 and hydrogen production from methanol/water decomposition

This study examined hydrogen production over Ag-TiO₂ photocatalysts containing Ag_xO, a conducting component. X-ray photon spectroscopy (XPS) confirmed that the Ag and Ag₂O components were dominant in the Ag-TiO₂ photocatalysts treated at 500 and 800 °C, respectively. The Ti2p bands in Ag-TiO₂ were shifted to lower binding energies, which were assigned to Ti³⁺, compared to pure TiO₂, and the shift was greater in the rutile structure than in the anatase. The measured full widths at half maximum (FWHM) of the Ag3d and Ti2p peaks were larger in the anatase structure than in the rutile structure in both TiO₂ and Ag-TiO₂. The H₂ production from methanol photodecomposition was greater over the rutile structure than over the anatase structure of TiO₂. Moreover, the amount of hydrogen was enhanced over Ag-TiO₂ compared to pure TiO₂; the production reached 17,124 μmol after 24 h over rutile Ag-TiO₂. After methanol photodecomposition, the amount of Ag component in the Ag-TiO₂ photocatalysts increased, while the Ag₂O component decreased.     

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.