Low-temperature Ti-containing 3:2 and 2:1 mullite nanocrystals from single-phase gels

TiO₂-containig single-phase gels with (Al₂O₃ + TiO₂)/(SiO₂) molar ratios 3/2 and 2/1 were prepared by gelling mixtures of aluminium nitrate, tetraethylorthosilicate and titanium isopropoxide. Gels were fast heated at several temperatures up to 1100 °C. Dried and heated gels were characterized by differential thermal analysis (DTA), magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray powder diffraction (XRD), and scanning and transmission electron microscopies (SEM and TEM). Coupled DTA and XRD results of gels fast heated at 900 °C showed the crystallisation of two mullites as well as a small amount of alumina-silica spinel. ²⁷Al NMR spectra showed the formation of pentacoordinated aluminium before mullite crystallization. The increase of lattice parameters of single-phase mullites heated at 1100 °C indicated that the amount of TiO₂ incorporated into the mullite structure increased on raising the amount of nominal TiO₂ in both series. SEM and TEM images of heated gels at 1100 °C displayed the formation of well-shaped parallelepiped of titanium-doped mullite nanocrystals with crystalline anisotropy.     

Structure and luminescence properties of Eu3+ doped TiO2 nanocrystals and prolate nanospheroids synthesized by the hydrothermal processing

We report on a new approach to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids. They were synthesized by shape transformation of hydrothermally treated titania nanotubes at different pH and in the presence of Eu³⁺ ions. The use of nanotubes as a precursor to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids opens the possibility of overcoming the problems related to molecular precursors. The shapes and sizes of the nanotubes, Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids were characterized by transmission electron microscopy (TEM) technique. Crystal structures of the resultant powders were investigated by X-ray diffraction (XRD) analysis. The percentage ratio of Eu³⁺ to Ti⁴⁺ ions in doped nanocrystals was determined using inductively coupled plasma atomic emission spectroscopy. The optical characterization was done by using fluorescence and ultraviolet-visible reflection spectroscopies. An average size of faceted Eu³⁺ doped TiO₂ nanocrystals was 13 nm. The lateral dimensions of Eu³⁺ doped TiO₂ prolate nanospheroids varied from 14 to 20 nm, while the length varied from 40 to 80 nm, depending on precursor concentrations. The XRD patterns revealed the homogeneous anatase crystal phase of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids independently of the amount of dopant. A postsynthetic treatment (filtration or dialysis) was applied on the dispersions of the doped nanoparticles in order to study the influence of the dopant position on photoluminescence (PL) spectra. In the red spectral region, room temperature PL signals associated with ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺ were observed in all samples. The increased contribution of dopants from the interior region of dialyzed nanocrystals to photoluminescence was confirmed by the increase of R value.     

Simple fabrication of thermally stable apertured N-doped TiO2 microtubes as a highly efficient photocatalyst under visible light irradiation

Apertured N-doped TiO₂ microtubes have been fabricated by simple hydrolysis of titania tetrachloride using ammonia without any external templates. The morphology and microstucture characteristics of apertured N-doped TiO₂ microtubes were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of microtubes and mesoporous microstructure were maintained after a heat treatment at 723 K for 3 h, exhibiting significantly thermal stability. The catalysts exhibited high ultraviolet and visible light photocatalytic activity in degrading phenol and methyl orange.     

Low-temperature molten salt synthesis of YAlO3 powders assisted by an electrochemical process

YAlO₃ (YAP) powders were successfully synthesized by a unique molten salt method, where YAP precursor was prepared by an electrochemical method at room temperature, followed by calcining it at a temperature of not exceeding 400 °C for 8 h using LiNO₃ as the molten salt medium. XRD analysis and TEM observation show that well-crystallized YAP powders can be obtained at 400 °C for a holding time of 8 h with 1:16 ratio of YAP precursor to LiNO₃ by weight. Greatly reduced temperature of forming YAP should be attributed to the incorporation of LiNO₃ salt in preparing process.     

Photocatalytic activities of N-doped nano-titanias and titanium nitride

TiO₂ doped with various loadings of nitrogen was prepared by nitridation of a nano-TiO₂ powder in an ammonia/argon atmosphere at a range of temperatures from 400 to 1100 °C. The nano-TiO₂ starting powder was produced in a continuous hydrothermal flow synthesis (CHFS) process involving reaction between a flow of supercritical water and an aqueous solution of a titanium salt. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. Products ranging from N-doped anatase TiO₂ to phase-pure titanium nitride (TiN) were obtained depending on post-synthesis heat-treatment temperature. The results suggest that TiN started forming when the TiO₂ was heat-treated at 800 °C, and that pure phase TiN was obtained at 1000 °C after 5 h nitridation. The amounts and nature of the Ti, O and N at the surface were determined by X-ray photoelectron spectroscopy (XPS). A shift of the band-gap to lower energy and increasing absorption in the visible light region, were observed by increasing the heat-treatment temperature from 400 to 700 °C.     

Rapid low temperature synthesis of a titanate pyrochlore by molten salt mediated reaction

Ytterbium titanate pyrochlore, Yb₂Ti₂O₇, was prepared by molten salt mediated synthesis (MSS) from titanium oxide (TiO₂) and ytterbium oxide (Yb₂O₃) reagents. Potassium and sodium chloride mixtures were used as the molten salt medium and the effects of salt to reagent ratio, salt composition, synthesis temperature, reaction time, and TiO₂ particle size were explored. Synthesis temperatures and times required for formation of single phase Yb₂Ti₂O₇ were found to be lower than those required for solid state synthesis (SSS). Whereas MSS synthesis of single phase Yb₂Ti₂O₇ was achieved with micron-sized powders after a single reaction at 1200 °C for 1 h, SSS with micron-sized powders required an extended reaction time of 36 h at 1350 °C. Yb₂Ti₂O₇ micron-sized powder prepared by MSS showed similar particle size and morphology to that of the TiO₂ precursor demonstrating a template growth mechanism. However, the use of TiO₂ nano-sized powder changed the dominant synthesis mechanism from template growth to dissolution–precipitation and facilitated synthesis of near single phase Yb₂Ti₂O₇ at the remarkably low temperature of 700 °C in only 1 h. The potential application for lanthanide and actinide immobilisation from molten salt reprocessing wastes was demonstrated by preparation of Yb₂Ti₂O₇ by molten salt mediated synthesis from TiO₂ and ytterbium chloride (YbCl₃) reagents.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Low temperature synthesis of nano-sized (Sn0.25,Ti0.75)O2 photocatalysts by a molten salt method

Nano-sized (Sn_0.25,Ti_0.75)O₂ photocatalysts were successfully synthesized by a molten salt (MS) method at 260 °C for 2 h, where a homogeneous precipitate containing titanium and tin cations as a precursor. The synthesized powders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis, respectively. The results show that the products are composed of homogeneously spherical particles with an average size of ca.10 nm, and have better UV absorption and visible light response when the reaction temperature is increased to 400 °C.     

Low temperature synthesis of nano-crystalline gadolinium titanate by molten salt route

Nano-crystalline Gadolinium Titanate (Gd₂Ti₂O₇) powder was successfully synthesized by “Single Step Molten Salt Technique”. LiCl–KCl eutectic mixture was used as a molten medium for the reaction. The duration of the synthesis was 10 h. Stoichiometric proportion of the reactants were mixed in an (LiCl–KCl) eutectic medium and treated at 750 °C in an electrical resistance furnace. Single phase Gadolinium Titanate compound was obtained by the thermal process. The synthesized powders were characterized using XRD, FT-IR, UV, EDAX and XPS analyses. The morphology of the powder was examined using SEM and TEM techniques. From the above studies, it has been concluded that pure crystalline Gadolinium Titanate powders can be synthesized via low temperature molten salt process.     

Synthesis,characterization, and photocatalytic properties of ZnO nano-flower containing TiO2 NPs

In this study, TiO₂-impregnated ZnO nano-flowers were synthesized by one-pot hydrothermal process. Aqueous suspension containing ZnO precursor and commercial TiO₂ NPs (P25) is heated at 140 °C for 2 h. The morphology and structure of as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), which revealed that TiO₂ NPs were attached on the surface of ZnO flower. It was observed that the presence of TiO₂ NPs in the hydrothermal solution could sufficiently decrease the size of ZnO flower. The hybrid nanostructure, with unique morphology, obtained from this convenient method (low temperature, less time, and less number of reagents) was found to be effective photocatalyst under UV-irradiation.     

Sacrificial template synthesis of core-shell SrTiO3/TiO2 heterostructured microspheres photocatalyst

The core-shell SrTiO₃/TiO₂ heterostructure was obtained via a combined hydrothermal route and calcination treatment using amorphous spherical TiO₂ as both template and reactant. Adjusting the hydrothermal environments can control the morphology of the post-calcined sample when it is hydrothermally treated at 180 °C/3 h and 200 °C/6 h, respectively. Following the heat treatment at 700 °C/4 h, the obtained powder illustrates the core-shell heterostructure with a hierarchical surface, and the diameter of the microsphere is about 700 nm. This synthesizing route facilitates the formation of a concentration gradient of SrTiO₃ and TiO₂, and subsequently constructs a gradient energy level, which helps the samples exhibited an excellent de-colorize activity over the methylene blue. The possible formation mechanism of core-shell SrTiO₃/TiO₂ heterostructures was proposed to guide the further improvement of their photocatalytic activity.     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

Kinetics of anatase transition to rutile TiO2 from titanium dioxide precursor powders synthesized by a sol-gel process

Kinetics of anatase transition to rutile TiO₂ from titanium dioxide precursor powders synthesized by a sol-gel process have been studied using differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high resolution TEM (HRTEM). The DTA result shows residual organic matter decomposed at 436 K. The transition temperature for amorphous precursor powders converted to anatase TiO₂ occurred at 739 K. Moreover, the full anatase transition to rutile TiO₂ occurred at 1001 K. The activation energy of anatase TiO₂ formation was 128.9 kJ/mol. On the other hand, the activation energy of anatase transition to rutile TiO₂ was 328.4 kJ/mol. Mesoporous structures can be observed in the TEM image.     

Syntheses of bismuth titanate templates obtained by the molten salt method

Bismuth titanate templates (Bi₄Ti₃O₁₂) were synthesized by the molten salt method in Na₂SO₄ and K₂SO₄ fluxes, using an amorphous Bi₄Ti₃O₁₂ precursor and a mechanically mixed Bi₂O₃+TiO₂ mixture as the starting materials. The templates were characterized by means of X-Ray Diffraction, FT-IR, FT-Raman, FEG-SEM and TEM. The templates are free of secondary phases and present orthorhombic structure with orientation in the c-plane. FT-IR suggests no traces of sulfate groups revealing that the molten salt synthesis was beneficial for elimination of inorganic species and for the arrangement of individual nanocrystals into ordered lattices. FEG-SEM analyses of BIT templates revealed that most of the grains were homogeneous with a length of 3.1 µm and a width of 0.3 µm and had plate-like morphology. TEM investigations show that the c-axis of the perovskite units is parallel to the thickness direction of the grains and no liquid-phase was formed during BIT phase formation.     

Effects of SiO2 addition on TiO2 crystal structure and photocatalytic activity

A series of TiO₂–SiO₂ mixtures – having the following stoichiometry Ti_1?xSi_xO₂, with x = 0, 0.1, 0.3 and 0.5 atoms per formula unit – were prepared by using precursor oxides and fired at three temperatures (900, 1000 and 1200 °C). The modifications in the structure and, consequently, on the photocatalytic activity, induced by the addition of SiO₂ into the TiO₂ powder, were thoroughly investigated by using various analytical techniques: X-ray powder diffraction, electron microscopy (FE-SEM and TEM), XPS, FT-IR, DRS and BET analysis. The results underlined as essentially no solid solution occurs between the two crystalline end-members. Nevertheless, silica addition caused a retarding effect on anatase-to-rutile phase transformation and on the crystallite growth.The photocatalytic activity of the powders was assessed in gas phase and the results were explained by taking into account the anatase and rutile relative amounts in the samples, their crystallite size, the surface hydroxyl groups adsorbed on the photocatalysts and the surface area of the mixtures.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Synthesis and structural properties of GaN particles from GaO2H powders

Gallium nitride(GaN) powders have been synthesized by nitriding gallium oxyhydroxide (GaO₂H) powders in the flow of NH₃ gas at a nitridation temperature of 950 °C for 35 min. X-ray powder diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra reveal that simple heat treatment of GaO₂H in the flow of NH₃ leads to the formation of hexagonl GaN with lattice constants a = 3.191 Å, and c = 5.192 Å at 950 °C through intermediate conversion of β-Ga₂O₃. X-ray photo-electron spectroscopy (XPS) confirms the formation of bonding between Ga and N, and yields that the surface stoichiometry of Ga : N approximates 1 : 1. Transmission electron microscopy (TEM) image indicates that GaN particle is a single crystal, and its morphology is ruleless.     

Molten salt synthesis of PZT powder for direct write inks

The preparation of lead zirconate titanate (PZT) powder by molten salt synthesis (MSS) is described and a mechanism proposed. The effect of process parameters, such as reaction time and temperature and heating rate, on particle size and shape was investigated. A reaction mechanism for the synthesis of PZT by molten salt method is proposed, where dissolved Pb initially reacts with insoluble TiO₂ to form intermediate PbTiO₃. Subsequently Zr diffuses into and reacts with PbTiO₃ to form PZT. Spherical particles, ～340 nm in size, were obtained, using a NaCl/KCl salt, by heating the starting materials at 850 °C for 60 min, with a ramp rate of 3.3 °C min^?1.     

Preparation and characterization of transparent indium- doped TiO2 films deposited by MOCVD

Titanium dioxide (TiO₂) films doped with different indium (In) concentrations have been prepared on SrTiO₃ (STO) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) analyses revealed the TiO₂ films doped with low In concentrations to be [001] oriented anatase phase and the films with high In concentrations to present polycrystalline structures. The 1.8% In-doped TiO₂ film exhibited the best electrical conductivity properties with the lowest resistivity of 8.68×10⁻² Ω cm, a Hall mobility of 10.9 cm² V⁻¹ s⁻¹ and a carrier concentration of 6.5×10¹⁸ cm⁻³. The films showed excellent transparency with average transmittances of over 85% in the visible range.     

Probing the oxidation behavior of Ti2AlC MAX phase powders between 200 and 1000 °C

Oxidation of commercial Ti₂AlC MAX phase powders at 200–1000 °C has been investigated by XRD, XPS, SEM, STA and TGA coupled with FTIR. These powders are a mixture of Ti₂AlC, Ti₃AlC₂, TiC and Ti_1.2Al_0.8. Oxidation at 400 °C led to disappearance of carbide phases from Ti 2p, Al 2p and C 1s XPS spectra. At 600 °C, powders changed from dark grey to light grey with a significant volume increase due to crack formation. Powders were severely oxidized by detecting rutile with minor anatase TiO₂. At 800 °C, α-Al₂O₃ was detected while anatase transformed into rutile TiO₂. The cracks were healed and disappeared. At 1000 °C, the Ti₂AlC powders were fully oxidized into rutile TiO₂ and α-Al₂O₃ with a change of powder color from light grey to yellow. FTIR detected the release of C as CO₂ from 200 °C onwards but with additional CO above 800 °C.