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.     

Colossal permittivity in (In1/2Nb1/2)xTi1−xO2 ceramics prepared by a glycine nitrate process

(In + Nb) co-doped TiO₂ nanoparticles with very low dopant concentrations were prepared using a glycine nitrate process. A pure rutile—TiO₂ phase with a dense microstructure and homogeneous dispersion of dopants was achieved. By doping TiO₂ with 1.5% (In + Nb) ions, a very high dielectric permittivity of ε′ = 42,376 and low loss tangents of tanδ = 0.06 (at room temperature) were achieved. The large conduction activation energy at the grain boundary decreased with decreasing dopant concentration. The colossal permittivity was primarily attributed to the internal barrier layer capacitor (IBLC) effect. The dominant effect of interfacial polarization at the non–Ohmic sample–electrode contact was observed when the dopant concentration was ≤1.0 mol%. Interestingly, the sample–electrode contact and resistive–outer surface layer effects, i.e., surface barrier layer capacitor (SBLC) effect, has also an effect on the colossal dielectric response in (In + Nb) co-doped TiO₂ ceramics.     

Effects of titanium dioxide on the flammability and char formation of water-based coatings containing intumescent flame retardants

Rutile-type TiO₂ (r-TiO₂) or anatase-type TiO₂ (a-TiO₂) in association with a conventional intumescent flame retardant system which contains ammonium polyphosphate/pentaerythritol/melamine (APP–PER–MEL) was introduced to silicone-acrylate coatings to improve the fire resistance. The effect of TiO₂ on the fire-resistance and thermal properties of APP–PER–MEL coating has been investigated by using big panel method and thermogravimetry (TG). The limit of fire-resistance of the sample containing 30 phr rutile-type TiO₂ (73 min) is much longer than that of the sample containing 30 phr anatase-type TiO₂ (34 min). The morphology and structure of charring layers were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The relationship between charring process and melt flow rate (MFR) of silicone-acrylate was also discussed. It is suggested that MFR value can significantly affect the formation of char, and a moderate silicone-acrylate MFR is required to form good quality char.     

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.     

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.     

Preparation and photocatalytic activity of silver and TiO2 nanoparticles/montmorillonite composites

Ag–TiO₂/montmorillonite (Ag–TiO₂/MMT) was synthesized as photocatalyst using TiCl₄ hydrolysis to introduce nanosized TiO₂ into the interlayer space of the montmorillonite (MMT). Stable pillared TiO₂/MMT was obtained by calcination at 500 °C, then silver was loaded by reduction of silver nitrate. The physico–chemical properties of the photocatalyst were determined by X-ray diffraction (XRD), infrared spectroscopy (IR), atomic absorption spectrophotometer (AAS), nitrogen gas adsorption (BET method) and UV–Visible spectra. The photooxidation activity for methylene blue (M.B.) degradation was as follows: Ag–TiO₂/MMT > TiO₂/MMT > TiO₂(P25). Among them Ag–TiO₂/MMT had the highest photooxidation activity because of its larger specific surface caused by pillaring and loading of silver for improving its light absorption.     

Preparation of graphene film decorated TiO2 nano-tube array photoelectrode and its enhanced visible light photocatalytic mechanism

Graphene film decorated TiO₂ nano-tube array (GF/TiO₂ NTA) photoelectrodes were prepared through anodization, followed by electrodeposition strategy. Morphologies and structures of the resulting GF/TiO₂ NTA samples were characterized by scanning electrons microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. In addition, the optical and photoelectrochemical properties were investigated through UV–visible light diffuse reflection spectroscopy, photocurrent response and Mott–Schottky analysis. Furthermore, the photodecomposition performances were investigated through yield of hydroxyl radicals and photocatalytic (PC) degradation of methyl blue (MB) under visible light irradiation. It was found that GF/TiO₂ NTA photoelectrode exhibited intense light absorption both in UV light and visible region, higher transient photoinduced current of 0.107 mA cm⁻² and charge carrier concentration of 0.84 × 10¹⁹ cm⁻³, as well as effective PC performance of 65.9% for the degradation of MB. Furthermore, contribution of several reactive species to the PC efficiency of GF/TiO₂ NTA photoelectrode was distinguished. Moreover, the enhanced visible light PC mechanism was proposed and confirmed in detail.     

Synthesis and characterization of Ba1−xSrxTiO3 nanopowders by citric acid gel method

Stoichiometric and monophasic Ba_1−xSr_xTiO₃ (x = 0.3) nanopowders were successfully prepared by the citric acid gel method using barium nitrate, strontium nitrate and tetra-n-butyl titanate as Ba, Sr, Ti sources and citric acid as complexing reagent. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared (IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the thermal decomposition behavior, the crystallization process and the particle size and morphology of the calcined powders. The results indicated that single-phase and well-crystallized Ba_1−xSr_xTiO₃ (x = 0.3) nanopowders with particle size around 80 nm could be obtained after calcining the dried gel at 950 °C for 2 h.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Novel simple solvent-less preparation,characterization and degradation of the cationic dye over holmium oxide ceramic nanostructures

Pure holmium oxide ceramic nanostructures were prepared via a new simple approach. Nanostructures were synthesized by heat treatment in air at 600 °C for 5 h, utilizing [Ho L(NO₃)₂]NO₃ (L=bis-(2-hydroxy-1-naphthaldehyde)-butanediamine Schiff base ligand), as precursor, which was prepared via a solvent-free solid–solid reaction from different molar ratios of holmium nitrate and Schiff base ligand. The as-prepared nanostructures were characterized by field emission scanning electron microscopy (FESEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. It was found that the calcination temperature and molar ratio of holmium nitrate and Schiff base ligand have significant and key effect on the morphology and particle size of the holmium oxide. To investigate the catalytic properties of as-obtained holmium oxide nanostructures, the photocatalytic degradation of rhodamine B as cationic dye under ultraviolet light irradiation was performed.     

Synergic effect of cation doping and phase composition on the photocatalytic performance of TiO2 under visible light

The synergic effect of cation doping and phase composition for the further improvement of the photocatalytic activity of TiO₂ under visible light is reported for the first time. Fe^3 + and Sn^4 + co-doped TiO₂ with optimized phase composition were synthesized through a simple soft-chemical solution method. The visible-light-driven photocatalytic activity of Fe^3 + and Sn^4 + co-doped TiO₂ was 5 times of that of Evonik P25 TiO₂ using degradation of methylene blue as model reaction. The synthesized photocatalysts were characterized by powder X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, ¹¹⁹Sn Mössbauer spectroscopy, and X-ray absorption fine structure spectroscopy. It is indicated that Sn^4 + doping can facilitate the phase transition from anatase to rutile. The different ratios of anatase and rutile can be achieved by tuning the amount of Sn^4 + doped into the lattice. Furthermore, the doping of Sn^4 + into TiO₂ lattice can stabilize the phase composition when Fe^3 + is co-doped. In the Fe^3 + and Sn^4 + co-doped TiO₂, Sn^4 + is mainly used to tune and stabilize the phase composition of TiO₂ and Fe^3 + acts as a doping cation to narrow the band gap of TiO₂. Both band gap and phase composition of TiO₂ can be tuned effectively by the simultaneous introduction of Fe^3 + and Sn^4 +. The synergic effect of optimized phase composition (anatase/rutile = 25/75) and narrowed band gap should be the two main reasons for the promoted photocatalytic activity of TiO₂ under visible light.     

Effect of calcium stoichiometry on the dielectric response of CaCu3Ti4O12 ceramics

Ca_xCu₃Ti₄O₁₂ (x = 0.90, 0.97, 1.0, 1.1 and 1.15) polycrystalline powders with variation in calcium content were prepared via the oxalate precursor route. The structural, morphological and dielectric properties of the ceramics fabricated using these powders were studied using X-ray diffraction, scanning electron microscope along with energy dispersive X-ray analysis, transmission electron microscopy, electron spin resonance (ESR) spectroscopy and impedance analyzer. The X-ray diffraction patterns obtained for the x = 0.97, 1.0 and 1.1 powdered ceramics could be indexed to a body-centered cubic perovskite related structure associated with the space group Im3. The ESR studies confirmed the absence of oxygen vacancies in the ceramics that were prepared using the oxalate precursor route. The dielectric properties of these suggest that the calcium deficient sample (x = 0.97) has a reduced dielectric loss while retaining the high dielectric constant which is of significant industrial relevance.     

Synthesis of CoFe2O4 powders with high surface area by solution combustion method: Effect of fuel content and cobalt precursor

High surface area cobalt ferrite (CoFe₂O₄) powders were synthesized by solution combustion method. The dependence of the adiabatic temperature and the released gases during combustion reaction on the fuel content and cobalt precursor type, cobalt nitrate and cobalt acetate, was thermodynamically calculated. Thermal analysis, infrared spectroscopy, X-ray diffractometry, nitrogen adsorption–desorption, electron microscopy and vibrating sample magnetometer were used for investigation of the phase evolution, surface areas, morphology and magnetic properties of the synthesized CoFe₂O₄ powders. The specific surface area decreased from 285.4 to 35.7 m²/g with increasing of fuel to oxidant molar ratio, ϕ, from 0.5 to 1.25 for the cobalt nitrate precursor, while the maximum surface area of 182.1 m²/g was attained at ϕ=1 for the cobalt acetate precursor. The synthesized CoFe₂O₄ powders from the cobalt nitrate precursor exhibited the higher saturation magnetization and coercivity on account of the higher purity and crystallinity.     

Dye sensitized solar cells based on hydrothermally grown TiO2 nanostars over nanorods

A rutile titanium dioxide nanostar over nanorods is synthesized by a simple and cost-effective hydrothermal deposition method onto conducting glass substrates. In order to study the effect of precursor concentrations on the growth of TiO₂, the amount of Ti precursor is varied from 0.1 mL to 0.5 mL at the interval of 0.1 mL. These TiO₂ thin films are characterized for their morphological, structural, optical and J–V properties using various characterization techniques. SEM images showed the formation of densely packed nanostars over nanorods for 0.3 mL titanium tetraisopropoxide (TTIP). XRD patterns show the formation of polycrystalline TiO₂ with tetragonal crystal structure possessing rutile phase. Further, the TiO₂ thin films are used for dye sensitized solar cells using N3-dye.The films were photoelectrochemically active and can be viewed as a promising application in DSSC with maximum current density of 1.459 mA/cm² with enhanced photovoltage of 696 mV for the sample prepared at 0.3 mL TTIP.     

Structural,thermal and electrical properties of Ti4+ substituted Bi2O3 solid systems

In the present study, the effect of TiO₂ doping on (1 ? x) Bi₂O₃ (x)TiO₂ (x = 0.05, 0.10, 0.15, 0.20) materials is investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), ac conductivity, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). XRD results show the formation of single phase Bi₁₂TiO₂₀ at x ≥ 0.15 concentration of TiO₂. It is observed that, the lower concentration of TiO₂ leads to the formation of mixed phase. The x = 0.15 and x = 0.20 samples exhibit regular and uniform distribution of the grains as compared to x = 0.10 sample. The highest conductivity is observed for x = 0.15 specimen, e.g., 9 × 10^?7 S cm^?1.     

Synthesis and catalytic properties of novel POM@TiO2 composite materials

Donor–π-bridge–acceptor (D–π–A) type polyoxometalates (POMs) were self-assembled for the first time on the surface of titanium dioxide (TiO₂) nanoparticles through the layer-by-layer (LBL) method. The obtained composite materials POM@TiO₂ were characterized by Transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FTIR), Raman spectrum and energy dispersive X-ray (EDX) spectroscopy. Catalytic properties of POM@TiO₂ were also investigated by treating organic pollutants (typically, removal of 40 mL 20 mg L^− 1 methylene blue (MB) by 10 mg POM@TiO₂ was up to 99.5% within 3 min under ambient conditions and the photodegradation efficiency was obviously higher than bare TiO₂ nanoparticles under irradiation).     

Water vapor adsorption and photocatalytic pollutant degradation with TiO2–sepiolite nanocomposites

A new nanocomposite containing a titanium dioxide photocatalyst and low-cost sepiolite was prepared and tested for its potential multifunctional application in water vapor adsorption and pollutant photodegradation. The nanocomposite was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric and differential thermogravimetric analyses (TGA/DTG), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and surface area (BET) measurements. The XRD patterns of the nanocomposites exhibited the characteristic sepiolite and anatase reflections, while the SEM images revealed the surface morphology of the raw sepiolite after the modification with the sol gel prepared with TiO₂. In the TGA/DTG, up to 100 °C, three stages of water removal were analyzed and attributed to surface and zeolitic water loss. Upon TiO₂ loading, the overall mass loss of sepiolite was reduced to half, but the three stages of water loss were rearranged with low loading (10 wt.%) or were reduced to two stages with higher loading (20 wt.%). The hydrophilic nature of the raw sepiolite was retained after the TiO₂ loading, while the water vapor uptake was reduced to 20–30% with relative humidities from 30 to 80% and loadings up to 20 wt.%. In addition, the efficiencies of the supported photocatalysts were investigated using β-naphthol as a model pollutant compound. All prepared catalysts exhibited higher activities than when using the bare TiO₂ sample. Therefore, the TiO₂–sepiolite nanocomposite can be potentially applied for combined photocatalytic degradation processes and water vapor adsorption to allow for evaporative cooling.     

A novel synthesis route of titanium dioxide with (NH4)0.3TiO1.1F2.1 as by-product

This work explores a new route for the synthesis of titanium dioxide using scraps and titanium chips, which are typically discarded as waste, as the precursor materials. The band-gap energy of the synthesised materials was determined using diffuse reflectance spectroscopy. The morphology, elemental analysis, crystallinity, and chemical structure of the synthesised materials were determined by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, and infrared and Raman spectroscopies, respectively. The X-ray and Raman analyses confirmed the formation of titanium dioxide in its tetragonal (anatase) crystalline form after heat treatment (400 °C, 2 h). Moreover, a mixture of (NH₄)_0,3TiO_1,1F_2,1 and anatase TiO₂ was obtained as a by-product. After heat treatment, this by-product was converted into fluorine-doped titanium dioxide, also in anatase crystalline form. The apparent crystallite size (L_c) of anhydrous titanium dioxide was found to be smaller than that of the calcined by-product. The diffuse reflectance spectroscopy analysis revealed that the calcined by-product has a significantly higher absorption capacity at higher wavelengths, as well as a lower band-gap energy value. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analyses showed large particulates on which smaller particles are deposited and good dispersion of the elemental components. The anhydrous titanium dioxide sample presents a smaller particle size than the calcined by-product.     

Chemically induced order disorder transition in magnesium aluminium spinel

Magnesium aluminate spinel (MgAl₂O₄) spinel powder was synthesized by nitrate citrate auto-ignition route taking different ratios of nitrate and citrate solution. The ‘as prepared’ black ash was calcined at different temperatures in the range 650–1250 °C for 9 h. Phase evolution of calcined powder samples as studied by X-ray diffraction indicates the presence of disorder at lower calcination temperatures, which transforms to an ordered structure at higher calcination temperatures. Finally, Raman spectroscopy confirms the order–disorder phase transition in spinel sample.     

The photo-catalytic activities of neodymium and fluorine doped TiO2 nanoparticles

A series of photo-catalysts were synthesized by neodymium and fluorine doped TiO₂, and their characteristics evaluated by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Neodymium and fluorine doped TiO₂ has obvious absorption in the visible light and the absorption edge shifts toward red wavelength. In addition, compared with pure TiO₂, the doped catalyst has intense absorption at 528, 587, 750, 808, and 881 nm. The catalytic efficiency was tested by monitoring the photo-catalytic degradation of methylene blue (MB) in visible light and ultraviolet light. The results showed that the optimum doping content was Nd:F:TiO₂ = 0.5:5:100 (molar ratio) heat treated at 500 °C, and the reaction rates of MB degradation were estimated to be about 1.76 times and 1.45 times higher than undoped TiO₂ in ultraviolet light and visible light.