Structural developments during heating in LiNbO3 precursors synthesized by the sol-gel method

LiNbO₃ precursor gels with a variety of molecular structures were prepared by the sol-gel method by changing the amount of added water and other conditions of synthesis. The molecular structures, as well as the thermal behaviour of the amorphous precursors, were studied by Raman spectroscopic analysis and differential thermal analysis-thermogravimetry in order to determine the influence of the structures on the resulting LiNbO₃ formation. The crystallization to LiNbO₃ by the combustion heat of the residual unhydrolysed alkyls was observed at 300 °C for the homogeneous precursors prepared from a double alkoxide (LiNb(OC₂H₅)₆) without added water, but the LiNbO₃ formed had low crystallinity. When using the hydrolysed double alkoxide, the synthesized precursors transformed to LiNbO₃ at 480 °C after the structural relaxation. This temperature can be assigned to the real crystallization point. Indeed the unhydrolysed double alkoxide is necessary to prepare the high-quality LiNbO₃ films, and heat treatment above 500°C is required to obtain good crystallinity. Even for the inhomogeneous precursors prepared from LiOC₂H₅ and NbO(C₂H₅)₅, lithium ion diffusion and the structural relaxation occur, to form the uniform molecular structures from 300–400 °C.     

Evaluating the potential of a new titania precursor for the synthesis of mesoporous Fe-doped titania with enhanced photocatalytic activity

Mesoporous Fe (III) doped TiO₂ nanoparticles with an anatase phase were prepared by using a stable precursor potassium hexafluorotitanate as Ti source for the first time and its physical as well as photocatalytic properties were compared with that of Fe doped titania prepared from the most common Ti source titanium isopropoxide. FeSO₄·7H₂O and Fe (NO)₃·9H₂O were used for doping titania with Fe (III). Physicochemical properties of the samples were characterized by XRD, XPS, FTIR, Raman spectroscopy, N₂ adsorption–desorption isotherms, UV–vis diffuse reflectance spectroscopy. EDX confirms the presence of Fe. DRS and TEM reveals that doping has taken place. It was found that Fe-doped nanostructured titania prepared from potassium hexafluorotitanate was much more effective in the photocatalytic decomposition of bromocresol green than undoped nanostructured titania as well as commercial titania.     

Microstructure and phase evolution of TiO2 precursors prepared by peptization-hydrolysis method using polycarboxylic acid as peptizing agent

Titanium dioxide precursors have been prepared by the peptization-hydrolysis process using titanium tetrachloride as the raw material and polycarboxylic acid as the peptizing agent. To avoid the aggregation of the original precursor particles, an anti-aggregating process is carried out after the hydrolysis by employing inorganic acids. FT-IR spectroscopy and elemental analysis indicate that a certain amount of residual dicarboxylic groups still remains in all TiO₂ precursors and that the chemical composition of the precursors is nonstoichiometric. It is verified by Raman spectroscopy that all the precursors present a short-range ordered structure in the octahedral coordination of the titanium with oxygen cluster and the particle size is in nanometer scale. It is also found that the microstructure of the precursors is affected to some extent by the modification of inorganic acid. Anatase nanophase exists in all of the precursors which are obtained in the anti-aggregating process. Apart from the anatase nanophase, small amounts of amorphous nanosize titania particles are formed under a lower pH value (less than two) during the anti-aggregating period. The chelating effect may play an important role in the formation of anatase nanophase during the hydrolysis process in the preparation of titania precursor. XRD and Raman analysis show that all the precursors transformed into pure anatase after being sintered at around 300 °C.     

氟对锂铝硅系统玻璃结构及析晶的影响

通过引入氟以降低锂铝硅玻璃的高温黏度,使"温度-黏度"曲线适应浮法工艺的需求,并采用激光拉曼光谱、XRD、高温旋转黏度计等测试手段研究氟对锂铝硅系统玻璃的结构及随后析晶的影响。结果表明:氟的引入使母体玻璃网络结构中的[Si(Al)O4]四面体相互之间形成的环结构向小环结构发展,[Si(Al)O4]四面体之间的相互连接程度降低,Si(Al)—O—Si(Al)键的振动减弱,从而能有效地降低母体玻璃的高温黏度。随着氟引入量从0.00mol增加到0.28mol,母体玻璃在晶化过程中析出的主晶相并未发生改变,皆为β-锂辉石固溶体,且析出的主晶相含量随氟引入量的增加而增加。此外,结合Raman光谱分析可以发现,试样中有微量的锐钛矿晶相析出。     

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.     

The crystalline phase stability of titania particles prepared at room temperature by the sol-gel method

Titania particles having anatase, brookite and rutile phase were prepared at various H⁺/TTIP (Titaniumtetraisopropoxide) mole ratios and room temperature by the sol-gel method. The crystalline phases according to the variation of the post heat treatment temperature were observed. The crystalline phase and the phase transformation, morphology, and crystallite size were identified by using XRD, TG/DTA, Raman spectroscopy and TEM. The brookite phase of titania particles prepared at the H⁺/TTIP mole ratio of 0.02 and room temperature was not transformed into anatase or rutile even with the heat treatment at 750°C, and also the anatase phase was stable at the temperature as high as 850°C. However, the titania particles prepared at the H⁺/TTIP mole ratio of 0.67, which contained the mixed phases of anatase, brookite, and rutile at room temperature, showed only rutile phase at temperature of 750°C. It was thus shown that the initial crystalline phase of the primary particles prepared at room temperature had an important effect on the phase transformation behavior upon post heating. Phase transformation from brookite to anatase and subsequently to rutile occurred with heating.     

Synthesis and characterization of CdS doped TiO2 nanocrystalline powder: A spectroscopic study

This report aimed to study the effect of CdS doping in TiO₂ on the phase transformation of TiO₂ from anatase to rutile using X-ray diffraction (XRD) and Raman spectroscopy. CdS-doped TiO₂ nanocomposites have been prepared and characterized using Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). We have observed that contrary to bare TiO₂, phase transformation of TiO₂ from anatase to rutile is hindered when doped with CdS at high temperature. Raman spectroscopy is found to be more sensitive for detection of the surface of TiO₂ as compared to XRD.     

Sn<Superscript>4+</Superscript> and La<Superscript>3+</Superscript> co doped TiO<Subscript>2</Subscript> nanoparticles and their optical,photocatalytic and antibacterial properties under visible light

Sn⁴⁺ and La³⁺ co-doped TiO₂ photocatalytic material with nanoparticle structure have been successfully prepared using SnCl₂·2H₂O and La(NO₃)₃·6H₂O as precursors. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy have been used to for the characterization of the morphology, crystal structure, particle size and optical properties of the samples. The photocatalytic properties of sample with various amount of La doped TiO₂ have been studied by photo degradation of methyl orange (MO) in water under visible light. XRD patterns showed both rutile and anatase phases for 5 mol% of Sn and 5–10 mol% of La. But anatase phase with a little rutile phase was formed for 5 mol%Sn and 10 mol%La. The prepared Sn and La co doped TiO₂ photo-catalyst showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of MO solution under visible irradiation. Antibacterial behavior towards E. coli was then studied under visible irradiation. The synthesized T-5%Sn-10%La powder exhibited superior antibacterial activity under visible irradiation compared to the pure TiO₂.     

New insights into anatase crystallization behavior in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

The anatase crystallization behaviors in ionothermal synthesis (sol–gel method containing ionic liquid) of nanostructured TiO₂ were studied in this paper. It was found that the specific physical chemical characteristics of the water/ionic liquid mixture caused the formation path and crystallinity of anatase TiO₂ to depend on the H₂O/titanium dioxide precursor (titanium tetraisopropoxide, TIP) molar ratio. Hydroxylated titanium compound was a key intermediate for forming anatase TiO₂. It could be directly formed from hydrolysis of titanium dioxide precursor or ionic liquid-induced water dissolution of the condensation product. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) data indicated that a higher hydroxyl group ratio content of hydroxylated titanium compound was obtained at medium H₂O/TIP molar ratio and from the system containing hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BuMIm]⁺[BF₄]⁻). The self organization ability of ionic liquid drove anatase crystallization through dehydration of the Ti–OH group of hydroxylated titanium compound in the thermal annealing process. As for the particle size of TiO₂, TEM results indicated smaller particle size of TiO₂ was obtained at medium H₂O/TIP molar ratio case.     

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.     

Solar photocatalytic degradation of methyl orange dye using TiO2 nanoparticles synthesised by sol–gel method in neutral medium

Anatase TiO₂ nanoparticles were synthesised by the sol–gel method in neutral medium, and its photocatalytic activity in the degradation of methyl orange dye under sunlight has been studied. The nanoparticles were characterised using high-resolution X-ray diffraction, high-resolution transmission electron microscopy, micro Raman analysis and diffuse reflectance spectroscopy. The blueshift and asymmetrical broadening associated with phonon confinement effect has been observed in the Raman spectra of pristine nanoparticles. The high temperature annealing of as prepared anatase samples resulted in the phase transformation in to rutile. The mixture of anatase and rutile TiO₂ nanoparticles exhibited faster photocatalytic activity in the degradation of methyl orange than the pristine anatase and rutile phases. The significant enhancement in the photocatalytic activity of mixed TiO₂ nanoparticles is due to the synergistic effects that consist of the antenna effect by the rutile phase and the activation effect by the anatase phase. Since method of preparation of the catalyst is comparatively simple and cost effective, and the energy source used is sunlight, the method can be easily implemented in waste water treatments.     

Characterization of titania thin films grown by dip-coating technique

A dip-coating technique was employed to prepare anatase phase of titania thin films. Fluorine doped tin oxide substrates were used to prepare titania thin films. The samples were annealed at 550 °C for 18 h. X-ray diffraction results revealed the amorphous and anatase phases of TiO₂ for as-synthesized and annealed samples, respectively. The crystallite size of anatase TiO₂ thin films was almost 25 nm for annealed samples. UV–visible confirmed the energy band gap 3.86 and 3.64 eV for as-prepared and calcinated titania thin films. The reduction in the energy band gap could be due to the change in crystallization and agglomeration of small grains after calcination. The morphology of the prepared films was investigated by field emission scanning electron microscopy which demonstrated the agglomeration of spherical particles of TiO₂ with average particle size of about 30 nm. The molecular properties (chemical bonding) of the samples were investigated by means of Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis exhibited the formation of titania, functional group OH, hydroxyl stretching vibrations of the C–OH groups, bending vibration mode of H–O–H, alkyl C–H stretch, stretching band of Ti–OH, CN asymmetric band stretching, and C=O saturated aldehyde.     

WO3 nano-ribbons: their phase transformation from tungstite (WO3·H2O) to tungsten oxide (WO3)

Tungsten oxide (WO₃) nano-ribbons (NRs) were obtained by annealing tungstite (WO₃·H₂O) NRs. The latter was synthesized below room temperature using a simple, environmentally benign, and low cost aging treatment of precursors made by adding hydrochloric acid to diluted sodium tungstate solutions (Na₂WO₄·2H₂O). WO₃ generates significant interests and is being used in a growing variety of applications. It is therefore important to identify suitable methods of production and better understand its properties. The phase transformation was observed to be initiated between 200 and 300 ^°C, and the crystallographic structure of the NRs changed from orthorhombic WO₃·H₂O to monoclinic WO₃. It was rigorously studied by annealing a series of samples ex situ in ambient air up to 800 ^°C and characterizing them afterward. A temperature-dependent Raman spectroscopy study was performed on tungstite NRs between minus 180 and 700 ^°C. Also, in situ heating experiments in the transmission electron microscope allowed for the direct observation of the phase transformation. Powder X-ray diffraction, electron diffraction, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy were employed to characterize precisely this transformation.     

Synthesis and thermal evolution of structure in alkoxide-derived niobium pentoxide gels

Niobium pentoxide gels in the form of transparent monoliths and powder have been synthesized from the controlled hydrolysis and polycondensation of niobium pentaethoxide under different experimental conditions using various mole ratios of Nb(OC₂H₅)₅:H₂O:C₂H₅OH:HCl. Alcohol acted as the mutual solvent and HCl as the deflocculating agent. In the absence of HCl, precipitation of colloidal particles was encountered on the addition of any water to the alkoxide. The gels were subjected to various thermal treatments and characterized by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and infra-red spectroscopy. After drying at 400°C, the gels were amorphous to X-rays. The amorphous powder crystallized into the low temperature orthorhombic form of Nb₂O₅ at ~ 500°C, which transformed irreversibly into the high temperature monoclinic -Nb₂O₅ between 900 to 1000°C. The kinetics of crystallization of the amorphous niobium pentoxide have been investigated by non-isothermal differential scanning calorimetry. The crystallization activation energy was determined to be 399 kJ mol^–1.     

Tartaric acid-assisted preparation and photocatalytic performance of titania nanoparticles with controllable phases of anatase and brookite

Titanium dioxide with different ratios of anatase to brookite has been prepared by a facile hydrothermal method in the presence of tartaric acid. The resulting samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectra, and Brunauer–Emmett–Teller analysis. The contents of anatase and brookite in the TiO₂ particles have been successfully controlled by simply adjusting molar ratio of tartaric acid to Ti in reaction system. The degradation of Rhodamine B in aqueous solutions reveals that the catalyst containing 78.7?% anatase and 21.3?% brookite has the highest photocatalytic activity. A proposed mechanism is discussed to interpret the evolution of the phases based on the effect of different C₄H₆O₆/Ti molar ratios.     

Innovative one-step immobilization of TiO2 on polymer material by the sol–gel method under IL/MW conditions

An innovative one-step immobilization of titanium dioxide (TiO₂) nano-particles on organic polymer (PMMA) substrate at ambient condition is reported in this article. This immobilization can be achieved by the sol–gel method under ionic liquid/microwave heating conditions. In this method, a sol–gel reaction is conducted at specific sites of the polymer surface. These sites are the tiny cavities of the rough surface resulting from the softening and swelling effect of an alcohol, such as isopropyl alcohol, on the polymer surface under microwave irradiation. The roughness of the polymer surface is an important factor for the effective immobilization. In addition, ionic liquid can induce low temperature surface anatase crystallization of immobilized titanium dioxide in a short time. From the field emission scanning electron microscopy and energy dispersive spectroscopy observation, the TiO₂ particles could be effectively immobilized on the PMMA substrate. Raman spectra analysis data showed that the immobilized TiO₂ was anatase phase. The experimental data also shows that the immobilized TiO₂ prepared by this novel method has good immobilization stability and photocatalytic water treatment performance.     

Phase transformations in sol-gel prepared PbTiO3

The sol-gel preparation of PbTiO₃ by two different methods is reported. Both methods began with titanium isopropoxide and lead acetate as organic precursors, but without or with hydrochloric acid as catalyst, respectively. Preparation procedures and working atmosphere also differred. The crystallization by thermal treatments and laser annealing was followed by XRD and Raman spectroscopy. When no hydrochloric acid was used, an intermediate pyrochlore phase, Pb₂Ti₂O₆, was observed during the thermal treatment, and the final perovskite was obtained together with PbTi₃O₇ as the minor phase. Using the catalyst, the pure perovskite, PbTiO₃, was obtained through an unidentified phase appearing at the beginning of the crystallization process. Frequency changes in the Raman spectra during the crystallization are attributed to pressure effects on the microcrystals.     

Surface and structural characterisation of coprecipitated CexZr1?xO2 (0?≤?x?≤?1) mixed oxides

Ce _x Zr_1−x O₂-mixed oxides with three different Ce/Zr ratios (Ce_0.8Zr_0.2O₂, Ce_0.5Zr_0.5O₂ and Ce_0.2Zr_0.8O₂) along with pure cerium and zirconium oxides were prepared by coprecipitation of the metal hydroxides in alkali media and subsequent calcinations at 500 °C, using two different cerium precursors (Ce(NO₃)₃·6H₂O or (NH₄)₂Ce(NO₃)₆). These samples were characterised by N₂ adsorption at −196 °C, XRD, Raman spectroscopy, XPS and H₂-temperature programmed reduction. Besides, the two mixed oxides with higher cerium content were calcined at higher temperature (1000 °C) with the additional purpose of studying their thermal stability and phase homogeneity. XRD and Raman spectroscopy confirm a significant improvement in the insertion of zirconium cations into the ceria lattice when the samples Ce_0.8Zr_0.2O₂ and Ce_0.5Zr_0.5O₂ are synthesised with (NH₄)₂Ce(NO₃)₆ instead of Ce(NO₃)₃·6H₂O. This is attributed to a more homogeneous coprecipitation of cerium and zirconium hydroxides, leading to mixed oxides with better bulk oxygen mobility and smaller lattice parameter. Moreover, the mixed oxides prepared with the (NH₄)₂Ce(NO₃)₆ precursor and calcined at 1000 °C exhibit a single phase whereas phase segregation occurs in the counterpart mixed oxides prepared with the Ce(NO₃)₃·6H₂O precursor. XPS analysis reveal correlations among O/(Ce + Zr) surface atomic ratio and total cerium content for both cerium precursors. Among the samples calcined at 1000 °C, Ce_0.8Zr_0.2O₂ synthesised with Ce(NO₃)₃·6H₂O is the only one that preserves the low-temperature surface reduction peak, and also shows a BET surface area slightly higher than those of the rest of samples calcined at high temperature.     

Anatase–CMK-3 nanocomposite development for hydrogen uptake and storage

The nanometric carbon CMK-3 modified with TiO₂ in anatase phase was synthesized and applied to energy uptake and storage. TiO₂ nanoclusters are important for hydrogen energy harvesting. The creation of porous structures or large surface with TiO₂ nanoclusters inside can potentially face the challenge of improving their efficiency. In the present work, we report the synthesis and characterization of TiO₂–CMK-3 material assembled from anatase nanoparticles dispersed in the nanometric carbon CMK-3. The resulting nanocomposite was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and N₂ adsorption–desorption analysis. The newly synthesized hybrid composites exhibited significantly enhanced H₂ storage, in which CMK-3-ordered porous carbon modified with anatase nanoclusters proved to be a material for hydrogen uptake. The nanoparticles of anatase (～5 nm) incorporated onto CMK-3 showed higher hydrogen uptake at low and high pressures (2.9 wt% of H₂ sorption at 10 bar and 77 K) than CMK-3. The approach includes a discussion of H₂ adsorption process and storage properties.     

Vibration spectroscopy study of hydrolyzed precursors for sintering calcium phosphate bio-ceramics

Diffuse reflectance infrared Fourier transform and Raman spectroscopy is applied to investigate the structure of hydrolyzed CaHPO₄ · 2H₂O (DCPD) processed to non-stoichiometric apatite to be used as starting material for preparing sintered calcium phosphate materials. The spectra of hydrolyzed DCPD samples, obtained under differing experimental conditions, are analyzed to check how the sintered phase composition correlates with the structure of the hydrolyzed precursor. It is shown that the addition of extra Ca²⁺ ions in the alkaline solution during the process of hydrolyzing affects strongly the degree of disorder in the structure of the hydrolyzed materials, thus increasing the relative amount of hydroxyapatite in the final sintered product. The addition of F^– ions to the synthesis mixture strengthens slightly the P-O bonds in the precursors and increases the content of hydroxyapatite phase in the sintered material. As a result bi-phase ceramics of highest content of hydroxyapatite can be produced using both fluorine additives and calcium compensators in the synthesis suspension.