Effect of NaHCO3 on synthesis of anatase TiO2 nanopowders by thermal processing of the precursor

Titanium dioxide (TiO₂) nanopowders were successfully prepared by thermal processing of the precursor of titanium hydroxide, urea and sodium acid carbonate (NaHCO₃). The products were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that NaHCO₃ has a certain effect on the average crystallite size and dispersity of TiO₂ nanopowders, at the same time other phases (Na₂SO₄ and Na₂CO₃) will be introduced. However, Na₂SO₄ has distinctive intercalation ability and catalytic activity. TiO₂ (anatase) powders can be prepared at ?600 °C for 2 h with addition of 2–10 wt% NaHCO₃, and the average crystallite size is 20.0–22.3 nm. The surface of the sample mainly consists of Ti, O, C, Na and S five species elements.     

Preparation and characterization of the bismuth sodium titanate (Na0.5Bi0.5TiO3) ceramic doped with ZnO

This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na_0.5Bi_0.5TiO₃), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi₂O₃, Na₂CO₃ and TiO₂) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.     

Preparation and characterization of sodium titanate nanowires from brookite nanocrystallites

Sodium titanate nanowires from brookite (or anatase) nanocrystallites were synthesized by a hydrothermal treating in 10 M NaOH aqueous solution at 180 °C. Their structures were characterized by XRD, TEM, HRTEM, XPS, and Raman spectra. The results indicated that though the structures of sodium titanate nanowires derived from brookite and antase were similar, there existed differences between them. The decrease of (2 0 0) plane spacing resulted from the increase of Na amount intercalated into TiO₂. The species of short TiO bonds in sodium titanate from brookite was more than that in sodium titanate from anatase. UV–vis absorption spectra showed a strong absorption not only in the ultraviolet range but also in the visible-light range.     

Effect of Na2SiO3 on synthesis of TiO2 nanopowders by thermal processing of the precursor

TiO₂ nanopowders could be prepared by thermal processing of the precursor of titanium hydroxide, urea and Na₂SiO₃. The powders were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that Na₂SiO₃ has an important effect on the average crystallite size and dispersity of TiO₂ nanopowders, and other phases (Na₂SO₄ and SiO₂) will be introduced. However, Na₂SO₄ has distinctive intercalation ability and catalytic activity; SiO₂ coating layers can effectively inhibit the agglomeration of TiO₂ nanopowders. TiO₂ (anatase) powders with well dispersity can be prepared at ～600 °C for 2 h with addition of 2–6 wt.% Na₂SiO₃, and the average crystallite size is 15.5–22.1 nm. The surface of the sample mainly consists of Ti, O, C, Si, Na and S six species elements.     

Study on crystallinity and morphology controlling of titania using acrylamide gel method and their photocatalytic properties

In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO₂ nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO₂ nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO₂ nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TEC_I), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min.     

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.     

Synthesis of BaTi2O5 nanobelts

BaTi₂O₅ nanobelts with 60–100 nm in thickness, 200–300 nm in width, and several micrometers in length have been successfully synthesized through a two-step hydrothermal reaction. Sodium titanate nanobelts are synthesized via the reaction of titania nanoparticles and NaOH aqueous solution at 180 °C for 24 h. After the reaction, resulting sodium titanate nanobelts are ion-exchanged with barium ions and then treated at 180 °C for 60 h under alkaline condition, BaTi₂O₅ nanobelts are formed. The morphologies and crystal structures of sodium titanate and BaTi₂O₅ nanobelts are characterized by field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray powder diffractometer (XRD), respectively.     

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.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

Combustion synthesis of WC powder in the presence of alkali salts

This paper deals with the formation of tungsten carbide sub-micrometer powders from WO₃ + Mg + C + sodium salts (NaCl, Na₂CO₃) system by combustion synthesis technique. The powders were characterized by XRD and FESEM. X-ray data demonstrate the superiority of the NaCl + Na₂CO₃ combined mixture in the WC formation process. Single phase, sub-micrometer WC powders were synthesized at temperatures as low as 1600 °C. The roles of sodium salts in combustion process were discussed and chemical mechanism of WC formation was proposed. WC powder produced by salt-assisted combustion synthesis technique has a size 0.2–3 μm, crystalline shape and low agglomeration degree.     

Synthesis and photocatalytic activity of mesoporous cerium doped TiO2 as visible light sensitive photocatalyst

Cerium doped titania materials were synthesized varying the cerium concentration from 0 to 10 wt%. Materials are characterised by XRD, TEM, XPS and N₂ adsorption desorption method. Surface area and visible light absorption substantially increases and crystallite size decreases with the increasing cerium content. Cerium doping stabilizes the anatase phase and surface area even at 600 °C calcination. Photocatalytic activity towards methylene blue decomposition and selenium (IV) reduction is found to increase with the cerium content up to 5 wt% and then decreases. Materials calcined at 600 °C shows better activity than that calcined at 400 °C, even though surface area decreases. Anatase crystallinity mostly decides the photocatalytic activity rather than only surface area. It can be concluded that the optimum visible light absorption and oxygen vacancy with 5% cerium doping enhances the photocatalytic activity. In addition photocatalytic performance is found to depend on the presence of Ce⁴⁺/Ce³⁺ rather than only visible light absorption.     

Zr doped anatase supported reticulated ceramic foams for photocatalytic water purification

Titanium dioxide films were deposited on macroporous reticulated Al₂O₃ and alumina–mullite foams with pore sizes of 15 ppi (pores per inch). Coatings were prepared from suspensions of precursor powders of Aeroxide^® P25 nanopowder and precipitated TiO₂ by using a dip coating process. The TiO₂ forms films with a thickness of ～2–20 μm. The photocatalytic activity was characterized as the mineralization rate of an aqueous phenol solution under UVA irradiation by the TOC technique. Precipitated TiO₂ films have nearly the same photocatalytic activity as a titania suspension, in which powder aggregates have a size comparable with the thickness of the films. Samples made of Aeroxide^® P25 nanopowder, in which the size of aggregates is ～0.1 μm show higher efficiency of photodecomposition in suspensions with films. The doping of precipitated anatase with Zr(IV) in the atomic ratio Zr/Ti = 0.008 significantly improves the photocatalytic activity of the foam supported titania. Zr doped anatase films show better performance as the films prepared only from Aeroxide^® P25 nanopowder.     

Effect of oxygen vacancies on ferroelectric behavior of Na1/2Bi1/2TiO3–BaTiO3 single crystals

One of the important lead-free ferroelectric solid solutions, sodium bismuth titanate–barium titanate Na_1/2Bi_1/2TiO₃–BaTiO₃ (NBT–BT) was grown by the conventional flux technique. In order to study the role of oxygen vacancies on the dielectric/ferroelectric properties, some of the crystal samples oriented along (0 0 1) and (1 0 0) planes were subjected to oxygen and nitrogen annealing processes to create different concentrations of oxygen vacancies in the samples. Dielectric and its loss measurements were carried out to analyze the role of oxygen vacancies and their corresponding dielectric behavior on NBT–BT crystals. Electron energy loss spectrum (EELS) has revealed that increasing oxygen vacancies has reduced oxidation states of Ti. X-ray rocking curve analysis has confirmed the degradation in the structural quality also on increasing the oxygen vacancies.     

Mechanochemical carboaluminothermic reduction of rutile to produce TiC–Al2O3 nanocomposite

This investigation aims to produce TiC–Al₂O₃ nanocomposite by reducing rutile with aluminum and graphite powder via a mechanochemical process. The effect of milling time on this process was investigated. The characterization of phase formation was carried out by XRD and SEM. Results showed that after a 10 h milling, the combustion reaction between Al, TiO₂ and C was started and promoted by a self-propagation high temperature synthesis. Extending the milling time to 20 h, the reaction was completed. The XRD study illustrated after a 20 h milling, the width of TiC and Al₂O₃ peaks increased while the crystallite sizes of these phases decreased to less than 28 nm. After annealing at 800 °C for 1 h in a tube furnace, TiC and Al₂O₃ crystallite sizes remained constant. However, raising the annealing temperature to 1200 °C caused TiC and Al₂O₃ crystallite size to increase to 49 nm and 63 nm, respectively. No new phase was detected after the heat treatment of the synthesised TiC–Al₂O₃ nanocomposite.     

A study on the mechanochemical behavior of TiO2–Al–Si system to produce Ti5Si3–Al2O3 nanocomposite

In the present study Ti₅Si₃–Al₂O₃ nanocomposite was synthesized by a displacement reaction between Al and TiO₂ in ball milling of TiO₂, Al and Si powders. The effect of milling time and heat treatment temperatures were also investigated. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffraction (XRD). Morphology and microstructure of powders were characterized by scanning electron microscopy (SEM). It was found that after 10 h of MA, the reaction between Al and TiO₂ initiated in a gradual mode and after about 45 h of milling, the reaction was successfully completed. The final product consisted of Ti₅Si₃ intermetallic compound with a crystallite size of 13 nm and amorphous Al₂O₃. Heat treatment of this structure at 1050 °C led to the crystallization of Al₂O₃ and ordering of Ti₅Si₃. The crystallite size of Ti₅Si₃ and Al₂O₃ after annealing at 1050 °C for 1 h remained in nanometer scale. So the final product appeared to be stable upon annealing.     

Synthesis and characterization of superfine pure tetragonal nanocrystalline sulfated zirconia powder by a non-alkoxide sol–gel route

Nanocrystalline sulfated zirconia powder was prepared by a non-alkoxide sol–gel route using acidic condition (pH 1–2). The samples had superfine crystallites and pure tetragonal phase at 700 °C. Zr(acac)₄ was used as zirconium precursor due to a better retention of sulfate species and H₂SO₄ 0.5 M was used as sulfating agent. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr and sulfate bonds. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles (calcined at 600 and 700 °C) with very small size and pure tetragonal phase with crystallite size between 5 and 10 nm.     

Facile route to obtain a highly bioactive SiO2–CaO–Na2O–P2O5 crystalline powder

This work describes a facile method to obtain highly bioactive crystalline powders of the SiO₂–CaO–Na₂O–P₂O₅ system using a simple route: solid state reaction. Success in obtaining the highly bioactive crystal phase of interest (sodium calcium silicate Na₂Ca₂Si₃O₉ containing phosphorus) involves heating the starting reactant powder mixture under an oxidizing atmosphere for 480 min in the temperature range 950–1000 °C. Despite a significant loss of phosphorus at heat treatment temperatures above 950 °C, the resulting Na₂Ca₂Si₃O₉ crystal phase is thermally stable up to 1100 °C. Longer treatment times favor the formation of a secondary phase (sodium calcium phosphate NaCaPO₄), which, according to recent studies, further increases the bioactivity of a similar material. Finally, in vitro bioactivity tests in acellular simulated body fluid (SBF) of a powder containing only the Na₂Ca₂Si₃O₉ phase has shown behavior similar to that of Biosilicate® — an ~ 99.5% crystalline glass–ceramic whose outstanding characteristics of interaction with living tissue have already been reported in the literature.     

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.     

Characterization of a calcium phosphate–TiO2 nanotube composite layer for biomedical applications

Well-ordered nanotube arrays of titania ~ 0.7 μm high and about 40 or 110 nm in diameter were prepared via electrochemical oxidation at constant voltage (10, 15, 20 or 25 V) in a mixture of 0.86 wt.% of NH₄F, glycerol and deionized water. The effect of annealing the nanotubes at 600 °C on their morphology and structure was examined using SEM and TEM techniques. These substrates are suitable supports for a calcium phosphate coating deposited by a simple immersion in Hank solution.The nucleation and growth of a calcium phosphate (Ca–P) coating deposited on TiO₂ nanotubes (NT) from Hanks' solution was investigated using SEM. XPS and FTIR surface analytical techniques were used to characterize the self-organized porous TiO₂ layers covered with calcium phosphate coatings before and after protein adsorption. Our results confirm that the nanotubular titania layer became stable after annealing at 600 °C, while its internal structure changed from amorphous to crystalline anatase, and eventually, a mixture of anatase and rutile. These thermally stabilized TiO₂ nanotubes significantly enhance apatite formation in Hanks' Balanced Salt Solution as compared to pure Ti covered with a native oxide layer. The Ca–P/TiO₂ NT/Ti surface adsorbs a higher amount of protein (bovine serum albumin, BSA) for a geometric surface area than does the Ti surface. The above difference in protein adsorption suggests a more promising initial cellular response for a Ca–P/TiO₂ NT/Ti composite than for a typical Ti implant surface.