Titanate Nanostructures Research Articles

Morphology-Controlled Synthesis of Barium Titanate Nanostructures

This study reports the synthesis of morphology-controlled BaTiO(3) nanostructures such as spherical, cube-shaped and rod-shaped BaTiO(3) using a molten-salt synthesis method. This method synthesized products from a reaction of BaO/BaCO(3) and TiO(2) with a eutectic mixture of NaCl-KCl flux at 700 degrees C for 1 h. The experiment used powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy to investigate the structure and morphology of the products. Moreover, the current work also provides a proposed synthetic mechanism of BaTiO(3) in the molten salt to illustrate the in situ transformation mechanism of BaTiO(3) nanostructures in the reaction. The results of the study revealed that the initial shape of the titania and the dissolution rate of the initial precursors critically determine the shapes of the final products.

Effect of preparation variables on morphology and anatase–brookite phase transition in sonication assisted hydrothermal reaction for synthesis of titanate nanostructures

The hydrothermal process coupled with sonication pretreatment has been employed to synthesize titanate nanostructures, including nanotubes and nanowires. By varying size of raw TiO 2 powder (400 nm and 1 μm), reaction temperature (90–180 °C), and sonication power (0–38 W), morphology of titanate nanostructures, length of titanate nanotube, and phase of titanate nanowire could be adjusted. Transmission electron microscope (TEM), nitrogen adsorption, and X-ray diffraction (XRD) were employed to analyze structure, specific surface area, and crystalline phase of the synthesized products. The titanate nanostructures transformed from the smaller TiO 2 particles provided higher specific surface area and shorter tube-length than those transformed from the larger ones. Morphology of titanate product transformed from TiO 2 spherical particle to titanate nanosheet, nanotube and nanowire with the gradual increase in the reaction temperature. The surface area of the samples corresponded well with the amount of titanate nanotube (hollow) and nanowire (non-hollow), whilst the length of titanate nanotube became longer with the applying sonication pretreatment. Interestingly, the formation of brookite phase was observed for the titanate nanowire synthesized at 180 °C with sonication pretreatment.

Electron microscopy of barium strontium titanate nanostructures in the aluminum oxide matrix

Electron microscopy has revealed the mechanism of formation of barium strontium titanate nanostructures during crystallization in the bulk of pores of the aluminum matrix. The nanostructures have the form of nanotubes or nanocolumns 100–200 nm in diameter and a few microns long, which are formed by barium strontium titanate crystals 3–100 nm in size.

Shape-controlled synthesis and electrocatalytic and direct electron transfer properties of bismuth titanate nanostructures

A facile hydrothermal synthesis strategy for the synthesis of bismuth titanate (Bi4Ti3O12, BT) nanorods (NRs) and nanosheets (NSs) is demonstrated, using which their shapes can be effectively controlled. The novel BT nanostructures were for the first time explored for protein immobilization and biosensing platform and further for studies of electrocatalytic and direct electron transfer (DET) properties. UV–visible absorption and Fourier-transform infrared spectroscopy investigations indicate that the Hb intercalated in the BTNRs and BTNSs well retains its native structure. Comparative experiments have confirmed that the Hb–Chi–BTNSs electrode has not only enhanced DET capacity but also displays excellent electrocatalytic properties such as higher sensitivity and wider linear range to the detection of hydrogen peroxide in comparison with the Hb–Chi–BTNRs electrode. We believe that BTNSs with unique structure and excellent DET and eletrocatalytic performance are expected to find potential applications in nanodevices and biomedicine, food and environmental analysis and detection.

Role of Ti−O Bonds in Phase Transitions of TiO2

A phase transition was achieved from TiO2 particles to titanate nanotubes by the breakage of Ti-O bonds without using expensive precursors, high temperatures, high chemical concentrations of alkaline solutions, and long synthesis times. The controlled preparation of one-dimensional nanostructures of titanates (H2Ti4O9.nH2O) has been conducted at a very low concentration of alkaline solution (1 M NaOH), and in a very short time (12 h) using TiO2 anatase and TiO2 P-25 (precursors) and a microwave enhanced soft chemical process. Temperature was used as a variable, and only low process temperatures (100-110 degrees C) were used. A combination of anatase nanoparticles/hydrogen tetratitanate nanotubes was synthesized using TiO2 (anatase) and a temperature of only 100 degrees C. When TiO2 (P-25) was used with the same concentration of alkaline solution (1 M NaOH), the same processing time of 12 h, and a higher temperature at 110 degrees C, only hydrogen tetratitanate nanotubes were observed. The linkages of "Ti-O" play a very important role in the structural features of different phases. X-ray diffraction (XRD) showed two crystalline phases (tetragonal and monoclinic) in the case of TiO2 (anatase) and one crystalline phase (monoclinic) for products of TiO2 (P-25). The role of Ti-O linkages is obvious in the Raman spectra as revealed by a shift in peak positions for a layered structure of the hydrogen tetratitanate and a nanosphere structure of the resulting TiO2. An X-ray photoelectron spectroscopy (XPS) study showed a shift to a lower binding energy of the 2p peaks (2p1/2, 3/2) in the Ti region for titanate and confirmed the formation of titanate nanostructures. Transmission electron microscopy (TEM) revealed nanotubes of hydrogen tetratitanates (H2Ti4O9.nH2O) in the form of bundles. High-resolution TEM (HRTEM) data supported findings of X-ray diffraction results of the products of TiO2 (anatase) and TiO2 (P-25).

ChemInform Abstract: Elongated Titanate Nanostructures and Their Applications

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stability and Photoelectronic Properties of Layered Titanate Nanostructures

Layered titanate nanostructures offer promising photoelectronic properties that are subject to surface chemistry-induced morphology changes. For a systematic evaluation of the bulk and surface contributions to the photoactivity of these structures, we investigated their photoelectronic properties and in particular their dependence on the condition of the gas-solid interface. We comprehensively explored the stability of Na(2)Ti(3)O(7) nanowires and scrolled up H(2)Ti(3)O(7) nanotubes by means of transmission electron microscopy, Raman, and FT-IR spectroscopy and subjected both titanate sheet-based structures to controlled thermal activation treatment under high vacuum conditions. We found that throughout thermal annealing up to T = 870 K the structure and morphology of Na(2)Ti(3)O(7) nanowires are retained. Consistent with the significant photoluminescence emission that is attributed to radiative exciton annihilation in the bulk, UV-induced charge separation is strongly suppressed in these structures. H(2)Ti(3)O(7) nanotubes, however, undergo transformation into elongated anatase nanocrystals during annealing at temperatures T >OR= 670 K. Photoexcitation experiments in O(2) atmosphere reveal that these structures efficiently sustain the separation of photogenerated charges. Trends in the abundance of trapped holes and scavenged electrons were characterized quantitatively by tracking the concentration of paramagnetic O(-) and O(2)(-) species with electron paramagnetic resonance spectroscopy EPR, respectively. An incisive analysis of these results in comparison to those obtained on airborne anatase nanocrystals underlines the critical role of surface composition and structure on charge separation and, in consequence, on the chemical utilization of photogenerated charge carriers.

Hierarchical Titanate Nanostructures through Hydrothermal Treatment of Commercial Titania Powders

AbstractHierarchical titanate nanostructures were hydrothermally synthesized in concentrated base solutions using commercial titania powders as starting materials. By varying the base concentration, nanowire arrays, flowers of nanosheets and nanotubes, and urchin‐like nanostructures of nanowires and nanotubes were sequentially fabricated. If the NaOH concentration was higher than 6 M, hydrated Na2Ti6O13 nanowire arrays, with nanowire diameters of 20–90 nm and an aspect ratio of 1100–5000, were produced at suitable reaction temperatures over a large area. In 10 M KOH solutions, aligned nanowires with a diameter of 30 nm and a lenght of 80 μm formed. In 4 M NaOH solutions, micrometer‐sized flowers of nanotubes and nanosheets formed. Reactions in 2 M NaOH solutions produced urchin‐like materials with a size of ca. 10 μm that were composed of nanotubes and nanowires. The adsorption behavior of the urchin‐like materials resembled macroporous materials with micropores. Since both base concentration and reaction temperature affected the reaction rate, the formation of various titanate nanostructures was proposed as a growth speed controlled process.

Elongated Titanate Nanostructures and Their Applications

AbstractRecent advances in the synthesis, characterisation and applications of elongated titanate and TiO2 nanostructures (including nanotubes, nanofibres and nanorods) are reviewed. The physicochemical properties of nanostructures, such as high surface area, efficient ion‐exchange properties, electron and proton conductivity and high aspect ratio, are described in connection with a particular application. Practical aspects of the preparation, stability and transformation of elongated titanates are considered. A critical survey of the literature is provided together with the development of prospectiveenergy applications of elongated titanates in catalysis, photocatalysis, electrocatalysis, solar cells, fuel cells, lithium batteries and hydrogen storage. Other applications utilising the high aspect ratio of elongated nanostructures include biomedical implants, sensors, drug delivery systems and smart, tribological composite coatings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Titanate Nanofiber Reactivity: Fabrication of MTiO3 (M = Ca, Sr, and Ba) Perovskite Oxides

Titanate nanofiber, as an important morphology of one-dimensional nanostructured titanate, not only can be regarded as the final product derived from alkaline-hydrothermal treatment of bulk TiO2 but also can serve as initial reactant for fabricating complex functional materials with their parent morphology, which may be difficult to achieve using their bulk material counterparts under mild hydrothermal conditions. Based on titanate nanofiber reactivity, ternary MTiO3 (M = Ca, Sr, and Ba) perovskite oxides with specific morphologies have been fabricated in alkaline solution at low temperature via a soft chemical route. The resulting CaTiO3 products possessed a microtubular structure with rectangular cross-section, while SrTiO3 and BaTiO3 showed the assemblies consisting of aggregated particles in a compact fashion. On the basis of the experimental results, we have proposed two types of growth mechanisms to elucidate the formation processes of CaTiO3, SrTiO3, and BaTiO3 microstructures, respectively. The fabrication of microtubular CaTiO3 undergoes the initial dissolution of titanate nanofibers by Ostwald ripening process to convert into micrometer-sized fiber-bundles, while recrystallization occurs simultaneously until tubular microstrucures are obtained. The formation of SrTiO3 and BaTiO3 microstructures involves ion exchange reaction and in situ growth process at the self-sacrifice of titanate nanofibers framework based on the chemical reactivity. In addition, the photoelectrochemical properties of the as-obtained products are presented, and CaTiO3 microtubes exhibit better photoeletrochemical response relative to SrTiO3 and BaTiO3 microstructures.

Phase Transformation in Titania Nanocrystals by the Oriented Attachment Mechanism: The Role of the pH Value

The oriented attachment (OA) mechanism has been investigated as an important process in the formation of anisotropic nanostructures such as depicted. The results showed that the control of a desired phase in this system may be attained by the control of OA mechanism through pH value, obtaining several morphologies.A new synthetic method for TiO(2) nanocrystals starting from metallic Ti and hydrogen peroxide was developed, in order to obtain minimal interferences to evaluate phase transformation in the system. The results revealed that the crystal morphology appeared to be dictated by the pH value, which shows a strong dependence on the surface energy. The involvement of the oriented attachment (OA) mechanism is important to modify the morphology and, hence, the distribution of the surface energy and confirmed that the mechanism can accelerate certain phase transitions, albeit pH dependence in terms of how the mechanism affects the final particle morphology and direction of crystalline growth. The importance of the mechanism was also apparent in extremely basic conditions, which indicates a possible correlation with the formation of hydrogen titanate nanostructures.

Effect of Reaction Temperature and Sonication Pretreatment in the Hydrothermal Process on the Morphology of Titanate Nano-Structure

Titanate nanostructures were synthesized by hydrothermal technique. The sonication pretreatment and reaction temperature were employed to investigate the morphology and specific surface area of the titanate nanostructure. Transmission electron microscopy, dynamic light scattering, and nitrogen adsorption were used to characterize and elucidate the behavior of titanate nanostructures in each experimental condition. By the effect of sonication pretreatment, the length and BET surface area of titanate nanotubes (TNTs) were raised from 50 nm to 490–1760 nm and from 180 to 260 m2 g–1, respectively, because of de-agglomeration of TiO2 particles in the precursor. The BET surface area of TNTs increased with increasing hydrothermal temperature from 90 to 150°C However, when the reaction temperature increased up to 180°C, BET surface area of TNTs inversely decreased. The reason of the decline in surface area could be explained by morphology of titanate formed. The nanotube structure (hollow) of titanate was transformed to nanofiber structure (non-hollow) at this high temperature.

Influence of bases on hydrothermal synthesis of titanate nanostructures

A hydrothermal treatment of titanium dioxide (TiO2) with various bases (i.e., LiOH, NaOH, KOH, and NH4OH) was used to prepare materials with unique morphologies, relatively small crystallite sizes, and large specific surface areas. The experimental results show that the formation of TiO2 is largely dependent on the type, strength and concentration of a base. The effect of the nature of the base used and the concentration of the base on the formation of nanostructures were investigated using X-ray diffraction, Raman spectroscopy, transmission and scanning electron microscopy, as well as surface area measurements. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) were both used to transform the morphology of starting TiO2 material.

A Biomimetic Hierarchical Scaffold: Natural Growth of Nanotitanates on Three-Dimensional Microporous Ti-Based Metals

Nanophase materials are promising alternative implant materials in tissue engineering. Here we report for the first time the large-scale direct growth of nanostructured bioactive titanates on three-dimensional (3D) microporous Ti-based metal (NiTi and Ti) scaffolds via a facile low temperature hydrothermal treatment. The nanostructured titanates show characteristics of 1D nanobelts/nanowires on a nanoskeleton layer. Besides resembling cancelous bone structure on the micro/macroscale, the 1D nanostructured titanate on the exposed surface is similar to the lowest level of hierarchical organization of collagen and hydroxyapatite. The resulting surface displays superhydrophilicity and favors deposition of hydroxyapatite and accelerates cell attachment and proliferation. The remarkable simplicity of this process makes it widely accessible as an enabling technique for applications from engineering materials treatment including energy-absorption materials and pollution-treatment materials to biotechnology.

Structural and mechanical properties of polystyrene nanocomposites with 1D titanate nanostructures prepared by an extrusion process

AbstractPolystyrene (PS) nanocomposites with titanate nanotubes and titanate nanoribbons were prepared by an extrusion process at 180°C. Nanocomposites with 1 wt% of nanofillers and pure PS that had also been exposed to the extrusion process were comparatively examined with scanning electron microscopy (SEM), electron dispersive X‐ray spectrometry (EDS) mapping, solid state proton nuclear magnetic resonance measurements (1H NMR), tensile tests, and shear creep measurements. SEM images and EDS mapping analysis show that titanate nanoribbons homogeneously distribute at a micrometer length‐scale in the PS matrix during the extrusion process. This is not the case for titanate nanotubes, which show a stronger tendency to form clusters. Solid state 1H NMR studies, however, proved that the nanocomposites are inhomogeneous at a nanometric scale where structural components with highly mobile PS molecules coexist with domains of rigid PS molecules. Differences in the 1H spin‐lattice relaxation at and above the glass transition temperature Tg = 373 K suggest that nanofillers affect the thermodynamic properties of nanocomposite domains. Only a slight increase in mechanical tensile properties was observed in the case of the nanocomposite containing 1 wt% of titanate nanoribbons (TiNRs) probably reflecting a weak interaction between the polymer matrix and the nanofiller. Nevertheless, our results prove that the use of functionalized TiNRs may, in combination with the extrusion process, represent a very promising starting point for the preparation of TiNR nanocomposites at the industrial level. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Growth Mechanism of Shape-Controlled Barium Titanate Nanostructures through Soft Chemical Reaction

Morphology-controlled barium titanate (BaTiO3) nanostructures, from single-crystal nanorods to nanoparticles, were synthesized by tuning the reaction time of a soft chemical process. Based on the morphology change of the nanostructures, the growth mechanism of the shape-controlled BaTiO3 nanostructures by the soft chemical reaction method was suggested. With the reaction time of 42 h, single-crystal BaTiO3 nanorods with flat surface of facets and defined crystal axis were obtained. As the reaction time was extended to 50 h, a certain volume of nanorods converted to nanoparticles generated by a redissolution−growth reaction. When the reaction time was further elongated to 72 h, the volume of nanoparticles in the product notably increased with single grains of particles that have diameters up to ∼200 nm. It was determined that an ion exchange and the structural transformation from the layer structure of the precursor into the perovskite structure prevailed at an early stage of the soft chemical reaction, and then the nanorods changed to nanoparticles due to the redissolution−growth reaction for reaction times over 42 h.

Fabrication and Characterization of Nanostructured Titanate Materials by the Hydrothermal Treatment Method

The synthesis and characterization of one-dimensional (1-D) tubular and fibrous nanostructured materials have recently received highly attention. Various morphologies of 1-D nanostructured titanate materials including nanosheets, nanotubes, nanowires, and nanoribbons have recently been successfully synthesized using the alkaline hydrothermal method. In spite of the controversy of the chemical structures and formation mechanisms, titanate nanostructures have attracted much attention on applications of dye-sensitized solar cell, hydrogen sensing, lithium storage and photocatalysis because of their unique features of high specific surface area, ion-exchange capacity and aspect ratio, and unique optical and electrochemical properties. The morphology and microstructure of titanate nanostructures are highly dependent on the preparation conditions. In this review, we highlight the synthesis of TiO(2)-derived nanomaterials under various hydrothermal conditions. The patents for fabrication of various morphologies of nanostructures are also introduced. Effects of preparation parameters including hydrothermal temperature, duration, alkaline concentration, starting materials, and post-treatment on the morphology and microstructure of titanate nanomaterials are reviewered. In addition, the microwave-assisted method for fabrication of 1-D titanate nanostructures is discussed and compared. The applications of titanate nanomaterials in photocatalysis, ion-exchange, and lithium storages are also introduced.

Shape-Controlled Monocrystalline Ferroelectric Barium Titanate Nanostructures: From Nanotubes and Nanowires to Ordered Nanostructures

We report for the first time on the controlled hydrothermal synthesis of barium titanate nanostructures using Na2Ti3O7 nanotubes and nanowires as synthetic precursors. A variety of nanostructured BaTiO3 have been prepared, exhibiting either simple shapes of nanowires, nanosheets, nanocubes, and hexagonal nanoparticles or ordered architectures of coral-like nanostructures of assembled nanorods, starfish-like nanostructures, and sword-like nanostructures. The shapes of the various BaTiO3 products are found to be dependent on the concentration of Ba(OH)2, the temperature, and the nature of the precursors. The synthesis route exploits the differences in the hydrothermal stability of the Na2Ti3O7 nanotubes and nanowires and the temperature-dependent crystal structure of barium titanate. Various nanoblocks, including nanosheets and nanorods formed from the Na2Ti3O7 nanotubes and nanowires, respectively, grow and assemble to form the ordered BaTiO3 nanostructures. This represents a new approach that is capable of assembling ordered perovskite nanostructures using relatively large nanoblocks formed from layered alkali-metal titanates. The process offers more flexibility than those using inorganic titanium salts or organometallic titanium compounds, which commonly leads to the formation of only BaTiO3 nanoparticles.

Transformation of layered titanate nanosheets into nanostructured porous titanium dioxide in polycation solution

Nanostructured porous TiO 2 particles constructed from nanorod-like crystals were prepared from a layered titanate nanosheet precursor. The synthesis process includes two steps: construction of a porous nanostructure by assembling the nanosheets with poly (diallyldimethylammonium) (PDDA) polycations, and topotactic transformation of the nanostructured titanate nanosheets into anatase-type TiO 2 nanocrystals by hydrothermal reaction. The reaction process and nanostructured porous particles were characterized by XRD, DTA-TG, SEM, TEM analyses, and measurements of specific surface area, pore size distribution, ruthenium dye (N719) adsorption, and photocatalytic activity. The morphology of the porous particles is dependent on the PDDA concentration in the reaction system. Spherical particles constructed from nanorod-like anatase crystals can be prepared under the high PDDA concentration conditions. The topotactic transformation reaction from the titanate nanosheet to anatase resulted in the formation of anatase nanocrystals which preferentially expose the (0 1 0) plane of anatase on the surface. The surface of the nanostructured porous anatase particles shows high N719 dye adsorption ability and high photocatalytic activity, which have potential application in dye-sensitized solar cells.

Shape-Control of Strontium Titanate Nanostructures by a Surface-Capping Soft Chemical Process

A surface-controlling soft chemical process is reported for tuning the morphologies of strontium titanate (SrTiO3) nanostructures. The conventional surfactant-free soft chemical process produced polycrystalline SrTiO3 nanoparticle aggregates generated by the dissolution-growth reaction. Alternatively, in order to synthesize single-crystal SrTiO3 nanorods, we employed the surface-capping soft chemical process using a polyacrylic acid (PAA) polymer capping-reagent. The single-crystal SrTiO3 nanorods prepared using PAA were observed to have facets with di erent diameters from a few nm to 200 nm, lengths up to several m, rectangular cross-sections, and crystal-axe perpendicular to the growth axis of the nanorods. A high-yield of nanorods over 90 % was also obtained in the total volume of the product.