Hydrothermal processing of hydrogen titanate/anatase-titania nanotubes and their application as strong dye-adsorbents

The nanotubes of pure hydrogen titanate and anatase-titania have been synthesized via hydrothermal treatment of as-received anatase-titania particles. The formation mechanism of anatase-titania nanotubes via hydrothermal has been discussed in detail in view of the finger-prints produced by characterizing the intermediate and end products using various microscopic and spectroscopic techniques such as scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, Brunauer, Emmett, and Teller specific surface-area measurement, Fourier transform infrared spectroscope, diffuse reflectance, photoluminescence, thermal gravimetric and differential thermal analyses. The obtained results strongly support the rollup mechanism, involving multiple nanosheets, for the formation of anatase-titania nanotubes with the formation of different intermediate hydrothermal products having various morphologies such as sodium titanate having aggregated rectangular block-like structures, hydrogen sodium titanate and pure hydrogen titanate having highly aggregated unresolved fine-structures containing nanotubes, and finally, the pure anatase-TiO2 nanotubes. It is demonstrated that, during the hydrothermal treatment, the nanotubes of pure hydrogen titanate are formed first coinciding with the stable solution-pH during washing, indicating the completion of ion-exchange process, and a drastic increase in the specific surface-area of the hydrothermal product. The anatase-titania nanotubes are then derived from the pure hydrogen titanate nanotubes via thermal treatment. The use of pure hydrogen titanate and anatase-titania nanotubes for an organic textile dye-removal, from an aqueous solution under the dark condition, via surface-adsorption mechanism has been demonstrated. It is shown that, the specific surface-area and the surface-charge govern the maximum dye-absorption capacity of the anatase-TiO2 nanotubes under the dark condition.     

Study of phase transformation and crystal structure for 1D carbon-modified titania ribbons

One-dimensional hydrogen titanate ribbons were successfully prepared with hydrothermal reaction in a highly basic solution. A series of one-dimensional carbon-modified TiO₂ ribbons were prepared via calcination of the mixture of hydrogen titanate ribbons and sucrose solution under N₂ flow at different temperatures. The phase transformation process of hydrogen titanate ribbons was investigated by in-situ X-ray diffraction at various temperatures. Besides, one-dimensional carbon-modified TiO₂ ribbons calcined at different temperatures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption isotherms, diffuse reflectance ultraviolet–visible spectroscopy, and so on. Carbon-modified TiO₂ ribbons showed one-dimensional ribbon crystal structure and various crystal phases of TiO₂. After being modified with carbon, a layer of uniform carbon film was coated on the surface of TiO₂ ribbons, which improved their adsorption capacity for methyl orange as a model organic pollutant. One-dimensional carbon-modified TiO₂ ribbons also exhibited enhanced visible-light absorbance with the increase of calcination temperatures.     

Fabrication of micrometer-scale spherical titanate nanotube assemblies with high specific surface area

Three-dimensional (3D) micrometer-scale spherical titanate nanotube assemblies have been successfully synthesized via hydrothermal synthesis from Ti powders. The obtained titanate nanotube assemblies have a diameter of around 4-7 µm. The titanate nanotubes have an outer diameter of around 9-10 nm, an inner diameter around 3-4 nm and a length of several micrometers. A proposed two-stage growth mechanism was applied to explain the formation process of these titanate nanotube assemblies. We have also demonstrated that these titanate assemblies have higher specific surface area and larger adsorption capacity than that of titanate nanotubes. And they could possibly be further used in photocatalysts, separation technologies, energy-storage technologies and so on.     

Syntheses, characterization and properties of novel nanostructures consisting of Ni/titanate and Ni/titania

Ni/titanate one-dimensional nanostructures and Ni/titania nanocrystal composites were produced by a facile synthetic procedure using protonic titanate nanotubes as the precursor templates. The formation mechanisms for the nanostructures were proposed. The nickel ions first enter into the titanate matrix through three approaches, ion-exchanges reaction with the interlayered hydrogen ions, capillary forces from the microcavities, and electrostatic adsorptions due to the negatively charged outer surface of the titanate nanotubes. The following metallic nickel nucleation and growth may have occurred for these three kinds of the nickel ions reduced under hydrogen gas flow at elevated temperatures. The supports' titanate nanotubes may phase transform into the anatase titania nanocrystals and further into the mixture of anatase and rutile titania along with the increases of temperature. The Ni/titanate nanocomposites demonstrate paramagnetic behaviors and the Ni/titania nanocrystals display typical ferromagnetic behaviors. The Ni/titania sample reduced at 550 °C containing 14.5% rutile has higher photocatalytic activities than the sample reduced at 350 °C containing pure anatase, which is ascribed to a synergistic effect between anatase and rutile. The ferromagnetic characteristics of the Ni/titania products make them available as magnetically separable photocatalysts, which can be separated and recovered quickly by applying an external magnetic field.     

Preparation and characterisation of ultrafine lead titanate (PbTiO3) powders

Ultrafine lead titanate (PbTiO₃) powders in tetragonal form have been successfully prepared via three processing routes, namely, conventional co-precipitation, microemulsion-refined freeze drying, and microemulsion-refined co-precipitation. The formation process of lead titanate from the resulting precursors was monitored using techniques such as thermal analyses and X-ray diffraction for phase identification. It was found that the two microemulsion-refined processing routes led to a lower formation temperature for lead titanate than that observed in the conventional co-precipitation route. The three lead titanate powders have also been compared for particle and agglomerate size distributions and specific surface area. It appears that the microemulsion-refined co-precipitation is the technique which results in the formation of the finest lead titanate powder amongst the three processing routes investigated in the present work. This revised version was published online in September 2006 with corrections to the Cover Date.     

Highly Excited Hydrogen in Strong D.C. Electric Fields: Atomic Engineering

Abstract

We excite atomic hydrogen from the ground state via a three-photon process to high-lying excited states in the presence of strong d.c. electric fields. The external field is used to manipulate, control, and design specific atomic structures. We can construct nearly ‘one-dimensional’ atoms whose electronic distributions are highly extended along the field, and which may have enormous electric dipole moments (‘giant-dipole atoms’).     

Room temperature magnetic properties of Cu-doped titanate, TiO2(B) and anatase nanorods synthesized by hydrothermal method

The Cu-doped hydrogen titanate nanorods are synthesized via a hydrothermal reaction and converted into Cu-doped TiO₂(B) and anatase phases by calcinations. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and selected area electron diffraction (SAED) pattern do not show the presence of any other phases and thus confirmed the intrinsic ferromagnetic behavior rather than it arising from metallic clusters. The blue shifting in absorption edge and increase in photoluminescence (PL) intensity from Cu-doped hydrogen titanate to anatase phase are strongly correlated with concentration of oxygen vacancies and defect formation. The higher concentration of oxygen vacancies and/or structural defects leads to the coalescence of ferromagnetic domains, which corroborates to the observed higher magnetization value of Cu-doped anatase phase compared to other phases.     

钛酸钾一维纳米结构的构筑及表征

以锐钛矿TiO2为起始原料,通过水热法制备了钛酸钾纳米管/棒,研究了在不同时间内合成不同长度和宽度的钛酸钾纳米管/棒的机理和形态的控制条件。用X射线衍射(XRD)和扫描电子显微镜(SEM)对其结构和形貌进行了表征。实验结果表明水热处理时间对产物形貌的控制有重要影响。处理温度在200℃下,不同的反应阶段得到钛酸钾不规则块状体、纳米管、纳米棒等结构。发现水热处理时间能对钛酸钾特定结构进行有效的控制,确定了水热处理时间和钛酸钾形貌结构的关系,从而可以通过选择反应的合理处理时间和温度,得到特定的钛酸钾纳米结构。此外还对比研究了后处理中加入酸处理时对产物的形貌和晶体结构的影响,发现酸处理过程中H+可取代K+,使得原来的单斜晶体K2Ti6O13转变为H2Ti3O7,从而让纳米棒表面更规整光滑。最后采用紫外-可见吸收光谱对比研究了各个阶段产物的光吸收性能。     

Protonated Titanates and TiO2 Nanostructured Materials: Synthesis,Properties, and Applications

Tubular and fibrous nanostructures of titanates have recently been synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO₂ are reviewed. The crystal structures, morphologies, and mechanism of formation of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar‐cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

Facile synthesis and characterization of novel nanocomposites of titanate nanotubes and rutile nanocrystals

The nanocomposites of one-dimensional (1D) titanate nanotubes and 0D rutile nanocrystals were fabricated by hydrothermal treatment of bulky rutile TiO₂ powders in a 10 M NaOH solution without using any templates and catalysts. The as-prepared samples were characterized with transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, Fourier transform infrared spectroscopy (FTIR), UV–visible spectrophotometry (UV–vis), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that many small rutile nanocrystal particles of about 5 nm could uniformly attach to the outer surface and in the inner of the titanate nanotubes, forming an interesting and novel nanocomposite structure. Adjusting reaction time could control the amount of rutile nanoparticles in the nanocomposites. With increasing reaction time, the specific surface areas, porosity, pore volume, UV absorption and band gap energies of the nanocomposites gradually increased due to the fact that rutile particles were steadily turned into the tubular nanocomposites, finally completely formed titanate nanotubes.     

锂离子电池负极材料Li4Ti5O12合成与改性的研究进展

钛酸锂(Li4Ti5O12)是一种“零应变”材料,在充放电过程中不会形成锂枝晶,消除了过充电对电池的安全隐患。本文系统的介绍了钛酸锂的制备方法和结构改性。在钛酸锂的合成方面固相法相对较为简单,生产效率高,较为适合工业中大批量生产,溶胶凝胶法则较为复杂,但得到的钛酸锂材料相对来说纯度、结晶度也比较高。在钛酸锂材料改性方面,纳米化、球化、多孔化都是以增大材料表面积提高材料的比容量;金属及离子掺杂改性主要是为了提高材料的导电性,其中不同的金属离子对材料的比容量有不同的影响。材料的表面复合改性是一种综合改性手段,是在提高材料比容量的同时提高材料导电性的一种改性手段。     

钛酸钾晶须填充新型PPESK的性能及形态研究

采用填料对含二氮杂萘结构的聚醚砜酮(PPESK)进行填充改性,能够快捷有效的提高其性能,为此采溶液共沉析的方法制备了含二氮杂萘结构的聚芳醚砜酮/钛酸钾晶须(PPESK/Whisker)复合材料.使用不同比例的钛酸酯偶联剂进行晶须表面处理,研究了晶须表面处理和晶须含量对PPESK复合材料机械性能的影响;考察了复合材料的热性能,并用扫描电镜观察了复合材料的形貌.结果表明,钛酸钾晶须作为填充材料,使得复合材料机械性能得到明显改善;对晶须进行适当的表面处理后,晶须与PPESK基体的相容得到改善.     

Fabrication and characteristics of three-dimensional flower-like titanate nanostructures

A novel and facile approach has been developed to fabricate three-dimension (3D) flower-like titanate nanostructures from Ti powders. The synthesized flower-like titanate nanostructures were composed of many thin nanoribbons and have an ultrahigh specific surface area of 572.3 m2/g. After high temperature heat treatment, the flower-like titanate nanostructures were totally transformed into corresponding anatase TiO2 nanostructures without destroying their 3D hierarchical structural motif. The flower-like TiO2 nanostructures exhibited high photocatalytic activity for photodecomposition of methyl blue, and they could possibly be further used in photovoltaic cell, sensors, Li-ion batteries, and so on.     

钛酸盐一维纳米材料向TiO2纳米材料的水热转化研究

采用强碱性水热处理法分别控制第一次水热反应为160℃和200℃,制备出一维纳米管和纳米棒2种形貌的产物,将其作为第二次水热反应的前驱体,考察了第二次水热体系中pH值和温度对TiO2纳米材料的晶相组成及其微观形貌的影响;采用XRD、TEM以及HRTEM对样品进行了分析.结果表明,当以纳米管为前驱体时,除在pH=0的体系中得到了以金红石相为主的单晶纳米棒外,在pH值为2、4和7的条件下均得到了单晶纯锐钛矿相TiO2纳米颗粒.当以纳米棒为前驱体时,在pH=0的体系中得到了金红石相与板钛矿相共存的纳米棒和纳米颗粒混合产物;在pH值为2、4和7的条件下均得到了纯锐钛矿相TiO2纳米棒;当二次水热温度低于180℃时,前驱体没有转化完全,所得产物为前驱体与锐钛矿相TiO2共存的纳米棒;当水热温度为180℃和210℃时,产物为纯锐钛矿相纳米棒.     

Effects of calcination temperature on microstructures and photocatalytic activity of titanate nanotube films prepared by an EPD method

Titanate nanotube films are fabricated on F-doped SnO(2)-coated glass substrates via an electrophoretic deposition method using hydrothermally prepared titanate nanotubes as precursors. The effects of calcination temperature on the microstructures and photoactivity of as-prepared titanate nanotube films are investigated and discussed. The results indicate that the intercalated sodium ions (Na(+)) in the as-prepared titanate nanotubes are easily removed during the electrophoretic deposition. The phase transformation of titanate to anatase and diffusion of Na(+) ions from glass substrates into films occur at 400?°C. With increasing calcination temperature, the crystallization of anatase enhances and sodium content in the films increases. At 500?°C, the tubular structure still holds and the films show the highest photocatalytic activity probably due to their good crystallization, large specific surface areas and tubular structures.     

Synthesis,Structure, and Heat Capacity of Bi4–xNdxTi3O12 (x = 0.4, 0.8, 1.2, 1.6) Solid Solutions

Inorganic Materials - Bi4–xNdxTi3O12 (x = 0.4, 0.8, 1.2, 1.6) bismuth neodymium titanate solid solutions have been prepared by solid-state reactions, via firing of mixtures of their...     

Fabrication of metal nanowires in carbon nanotubes via versatile nano-template reaction

A nano-template reaction has been developed to fabricate metal nanowires using metallofullerene nanopeapods (i.e., carbon nanotubes (CNTs) encapsulating endohedral metallofullerenes) as starting materials. In this nanometer-scale reaction, the structure of resulting products should possess specific low-dimensional structures, because of their uniform starting orientation of metallofullerene molecules and the rigid restriction of reaction space by the presence of walls of CNTs. Using the nano-template reaction, we have fabricated various Gd nanowires, including a single Gd atomic chain, a one-dimensional alignment of Gd squares, and Gd nanowires that correspond to a one-dimensional segment of the bulk close-packed structure. The same reaction, in principle, can be applied to fabricate more than 20 different types of metal nanowires in the CNTs, which simply are dependent on the use of the corresponding different types of metallofullerenes as encapsulates in the CNTs. The present novel reaction will provide a wide variety of unusual low-dimensional nanowires and nanomaterials in the CNTs, which have not been synthesized via the fabrication techniques that have been reported so far.     

Effect of Ultrasonic Processing on the Synthesis of Barium Titanyl Oxalate and the Characteristics of the BaTiO<Subscript>3</Subscript> Powder Prepared from It

Barium titanyl oxalate (BTO) with small deviations from stoichiometry has been synthesized by a chemical and a sonochemical method (under ultrasonication). Ultrasonic processing has been shown to reduce the particle size of the resultant BTO powder by about ten times and ensure a nearly spherical shape of the particles. The morphology of barium titanate powders prepared by decomposing the BTO at a temperature of 900°C is similar to that of the parent BTO and independent of stoichiometry. The powders have a barium to titanium ratio Ba/Ti = 1.002 and 0.987. The barium titanate powders synthesized using the sonochemical method contain a smaller amount of residual phases and have a larger specific surface area, smaller crystallite size (~100 nm), and smaller unit-cell parameters than do the powders prepared without ultrasonication.     

浸渍-沉积法制备一维Au/TiO_2的光催化性能研究

以钛酸纳米管为载体、HAuCl4为金前驱体,通过浸渍-沉积法制备一维金修饰TiO2光催化剂(Au/TiO2)。通过X射线衍射和紫外-可见漫反射吸收光谱研究材料的结构和性质。以甲基橙溶液作为模拟废液,研究Au/TiO2材料在紫外光条件下的光催化活性。研究表明,由于金可以接受电子,从而促进光生电子和光生空穴的分离,使TiO2的光催化活性提高;Au/TiO2的光催化活性还与金的含量密切相关,金的最佳负载量为1%(质量分数)。