Synthesis of titanate/anatase composites with highly photocatalytic decolorization of dye under visible light irradiation

Titanate/anatase nanocomposites consisting of titanate nanotubes and leaf-like anatase TiO₂ nanoparticles were successfully prepared via a novel combinational hydrothermal method. The samples were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The activity of the nanocomposites was examined by photocatalytic decolorization of rhodamine B under visible light irradiation. It is found that the nanocomposites exhibited a much improved photocatalytic activity in comparison with titanate nanotube, anatase TiO₂ nanoparticle, and even the commercial Degussa P-25. The photocatalytic mechanism of the as-prepared nanocomposites was discussed.     

Voltammetric study of fullerene C60 and fullerene C60 nanotubes with sandwich method

Two sandwich-type electrodes (RTIL/C₆₀/SWNT/GCE and RTIL/C₆₀ nanotube/SWNT/GCE) with fullerene C₆₀ or fullerene C₆₀ nanotubes interlayer covered by room temperature ionic liquid (RTIL) membrane on single-walled carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE) surface were fabricated. Cyclic voltammetry and differential pulse voltammetry were used to characterize their electrochemical behaviors and the difference between fullerene C₆₀ and fullerene C₆₀ nanotubes was investigated and the reason was presumed for the first time. It has been observed that 4 pairs of quasi-reversible redox peaks occurred at the RTIL/C₆₀/SWNT/GCE, while only two peaks at the RTIL/C₆₀ nanotube/SWNT/GCE. The cathodic and anodic peak potentials did not shift with the change of pH, indicating that no protons were involved in the electrode reaction processes. So the redox reaction of the fullerene C₆₀ or fullerene C₆₀ nanotubes could be considered as a multi-step one-electron transfer process and fullerene C₆₀ behaved like an electron accumulator to accept and release electrons. While, the reductive products of fullerene C₆₀ nanotubes could not be oxidized again in the reverse scan and the electrode process was irreversible. The fullerene C₆₀ monomer released the accumulated electrons more easily than the fullerene C₆₀ nanotubes. The electrochemical behaviors showed that the electrochemical processes at both electrodes were adsorption-controlled processes.     

Synthesis and dielectric properties of substituted barium titanate ceramics

Barium titanate is one of the most studied ferroelectric materials which has been used in various forms, e.g. bulk, thin and thick films, powder, in a number of applications. In order to achieve a material with desired properties, it is modified with suitable substituents. Most common substituents have been strontium, calcium and zirconium. Here, we report studies on lead and zirconium substituted barium titanate. The material series with compositional formula Ba_0.80Pb_0.20Ti_1?xZr_xO₃, with x varying from 0 to 0.1, was chosen for investigations. The material was synthesized by solid-state reaction method. Reacted powders compacted in the form of circular discs were sintered at 1300 °C. All the samples were subjected to X-ray diffraction (XRD) analysis and found to have single phase perovskite structure. Dielectric behavior was studied as a function of frequency and temperature. Curie temperature (T_c) was found to decrease with increasing x.     

纳米棒状Li-Ti-O化合物的制备与电化学嵌锂性能

采用在碱性条件下的水热法,合成了钛酸钠纳米棒,在此基础上用熔融盐离子交换方法制备了钛酸锂中间体,在400~700 ℃的空气气氛下烧结,得到的纳米棒状Li-Ti-O化合物由贫锂的锐钛矿结构LixTiO2和立方尖晶石结构Li4Ti5O12 两相构成。用恒电流充放电研究了其电化学嵌/脱锂性能。结果表明,经600 ℃热处理的纳米棒状Li-Ti-O化合物具有最佳的比容量、循环稳定性和高倍率放电性能。     

Room temperature chemical synthesis of highly oriented PbSe nanotubes based on negative free energy of formation

The sacrificial template free chemical synthesis of PbSe nanotubes at room temperature has been performed by lead hydroxination from cadmium hydroxide nanowires. This process was based on the ion exchange reaction to replace Cd²⁺ with Pb²⁺ ions from hydroxyl group followed by replacement of hydroxyl group with selenium ions. The reaction kinetics was accomplished due to more negative free energy of formation and thus the difference in the solubility products. The formed nanotubes were inclusive of Pb and Se with proper inter-chemical bonds with preferred orientations having diameter in tens of nanometer. These nanotubes can have future applications in electronic, optoelectronics and photovoltaic's as well.     

Kinetics of simultaneous leaching of Ag and Pb from hydrometallurgical zinc residues by chloride

The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated.The effects of stirring speed,temperature,sodium chloride concentration,particle size and liquid/solid ratio on Ag and Pb dissolution in sodium chloride were studied.It was determined that the dissolution rates increased with increasing sodium chloride concentration,temperature and decreasing particle size.The dissolution kinetics followed a shrinking core model,with inter-diffusion through gangue layer as the rate determining step.This finding is in accordance with the apparent activation energy(Ea)of 26.8 kJ.mol-1(Ag)and 26.5 kJ.mo1-1(Pb),and a linear relationship between the rate constant and the reciprocal of squared particle size.The orders of reaction with respect to sodium chloride concentration,temperature and particle size were also achieved.The rate of reaction based on diffusion-controlled process can be expressed by semi-empirical equations.     

Polyethyleneimine surfactant effect on the formation of nano-sized BaTiO3 powder via a solid state reaction

Barium titanate powder is widely used in multilayer ceramic capacitors (MLCC) because of its’ superior ferroelectric and dielectric properties. Presently, barium titanate powder is mass-produced using a conventional solid state reaction. However, the conflicting literature reports clearly show that the solid state reaction mechanism is not well understood. Synthesizing nano-sized barium titanate powders with less agglomeration using a solid state reaction method at a low calcination temperature has become a hot research topic. This study examines the effect of polyethyleneimine (PEI) surfactant addition on BaTiO₃ formation in a solid sate reaction. XRD, DTA and TEM are used in this investigation. The results indicate that PEI addition can promote BaCO₃ and TiO₂ mixing homogeneity, which enhances the interfacial reaction between BaCO₃ and TiO₂. BaTiO₃ formation can be obtained through the interfacial reaction between BaCO₃ and TiO₂ at the intimate contact between the reactants and Ti⁺⁴ ion diffusion along the surfaces or grain boundaries of BaTiO₃ powders, thereby obtaining a single phase BaTiO₃ powder when calcining at low temperatures for a long period.     

Preparation of platinum-iridium nanoparticles on titania nanotubes by MOCVD and their catalytic evaluation

Pt based catalysts are commonly used in several industrial processes involving hydrogenation and dehydrogenation reactions. New deposition methods as well as support materials are being investigated to generate new catalysts with superior catalytic activity. In this work, platinum-iridium (Pt-Ir) nanoparticles of about 5 nm in size were supported on titania (TiO₂) nanotubes by metal organic chemical vapor deposition (MOCVD). The TiO₂ nanotubes were prepared by an alkali hydrothermal method using sodium hydroxide solution at 100 °C, during 64.8 ks. Pt-Ir nanoparticles were obtained by controlling the MOCVD conditions at 400 °C and 66.6 kPa.Textural properties and particle size were investigated by nitrogen physisorption (BET method), X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. Catalytic activity was measured in cyclohexene disproportion as the test molecule for hydrogenation/dehydrogenation reactions. The TiO₂ nanotubes exhibit a considerable high surface area of about 425,000 m²/kg, however, after calcination at 400 °C their nanotubular morphology was partially transformed. In spite of this change, the 5 nm Pt-Ir nanoparticles supported on TiO₂ nanotubes were more active in the cyclohexene disproportion reaction than conventional Pt-Ir/alumina catalysts in the whole range of temperatures investigated (50–250 °C). Hydrogenation reactions (high selectivity to cyclohexane) predominate at temperatures below 150 °C.     

Synthesis of polyaniline nanotubes using Mn2O3 nanofibers as oxidant and their ammonia sensing properties

In this work, a new method for the synthesis of polyaniline (PANI) nanotubes was presented. Experimentally, Mn₂O₃ nanofibers prepared by electrospinning technique were used as the oxidant template to initiate the polymerization of aniline in acid solution. After reaction, polyaniline shells were formed on the Mn₂O₃ nanofiber surface, and the Mn₂O₃ nanofibers were spontaneously removed. As a result, PANI nanotubes were obtained. As-prepared PANI nanotubes show an average diameter of 80 nm and inner diameter of 38 nm. The final PANI nanotubes were characterized by SEM, EDX, TEM, FTIR and XRD. The gas sensing of as-obtained PANI nanotubes was also investigated. It was found that the PANI nanotube sensing device could detect as low as 25 ppb NH₃ in air at room temperature with good reversibility.     

锂离子占位情况对钛酸锂结构及性能的影响

Li₄Ti₅O₁₂在快速充放电条件下具有优异的结构稳定性和高安全性,使其受到新能源汽车和储能领域的青睐。大量的研究人员已经对钛酸锂的锂离子插层过程进行了研究,研究表明放电过程中外界和位于8a位的锂离子全部转移到16c位,钛酸锂的容量受限于参与其中晶格位点和可逆锂离子的数量。然而,钛酸锂晶胞结构表明可容纳锂离子的晶格位点不止于此。锂离子可能取代Ti原子占据八面体16d位点,位于四面体48f位点,重新占据相变后空出的四面体的8a位点。本文主要综述了在Li₄Ti₅O₁₂的制备过程或成品中,通过化学或电化学方法处理后,LTO中锂离子占位情况与传统认知发生的改变及其这种变化带来的影响。同时,本文对这种变化和影响之间的内在机理展开了讨论和分析。     

The TiCl3 catalyst in NaAlH4 for hydrogen storage induces grain refinement and impacts on hydrogen vacancy formation

TiCl₃ acts as an efficient catalyst for NaAlH₄ (sodium alanate), altering its hydrogen sorption kinetics and reversibility considerably. In order to clarify its role, we performed in situ neutron diffraction experiments on protonated catalysed and uncatalysed NaAlH₄. The phase transformations were monitored in the first two reaction steps during hydrogen release and in the second step during reloading. Our study for the first time provides clear indications that both Ti_xAl_1−x and NaCl formed act as grain refiner for Al and NaH, respectively, preventing particle growth. Particle sizes generally stay small upon desorption and reloading of TiCl₃ catalysed NaAlH₄, while significant particle growth is observed for uncatalysed NaAlH₄. The small crystallite sizes and observed hydrogen vacancy formation greatly facilitate the mass transfer during loading and unloading. This study underlines the importance of grain refining for achieving reversibility and faster kinetics of the hydrogen sorption processes, with a crucial double role played by the catalyst.     

Electrochemical synthesis,studies and modification of TiO<Subscript>2</Subscript> nanotubes

TiO₂ nanotubes (TiO₂ NTs) were synthesized using the electrochemical method in a 1 M H₂SO₄ + 0.15% HF electrolyte. The initial nanotubes have a diameter of 100 ± 10 nm (with the length of up to 150–200 nm) and a wall thickness of 20 ± 5 nm. Nanotube treatment at 400°C results in negligible changes in their structure compared to the initial samples. At 600°C, a change occurs in the nanotube structure and morphology, i.e., the amount decreases drastically; the diameter changes; and, as a consequence, the surface area value decreases. Changes in the structure lead to changes in the electrochemical properties, which is apparently related to a transition from the amorphous structure to anatase and rutile. It is shown that a reversible two-electron reaction, including hydrogen intercalation and Ti⁴⁺/Ti³⁺ oxidation/reduction in the potential range of (−0.6−0.4 V), occurs as a result of moderate thermal treatment. The possibility of the use and promising character of TiO₂ NTs as support for a nonplatinum catalyst based on cobalt tetra(p-methoxyphenyl)porphyrin are brought to light. The electrocatalytic activity of the synthesized catalyst per nominal CoTMPP mass in the reaction of O₂ reduction at E = 0.7 V is ≈25 A/g_CoTMPP, which is comparable to nonplatinum systems on a carbon support.     

Hydrothermal conversion of Ti-containing minerals in system of Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–CaO–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na₂O–Al₂O₃–SiO₂–CaO–TiO₂–H₂O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al₄Ti₂SiO₁₂ at low temperatures (60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al₄Ti₂SiO₁₂ decomposes gradually and converts to Ca₃TiSi₂(Al₂Si_0.5Ti_0.5)O₁₄ at 200 °C. When the temperature reaches 260 °C, CaTiO₃ forms as the most stable titanate species for its hexagonal closest packing with O^2? and Ca²⁺. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

多孔钛表面TiO2纳米管的阳极氧化制备及光催化性能（英文）

对多孔钛表面制备TiO2纳米管的阳极氧化工艺进行研究。在两种电解质溶液中采用阳极氧化法分别对多孔钛和钛箔进行表面处理。一种电解质溶液是含有0.5%HF的冰醋酸,另一种电解质溶液是含有0.5%NH4F(质量分数)的乙二醇溶液(醇水体积比4:1)。结果表明:两种方法在钛箔上都可以生成TiO2纳米管,而多孔钛表面只能在NH4F电解质溶液中生成纳米管,HF溶液中过高的电流密度是纳米管在多孔钛基体上难以生成的主要原因。采用扫描电子显微镜和X射线衍射仪对不同基体上的TiO2纳米管进行表征,相比钛箔基体上的纳米管管壁,多孔钛上的纳米管管壁更薄。对所制备的TiO2热处理研究表明,锐钛矿相在400°C时形成,并在700°C完全转变为金红石相。经450°C热处理样品的光催化性能最好。光催化性能也受到多孔钛孔隙率的影响,在孔隙率为60%时光催化性能最好。     

Effects of silver addition on microstructure and electrical properties of barium titanate ceramics

Barium titanate-silver composites were prepared by using a solid state reaction process with silver contents ranging from 0 mol% to 20 mol%. XRD results and Raman spectra indicated that there was no phase other than BaTiO₃ and Ag in the ceramics and tetragonality of barium titanate reduced with increasing Ag content. SEM images illustrated that Ag influenced densification and microstructure of BaTiO₃ ceramics. Besides, addition of Ag led to increase in dielectric permittivity and broadening of ferroelectric-paraelectric phase transition peak. Also addition of Ag had effects on dielectric loss and dc conductivity. Dielectric and conductivity properties as a function of Ag volume fraction were explained by the percolation theory.     

TiO2/膨润土复合光催化材料的常温制备及性能研究

采用改进的溶胶-凝胶法,在以水为主要溶剂的反应体系中,控制钛酸四丁酯充分水解、缓慢聚合,在 常压、低温(70℃)的温和条件下制备出稳定的TiO₂纳米晶溶胶,并利用TiO₂纳米晶溶胶在膨润土表面负载,获得TiO₂/膨润土复合光催化材料。采用 X 射线衍射、扫描电镜、比表面积测定等研究手段对样品的结构形貌进行了表征,并考察了其光催化活性。结果表明：较高的水用量有利于TiO₂晶体形成,当去离子水:钛酸四丁酯摩尔比大于167:1时,在溶胶体系中出现了锐钛矿型TiO₂纳米晶体;TiO₂纳米晶主要负载于膨润土表面,并未嵌入到膨润土层间结构,但相对于单一膨润土,TiO₂负载显著提高了材料比表面积;当去离子水:钛酸四丁酯摩尔比=192:1时,在紫外光照射下,复合光催化材料表现出最高的光催化活性,对亚甲基蓝的降解率达到93.8%。     

Precursor-based synthesis and electrochemical performance of LiMnPO4

Olivine-like LiMnPO₄ was prepared from the NH₄MnPO₄·H₂O precursor precipitated from the aqueous solution. Different morphologies of the LiMnPO₄ were obtained by the solid-state reaction of the precursor with LiOH (granular, 100–300 nm) and by ion-exchange reaction with eutectic mixture LiCl–LiNO₃ (flake-like crystallites up to 10 μm). The morphology and size distribution of the precursor NH₄MnPO₄·H₂O is preserved during ion-exchange, establishing a new preparation route for nanosized LiMnPO₄. After ball-milling with carbon black the granular material delivers 30% of the theoretical capacity at C/5. The rate capabilities of the obtained materials are compared with the results from sol–gel synthesis in the light of particle size effect.     

Preparation of niobium nanoparticles by sodiothermic reduction of Nb2O5 in molten salts

Niobium nanoparticles with high purity were prepared by a sodiothermic reduction process using Nb2O5 as the raw material, LiCl, NaCl, KCl and CaCl2 as the diluents and sodium as the reducing reagent. The effects of the different molten salt systems, CaCl2 content, reaction time, excessive sodium and reaction temperature on the characteristics of the obtained niobium powder were discussed. The as-prepared niobium nanoparticles under the optimum experimental conditions were obtained by sodiothermic reduction ...     

Low-temperature phase transitions of sodium aluminate solutions

A series of low-temperature phase transitions of sodium aluminate solutions were studied by differential scanning calorimetry (DSC) and Raman spectroscopy. The results indicate that NaOH concentration is a primary impact factor for the binary eutectic point and ice melting temperature of sodium aluminate solutions with low NaOH concentration. In addition, the phase transition process of sodium aluminate solutions with low NaOH concentration from 123.15 to 283.15 K is divided into four steps: non-crystal to crystal, ternary eutectic reaction, binary eutectic reaction and ice melt. The projection phase diagram of NaOH-Al(OH)₃-H₂O system at low temperature was plotted, in which the ternary eutectic temperature for sodium aluminate solutions is 183.15 K.     

Rapid anodic oxidation of highly ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays prepared by anodic oxidation have attracted increasing research interests due to their promising applications in many scientific areas. To the best of our knowledge, a factor limiting the application of TiO₂ nanotube arrays was their long sustaining reaction time by anodic oxidation, usually lasting 6-12 h and even longer when synthesizing thicker nanotubular layers. In the present paper, we reported for the first time a facile but effective approach to accelerate the anodic formation of TiO₂ nanotube arrays by proper addition of sodium carbonate (Na₂CO₃) into the anodization electrolyte. We adopted the 0.3 M NH₄F + 0.03 M Na₂CO₃ + EG (ethylene glycol) + 3.0 vol.% H₂O electrolyte and the average growth rate of the nanotubes achieved in our experiments could be accelerated to 1100 nm/min. The possible mechanism of the rapid electrochemical process was also presented.