Size- and shape-dependent transformation of nanosized titanate into analogous anatase titania nanostructures

A size- and shape-dependent morphological transformation was demonstrated during the hydrothermal soft chemical transformation, in neutral solution, of titanate nanostructures into their anatase titania counterparts. Specifically, lepidocrocite hydrogen titanate nanotubes with diameters of approximately 10 nm were transformed into anatase nanoparticles with an average size of 12 nm. Lepidocrocite hydrogen titanate nanowires with relatively small diameters (average diameter range of < or = 200 nm) were converted into single-crystalline anatase nanowires with relatively smooth surfaces. Larger diameter (>200 nm) titanate wires were transformed into analogous anatase submicron wire motifs, resembling clusters of adjoining anatase nanocrystals with perfectly parallel, oriented fringes. Our results indicate that as-synthesized TiO2 nanostructures possessed higher photocatalytic activity than the commercial titania precursors from whence they were derived.     

Ultralong cadmium hydroxide nanowires: synthesis, characterization, and transformation into CdO nanostrands

Ultralong Cd(OH)2 nanowires were fabricated by a hydrothermal method from Cd(CH3COO)2 x H2O (0.01 mol/L) and C6H12N4 (0.015 mol/L) aqueous solution at 95 degrees C for 16 h without using any templates and were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). The length of the nanowires reached several micrometers, giving an aspect ratio of a few thousands. The formation mechanism of the nanowires is attributed to the oriented attachment of small particles. The growth method for the 1D nanostructure presented here offers an excellent tool for the design of other advanced materials with anisotropic properties. The Cd(OH)2 nanowires efficiently captured negatively charged dye, and the adsorbed dye molecules can be released after the addition of EDTA. The Cd(OH)2 nanowires as template compounds were further transformed into CdO semiconductor nanomaterials with similar morphology by calcination under 350 degrees C in air for 3 h.     

水热合成α-Ni（OH）2纳米线的形成机理研究

设计实验研究了以无机镍盐和NaOH为原料,利用水热法制备Ni(OH)2纳米线,OH-和SO24-对于产物形貌的影响,并利用X射线衍射(XRD),傅立叶变换红外光谱(FTIR),透射电镜(TEM)等对材料结构、形貌和成分进行了表征,研究了Ni(OH)2纳米线形成的相关机理.结果表明,低的OH-浓度与高纯的SO24-水热环境是α-Ni(OH)2纳米线形成的关键因素.SO24-能够加速α-Ni(OH)2晶体沿[001]方向的生长,而OH-含量较低时,较低的库伦斥力不足以阻碍晶体沿[001]方向生长过程的进行.     

Large aspect ratio titanate nanowire prepared by monodispersed titania submicron sphere via simple wet-chemical reactions

A facile one-step hydrothermal reaction among monodispersed titania submicron spheres and KOH solution was found to result in potassium titanate nanowires with a large aspect ratio. The diameter of these nanowires falls in the range of 50-200 nm and the length ranges from several micrometers to several tens of micrometers. It is found that the reaction temperature, duration, titanium source and the size distribution of titania raw powders have a great impact on the resultant morphology. Monodispersed TiO₂ submicron sphere is beneficail for the formation and growth of large-area lamellar potassium titanate and consequently it is in favor of the production of nanowires with a large aspect ratio. The nanowires were analyzed by a range of methods including powder X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectrometer (EDX) and UV/Vis spectrophotometer. UV-absorption study showed that these nanowires are wide-band semiconductors with a band gap 3.4 eV. A formation mechanism is proposed on the basis of the dissolving, growth, thickening and splitting of K₂Ti₆O₁₃ nanointermediates.     

氢氧化镍纳米线/三维石墨烯复合材料的制备及其电化学性能

采用水热法制备了氢氧化镍纳米线/三维石墨烯复合材料及作为比较的三维石墨烯、氢氧化镍纳米线、还原氧化石墨烯和氢氧化镍纳米线/还原氧化石墨烯, 通过X射线衍射、扫描电镜、热失重分析和氮气吸脱附表征了材料的形貌、结构和组成, 并采用循环伏安法和恒电流充放电测试了复合材料的电化学性能. 结果表明: 氢氧化镍纳米线/三维石墨烯复合材料中直径为20-30 nm的氢氧化镍纳米线和三维结构的石墨烯紧密结合, 相互交联形成网状结构, 其比表面积达到136 m²·g^-1, 孔径分布20-50 nm, 氢氧化镍纳米线的含量达到88% (w,质量分数). 在6 mol·L^-1的KOH电解液中, 复合材料的比电容在1 A·g^-1电流密度下达到1664 F·g^-1, 在1 A·g^-1电流密度下循环3000 次后的比电容保持率为93%. 将复合材料的比电容和循环性能与氢氧化镍纳米线、氢氧化镍纳米线/还原氧化石墨烯、三维石墨烯和还原氧化石墨烯的性能进行比较, 发现三维石墨烯较还原氧化石墨烯具有更高的比表面积和三维多孔结构, 可以更大地提高活性物质的利用率, 进而提高复合材料的比电容和稳定性.     

钛酸盐纳米管与二硫化碳修饰钛酸盐纳米管的合成、表征及其去除重金属离子性能

在水热法制备钛酸盐纳米管的基础上, 通过形成黄原酸基反应合成了CS2修饰的钛氧纳米管. 采用粉末X射线衍射(XRD)、透射电镜(TEM)、红外光谱(FTIR)和拉曼光谱(Raman)等技术对产物进行了表征. 以水溶液中铅离子、铜离子和银离子作为目标重金属离子, 分别用纯钛酸盐纳米管和CS2修饰后的钛氧纳米管对其进行反应和吸附, 通过一系列对比性实验, 评价了不同形式纳米管去除重金属的能力. 实验结果表明, 与文献报道的吸附剂对重金属离子的吸附量相比, 纯钛酸盐纳米管和CS2修饰的钛氧纳米管吸附重金属离子的容量非常大, 尤其是经CS2修饰后的钛氧纳米管去除铅离子的能力明显增强, 它们去除重金属离子的能力还与重金属盐的阴离子、溶液的pH值相关. 在相同的pH条件下, 钛酸盐纳米管去除铅离子、铜离子和银离子的能力分别为599.37, 163.22和474.73 mg/g; CS2修饰的钛氧纳米管去除铅离子、铜离子和银离子的能力分别为663.37, 160.21和423.05 mg/g.     

The adsorption and reaction of a titanate coupling reagent on the surfaces of different nanoparticles in supercritical CO2

The adsorption and reaction in supercritical CO2 of the titanate coupling reagent NDZ-201 on the surfaces of seven metal oxide particles, SiO2, Al2O3, ZrO2, TiO2 (anatase), TiO2 (rutile), Fe2O3, and Fe3O4, was investigated. FTIR and TG analysis indicated that the adsorption and reaction were different on different particle surfaces. On SiO2 and Al2O3 particles, there was a chemical reaction of the titanate coupling reagent on the surfaces. On the surfaces of ZrO2 and TiO2 (anatase) particles, there were two kinds of adsorption, weak and strong adsorption. On the surfaces of TiO2 (rutile), Fe2O3, and Fe3O4 particles, there was only weak adsorption. The acidity or basicity of the OH groups on the particle surface was the key factor that determined if a surface reaction occurred. When the OH groups were acidic, the titanate coupling reagent reacted with these, but otherwise, there was no reaction. The surface density of OH groups on the original particles and the amount of titanate coupling reagent adsorbed and reacted were estimated from TG analysis. The reactivity of the surface OH groups of Al2O3 particles was higher than that of the SiO2 particles.     

Comparable Studies of Adsorption and Magnetic Properties of Ferrite MnFe_2O_4 Nanoparticles,Porous Bulks and Nanowires

The spinel ferrites MnFe2O4 nanowires were synthesized by hydrothermal route,porous MnFe2O4 and nanoparticles morphologies were synthesized by sol-gel method with egg white.The structures,morphologies,magnetic properties and adsorption properties of these obtained ferrites with different morphologies were studied contrastively.Results show that the obtained samples exhibit ferromagnetic properties.This realizes convenient magnetic separation from solution when they are used in the treatment of organic dyes ...     

一步法水热合成 TiO2纳米线及其光催化性能

以钛酸丁酯和异丙醇为原料, 采用一步法在NaOH溶液中水解后直接进行水热反应, 经焙烧处理, 得到TiO2纳米线. 采用扫描电子显微镜(SEM)、X射线衍射(XRD)和能谱分析(EDX)对产物进行了形貌、结构及成分的表征. 考察了不同水热温度、碱液浓度、水热反应时间及焙烧温度等因素对产物的影响. 结果表明, 获得较好形貌TiO2纳米线的最佳水热温度、碱液浓度和水热反应时间分别是180 ℃, 10 mol/L和24 h. 所得TiO2纳米线焙烧至950 ℃时仍为锐钛矿相, 说明本文制备方法迟滞了TiO2纳米线由锐钛矿相向金红石相的转变. 以甲基橙为目标降解物, 采用紫外-可见分光光度计研究了未掺杂和铕掺杂TiO2纳米线(Eu-TiO2)的光催化性能. 结果显示, 最佳掺铕量(摩尔分数)为1.6%. 在300 W紫外灯照射60 min时, 此掺铕量的TiO2纳米线对甲基橙溶液的降解率是未掺杂样品的1.5倍.     

Synthesis and growth mechanism of titanate and titania one-dimensional nanostructures self-assembled into hollow micrometer-scale spherical aggregates

Three-dimensional, dendritic micrometer-scale spheres of alkali metal hydrogen titanate 1D nanostructures (i.e., nanowires and nanotubes) have been generated using a modified hydrothermal technique in the presence of hydrogen peroxide and an alkali metal hydroxide solution. Sea-urchin-like assemblies of these 1D nanostructures have been transformed into their hydrogen titanate analogues (lepidocrocite HxTi2-x/4squarex/4O4 (x approximately 0.7, square: vacancy)) by neutralization as well as into their corresponding anatase TiO2 nanostructured counterparts through a moderate high-temperature annealing dehydration process without destroying the 3D hierarchical structural motif. The as-prepared hollow spheres of titanate and titania 1D nanostructures have overall diameters, ranging from 0.8 to 1.2 microm, while the interior of these aggregates are vacuous with a diameter range of 100 to 200 nm. The constituent, component titanate and TiO2 1D nanostructures have a diameter range of 7+/-2 nm and lengths of up to several hundred nanometers. A proposed two-stage growth mechanism of these hollow micrometer-scale spheres was supported by time-dependent scanning electron microscopy, atomic force microscopy, and inductively coupled plasma atomic emission spectrometry data. We have also demonstrated that these assemblies are active photocatalysts for the degradation of synthetic Procion Red dye under UV light illumination.     

Syntheses of TiO2(B) nanowires and TiO2 anatase nanowires by hydrothermal and post-heat treatments

TiO₂(B) nanowires and TiO₂ anatase nanowires were synthesized by the hydrothermal processing in 10 M NaOH aq. at 150 °C followed by the post-heat treatment at 300-800 °C. As-synthesized Na-free titanate nanowires (prepared by the hydrothermal treatment and repeated ion exchanging by HCl (aq.) were transformed into TiO₂(B) structure with maintaining 1-D morphology at 300-500 °C, and further transformed into anatase structure at 600-800 °C with keeping 1-D shape. At 900 °C, they transformed into rod-shaped rutile grains. Microstructure of these 1-D TiO₂ nanomaterials is reported.     

Single nanocrystals of anatase-type TiO2 prepared from layered titanate nanosheets: formation mechanism and characterization of surface properties

Anatase-type TiO2 single nanocrystals with boatlike, comblike, sheetlike, leaflike, quadrate, rhombic, and wirelike particle morphologies were prepared by hydrothermal treatment of a layered titanate nanosheet colloidal solution. The formation reactions and surface properties of the TiO2 nanocrystals were investigated using XRD, TEM, TG-DTA analyses, and measurements of BET specific surface area, photocatalytic activity, and ruthenium dye (N719) adsorption. The crystal morphology can be controlled by reaction temperature, pH value of reaction solution, and exfoliating agent. The titanate nanosheets were transformed to the TiO2 nanocrystals by two types of reactions. One is an in situ topotactic structural transformation reaction, and the other is a dissolution-deposition reaction on the surface. The anatase nanocrystals formed by the in situ topotactic structural transformation reaction retain the sheetlike particle morphology of the precursor, and they preferentially expose the (010) plane of anatase structure. The crystal surface of anatase nanocrystals prepared in this study showed higher photocatalytic activity and higher ruthenium dye adsorption capacity than did the Ishihara ST-01 sample, a standard anatase nanocrystal sample. The results indicated the (010) plane of the anatase structure has high photocatalytic activity and high ruthenium dye adsorption ability.     

Formation of titanate nanostructures under different NaOH concentration and their application in wastewater treatment

The effects of the concentration of NaOH on the formation and transformation of various titanate nanostructures were studied. With increasing NaOH concentration, three different formation mechanisms were proposed. Nanotubes can only be obtained under moderate NaOH conditions, and should transform into nanowires with prolonged hydrothermal treatment, and their formation rate is accelerated by increasing NaOH concentration. Low concentration of NaOH results in the direct formation of nanowires, while extra high concentration of NaOH leads to the formation of amorphous nanoparticles. Adsorption and photocatalysis studies show that titanate nanowires and nanotubes might be potential adsorbents for the removal of both heavy metal ions and dyes and photocatalysts for the removal of dyes from wastewater.     

Heterogeneous photocatalysis of methylene blue over titanate nanotubes: effect of adsorption

Titanate nanotubes were synthesized with hydrothermal reaction using TiO(2) and NaOH as the precursors and subsequent calcination at 400°C for 2h. The products were characterized with SEM and XRD. Adsorption and photocatalysis of methylene blue over titanate nanotubes and TiO(2) were investigated. The results indicated that titanate nanotubes exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system than that in equilibrium adsorption followed by a photodegradation system, whereas TiO(2) showed no significant differences in photocatalytic activity in the two systems. The methylene blue overall removal efficiency over TNTs in the first system even exceeded that over TiO(2). The different catalytic performances of titanate nanotubes in the two systems were tentatively attributed to different effects of adsorption of methylene blue, i.e., the promoting effect in the former and the inhibition effect in the latter. Decantation experiments showed that the titanate nanotube photocatalyst could be easily separated from the reaction medium by sedimentation. Thus titanate nanotubes with high sedimentation rates and concurrent adsorption represent a new catalyst system with a strong potential for commercial applications.     

A multistep attachment process: Transformation of titanate nanotubes into nanoribbons

The mechanism of the conversion of titanate nanotubes into nanoribbons is of considerable interest.The details of the transformation processes involved when nanoribbons are produced from a P25 TiO 2 powder precursor by alkaline hydrothermal treatment have been investigated systematically by transmission electron microscopy.A multistep attachment model is proposed for the growth at the early stage of coarsening.The treatment duration has a strong effect on the change in product morphology from hollow nanotubes into nanoribbons,since the nanotubes cannot retain their morphology in the strong alkaline solution for extended periods of time.Most of the nanotubes were etched and dissolved,providing the nutrients for subsequent nanoribbon growth.Some stable nanotubes grew spirally internally to form nanowires or became connected together to form rafts which acted as the grains for nanoribbon growth.With increasing hydrothermal time,a large number of nanotubes and other fragments became attached to the grains which began to grow larger and eventually formed the nanoribbons,in a process in which the stepped faces and kinked faces became fused and were eliminated while the flat faces were retained in the nanoribbon morphology.     

Bi3.25La0.75Ti3O12纳米线的可见光催化性能

研究了用一步水热法制备的掺镧钛酸铋(Bi_3.25La_0.75Ti₃O₁₂, BLT)纳米线的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. 结果表明, 制备的纳米线为纯相的Bi_3.25La_0.75Ti₃O₁₂, 平均直径约为25 nm. 室温光致发光谱(PL)显示BLT纳米线在433和565 nm附近有较强的发射峰, 分别对应激子发射和表面缺陷发光. 紫外-可见漫反射光谱(UV-Vis DRS)表明BLT样品的带隙能约为2.07 eV. 利用可见光(λ>420 nm)照射下的甲基橙降解实验评价了BLT样品的光催化性能. 结果表明, BLT的光催化活性比商用TiO₂催化剂P25、掺氮TiO₂和纯相钛酸铋(Bi₄Ti₃O₁₂, BIT)高得多. BLT光催化剂具有更高催化活性的原因是La³⁺离子掺杂拓展了BIT对可见光的吸收范围, 同时抑制了BIT的光生电子-空穴的复合.     

Photocathodic protection properties of three-dimensional titanate nanowire network films prepared by a combined sol–gel and hydrothermal method

A combined sol–gel and hydrothermal method was developed for preparing a three-dimensional titanate nanowire network film on titanium substrates to achieve an especial photocathodic protection effect for 403 stainless steel. Photopotential measurements were performed to study the protection effect of the film. The results indicated that the titanate film exhibited a special all-dimensional uniform porous structure composed of branched titanate nanowires. When we coupled the steel in a 0.5 M NaCl solution to the titanate film photoanode in a 1.0 M NaOH solution under illumination, its potential decreased by 560 mV. Especially after the light source was cut off, the photopotential of the steel increased by only 50–145 mV, and kept at the lower values than the corrosion potential under dark conditions for over 10 h, indicating that the titanate nanowire network film could produce a striking photocathodic protection effect for 403 stainless steel under illumination and dark conditions.     

Effects of pore structure and surface chemical characteristics on the adsorption of organic vapors on titanate nanotubes

Effects of pore structure and surface chemical characteristics of titanate nanotubes (TNTs) on their adsorptive removal of organic vapors were investigated. TNTs were prepared via a hydrothermal treatment of TiO₂ powders in a 10 M NaOH solution at 150?°C for 24?h, and subsequently washed with HCl aqueous solution of different concentrations. Effects of acid washing process (or the sodium content) on the microstructures and surface chemical characteristics of TNTs were characterized with nitrogen adsorption-desorption isotherms, FTIR, and water vapor adsorption isotherms. For the adsorption experiments, gravimetric techniques were employed to determine the adsorption capacities of TNTs for four organic vapors with similar heats of vaporization (i.e., comparable heats of adsorption) but varying dipole moments and structures, including n-hexane, cyclohexane, toluene, and methyl ethyl ketone (MEK), at isothermal conditions of 20 and 25?°C. The experimental data were correlated by well-known vapor phase models including BET and GAB models. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms of organic vapors on TNTs were type II, characterizing vapor condensation to form multilayers. The specific surface area (and pore volume) and hydrophilicity of TNTs were the dominating factors for the determination of their organic vapors adsorption capacity. The GAB isotherm equation fitted the experimental data more closely than the BET equation. The heats of adsorption showed that the adsorption of organic vapors on TNTs was primarily due to physical forces and adsorbates with larger polarity might induce a stronger interaction with TNTs.     

Preparation of hollow titania and strontium titanate spheres using sol–gel derived silica gel particles as templates

A facile approach, based on polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloidal templates and hydrothermal treatment, is presented for the formation of hollow titania (TiO₂) and strontium titanate (SrTiO₃) spheres. Monodispersed silica gel particles were prepared by the sol?Cgel method and adopted as core templates. Deposition of a water-soluble titanium complex, titanium (IV) bis(ammoniumlactato)dihydroxide (TALH), on the silica gel particles was carried out via the layer-by-layer assembly technique. Hollow spheres were successfully formed from the core?Cshell particles. The silica gel particles used as core templates dissolved during hydrothermal treatment because of the particles?? undeveloped siloxane network. In addition, the hydrothermal treatment induced crystallization of the hollow shells. Therefore, the hydrothermal treatment played two roles; removal of the silica templates and crystallization of the hollow shells. When deionized water was used, hollow TiO₂ spheres were obtained. Hollow SrTiO₃ spheres could also be formed when an aqueous solution of Sr(OH)₂ was used. The approach presented here could be exploited as a novel and sustainable approach for the fabrication of a range of different inorganic hollow spheres.     

Plate, wire, mesh, microsphere, and microtube composed of sodium titanate nanotubes on a titanium metal template

Sodium titanate nanotube/titanium metal composites were synthesized by hydrothermal treatment of titanium metals with various morphologies such as plate, wire, mesh, microsphere, and microtube at 160 degrees C in aqueous NaOH solution and by the subsequent fixation treatment by calcination at 300 degrees C. The surface of the composite was covered with sodium titanate nanotubes with a diameter of approximately 7 nm, and the core part of the composite was titanium metal phase. The raw titanium metal acts as a template or a morphology-directing agent of micrometer size or more to arrange the nanotubes as well as a titanium source for the formation of nanotubes. The concentration of titanium species increases in the reaction solution as the dissolution of titanium metal is accelerated by the reaction between titanium and OH-. Furthermore, with an increase in concentration of titanium species in the reaction solution, the titanium species are re-precipitated as sodium titanate nanotubes onto the titanium metal. Titanium metal with a large surface area and volume can form sodium titanate nanotubes on the surface of the titanium metal, though titanium metal with a small volume and surface area tends to dissolve with the hydrothermal treatment. Even in the synthesis using titanium metal with a small volume and surface area, sodium titanate nanotubes are formed and cover the surface of the titanium metal by adding another titanium metal as a source of titanium species in the reaction solution.