Controlled synthesis of Ag/TiO2 core-shell nanowires with smooth and bristled surfaces via a one-step solution route

Ag/TiO2 core-shell nanowires were synthesized via a one-step solution method without using a template. Interestingly, the shell morphologies can be controlled to be smooth or bristled by altering the reaction temperature. Moreover, the TiO2 shell thickness and bristle length can be tuned by changing the AgNO3 concentration. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the resultant Ag/TiO2 core-shell nanowires. Moreover, the absorption peaks of our samples are significantly red-shifted compared with those of the uncoated pure silver nanowires, indicating that interaction between the core and shell occurred. On the basis of the experimental results, we proposed a template-induced Oswald ripening mechanism to explain the formation of the Ag/TiO2 core-shell nanowires.     

新颖的TiO2@C核壳结构纳米纤维阵列电极制备及其在电化学传感器中的应用

本文提出以金属钛为基底, 在丙酮蒸气和无催化剂条件下, 通过高温反应, 直接在金属钛片上一步合成出具有核壳结构的TiO2@C纳米纤维阵列. 由于TiO2@C纳米纤维阵列在金属钛片上分布均一, 与金属钛基底有良好的结合力和电接触性能, 可直接作为电化学传感器电极. 进一步的电化学检测表明, 该电极对铁氰化钾及多巴胺等物质有良好的电化学响应, 对多巴胺检测灵敏度高, 响应的线性范围为1.0×10-7~1.0×10-4 mol/L, 检测限达2.45×10-8 mol/L. 该电极有望在生物传感、环境分析及药物分析等领域发挥重要作用.     

不同形貌WO3的水热合成及其在水处理中的应用研究

三氧化钨(WO₃)以其较窄的带隙,成为继二氧化钛(TiO₂)之后颇具发展潜力的n型半导体光催化剂.本文采用水热合成法,通过调控反应参数,如原料组成、沉淀时间等,合成了不同形貌和晶型的WO₃;采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FT-IR)、氮气吸附-脱附(N₂ adsorption-desorption)等表征了所合成的WO₃产品,发现原料组成、沉淀时间等条件对WO₃的晶型和形貌都有影响;研究了所合成的WO₃产品去除水中亚甲基蓝染料污染物的性能,结果表明,所制备的WO₃对水中亚甲基蓝具有较好的去除效果,去除率可达97%.     

Hybrid Nanomaterial Architectures: Combining Layers of Carbon Nanowalls,Nanotubes, and Particles

The paper focuses on the integration in hybrid architectures of plasma produced nanomaterials. The routes for the fabrication of layered structures consisting of carbon nanowalls on carbon nanotubes (CNW/CNT), of carbon nanotubes on carbon nanowalls (CNT/CNW), and nanoparticles on carbon nanowalls (NP/CNW) are presented. The morphology and structure of the hybrid architectures were investigated by electron microscopy techniques. We show that higher substrate temperature promotes the formation of high mass hydrogenated carbon clusters which favors the dominance of CNW growth over that of CNT. On this basis, a procedure of obtaining CNT/CNW architectures by switching the growth regime via substrate temperature is described. The specific limitations or advantages concerning the control or the properties of the obtained architectures are discussed.     

Unconventional zigzag indium phosphide single-crystalline and twinned nanowires

Unconventional zigzag indium phosphide (InP) single-crystalline and twinned nanowires were produced via thermal evaporation of indium phosphide in the presence of zinc selenide. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that two type of nanowires exist in the products, namely, the periodic-rhombus-decorated single-crystalline InP (type I) nanowires and jagged twinned InP (type II) nanowires. Both of them have preferential 111 growth directions. The optical properties were also investigated at room temperature, and they show that the nanowires display a strong emission at approximately 750 nm, which is quite different from that observed in all previous reports related to the InP nanostructures.     

Synthesis of copper-core/carbon-sheath nanocables by a surfactant-assisted hydrothermal reduction/carbonization process

A simple hydrothermal method has been developed for the one-step synthesis of copper-core/carbon-sheath nanocables in solution. The obtained nanostructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM), Raman, and UV-vis spectrum analysis. These copper@carbon nanocables formed through the hydrothermal reduction/carbonization in the presence of surfactant cetyltrimethylammonium bromide (CTAB) acting as the structure-directing agent by hydrothermal treatment. HRTEM and selected-area electron diffraction (SAED) indicate that the resulted Cu nanowires had the preferred [110] growth direction. The influence of the reaction temperature, reaction time, and pH on the final products was investigated in detail. The possible formation mechanism for copper-core/carbon-sheath nanocables was also proposed. Amorphous carbon nanotubes can be obtained by etching the copper core in the nanocables.     

微波热解法制备Cu/Cu2O纳米材料

在二乙二醇溶剂体系中利用微波介电加热分解醋酸铜前体,进一步还原得到Cu2O和Cu纳米粒子以及Cu/Cu2O核壳结构。 采用X射线衍射、透射电子显微镜、扫描电子显微镜和紫外吸收光谱测试技术对产物的形貌、结构和组成进行了研究,结果表明,得到的Cu/Cu2O核壳结构直径为500 nm左右。 对比实验研究了不同聚合度乙二醇系列溶剂、反应时间以及表面活性剂或配位剂对产物形貌、组成的影响,表明低聚合度乙二醇和长的反应时间有利于醋酸铜还原形成铜。     

Depositional characteristics of metal coating on single-crystal TiO2 nanowires

Ultralong single-crystalline TiO(2) nanowires were prepared by a simple, low-cost solvothermal process. Silver nitrate, neodymium chloride, ceric nitrate, stannic chloride hydrate, and cadmium chloride were used as metal sources and deposited by reduction on the surface of TiO(2) nanowires. The composites were subsequently characterized by transmission electron microscopy, and their coverage was compared. The nature of the coatings on the TiO(2) nanowires varies from metal to metal. A novel approach on modified one-dimensional nanostructures with metal coating was developed, which has great potential applications in catalysts, sensors, and nanoscale devices.     

核壳结构AlOOH的制备、表征及其生长机制

在柠檬酸钠和硝酸铝水溶液体系中, 通过一步水热法制备了蜷缩刺猬状和核壳结构的AlOOH微球, 并用X射线衍射(XRD)、Fourier变换红外(FTIR)光谱、扫描电镜(SEM)、透射电镜(TEM)、氮气吸脱附和光致发光等分析手段对制备的样品进行了形貌和结构表征. 对反应时间、反应物浓度等影响因素进行了研究. 实验结果表明: 反应时间和反应物柠檬酸钠的浓度对所得AlOOH微球结构的尺寸和形貌具有重要影响; 蜷缩刺猬状和核壳结构AlOOH微球都具有较大的比表面积, 分别为171.5和178.6 m2·g-1; 不同形貌的AlOOH具有不同的荧光发射峰. 并初步探讨了核壳结构AlOOH微球的生长机制.     

Vapor-liquid-solid and vapor-solid growth of phase-change Sb2Te3 nanowires and Sb2Te3/GeTe nanowire heterostructures

We report the synthesis and characterization of radial heterostructures composed of an antimony telluride (Sb2Te3) core and a germanium telluride (GeTe) shell, as well as an improved synthesis of Sb2Te3 nanowires. The synthesis of the heterostructures employs Au-catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms. Energy-dispersive X-ray spectrometry indicates that Sb and Ge are localized in the Sb2Te3 and GeTe portions, respectively, confirming the alloy-free composition in the core/shell heterostructures. Transmission electron microscopy and diffraction studies show that Sb2Te3 and GeTe regions exhibit rhombohedral crystal structure. Both Sb2Te3 and GeTe grow along the [110] direction with an epitaxial interface between them. Electrical characterization of individual nanowires and nanowire heterostructures demonstrates that these nanostructures exhibit memory-switching behavior.     

Photoelectrochemical study on charge transfer properties of TiO2-B nanowires with an application as humidity sensors

One-dimensional (1-D) TiO2-B nanowires have been synthesized via a facile solvothermal route. The morphology and crystalline structures of the nanowires were characterized by using powder X-ray diffraction, low/high-resolution transmission electron microscopy, and Brunauer-Emmett-Teller methods. It is important with the calcination treatment at 350 degrees C to maintain 1-D morphologies of the material in the form of single-crystalline TiO2-B nanowires. In addition, a simple method was used to study the photogenerated charge transfer and photoelectrochemical properties of the TiO2-B nanowires in comparison with commercial TiO2 P25 nanoparticles based on the experimental data from the electric field-effected photocurrent action spectrum and Mott-Schottky measurements. It was revealed that TiO2-B nanostructures played an important role in the photoelectrochemical processes. The synthetic TiO2-B nanowire electrode exhibited unique electronic properties, e.g., favorable charge-transfer ability, negative-shifted appearing flat-band potential, existence of abundant surface states or oxygen vacancies, and high-level dopant density. Moreover, the obtained TiO2-B nanowires were found to display excellent humidity sensing abilities as functional materials in the humidity sensor application. With relative humidity increased from 5% to 95%, about one and half orders of magnitude change in resistance was observed in the TiO2-B nanowire-based surface-type humidity sensors.     

MFI/MFI核壳分子筛的合成及催化性能研究

通过对核相ZSM-5的预处理步骤和在温和水热条件下的二次生长, 合成了壳层硅铝比高、核相硅铝比低、纳米晶壳层致密的MFI(核)/MFI(壳)型核壳分子筛材料. 考察了晶化温度和晶化时间对高硅壳层MFI/MFI核壳型沸石分子筛的合成的影响, 其适宜的合成条件为晶化温度高于130 ℃, 晶化时间19 h. 核相ZSM-5的预处理步骤对于成功合成此特殊核壳型分子筛材料十分关键. 与普通ZSM-5沸石分子筛相比, MFI/MFI核壳分子筛在催化甲苯甲基化反应时的失活效率显著降低.     

Rational design of 3D dendritic TiO2 nanostructures with favorable architectures

Controlling the morphology and size of titanium dioxide (TiO(2)) nanostructures is crucial to obtain superior photocatalytic, photovoltaic, and electrochemical properties. However, the synthetic techniques for preparing such structures, especially those with complex configurations, still remain a challenge because of the rapid hydrolysis of Ti-containing polymer precursors in aqueous solution. Herein, we report a completely novel approach-three-dimensional (3D) TiO(2) nanostructures with favorable dendritic architectures-through a simple hydrothermal synthesis. The size of the 3D TiO(2) dendrites and the morphology of the constituent nano-units, in the form of nanorods, nanoribbons, and nanowires, are controlled by adjusting the precursor hydrolysis rate and the surfactant aggregation. These novel configurations of TiO(2) nanostructures possess higher surface area and superior electrochemical properties compared to nanoparticles with smooth surfaces. Our findings provide an effective solution for the synthesis of complex TiO(2) nano-architectures, which can pave the way to further improve the energy storage and energy conversion efficiency of TiO(2)-based devices.     

空心玻璃微珠/TiO2复合微球的制备及其性能研究

本文以脲为沉淀剂,通过化学沉淀法成功实现了锐钛矿型二氧化钛壳层在空心玻璃微珠表面的可控组装,从而制备出玻璃/二氧化钛核壳空心微球,并通过XRD、SEM、EDX和拉曼光谱对其结构、形貌、粒径、壳厚和化学组成进行了表征.提出了二氧化钛在空心玻璃微珠表面的定向生长的可能机制和形成过程.     

Biomolecule-assisted route to prepare titania mesoporous hollow structures

Amino acids, as a particularly important type of biomolecules, have been used as multifunctional templates to intelligently construct mesoporous TiO(2) hollow structures through a simple solvothermal reaction. The structure-directing behaviors of various amino acids were systematically investigated, and it was found that these biomolecules possess the general capability to assist mesoporous TiO(2) hollow-sphere formation. At the same time, the nanostructures of the obtained TiO(2) are highly dependent on the isoelectric points (pI) of amino acids. Their molecular-structure variations can lead to pI differences and significantly influence the final TiO(2) morphologies. Higher-pI amino acids (e.g., L-lysine and L-arginine) have better structure-directing abilities to generate nanosheet-assembled hollow spheres and yolk/shell structures. The specific morphologies and mesopore size of these novel hollow structures can also be tuned by adjusting the titanium precursor concentration. Heat treatment in air and vacuum was further conducted to transform the as-prepared structures to porous nanoparticle-assembled hollow TiO(2) and TiO(2)/carbon nanocomposites, which may be potentially applied in the fields of photocatalysts, dye-sensitized solar cells, and Li batteries. This study provides some enlightenment on the design of novel templates by taking advantage of biomolecules.     

Fabrication of hydroxyl group modified monodispersed hybrid silica particles and the h-SiO(2)/TiO(2) core/shell microspheres as high performance photocatalyst for dye degradation

The monodisperse hybrid silica particles (h-SiO(2)) were firstly prepared by a modified sol-gel process and the surface was modified in situ with double bonds, then abundant carboxyl moieties were introduced onto the surface of the silica core via thiol-ene click reaction. Afterward, the h-SiO(2)/TiO(2) core/shell microspheres were prepared by hydrolysis of titanium tetrabutoxide (TBOT) via sol-gel process in mixed ethanol/acetonitrile solvent, in which the activity of TBOT could be easily controlled. The carboxyl groups on the surface of silica particles promote the formation of a dense and smooth titania layer under well control, and the layer thickness of titania could be tuned from 12 to 100nm. The well-defined h-SiO(2)/TiO(2) core/shell structures have been confirmed by electron microscopy and X-ray photoelectron spectroscopy studies. After calcination at 500°C for 2h, the amorphous TiO(2) layer turned into anatase titania. These anatase titania-coated silica particles showed good photocatalytic performance in degradation of methyl orange aqueous solution under UV light.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

High sintering resistance of platinum nanoparticles embedded in a microporous hollow carbon shell fabricated through a photocatalytic reaction

Platinum (Pt) nanoparticles encapsulated in microporous carbon with a hollow structure (nPt@hC) were fabricated on the basis of a titanium(IV) oxide (TiO2) photocatalytic reaction. From the tomogram of a sample studied by using a transmission electron microscope (TEM), the Pt nanoparticles were found to be embedded in the carbon shell and were physically separated from each other by the carbon matrix. Owing to this unique structure, the Pt particles showed high resistance to sintering when subjected to thermal treatment at temperatures up to 800 degrees C. As a result, hydrogenation reactions using various heat-treated nPt@hCs as catalysts indicated that loss of catalytic activity was minimized. Thus, the present system will be a promising system for optimizing catalyst nanostructures utilized in processes requiring rigorous conditions.     

Hierarchical saw-like ZnO nanobelt/ZnS nanowire heterostructures induced by polar surfaces

Saw-like nanostructures composed of single-crystalline ZnO nanobelts and single-crystalline ZnS nanowires have been successfully synthesized by a vapor-solid process. Several techniques, including scanning electron microscope, transmission electron microscopy, and photoluminescence spectroscopy, were used to investigate the structures, morphology, and photoluminescence properties of the products. Due to the similar crystal habits of wurtzite ZnO and ZnS with chemically active Zn-terminated (0001) and chemically inactive O-terminated (or S-terminated) (000) polar surfaces, hierarchical saw-like nanostructures were considered to be formed by the initiation of a chemically active Zn-terminated ZnO (0001) polar surface. Photoluminescence properties of the heterostructures, different from pure ZnO nanobelts or ZnS nanowires, were also studied at room temperature.     

Direct synthesis of nanowires with anatase and TiO2-B structures at near ambient conditions

In this study, we present a new approach toward titanium oxide nanowires. In this approach, the growth formation of the wires sets in at a temperature as low as 40 degrees C under ambient pressure. Moreover, we provide evidence that nanowires with distinctive TiO2-anatase and TiO2-B structures can be directly produced without further thermal treatment using controlled reaction conditions.