Nanostructure Synthesis at the Solid–Water Interface: Spontaneous Assembly and Chemical Transformations of Tellurium Nanorods

Bottom‐up synthesis offers novel routes to obtain nanostructures for nanotechnology applications. Most self‐assembly processes are carried out in three dimensions (i.e. solutions); however, the large majority of nanostructure‐based devices function in two dimensions (i.e. on surfaces). Accordingly, an essential and often cumbersome step in bottom‐up applications involves harvesting and transferring the synthesized nanostructures from the solution onto target surfaces. We demonstrate a simple strategy for the synthesis and chemical transformation of tellurium nanorods, which is carried out directly at the solid–solution interface. The technique involves binding the nanorod precursors onto amine‐functionalized surfaces, followed by in situ crystallization/oxidation. We show that the surface‐anchored tellurium nanorods can be further transformed in situ into Ag₂Te, Cu₂Te, and SERS‐active Au–Te nanorods. This new approach offers a way to construct functional nanostructures directly on surfaces.     

Synthesis of high aspect ratio quantum-size CdS nanorods and their surface-dependent photoluminescence

Colloidal CdS nanorods with diameters near 4 nm and narrow size distributions ( approximately +/-10%) were synthesized up to 300 nm long by a sequential reactant injection technique that utilizes phosophonic acids as capping ligands. The phosphonic acid strongly passivates the nonpolar CdS surfaces and sequential reactant injection provides controlled CdS formation kinetics to enable heterogeneous and facet-selective CdS deposition on the more reactive {002} surfaces. With this process, the nanorod length can be systematically increased by increasing reactant addition to extend nanorod growth. The phosphonic acid concentration, however, is quite important, as "low" concentrations allow radial deposition and branching to occur. These high aspect ratio (>100) CdS nanorods luminesce with relatively high efficiencies of 10.8% quantum yield at room temperature. The luminescence, however, mostly arises from trap-related recombination, and the emission is significantly red-shifted from the absorption edge. Various surface passivation treatments were explored to eliminate trap emission and increase the luminescence quantum yield. Thiol and amine passivation both significantly reduced trap emission and enhanced band-edge emission, but the total luminescence quantum yields dropped significantly, with a maximum measured value of 1.5% for the amine-passivated CdS nanorods.     

Controlled Anisotropic Growth of Co‐Fe‐P from Co‐Fe‐O Nanoparticles

A facile approach to bimetallic phosphides, Co‐Fe‐P, by a high‐temperature (300 °C) reaction between Co‐Fe‐O nanoparticles and trioctylphosphine is presented. The growth of Co‐Fe‐P from the Co‐Fe‐O is anisotropic. As a result, Co‐Fe‐P nanorods (from the polyhedral Co‐Fe‐O nanoparticles) and sea‐urchin‐like Co‐Fe‐P (from the cubic Co‐Fe‐O nanoparticles) are synthesized with both the nanorod and the sea‐urchin‐arm dimensions controlled by Co/Fe ratios. The Co‐Fe‐P structure, especially the sea‐urchin‐like (Co_0.54Fe_0.46)₂P, shows enhanced catalysis for the oxygen evolution reaction in KOH with its catalytic efficiency surpassing the commercial Ir catalyst. Our synthesis is simple and may be readily extended to the preparation of other multimetallic phosphides for important catalysis and energy storage applications.     

Morphology Tailoring of Sulfonic Acid Functionalized Organosilica Nanohybrids for the Synthesis of Biomass‐Derived Alkyl Levulinates

Morphology evolution of sulfonic acid functionalized organosilica nanohybrids (Si(Et)Si‐Pr/ArSO₃H) with a 1D tubular structure (inner diameter of ca. 5 nm), a 2D hexagonal mesostructure (pore diameter of ca. 5 nm), and a 3D hollow spherical structure (shell thickness of 2–3 nm and inner diameter of ca. 15 nm) was successfully realized through P123‐templated sol–gel cocondensation strategies and fine‐tuning of the acidity followed by aging or a hydrothermal treatment. The Si(Et)Si‐Pr/ArSO₃H nanohybrids were applied in synthesis of alkyl levulinates from the esterification of levulinic acid and ethanolysis of furfural alcohol. Hollow spherical Si(Et)Si‐Pr/ArSO₃H and hexagonal mesoporous analogues exhibited the highest and lowest catalytic activity, respectively, among three types of nanohybrids; additionally, the activity was influenced by the ?SO₃H loading. The activity differences are explained in terms of different Brønsted acid and textural properties, reactant/product diffusion, and mass transfer rate, as well as accessibility of ?SO₃H sites to the reactant molecules. The reusability of the nanohybrids was also evaluated.     

用于锂离子电池的锡纳米棒电极的制备与表征

为了克服脱嵌锂过程中体积变化引起的机械疲劳导致使用纯锡作为锂离子电池负极时锡的循环性能很差这一问题, 通过氧化铝(AAO)模板辅助生长方法制备了锡纳米棒电极. 用扫描电子显微镜, X射线衍射分析, 循环伏安和恒流充放电测试对锡纳米棒电极的结构和电化学性能进行了初步表征. 扫描电子显微镜观察显示, 铜集流体表面均匀分布着锡纳米棒, 锡纳米棒的平均直径约250 nm. 电化学测试结果表明, 锡纳米棒电极比平面薄膜电极具有更好的容量保持率和倍率性能. 在C/10充放电倍率条件下, 第10次循环的容量仍达到第一次循环的80%, 即使在1C倍率下, 容量仍高于540 mAh·g-1.     

Saturated Heavier Group 14 Compounds as ‐Electron‐Acceptor (Z‐Type) Ligands

This review article describes the chemistry of transition‐metal complexes containing heavier group 14 elements (Si, Ge, and Sn) as the σ‐electron‐acceptor (Z‐type) ligands and discusses the characteristics of bonds between the transition metal and Z‐type ligand. Moreover, we review the iridium hydride mediated cleavage of E–X bonds (E=Si, Ge; X=F, Cl), where the key intermediates are pentacoordinate silicon or germanium compounds bearing a dative M→E bond.     

Synthesis,Structures, and Light‐Induced Transformation of Keto‐Functionalized Selenidogermanate Complexes

A double‐decker (DD) type selenidogermanate complex with C=O functionalized organic decoration, [(R¹Ge₄)Se₆] ( 1 , R¹ = CMe₂CH₂COMe), was synthesized by reaction of R¹GeCl₃ with Na₂Se, and subsequently underwent a light‐induced transformation reaction to yield [Na(thf)₂][(RGe^IV)₂(RGe^III)(Ge^IIISe)Se₅] ( 2 ). Similar to the observations reported previously for the Sn/S homologue of 1 , the product comprises a mixed‐valence complex with a newly formed Ge–Ge bond. However, different from the transformation of the tin sulfide complex, the selenidogermanate precursor did not produce a paddle‐wheel‐like dimer of the DD type structure, but led to the formation of a noradamantane (NA) type architecture, which has so far been restricted to the Si/Se and Ge/Te elemental combination.     

Surface analysis of epitaxially grown GeSn alloys with Sn contents between 15% and 18%

Metastable Germanium–tin (GeSn) layers with rather high Sn content between 15% and 18% grown on Si substrates by molecular beam epitaxy were analyzed for the morphological changes on a surface before and after reaching critical layer parameters (thickness, Sn content, and growth temperature) for surface roughening. Atomic‐force microscopy investigations were performed as a function of thickness and separately for varying Sn concentrations in the GeSn layer. Epitaxial growth of metastable, uniform GeSn (15% Sn content) layers is obtained up to a critical thickness which increases from about 80 to above 200 nm by reducing the nominal growth temperature from 160 to 140 °C. Phase separation of the complete layer into tin‐rich surface protrusions and a Ge‐rich matrix takes place beyond the critical thickness. This surface roughening via phase separation was not observed in earlier investigations with lower Sn concentrations (<6%). Tin depletion in the GeSn matrix was confirmed by using energy‐dispersive X‐ray spectroscopy measurements showing residual Sn concentration below 5%. Additionally, creation of droplets with high concentration of tin on the surfaces was confirmed by energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Tuning the Dimensions of ZnO Nanorod Arrays for Application in Hybrid Photovoltaics

ZnO nanorod arrays are a very eligible option as electron acceptor material in hybrid solar cells, owing to their favorable electrical properties and abundance of available, easy, and low‐cost synthesis methods. To become truly effective in this field, a major prerequisite is the ability to tune the nanorod dimensions towards optimal compatibility with electron‐donating absorber materials. In this work, a water‐based seeding and growth procedure is used to synthesize ZnO nanorods. The nanorod diameter is tuned either by modifying the zinc concentration of the seeding solution or by changing the concentration of the hydrothermal growth solution. The consequences of this morphological tailoring in the performance of hybrid solar cells are investigated, which leads to a new record efficiency of 0.82 % for hydrothermally grown ZnO nanorods of size 300 nm in combination with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). This improvement is attributed to a combined effect of nanorod diameter and orientation, and possibly to a better alignment of the P3HT backbone resulting in improved charge transport.     

GaN纳米棒的催化合成及其发光特性

使用稀土元素Tb作催化剂, 通过氨化溅射在Si(111)衬底上的Ga2O3/Tb薄膜, 成功制备出GaN纳米棒. X射线衍射测试显示, GaN纳米棒具有六方结构. 利用扫描电子显微镜和高分辨透射电子显微镜观察分析得出, 纳米棒为单晶GaN, 纳米棒的直径为50-150 nm, 长度约10 μm. 光致发光谱在368.6 nm处有一强的紫外发光峰, 说明纳米棒具有良好的发光特性. 讨论了GaN纳米棒的生长机制.     

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.     

Synthesis of hybrid CdS-Au colloidal nanostructures

We explore the growth mechanism of gold nanocrystals onto preformed cadmium sulfide nanorods to form hybrid metal nanocrystal/semiconductor nanorod colloids. By manipulating the growth conditions, it is possible to obtain nanostructures exhibiting Au nanocrystal growth at only one nanorod tip, at both tips, or at multiple locations along the nanorod surface. Under anaerobic conditions, Au growth occurs only at one tip of the nanorods, producing asymmetric structures. In contrast, the presence of oxygen and trace amounts of water during the reaction promotes etching of the nanorod surface, providing additional sites for metal deposition. Three growth stages are observed when Au growth is performed under air: (1) Au nanocrystal formation at both nanorod tips, (2) growth onto defect sites on the nanorod surface, and finally (3) a ripening process in which one nanocrystal tip grows at the expense of the other particles present on the nanorod. Analysis of the hybrid nanostructures by high-resolution TEM shows that there is no preferred orientation between the Au nanocrystal and the CdS nanorod, indicating that growth is nonepitaxial. The optical signatures of the nanocrystals and the nanorods (i.e., the surface plasmon and first exciton transition peaks, respectively) are spectrally distinct, allowing the different stages of the growth process to be easily monitored. The initial CdS nanorods exhibit band gap and trap state emission, both of which are quenched during Au growth.     

Robust Nonsticky Superhydrophobicity by the Tapering of Aligned ZnO Nanorods

The robust nonsticky superhydrophobicity of aligned nanoneedle films is reported. A facile, efficient, cheap, and available method based on the diffusion‐limited crystal growth principle is proposed for controlling the tapering of ZnO nanorods, the profiles of which can be tuned effectively by synergetic control over reaction time and temperature in an extremely strong alkaline reaction system. The synthesized nanoneedle, nanopencil, and nanorod arrays are chosen for studying the effects of nanoscale topography on anti‐droplet‐sticking ability. After silanization, all of them show excellent quasi‐static anti‐droplet‐stickiness, and water adhesion along the normal and lateral directions can be greatly reduced by the tapering of nanorods and eliminated by sharp nanoneedles. However, their antisticking stability is distinct under the droplet impact: the nanoneedle sample is still nonsticky but the nanorod sample loses its antisticking ability. Only ensuring the liquid/air interface is in the suspended nonwetting state is insufficient to obtain robust nonsticky surfaces, which also require extremely low solid–liquid van der Waals attraction.     

Synthesis and microstructural analysis of Si3N4 nanorods.

Alpha-Si3N4 nanorods with 20-80 nm width were synthesized by carbothermal reduction of SiO with amorphous activated carbon (AAC) as a reductant. Microstructural characterization of the synthesized nanorods was carried out by high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis. Many Si3N4 nanorods were found to be twisted. Each twisted nanorod contained several straight Si3N4 parts. The straight parts had the rod axes orientated along the (1010) direction, which is the closest packing direction of alpha-Si3N4. There were two kinds of joints between the two adjacent straight Si3N4 parts. Formation mechanism of the Si3N4 nanorods is discussed.     

Metallodielectric Hollow Shells: Optical and Catalytic Properties

Metallodielectric composites with tunable optical properties were prepared by layer‐by‐layer assembly of gold nanorods on polystyrene (PS) spheres and subsequent deposition of SiO₂ or TiO₂ encapsulating shells through a sol–gel process. The optical properties of the core‐shells were tailored in the visible and the near‐infrared region through the gold nanorod aspect ratio and the gold nanoparticle density. Removal of the PS core by dissolution in an appropriate solvent, such as THF, yielded metallodielectric hollow shells with optical properties identical to those of the original composites. The presence of gold and the porosity of the SiO₂ or TiO₂ shells, suitable to allow diffusion of reactants and products, make these materials of interest as catalysts, as demonstrated by the reduction of potassium hexacyanoferrate(III) with NaBH₄.     

Solid polymer electrolytes. VI. Microstructure of organic–inorganic hybrid networks composed of 3‐glycidoxypropyltrimethoxysilane and LiClO4 and affected by different synthetic routes

Hybrid organic–inorganic materials derived from 3‐glycidoxypropyltrimethoxylsilane were prepared via two different synthetic routes: (1) the HCl‐catalyzed sol–gel approach of silane followed by the lithium perchlorate (LiClO₄)/HCl‐catalyzed opening of epoxide and (2) the simultaneous gelation of tin/LiClO₄‐catalyzed silane/epoxide groups. LiClO₄ catalyzed the epoxide polymerization, and its effects on the structures of these hybrid materials were studied by NMR. The structure of the inorganic side was probed by solid‐state ²⁹Si NMR spectroscopy, and the characterizations of the organic side and the chemical processes involved in the different synthetic routes were performed with solid‐state cross‐polarity/magic‐angle‐spinning ¹³C NMR. The different synthetic routes significantly affected the polymerization behaviors of the organic and inorganic sides in the presence of LiClO₄. A larger amount of LiClO₄ promoted the opening of epoxide and led to the formation of longer poly(ethylene oxide) chains via the HCl‐catalyzed sol–gel approach, whereas in the case of the tin‐catalyzed approach, the faster polymerization of the inorganic side hindered the growth of the organic network. The addition of LiClO₄ was proven to be without crystalline salt present in the hybrid networks by wide‐angle X‐ray powder diffraction. Also, the interactions between the ions and hybrid host, examined with Fourier transform infrared and ⁷Li proton‐decoupled magic‐angle‐spinning NMR, further demonstrated that extensive ion aggregation existed in these hybrid materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 151–161, 2004     

氧化锌纳米棒微结构光电极的制备

通过两步法,即首先热分解醋酸锌制备氧化锌晶种层,在晶种的诱导下,再采用低温水热法在氟掺杂的SnO₂导电玻璃(fluorine-doped tin oxide, FTO)基底导电面上成功制备出高取向性的氧化锌纳米棒阵列光电极。系统研究了前驱液浓度、溶液pH值、反应时间等实验条件对光电极微结构的影响。实验结果表明在一定变化范围内,随着前驱液浓度和溶液pH值的增大,纳米棒的直径增大;随着反应时间的延长,纳米棒的长度增长。将氧化锌纳米棒阵列薄膜制作成染料敏化太阳电池(dye-sensitized solar cell, DSSC)的光电极,并对电池的I-V特性进行了表征。     

Growth and magnetic properties of oriented alpha-Fe2O3 nanorods

alpha-Fe(2)O(3) nanorods have been deposited on Si substrates using the metal-organic chemical vapor deposition method. Structural analyses indicated that alpha-Fe(2)O(3) nanorods are preferentially oriented in the [104] direction on Si(100) substrates, and the nanorod possesses the single-crystalline structure. MFM image suggests that a spin domain is formed in the alpha-Fe(2)O(3) nanorod. Anisotropic magnetic property of the alpha-Fe(2)O(3) nanorods, i.e., the discrepancy of the saturation magnetization, is observed from SQUID measurements when the magnetic field are applied parallel and perpendicular to the substrate. A lower Morin temperature than that of the macroscopically crystalline hematite is observed when the magnetic field is applied parallel to the substrate.     

Improved performance of dye sensitized ZnO nanorod solar cells prepared using TiO2 seed layer

Zinc oxide (ZnO) nanorods of different structures have been grown on indium-doped tin oxide substrates by using TiO₂ as seed layer. The ZnO nanorods have been prepared using TiO₂ seed layers annealed at different temperatures via a simple sol–gel method. The X-ray diffraction result indicates that the prepared samples are of wurtzite structure. Dye sensitized solar cells have been fabricated using the prepared ZnO nanorods. The open circuit voltage, short circuit current density, fill factor, and power conversion efficiency of the ZnO nanorod based dye sensitized solar cells prepared using TiO₂ seed layers annealed at different temperatures have been determined. The improvement in power conversion efficiency may be due to the flower like structured ZnO nanorods with smaller diameter and large specific surface area which paves way for the efficient electron transfer in hybrid solar cells.     

Synthesis and photophysical characterization of amphiphilic dendritic–linear–dendritic block copolymers

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl‐terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D ‐Si‐1G) and second (PEO–D ‐Si‐2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore‐type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 10⁴ for PEO–D ‐Si‐1G and 9.57 × 10⁴ for PEO–D ‐Si‐2G). The steady‐state fluorescence anisotropy values (r) of 1,6‐diphenyl‐1,3,5‐hexatriene were 0.06 for PEO–D ‐Si‐1G and 0.09 for PEO–D ‐Si‐2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 918–926, 2001