Synthesis and growth mechanism of Bi2S3 nanoribbons

This article describes a facile solvothermal method by using mixed solvents for the large-scale synthesis of Bi(2)S(3) nanoribbons with lengths of up to several millimeters. These nanoribbons were formed by a solvothermal reaction between Bi(III)-glycerol complexes and various sulfur sources in a mixed solution of aqueous NaOH and glycerol. HRTEM (high-resolution transmission electron microscopy) and SAED (selective-area electron diffraction) studies show that the as-synthesized nanoribbons had predominately grown along the [001] direction. The Bi(2)S(3) nanoribbons prepared by the use of different sulfur sources have a common formation process: the initial formation of NaBiS(2) polycrystals, which serve as the precursors to Bi(2)S(3), the decomposition of NaBiS(2), and the formation of Bi(2)S(3) seeds in the solution through a homogeneous nucleation process; the growth of Bi(2)S(3) nanoribbons occurs at the expense of NaBiS(2) materials. The growth mechanism of millimeter-scale nanoribbons involves a special solid-solution-solid transformation as well as an Ostwald ripening process. Some crucial factors affect nanoribbon growth, such as, solvothermal temperature, volume ratio of glycerol to water, and the concentration of NaOH; these have also been discussed.     

Synthesis of Ag2O nanocrystals with systematic shape evolution from cubic to hexapod structures and their surface properties

We report the development of a facile method for the synthesis of Ag(2)O crystals with systematic shape evolution from cubic to edge- and corner-truncated cubic, rhombicuboctahedral, edge- and corner-truncated octahedral, octahedral, and hexapod structures by mixing AgNO(3), NH(4)NO(3), and NaOH at molar ratios of 1:2:11.8. A sufficient volume of NaOH solution was first added to a mixture of AgNO(3) and NH(4)NO(3) solution to promote the formation of Ag(NH(3))(2)(+) complex ions and the growth of Ag(2)O nanocrystals with good morphological control. The crystals are mostly submicrometer-sized. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization has been performed to determine the crystalline surface facets. A band gap value of approximately 1.45 eV has been found for the octahedral Ag(2)O crystals. By changing the molar ratios of AgNO(3)/NH(4)NO(3)/NaOH to 1:2:41.8, corner-depressed rhombicuboctahedra and elongated hexapods were obtained as a result of enhanced crystal growth along the [100] directions. Smaller nanocubes with average sizes of approximately 200 and 300 nm and octapods can also be prepared by adjusting the reagent molar ratios and their added volumes. Both the octahedra and hexapods with largely silver atom-terminated {111} surface facets responded repulsively and moved to the surface of the solution when dispersing in a solution of positively charged methylene blue, but can be suspended in a negatively charged methyl orange solution. The cubes and octapods, bounded by the {100} faces, were insensitive to the molecular charges in solution. The dramatic facet-dependent surface properties of Ag(2)O crystals have been demonstrated.     

Ag2S/Ag2WO4微米棒的声化学合成、表征及其高光催化性能

TiO2作为一种光催化剂广泛应用于各种污染物的降解.但是它较大的宽禁带(~3.2 eV)导致其很难吸收可见光,因此寻找窄禁带的具有可见光响应的半导体光催化剂成为近年来光催化研究的热点.在众多窄禁带光催化剂中,纯 Ag2S在降解污染物方面并不出色,但是作为一种窄禁带的直接带隙半导体,它在加快电子迁移和提高光量子效率方面表现出色.目前有许多高催化活性的 Ag2S异质结复合半导体光催化剂的报道,如 Ag2Mo3O10-Ag2S, TiO2-Ag2S, ZnS-Ag2S和NiO-Ag2S等. Ag2WO4是一种具有新颖物理化学性质的半导体材料,在催化、传感器、抗菌和光致发光等方面有着广泛应用.但是, Ag2WO4的理论带隙较宽,约为3.5 eV,而且光照下Ag2WO4很容易产生光化学腐蚀而分解出单质银,作为光催化剂存在太阳光利用率低和稳定性较差等缺点.声化学是一种特殊纳米材料的合成方法.它主要是利用超声空化产生特殊的物理化学环境来强化化学键的生成,同时实现半导体从无定形态到固定晶型转变.本文采用超声辅助共沉淀法制备了长为0.2?1μm、直径为20?30 nm的 Ag2S/Ag2WO4微米棒复合光催化剂.利用 X射线衍射(XRD)、N2物理吸附、扫描电镜、透射电镜、光电子能谱、光致发光谱(PL)和紫外-可见漫反射吸收光谱(UV-vis DRS)和光电流等手段对所制 Ag2S, Ag2WO4和 Ag2S/Ag2WO4进行了表征.结果表明,合成的样品比表面积较小(2.7?3.6 m2/g). UV-vis DRS测试表明,声化学处理能有效拓宽 Ag2S/Ag2WO4在可见光区的吸收范围,提高其可见光响应性能.另外, PL和光电流测试结果证实,在声化学制备的 Ag2S/Ag2WO4体系中,光生电子(e?)-空穴(h+)的复合过程被极大地限制,具有较高的 e?-h+分离效率.以金卤灯为光源进行了光催化降解染料亚甲基蓝的性能测试.结果表明,声化学合成的 Ag2S/Ag2WO4的反应速率常数(0.150 min?1)分别为单纯 Ag2WO4(0.031 min?1)和 Ag2S (0.004 min?1)的4.7和29.8倍.自由基捕获实验表明,在 Ag2S/Ag2WO4光催化降解甲基橙过程中主要的活性物种为超氧自由基(?O2?)和光生空穴(h+).此外,声化学合成的 Ag2S/Ag2WO4表现出很好的光催化稳定性.循环使用3次后,该样品对亚甲基蓝的光催化活性仍高达80.4%,而纯 Ag2WO4几乎完全失活. Ag2S/Ag2WO4具有很高的光催化活性的原因,一方面是声化学处理提高了催化剂的结晶度,同时生成了独特的棒状结构;另一方面是在超声作用下, Ag2S和 Ag2WO4两相紧密接触形成异质结,促进了可见光的吸收和光生 e?与 h+的分离.     

Controlled hydrothermal synthesis and growth mechanism of various nanostructured films of copper and silver tellurides

Various nanostructured films of copper and silver tellurides were hydrothermally grown on the corresponding metal substrates through reactions between metal foils and tellurium powder in different media. Interesting morphologies including nanowires, nanorods, nanobelts, nanosheets, and hierarchical dendrites were obtained. The nanostructured films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). A growth mechanism was proposed based on the characterization results. This study provides a low-temperature, solution-phase approach to grow low-dimensional, nanostructured metal tellurides with controllable morphologies.     

Facile Synthesis of Well‐Dispersed Silver Nanoparticles on Hierarchical Flower‐like Ni3Si2O5(OH)4 with a High Catalytic Activity towards 4‐Nitrophenol Reduction

Layered nickel silicate nanoflowers (NSFs) with a hierarchical nanostructure have been successfully fabricated by a template‐free solvothermal method. The as‐prepared nanoflowers were composed of many interconnected edge‐curving lamellae with a thickness of about 15 nm and had a high specific surface area (279 m² g^?1) and large pore volume (0.67 cm³ g^?1). The highly dispersed small silver nanoparticles (AgNPs) were immobilized on the surface of NSFs through the in situ reduction of Ag⁺ by Sn²⁺. The AgNP/NSF nanocomposites showed a high performance in the catalytic reduction of 4‐nitrophenol. In particular, there was no visible decrease in the catalytic activity of the reused catalysts even after being recycled four times. The as‐prepared AgNP/NSF nanocomposites might be an excellent catalyst owing to their availability, formability, chemical and thermal stability, and high specific surface area.     

Hollow Ag/MnO2 Nanostructures with Controllable Shells: Synthesis and Oxygen Reduction Reaction Catalytic Performance

Novel hollow Ag/MnO₂ nanostructures with controlled shell composition and structure were designed and synthesized. In the present synthetic procedure, silver nanocrystals were oxidized by KMnO₄, and MnO₂ was heterogeneously formed on the surface of silver nanocrystals, then released Ag⁺ was photoreduced to silver adjacent to MnO₂. By simply changing the photoreduction moment, simultaneously with or after the addition of KMnO₄, hollow Ag/MnO₂ structures with different shell architectures—a monolayered shell composed of evenly mixed silver and MnO₂ and a double‐layered shell composed of an inner MnO₂ layer and an outer silver layer—can be obtained. Furthermore, the morphology of the hollow structure can be tuned by selecting different silver precursors, and the ratio of silver to MnO₂ in the shell can also be controlled by adjusting the ratio in the original reaction mixture. Electrochemical measurements revealed significantly enhanced catalytic performance in the oxygen reduction reaction for the prepared hollow structures. Compared with the Ag/MnO₂ composite, the onset potentials positively shift by about 50.0 mV and limiting current densities are nearly 2.0 times higher.     

Synthesis and Crystal Structures of New Antimony Polysulfido Complexes: [P(C6H5)4]3Sb3S25 and [P(C6H5)4]2Sb2S15 · 2(C3N2H6)

Reaction of elemental antimony with sulfur under mild hydrothermal conditions yielded different polysulfido-clusters of antimony. These were isolated as tetraphenylphosphonium salts [P(C₆H₅)₄]₃Sb₃S₂₅ and [P(C₆H₅)₄]₂Sb₂S₁₅ · 2(C₃N₂H₆) and their crystal structures were determined. In the first compound two different polysulfide anions are observed, Sb₂S₁₇^2– and Sb₂S₁₆^2–, whereas the second contains the Sb₂S₁₅^2– complex. These dinuclear anions show as a common building principle two ψ-trigonal bipyramidal coordinated Sb centers bridged by two S_x^2– units and an additional S_x^2– chelate ligand bound to each Sb center giving a tricyclic structure.     

Structure and morphology of nanocomposite films prepared from polyvinyl alcohol and silver nitrate: Influence of thermal treatment

Hybrid organic/inorganic films have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO₃). The silver nanoparticles have been generated in the PVA matrix by thermal treatments. The structure and the morphology of the hybrid films have been studied as a function of the silver precursor concentration and of the annealing conditions for a wide range of annealing temperatures. It was shown that in the uncured hybrid film most of the silver ions were initially coordinated with the polymer OH groups to form a chelate structure. A nanostructuration effect leading to the formation of crystalline silver nanoparticles was evidenced for annealing treatments performed at temperatures higher than 90 °C. For a curing temperature equal to 110 °C, the sizes of the formed nanoparticles were only slightly increasing as a function of annealing time and the effect of AgNO₃ complex amount in this curing condition was also significant, but slight. Annealing at a temperature equal to 160 °C thus at a temperature for which a part of the crystalline phase of PVA was melt led to an important increase of the size of the generated metal nanoparticles. The evolution of the morphology was discussed for each curing temperature as a function of the kinetics of the nanostructuration, of the size of the matrix amorphous lamellae and of the polymer chain mobility. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2657–2672, 2007     

Synthesis and Crystal Structure of a Decanuclear Silver（I）-thiolate Compound Ag10S[S2P（OEt）2]8

A new decanuclear silver(I) compound Ag₁₀(μ₈‐S)(dtp)₈ [dtp=S₂P(OEt)₂] was isolated from a reaction mixture containing W₂S₄(dtp)₂ and AgN0₃, and its solid‐state molecular structure was determinated by X‐ray crystallography. The crystallographic study revealed that the compound contains a distorted mono‐capped quasi‐prism [Ag_io] with an octat‐bridging S atom at the center of the prism. The compound (C₃₂H₈₀Ag₁₀O₁₆P₈S₁₇, M_r=2592.46) crystallizes in the monoclinic P2₁/n space group, with a = 1.5111(5) nm, b=2.3656(8) nm, c=2.284(1) nm, β= 96.88(3)°, V=8.107(5) nm³, Z=4 and D,=2.12 g · cm^?3. The solution using direct method and full‐matrix least‐squares refinement led to R=0.066, Rw=0.078 for 3928 reflections with I3σ(I).     

Metal nanocomposite films prepared in situ from PVA and silver nitrate. Study of the nanostructuration process and morphology as a function of the in situ routes

Cast‐hybrid films composed of polyvinyl alcohol (PVA) and silver nitrate were treated according to three different ways, thermal annealing, UV‐irradiation, and chemical reduction by a borohydride solution, to obtain PVA/silver nanocomposite films. The nanostructuration process was studied as a function of the treatment conditions, and discussed as a function of the mobility state of the polymer chains in the nanocomposite matrix during treatment. A homogeneous dispersion of crystalline silver nanoparticles was obtained by thermal annealing above T_g and below T_m and UV‐lamp irradiation below T_g. For these two treatments, the major processing parameters were the annealing temperature and time and the UV‐exposure time, respectively. For low‐conversion rate in Ag(0), the films evolved upon ageing at room temperature. Totally different morphology and Ag(0) conversion were achieved by chemical reduction in a borohydride solution. All the silver ions were reduced into Ag(0), and crystalline silver nanoparticles layers parallel to the film surface were observed after the treatment. This morphology was related to the high‐swollen state of the polymer matrix during treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2062–2071, 2008     

簇合物[(WS4)2Ag4(dppm)3]·Py·DMF的低加热固相合成与晶体结构

通过低加热固相合成法制备了六核簇合物[(WS4)2Ag4(dppm)3]·Py·DMF,用单晶X-射线衍射法测得该晶体属单斜晶系,空间群P21/c,晶胞参数a＝2.2990(4),b＝1.4094(2),c＝2.8083(5)nm,β＝107.472(2)°,V＝8.680(2)nm3,Z＝4,DC＝1.807 g/cm3,μ＝38.72 cm-1,F(000)＝4608,R＝0.0482,wR＝0.0987.[(WS4)2Ag4(dppm)3]的分子结构含有二个WS4Ag2簇单元和三个dppm配体,其中一个dppm配体连接同一WS4Ag2簇单元内的Ag(1)和Ag(2)原子,而另二个dppm配体则分别和不同WS4Ag2簇单元内的二个Ag原子桥联.     

High-pressure Synthesis,Structure, IR Spectroscopy,and Theoretical Calculations of the New Silver Tetraborate Ag2B4O7 with a Unique Crystal Structure

Ag₂B₄O₇ is synthesized at high-pressure/high-temperature conditions of 11 GPa and 1073 K in a multianvil device. It crystallizes in the monoclinic centrosymmetric space group P2₁/c (no. 14) with four formula units per unit cell (Z=4). The cell parameters are a=787.53(3), b=651.63(2), c=943.88(3) pm, β=107.911(2)°, and V=460.90(3) ų. Ag₂B₄O₇ crystallizes in a unique crystal structure that consists of complex anionic borate layers with Ag⁺ ions in between. Additionally, the silver cations show argentophilic interactions. The compound was analysed via single-crystal and powder diffraction as well as infrared spectroscopy. Furthermore, theoretical calculations at HSEsol level were conducted.