Formation of Metal Selenide and Metal–Selenium Nanoparticles using Distinct Reactivity between Selenium and Noble Metals

Small Se nanoparticles with a diameter of ≈20 nm were generated by the reduction of selenium chloride with NaBH₄ at ?10 °C. The reaction with Ag at 60 °C yielded stable Ag₂Se nanoparticles, which subsequently were transformed into M–Se nanoparticles (M=Cd, Zn, Pb) through cation exchange reactions with corresponding ions. The reaction with Pt formed Pt layers that were evenly coated on the surface of the Se nanoparticles, and the dissolution of the Se cores with hydrazine generated uniform Pt hollow nanoparticles. The reaction with Au generated tiny Au clusters on the Se surface, and eventually formed acorn‐shaped Au–Se nanoparticles through heat treatment. These results indicate that small Se nanoparticles with diameters of ≈20 nm can be used as a versatile platform for the synthesis of metal selenide and metal–selenium hybrid nanoparticles with complex structures.     

同轴静电纺丝法在纳米中空Ti02纤维中填充Ag的应用

以聚乙烯吡咯烷酮(PVP)溶胶,钛酸四正丁酯和PVP溶胶,银颗粒为前驱体,以共轴静电纺丝法制备了银填充的TiO2中空纳米纤维.将双组分纤维在200℃下热处理去除乙醇与表面吸附水后,继而在空气气氛中焙烧至600℃.可以得到在内表面上沉积银颗粒的TiO2纳米管,银颗粒的直径为5-40 nm,TiO2纳米管的外径150-300 nm.管臂厚10-20 nm.用红外吸收光谱(IR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等测试手段对超细纤维进行了表征.中空纤维的直径和管壁可以通过改变电纺参数来调节.与Ag-TiO2纳米纤维、TiO2纳米中空纤维、TiO2纳米纤维及TiO2纳米粉体相比较,Ag颗粒填充的TiO2纳米中空纤维在光分解亚甲基蓝上表现出了更好的光催化性能.     

高活性Ag修饰TiO2空心八面体光催化剂的简易模板诱导合成

贵金属修饰的TiO2空心纳米光催化材料由于具有大的比表面积、低的质量密度、良好的表面渗透性、强的光吸收能力以及界面电荷的快速转移,因而表现出优异的光催化性能.为了制备结构可控且精良的贵金属修饰TiO2空心纳米光催化材料,人们先后采用湿化学法、高温固相法、声化学法及光化学沉积法等.由于在制备过程中涉及多种异相材料的合成和结构控制,因此上述合成方法通常需要复杂且多步过程(有些过程甚至很容易导致结构破坏),从而限制了其在光催化领域的实际应用.本文开发了一种简单的模板诱导法,成功制备了Ag纳米粒子修饰的TiO2空心八面体光催化剂.合成过程包括模板指导沉积和原位模板溶解.以Ag2O八面体为模板, TiF4水溶液为前驱体,首先通过TiF4水解形成TiO2纳米粒子沉积在Ag2O模板表面,而TiF4水解产生的酸性HF水溶液可原位溶解碱性的Ag2O模板,从而一步制得TiO2空心八面体.同时,利用Ag2O以及Ag+离子的光敏特性,在光照条件下使Ag2O和Ag+离子生成Ag纳米颗粒,直接沉积在TiO2空心八面体的内外表面,得到Ag/TiO2光催化剂.由此可见,该合成方法具有明显的步骤少的优点.扫描电镜、透射电镜、能量散射和紫外-可见光谱等表征结果表明成功制得内外Ag纳米粒子修饰的TiO2空心八面体光催化剂,其中TiO2空心八面体的壁厚约为25 nm,边长约为1μm,而修饰在其表面的Ag纳米粒子尺寸仅为5–10 nm.此外,通过控制TiF4前驱体浓度,还可制备核壳结构的Ag2O@TiO2八面体以及不同壁厚Ag修饰的TiO2空心八面体,表明该方法在Ag/TiO2形貌合成上的多样性和可控性.为了获得良好的光催化活性,对制备的Ag纳米粒子修饰的TiO2空心八面体光催化剂进行了不同温度的热处理. X射线衍射结果表明,即使在600 oC高温下,制备的Ag/TiO2空心八面体光催化剂依然能够保持原有的特殊形貌和锐钛矿TiO2晶型.该温度明显高于TiO2从锐钛矿向金红石转变的温度.这说明合成的Ag/TiO2能在保持高活性锐钛矿相的同时获得更好的结晶性.这可能是由于分散在TiO2原始晶粒周围的Ag纳米粒子能阻止其进一步长大,从而抑制了其晶型转变.不同样品光催化降解甲基橙的结果表明,经600oC高温热处理的样品表现出最高的光催化活性,相应的反应速率常数为0.11 min？1.这应得益于该光催化剂具有以下三个特点：(1) TiO2空心八面体的薄壁结构能够缩短光照条件下光生电子和空穴从内部扩散到表面的距离;(2)由于贵金属Ag纳米粒子沉积在TiO2薄壁的内外两个表面以及TiO2和Ag形成肖脱基势垒,因此在它们接触的界面上能够发生更快的界面电荷转移;(3)高温处理导致TiO2良好的晶化以及高活性锐钛矿TiO2晶型的保持.     

Ag, Ag2S, and Ag2Se nanocrystals: synthesis, assembly, and construction of mesoporous structures

Synthesis of mesoporous materials has become more and more important due to their wide application. Nowadays, there are two main ideas in their preparation. One is focused on the templating method. The other is based on metal-organic frameworks (MOFs) constructed from molecular building blocks. Herein, we exploit a new idea for their facile and general synthesis, namely, using "artificial atoms" (monodisperse nanoparticles) as uniform building blocks to construct ordered mesoporous materials. Mesoporous Ag, Ag2S, and Ag2Se have been obtained to demonstrate this concept. On the other hand, we also describe a facile method to prepare the "building blocks". Ag nanoparticles were obtained by direct thermal decomposition of AgNO3 in octadecylamine, and Ag2S/Ag2Se nanoparticles were synthesized by reaction between sulfur or selenium powder and Ag nanoparticles formed in situ. This approach for Ag, Ag2S, and Ag2Se nanoparticles is efficient, economical, and easy to scale up in industrial production.     

Fabrication and SERS properties of Ag/Cu2S composite micro-nanostructures over Cu foil

A new kind of Ag/Cu2S composite micro/nanostructures has been prepared via a convenient galvanic reduction method. SEM images of these micro/nanostructures showed that Ag nanoparticles with the size of around 50-100 nm were well deposited on the surface of Cu2S micro/nanostructures. The SEM images also indicated that the Ag nanoparticles were preferentially grown on the big polygonal Cu2S microstructures, which could be explained by a localization of the electrons on the surface of the polygonal Cu2S microstructures after the electron transfer step. Owing to the introduction of Ag nanoparticles on the surface of Cu2S micro/nanostructures, the resulting Ag/Cu2S composite micro-nanostructures could be used as a versatile substrate for surface enhanced Raman scattering.     

Antibacterial properties of Ag nanoparticle loaded multilayers and formation of magnetically directed antibacterial microparticles

Antibacterial coatings based on hydrogen-bonded multilayers containing in situ synthesized Ag nanoparticles were created on planar surfaces and on magnetic colloidal particles. We report the antibacterial properties of these coatings, determined using a disk-diffusion (Kirby-Bauer) test, as a function of the film thickness and the concentration of Ag nanoparticles in the hydrogen-bonded multilayers. The zone of inhibition (ZoI) determined by the disk-diffusion test increases as the thickness of the multilayer film is increased. Results obtained for the values of the ZoI as a function of film thickness can be described adequately with a simple diffusion model (i.e., the square of the zone of inhibition (ZoI) depended linearly on the logarithm of the thickness of the silver-loaded films). This observation suggests that, in order to incrementally increase the ZoI, an exponentially increasing amount of Ag is required within the multilayers. In general, there was no statistically significant correlation between the zone of inhibition and the number of Ag loading and reduction cycles. The duration of sustained release of antibacterial Ag ions from these coatings, however, could be prolonged by increasing the total supply of zerovalent silver in the films via multiple loading and reduction cycles. These results indicate that the release of silver is controlled by an oxidation mechanism at the surface of the nanoparticles and that repeated loading and reduction of silver leads preferentially to growth of the existing silver nanoparticles in the film as opposed to nucleation of new Ag nanoparticles. We also show that magnetic microspheres coated with silver nanoparticle loaded hydrogen-bonded multilayer thin films can be used to deliver antibacterial agents to specific locations. The minimum inhibitory concentration (MIC) of nanocomposite coated microspheres was determined by the agar dilution technique: antibacterial magnetic microspheres with higher concentrations of Ag nanoparticles exhibited lower MIC values.     

A reverse cation-exchange route to hollow PbSe nanospheres evolving from Se/Ag2Se core/shell colloids

A reverse cation-exchange approach for the synthesis of hollow PbSe nanospheres is successfully established. This route involves a new strategy of a stepwise, in-situ template-based evolution from spherical amorphous Se colloids to Se/Ag(2)Se core/shell colloids, then to hollow PbSe nanospheres. Se colloids are prepared as the initial product by utilizing the chelation of ethylenediamine to bulk Se. They are converted into Se/Ag(2)Se core/shell colloids through the reaction with Ag(+) in ethylene glycol. During the conversion from Ag(2)Se shell to PbSe shell, a small amount of tributylphosphine is crucial as the capping agent. The characterization results, including XRD, SEM, TEM, HRTEM, and EDX, reveal that hollow PbSe nanospheres with polycrystalline and cubic structure are prepared. The corresponding optical band gap is calculated to be 0.56 eV. This conformation is potentially beneficial to the improvement concerning the applications of PbSe nanostructures.     

Metal oxide and sulfide hollow spheres: layer-by-layer synthesis and their application in lithium-ion battery

A novel layer-by-layer approach has been developed to synthesize polycrystalline SnO(2) hollow spheres with tunable shell thickness and size using SiO(2) spheres as a template. The surface of the SiO(2) spheres has been first modified by the polyelectrolyte, and subsequently, the compact SnO(2) layer has deposited on the surface of the SiO(2) spheres through a redox reaction because of the electrostatic attraction between the charged species. After HF etching treatment, the uniform SnO(2) hollow spheres have been obtained. The approach presented herein has been extended to synthesize other metal oxide and sulfide hollow spheres such as In(2)O(3) and ZnS. Moreover, the as-synthesized SnO(2) hollow spheres have been applied in lithium-ion battery and show improved performance compared with SnO(2) nanoparticles. The high surface area and stable hollow structure of the SnO(2) hollow spheres may be responsible for the improved performance.     

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on St?ber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).     

SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.     

A bis(p-sulfonatophenyl)phenylphosphine-based synthesis of hollow Pt nanospheres

We report herewith the synthesis of hollow Pt nanospheres by using bis(p-sulfonatophenyl)phenylphosphine to selectively remove the Ag cores of Ag-Pt core-shell nanoparticles. Core-shell Ag-Pt nanoparticles were first obtained by the successive reduction method with a discontinuous Pt shell to allow the BSPP passage. Transmission electron microscopy imaging of the core-shell Ag-Pt nanoparticles before and after BSPP dissolution showed little changes in the particle size, indicating that the removal of the Ag cores had occurred isomorphously. The hollow Pt nanospheres, together with the predecessor Ag-Pt core-shell particles of the same size, were transferred from water to toluene and surface modified by dodecylamine in toluene. This allows the catalytic activities of solid and hollow Pt particles in room temperature methanol oxidation reaction to be compared under conditions of identical particle size and the same surface environment. The measured higher specific activity of the Pt hollow nanospheres could then be attributed unambiguously to the larger specific surface area prevalent in the porous hollow structure.     

同轴静电纺丝法在纳米中空TiO2纤维中填充Ag的应用

以聚乙烯吡咯烷酮(PVP)溶胶/钛酸四正丁酯和PVP溶胶/银颗粒为前驱体, 以共轴静电纺丝法制备了银填充的TiO2中空纳米纤维. 将双组分纤维在200 ℃下热处理去除乙醇与表面吸附水后, 继而在空气气氛中焙烧至600 ℃, 可以得到在内表面上沉积银颗粒的TiO2纳米管, 银颗粒的直径为5-40 nm, TiO2纳米管的外径150-300 nm, 管臂厚10-20 nm. 用红外吸收光谱(IR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等测试手段对超细纤维进行了表征. 中空纤维的直径和管壁可以通过改变电纺参数来调节. 与Ag-TiO2纳米纤维、TiO2纳米中空纤维、TiO2纳米纤维及TiO2纳米粉体相比较, Ag颗粒填充的TiO2纳米中空纤维在光分解亚甲基蓝上表现出了更好的光催化性能.     

Control of TiO2 structures from robust hollow microspheres to highly dispersible nanoparticles in a tetrabutylammonium hydroxide solution

A new process for controlling the structure of TiO2 from hollow microspheres to highly dispersible nanoparticles has been developed by altering the concentration of tetrabutylammonium hydroxide (TBAH) in the solvothermal reaction of titanium isopropoxide. Robust and size-controllable hollow TiO2 microspheres, constructed by the assembly of 18 nm TiO2 nanoparticles, were synthesized at relatively high TBAH concentration. The diameters of hollow spheres, with a shell thickness of approximately 250 nm, were controlled to 1.5-4 microm by varying the concentration of TBAH in the range of 0.1-0.5 M. After calcination at 450 degrees C, the hollow microspheres were not appreciably deformed and were still floating on the surface of the water. However, highly dispersible TiO2 nanoparticles with an average diameter of 13 nm were obtained at a low TBAH concentration such as 9.2 mM. The colloidal particle size of TiO2 in an aqueous suspension at pH 2 was 12.5-13.5 nm, which indicates that the each nanoparticle is completely separated. The overall procedure is simple and highly reproducible, and large-scale synthesis is available at low cost.     

Formation of Ag2Se nanotubes and dendrite-like structures from UV irradiation of a CSe2/Ag colloidal solution

Ag2Se nanotubes have been successfully synthesized by UV photodissociation of adsorbed CSe2 on the surface of Ag nanowires under ambient conditions. Transmission electron microscopy was used to trace the growth of hollow interiors, allowing a detail study of the Kirkendall effect in 1-dimensional nanosystems. Voids were observed to grow from both ends of the nanowires along the longitudinal axis and ultimately merged to form hollow nanotubes. This phenomenon is attributed to the crystallographic selective adsorption of poly(vinylpyrolidone) on Ag nanowire templates. In addition, we observed the formation of dendrites on aging of the reaction mixture and explained its growth based on a diffusion-limited aggregation model.     

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the approximately 6 nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57 V for oxygen reduction, which is about 200 mV more positive than that obtained by using a approximately 6 nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that approximately 6 nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated H(2)SO(4) (0.5 M). Finally, compared to the approximately 6 nm Pt nanoparticle catalyst, the approximately 6 nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings.     

Characterization of Ag/Pt core-shell nanoparticles by UV-vis absorption, resonance light-scattering techniques

The water-soluble Ag/Pt core-shell nanoparticles were prepared by deposition Pt over Ag colloidal seeds with the seed-growth method using K2PtCl4 with trisodium citrate as reduced agent. The Ag:Pt ratio is varied from 9:1 to 1:3 for synthesizing Pt shell layer of different thickness. A remarkable shift and broadening of Ag surface plasmon band around 410 nm was observed. The contrast of TEM images of Ag/Pt colloids has been obtained. Various techniques, such as transmission electron microscopy (TEM), UV-vis absorption and resonance light-scattering spectroscopy were used to characterize nanoparticles. The data of TEM, UV-vis and resonance light-scattering spectrum all confirm formation of Ag/Pt core-shell nanoparticles. Resonance light-scattering and emission spectrum show the Ag and Ag/Pt core-shell nanoparticles have a nonlinear light-scattering characteristic.     

Cu2O/Ag纳米复合物的表面增强拉曼光谱

用一种简单的化学还原方法制备了银纳米粒子包覆的氧化亚铜（Cu2O）纳米复合物。扫描电子显微镜显示Cu2O 为八面体型的纳米粒子,表面光滑,结构对称。包覆的Ag部分占据Cu2O粒子表面。通过比较Ag/Cu2O纳米复合物、Ag溶胶及Cu纳米粒子表面吸附的4-巯基吡啶（4-Mpy）分子表面增强拉曼光谱（SERS）发现,利用此方法得到了Cu2O粒子表面吸附分子的拉曼光谱。银纳米粒子所产生的电磁场增强又增强了吸附在Cu2O上的4-Mpy拉曼信号。这种方法为初步研究Cu2O表面吸附分子性质提供了依据,扩宽了SERS的使用范围,使SERS应用在纳米半导体材料上成为可能。     

Rapid Synthesis of Hollow Ag–Au Nanodendrites in 15 Seconds by Combining Galvanic Replacement and Precursor Reduction Reactions

Metallic nanomaterials displaying hollow interiors as well as sharp tips/branches at their surface (such as hollow nanodendrites) are attractive, because these features enable higher surface‐to‐volume ratios than their solid and/or rounded counterparts. This paper describes a simple strategy for the synthesis of Ag–Au nanodendrites in 15 s using Ag nanospheres prepared in a previous synthetic step as seeds. Our approach was based on the utilization of Ag nanospheres as seeds for Au deposition by a combination of galvanic replacement reaction between Ag and AuCl₄^?(aq) and AuCl₄^?(aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) as a stabilizer and water as the solvent. The produced Ag–Au nanodendrites presented monodisperse sizes, and their surface morphologies could be tuned as a function of growth time. Owing to their hollow interiors and sharp tips, the Ag–Au nanodendrites performed as effective substrates for surface‐enhanced Raman scattering (SERS) detection of 4‐MPy (4‐mercaptopyridine) and R6G (rhodamine 6G) as probe molecules. We believe that the approach described herein can serve as a protocol for the fast and one‐step synthesis of Ag–Au hollow nanondendrites with a wide range of sizes, compositions, and surface morphologies for applications in SERS and catalysis.     

Synthesis of Ag-coated polystyrene colloids by an improved surface seeding and shell growth technique

In this paper, an improved surface seeding and shell growth technique was developed to prepare Ag-polystyrene core shell composite. Polyethyleneimine (PEI) could act as the linker between Ag ions (Ag nanoparticles) and polystyrene (PS) colloids and the reducing agent in the formation of Ag nanoparticles. Due to the multi-functional characteristic of PEI, Ag seeds formed in-situ and were immobilized on the surface of PEI-modified PS colloids and no free Ag clusters coexist with the Ag “seeding” PS colloids in the system. Then, the additional agents could be added into the resulting dispersions straightly to produce a thick Ag nanoshell. The Ag nanoshell with controllable thickness was formed on the surface of PS by the “one-pot” surface seeding and shell growth method. The Ag-coverage increased gradually with the increasing of mass ratio of AgNO₃/PS. The optical properties of the Ag-PS colloids could be tailored by changing the coverage of Ag.     

Transportation of silver nanopaticles in nanochannels of carbon nanotubes with supercritical water

Supercritical water (SCW) as a highly destructive environment has been utilized to open multiwall carbon nanotubes (MWNTs) and to break silver aggregates into nanoparticles (diameter 2-20 nm). Water was drawn into open-ended MWNTs by capillary suction, pulling Ag nanoparticles into the MWNTs. The Ag nanoparticles (solid), presumably transported in the nanochannels of MWNTs by the fluidity of SCW, stacked, and fused to form nanorods, suggesting SCW associated with MWNTs (hollow interior) might be exploited as a nanoreactor.