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.     

相转移方法制备银纳米粒子单层膜

在油酸钠保护下用NaBH_4还原AgNO_3，制得了银纳料粒子胶体溶液。利用相转 移剂NaH_2PO_4等，使Ag纳料粒子在水／朋机相界面之间形成薄膜。形成的Ag纳料 粒子膜可以转移到玻璃等基质上，讨论了其转移机理；并用石英晶体微天平（QCM ）宣检测了银纳料粒子的相转移量。     

Ag/SBA-15表面催化过程的现场SERS研究

以三嵌段共聚物P₁₂₃为模板剂, 正硅酸乙酯为硅源, 水热合成了介孔分子筛SBA-15, 通过对SBA-15内外表面修饰, 使用银氨溶液和硝酸银溶液作为金属源合成Ag/SBA-15, 透射电镜(TEM)研究表明在SBA-15孔道内较好地分散了颗粒状和棒状的Ag纳米粒子. 以苯硫酚作为探针分子, 研究了负载Ag纳米粒子的SBA-15的SERS效应, 结果表明Ag/SBA-15具有良好的SERS活性. 另外, 该材料对催化硼氢化钠还原对硝基苯酚具有良好的催化效果, 通过结合现场SERS技术, 研究了该催化过程的机理.     

Synthesis of confined Ag nanowires within mesoporous silica via double solvent technique and their catalytic properties

Ag nanowires within the channels of mesoporous silica have been successfully synthesized via a double solvent technique, in which n-hexane is used as a hydrophobic solvent to disperse mesoporous silica and an AgNO(3) aqueous solution is used as a hydrophilic solvent to fill mesochannels. The morphology of the obtained Ag (nanowires, nanoparticles or nanorods) can be controlled by adjusting the concentration of AgNO(3) solution and the template pore size. HRTEM images demonstrate extensive Ag nanowires with several to tens of hundreds nanometers in length are deposited along the long axis of mesochannels when the atomic AgNO(3)/Si ratio is 0.090. When the atomic AgNO(3)/Si ratio is 0.068 or 0.11, there is a combination of Ag nanoparticles and nanowires; nanoparticles are mainly formed when the atomic AgNO(3)/Si ratio is higher than 0.14. Further, the catalytic results of the oxidation of styrene show that styrene oxide and benzaldehyde are the main products of the reaction, and the morphology and diversity of Ag in Ag/mesoporous silica composites have an effect on the conversion of styrene and selectivity of styrene oxide.     

Preparation of size-controlled, highly populated, stable, and nearly monodispersed Ag nanoparticles in an organic medium from a simple interfacial redox process using a conducting polymer

The reducing property of an organically soluble conducting polymer (poly(o-methoxyaniline), POMA) is used to prepare monodisperse, size-controlled, highly populated, and highly stable silver nanoparticles in an organic medium through an interfacial redox process with an aqueous AgNO3 solution. The transition of emeraldine base (EB) to the pernigraniline base (PB) form of POMA occurs during nanoparticle formation, and the nitrogen atoms of POMA(PB) stabilize Ag nanoparticles by coordination to the adsorbed Ag(+) on the nanoparticle surface. The conductivity of the nanocomposite is on the order of 10(-11) S/cm, indicating that no doping of POMA occurs under the preparation conditions. The nanoparticles are free of excess oxidant and external stabilizer particles. The POMA (EB) concentration tailors the size of nanoparticles, and at its higher concentration (0.01% POMA with 0.01 N AgNO3), very dense Ag nanoparticles (6 x 10(15) particles/m(2)) of almost uniform size and shape are produced. The rate constant and Avrami exponent values of the nanoparticle formation are measured from the time-dependent UV-vis spectra using the Avrami equation. The Avrami exponent (n) values are close to 1, indicating 2D athermal nucleation with the circular shape of the nuclei having diffusion-controlled growth. The rate constant values are almost independent of AgNO3 concentration but are strongly dependent on POMA concentration. The higher rate constant with increasing POMA(EB) concentration has been attributed for the lowering of nanoparticle size due to increased nucleation density.     

Facile synthesis, stabilization, and anti-bacterial performance of discrete Ag nanoparticles using Medicago sativa seed exudates

The biogenic synthesis of metal nanomaterials offers an environmentally benign alternative to the traditional chemical synthesis routes. Colloidal silver (Ag) nanoparticles were synthesized by reacting aqueous AgNO(3) with Medicago sativa seed exudates under non-photomediated conditions. Upon contact, rapid reduction of Ag(+) ions was observed in <1 min with Ag nanoparticle formation reaching 90% completion in <50 min. Effect of Ag concentration, quantity of exudate and pH on the particle size and shape were investigated. At [Ag(+)]=0.01 M and 30°C, largely spherical nanoparticles with diameters in the range of 5-51 nm were generated, while flower-like particle clusters (mean size=104 nm) were observed on treatment at higher Ag concentrations. Pre-dilution of the exudate induced the formation of single-crystalline Ag nanoplates, forming hexagonal particles and nanotriangles with edge lengths of 86-108 nm, while pH adjustment to 11 resulted in monodisperse Ag nanoparticles with an average size of 12 nm. Repeated centrifugation and redispersion enhanced the percentage of nanoplates from 10% to 75% in solution. The kinetics of nanoparticle formation were monitored using ultraviolet-visible spectroscopy and the Ag products were characterized using transmission electron microscopy, selected-area electron diffraction, scanning electron microscopy, X-ray powder diffraction, and atomic force microscopy. X-ray photoelectron spectroscopy was used to investigate the elements and chemical environment in the top layers of the as-synthesized Ag nanoparticles, while the metabolites in the exudate were analyzed using gas chromatography-mass spectroscopy. To our knowledge, this is the first account of M. sativa seed exudate assisted synthesis and stabilization of biogenic Ag nanoparticles; the nanoplates are notably smaller and better faceted compared with those synthesized by vascular plant extracts previously reported. Stabilized films of exudate synthesized Ag nanoparticles were effective anti-bacterial agents.     

Metal ion redox potential plays an important role in high-yield synthesis of monodisperse silver nanoparticles

A facile method is developed to prepare monodisperse silver nanoparticles in a much enhanced yield by adding a trace amount of Fe(3+) ions into the reaction of AgNO(3) with oleic acid and oleylamine. We propose that Fe(2+) ions speed up the nucleation and growth of silver nanoparticles due to the electron-transfer between Ag(+) and Fe(2+), in which Fe(2+) is from Fe(3+) reduced by oleylamine.     

Preparation, characterization, surface modification and redox reactions of silver nanoparticles in the presence of tryptophan

The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques.     

Rapid synthesis of highly monodisperse Au(x)Ag(1-x) alloy nanoparticles via a half-seeding approach

Gold-silver alloy Au(x)Ag(1-x) is an important class of functional materials promising new applications across a wide array of technological fields. In this paper, we report a fast and facile synthetic protocol for preparation of highly monodisperse Au(x)Ag(1-x) alloy nanoparticles in the size range of 3-6 nm. The precursors employed in this work are M(I)-alkanethiolates (M = Au and Ag), which can be easily prepared by mixing common chemicals such as HAuCl(4) or AgNO(3) with alkanethiols at room temperature. In this half-seeding approach, one of the M(I)-alkanethiolates is first heated and reduced in oleylamine solvent, and freshly formed metal clusters will then act as premature seeds on which both the first and second metals (from M(I)-alkanethiolates, M = Au and Ag) can grow accordingly without additional nucleation and thus achieve high monodispersity for product alloy nanoparticles. Unlike in other prevailing methods, both Au and Ag elements present in these solid precursors are in the same monovalent state and have identical supramolecular structures, which may lead to a more homogeneous reduction and complete interdiffusion at elevated reaction temperatures. When the M(I)-alkanethiolates are reduced to metallic forms, the detached alkanethiolate ligands will serve as capping agent to control the growth. More importantly, composition, particle size, and optical properties of Au(x)Ag(1-x) alloy nanoparticles can be conveniently tuned with this approach. The optical limiting properties of the prepared particles have also been investigated at 532 and 1064 nm using 7 ns laser pulses, which reveals that the as-prepared alloy nanoparticles exhibit outstanding broadband optical limiting properties with low thresholds.     

Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.     

银纳米棱镜的形成及其光学性能研究

以有机溶剂作为反应介质,聚合物为稳定剂,通过微波辅助溶液法成功地制备了具有特殊光学性能的银纳米棱镜.利用X射线衍射、透射电子显微镜和紫外-可见光谱等手段跟踪反应过程.结果显示,随着反应的进行,银纳米粒子由10nm左右的球形颗粒逐渐转变为具有规则三角形(或缺角的三角形)形貌的纳米棱镜;同时,紫外-可见吸收峰不但显示出明显的量子尺寸效应,而且吸收峰也由单一的等离子共振吸收峰变为多重的多极吸收峰共同存在,胶体溶液也随之显示出不同的颜色.改变反应物的配比、体系的浓度及无机前驱物都会得到位置和峰形各不相同的吸收曲线,从而得到多彩的纳米银胶体溶液.     

Novel preparation of snowflake-like dendritic nanostructures of Ag or Au at room temperature via a wet-chemical route

In this letter we describe a novel but effective wet-chemical route for the simple preparation of snowflake-like dendritic nanostructures of Ag, which are homogeneous in size, carried out by directly mixing AgNO3 and p-phenylenediamine (PPD) aqueous solutions at room temperature. It reveals that such dendrites are aggregates of nanoparticles and highly crystalline in nature. It is found that the molar ratio of [PPD]/[Ag+] influences the final morphologies of the structures formed and that excessive PPD (the molar ratio of [PPD]/[Ag+] is higher than 1:1) is crucial to achieving dendrites. The possible dendritic growth mechanism is also predicted. This method can also be extended to the preparation of Au dendrites.     

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 °C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO₃⁻) in the PVA nanofibers had an adverse effect on the culture of both cells.     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Low-temperature metallic alloying of copper and silver nanoparticles with gold nanoparticles through digestive ripening

We describe a remarkable and simple alloying procedure in which noble metal intermetallic nanoparticles are produced in gram quantities via digestive ripening. This process involves mixing of separately prepared colloids of pure Au and pure Ag or Cu particles and then heating in the presence of an alkanethiol under reflux. The result after 1 h is alloy nanoparticles. Particles synthesized according to this procedure were characterized by UV-vis spectroscopy, EDX analysis, and high-resolution electron microscopy, the results of which confirm the formation of alloy particles. The particles of 5.6+/-0.5 nm diameter for Au/Ag and 4.8+/-1.0 nm diameter for Cu/Au undergo facile self-assembly to form 3-D superlattice ordering. It appears that during this digestive ripening process, the organic ligands display an extraordinary chemistry in which atom transfer between atomically pure copper, silver, and gold metal nanoparticles yields monodisperse alloy nanoparticles.     

Preparation of hybrid hydrogel containing ag nanoparticles by a green in situ reduction method

In this Article, large and uniform Ag nanoparticle-containing hybrid hydrogels were prepared by in situ reduction of Ag ions in cross-linked tapioca dialdehyde starch (DAS)-chitosan hydrogels. In the hybrid hydrogels, chitosan was chosen as a macromolecular cross-linker because of its abundant source and good biocompatibility. The hybrid hydrogel showed good water-swelling properties, which could be controlled by varying the ratio of chitosan to tapioca DAS in the hydrogel. The reductive aldehyde groups in the cross-linked hydrogels could be used to reduce Ag ions to Ag nanoparticles without any additional chemical reductants. Interestingly, by controlling the reduction conditions such as the tapioca DAS concentration, aqueous AgNO(3) concentration, reaction time, and aqueous ammonium concentration, Ag nanoparticles with different sizes and morphologies were obtained. Because of their biocompatibility, degradable constituents, mild reaction conditions, and controlled preparation of Ag nanoparticles, these tapioca DAS-chitosan/Ag nanoparticle hybrid hydrogels show promise as functional hydrogels.     

Synthesis of silver nanoparticles in an aqueous suspension of graphene oxide sheets and its antimicrobial activity

A solution-based approach to the synthesis of silver (Ag) nanoparticles by chemical reduction of AgNO(3) in a graphene oxide (GrO) suspension is demonstrated. X-ray diffraction and transmission electron microscopy indicate that the Ag nanoparticles, of size range 5-25nm, were decorated on the GrO sheets. The size and shape of the Ag nanoparticles are dependent on the concentration of the AgNO(3) solution. Antimicrobial activity of such hybrids materials is investigated against the Gram negative bacteria Escherichia coli and Pseudomonous aeruginosa. The bacterial growth kinetics was monitored in nutrient broth supplemented with the Ag nanoparticle-GrO suspension at different conditions. It was observed that P. aeruginosa is comparatively more sensitive to the Ag nanoparticle-GrO suspension.     

Supramolecular assemblies of a series of 2-arylbenzimidazoles at the air/water interface: in situ coordination, surface architecture and supramolecular chirality

The spreading behavior and supramolecular assemblies of some arylbenzimidazoles with 2-substituted aromatic groups such as phenyl, naphthyl, anthryl and pyrenyl on water surface and the subphase containing AgNO3 were investigated. It was observed that although these compounds lack long alkyl chains, they showed surface activity when spread from chloroform solution on water surface and formed the supramolecular assemblies. When AgNO3 was present in the subphase, a coordination between the imidazole group of the compounds and Ag(I) occurred in situ in the spreading film, which was verified by the surface pressure/area (pi-A) isotherms and UV/Vis absorption spectra. Both the spreading films from water and the aqueous AgNO3 subphase were transferred onto solid substrates and their surface morphologies as well as properties were characterized by AFM, UV/Vis absorption and CD spectra. Various surface morphologies such as nanoparticles, block domains and nanoutensils were observed depending on the substituted aromatic groups. Interestingly, although all of these compounds were achiral, supramolecular chirality was obtained for some of the arylbenzimidazole films assembled from either the water surface or the subphase containing AgNO3. It was revealed that chiral assemblies could be obtained from water surface for the benzimidazoles which have pyrenyl or alpha-naphthyl groups. For benzimidazole derivative with anthryl group, chiral assemblies could be obtained when spreading on the aqueous AgNO3 subphase. For the benzimidazoles with phenyl or beta-naphthyl groups, no chirality was obtained. It was suggested that both the overcrowded stacking of the aromatic groups and the cooperative arrangement of the molecules on water surface or aqueous AgNO3 subphase play a crucial role in forming the chiral supramolecular assemblies.     

Spontaneous formation of Ag nanoparticles in dimethylacetamide solution of poly(ethylene glycol)

The spontaneous formation of Ag nanoparticles in a dimethylacetamide (DMAC) solution of poly(ethylene glycol) (PEG) was studied. FTIR analysis showed the formation of carbonyl groups, revealing that PEG acted as not only a protective agent but also a reducing agent in the formation of Ag nanoparticles. Since no significant reactions were observed when poly(tetramethylene glycol) (PTMG) was used to replace PEG or acetonitrile was used to replace DMAC, it was suggested that PEG molecules might be coiled to form pseudo-crown ether cavities, in which Ag complexes were bound to the oxyethylene groups and reduced, and that the use of a solvent which might appropriately solvate the Ag salt was important for the formation of Ag nanoparticles. In addition, the mean diameters of the resultant Ag nanoparticles were 3.8-9.0 nm, increasing with increasing AgNO(3) concentration. A sufficiently high PEG concentration relative to AgNO(3) was necessary for the formation of smaller Ag nanoparticles. This work provided a simple route for the in situ synthesis of Ag nanoparticles.     

Ag/AgCl复合纳米粒子/聚丙烯腈纳米纤维膜的制备及可见光催化降解甲基橙

通过电纺丝法结合原位还原及原位氧化反应, 成功制备了均匀负载Ag/AgCl复合纳米粒子/聚丙烯腈(PAN)复合纳米纤维膜. 首先利用电纺丝技术制备了PAN/AgNO₃复合纳米纤维, 然后用乙二醇将硝酸银还原成银纳米粒子, 最后采用三氯化铁溶液对材料进行原位氧化. 所得纤维膜材料可以作为高效的可见光催化剂, 具有高可见光利用率, 优异的柔性和高光催化动力学等特性.