Silver halide colloid precursors for the synthesis of monolayer-protected clusters

A new method for the synthesis of monolayer-protected silver clusters (MPCs) based on the two-phase reduction of a stable negatively charged silver bromide sol is described. Phase transfer of the colloid to toluene is accomplished using tetra-n-octylammonium bromide as the phase transfer reagent. The advantage of this synthesis is to uncouple the formation of the silver halide colloid from its transfer and reduction in the organic phase, thus allowing control over each reaction step. The silver colloid in toluene was reduced with aqueous borohydride in the presence of 4-bromobenzenethiol as the passivating agent. The UV-visible absorption spectra indicate the intermediate formation of Ag(core)AgBr(shell) clusters during reduction. The resulting MPCs have been characterized by optical and transmission electron microscopy, energy-dispersive X-ray analysis, thermogravimetry, and UV-vis absorption spectroscopy. The formation of spiral cracks in the nanoparticulate agglomerates on solvent evaporation was observed. The spectra of thin films obtained by solvent evaporation have been analyzed using an effective medium theory.     

Silver nanocluster redox-couple-promoted nonclassical electron transfer: an efficient electrochemical Wolff rearrangement of alpha-diazoketones

In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.     

Kinetics of the formation of silver dimers: early stages in the formation of silver nanoparticles

Silver clusters too small to support a plasmon band possess interesting fluorescence properties as well as being a convenient route to studying the early stages of nanoparticle formation. Fluorescent silver clusters are synthesized in toluene solution, and the formation is monitored herein by laser flash photolysis (LFP). Kinetic analysis of the formation of the Ag clusters is consistent with the formation of the smallest possible clusters, silver dimers (Ag(2)), whereby a mechanism for the formation of these clusters is provided as well as the first reported extinction coefficient and association constant for Ag(0) to form Ag(2). The formation of Ag(2) clusters is contrasted with the formation of Ag nanoparticles in aqueous media, and the particular stability and selectivity toward Ag(2) in this system is also studied using LFP.     

Au/Ag核一壳结构复合纳米粒子形成机制的研究

在已制备好的Au纳米粒子表面,通过化学还原的方法沉积生长Ag包覆层,通过 控制Au, Ag的比列,制备了粒度均匀且粒径可控的Au/Ag核-壳结构纳米粒子。利用 UV-vis吸收光谱和透射电子显微镜（TEM）对SAu, Ag摩尔比为1：10的复合纳米粒 子的光学性质和形态进行随时监测,直接观察了核-壳结构纳米粒子的生长过程： 一部分Ag+在Au核表面还原生长,溶液中其余Ag+还原形成银的纳米团簇向粒子表面 的继续沉积生长,壳层增厚。     

Development kinetics of silver clusters on silver halides

Silver nuclei are produced by pulse radiolysis at the surface of AgCl nanocrystallites in the presence of an electron donor, the methyl viologen, which induces the growth of silver nuclei. The experimental results observed on the increase of the silver atom concentration and on the decay of the donor concentration during this process, which is similar to the photographic development by an electron donor, are compared with the kinetics obtained from numerical simulation. The model assumes that the formation of silver clusters with a supercritical nuclearity is required before the start of an electron transfer reaction from the two reduced forms of the donor methyl viologen to the silver clusters. The reaction is controlled by the access of the donor to the surface sites of the AgCl crystallite. The rate constant values of the successive steps of the mechanism are derived from the adjustment of calculated kinetics to experimental signals under various conditions, using a single set of parameters which are fairly suitable under all conditions studied.     

Use of dicyclohexano-18-crown-6 to separate traces of silver(I) from potassium thiocyanate in hydrochloric acid media,and determination of the silver by atomic absorption spectrometry

Solvent extraction with 0.05 mol L(-1) dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane, coupled with flame atomic absorption spectrometry (AAS), has been investigated as a new method for separation of trace amounts of silver(I) from 0.05 mol L(-1) potassium thiocyanate in 1.0 mol L(-1) hydrochloric acid media and quantification of the amount of silver present. The method is based on the formation of an extractable ion-association product, [DC18C6.K](+)[Ag(SCN)(2)](-), with a metal-to-crown ether ratio of 1:1 (as derived from slope analysis data). Stripping of the extracted silver(I) in the 1,2-dichloroethane phase was achieved within 5 min by use of 3.0 mol L(-1) potassium thiocyanate. Reducing the concentration of acid in the sample solution to 0.1 mol L(-1) improved the preconcentration factor severalfold. Excellent tolerance of the proposed method to the presence of foreign ions in solution with silver(I) was demonstrated. A detection limit of 13 ng mL(-1) was derived from the mean value of the blank plus three times its standard deviation. The method was used to determine traces of silver(I) after separation from gold(III), platinum(IV), and palladium(II) matrices on the basis of extractability differences with 18-membered crown ethers under specified conditions. The efficiency of the adopted ion-association mechanism for silver(I) extraction was apparent from the average recovery of 96% for spiked standards by use of the back-washing technique. The proposed extraction procedure was applied to the determination of traces of silver(I) in a selection of chemical reagents.     

A photoelectronic switching device using a mixed self-assembled monolayer

A cathodic-anodic biway photoelectronic device has been successfully constructed using a self-assembled monolayer (SAM). The SAM consists of two kinds of photofunctional thiol derivatives, a ruthenium complex-viologen linked compound (RuVS) and a phthalocyanine derivative (PcS), on a gold electrode. Structural characterization of the SAM has been carried out by absorption spectroscopy, cyclic voltammetry, and differential pulse voltammetry. Photocurrent responses were measured in the presence of methyl viologen (MV2+) and oxygen as electron acceptors and triethanolamine (TEOA) as a sacrificial reagent. For the SAM of RuVS alone, intramolecular electron transfer (ET) was superior to intermolecular ET, resulting in anodic photocurrents even in the presence of MV2+ and oxygen at 0 V vs Ag/AgCl. On the contrary, only cathodic photocurrents were observed at 0 V for the SAM of PcS alone. Photocurrents from the mixed SAM of RuVS and PcS were roughly the sum of individual photocurrents from RuVS and PcS. In fact, photocurrents from the mixed SAM of RuVS and PcS were observed in the anodic direction below approximately 550 nm, and in the cathodic direction above approximately 550 nm at 0 V vs Ag/AgCl. In the case of the mixed SAM of RuS (ruthenium complex disulfide) and PcS, only cathodic photocurrents were observed at 0 V vs Ag/AgCl, due to the lack of an intramolecular ET pathway. The results indicate that in the mixed SAM of RuVS and PcS both dyes can individually function for opposite photocurrent generation. We have also applied the mixed SAM as a photoelectronic logic device by using two LEDs (470 and 640 nm). The system clearly operated as an XOR logic device.     

Density functional study of the interaction of chlorine atom with small neutral and charged silver clusters

Chlorine adsorption on small neutral, anionic, and cationic silver clusters Ag(n) (n=2-7) has been studied using the PW91PW91 density functional method. It was found that the adsorption of chlorine on the lowest-energy bare clusters does not always produce the lowest-energy complexes. In addition, the binding of chlorine can greatly change the geometries of the silver clusters in some cases. Among various possible adsorption sites, bridge site is energetically preferred for the neutral Ag(n) while top site is energetically more preferred for the anionic Ag(n) with n< or =6. For cationic clusters, adsorptions on bridge and face sites have similar binding energies, which are much larger than those on top sites. Natural bond orbital analyses show that irrespective of charge state, electrons always transfer from silver atoms to adsorbate and silver acts like alkali metals in the interaction with chlorine atom. Significant odd-even alternation patterns in the properties of the complexes have been observed: Even-electron clusters often have higher ionization energies, lower electron affinities, and higher dissociation energies than their odd-electron neighbors. It was also found that chlorine atoms bind more strongly with odd-electron bare clusters than with even-electron bare clusters. These patterns reveal that even-electron clusters are more stable than odd-electron clusters.     

Catalytic activation of nitrobenzene on PVP passivated silver cluster: A DFT investigation

Poly(N‐vinyl‐2‐pyrrolidone) (PVP) has been used extensively to stabilize the surface of noble metal nanoparticles against aggregation and also to produce anisotropic nanostructures. Naturally, it is very important to understand the effect of such surface stabilization by PVP on the catalytic activity of these nanoparticles. This communication investigates through DFT calculations the electronic properties of PVP stabilized 13‐atom Ag cluster for catalytic activation of nitrobenzene (NB). These computations suggest that poly(N‐vinyl‐2‐pyrrolidone) (PVP) interact with silver (Ag) cluster mainly through oxygen atom and acts not only as a stabilizer to prevent the aggregation of Ag clusters but also as an electron donor to activate the Ag clusters for further reaction. Natural Bonding Orbital (NBO) calculations show that catalytic activation of NB by PVP passivated Ag cluster occurs due to interaction of the oxygen of the nitro group with the Ag cluster. Weak back donation of electrons from M(dπ) orbital of Ag to antibonding σ* of one of the N O bond, facilitates the formation of the nitroso intermediate. To understand the extent and the nature of this interaction better, vibrational frequency calculation of nitrobenzene association with Ag13‐2PVP cluster is carried out. Red shift in the frequencies is consequence of strong interaction with that of silver cluster present in Ag13‐2PVP‐NB model.     

含类立方烷银(Ⅰ)簇的光致蓝光配位聚合物的原位溶剂热合成

A blue photoluminescent coordination polymer [Ag₄Cl₄(dppe)₂]_n has been prepared solvothermally and characterized structurally. The crystal structure was determined by single-crystal X-ray diffraction. The crystal is of tetragonal, space group I4₁/a, a=b=1.936 03(6) nm, c=1.465 63(8) nm, V=5.493 5(4) nm³, Z=4, D_calcd=1.657 Mg·m^-3, μ=1.749 mm^-1. Reflections collected: 17 147, independent reflections: 3 247, R_int=0.021 1. Final R indices [I> 2σ(I)]: R₁=0.044 8, wR₂=0.111 0. The structure of [Ag₄Cl₄(dppe)₂]_n is a 3D-diamond highly symmetrical polymeric network containing Ag₄Cl₄ cubane-like clusters connected by 1,2-bis(diphenylphosphino)ethane (dppe). Each Ag₄Cl₄ cluster is composed of four silver and four chlorine atoms situated at alternate vertexes of a highly distorted cube with each silver atom being further coordinated to one phosphorus atom from a dppe ligand. The stripping of chloride ions from CHCl₃ provides the source for chlorine in the formation of Ag(Ⅰ) clusters. In addition, the emission spectrum of the complex 1 in solid state has been studied. CCDC: 288080.     

Self-assembly of Ag nanoparticle-biotin composites into long fiberlike microstructures

An end-to-end assembly of spherical Ag nanoparticles takes place in the presence of biotin to form long fiberlike microstructures. These microstructures are about 4 mum long with a thickness of 1 mum, obtained from SEM studies. TEM studies showed the presence of spherical silver nanoparticles having an average size of 20 nm. ATR-FTIR studies revealed that silver ions interact with biotin involving the carboxylate group. A weak binding of the silver particles with the thioether and ureido groups helps in connecting the Ag nanoparticles to form long fiberlike structures. Elucidation of the mechanism of formation of the spherical Ag clusters was done by pulse radiolysis.     

A novel nonenzymatic hydrogen peroxide sensor based on multi-wall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed based on multi-wall carbon nanotube/silver nanoparticle nanohybrids (MWCNT/Ag nanohybrids) modified gold electrode. The process to synthesize MWCNT/Ag nanohybrids was facile and efficient. In the presence of carboxyl groups functionalized multi-wall carbon nanotubes (MWCNTs), silver nanoparticles (Ag NPs) were in situ generated from AgNO₃ aqueous solution and readily attached to the MWCNTs convex surfaces at room temperature, without any additional reducing reagent or irradiation treatment. The formation of MWCNT/Ag nanohybrids product was observed by transmission electron microscope (TEM), and the electrochemical properties of MWCNT/Ag nanohybrids modified gold electrode were characterized by electrochemical measurements. The results showed that this sensor had a favorable catalytic ability for the reduction of H₂O₂. The resulted sensor could detect H₂O₂ in a linear range of 0.05-17 mM with a detection limit of 5 × 10⁻⁷ M at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.42 μA/mM at a potential of −0.2 V. Additionally, it exhibited good reproducibility, long-term stability and negligible interference of ascorbic acid (AA), uric acid (UA), and acetaminophen (AP).     

In situ depositing silver nanoclusters on silk fibroin fibers supports by a novel biotemplate redox technique at room temperature

Evolvement of bioinspired approaches for the construction of well-ordered nanostructures is a crucial intersection of branches of materials science and biotechnology. In this paper, floriated clusters of silver nanocrystallites, which consist of polycrystalline grains about 5 nm in diameter, have been successfully prepared on silk fibroin fibers (SFFs) through an in situ biotemplate redox approach at room temperature. The reductive amino acid tyrosine of SFFs mainly provided both reduction and location functions under alkaline conditions and could reduce Ag(I) ions to Ag(0). Finally, stable silver nanoclusters were generated on SFF substrates. The morphologies of silver nanoclusters were mostly attributed to the concentration of silver nitrate solution as well as special configurations and structures of silk fibroin macromolecules. A possible mechanism was explored intensively for tyrosine-residue-based silver nanocrystal formation.     

Gas phase synthesis and reactivity of Agn+ and Ag(n-1)H+ cluster cations

Multi-stage mass spectrometry (MSn) on [(M + Ag - H)x + Ag]+ precursor ions (where M = an amino acid such as glycine or N,N-dimethylglycine) results in the formation of stable silver (Ag3+, Ag5+ and Ag7+) and silver hydride (Ag2H+, Ag4H+ and Ag6H+) cluster cations in the gas phase. Deuterium labelling studies reveal that the source of the hydride can be either from the alpha carbon or from one of the heteroatoms. When M = glycine, the silver cyanide clusters Ag4CN+ and Ag5(H,C,N)+ are also observed. Collision induced dissociation (CID) and DFT calculations were carried out on each of these clusters to shed some light on their possible structures. CID of the Agn+ and Ag(n-1)H+ clusters generally results in the formation of the same Ag(n-2)+ product ions via the loss of Ag2 and AgH respectively. DFT calculations also reveal that the Agn+ and Ag(n-1)H+ clusters have similar structural features and that the Ag(n-1)H+ clusters are only slightly less stable than their all silver counterparts. In addition, Agn+ and Ag(n-1)H+ clusters react with 2-propanol and 2-butylamine via similar pathways, with multiple ligand addition occurring and a coupled deamination-dehydration reaction occurring upon condensation of a third (for Ag2H+) or a fourth (for all other silver clusters) 2-butylamine molecule onto the clusters. Taken together, these results suggest that the Agn+ and Ag(n-1)H+ clusters are structurally related via the replacement of a silver atom with a hydrogen atom. This replacement does not dramatically alter the cluster stability or its unimolecular or bimolecular chemistry with the 2-propanol and 2-butylamine reagents.     

过硫酸钾氧化偶氮荧光桃红催化光度法测定痕量银

以过硫酸盐氧化偶氮类试剂催化动力学法测定银,多数线性范围较窄、选择性欠佳。本文建立了以偶氮荧光桃红作指示物质、α,α′-联吡啶作活化剂的催化光度法,测定痕量银检出限为1.0×10^-4μg/mL,线性范围2.0×10^-4～4.0×10^-2μg/mL,灵敏度高,选择性好。用于测定鄂铜矿中银,结果满意。采用自装的微机动力学数据处理系统,测试简便、准确。     

银在甲烷选择性催化还原NOx反应中不同催化行为的研究

 采用XRD,TEM和UV－Vis方法研究了Ag－HZSM－5催化剂中活性组分银的价态和结构变化,并将这种变化与其在CH4选择性催化还原NOx反应中的活性和选择性相关联．结果表明,惰性气氛下高温处理使交换到分子筛阳离子位上的Ag＋自还原为Ag0,并在热的作用下聚集成纳米尺度的银颗粒Agn．纳米银颗粒Agn的形成提高了银催化剂在CH4选择性催化还原NOx反应中的活性,但它的长大又促进了CH4和O2的直接燃烧,使CH4选择性催化还原NOx反应的选择性降低．氧气气氛下高温预处理抑制了银颗粒的长大,并且氧气的氧化作用使银颗粒带有一定电荷,形成小的荷电纳米银粒子Agy＋x．荷电纳米银粒子的形成使催化剂的活性降低,但提高了CH4选择性催化还原NOx反应的选择性．     

The reduction process of phytic acid–silver ion system: A pulse radiolysis study

Reduction of silver ion in a silver–phytic acid (1:1 ratio) system has been studied using pulse radiolysis technique. Time-resolved transformation of the intermediates, Ag⁺→Ag⁰→Ag₂⁺→Ag₃²⁺, has been clearly observed in the reduction of silver–phytic acid (1:1) system. The effect of phytic acid on the formation and decay of initial silver clusters has been also studied. The surface plasmon absorption band of stable silver nanoparticle (410 nm) and dynamic light scattering technique has been used to characterize the nanoparticles and measure the average size (R_av=100 nm).     

水合肼在BmimPF_6银电极上的电化学行为研究

应用电化学循环伏安法,以银作工作电极研究了水合肼在离子液体BmimPF6中的氧化过程.结果显示,银离子对水合肼的氧化过程具有催化作用,其氧化峰电位0.16V(vs.SCE)电催化反应速率决定步骤为1电子的氧化还原过程.在0～3.4mmol/L肼浓度范围内,催化反应峰电流与肼浓度间具有良好的线性关系.     

Structure, bonding, and linear optical properties of a series of silver and gold nanorod clusters: DFT/TDDFT studies

DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag(n), Au(n), n = 12-120) whose structures are of cigar-type. Pentagonal Ag(n) clusters with n = 49-121 and hexagonal Au(n) clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag(n) clusters. Many differences in the calculated properties are found between the Ag(n) and Au(n) clusters, which can be explained by relativistic effects.     

Infrared spectra of the (AgCO)2 and AgnCO (n=2-4) molecules in rare-gas matrices

Reactions of laser-ablated silver atoms with carbon monoxide molecules in solid argon and neon have been investigated using matrix-isolation IR spectroscopy. Small silver cluster carbonyls, (AgCO)2 and AgnCO (n=2-4), as well as mononuclear silver carbonyls, Ag(CO)2 and Ag(CO)3, are generated upon sample annealing in the argon experiments and are characterized on the basis of the isotopic substitution, the CO concentration change, and the comparison with theoretical predictions. However, these polynuclear carbonyls are absent from the neon experiments. Density functional theory calculations have been performed on these silver carbonyls and the corresponding ligand-free silver clusters, which support the identification of these silver carbonyls from the matrix IRspectrum. A terminal CO has been found in the most stable structures of (AgCO)2, Ag2CO, Ag3CO, and Ag4CO. Furthermore, a plausible reaction mechanism has been proposed to account for the formation of the (AgCO)2 and AgnCO (n=2-4) molecules.