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1.
Ulrich-Walter Grummt Matthias Geissler Till Drechsler Harald Fuchs Ralf Staub 《Angewandte Chemie (International ed. in English)》1998,37(23):3286-3289
Small silver clusters Ag n (primarily probably Ag4 clusters which aggregate to Agn (400<n<2000)) are generated in the immediate vicinity of a four-electron reducing agent (based on hydroquinone) which is incorporated in a monolayer of long-chain alkanethiols. The hydroquinone derivative is oxidized to quinone (see the picture). Molecularly resolved scanning tunneling microscopy (STM) images were obtained of self-assembled monolayers with and without silver clusters. 相似文献
2.
Different Silver Nanoparticles in One Crystal: Ag210(iPrPhS)71(Ph3P)5Cl and Ag211(iPrPhS)71(Ph3P)6Cl
Jun‐Yan Liu Fahri Alkan Zhi Wang Zhen‐Yi Zhang Mohamedally Kurmoo Zier Yan Quan‐Qin Zhao Christine M. Aikens Chen‐Ho Tung Di Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(1):201-205
Two pure silver nanoparticles (Ag210(iPrPhS)71(Ph3P)5Cl and Ag211(iPrPhS)71(Ph3P)6Cl labeled as SD/Ag210 and SD/Ag211 (SD=SunDi), were found to co‐crystallize in forming compound 1 . Single‐crystal X‐ray diffraction (SCXRD) revealed that they differ by only one Ag(PPh3). Their four‐shell nanoparticles consist of three pure Ag metal shells (Ag19@Ag52@Ag45) shielded by a silver‐organic Ag89(iPrPhS)71Cl[Ag(Ph3P)]n outermost shell. The number (n) of Ag(Ph3P) is five for SD/Ag210 and six for SD/Ag211. The pseudo‐fivefold symmetric Ag nanoparticles exhibit surface plasmon absorption similar to a true metallic state but at the nanoscale. This work exemplifies the important effects of phosphine in stabilizing large silver nanoparticles; and offers a platform to investigate the origin of differences in nanoscale metal materials, even differing by only one metal atom; it also sheds light on the regioselective binding of auxiliary Ph3P on the surface of silver nanoparticles. 相似文献
3.
G5.0‐OH PAMAM dendrimers were used to prepare fluorescent silver clusters with weaker ultraviolet irradiation reduction method, in which the molar ratio of Ag+ to PAMAM dendrimers was the key factor to determine the geometry and properties of silver nanoparticles. The results showed that because of G5.0‐OH PAMAM dendrimers as strong encapsulatores, when the molar ratios of Ag+ to PAMAM dendrimers was smaller than 5, the obtained Agn clusters (n<5) had line structures and "molecular‐like" properties, which were highly fluorescent and quite stable in aqueous solution. Whereas when the molar ratios were between 5 and 8, the obtained Agn clusters were 2D structures and their fluorescence was weaker. When the molar ratio was larger than 8, the structure of silver nanoparticles was 3D and no fluorescence was observed from the obtained silver nanoparticles. 相似文献
4.
Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag
n
H (n = 1–10) clusters. For the lowest energy geometries of Ag
n
H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold
coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag
n
structures are slightly perturbed and only the Ag6 structure in Ag6H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation
like the strength of Au–H bond in Au
n
H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption
strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the
strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed
in Ag
n
H systems, indicating that the Ag
n
H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver
cluster. 相似文献
5.
Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters
Zhen‐Yi Jiang Yu‐Qin Hou Kuo‐Hsing Lee San‐Yan Chu 《International journal of quantum chemistry》2009,109(6):1348-1356
The structures and relative stabilities of high‐spin n+1Aun?1Ag and nAun?1Ag+ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Aun?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Aun clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Aun?1Ag neutral and cationic species, 5Au3Ag, 3AuAg and 5Au4Ag+ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
6.
Shuang Zhao Yunlai Ren Yunli Ren Jianji Wang Weiping Yin 《International journal of quantum chemistry》2011,111(10):2428-2435
Small AgnPd (n = 5) clusters and their hydrides AgnPdH (n = 5) have been studied by density functional theory calculations. For bare clusters, the structures in which the Pd atom has a maximum number of neighboring Ag atoms tend to be energetically favorable. Hydrogen prefers binding to Ag? Pd bridge site of AgnPd clusters except for Ag5Pd. The binding energy has a strong odd–even oscillation. The electron transfers are from Ag atoms to Pd in bare clusters and are from metal clusters to H in cluster hydrides. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
7.
A Facile Molecular Precursor‐based Synthesis of Ag2Se Nanoparticles and Its Composites with TiO2 for Enhanced Photocatalytic Activity
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Dr. Shashank Mishra Dan Du Dr. Erwann Jeanneau Frederic Dappozze Dr. Chantal Guillard Prof. Jinlong Zhang Prof. Stéphane Daniele 《化学:亚洲杂志》2016,11(11):1658-1663
The reactions of different silver(I) reagents AgX (X?=iodide, trifluoroacetate, triflate) with selenoethers R2Se (R=Me, tBu) in a variety of solvents were investigated in relation with their use as precursors for Ag2Se nanomaterials. Different reaction conditions led to different reactivities and afforded either molecular complexes or metal selenide nanoparticles. The reactions leading to in situ formation of the metal selenide nanoparticles were then extended in the presence of commercial TiO2 (P25) to prepare silver selenide–titania nanocomposites with different Ag/Ti ratios. These nanocomposites, well characterized by elemental analysis (Ag, Se), PXRD, TEM, BET, XPS and UV/Vis studies, were investigated as photocatalysts for the degradation of formic acid (FA) solution. The xAg2Se‐TiO2 nanocomposites (x=0.01, 0.13 and 0.25 mol %) exhibited a much higher catalytic activity as compared to P25, which is an established benchmark for the photocatalysis under UV light, and retained a good photocatalytic stability after recycling for several times. 相似文献
8.
O. A. Boryak M. V. Kosevich V. V. Chagovets V. S. Shelkovsky 《Journal of Analytical Chemistry》2017,72(13):1289-1294
In the problem of the production silver nanoparticles, mass spectrometry allows one to identify nanoclusters as nuclei or intermediates in the synthesis of nanoparticles and to understand the mechanisms of their formation. Using low-temperature secondary emission mass spectrometry, we determined the cluster composition of a system formed in the microwave treatment of a solution of AgNO3 in ethylene glycol (M). Along with silver ion–ethylene glycol associates М m ? Ag+ (m = 1–5) and small silver clusters AgM n + (n = 1–9), unusual silver clusters with one hydrogen atom [Ag n H]+ (n = 2, 4) were observed. Possible pathways for the formation of silver nanoparticles taking into account hydrogen-containing cluster intermediates are discussed. 相似文献
9.
Shan Wang Jie Bai Chunping Li Yongfeng Zhang Jianbin Zhang 《Colloid and polymer science》2012,290(7):667-672
Ag nanoparticle-embedded one-dimensional β-CD (β-cyclodextrin)/PVP composite nanofibers were prepared using a one-step electrospinning
technique. Ag nanoparticles were obtained in the AgNO3/β-CD/DMF solution, in which silver nitrate been introduced as the precursor, DMF as solvent, β-CD as reducing and capping
agent. After electrospinning of the composite solution at room temperature, the β-CD/PVP nanofibers containing Ag nanoparticles
were obtained. The electrospun composite solution containning Ag nsnopsrticles were confirmed by UV-visible absorption spectra;
the resulting composite nanofibers were characterized by scanning electron microscopy , transmission electron microscopy,
and X-ray diffraction. Ag-β-CD/PVP nanofiber exhibits good antibacterial property for Escherichia coli and Staphylococcus aureus. Consequently, we propose that these Ag nanoparticle-embedded 1D-nanostructures prepared via electrospinning may be used
as antibacterial material. 相似文献
10.
Masahiro Inoue Yamato Hayashi Hirotsugu Takizawa Katsuaki Suganuma 《Colloid and polymer science》2010,288(10-11):1061-1069
Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag2O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag2O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag+ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag+ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag+, Ag 4 2+ and Agn (n?≈?3). The Agn clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag2O particles with ethanol under ultrasonication. The reactions of Ag+ ions in ethanol to form Ag nanomaterials (through the formation of Ag 4 2+ clusters) were also accelerated by ultrasonication. 相似文献
11.
Guang-nian Xu Xue-liang Qiao Xiao-lin Qiu Jian-guo Chen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,320(1-3):222-226
Silver nanoparticles were synthesized by UV irradiation of [Ag(NH3)2]+ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag2O was much quicker than that from AgNO3, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λmax) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH3)2]+ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C). 相似文献
12.
Yejun Li Prof. Jonathan T. Lyon Alex P. Woodham Dr. André Fielicke Prof. Ewald Janssens 《Chemphyschem》2014,15(2):328-336
Cationic silver‐doped silicon clusters, SinAg+ (n=6–15), are studied using infrared multiple photon dissociation in combination with density functional theory computations. Candidate structures are identified using a basin‐hopping global optimizations method. Based on the comparison of experimental and calculated IR spectra for the identified low‐energy isomers, structures are assigned. It is found that all investigated clusters have exohedral structures, that is, the Ag atom is located at the surface. This is a surprising result because many transition‐metal dopant atoms have been shown to induce the formation of endohedral silicon clusters. The silicon framework of SinAg+ (n=7–9) has a pentagonal bipyramidal building block, whereas the larger SinAg+ (n=10–12, 14, 15) clusters have trigonal prism‐based structures. On comparing the structures of SinAg+ with those of SinCu+ (for n=6–11) it is found that both Cu and Ag adsorb on a surface site of bare Sin+ clusters. However, the Ag dopant atom takes a lower coordinated site and is more weakly bound to the Sin+ framework than the Cu dopant atom. 相似文献
13.
《International journal of quantum chemistry》2018,118(3)
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. 相似文献
14.
《Journal of Coordination Chemistry》2012,65(1):155-168
A polymeric silver(I) complex, [Ag4(μ-pydc)2(μ-pm)2]n (1) (pydc = pyridine-3,5-dicarboxylate and pm = pyrimidine), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. X-ray crystallographic data of 1 revealed that pydc exhibits two different coordinaton modes that play a key role in the construction of the 3-D crystal network including Ag–carboxylate clusters in which close Ag–Ag distances exist. The magnitudes of close Ag–Ag interactions in second-order energy (E2) have been revealed by natural bond orbital analysis performed with single point energy calculation using the experimental geometry of 1. Furthermore, the luminescent properties of 1 show strong fluorescence with two emission maxima in the visible region. Also, 1 has antifungal activity on Candida albicans (MIC value, 4 μg mL?1) and good antibacterial activity on micro-organisms (MIC value, 64–256 μg mL?1). 相似文献
15.
Mingquan Yu Gun‐hee Moon Rebeca G. Castillo Serena DeBeer Claudia Weidenthaler Harun Tüysüz 《Angewandte Chemie (International ed. in English)》2020,59(38):16544-16552
Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag2O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag2O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co3O4 at 1.7 VRHE is increased from 102 to 211 mA cm?2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co3O4. 相似文献
16.
Xueqin Wang Hao Wen Tianjing He Jian Zuo Cunyi Xu Fan-Chen Liu 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2495-2504
Surface enhancement mechanism of Raman scattering from molecules adsorbed on silver oxide colloids is reported. Absorption spectra and Raman spectra of the cyanine dye D266 and pyridine molecules adsorbed on Ag2O colloids, and the influences of S2O32− and OH− on the SERS are studied respectively. The results indicate that ‘chemical' enhancement is dominant in Ag2O colloidal solution. Surface complexes of adsorbed molecules and small silver ion clusters Agn+ as the SERS active sites make an important contribution to surface enhanced Raman scattering (SERS). At these active sites, charge transfer between the adsorbed molecules and the small silver ion clusters is the main enhancement origin. The enhancement factor of D266 adsorbed on Ag2O colloids is theoretically estimated with the excited-state charge transfer model, which is roughly in accordance with the experiments. 相似文献
17.
The complex formation of silver(I) has been studied with the anions of simple mercaptans RSH which have been rendered soluble by replacing some H in the substituent R by OH. All equilibria constants refer to a solvent of ionic strength μ = 0,1 and 20°C. Monothioglycol HO? CH2? CH2? SH (pK = 9.48) forms an amorphous insoluble mercaptide {AgSR} (s), ionic product [Ag+] [SR?] = 10?19.7. The solution in equilibrium with the solid contains the molecule AgSR at a constant concentration of 10?6.7 M which furnishes the formation constant of the 1:1-complex: K1 = 1013. 0. The solid is soluble in excess of mercaptide (AgSR+SR? → Ag(SR)2?: K2 = 104. 8) as well as in an excess of silver ion (AgSR + Ag+ → Ag2SR+K ≈? 106). With the bulky monothiopentaerythrite (HO? CH2? )3C? CH2? SH (pK = 9.89) no precipitation occurs with silver when the mercaptan concentration is below 10?3. 2M. A single polynuclear Ag10(SR)9+ (β10.9 = 10175) is formed in acidic solutions which breaks up with the formation of Ag2SR+ (β2.1 = 1019.0) when an excess of silver ion is added. Below the mononuclear wall ([RS]total < 10?6) Ag2SR+ is formed via the mononuclear AgSR (K1 = 1013). At higher mercaptan concentrations ([RS]tot > 10?3.2) an amorphous precipitate is formed which has almost the same solubility product as silver thioglycolate ([Ag+] [SR?] = 10?19.1). Apparently silver(I) forms with mercaptans always the complexes Ag2SR+, AgSR and Ag(SR)2?. Above the mononuclear wall, these species condense to chain-like polynuclears which are cations Ag(SRAg)n+ in presence of an excess of Ag+, and anions SR (AgSR)n? when the concentration [RS?] is larger than [Ag+]. Usually n becomes rapidly very large as soon as the condensation starts (n → ∞: precipitate). The decanuclear Ag(SRAg)9+ formed with thiopentaerythrit is somewhat more stable than the shorter chains (n < 9) and larger chains (n > 9), because it can tangle up to a ball by coordination of bridging mercapto-sulfur to the terminal silver ions (figure 12, page 2179). This ball seems to be further stabilized by hydrogen bonds between the many alcoholic OH groups of the substituent R = (HO? CH2)3C? CH2? . The stability of the bonds Ag? S, however, is little influenced by the substituent R which carries the mercaptide sulfure. 相似文献
18.
Yu Wang Xiao‐He Liu Qiankun Wang Martin Quick Sergey A. Kovalenko Qing‐Yun Chen Norbert Koch Nicola Pinna 《Angewandte Chemie (International ed. in English)》2020,59(20):7748-7754
The deposition of an atomically precise nanocluster, for example, Ag44(SR)30, onto a large‐band‐gap semiconductor such as TiO2 allows a clear interface to be obtained to study charge transfer at the interface. Changing the light source from visible light to simulated sunlight led to a three orders of magnitude enhancement in the photocatalytic H2 generation, with the H2 production rate reaching 7.4 mmol h?1 gcatalyst?1. This is five times higher than that of TiO2 modified with Ag nanoparticles and even comparable to that of TiO2 modified with Pt nanoparticles under similar conditions. Energy band alignment and transient absorption spectroscopy reveal that the role of the metal clusters is different from that of both organometallic complexes and plasmonic nanoparticles: A type II heterojunction charge‐transfer route is achieved under UV/Vis irradiation, with the cluster serving as a small‐band‐gap semiconductor. This results in the clusters acting as co‐catalysts rather than merely photosensitizers. 相似文献
19.
The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C3H8-SCR conditions. The UV–VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Agnδ+ clusters due to partial reduction and agglomeration of Ag species. The coincidence of the formation of the Agnδ+ clusters and the increment of NO conversion suggests that Agnδ+ clusters are the highly active species for HC-SCR. From analysis by H2-TPR, UV–VIS, and EXAFS, the structure of Agnδ+ clusters on Ag-MFI is identified as being Ag42+ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag+ ions for MOR, Agnδ+ clusters for MFI and BEA, and relatively large metallic Agmparticles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Agnδ+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Agnδ+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O2) and reductants (H2, HC), and also on the number and strength of the zeolite acid sites. 相似文献
20.
Alexander Vvedenskii Svetlana Grushevskaya Dmitrii Kudryashov Sergei Ganzha 《Journal of Solid State Electrochemistry》2010,14(8):1401-1413
The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i ph and photopotential E ph measurements, the n-type conductivity of Ag2O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i ph ~L and E ph ~L 2. The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag2O. The parameters of Ag2O film (optical absorption coefficient α, donor defects concentration N D, space charge region W, and Debye’s length of screening L D) depend on the index of a crystal face of silver, volume concentration of gold X Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag2O formed on Agpoly, Aghkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Agpoly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag2O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer. 相似文献