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负载金催化剂上CO氧化反应活性与金属氧化物载体中金属-氧结合能之间的关系 总被引:1,自引:0,他引:1
Takashi Fujita Masanori Horikawa Takashi Takei Toru Murayama Masatake Haruta 《催化学报》2016,(10):1651-1655
讨论了金属氧化物载体(MOx)对其负载纳米金催化剂(Au/MOx)上CO氧化反应的影响。采用典型的共沉淀法和沉积-沉淀法在完全相同的焙烧条件下制备了一系列MOx负载金催化剂,以CO氧化转化50%时的反应温度(T1/2)定量评价了MOx载体和Au/MOx催化剂的催化活性。进一步将MOx载体与相应Au/MOx催化剂的T1/2值之差对MOx载体的金属-氧结合能做曲线进行关联,发现二者呈明显的火山型关系。这一结果表明,采用具有适当金属-氧结合能(300–500 atom O)的MOx可大大提高沉积于其上的Au纳米颗粒的催化活性。 相似文献
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研究了[Ru(bpy)3]2+溶液中引入纳米银粒子的光谱学性质变化规律以及[Ru(bpy)3]2+与纳米银粒子所构成的溶液体系([Ru(bpy)3]2+-Ag)的电解质效应.研究结果表明,[Ru(bpy)3]2+吸附在纳米银粒子表面使纳米银粒子相互桥连形成规则的类链状网络聚集体.纳米银粒子造成[Ru(bpy)3]2+溶液荧光猝灭,且大尺寸的纳米银粒子引起的荧光猝灭程度较大.在[Ru(bpy)3]2+-Ag体系中引入电解质造成纳米银粒子不同程度的聚集和生长.电解质对纳米银聚集影响为:CaCl2MgCl2Ca(NO3)2KClKNO3.随着[Ru(bpy)3]2+-Ag体系中引入电解质含量的增加,溶液的荧光强度先降低而后又逐渐增强,直至达到定值,表明一定量的电解质可产生荧光猝灭释放效应.电解质对荧光强度影响顺序为:Ca(NO3)2CaCl2MgCl2KClKNO3.采用透射电子显微镜、紫外-可见吸收分光光度计和荧光分光光度计等手段从分子间相互作用和能量传输等方面初步探讨了纳米银粒子对表面吸附[Ru(bpy)3]2+溶液光谱学性质的影响机制以及电解质效应. 相似文献
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在琥珀酸二异辛酯磺酸钠(AOT)为表面活性剂、环己烷为连续相形成的微乳体系中, 利用水合肼还原AgNO3制备了分散性良好的纳米银. 利用紫外-可见(UV-Vis)光谱和透射电镜(TEM)对所得产物进行了表征, TEM显微图像表明形成粒子为球形结构, 平均粒径为5.10 nm, 标准偏差为2.84 nm. 分别利用正己烷、正庚烷、正辛烷、环己烷和十二烷等作连续介质, 研究了微乳液中连续相对纳米银形成的影响. 随着正烷烃碳链长度的增加, 微乳液中胶束之间的交换速率增大, 形成粒子的平均粒径逐渐减小. 十二烷形成的微乳体系制备的纳米银溶胶具有最宽的共振吸收峰, 所得的纳米银粒子平均粒径最小. 环己烷形成的微乳液中反胶束具有特殊的界面强度, 导致纳米银晶核的形成速率过低, 纳米银晶粒的生长不完全. 相似文献
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Priyanka Murawala S.M. Phadnis R.R. Bhonde B.L.V. Prasad 《Colloids and surfaces. B, Biointerfaces》2009,73(2):224-228
A simple and convenient one step room temperature method is described for the synthesis of bovine serum albumin (BSA) capped gold and silver nanoparticles. BSA reduces silver ions to silver nanoparticles but does not directly reduce gold ions to gold nanoparticles at room temperature and varying pH conditions. However, when silver and gold ions are simultaneously added to BSA, silver ions get reduced to metallic silver first and these in turn reduce gold ions to gold nanoparticles through a galvanic exchange reaction. The so synthesized silver and gold nanoparticles are easily water dispersible and can withstand addition of salt even at high concentrations. It is shown that the capped protein retains its secondary structure and the helicity to a large extent on the nanoparticles surface and that the protein capping makes the nanoparticles cytocompatible. 相似文献
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Jagdeep Singh 《Analytical letters》2019,52(2):213-230
Bioinspired silver nanoparticles were synthesized using nontoxic, eco-friendly, and novel root extract of Nepeta leucophylla. The reduction of silver nitrate salt into nanoparticles is performed using the root extract, which is rich in polyphenolic and flavonoid contents. The reduction of silver salt by this extract is occurred at several temperatures and the reaction mixture turns brown and displayed representative absorbance spectra of silver nanoparticles. The influence of numerous synthesis parameters such as the concentration of root extract, time, temperature, and reaction pH on the synthesis of silver nanoparticles was also examined. Furthermore, the synthesized silver nanoparticles were characterized by ultraviolet–visible spectroscopy, Fourier transformed infrared spectroscopy, X-ray diffraction, and transmission electron and field emission scanning electron microscopy. The formation of silver nanoparticles was enhanced with time, temperature, and at basic pH. The surface plasmon resonance band characteristics of silver nanoparticles were detected at 410?nm in the ultraviolet–visible absorbance spectra. The infrared spectroscopy results show that the extract contains phenol which is responsible for reduction and proteins may be capping the silver nanoparticles which prevent agglomeration. Transmission electron microscopy revealed that silver nanoparticles were spherical and the sizes matched well with X-ray diffraction and theoretical calculations by Mie theory. Furthermore, the antioxidant potential of the synthesized silver nanoparticles was assessed using 2,2-diphenyl-1-picrylhydrazyl assay and showed considerable antioxidant potential. 相似文献
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纳米银对表面吸附荧光素的荧光增强和荧光猝灭效应及KCl的荧光猝灭释放效应 总被引:1,自引:0,他引:1
制备了两种不同粒径的纳米银溶胶,研究了在水溶液条件下其对表面吸附荧光素(FL)的荧光性能的影响及KCl电解质对该体系荧光性能的影响。FL溶液中加入纳米银,FL分子吸收峰位发生红移。随着纳米银浓度的增加,FL分子荧光先出现增强,而后又逐渐猝灭。粒径较大的纳米银产生最大荧光增强比率所需浓度较低。在纳米银猝灭FL分子荧光的溶液中加入KCl电解质,随着KCl浓度的增加,荧光逐渐增强,出现了荧光猝灭释放效应。研究结果表明,纳米银对表面吸附FL的荧光作用与FL分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程决定并与纳米银的浓度、尺寸及电解质等密切相关。 相似文献
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Mengtao Sun Lixin Xia Maodu Chen 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):509-514
Self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles were investigated experimentally with surface-enhanced Raman scattering (SERS) and theoretically with density functional theory (DFT) and finite difference time domain (FDTD) method. The absorption spectroscopy of 1,4-BDT in silver sol at different time intervals was measured, which give the indirect evidence of self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles. To obtain the direct evidence of self-assembled dynamics of silver nanoparticles and self-assembled dynamics of 1,4-benzenedithiol (1,4-BDT) adsorbed on silver nanoparticles, the SERS of 1,4-BDT were measured experimentally and investigated theoretically. The appearances of S–S stretching band (revealing the formation of multilayers of 1,4-BDT), and strongly enhanced S–C stretching, C–C ring stretching vibrational modes clearly show self-assembled dynamics of 1,4-BDT. 相似文献
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《Journal of Dispersion Science and Technology》2013,34(4):375-388
Abstract The future prospect of silver halide imaging materials was outlined and proceeded to the elucidation of the nanoparticles and nanotechnology, which would contribute to it. They include silver halide grains, J‐aggregates of sensitizing dyes, dispersions of dyes and couplers, silver nanoparticles and nanowires. A focus is placed on the combination of silver clusters and nanoparticles with silver halide grains, which makes greatest contribution to high performance of silver halide imaging materials. 相似文献
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Her Shuang Toh Christopher Batchelor-McAuley Kristina Tschulik Richard G. Compton 《中国科学:化学(英文版)》2014,57(9):1199-1210
The interaction between citrate capped silver nanoparticles and two different thiols, mercaptohexanol(MH) and cysteine, was investigated. The thiols interacted with silver nanoparticles in a significantly contrasting manner. With MH, a sparingly soluble silver(I) thiolate complex AgSRm(Rm = –(CH2)6OH) was formed on the silver nanoparticle surface. Cyclic voltammograms and UV-vis spectra were used to infer that the AgSRm complex on the nanoparticle surface undergoes a phase transition to give a mixture of AgSRm and Ag2S-like complexes. In contrast, when silver nanoparticles were exposed to cysteine, the citrate capping agent on the silver nanoparticles was replaced by cysteine to give cysteine capped nanoparticles. As cysteine capped nanoparticles form, the electrochemical data displayed a decrease in oxidative peak charge but the UV-vis spectra showed a constant signal. Therefore, cysteine capped nanoparticles were suggested to have either inactivated the silver surface or else promoted detachment from the electrode surface. 相似文献
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Silver nanoparticles stabilized in a solution of sodium carboxymethyl cellulose with a degree of substitution of 0.85 and a degree of polymerization of 600 have been synthesized. The structuring; physical, chemical, and mechanical properties; and antimicrobial activities of films prepared from sodium carboxymethyl cellulose solutions containing silver nanoparticles have been studied. The shapes, quantities, and sizes of the silver nanoparticles occurring in the sodium carboxymethyl cellulose films were determined with the use of transmission electron microscopy, atomic force microscopy, and UV spectroscopy. It was found that an increase in the concentration of silver nitrate in sodium carboxymethyl cellulose solutions, as well as photoirradiation of the films, leads to the changes in the sizes and shapes of silver nanoparticles. The shapes, sizes, and quantities of silver nanoparticles determine their biological activity. An increase in the quantity of 5- to 25-nm silver nanoparticles was found to enhance the microbicidal activities of the carboxymethyl cellulose films. 相似文献
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J. Luis Lopez-Miranda M. A. Vázquez González F. Mares-Briones J. A. Cervantes-Chávez R. Esparza G. Rosas R. Pérez 《Research on Chemical Intermediates》2018,44(12):7479-7490
In this work, silver nanoparticles were synthesized using Salvia microphylla Kunth leaves extract as reducing agent and stabilizing agent. The effect of reaction time and plant extract amount on the biosynthesized nanoparticles were studied. The UV–Vis spectrum indicated that silver nanoparticles show a characteristic surface plasmon resonance at 427 nm. X-ray diffraction experiments show that the silver nanoparticles have a face-centered cubic crystal structure. The density of nanoparticles increases with increasing extract concentration and reaction time. TEM and SEM observations showed well-dispersed quasi-spherical nanoparticles sized in the range of 15–45 nm. The FT-IR analysis suggested the involvement of phenolic compounds in the reduction and stabilization of silver nanoparticles. Synthesized silver nanoparticles showed good antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Finally, the catalytic properties of silver nanoparticles were demonstrated through the degradation of congo red and methyl orange. 相似文献
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In the ultrasonic field, stable silver colloids were produced by the reduction of AgNO3 with the protection of PVP using KBH4 or N2H4·H2O as reductant. The main factors affecting the morphology of silver nanoparticles, such as distribution of the ultrasonic
field, ultrasonic time, ultrasonic power, and the species of reductant, were studied. The silver colloids were identified
by TEM and spectrophotometry. The results indicate that the factors such as distribution of the ultrasonic field, ultrasonic
time, ultrasonic power, and the species of reductant have a great impact on the morphology of the silver nanoparticles. The
size of the silver nanoparticles decreases with the ultrasonic power and ultrasonic time increasing. Ag nanoparticles prepared
in standing wave field preferentially grow in a certain direction, which is propitious for forming hexagonal-and spherical-like
silver nanoparticles. Monodispersed spherical silver nanoparticles are easily synthesized in the diffusion field. The stability
of silver colloid becomes improved by ultrasonic treatment. For example, precipitate is not found after several weeks for
the silver colloid prepared with an ultrasonic treatment time of 180 min. The silver nanoparticles prepared without ultrasonic
treatment are large spherical-like and hexagonal. Well-dispersed spherical silver particles with a mean size of about 20 nm
have been prepared under ultrasonic treatment. Spherical, spherical-like, and hexagonal silver nanoparticles can be obtained
by changing the reductants.
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Translated from Journal of Tianjin University, 2006, 39(1) (in Chinese) 相似文献
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The hydration of mesityl oxide (MOx) was investigated through a sequential quantum mechanics/molecular mechanics approach.
Emphasis was placed on the analysis of the role played by water in the MOx syn–anti equilibrium and the electronic absorption spectrum. Results for the structure of the MOx–water solution, free energy of solvation
and polarization effects are also reported. Our main conclusion was that in gas-phase and in low-polarity solvents, the MOx
exists dominantly in syn-form and in aqueous solution in anti-form. This conclusion was supported by Gibbs free energy calculations in gas phase and in-water by quantum mechanical calculations
with polarizable continuum model and thermodynamic perturbation theory in Monte Carlo simulations using a polarized MOx model.
The consideration of the in-water polarization of the MOx is very important to correctly describe the solute–solvent electrostatic
interaction. Our best estimate for the shift of the π–π* transition energy of MOx, when it changes from gas-phase to water solvent, shows a red-shift of −2,520 ± 90 cm−1, which is only 110 cm−1 (0.014 eV) below the experimental extrapolation of −2,410 ± 90 cm−1. This red-shift of around −2,500 cm−1 can be divided in two distinct and opposite contributions. One contribution is related to the syn → anti conformational change leading to a blue-shift of ~1,700 cm−1. Other contribution is the solvent effect on the electronic structure of the MOx leading to a red-shift of around −4,200 cm−1. Additionally, this red-shift caused by the solvent effect on the electronic structure can by composed by approximately 60 %
due to the electrostatic bulk effect, 10 % due to the explicit inclusion of the hydrogen-bonded water molecules and 30 % due
to the explicit inclusion of the nearest water molecules. 相似文献
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Ken-Tye Yong Yudhisthira Sahoo Mark T. Swihart Paras N. Prasad 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):89-105
Simple methods of preparing silver and gold nanoshells on the surfaces of monodispersed polystyrene microspheres of different sizes as well as of silver nanoshells on free-standing gold nanoparticles are presented. The plasmon resonance absorption spectra of these materials are presented and compared to predictions of extended Mie scattering theory. Both silver and gold nanoshells were grown on polystyrene microspheres with diameters ranging from 188 to 543 nm. The commercially available, initially carboxylate-terminated polystyrene spheres were reacted with 2-aminoethanethiol hydrochloride (AET) to yield thiol-terminated microspheres to which gold nanoparticles were then attached. Reduction of silver nitrate or gold hydroxide onto these gold-decorated microspheres resulted in increasing coverage of silver or gold on the polystyrene core. The nanoshells were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis spectroscopy. By varying the core size of the polystyrene particles and the amount of metal (silver or gold) reduced onto them, the surface plasmon resonance of the nanoshell could be tuned across the visible and the near-infrared regions of the electromagnetic spectrum. Necklace-like chain aggregate structures of gold core–silver shell nanoparticles were formed by reducing silver nitrate onto free citrate-gold nanoparticles. The plasmon resonance absorption of these nanoparticles could also be systematically tuned across the visible spectrum. 相似文献
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Preparation and study of polyacryamide-stabilized silver nanoparticles through a one-pot process 总被引:2,自引:0,他引:2
Chen M Wang LY Han JT Zhang JY Li ZY Qian DJ 《The journal of physical chemistry. B》2006,110(23):11224-11231
A one-pot route was illustrated to synthesize stable well-dispersed silver colloids stabilized by polyacrylamide on a large scale. Reduction of silver ions and polymerization of acrylamide occurred almost simultaneously in the absence of a commonly used reducing agent and initiator. A possible mechanism for the formation of silver nanoparticles with bimodal size distribution was proposed. The structure and composition of the obtained nanoparticles were characterized carefully. Furthermore, light scattering simulation and UV-vis absorption studies confirmed that the obtained colloids were the mixture of Ag and Ag2O nanoparticles. The presence of silver oxide layers on the nanoparticle surface should be responsible for the broadening of the surface plasmon band of silver nanoparticles. Ag2O layers could be added or removed from Ag nanoparticle surfaces by the addition of HNO3, HAc, or NaCl solution to the as-obtained silver colloids. 相似文献