金属纳米颗粒的热导率

本文使用统计模拟方法对金属纳米颗粒的电子平均自由程进行了计算,并考察了纳米颗粒的晶格比热和声子平均群速度,最后应用动力学理论对纳米颗粒的电子热导率和声子热导率分别进行了求解.研究结果表明:具有相同特征尺寸的方形、球形纳米颗粒的无量纲电子(或声子)平均自由程比较接近.金属纳米颗粒的电子热导率远大于声子热导率;电子、声子热导率随着直径减小呈现降低趋势,而电子热导率的颗粒尺度依赖性比声子热导率更为明显;随着颗粒直径进一步减小,声子热导率与电子热导率趋于同一数量级.当纳米颗粒特征尺寸大于4倍块材电子(或声子)平均自由程,其电子(或声子)热导率的颗粒尺度依赖性将减弱.     

MHD squeezed flow of water functionalized metallic nanoparticles over a sensor surface

Present study is devoted to analyze the magnetohydrodynamics (MHD) squeezed flow of nanofluid over a sensor surface. Modeling of the problem is based on the geometry and the interaction of three different kinds of metallic nanoparticles namely: copper (Cu), alumina (Al₂O₃) and titanium dioxide (TiO₂) with the homogeneous mixture of base fluid (water). The self-similar numerical solutions are presented for the reduced form of the system of coupled ordinary differential equations. The effects of nanoparticles volume friction, permeable velocity and squeezing parameter for the flow and heat transfer within the boundary layer are presented through graphs. Comparison among the solvent are constructed for both skin friction and Nusselt number. Flow behavior of the working nanofluid according to the present geometry has analyzed through Stream lines. Conclusion is drawn on the basis of entire investigation and it is found that in squeezing flow phenomena Cu–water gives the better heat transfer performance as compare with the rest of mixtures.     

Ag‐doped TiO2 enhanced photocatalytic oxidation of 1,2‐cyclohexanediol

The superiority of silver‐doped titania for photocatalytic oxidation (PCO) of organic compounds inspired us to investigate PCO of 1,2‐cyclohexanediol. Ag/TiO₂ was prepared, characterized (nanosize 19–24 nm) and used for oxidation of 1,2‐cyclohexanediol (1) in acetonitrile. The photolysate was analyzed using GC and GC/MS techniques. The PCO products are 2‐hydroxylcyclohexanone (2), 1,2‐cyclohexandione (3), 2‐cyclohexenone(4), cyclohexanone (5), and adipic acid (6).The formation of electron–hole pair at the surface of the catalyst followed by oxidation reactions was the suggested mechanism. Kinetic studies revealed first‐order mechanism for PCO of 1 and rate constant (k) = ?0.145 h^–1. Copyright © 2012 John Wiley & Sons, Ltd.     

Enhanced field ionization of water adsorbed on a carbon monoxide-covered, platinum field emitter tip

The influence of carbon monoxide, adsorbed on a platinum field emitter tip, on field ionization of adsorbed water was examined. Ramped field desorption (RFD) measurements of water ionization were performed at 108 K for water layer thicknesses up to 80 ML on a clean or CO-saturated tip surface. In RFD the applied field is ramped linearly in time until water ionization is detected, giving the onset field of ionization. Water ionization yields hydrated hydroxide ions and protons; the hydroxide ions remain within the water layer on the tip, while the hydrated protons are emitted into vacuum. At a low water coverage of 1.5 ML, the CO adlayer substantially reduced the onset field of ionization (that is, facilitated ionization) of water by 40%, from a value of 0.43 V/Å for water on clean Pt to 0.26 V/Å for water on CO-covered Pt. The extent of the reduction gradually diminished with thicker coverages of water and was absent at coverages of 20 ML or greater. The characteristic decay length of the field enhancement was 4.7 ± 1 ML. The results were analyzed with the charge exchange model of ionization kinetics and changes in dipole moments of water adsorbed without and with CO. The analysis reveals that a change in water structure (dipole moment) caused by CO is an important contributor in field enhancement and that the dipole moment for hydrated hydroxide ion in an ice-like layer must be greater than that for bulk ice-like water. The significance of these results with respect to electrochemical oxidation of CO is discussed.     

偶联分子对金纳米粒子在玻片上组装的影响

将金纳米粒子组装在用3-氨基丙基-三乙氧基硅烷(APES)修饰的普通玻片上,再分别用偶联分子对巯基苯胺、1,4-二巯基苯在该基底上再次组装金纳米粒子,结果表明用对巯基苯胺作为组装的偶联分子得到双层金纳米粒子结构,对巯基苯胺的表面增强拉曼光谱信号得到增强,而用1,4-二巯基苯作为组装的偶联分子得到单层金纳米粒子结构。     

纳米随机激光

介绍了以纳米ZnO粉末作为增益介质产生的随机激光。讲述了随机激光的特点、发展历史和它的应用前景。文章以随机激光的理论为基础，描述了四种主要的用于随机激光研究的方法。     

Metal deposition onto thiol-covered gold: Platinum on a 4-mercaptopyridine SAM

In this study we describe details of a new technique that allows to deposit metal on top of a self-assembled monolayer (SAM). Monoatomic high platinum islands were formed on a 4-mercaptopyridine SAM on Au(1 1 1) by first immersing the SAM-covered gold electrode in an aqueous solution of K₂PtCl₄ without potential control to allow Pt(II) ions to form a complex with the pyridine nitrogen. The complexed Pt(II) ions were then reduced electrochemically to Pt(0) after transferring the electrode to a Pt(II) ion-free solution. Upon reduction, monoatomic high Pt islands were observed in STM, the total coverage depending on the time for complexation. Ex situ angle-resolved XPS studies reveal that the Pt islands indeed reside on top of the SAM.     

Synthesis of Nanoscale Bimetallic Particles in Polyelectrolyte Membrane Matrix for Reductive Transformation of Halogenated Organic Compounds

Nanosized Fe/Ni and Fe/Pd particles were synthesized in the polyacrylic acid (PAA)/polyether sulfone (PES) composite membrane matrix for reductive transformation of halogenated organic compounds (HOCs). The advantages of using membrane to immobilize nanoparticles are the reduction of particles loss, prevention of particles agglomeration, and potential application of convective flow. Cross-linked PAA/PES composite membranes containing metal ions as particles precursor were prepared by heat treatment with ethylene glycol (EG) as a cross-linking agent. Nanoscale metal particles were formed and immobilized inside the membrane matrix after reduction with sodium borohydride. Membrane morphology and structure were observed by scanning electron microscopy (SEM). Particle size and distribution were characterized by SEM and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) was used to obtain the qualitative and quantitative element information of particles. A specimen-drift-free EDS line profile and EDS mapping system was performed in a scanning transmission electron microscopy (STEM) to determine the two-dimensional element distribution of iron and nickel in the nano domain. In the dechlorination study with trichloroethylene (TCE) as a representative HOCs, rapid and complete destruction of TCE was achieved by using nanosized bimetallic Fe/Ni or Fe/Pd in PAA/PES composite membranes. Typically more than 95% of 10 mg/l TCE was reduced within 1 h. Ethane was found in the headspace as the main product.     

Converged properties of clean metal surfaces by all-electron first-principles calculations

All-electron full-potential linearized augmented plane-wave calculations of the surface energy, work function, and interlayer spacings of close-packed metal surfaces are presented, in particular, for the free-electron-like metal surfaces, Mg(0 0 0 1) and Al(1 1 1), and for the transition metal surfaces, Ti(0 0 0 1), Cu(1 1 1), Pd(1 1 1), and Pt(1 1 1). We investigate the convergence of the surface energy as a function of the number of layers in the slab, using the Cu(1 1 1) surface as an example. The results show that the surface energy, as obtained using total energies of the slab and bulk from separate calculations, converges well with respect to the number of layers in the slab. Obviously, it is necessary that bulk and surface calculations are performed with the same high accuracy. Furthermore, we discuss the performance of the local-density and generalized gradient approximations for the exchange-correlation functional in describing the various surface properties.     

Formation of long range ordered arrangement of quantum dots with the help of lateral centripetal flow

A simple “chimney” method was used to eliminate the voids in an arrangement of quantum dots sized 2 nm on a solid substrate, which resulted in a large well ordered superlattice of area in the order more than 1 μm². Based on the principle of speeding up the interparticle interaction of nanoparticles to overcome the particle-substrate one, a lateral centripetal force originated from a glass tube acting as a chimney in a simple evaporation device is imposed. This method allows the packing process to be controlled in a mechanical force field, that is, with the same nanogold dispersion different patterns on a substrate—from separate dots to an ordered compact monolayer or even a multilayer structure—could be easily obtained.