Computer study of the effects of ozone absorption by an ultradisperse aqueous medium

The interaction of ozone molecules with water clusters at a temperature corresponding to the middle zones of the troposphere and the stratosphere has been studied by the molecular-dynamics method. It has been established that the integral intensities of the infrared absorption spectrum and the Raman spectrum of an ultradisperse aqueous system decrease substantially in absorption of ozone by it. It has been shown that in this case the emission power of the IR-radiation energy stored by the entire ozonized disperse aqueous medium grows.     

Computer study of methane adsorption by water clusters

Methane adsorption by water clusters including 50 molecules was studied by the molecular dynamics (MD) technique. The calculated frequency dependence of the real and imaginary parts of the dielectric permittivity points to the prevalence of a high-frequency mode in the spectra of these parameters after methane is adsorbed by water clusters. Such changes are also observed in the spectrum of the IR radiation absorption coefficient; however, the average value of this coefficient remains nearly the same. Methane adsorption causes a considerable increase in the reflection coefficient of the disperse water medium and the integrated power of IR radiation emission.     

Molecular-dynamic modeling of the spectral characteristics of the ozone-water cluster system

The absorption of one to six ozone molecules by the (H₂O)₂₅ cluster is studied by the method of molecular dynamics under near-atmospheric conditions. The capture of O₃ molecules by a water cluster produces a decrease in the integral intensity of IR absorption, reflection, and Raman spectra. IR absorption spectra are highly sensitive to the number of ozone molecules absorbed by a water cluster. The observed photon emission time and the radiation intensity of a dispersed aqueous system with absorbed ozone molecules are appreciably reduced relative to the analogous characteristics of a pure water cluster system.     

Molecular-dynamic modeling of ultradisperse water in the earth atmosphere

Molecular-dynamic calculations are used for analyzing the vapor quality of water monomers, clusters, droplets, and crystals in the Earth atmosphere. It is demonstrated that the integral intensity of absorption of infrared radiation for the initial series of water clusters does not increase with their size and stays smaller than the respective characteristic for free water molecule. The anti-greenhouse effect developed by clusters is defined as the difference between the greenhouse effects exhibited by free molecules of water making up the clusters and by the clusters proper. The value of anti-greenhouse effect is 3.6 K, and the greenhouse effect of atmospheric water clusters is estimated at 1.1 K.     

Molecular dynamics simulation of adsorption of ozone and nitrate ions by water clusters

Coadsorption of ozone molecules and nitrate ions by water clusters was studied by the molecular dynamics technique. The maximum value of an average O-H…O bond length in a water carcass is realized at the minimum specific number of such bonds when the ratio of adsorbed ozone molecules to nitrate ions captured by a cluster is two. IR absorption and reflection spectra were reshaped significantly, and new peaks appeared at Raman spectra due to the addition of ozone and nitrate ions to the disperse water system. After ozone and nitrate ions were captured, the average (in frequency) IR reflection coefficient of the water disperse system increased drastically and the absorption coefficient fell.     

Interaction of CO,NO, and H<Subscript>2</Subscript> molecules on the surface of a Ni/MgO(111) metal oxide system

The adsorption and interaction of carbon monoxide (CO), nitrogen oxide (NO), and hydrogen (H₂) molecules on the surface of a system produced when nanosize nickel clusters are formed on the surface of a magnesium oxide film [MgO (111)] has been studied in an ultrahigh vacuum by IR, thermal desorption, and photoelectron spectroscopy. It is shown that, at a substrate temperature of 85 K, CO and NO molecules at low surface concentrations, are mostly adsorbed on the surface of Ni particles, whereas at higher surface coverage CO molecules are forced to the Ni/MgO(111) interface. The adsorption of hydrogen results in NO molecules also being displaced to the interface. The particular state of the molecules at the interface between the metal and the polar surface of the oxide is responsible for the observed processes in which CO is converted to CO₂ due to the reduction of NO to N₂.     

Modeling of thermal radiation of polymer coating containing hollow microspheres

The paper deals with the effect of hollow microspheres added to paint or another polymer coating for open surfaces of a building on the heat loss due to thermal radiation. An approximate theoretical model is suggested, which is based on the spectral calculation of the radiative characteristics of a disperse system and determination of the integral flux of thermal radiation. Calculations are performed for a layer of paint with hollow glass microspheres. It is demonstrated that the microsphere shell thickness has the strongest effect on the reduction of heat loss.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 2, 2005, pp. 256–266.Original Russian Text Copyright © 2005 by L. A. Dombrovsky.     

Far-infrared radiation absorption cross section of clusterized water vapor

A molecular dynamics simulation of an ensemble of water molecules has been performed using a flexible polarizable model. Far-infrared (FIR) radiation absorption cross sections of water vapor with various degrees of clusterization have been calculated in the dipole oscillator approximation. It is shown that the radiation absorption by libration vibrational modes is already observed for the clusters involving about ten molecules and shifts the absorption spectrum toward the maximum of the thermal radiation spectrum of the Earth.     

Numerical simulation of IR absorption,reflection, and scattering in dispersed water-oxygen media

The method of molecular dynamics along with the flexible model of molecules are used to study the spectral characteristics of systems of clusters of (H₂O) _n , (O₂) _m (H₂O) _n , and (O) _i (H₂O) _n , m ≤ 2, i ≤ 4, 10 ≤ n ≤ 50. It is demonstrated that the integral intensity of absorption of IR radiation decays after water clusters adsorb oxygen. In addition, the adsorption of oxygen causes a significant decrease in the reflection coefficient R of monochromatic IR radiation. In so doing, the R(ω) spectrum splits into bands and exhibits seven peaks in the frequency region of 0 ≤ ω ≤ 3500 cm^?1. The dissociation of oxygen molecules captured by clusters makes the peaks of R(ω) spectrum more resolved. The attachment of molecular oxygen by clusters leads to decay of the power of their IR radiation, while the capture of atomic oxygen, on the contrary, is accompanied by an increase in the rate of dissipation of energy accumulated by water aggregates.     

A computer study of the absorption of infrared radiation by systems of molecular clusters

The method of molecular dynamics is used to investigate the process of absorption of N₂O and CH₄ molecules by water clusters and to determine the frequency spectra of permittivity for systems consisting of clusters mixed in different ratios, namely, (H₂O)_n, (N₂O)_i(H₂O)₁₀, and (CH₄)_i(H₂O)₁₀. IR-radiation absorption spectra for these systems are calculated and analyzed; the radiation power scattered by these systems and the tangent of dielectric loss angle are determined. The inclusion of anharmonicity of phonon oscillation makes it possible to explain the origin of characteristic frequencies appearing in IR spectra of mixtures of cluster systems. The capture of molecules of greenhouse gases by an ultradisperse aqueous medium affects the ability of this medium to absorb terrestrial radiation, i.e., reduces the greenhouse effect.     

Molecular-dynamic calculation of spectral characteristics of absorption of infrared radiation by (H2O)j and (CH4)i(H2O)n clusters

The method of molecular dynamics is used to investigate the stability and physical properties of (CH₄)_i(H₂O)_n clusters. The possibility of methane molecules being absorbed by clusters containing ten and twenty water molecules is demonstrated. Such clusters retain the thermodynamic stability when the number of CH₄ molecules they absorbed does not exceed six. The frequency dispersion of complex permittivity of (CH₄)_i(H₂O)_n aggregates reflects the resonant behavior of polarizability depending on the applied electric field. The dependence of the absorption coefficient α on the frequency of infrared radiation varies significantly after even one CH₄ molecule is absorbed by water clusters. The maximal value of α for water aggregates which absorbed CH₄ molecules is much lower than the respective value for pure water clusters of appropriate size.     

添加剂和纳米粒子强化溴化锂水溶液／氨水吸收特性研究进展

吸收式制冷以其节能、环保等诸多优点得到了越来越广泛的应用。本文总结与分析添加剂和纳米粒子强化溴化锂水溶液及氨水吸收特性的机制和相关实验研究的发展现状。针对吸收式制冷系统中吸收器传质系数和换热系数小而导致的制冷效率低的问题,很多学者进行了添加剂和纳米粒子对吸收过程影响的实验研究,并据此采取措施增大传质传热效率。实验主要包括以下几个方面：表面张力实验、静态池吸收实验、降膜吸收实验和氨水鼓泡吸收实验。实验结果均表明添加剂和纳米粒子可以提高吸收器中溴化锂水溶液及氨水的传热传质性能。该研究对于提高吸收式制冷系统的制冷效率有很大帮助,同时为该技术在实际系统中的应用奠定基础。     

Atomic absorption by free atoms in solution following chemical reduction from the ionic state

The initial stages of chemical reduction of metallic ions in solution must proceed through the formation of single atoms, followed by the rapid formation of clusters with other atoms until continued coalescence produces observable precipitates or evidence of stable sol formation. Dilute solutions of sodium borohydride (0.0025%) merged with microgram per milliliter concentration solutions of Ag, Pd, and Cu in a custom spectrophotometric flow cell produce transient background-corrected atomic absorption signals during the initial few seconds of the reaction. High-resolution atomic absorption with both a hollow cathode line source and a continuum source reveals that the absorption line profile of the absorbing species is extremely narrow (11 pm for Ag) and not influenced by the aqueous environment. Such selective absorption of radiation suggests that free atoms are being observed in aqueous solution.     

Facile preparation of porous carbon nitride for visible light photocatalytic reduction and oxidation applications

In this work, we have employed melamine, cyanuric acid and thymine to fabricate triazine-based carbon nitrides (CNs) by supramolecular approach. The resultant CNs possess large specific surface area, hierarchical porous structure, better light absorption capacity and high separation rate of photoinduced carriers. Then, the photocatalytic reduction and oxidation performance has been evaluated. The obtained CNs exhibit enhanced photocatalytic reduction performance on water splitting to H₂, the largest hydrogen evolution rate can reach 8466.3 μmol g^?1 h^?1, which is 81.9 times as high as that of bulk CN. Simultaneously, the porous CNs show excellent photocatalytic reduction ability on the conversion of CO₂ to H₂, CO and CH₄. Of particular interest is that they have high selectivity for CO. It’s worth noting that the porous CNs also possess outstanding photocatalytic oxidation ability on high concentration nitric oxide (NO), and the highest NO conversion rate can reach 79.3% under visible light. The enhanced photocatalytic performance for the multifunctional porous CN can be ascribed to the synergic effect of large specific surface area, strong light absorption capacity and fast separation of photoinduced electron–hole pairs. Finally, the photocatalytic reduction and oxidation mechanism of the porous CN is also proposed and discussed.     

Selective adsorption of organosilane molecules along step edges of atomically flattened Si(111) surfaces

We investigate the selective adsorption of organosilane molecules (3-aminopropyltriethoxysilane (APTES) and octadecyltrichlorosilane (OTS)) at the step edges of a flattened Si(111) surface by atomic force microscopy. The flattened Si(111) surface is formed by dipping a vicinal Si(111) wafer into ultralow-dissolved-oxygen water after treatment with HF. The selective adsorption of these organosilanes is achieved only when the Si(111) sample is pretreated with a Cu-containing solution to form Cu wires along the step edges of the Si(111) surface. This is probably due to the simultaneous formation of one-dimensional Si oxide covered with hydroxyl (OH) groups underneath Cu wires during the electroless reduction of Cu ions in water. At the step edges, APTES and OTS molecules are adsorbed as disperse clusters and as rows of bumps, respectively. The reason for this difference is still unclear, but a key factor is probably the control of the moisture content in the environment. The step edges, which are functionalized by organosilane molecules with various terminations such as -NH2 and -CH3, are expected to be utilized in novel nanoscale devices and processes.     

Coupled heat and mass transfer during nonisothermal absorption by falling droplet with internal circulation

We considered mass and heat transfer during nonisothermal absorption of a gas by a falling droplet with internal circulation. Gas phase is assumed to be free of inert admixtures and mass transfer is liquid phase controlled. Mass flux is directed from a gaseous phase to a droplet, and the interfacial shear stress causes a fluid flow inside the droplet. Droplet deformation under the influence of interface shear stress is neglected. Absorbate accumulation and temperature increase in the bulk of liquid phase are taken into account. The problem is solved in the approximations of a thin concentration and temperature boundary layers in the liquid phase. The thermodynamic parameters of the system are assumed constant. The system of transient partial parabolic differential equations of convective diffusion and energy balance with time-dependent boundary conditions is solved by combining the similarity transformation method with Duhamel's theorem, and the solution is obtained in a form of Volterra integral equation of the second kind which is solved numerically. Theoretical results are compared with available experimental data for water vapor absorption by falling droplets of aqueous solution of LiBr.     

水性聚氨酯-分散蓝14高分子染料的合成与性能

用聚氧化丙烯二醇、2,4-甲苯二异氰酸酯、二羟甲基丙酸、三乙胺和分散蓝14通过丙酮法合成了水性聚氨酯-分散蓝14(PU-DB14)高分子染料.红外和紫外-可见吸收光谱显示分散蓝14已被化学键入聚氨酯链中.研究还发现,PU-DB14水分散体的紫外-可见吸收光谱在760 nm处现一新吸收峰,可能与PU-DB14在水分散体中的形态有关.本文还用差热分析和广角X射线衍射对PU-DB14作了初步的性质表征.     

高吸水性纤维复合体的研究

将含聚合引发剂的丙烯酸盐单体水溶液涂布到天然纤维布基材上，在微波辐照下聚合，制得高吸水性纤维复合体。该复合体吸去离子水８０ｇ／ｇ，吸０．９％ＮＡＣｌ水溶液２２ｇ／ｇ。研究了引发剂和交联剂用量、单体浓度、微波辐照功率；时间及中和度等因素对复合体吸液性能的影响。