The origin of the catalysis of hydrogen peroxide reduction by functionalized graphene surfaces: A density functional theory study

The adsorption of hydrogen peroxide on pristine and modified graphene sheets is studied by means of density functional theory calculations. The system considered involves perfect and defective layers, which can be pristine or functionalized with carboxyl groups.It is found that functionalization increases (in absolute value) the adsorption energy of hydrogen peroxide and improves the reduction reaction due to a favourable change in the properties of the defective layer. These changes are analyzed and mechanisms for the reduction reaction of hydrogen peroxide on the different surfaces are proposed. The associated energy barriers are calculated by means of state-of-the-art calculation methods.     

新颖的固体吸附式制冷与供热系统

介绍了一种新颖的固体吸附式制冷与供热系统及其研究现状。该系统主要由吸附器,冷凝器和蒸发器组成。以太阳能,工业废热低品位能源为动力,通过在封闭系统中吸附剂对制冷剂的解吸再生一吸附制冷循环来实现制冷与供热。整个装置无任何运动部件,无须润滑油,具有良好的能量供求关系。     

吸附蓄热材料性能研究进展

可再生能源的利用不仅可降低环境污染,还有助于实现“碳中和”目标,蓄热技术是有效利用太阳能等不稳定可再生能源的重要途经之一。热化学蓄热材料由于储能密度高、热损失小等优点可实现低品位热能的跨季节应用。本文对现有文献内吸附蓄热材料的蓄热性能进行总结分析,对比四类蓄热材料在不同运行工况下的储能密度、输出功率与蓄热效率等蓄热性能,并论述各类材料的典型应用案例。文中指出：溶液吸收材料脱附温度较低,但系统传热传质性能较差,实际应用中无法满足建筑供暖需求;固体吸附材料循环稳定性好,可采用太阳能集热器作为热源使其再生,它是目前建筑供暖中具有较大潜力的蓄热材料;纯热化学反应材料储能密度最高,然而其循环稳定性差,仍处于实验室研究阶段;兼有固体吸附材料与无机盐优点的复合材料有望成为建筑内理想的蓄热材料。最后文章针对各类材料提出其未来的研究方向。     

Microstructure and crystal structure of an equimolar Mg-Ti alloy processed by Simoloyer high-energy ball mill

The solid solubility of 50-50 at.% Mg-Ti powder mixtures was achieved by means of high energy ball milling in a Simoloyer equipment. XRD and HRTEM analyses revealed the existence of FCC and BCC matrix of Ti solid solution in Mg containing small amounts of an HCP Ti-rich phase formed after milling for 48 and 72 h, respectively at 800 rpm. An intermediate FCC solid solution of Ti in Mg was identified in powders milled for 24 h or less. The chemical composition of the matrix products extended from Ti56:Mg44 to Ti50:Mg50, which is close to the targeted equimolar ratio. XRD analysis of the structure suggested that the release of the lattice strain energy contributed to the driving force for transformation and solid solution between Mg and Ti after ball milling. Twinning was observed in Ti-rich crystallites at intermediate milling time. The twinning observed could be attributed to the deformation of Ti particles. However, in the Mg-Ti system, it might also indicate a strain induced martensitic transformation of the metastable ω-FCC into BCC product. The crystallite boundaries acted as preferential sites for the heterogeneous nucleation of the twins and for the formation of solid solution by release of the lattice strain energy.     

Anwendung von Tensiden bei der mechanischen Flüssigkeitsabtrennung

Use of Surfactants for Mechanical Liquid Separation . Mechanical dewatering of finegrained solid materials can be improved by the addition of surfactants. As interface-active substances surfactants reduce surface tension and consequently the capillary forces within the bed of solid particles. A hydrophobization of the solid surface due to the adsorption of surfactants may contribute to further reduction of moisture as well. The development of non-foaming surfactants enables the use without distrubing other ongoing processes by the formation of foam. Investigations on the interaction between the adsorption behaviour, type of material surface, and contact time during dewatering processes support the optimization of dewatering agents. The use of surfactants is an attractive means of improving or replacing other methods of mechanical dewatering.     

Adsorptive reactor technology for VOC abatement

The use of the monolith as an adsorptive reactor (M_AR) is proposed as a viable and novel alternative for VOC disposal. The M_AR combines adsorptive separation and catalytic combustion of the VOC in a single reactor unit and is thought to make effective utilisation of energy due to efficient heat integration. Theoretical studies on the feasibility and application of the adsorptive reactor concept for VOC oxidation is presented in this paper. Thus unlike previous work, present studies focus on an exothermic reaction system and the ability of the M_AR to control thermal runaway. A two dimensional mathematical model accounting for non isothermal adsorption and reaction, mass transfer limited adsorption kinetics and non linear (Tóth) adsorption equilibria, has been developed. The process is operated cyclically in two steps: adsorption and desorption/reaction. The VOC is fed into the reactor in the adsorption step and captured to produce a pure carrier gas effluent. Concentration and thermal swing is induced in the second step by means of an air feed. The most outstanding feature of the M_AR is its ability to prevent thermal runaway whilst maintaining a high VOC conversion. Simulation results indicate that the careful selection of step times for adsorption and desorption, feed temperatures and inlet velocities lead to stability and energy requirements which outperform equivalent conventional designs. The M_AR is thermally more stable due to the controlled release of the reactant from the adsorbed phase into the reaction zone, and also the heat integration of endothermic desorption and exothermic reaction.     

Discussion of the theoretical isotherms describing adsorption from multicomponent liquid mixtures on heterogeneous solids of quasi-Gaussian energy distribution

Discussion of two isotherm equations describing adsorption from the non-electrolyte solutions over the whole concentration region on the solids characterized by the quasi-Gaussian energy distribution is presented. Some physical and mathematical features of the isotherms are discussed and compared and the aspects of correct equation choice for a given adsorption system are considered. This theoretical discussion is illustrated by using the experimental data of adsorption from binary and ternary solutions on different solid surfaces.     

吸附式制冷新技术

固体吸附式制冷技术是充分利用低品位热能的一种有效手段 ,本文结合国际上吸附制冷研究的最新动态以及作者实验研究成果 ,对吸附式制冷系统及其在能量综合利用中的一些新技术进行了总结及探讨 .     

溶液除湿能力强化

利用溶液除湿的制冷空调系统有着非常积极的节能意义,但与固体吸附除湿相比,溶液吸收除湿暴露了它除湿能力较差的缺点,这使它的应用普及受到了一定程度上的抑制。为了提高溶液除湿能力,本文介绍了从除湿器和除湿溶液两个方面进行改进的研究结果：利用固体吸附剂对溶液除湿器表面进行了处理;利用混合溶液作为溶液除湿剂。本文利用电解质溶液理论对LiCl和CaCl₂为代表的混合溶液进行了相关热物性的研究,并提出了选择理想溶液除湿剂及其合适配比的解决方案;进行了相应的除湿实验：实验结果揭示了改进的除湿器不仅从增大除湿面积方面对溶液除湿能力强化有所贡献,还可能存在着吸附势叠加的功效;混合溶液的使用使得溶液除湿能力相对于使用单种溶液大大提高。     

Activated carbon surface heterogeneity seen by parallel probing by inverse liquid chromatography at the solid/liquid interface and by gas adsorption analysis at the solid/gas interface

The energetic surface heterogeneity of four different activated carbons was assessed by the parallel probing at the solid/liquid and solid/gas interfaces. At the solid/liquid interface a method of inverse liquid chromatography, frontal analysis by characteristic point was applied using phenylalanine in water solution as a probe molecule. At the solid/gas interface, argon was used as a probe in the low pressure quasi equilibrium volumetry method. The treatment of the adsorption isotherms by the derivative isotherm summation procedure revealed similar adsorption energy distributions for both argon and phenylalanine. Such an agreement between both methods suggests that, at the solid/liquid interface and on the solid/gas interface, the adsorption was mainly controlled by geometric parameters and no specific interaction was observed and physisorbed water did not played a significant role in adsorption process on three from four studied carbons.     

The Nanocrystalline SnO2–TiO2 System‒Part II: Surface Energies and Thermodynamic Stability

The thermodynamic stability of nanocrystalline SnO₂–TiO₂ solid solutions was studied experimentally. Microcalorimetry of water adsorption revealed a systematic decrease in the surface energy with increasing Ti⁴⁺ content in the SnO₂‐rich compositions, consistent with previous reports of Ti⁴⁺ segregation on the surface. The surface energy change was accompanied by an increase in the magnitude of the heat of water adsorption, also indicating a modification of the SnO₂ surface by Ti⁴⁺. Supporting the water adsorption data, calculations using high‐temperature oxide melt solution calorimetry data also suggest a decrease in the interface energies. A thermodynamic analysis showed that the observed surface energy decrease is responsible for an increase in the stability of solid solutions in the nanophase regime. Although a miscibility gap is expected in this system from bulk phase diagrams, the surface energy contribution modifies the bulk trend and promotes extensive solid solutions when the surface area is above a critical value dependent on the surface energy and the bulk enthalpy of mixing.     

The influence of temperature on effective diffusivity and adsorption kinetics for humid air—porous alumina

The kinetics of water adsorption from an air stream on porous alumina is studied experimentally in a differential bed at five temperatures in the range 9·8–64·0°C. The mass transfer rate is calculated theoretically by means of a model, which considers simultaneous resistance to mass transfer in the pore system of the solid and in a film surrounding the particle. The adsorption equilibrium is described by the non-linear Freundlich isotherm. Comparison of experiments with theory shows that the model describes the adsorption kinetics adequately and allows the effective diffusivity in the porous solid to be calculated. This leads to the result that the effective diffusivity is decreased by a factor 3 when temperature is increased from 9·8–64·0°C.     

Heats of Chemisorption of O2, H2, CO, CO2, and N2 on Polycrystalline and Single Crystal Transition Metal Surfaces

One of the important physical-chemical properties that characterizes the interaction of solid surfaces with gases is the bond energy of the adsorbed species. The determination of the bond energy is usually performed indirectly by measuring the heat of adsorption (or heat of desorption) of the gas [1, 2], In order to define the heat of adsorption, let us consider the chemisorption of a diatomic molecule, X₂, onto a site on a uniform solid surface, M. The molecule may adsorb without dissociation to form MX₂. M represents the adsorption site where bonding occurs to a cluster of atoms or to a single atom. In this circumstance, the heat of adsorption, ΔH_ads, is defined as the energy needed to break the MX₂ bond:     

吸附-吸收复叠式三效制冷循环

提出一种以沸石 -水为工质对的单效吸附式制冷单元为高温级、以双效溴化锂吸收式制冷单元为低温级的吸附 -吸收复叠式三效制冷循环 .高温热源首先加热吸附式单元 ,通过能量在系统中的多效利用 ,从而提高系统性能系数 (COP) .相比于三效溴化锂吸收式制冷循环 ,复叠式循环中吸附式单元工质对温度高于 2 0 0℃时 ,也不会腐蚀材质 ,因而是一种工程上易于实现的新型制冷循环 .对该循环的热力性能进行了研究     

碳捕集固体胺吸附剂载体性能优化策略及分析

碳捕集是“双碳”下推动化石能源低碳应用的有效途径,固体胺吸附剂是实现碳捕集、利用与封存的重要手段。其中,载体改性和胺种类优化是固体胺吸附剂研究热点策略。综述和评论了国内外固体胺吸附剂优化策略的作用机制、技术难点和碳捕集效果等,重点阐述并比较了硅基、多孔碳和有机框架载体优化策略在改善CO2选择性、吸附容量和稳定性等方面的作用,展望了固体胺吸附剂未来在高效稳定捕集、生物质吸附和碳利用与封存等研究方向和应用前景。     

Adsorption of Water Vapor on E-Glass

The thermodynamics of a water-vapor-E-glass system were studied by adsorption-isotherm analysis. The seven isotherms completed were Brunauer type IV with permanent hysteresis. The first adsorbed water layer could not be removed by pumping, indicating permanent hydrolysis. Application of heat removed the remaining water to close the hysteresis loop. Calculation of isosteric heat of adsorption indicates that the adsorbed state is between the solid and the liquid states, equivalent to the loss of one vibrational and one translational degree of freedom. A new plot of energy vs thickness is proposed which describes the adsorption independent of surface area, as contrasted to the usual energy-vs-volume plot which was found to depend on surface area. A modified Clausius-Clapeyron equation is proposed for computing the isosteric heat of adsorption.     

Heats of Chemisorption of O2, H2, CO,CO2, and N2 on Polycrystalline and Single Crystal Transition Metal Surfaces

Abstract

One of the important physical-chemical properties that characterizes the interaction of solid surfaces with gases is the bond energy of the adsorbed species. The determination of the bond energy is usually performed indirectly by measuring the heat of adsorption (or heat of desorption) of the gas [1, 2], In order to define the heat of adsorption, let us consider the chemisorption of a diatomic molecule, X₂, onto a site on a uniform solid surface, M. The molecule may adsorb without dissociation to form MX₂. M represents the adsorption site where bonding occurs to a cluster of atoms or to a single atom. In this circumstance, the heat of adsorption, ΔH_ads, is defined as the energy needed to break the MX₂ bond:     

Application of a linear-three-phase model to a fluidized-bed reactor

A linear three-phase model for fluidized bed reactors is proposed. The progress of that model is, that it considers the adsorption of the gas on the solid particles, which will influence the residence time behavior of the system. The solution in the Laplace-domain is given explicitly, the time-domain solutions have been approximated by a numerical method. The applicability of the model is shown by means of a 19cm-diameter fluidized bed.     

Characterization of epoxy resin surface energetics

This study has characterized the energetics of both the liquid state and the solid state of two commercially available epoxy resins: a DGEBA- and a TGMDA-based epoxy system. The surface properties of the liquid epoxies were evaluated by wetting measurements using a dynamic contact angle analysis (DCA). The Lifshitz-van der Waals components of the surface tension were found to be similar for both epoxy systems, while the acid-base components were found to be slightly different. Two different techniques were used to characterize the cured epoxy surface properties: wetting measurements and vapor adsorption measurements by means of inverse gas chromatography (IGC). The Lifshitz-van der Waals components of the surface energy were observed to be nearly the same for both epoxies, confirming that both resins have the same potential for non-specific interactions, in both liquid and solid states. Evaluations of the acid-base components of the work of adhesion by DCA and the Gibbs free energy change by IGC suggest that both cured epoxies show non-negligible specific interactions with both acidic and basic probes. However, computations of the accepticity and donicity parameters showed that both cured epoxies are predominantly basic, but also possess non-negligible acidity. It is likely that the presence of water on the solid surface contributes to the acidic character of the cured epoxies. The temperature dependence of the liquid surface tension for both epoxy systems was investigated. The same temperature dependence was observed: the surface tension decreased with temperature, following a linear regression. Corrections for viscous-drag effects on the liquid surface tension measurements were also made.     

A Comparison of the Work of Adhesion Obtained from Wetting and Vapor Adsorption Measurements

Some of the limitations to determining experimental values of the work of adhesion are discussed. Wetting measurements appear to provide the most direct means of assessing the work of adhesion for a solid-liquid system, but they require the formation of a finite contact angle by the liquid against the solid of interest, and the need for independent knowledge of the equilibrium spreading pressure of the liquid's vapor on the solid further limits their applicability. Vapor adsorption measurement using the technique of inverse gas chromatoraphy (IGC) provides a promising alternative means of determining the work of adhesion not subject to these limitations. The measurements are, furthermore, amenable to solids which are difficult to use with wetting measurements, e.g., those which are porous or granular. An attempt is made here to compare values of the work of adhesion determined using both wetting and vapor adsorption measurements. Good agreement is attained between the two methods for diiodomethane in contact with poly (vinyl chloride), poly (methyl methacrylate), and chemi-thermo-mechanical wood pulp fibers, suggesting that the technique of IGC is particularly well-suited for rapid determination of the work of adhesion.