Reaction Kinetic Processes Research Articles

Surface/Interfacial Engineering of Inorganic Low-Dimensional Electrode Materials for Electrocatalysis.

Exploitation of highly active and cost-effective electrode materials for the design of new types of renewable energy storage and conversion systems has been tremendously stimulated by the higher attention being paid to global energy security and invention of alternative clean sustainable energy technologies. Low-dimensional solid materials with special atomic and electronic structures are deemed desirable platforms for establishing clear relationships between surface/interface structure characteristics and electrocatalytic activity, representing enormous potential in the pursuit of high-performance electrocatalysts. Recent achievements revealed that surface and interfacial atomic engineering is capable of achieving novel physical and chemical properties as well as superior synergistic effects in inorganic low-dimensional nanomaterials for electrocatalysis. Compared to bulk counterparts, the electronic structure in the surface of inorganic low-dimensional nanomaterials is more sensitive to and can thus be regulated more easily by surface and interfacial modification strategies, resulting in greatly optimized electrocatalytic performance. In this Account, we focus on recent progress in surface and interfacial modification strategies to efficaciously engineer the electrocatalytic performance of inorganic low-dimensional electrode materials. We summarize several important regulation strategies of dimensional confinement, incorporation, surface reconstruction, interface modulation, and defect engineering, which immensely optimize the spin configuration, electrical conductivity, catalytic active site exposure, and reaction energy barrier of inorganic electrode material. At dimensionally confined atomic-scale thickness, more surface-facet atoms are exposed as active sites, which provide an ideal platform for applying surface incorporation and defect engineering, subsequently producing more catalytic active sites and better adsorption free energy for the improvement of catalytic activity. Moreover, regulation of the interfacial character of electrode materials, such as the surface strain, contact area, and bridged bonds, can optimize the electron transfer capacity and reaction kinetics process. On the other hand, once exposed to a strong alkaline solution under oxidizing potentials, the real active layer of electrode materials (such as transition-metal sulfides, nitrides, and phosphides) could be activated by a surface reconstruction strategy, realizing a unique core-shell structure with a highly conductive electron transfer channel inside and highly active catalytic sites outside for electrocatalysis. Based on these points of view, focusing on inorganic low-dimensional electrode materials, the proper choice of surface and interfacial modification strategies would effectively modulate their electrocatalytic activity, realizing unlimited potential applications in promising areas of electrocatalytic water splitting, rechargeable metal batteries, and fuel cells. Overall, we anticipate that surface and interfacial regulation approaches can provide a new understanding of the design of inorganic electrode materials, facilitating the rapid promotion of electrocatalytic performance in electrode materials for electrocatalysis.

Inhibition mechanism of baicalein and baicalin on xanthine oxidase and their synergistic effect with allopurinol

Suppression of xanthine oxidase (XO) may contribute to control hyperuricemia and gout. In this study, baicalein and baicalin, two dietary flavones, were found to inhibit the formation of uric acid and generation of superoxide anion (O2−) catalysed by XO through interaction with primary amino acid residues located in flavin adenine dinucleotides center of XO. Baicalein or baicalin binding to XO mainly facilitated by hydrophobic interactions and hydrogen bonds resulted in more compact of XO structure. The concentration profiles and pure spectra of the components extracted from highly overlapping spectral signal by multivariate curve resolution–alternating least squares chemometrics algorithm confirmed the formation of complexes and monitored the reaction kinetics process between XO and these flavones. Furthermore, the isobolographic analysis found that baicalein or baicalin exhibited a moderate synergy on the inhibition of XO when it combined with allopurinol as well as the joint use of baicalein and baicalin.

Corrosion Resistance of TiCN Films Prepared with Combining Multi-arc Ion Plating and Magnetron Sputtering Technique

TiCN films were deposited on AISI 304 stainless steel substrate by combining multi-arc ion plating and magnetron sputtering technique with ionizing titanium and graphite targets in an Ar+N2 mixture gas. The effect of duty ratio on the microstructure and corrosion resistance of TiCN films in a NaCl 3.5 wt% solution was investigated. The results show that the as-deposited films exhibit smooth, uniform and dense morphologies, mainly forming a fcc-TiN type structure with Ti-(C, N) bond as well a as few α-CNx, and present (111) preferred orientation with the increase of duty ratio. TiCN films display a better resistance to corrosion than the bare substrate; as the duty ratio increases, the corrosion resistance is enhanced gradually. When the duty ratio is 40%, the TiCN film shows the optimal corrosion resistance with a corrosion current density (icorr) of 3.262×10−7 A·cm−2 and a polarization resistance (Rp) of 238.4 kΩ·cm2. Electrochemical impedance spectroscopy (EIS) of the films also indicates that the penetration behavior of corrosive ions and the local corrosion process are two key factors affecting the electrode corrosion reaction kinetics process, which is consistent with the polarization curves analyses.

On improved understanding of plasma-chemical processes in complex low-temperature plasmas

Over the last years, chemical sensing using optical emission spectroscopy (OES) in the visible spectral range has been combined with methods of mid infrared laser absorption spectroscopy (MIR-LAS) in the molecular fingerprint region from 3 to 20 μm, which contains strong rotational–vibrational absorption bands of a large variety of gaseous species. This optical approach established powerful in situ diagnostic tools to study plasma-chemical processes of complex low-temperature plasmas. The methods of MIR-LAS enable to detect stable and transient molecular species in ground and excited states and to measure the concentrations and temperatures of reactive species in plasmas. Since kinetic processes are inherent to discharges ignited in molecular gases, high time resolution on sub-second timescales is frequently desired for fundamental studies as well as for process monitoring in applied research and industry. In addition to high sensitivity and good temporal resolution, the capacity for broad spectral coverage enabling multicomponent detection is further expanding the use of OES and MIR-LAS techniques. Based on selected examples, this paper reports on recent achievements in the understanding of complex low-temperature plasmas. Recently, a link with chemical modeling of the plasma has been provided, which is the ultimate objective for a better understanding of the chemical and reaction kinetic processes occurring in the plasma.

Model for compressive strength development of OPC concrete and fly ash concrete with time

Towards promoting the use of higher percentage levels of fly ash in concrete in order to reduce its carbon dioxide footprint, rational models for estimating the mechanical properties of fly ash concrete (FAC) are required. A simple model for predicting the mean compressive strength development with age of both FAC and ordinary Portland cement concrete (OPCC) is proposed. The model is applicable to concrete containing 0–75% class F fly ash, type I cement and normal-weight aggregates and having a 28 d average compressive strength up to 65 MPa. The model was developed based on two-stage regression analyses of the experimental data of 512 concrete mixtures collected from the literature. The predictions made using the model were found to be in good agreement with the results of experimental investigations carried out at CSIR-Structural Engineering Research Centre and additional experimental data collected from the literature. From a comparison with a reaction-kinetics-based strength development model available in the literature, it was noted that the proposed model is able to reflect the reaction kinetic processes involved in strength development in both OPCC and FAC. The proposed model should help in developing specifications related to strength development for FAC similar to that given in fib Model Code 2010 for OPCC.

Investigation on stability and degradation kinetics of febrifugine

To investigate the stability and degradation kinetics of febrifugine. The results showed that within 24 hours, febrifugine content was decreased by only 1% in mobile phase solvent, but its content was decreased to be 90% of the initial content in the water, methanol, 50% methanol and 10% acetonitrile solution. When the pH value of the solution was between 3 and 7, the retention rate of febrifugine in 24 hours was over 98%, but its content was decreased by about 12% in alkaline solution (pH 9.0). The higher the temperature, the worse the stability of febrifugine. At 40-80 ℃, the content of febrifugine was decreased to be 60% of its initial content in 10 hours, but the content was decreased by only 5% in 10 h at 20 ℃.However, no matter 40 ℃or 60 ℃, febrifugine was mainly transformed into isofebrifugine, and the total content of febrifugine and isofebrifugine was equal to their initial total content in 10 hours, while incase of 80 ℃, the total content was decreased to be 83.33% in 10 h, which suggested that the structure of febrifugine was absolutely changed, not just isomerized to be isofebrigugine at high temperature. Light had a significant impact on the stability of febrifugine. Under bright light, the content of febrifugine was reduced by about 23% in 108 h, but it only decreased by about 10% in the natural light or darkness. In artificial gastric fluid (pH 1.4) and artificial intestinal fluid (pH 6.8), the content of febrifugine was decreased by less than 5% in 10 h. After storage at high temperature(60 ℃), high humidity [(75±1)%] and strong light (3 000 lx) conditions for 10 d, the content of solid febrifugine was decreased by 0.27%, 7.6% and 5.39%, respectively. The degradation of febrifugine basically complied with the first-order reaction kinetic process in the following conditions: in water, methanol, 50%methanol and 10% acetonitrile solvents, alkaline solution (pH>7), different light intensity and different temperatures (20,40 ℃). Therefore, no matter the isolation and purification of febrifugine or the production of the related preparations, it should be done fast in the acidic solution, low temperature and dark conditions, while the febrifugine solid should be kept in dry and dark conditions.

Influence Factors of Aluminum–Slag Interfacial Reaction Under Electric Field

The interfacial reaction between aluminum melt and molten slag under an electric field plays a significant role in aluminum electro-slag refining. Here we studied this interfacial reaction within 680 and 820 °C under an electric field between 0 and 9 V. The evolution of aluminum composition was analyzed by inductively coupled plasma atomic emission spectroscopy. The dominant factor during the interfacial reaction was identified through orthogonal experiments, in which the slag-to-aluminum mass ratio, initial silicon concentration, electric voltage, reaction time, and temperature were selected as the influence factors. The greatest influence factor on the interfacial reaction was found to be the reaction time. Also, single-factor experiments revealed that the reaction kinetic processes largely obeyed an irreversible kinetic model, and the silicon removal efficiency was enhanced by increasing the voltage and slag/metal ratio.

Control of charge transport in the perovskite CH3 NH3 PbI3 thin film.

Carrier density and transport properties in the CH3 NH3 PbI3 thin film have been investigated. It is found that the carrier density, the depletion field, and the charge collection and transport properties in the CH3 NH3 PbI3 absorber film can be controlled effectively by different concentrations of reactants. That is, the carrier properties and the self-doping characteristics in CH3 NH3 PbI3 films are strongly influenced by the reaction thermodynamic and kinetic processes. Furthermore, by employing mixed solvents with ethanol and isopropanol to deposit the CH3 NH3 PbI3 film, the charge collection and transport efficiencies are improved significantly, thereby yielding an overall enhanced cell performance.

131 Proposal of reaction kinetic model for cell death due to extracellular freezing based on two-factor hypothesis

Post-thaw cell viability (CV) as a function of cooling rate generally shows the bell-shaped distribution with an optimal cooling rate. The characteristic distribution is understood on the basis of a two-factor hypothesis, i.e. the cell damage is caused by two factors: the intracellular freezing (IIF) and the extracellular freezing (EIF) without IIF [Mazur, P. et al., Experimental Cell Research 71 (1972) 345–355]. Mathematical description and prediction of the cell survival curve (CSC) is one of important problems in the area of cryobiology. Contribution to the cell death by IIF was already modelled successfully based on nucleation in the cells [Toner, M. et al., J. Appl. Phys., 67(3) (1990) 1582–1593]. In the present study, a reaction kinetic model was proposed to describe the cell death caused due to EIF without IIF. According to the two-factor hypothesis, the post-thaw cells are classified by freezing pattern into two categories: those with IIF experience and those with only EIF and no IIF experience. The former is regarded as dead, and the latter consists of live and dead cells. Regarding the cells with only EIF as a population, the model to describe mathematically CV of the population as a function of cooling rate was developed on the basis of phenomenological investigation of CV without considering the mechanisms of cell damage and death. Four assumptions for the modelling were made as follows: (1) Cell damage and death are described as one overall reaction kinetic process, (2) Cells have three states: normal, damaged (but still alive) (intermediate state) and dead, (3) Cells change from normal state through damaged into dead, (4) Change rate of the number of cells is expressed by the first-order reaction. Rate constants for the changes in the number of cells were assumed to depend on the time elapsed during the freezing and thawing. Also, the simplest formulation was investigated for comparison: cells changed from normal directly into dead. Conservation equations of the number of cells in each state, were expressed by a set of simultaneous first-order linear ordinary differential equations. Under the condition that all the cells were initially normal, analytical solutions of CV of the population were found for the rate constants depending on time. On condition of constant cooling rate, the time integral of rate constant in the solutions was changed into a temperature integral of it, and a value of the latter was defined as a model constant. Therefore, a basic function of cooling rate for CSC was found. Further, three functions with cooling rate modified by another model constant for CSC were also proposed. A parameter study of model constants was performed to evaluate CSC as a function cooling rate. The model constants were also determined by inverse problem analysis based on the experiment with human erythrocytes [MAZUR, P., Am. J. Physiol. 247, C125–C142 (1984)] as the experimental data on the viability of the cells with only EIF were unavailable. The experiment and prediction by the model were compared on CSC. The result shows that EIF-induced cell death is successfully described by the reaction kinetic mode. Source of funding: Grant-in-Aid for Scientific Research #24360083 and #21360098 to H.I. from Japan Society for the Promotion of Science. Conflict of interest: None declared. ishiguro@life.kyutech.ac.jp

Assessment of Damage of Glutathione by Glow Discharge Plasma at the Gas–Solution Interface through Raman Spectroscopy

AbstractAlthough non‐thermal discharge plasma is more and more applied in biological field, the molecular mechanisms of plasma acting on biomolecules are still unclear, which are indispensable for understanding the plasma‐induced biological effects. In this work, discharge plasma at the gas–solution interface was employed to irradiate on reduced glutathione (GSH), the most abundant low molecular weight thiol‐containing antioxidant in cells. Through Raman spectroscopy, both the irreversible damage and reversible conversion of GSH to oxidized glutathione (GSSG) were monitored in a non‐destructive fashion, so that the reaction kinetic processes through multi‐pathways could be evaluated quickly and quantitatively. Based on the experimental data, the reaction mechanism was discussed. magnified image

Reaction products and their solidification process of the plasma sprayed Fe2O3–Al composite powders

Fe2O3–Al composite powders were deposited onto steel substrate by plasma spraying. The reaction products of the Fe2O3–Al composite powders in the plasma flame and their solidification process were investigated. The results showed that the reaction products of the Fe2O3–Al composite powders in the plasma flame were Fe–Al–O ceramic melt and Fe melt. Fe was not always formed in the reaction products of each composite particle, and the formation of Fe was dependent on the composition distribution and the reaction kinetics process of each composite particle. The composition inhomogeneity, discontinuity and porousness of the composite particles resulted in the difference of the reaction kinetics of each composite particle and the composition difference of the droplets. Hercynite solid solution, Fe, Al2O3 and FeAl phases were formed by non-equilibrium solidification of the Fe–Al–O ceramic melt. For the smaller size droplet, when it spread on the substrate, the spreading droplet was quickly chilled to form equiaxed grains with size of 100–200nm. Nano-sized or submicron equiaxed grains, nano-sized columnar grains and cellular structure were formed in the larger spreading droplet. Fe rich hercynite solid solution nucleated and grew preferentially and then Al rich hercynite solid solution grew, which form composition segregation in the columnar grains. The main phases in the composite coating were hercynite solid solution.

Study on the Kinetics of NO Removal from Simulated Flue Gas by a Wet Ultraviolet/H2O2 Advanced Oxidation Process

On the basis of the steady-state approximation theory and the two-film theory, the kinetic model of NO removal by a wet ultraviolet (UV)/H2O2 advanced oxidation process (AOP) was established. The mass-transfer reaction kinetic process of NO removal was also analyzed preliminarily. The results showed that the NO removal process by the wet UV/H2O2 AOP was a pseudo-first-order reaction for NO. The NO absorption process in the wet UV/H2O2 AOP system belonged to the fast reaction kinetic region. The chemical reaction process could be completed in the liquid film. The NO absorption rate mainly depended upon the chemical reaction rate, the diffusion rate, and the NO partial pressure, but it was not affected by the liquid-phase mass-transfer coefficient. Therefore, the NO absorption rate could be increased by improving the chemical reaction conditions, increasing the gas−liquid contact area, and raising the NO partial pressure. The comparison of experimental values and model values of pseudo-first-order reaction rate constants showed that the mass-transfer reaction kinetic model deduced had good reliability.

ChemInform Abstract: Reaction Kinetics and Kinetic Processes in Modern Liquid Chromatographic Reactors

Abstract The analysis and use of liquid chromatographic columns as chemical reactors are explained. Multifold applications of liquid chromatographic reactors with a wide range of materials are described and illustrated. Means for extracting chemical kinetic rate data from liquid chromatographic reactor experiments in the presence of other dynamic processes are emphasized. Techniques for controlling reactivity and selectivity are explained. It is also shown that useful information about the stationary phase and protein interaction with the stationary phase can be accessible from these experiments. Several explanations for multiple zone formation including results from interconversion studies are presented. It appears that a broader awareness of chromatographic reactor applications would be beneficial to workers in a variety of different fields. There are a number of additional possibilities for the future including the removal and detoxification through transformation of environmentally undesirable materials.

Photocatalytic degradation kinetics of Rhodamine B catalyzed by nanosized TiO2 film

A fixed bed photocatalytic reactor was designed, and dynamic fast scan of UV-Vis adsorption spectrum was adopted to study the photocatalytic degradation dynamic behavior of Rhodamine B, a kind of dye generally recognized as to be degraded difficultly, on the surface of nanosized TiO2 thin film. The results indicate that the photocatalytic degradation process of Rhodamine B does not comply with the first-order reaction kinetic process. As a result, a kinetic model of Rhodamine B photocatalytic degradation reaction is brought forward, and the model is proved by the theoretical deduction and experiment.

Friedel—Crafts Acylation on Porous Divinyl Benzene Polymer Particles: A Reaction Kinetic Process Studied by Mid- and Near-Infrared Spectroscopy

Porous poly(para-divinylbenzene) and poly(meta-divinylbenzene) particles were synthesized from para-divinylbenzene and meta-divinylbenzene monomers with toluene and 2-ethylhexanoic acid as porogens. The residual vinyl groups in the particles were thereafter reacted with lauroyl chloride by using the Friedel–Crafts reaction. The conversion of vinyl groups was followed by analyzing polymer particles taken from the reaction mixture at different time intervals. Infrared spectroscopy in both the mid- and near-infrared region was used as the analytical technique. The intensity changes in the overtone absorption at 1628 nm due to the vinyl bonds were used as the basis for the quantification of the reaction. Spectra of the particles in the mid-IR region provide understanding of the changes taking place in the polymer matrix during the acylation reaction. The results indicated that the reaction took place at a faster rate in the polymer particles synthesized from para-DVB monomer compared with the poly(meta-DVB) particles. The polymer particles synthesized with toluene as porogen react faster than the polymer particles prepared with 2-ethylhexanoic acid as the porogen. The analysis also indicated that the acylation takes place at the early stages of the reaction and the product formed transforms into more stable products at the latter stages. On the basis of the infrared analysis, mechanisms for the formation of the different products are proposed.

Absorption of Sulphur Dioxide with Sodium Hydroxide Solution in Packed Columns

The absorption of sulphur dioxide from effluent gases by using aqueous sodium hydroxide solution as a solvent has become established practice in industry where a high degree of purity of the effluent gases must be ensured in a reliable manner. Although it has long been known that it is basically possible to clean effluent gases containing sulphur dioxide effectively by using sodium hydroxide solution, there are only few publications to date which discuss the reaction-kinetic processes in the wash solution.

A STUDY ON REACTION KINETICS OF THE RADICALS PRODUCED IN THE LASER-INDUCED SILANE PLASMA

The reaction kinetic processes of species produced in a pulsed TEA CO2 laser induced si-lane plasma were studied with the time-resolved OES. It is showed that the time position of main peaks for different fragments' charactristic lines are appreciably different. The reaction kinetic processes are discussed based on the results. By comparing the time evolution of the lines of the fragments and considering the other results of OES, We infer that the final reaction channel of the laser-induced silane plasma is a Si producing channel.

On the Reaction Kinetics in a Mercury Photosensitized CVD of a-Si:H Films

The reaction kinetic processes for mercury photosensitized CVD (Hg*–CVD) in silane were analyzed using a time-dependent, one-dimensional calculation based on mass-, momentum- and energy-conservation equations, including simplified surface reactions such as radical adsorption and hydrogen elimination from the substrate. A good agreement between the measured and the calculated time-varying concentrations of species provides sufficient validity regarding the present model. It is also shown that the saturation of the SiH4 decomposition observed by many authors in closed systems can be explained by the abstraction of SiH4 from the surfaces by radicals peculiar to the Hg*–CVD (e.g., HgH); gas-phase reactions are significantly influenced by surface reactions when the volume-to-surface ratio becomes small.

Stable species concentration of a turbulent premixed methane-air flame

Experimental and predicted values of species concentration in a premixed turbulent methane-air flame are reported. The flow-stabilized flame experiment explained in [1, 2] was investigated by means of gas samples taken by an isokinetic sampling probe. Five different gas analyzers were used to determine the gas composition at several locations within the flame. These measurements for oxygen, carbon dioxide, carbon monoxide, and nitric oxide are compared with calculated results. In the numerical calculation the κ-ϵ model of [3] was used to describe the turbulent flow. A system of 33 reactions [4] was used to calculate the 16 species concentrations. Experimental results and numerical prediction are in good agreement and the shape of the reaction cone of the premixed flame was predicted almost perfectly. The results for the pollutants NO and CO allow a validation of the reaction kinetic processes of small-scale turbulence in combusting systems.

Shock-Tube Studies in Exothermic Systems

Three types of behavior are possible: (1) planar incident shocks, with reaction, may be produced and studied; (2) detonation may be initiated by longitudinal nonsteady processes; or (3) distinct transverse instabilities may appear. Case (2) occurs when the incident shock velocity is adjusted to be less than the Chapman-Jouguet velocity. Here, if a reaction occurs, it leads to nonsteady processes which may initiate detonation. Examples are presented to discuss the inherent limitations of this case, and to show that reaction kinetic processes may be studied even though nonsteady flow processes are occurring. Cases (1) and (3) occur when the shock is adjusted to be above the Chapman-Jouguet velocity, usually in diluted mixtures. Case (3) instabilities (which negate the quantitative study of reaction kinetics) are always observed when the reaction zone length becomes of the order of, or less than, the tube diameter. Case (1) behavior is observed for longer reaction zone length, even though there are also recorded cases of unstable flow under these circumstances. An acoustic theory of transverse waves is used to discuss the possible occurrence of case (1) and case (3) flows.