Highly reusable chitosan-stabilized Fe-ZnO immobilized onto fiberglass cloth and the photocatalytic degradation properties in batch and loop reactors

The new design of the photocatalytic reactor is crucial to study for improving compatibility and scaling up the operation. A compatible loop photocatalytic reactor has been designed and used for rhodamine B decomposition. The photocatalysts were either ZnO or Fe-ZnO immobilized onto fiberglass cloth. The ZnO catalyst exhibited high crystallinity with or without Fe as the dopant. The crystallite size increased with the presence of Fe in the lattices. Most of the crystal parameters matched the standard ZnO data, and the cluster size was comparable to most reported studies. Diffuse Reflectance Spectroscopy (DRS) analysis confirmed the photon absorption shifted to the visible light range. The Fe dopant decreased the ZnO bandgap, and SEM-EDS confirmed the catalysts adhered to the fiberglass surface. The volume, thickness of the substrate solution, and reaction temperature influenced the photocatalytic-degradation rate. The photocatalytic degradation rate was higher under sunlight than ultraviolet irradiation. The reaction rate was lower in the batch reactor than in the loop reactor. The photocatalytic reaction almost completely mineralized RhB and changed the red solution to colorless. The immobilized photocatalyst has been reused more than 50 times without significantly decreasing the catalytic activity.     

Theoretical Investigations on Photodissociation Dynamics of Deuterated Alkyl Halides CD3CH2F

The product branching ratio between different products in multichannel reactions is as important as the overall rate of reaction, both in terms of practical applications (\emph{e.g}. models of combustion or atmosphere chemistry) in understanding the fundamental mechanisms of such chemical reactions. A global ground state potential energy surface for the dissociation reaction of deuterated alkyl halide CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F was computed at the CCSD(T)/CBS//B3LYP/aug-cc-pVDZ level of theory for all species. The decomposition of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F is controversial concerning C\begin{document}$ - $\end{document}F bond dissociation reaction and molecular (HF, DF, H\begin{document}$ _2 $\end{document}, D\begin{document}$ _2 $\end{document}, HD) elimination reaction. Rice-Ramsperger-Kassel-Marcus (RRKM) calculations were applied to compute the rate constants for individual reaction steps and the relative product branching ratios for the dissociation products were calculated using the steady-state approach. At the different energies studied, the RRKM method predicts that the main channel for DF or HF elimination from 1, 2-elimination of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F is through a four-center transition state, whereas D\begin{document}$ _2 $\end{document} or H\begin{document}$ _2 $\end{document} elimination from 1, 1-elimination of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F occurs through a direct three-center elimination. At 266, 248, and 193 nm photodissociation, the main product CD\begin{document}$ _2 $\end{document}CH\begin{document}$ _2 $\end{document}+DF branching ratios are computed to be 96.57%, 91.47%, and 48.52%, respectively; however, at 157 nm photodissociation, the product branching ratio is computed to be 16.11%. Based on these transition state structures and energies, the following photodissociation mechanisms are suggested: at 266, 248, 193 nm, CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F\begin{document}$ \rightarrow $\end{document}absorption of a photon\begin{document}$ \rightarrow $\end{document}TS5\begin{document}$ \rightarrow $\end{document}the formation of the major product CD\begin{document}$ _2 $\end{document}CH\begin{document}$ _2 $\end{document}+DF; at 157 nm, CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F\begin{document}$ \rightarrow $\end{document}absorption of a photon\begin{document}$ \rightarrow $\end{document}D/F interchange of TS1\begin{document}$ \rightarrow $\end{document}CDH\begin{document}$ _2 $\end{document}CDF\begin{document}$ \rightarrow $\end{document}H/F interchange of TS2\begin{document}$ \rightarrow $\end{document}CHD\begin{document}$ _2 $\end{document}CHDF\begin{document}$ \rightarrow $\end{document}the formation of the major product CHD\begin{document}$ _2 $\end{document}+CHDF.     

甲基肼自由基在高温燃烧分解反应下的非谐振效应

In this work, the harmonic and anharmonic rate constants of the decomposition reaction of monomethylhydrazine (MMH) radicals have been calculated by using transition state (TS) and Rice-Ramsperger-Kassel-Marcus (RRKM) theories with either MP2 or B3LYP method at 6-311++G (3df, 2p) basis set, respectively. The reaction mechanism and anharmonic effect of the MMH radicals are studied in detail and both of the harmonic and anharmonic rate constants increase sharply with increasing temperature in the canonical system. In the microcanonical system, these constants also show sharp increase with the energies. Overall, the anharmonic effect becomes more pronounced with the increasing temperature or energy in the canonical and microcanonical systems, respectively. These results indicate that the anharmonic effect of the decomposition reaction of MMH radicals is quite significant and cannot be ignored.     

Grand canonical ensemble approach to electrochemical thermodynamics,kinetics, and model Hamiltonians

The unique feature of electrochemistry is the ability to control reaction thermodynamics and kinetics by the application of electrode potential. Recently, theoretical methods and computational approaches within the grand canonical ensemble (GCE) have enabled to explicitly include and control the electrode potential in first principles calculations. In this review, recent advances and future promises of GCE density functional theory and rate theory are discussed. Particular focus is devoted to considering how the GCE methods either by themselves or combined with model Hamiltonians can be used to address intricate phenomena such as solvent/electrolyte effects and nuclear quantum effects to provide a detailed understanding of electrochemical reactions and interfaces.     

Li2MnO3 content effects on thermal,structural, electrical and electrochemical properties of xLi2MnO3-(1-x)LiNi0.9Zn0.1O2 cathode materials

xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂ (x = 0.1, 0.2 and 0.3) cathodes were prepared by two steps solid-state reaction method. Layered crystalline phases (space groups of C2/m for Li₂MnO₃ and R3m for LiNi_0.9Zn_0.1O₂) were detected in all cathodes. FTIR study also revealed the formation of the layered-type structures of all cathodes. The structural parameters were greatly influenced by the contents of Li₂MnO₃ in xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂. The electrical conductivities were found in the range of 1.2 × 10^?6 to 2.7 × 10^?6 S/cm. The dielectric spectra revealed the interfacial polarization Maxwell–Wagner type dielectric dispersion existing in all samples. The cathodes delivered the discharge capacities of 149 (x = 0.1), 151 (x = 0.2) and 157 mAh/g (x = 0.3) with capacity retention between 94.6 and 96.8% when they were cycled from 3.0 to 4.5 V under 0.1C rate. The x = 0.3 cathode exhibited the highest cyclic performance (96.8%) after 10 cycles due to its lower cations disorder.     

Nonequilibrium vibration-dissociation phenomena behind a propagating shock wave: Vibrational population calculation

An analysis of nonequilibrium phenomena behind a plane shock is presented concerning the vibrational relaxation and the dissociation of a pure diatomic gas. In the first part, the temperature range is 600 K–2500 K and the dissociation processes are neglected. The population of each vibrational level is computed by solving relaxation and conservation equations. The relaxation process is described by the master equations of each vibrational level. The vibrational transition probabilities appearing in the relaxation equations are calculated analytically and take into account the anharmonicity of molecular vibration and the potential angular dependence. The populations obtained are compared to those calculated using a Treanor model and to those calculated with a nonequilibrium Boltzmann distribution. For moderately high levels significant differences may be observed. The importance of the V-V process is found to be weak for the transitions involving the lowest levels. In the second part, the temperature range is 2500 K–5500K and the dissociation process is taken into account as well as the gas dynamic behavior which did not appear in several recent works. The kinetic equations are transformed to obtain a first order differential system and the resolution of such a system coupled with the conservation equations leads to the population of each vibrational level. The vibrational transition probabilities associated with the atom-molecule interaction are deduced from the cross section calculation used in the first part. The bound-free transition probabilities are obtained, following Marrone and Treanor, assuming that dissociation must occur preferentially from the higher vibrational states: the Marrone and Treanor probability model is extended and employed with an anharmonic oscillator. In the present investigation, behind the shock wave, the evolution of the population distribution expressed as a function of the distance is not monotonous: a lag time appears as shown experimentally in previous works for the macroscopic parameters. For moderately high levels the influence of the anharmonicity and those of the V-V processes appear significant and strongly related. In a general way, in both temperature ranges investigated, the V-V processes reduce the effects of the T-V transfer. Finally the influence of thecharacteristic probability temperature U of Marrone and Treanor is analyzed and a method of determination of local varying U is proposed.     

基于最新势能面的C(1D)+H2反应的环聚合分子动力学研究

本文利用环聚合分子动力学方法对C(¹D)+H₂反应开展了详细的理论研究. 计算中使用了最近构建的Zhang-Ma-Bian(ZMB)从头算势能面,该势能面对锥形交叉附近区域以及范德华区域均有精确的描述. 环聚合分子动力学计算得到的热反应速率常数与最新实验值吻合很好. 与前人计算结果比较,发现在?¹A′电子基态的ZMB-a势能面上获得的反应速率常数远大于前人构建的RKHS势能面上的结果,这是由于ZMB势能面上的范德华鞍具有与之前势能面上的范德华阱完全不同的动态学作用,表明环聚合分子动力学方法能够处理范德华作用引起的势能面拓扑结构所导致的动态学效应. 本文还揭示了b¹A′′电子激发态ZMB-b势能面以及量子效应对反应的重要性.     

A family of minimax rates for density estimators in continuous time

In continuous time, rates of convergence of density estimators fluctuate with the nature of observed sample paths. In this paper, we give a family of rates reached by the kernel estimator and we show that these rates are minimax. Finally, we study applications of these results for specific classes of processes including the Gaussian ones