Annealing effects on the structure, photoluminescence, and magnetic properties of GaN/Mn3O4 core-shell nanowires

Nanowires consisting of GaN/Mn₃O₄ were prepared using a two-step approach that involved dipping the as-synthesized GaN nanowires into an aqueous manganese acetate solution. To examine the effects of annealing, GaN/Mn₃O₄ core-shell nanowires were heated thermally to 700 °C in N₂ ambient. Transmission electron microscopy showed that the continuous Mn₃O₄ shell layer had agglomerated to expose a bare GaN core surface after thermal annealing. The magnetic measurements showed that the ferromagnetic behavior of the GaN nanowires had been suppressed by coating with the Mn₃O₄ shell, without significant change by the subsequent thermal annealing. The GaN/Mn₃O₄ core-shell nanowires exhibited blue, green, and red photoluminescence (PL) emission. The red emission was enhanced by thermal annealing. This paper discusses the associated mechanism for the variations in PL and magnetic properties of GaN/Mn₃O₄ core-shell nanowires.     

Design of pseudo-simulated moving bed process with multi-objective optimization for the separation of a ternary mixture: Linear isotherms

Pseudo-SMB, often called “J-O process”, is a modified SMB process to completely separate a ternary mixture with two discrete steps per one cycle. For improved separation, two new design parameters, the position of step 1 (χ_S1) and the number of port switches during step 2 (n_SMB), were introduced. A multi-objective optimization method was used to optimize the operating conditions of the pseudo-SMB process with four average zone flow-rate ratios for one cycle. Nadolol isomers were selected for the model solutes and the global objective for the design of the pseudo-SMB was to collect 99% of the intermediate retained solute. The separation was optimized for 8-column pseudo-SMB system with three column lengths (2.5, 5.0, and 10 cm) and three feed composition ratios (1/1/1, 1/2/1, and 2/1/2). The simulation results showed that productivity was increased 4.3 times (n_SMB = 20, χ_S1 = 0.5, 1/1/1) and desorbent to feed ratio D/F was decreased 45% (n_SMB = 16, χ_S1 = 0.5, 1/1/1) compared to normal operation (n_SMB = 8, χ_S1 = 0.5, 1/1/1). Productivity and D/F were significantly improved when short columns were used in the pseudo-SMB process. The pseudo-SMB was compared with recycle chromatography and SMB cascades for the same total amount of adsorbent. Recycle chromatography and 8-column SMB cascades using 20 cm and 40 cm of total column lengths were not able to separate the intermediate component with the target purity and the same feed rate of the pseudo-SMB process.     

Intricate role of water in proton transport through cytochrome c oxidase

Cytochrome c oxidase (CytcO), the final electron acceptor in the respiratory chain, catalyzes the reduction of O(2) to H(2)O while simultaneously pumping protons across the inner mitochondrial or bacterial membrane to maintain a transmembrane electrochemical gradient that drives, for example, ATP synthesis. In this work mutations that were predicted to alter proton translocation and enzyme activity in preliminary computational studies are characterized with extensive experimental and computational analysis. The mutations were introduced in the D pathway, one of two proton-uptake pathways, in CytcO from Rhodobacter sphaeroides . Serine residues 200 and 201, which are hydrogen-bonded to crystallographically resolved water molecules halfway up the D pathway, were replaced by more bulky hydrophobic residues (Ser200Ile, Ser200Val/Ser201Val, and Ser200Val/Ser201Tyr) to query the effects of changing the local structure on enzyme activity as well as proton uptake, release, and intermediate transitions. In addition, the effects of these mutations on internal proton transfer were investigated by blocking proton uptake at the pathway entrance (Asp132Asn replacement in addition to the above-mentioned mutations). Even though the overall activities of all mutant CytcO's were lowered, both the Ser200Ile and Ser200Val/Ser201Val variants maintained the ability to pump protons. The lowered activities were shown to be due to slowed oxidation kinetics during the P(R) → F and F → O transitions (P(R) is the "peroxy" intermediate formed at the catalytic site upon reaction of the four-electron-reduced CytcO with O(2), F is the oxoferryl intermediate, and O is the fully oxidized CytcO). Furthermore, the P(R) → F transition is shown to be essentially pH independent up to pH 12 (i.e., the apparent pK(a) of Glu286 is increased from 9.4 by at least 3 pK(a) units) in the Ser200Val/Ser201Val mutant. Explicit simulations of proton transport in the mutated enzymes revealed that the solvation dynamics can cause intriguing energetic consequences and hence provide mechanistic insights that would never be detected in static structures or simulations of the system with fixed protonation states (i.e., lacking explicit proton transport). The results are discussed in terms of the proton-pumping mechanism of CytcO.     

杂环型稳定硅烯插入HF、H_2O和NH_3反应

硅烯为卡宾的硅类似物,在有机光和热化学中作为一类重要的反应活性中间体引起了化学界的广泛兴趣.杂环型硅烯是实验合成的稳定硅烯,因其在有机硅化学中的重要作用,十几年来在实验和理论上均有研究报道.本文基于单重态杂环型硅烯的特殊电子性质和丰富的化学反应性,系统探讨了几种杂环型硅烯的插入反应.使用密度泛函理论(DFT),在B3LYP/6-311++G(d,p)水平上研究了三种氮杂环型不饱和硅烯(1,3,4)和两种氮杂环型饱和硅烯(2,5)分别与H—X(X=F,OH,NH2)键的插入反应,阐明了插入反应的机理并对各反应的结果进行了比较.杂环型硅烯与H—X的插入反应机理类似于简单硅烯,体现了硅烯的亲电亲核的双重反应性.由反应势垒和反应热看,五种硅烯与H—X键的插入反应均为HF最容易,H2O次之,NH3最难.饱和硅烯的反应性比不饱和硅烯的反应活性高,这也间接验证了杂环型饱和硅烯在实验中较难合成.     

Fixation of CO_2 by electrocatalytic reduction to synthesis of dimethyl carbonate in ionic liquid using effective silver-coated nanoporous copper composites

<正>With high surface area,open porosity and high efficiency,a catalyst was prepared and firstly employed in electrocatalytic reduction of CO_2 and electrosynthesis of dimethyl carbonate(DMC).The electrochemical property for electrocatalytic reduction of CO_2 in ionic liquid was studied by cyclic voltammogram(CV).The effects of various reaction variables like temperature,working potential and cathode materials on the electrocatalytic performance were also investigated.80%yield of DMC was obtained under the optimal reaction conditions.     

Pattern and feature designed growth of ZnO nanowire arrays for vertical devices

An approach is demonstrated for growing aligned ZnO nanowire/nanorod arrays following a predesigned pattern and feature with controlled site, shape, distribution, and orientation. The technique relies on an integration of atomic force microscopy (AFM) nanomachining with catalytically activated vapor-liquid-solid (VLS) growth. The pattern and growth locations are defined by the catalyst distribution created by AFM, and the orientation is determined by the epitaxial growth on a single-crystal substrate. The technique opens a variety of possibilities of using nanowire arrays as sensor arrays, piezoelectric antenna arrays, nanolasers, photonic band gap crystal, biosensors, and field emitters with controlled density, location, shape, and distribution according to a designed pattern and feature.     

Determination of Ba, Fe, Sr, and Zr in silicate materials with ED-XRF using241Am excitation source

The possibilities of ED-XRF with²⁴¹Am excitation source are evaluated in the analysis of geological materials: rocks, clays, soils, and sediments. The calibration curves are made using different SRM's. Data from the analysis of various SRM's are presented.     

Evolution of quasi-stationary states of an electron in an open spherical quantum dot

Physics of the Solid State - A theory of the evolution of spectral parameters of quasi-stationary states of an electron in an open spherical quantum dot is proposed in terms of the effective-mass...     

A mononuclear manganese(III) complex of an asymmetric macrocyclic ligand with a ring contraction [MnHL2(ClO4)](ClO4) · 2.5H2O

The template reaction of sodium 2,6-diformyl-4-chlorophenolate and N,N-bis(2-aminoethyl)–hydroxyethylamine followed by in situ transmetallation of Mn(ClO₄)₂ results in a mononuclear manganese(III) complex of one 21-membered asymmetric 2:2 Schiff base macrocycle, in which a hydroxyethyl group of the amine has been eliminated and ring contraction at one chamber of the macrocycle has occurred to form an imidazolidine ring. An X-ray study indicates that the geometry about the manganese(III) ion is distorted octahedral. The electrochemical behavior of this complex in MeCN has been studied by cyclic voltammetry.