Morphology-controlled synthesis of SrTiO3 micro-scale particles

A novel and simple strategy of morphology-controlled Sr Ti O3（ST） micro-scale particle synthesis by the flux method is reported. Systematic experiments are designed to realize the tunable morphologies of the particles when the flux salt,sintering process, and the precursors are changed. The ST plates can be synthesized by plate-like Bi4Ti3O12（BIT） precursors in Na Cl flux. However, the as-synthesized Bi4Ti3O12 grains transform into reticular particles and finally into rods at higher temperature in Na Cl and KCl compounds. Besides, cubic ST particles are also prepared using different precursors as a comparative experiment. This study provides a strategy for further investigations in designing the morphology-controlled particles and efficient anisotropic materials of perovskite structure such as ferroelectric and photocatalyst.     

Enhancing the efficiency of TiO2–perovskite heterojunction solar cell via evaporating Cs2CO3 on TiO2

In a TiO₂–perovskite heterojunction solar cell (TiO₂–PHSC), besides the perovskite CH₃NH₃PbX₃, TiO₂ as one side of the TiO₂/CH₃NH₃PbX₃ heterojunction also plays an important role in the photovoltaic effect. In order to improve the performance of the TiO₂–PHSC with the structure of glass/FTO/compact TiO₂/mesoporous TiO₂/CH₃NH₃PbI_3–xCl_x /poly‐TPD (poly(N,N ′‐bis(4‐butylphenyl)‐N,N ′‐bis(phenyl)benzidine))/Au, a 2 nanometer thick Cs₂CO₃ layer is thermally evaporated on the mesoporous TiO₂ layer. The short‐circuit current density (J_sc) raises from 17.7 mA cm^–2 to 18.9 mA cm^–2, the open‐circuit voltage (V_oc) from 0.81 V to 0.87 V, and the fill factor (FF) from 55.2% to 67.3%; as a result, the power conservation efficiency (PCE) increases from 8.0% to 11.1% under AM 1.5G solar illumination (100 mW cm^–2). Moreover, in a TiO₂–PHSC free of mesoporous TiO₂, where Cs₂CO₃ is evaporated on the compact TiO₂ layer, the J_sc, V_oc, FF and PCE values increase from 16.0 mA cm^–2, 0.83 V, 50.8% and 6.7% to 17.9 mA cm^–2, 0.90 V, 59.3%, and 9.5%, respectively. The reasons of the PCE increase for either the first kind of TiO₂–PHSC or the mesoporous‐TiO₂‐free TiO₂–PHSC with a nanometer‐thick Cs₂CO₃ layer on mesoporous TiO₂ or compact TiO₂ are discussed. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Mathematical analysis and solutions for multi-objective line-cell conversion problem

The line-cell (or line-seru) conversion is an innovation of assembly system applied widely in the electronics industry. Its essence is tearing out an assembly line and adopting a mini-assembly unit, called seru (or Japanese style assembly cell). In this paper, we develop a multi-objective optimization model to investigate two line-cell conversion performances: the total throughput time (TTPT) and the total labor hours (TLH). We analyze the bi-objective model to find out its mathematical characteristics such as solution space, combinatorial complexity and non-convex properties, and others. Owing to the difficulties of the model, a non-dominated sorting genetic algorithm that can solve large size problems in a reasonable time is developed. To verify the reliability of the algorithm, solutions are compared with those obtained from the enumeration method. We find that the proposed genetic algorithm is useful and can get reliable solutions in most cases.     

1H-NMR评价不同重油缓和热转化过程中的相对供氢能力

以蒽为化学夺氢探针,采用 ¹H-NMR为检测手段测定了三种典型重质渣油及其亚组分在380℃、临氮初压4MPa、反应8 min条件下的可供氢含量,并分析了产物的甲苯不溶物、液体馏程分布以及气体组成。结果表明,本实验条件下的热反应较为缓和,渣油及组分反应前后结构变化不明显,样品体系内部主要发生渣油及组分向夺氢体(蒽)的氢转移反应。¹H-NMR中化学位移在1.4~2.0的H_cβ和2.5~4.7的H_cα含量的变化值与化学探针法测定的实际可供氢量有较好的线性关联,可利用此两段化学位移内的氢含量评价不同重质油品在缓和热改质过程中的相对供氢能力。     

Density Functional Theory Investigations on M + CO2 towards MO + CO (M =B, Al, Si)

The catalytic activation of carbon dioxide by metals and non-metals is one of the attractive scientific challenges in scientific community. In this work, the conversion mechanisms of CO2 to CO by B, Al and Si were elucidated extensively at the B3LYP/6-311++G(d,p) basis set level. Our theoretical mode testifies that the reaction mechanisms of these three systems are significantly different from each other, and both boron and silicon have good performance in the conversion of CO2 to CO.     

Termination Mechanism in the Anionic Polymerization of Methyl Methacrylate

Recent studies have revealed that at temperatures around 200°K in tetrahydrofuran solvent, poly(methy1 methacrylate) ion pairs are long-lived and very reactive. At higher temperatures however termination of the ion pairs occurs, as evidenced by the broadening of the molecular weight distribution of the resultant polymer and by the incomplete polymerization of the monomer. Three mechanisms have been proposed to describe these termination reactions; an inter molecular reaction with the monomer ester function, an intramolecular cyclization of the anion, or reaction with the polymer ester function. In the absence of monomer only the last two mechanisms can be operative. A series of experiments was undertaken in which the molecular weight distribution broadening with temperature increase was measured under typical polymerization conditions or in the absence of monomer. The effect of each of the three counterions Li, Na, and K was also monitored. The results obtained are discussed in terms of these three possible termination mechanisms. Termination rate constants calculated from the molecular weight distribution are also presented.     

Eco‐friendly conductive polymer nanocomposites (CPC) for solar absorbers design

To reduce both the cost and the environmental impact of copper‐based thermal solar absorbers, we have investigated their possible substitution by bio‐based conductive polymer nanocomposite (CPC) elements. Our results show that carbon nanotubes (CNT) have no significant influence on polymers’ calorimetric properties such as T_m and T_g but lead to a strong increase in crystallinity of poly(lactic acid) (PLA) and to a lesser extent of poly(amide 12) poly(amide 12) (PA12) for 2 and 3 CNT wt % respectively. Percolation thresholds as low as 0.5 and 0.58 were obtained for PA12 and PLA, respectively, and visco‐elastic properties such as η*, G’ and G” were found to increase exponentially with CNT content confirming the formation of a CNT network within the matrix. All CPC are absorbing more energy in the visible and infrared than in the ultraviolet wavelength ranges. Finally, the thermal conductivity k of PLA–CNT and PA12–CNT were increased, respectively, of 85% and 24%, to reach 0.28 W.m^?1.K^?1 and 0.26 W.m^?1.K^?1, for only 5 wt% CNT. The figure of merit suggests that PA12 is the polymer which satisfies at best all criteria, particularly combining a lower viscosity at almost equivalent thermal conductivity and absorptivity. Copyright © 2013 John Wiley & Sons, Ltd.     

“蒸汽相转化”法制备纳米晶组成的块状方钠石多级孔沸石催化材料

将实验室合成的聚苯乙烯乳胶微球（PS）加入制备方钠石（SOD）沸石的前驱体凝胶中,在45℃条件下制得干凝胶,随后采用“蒸汽相转化”法制备了大块状SOD沸石材料。对影响多级SOD沸石形成因素进行了详细讨论。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、N₂吸附-脱附和压汞技术等表征手段对制备的材料进行了详细表征。结果表明通过“蒸汽相转化”法制备的大块状SOD沸石由球状多晶聚集体构成,这些球状多晶聚集体又是由粒径为50~100 nm的初级纳米晶粒组成,在初级纳米晶粒上和纳米晶粒之间形成了2~50 nm介孔结构以及由脱除PS微球形成的50~300 nm的大孔结构。     

Structural Principles and Thermoelectric Properties of Polytypic Group 14 Clathrate‐II Frameworks

We have investigated the structural principles and thermoelectric properties of polytypic group 14 clathrate‐II frameworks using quantum chemical methods. The experimentally known cubic 3C polytype was found to be the energetically most favorable framework, but the studied hexagonal polytypes (2 H, 4 H, 6 H, 8 H, 10 H) lie energetically close to it. In the case of germanium, the energy difference between the 3C and 6H clathrate‐II polytypes is ten times smaller than the difference between the experimentally known 3C‐Ge (α‐Ge) and 4H‐Ge polytypes. The thermoelectric properties of guest‐occupied clathrate‐II structures were investigated for compositions Na–Rb–Ga–Ge and Ge–As–I. The clathrate‐II structures show promising thermoelectric properties and the highest Seebeck coefficients and thermoelectric power factors were predicted for the 3C polytype. The structural anisotropy of the largest studied hexagonal polytypes affects their thermoelectric power factors by over a factor of two.     

Edge‐Selectively Functionalized Graphene Nanoplatelets

Graphene, as a single layer of graphite, is currently the focal point of research into condensed matter owing to its promising properties, such as exceptional mechanical strength, high thermal conductivity, large specific surface area, and ultrahigh electron‐transport properties. Therefore, various physical and chemical synthetic procedures to prepare graphene and/or graphene nanoplatelets have been rapidly developed. Specifically, the synthesis of edge‐selectively functionalized graphene (EFG) has been recently reported by using simple and scalable approaches, such as “direct” Friedel‐Crafts acylation reactions in a mild acidic medium and a mechanochemical ball‐milling process. In these approaches, chemical functionalization predominantly take place at the edges of the graphitic layers via the covalent attachment of targeted organic “molecular wedges”. In addition, the distortion of the crystalline structures in the basal plane, which is beneficial for preserving the unique properties of the graphitic framework, can be minimized. In addition, the efficient exfoliation of graphene can be achieved, owing to the strong repulsive forces from the covalently linked wedges and strong shear forces during the reaction. Furthermore, EFG shows promising potential in many useful applications, such as highly conductive large‐area films, metal‐free electrocatalysts for the oxygen‐reduction reaction (ORR), and as additives in composite materials with enhanced properties. Herein, we summarize the recent progress and general aspects of EFG, including synthesis, reaction mechanism, properties, and applications.