Efficient oxidation of benzyl alcohol with heteropolytungstate as reaction-controlled phase-transfer catalyst

A series of heteropolytungstates has been synthesized and utilized as catalysts to catalyze oxidation of benzyl alcohol with aqueous hydrogen peroxide.The results indicated that three of these catalysts showed the properties of reaction-controlled phase- transfer catalysis,and they had excellent catalytic ability to the oxidation of benzyl alcohol.No other by-products were detected by gas chromatography.Once the hydrogen peroxide was consumed completely,the catalyst precipitated from solvent,and the results of the catalyst recycle showed that the catalyst had high stability.     

Influence of Annealing on Properties of ZnO Films Grown via Plasma－enhanced MOCVD

The structural and the optical properties of ZnO films with high quality grown via plasma-enhanced met-al-organic chemical vapour deposition(MOCVD) on C-plane sapphire substrate were studied. The crystallini-ty and the optical properties of the films are greatly improved having been annealed in oxygen plasma atmo-sphere. The structure, the band gap and the binding energy of O1s electrons, and the molar ratio of O to Zn were determined by X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron scan meth-ods. For both the annealed and the as-grown films, the exciton peak features were observed at room temper-ature. The band-edge photolof the annealed film is much stronger than that of the as-grown film, and the exciton peak relating to the deep level at 439 nm disappears. The molar ratio of O to Zn in the annealed film is 0. 91, while it is 0. 78 for the as-urown film.     

Modification of Carbon Nanotube Powder Microelectrode and Nitrite Reduction

The properties of the carbon nanotube powder microelectroes (denoted CNTPME) are remarkably altered by anodic pretreatment and preadsorption of mediators. It seems that anodic pretreatment leads the long and tangled carbon nanotubes to be partially cut shorter, resulting in more openings as shown by TEM. Besides, the anodic pretreatment may adjust the hydrophobicity of nanotubes to match with that of Os(bpy)3^2 . As a result, the real surface area and the ability of adsorbing mediator Os(bpy)3^2 of the nanotubes are markedly increased so as to effectively catalyze NO2^- reduction in acidic solution.     

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.     

Polypeptide Brushes Grown via Surface-initiated Ring-opening Polymerization of α-Amino Acid N-Carboxyanhydrides

Polypeptide brushes are attractive platforms to generate functional and responsive interfaces that are of potential interest due to their possible biodegradability, biocompatibility and tunable secondary structures. Surface-initiated ringopening polymerization(SI-ROP) of α-amino acid N-carboxyanhydrides represents a powerful and versatile strategy to generate polypeptide brushes. This review is an attempt to capture the state-of-the-art in this field and highlights the latest developments in several selected areas. In addition to presenting an overview of the synthetic methods that have been used to generate polypeptide brushes via SI-ROP, this article will discuss the preparation of patterned polypeptide brushes, the conformational properties of surface-tethered polypeptides, ways to control chain orientation at surfaces as well as properties and applications of these thin polymer films.     

高效液相色谱手性固定相的研究 I:L-缬氨酸-叔丁酰胺型固定相的制备及对映体拆分

A new chiral chemically bonded stationary phase for direct resolution of optical isomers in HPLC was prepared. The experiemental data showed that the chiral stationary phase gave good resolution for the racemic α-amino acid derivatives and that there was no significant influence on the resolution as the eluting rate varied from 0.6 to 2.0 mL/min. The content of isopropanol in the eluent significantly affected the resolution of the enantiomers. The eluent consisting of 1% isopropanol in hexane gave most favorable result, but the retention times were a little longer. It is evident that the resolution was also influenced by the structure of the solute. In all cases, the resolution of N-Ac-DL-Phe-OMe is lower than that of N-Ac-DL-Leu-OMe and N-Ac-DL-Val-OMe. Although the capacity factor of N-Ac-DL-Tyr-Ome varied greatly in different eluting systems, the separation factor and resolution were very close. It was observed that D-amino acid derivatives eluted faster than the corresponding L-isomers. In the above chromatographic conditions N-acetyl-DL-α-phenylethylamine could not be resolved.     

Description of the Structure and Properties of Atactic Polystyrene Melt Using Integral Equation Theory

The polymer reference interaction site model （PRISM） integral equation theory was used to describe the structure and thermodynamic properties of atactic polystyrene （aPS） melt, in which the monomer of aPS is represented with an eight-site model to characterize its microstructure. The intramolecular structure factors needed in the PRISM calculations were obtained from single chain MD simulations. The calculated results indicate that the results by the integral equation method agrees well with experiments, and can reflect the fine microscopic structure of real aPS melt. This work shows that the PRISM theory is a powerful tool for investigating the structure and properties of complex polymers.     

Formation of Network by Carbon Black，Silica and Their Mixing Fillers in Isoprene Rubber北大核心CSCD

The network formed by fillers has great influence on the mechanical properties of rubber materials. To understand the formation of network by carbon black,silica,and carbon black/silica mixing fillers in rubber and its influence on the properties of rubber,isoprene rubber/filler composites with different filler loadings are prepared and their micromorphology,rheological and tensile properties are investigated. It is found that the dispersion of fillers is better in rubber after cure than that in rubber before cure for all three rubber systems,and the filler size of silica is smaller than that of carbon black,but the aggregation is more severe in silica filled rubber system. In mixed filler system,the two fillers tend to aggregate separately, leading to the low modulus at small strain than that in single filler system. With the increase of the filler loading,the tensile strength increases first and then decreases,the elongation at break decreases,and the temperature rise in compression flexometer tests increases. Moreover,the temperature rise in mixed filler system is higher than that in single filler system at high filler loading. © 2022, Science Press (China). All rights reserved.     

Morphology and Mechanical Properties of Nylon 6/PBT Blends Compatibilized with Styrene/Maleic Anhydride Copolymer

The mechanical properties and dynamic mechanical properties of blends composed of Nylon 6 and poly(butylenes terephthalate)(PBT),with styrene/maleic anhydride(SMA)as compatibilizer,were studied.The observation on the morphologies of the etched surfaces of the cryogenically fractured specimens via scanning electron microscopy(SEM)demonstrated that in the compatibilized Nylon 6/PBT blends,there exists a finer and more uniform dispersion induced by the in-situ interfacial chemical reactions during the preparation than that in the corresponding uncompatibilized blends.On the other hand,the overall mechanical properties of the compatibilized blends could be remarkably improved compared with those of the uncompatibilized ones.Moreover,increasing the amount of the compatibilizer SMA leads to a more efficient dispersion of the PBT phase in Nylon 6/PBT blends.Furthermore,there exists an optimum level of SMA added to achieve the maximum mechanical properties.As far as the mechanism of this reactive compatibilization is concerned,the enhanced interfacial adhesion is necessary to obtain improved dispersion,stable phase morphology,and better mechanical properties.     

Synthesis of New Chiral Phosphine Ligands and Their Application in Asymmetric Hydrogenation of Ketones

The design of new chiral ligands is the key in the development of transition metal catalyzed asymmetric synthesis. Many chiral diphosphine ligands have been prepared and applied in asymmetric catalytic reactions with excellent enantioselectivities. Among the chiral diphosphine ligands that have been reported, the atropisomeric C2-symmetric phosphines with a biaryl scaffold initiated by Noyori and co-workers with BINAP were found to have the widest application in the transition metal catalyze…     

Tuning the Reactivity of Ultrathin Oxides: NO Adsorption on Monolayer FeO(111)

Ultrathin metal oxides exhibit unique chemical properties and show promise for applications in heterogeneous catalysis. Monolayer FeO films supported on metal surfaces show large differences in reactivity depending on the metal substrate, potentially enabling tuning of the catalytic properties of these materials. Nitric oxide (NO) adsorption is facile on silver‐supported FeO, whereas a similar film grown on platinum is inert to NO under similar conditions. Ab initio calculations link this substrate‐dependent behavior to steric hindrance caused by substrate‐induced rumpling of the FeO surface, which is stronger for the platinum‐supported film. Calculations show that the size of the activation barrier to adsorption caused by the rumpling is dictated by the strength of the metal–oxide interaction, offering a straightforward method for tailoring the adsorption properties of ultrathin films.     

铁、锰氧化物在自然水体生物膜上的分布

在自然水体中 ,生物膜是一个开放的动力学系统 ,生物膜的形成及其组分处于动态的变化中——水环境中的各种成分在生物膜上发生着合成、聚结、转化、降解等作用 ,从而成为生物膜的一部分 ,还会随着生物膜的脱落重新进入水相中 ,所有这些变化 ,与生物膜本身的性质是分不开的 [1～ 3] 。从环境化学角度看 ,自然水体中生物膜主要化学组分包括金属氧化物 (铁氧化物、锰氧化物和铝氧化物等 )、有机质及少量的矿物质 ,其中 ,铁、锰氧化物在影响痕量重金属在水环境中的迁移、最终归宿、生物地球化学特性、生物可利用性和毒性过程中起着非常重要的作…     

Contribution to direct measurement of double-layer potential at the oxide/electrolyte interface

A method for direct measurement of surface-potential changes at the oxide/electrolyte interface is described. It is based upon the semiconductor effect, and, in contrast to the well-known transistor method, it uses an easier-to-prepare field-effect diode.Measurements of the systems SiO₂/electrolyte solution and Al₂O₃/electrolyte solution show, that the Nernst relation is only valid for Al₂O₃, whereas in the case of SiO₂, besides H⁺ and OH^– ions, also electrolyte ions of alkaline chlorides and MgCl₂ are potential-determining.Mitteilung Nr. 814 aus dem Forschungsinstitut für Aufbereitung der AdW der DDR, Freiberg.     

负载钨催化剂的载体效应及其表面酸性

运用BET、XRD、FT-Raman以及微量吸附量热等手段对由浸渍三种晶型氧化锆及其前体氢氧化锆制备的负载钨催化剂的结构及其表面酸性进行了研究。结果表明起始原料和制备条件对氧化锆的结构有显著影响。浸渍在氢氧化锆上的钨物种会使氢氧化锆转变为四方晶型氧化锆。但浸渍于氧化锆上的钨物种使氧化锆发生晶型转变相对较难。负载钨催化剂表面强酸位的形成与载体晶型、表面钨物种WO_x以及WO_x与载体氧化锆之间的相互作用有关。催化剂上的强酸位可因残留的Na⁺离子所毒化或阻抑。少量Y³⁺离子对表面酸性则无明显影响。     

High Temperature Oxidation of Fe22Cr-alloy

The isothermal and constant heating rate oxidation behaviour of the alloy Fe₇₈Cr₂₂ was examined in air with 1% H₂O and in 7% H₂/93% Ar with 1% or 12% H₂O. The measurements were performed in the temperature range 700–1300°C. The effect of surface treatment prior to oxidation was examined. A Cr₂O₃ scale developed slowly up to900°C. At 1100°C a catastrophic oxidation was observed after heat treatment for 70 h in air with 1% H₂O and in 7% H₂/93% Ar with 12% H₂O. The scale developed in these cases consisted of iron rich oxides such as Fe₂O₃ or FeCr₂O₄, in contrast to the more protective Cr₂O₃ scale seen under other test conditions. Possible causes for the catastrophic oxidation are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

激光促进甲醇在氧化物上的表面反应

运用红外光谱（IR）、程序升温脱附（TPD）技术,对甲醇吸附在氧化物SiO2、γ－Al2O3和MgO表面所形成的反应体系进行了红外振动结构和化学吸附形态分析,并引入1052cm^-1激光,研究了上述体系的激光促进表面反应（LSSR）规律。结果表明：所选固体材料能够明显促进甲醇光促分解反应,室温条件下即可在SiO2上达到40.5%的转化率;另外与甲醇吸附强度和吸附量相比,反应体系的振动结构对LSSR效率起着更为重要的作用,SiO2因能够较好地吸收、传送激光能量而具有比γ－Al2O3和MgO更好的促进反应性能。最后,根据表征和反应结果给出了反应机理的模型。     

电子能谱法研究锡铅合金镀层的表面状态及其与可焊性的关系

本文用X射线光电子能谱(XPS)和俄歇电子能谱(AES)研究了Sn-Pb合金镀层的表面氧化物膜状态并用润湿称量法测定了可焊性。结果表明,Sn-Pb合金镀层表面生成的氧化物膜主要由四价锡的氧化物(SnO_2·XH_2O和SnO_2)组成,铅的氧化物只占很少部分。这说明Sn-Pb合金镀层中锡组分较铅容易氧化。 Sn-Pb合金镀层经155℃加热16小时后,表面氧化物膜的厚度增长很大,同时可焊性明显下降。当Sn-Pb合金镀层经过热熔后,表面变得致密光亮;经155℃加热16小时后生成氧化物膜的厚度较未经热熔的在相同条件下要薄。同时可焊性也较未热熔的好。这说明Sn-Pb合金表面生成氧化物膜的厚度是影响可焊性的重要因素,热熔使Sn-Pb镀层均匀的再结晶改变了镀层结构,使之成为致密的细晶结构,增加了镀层表面的抗氧化能力。故经热熔处理的Sn-Pb合金镀层具有较长的贮存期仍能保持良好的可焊性。     

Al (110) surface oxide thermal stability in ultrahigh vacuum

This research characterizes the stability of the Al₂O₃ surface oxide on Al (110) as a function of temperature and within an ultrahigh vacuum environment (p < 5 × 10^?12 Torr). Auger electron spectroscopy and temperature desorption spectroscopy were used to correlate the change in oxygen and carbon surface concentration. The surface oxide was observed to remain stable up to 350–400 °C. Above this temperature, the oxide began to dissociate resulting in a CO desorption peak at 425 °C followed by extensive dissolution of the C and O into the Al bulk. A second and much smaller CO desorption peak was observed at 590 °C in concert with complete oxide breakdown and the virtual disappearance of surface carbon and oxygen. Extrapolation of the Auger electron spectral ratios of C_KLL and O_KLL peaks to the sum of the Al⁰_LVV and Al³⁺_LVV peak suggests that the surface concentration of each approaches zero at ~640 °C. The predominant mechanism for reduction of the surface oxide occurs by dissolution into the bulk instead of desorption. Copyright © 2013 John Wiley & Sons, Ltd.     

Festkörperaktivität und Mechanismen in Oxidsystemen. X. Untersuchung der Umsetzung von α-Fe2O3 mit BaCO3 mittels RBS-Spektrometrie

Solid State Reactivity and Mechanisms in Oxide Systems. X Investigation of the Reaction of α-Fe₂O₃ with BaCO₃ by RBS-Spectrometry Plate-like shaped α-Fe₂O₃ single crystals with the hexagonal axis perpendicular to the plane are characterized by Rutherford-Back-Scattering measurements. The preparation of dense BaCO₃ layers of a defined thickness is reported. The reaction at 650°C and 800°C leads to the formation of BaFe₂O₄ at the surface. Supported by model calculations the RBS spectra are interpreted by a sequence of phases which are in accordance with the phase diagram. PbO evaporates from the α-Fe₂O₃ single crystal surface at 500°C without reaction.     

Effect of WO3 particle size on the type and concentration of surface oxygen

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