苯并噻吩/二苯并噻吩在改性Y型分子筛上的吸附

主要研究了金属离子交换分子筛对有机硫化物苯并噻吩和二苯并噻吩的吸附.首先通过液相离子交换法对商品的Na(Ⅰ)/Y分子筛进行改性,分别制备了5种过渡金属离子的Y型分子筛Ag(Ⅰ)/Y、Ni(Ⅱ)/Y、Zn(Ⅱ)/Y、Cu(Ⅱ)/Y和Fe(Ⅲ)/Y,用静态吸附法测定了苯并噻吩和二苯并噻吩分别在6种Y型分子筛上的吸附等温线,应用软硬酸碱理论分析和讨论了其吸附能力的差异.结果表明: Na(Ⅰ)/Y对苯并噻吩有吸附,而对二苯并噻吩无吸附作用;a(Ⅰ)/Y分子筛经离子交换Ag 、Ni2 、Zn2 、Cu2 、Fe3 后,其吸附苯并噻吩和二苯并噻吩的能力得到了不同程度的提高,其中交换软酸离子的Ag(Ⅰ)/Y其吸附容量增加最多,交换交界酸的Ni(Ⅱ)/Y、Zn(Ⅱ)/Y、Cu(Ⅱ)/Y次之,而交换硬酸的Fe(Ⅲ)/Y增加最少.这表明,当Na(Ⅰ)/Y分子筛上分别离子交换以上5种软酸性大于Na 的金属离子时,所得到的改性分子筛其对苯并噻吩和二苯并噻吩的吸附容量均增强.同时,这种吸附能力的大小顺序基本上与这些离子的绝对硬度η成反比.     

Crystallographic characteristics and fine structures of semiconducting transition metal silicides

Silicide-based photonic materials have attracted a great deal of research interest due to their compatibility with the well-developed silicon technology. Extensive efforts have been made for the synthesis and characterisation of these materials. This paper covers some aspects of the microstructural and crystallographic characteristics of ion beam synthesised silicides such as the semiconducting iron and ruthenium silicides, using transmission electron microscopy. A previously predicted new orientation relationship has been found to exist between the Si substrate and ion beam synthesised βFeSi₂ nanocrystals, which are free of 90° rotational order domain boundaries.     

Structural characteristics and spectral response of composite transition metal oxide photocatalytic materials

Layered composite materials formed by the transition metal oxides, including the niobates, titanates, titanoniobates, and tantalates, have been studied as a kind of new photocatalytic materials because of their unique structures and properties. Their photocatalytic performance could be modified by adjusting the laminate composition, selecting appropriate phase structure, exchanging interlayer cations or intercalated-pillaring, exfoliated-assembling, etc. The purpose of this present paper is to review the main factors affecting photocatalytic performance of the layered composite transition metal oxides and to provide reference for further construction of new photocatalytic materials.     

The gas-phase decomposition of nitromethane over metal ion-exchanged sodium Y zeolite and sodium X zeolite

The major products formed in the gas decomposition of nitromethane at 573 K over nickel(II)-, uranyl(VI)-, or zinc(II)-exchanged sodium Y zeolite are ammonia, carbon dioxide, and water, much of which is isolated on cooling as the ammonium bicarbonate: ammonium carbamate double salt, along with significant amounts of molecular nitrogen and carbon monoxide. Much less carbonate double salt is isolated when using the copper(II)-exchanged sodium Y zeolite where molecular nitrogen, carbon monoxide, and carbon dioxide are the major products with a smaller amount of water. An even smaller amount of carbonate double salt is isolated when the decomposition occurs over the sodium Y zeolite, the major product being carbon monoxide with smaller amounts of molecular nitrogen, carbon dioxide, and water and minor amounts of molecular hydrogen, methane, and nitrous oxide. The decomposition of nitromethane over cadmium(II)-, lanthanum(III)-, and cobalt(II)-exchanged sodium X zeolite leads to the isolation of the carbonate double salt in amounts comparable to those formed using the nickel(II)-, zinc(II)-, or uranyl(V)-exchanged sodium Y zeolite, though the zinc(II)- or nickel(II)- exchanged sodium X zeolite leads to isolation of significantly less carbonate double salt and the sodium X zeolite to hardly any. The mechanism of the metal-exchanged zeolite-catalyzed decomposition of nitromethane is considered in terms of two major pathways for decomposition. Using the same conditions for the catalytic conversion of nitromethane to products, nitroethane is recovered unchanged.     

Infrared studies on nitrogen oxides adsorbed on alkali metal ion-exchanged ZSM-5 zeolites

The adsorption of nitrogen oxides (NO_x) on a series of alkali metal ion-exchanged ZSM-5 zeolites at 226 K was investigated by in situ infrared spectroscopy. In the low NO pressure region, the main species found on each zeolites was an NO monomer linearly adsorbed onto the cation through an O atom (M⁺ ··· ON), but an M⁺ ··· NO species was not detected. On the other hand, a part of adsorbed NO disproportionated into N₂O and N₂O₃ under high NO pressures (higher than 1.3 kPa). The formation of N₂O₃ was enhanced at a high density of nitrogen oxides (NO_x) in the ZSM-5 pore.     

Amorphous transition metal carbides

Titanium carbide films were deposited by chemical vapor deposition from tris(2,2'-bipyridine)titanium. Other films of titanium carbide and niobium carbide were obtained by electron beam vaporization of the corresponding crystalline compound. X-ray and electron diffraction studies showed that the structure of the deposits ranged from microcrystalline to amorphous. The coatings were analyzed by secondary ion mass spectroscopy, Auger electron spectroscopy and electron spectroscopy for chemical analysis. The results of these studies lead to an understanding of the formation and nature of the films. The objective is to modify the mechanical properties of brittle transition metal carbides.     

Amorphous transition metal films

The structure and magnetic properties of amorphous transition elements is reviewed. The methods of obtaining suitable samples will be discussed, the structural investigations so far carried out will be described, and the results compared with those obtained from model building. The experimental measurements on the effect of structural disorder on the magnetic moment and Curie temperature of the transition elements will be reviewed in the light of current theoretical progress.     

Ternary transition metal germanides and arsenides

Crystallographic data are given for TiCrAs, TiMnAs, and TiFeAs with the Fe₂P structure, VCoAs, VNiAs, MnCoAs, and ZrMnGe with the Co₂P structure, and TiMnGe with the TiFeSi structure. Magnetic properties of MnCoAs and VCoAs are briefly described. A further discussion of metal-metal bonding in these and other NiAs-related structures is given.     

Swelling and ketoprofen release characteristics of thermo- and pH-responsive copolymer gels

Swelling-controlled drug delivery copolymer gels were newly synthesized by introducing thermo- and pH-responsive methacryloyl-glycine (MA-Gly) or pH-responsive methacrylic acid (MA-Ac) for comparison with thermoresponsive acryloyl-L-proline ethyl ester (A-ProOEt). A homopolymer gel of A-ProOEt was kept at degrees of swelling that were less than 0.5 at a pH from 2.5 to 7.5 at 37 degrees C. The thresholds of swelling for copolymer gels consisting of A-ProOEt/MA-Gly and A-ProOEt/MA-Ac with a composition of 40/60 mol% were found to be pH 3.0 and pH 5.5, respectively, in buffer solutions at 37 degrees C. The diffusion characteristics of 2-(3-benzoylphenyl)propionic acid (ketoprofen) from such copolymer gels was evaluated in buffer solutions at pH's more than 5.5, and it was found that A-ProOEt/MA-Gly gel possesses a case II transport mechanism that is completely linear time dependent in both the amount diffused and the penetrating swelling front position. On the other hand, A-ProOEt/MA-Ac gel exhibited a non-Fickian (or anomalous) diffusion behavior under the same conditions.     

Preparation of some transition metal sulphides

Ternary sulphides, LnMS₃ (Ln=rare earth metal; M=first row transition metal) and MV₂S₄ (M=Mg, Fe, Co, Ni and Zn) have been prepared by the reaction of appropriate ternary metal oxides with H₂S or CS₂/N₂ vapours at elevated temperatures. Chemical analysis and x-ray powder diffraction of the products indicate formation of single-phases with unique crystal structures in many cases. Communication No. 117 from the Solid State and Structural Chemistry Unit.     

New chemistry of transition metal oxyhydrides

Abstract

In this review we describe recent advances in transition metal oxyhydride chemistry obtained by topochemical routes, such as low temperature reduction with metal hydrides, or high-pressure solid-state reactions. Besides the crystal chemistry, magnetic and transport properties of the bulk powder and epitaxial thin film samples, the remarkable lability of the hydride anion is particularly highlighted as a new strategy to discover unprecedented mixed anion materials.     

Thermal oxidation of transition metal silicides

A survey has been made of most publications on the oxidation of transition metal silicide films on either silicon or an SiO₂ substrate.On silicon substrates the general trend is that SiO₂ forms on the sample surface in preference to metal oxides, with the silicide layer being morphologically preserved. Thermodynamics, in terms of heats of formation and ternary phase diagrams, has been used successfully to explain the general absence of metal oxides and also to explain the exceptions to that rule. Kinetics also plays a part in the determination of the reaction products. The growth rate of SiO₂ on silicon substrates obeys the linear-parabolic law. The parabolic rate constant of silicide oxidation is essentially the same as that of silicon oxidation, indicating that the oxide and its diffusivity for the oxidant are the same for silicon and silicides. However, the linear rate constant of silicides exceeds that of silicon, and its value varies with the silicide. The differences among silicides might be attributed to differences in the atomic transport processes within the silicide; the enhancement with respect to silicon has been ascribed to the metallic nature of the silicides.On SiO₂ substrates, the oxidation ultimately leads to the formation of metal oxides as well. Instabilities of structure and loss of material can occur.The properties of the grown SiO₂ are reviewed and directions for further studies are outlined.     

Transistor-like behavior of transition metal complexes

Electron transport through semiconductor and metallic nanoscale structures, molecular monolayers, and single molecules connected to external electrodes display rectification, switch, and staircase functionality of potential importance in future miniaturization of electronic devices. Common to most reported systems is, however, ultrahigh vacuum and/or cryogenic working conditions. Here we introduce a single-molecule device concept based on a class of robust redox active transition metal (Os(II)/(III)) complexes inserted between the working electrode and tip in an electrochemical scanning tunneling microscope (in situ STM). This configuration resembles a single-molecule transistor, where the reference electrode corresponds to the gate electrode. It operates at room temperature in a condensed matter (here aqueous) environment. Amplification on-off ratios up to 50 are found when the redox level is brought into the energy window between the Fermi levels of the electrodes by the overpotential ("gate voltage"). The current-voltage characteristics for two Os(II)/(III) complexes have been characterized systematically and supported by theoretical frames based on molecular charge transport theory.     

Aspects of transition metal mediated polymerizations

Catalysts based on metallocene complexes of early transition metals herald a new era in Ziegler—Natta olefin polymerization. The developments are driven primarily by the flexibility and high activity of metallocene catalysts, which allow excellent control of polymer properties and have led to a remarkably wide spectrum of polymers and copolymers. In-depth mechanistic understanding is proving crucial for catalyst design and has opened up the use of metallocenes in non-Ziegler chemistry, notably as initiators for carbocations polymerizations. Recently developed late transition metal complexes have substantially added to the range of olefin (co)polymers that are now accessible, including copolymerizations with carbon monoxide and polar monomers.     

Route to transition metal carbide nanoparticles through cyanamide and metal oxides

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.     

Optical and magnetic properties of transition metal oxides

The extremely strong coupling of conduction electrons with local spins in transition metal oxides leads to many intriguing electronic and optical properties, which are currently of great interest. Among these intriguing properties, the discovery of colossal magnetoresistance in manganese oxides has sparked a number of studies on the magnetic and electronic properties of these materials as well as the exploration of the relevant new materials phase.     

不同结构聚酰亚胺膜在乙醇/水体系中的溶胀特性

用5种二胺和4种二酐合成了2个系列8种不同结构的聚酰亚胺(PI)均质膜.测定了不同结构PI膜在质量分数为88%乙醇/水溶液中的溶胀特性,并讨论了不同二胺和二酐结构对渗透物分子在膜内的溶解特性的影响.     

Swelling and diffusion characteristics of modified poly (N-isopropylacrylamide) hydrogels

Thermo-responsive hydrogels are capable of swelling changes to external temperature. A series of modified poly (N-isopropylacrylamide) (PNIPA) hydrogels was synthesized by free radical polymerization in aqueous solution. Acrylamide (AAm) was used to increase the lower critical solution temperature (LCST), while sodium alginate (SA) was used to improve the swelling performance of the hydrogels. Experiments show that 5.5% mass ratio of AAm increased the LCST by about 9 °C above that of conventional PNIPA. Also, SA significantly improved the equilibrium swelling ratio associate with temperature change. Trypan blue diffusion revealed significant differences in the fluid release obtained from hydrogels with modified LCST and swelling properties. The implications of the modified fluid release and swelling characteristics are also discussed for the device design of thermo-sensitive hydrogels for localized drug delivery.     

Diffraction from transition metal chalcogenide nanotubes

Quasi-one dimensional crystals are built of elements pertaining to fifteen elementary conformation classes. Quite recently, general expressions for diffraction intensity have been found for each of these classes. Here, these results are used to predict diffraction patterns from inorganic MS₂ (M = Mo,W) single-wall nanotubes. It is shown that although the considered nanotubes are many-orbit systems they can be fully characterized by comparing their normal incidence diffraction patterns with the simulated ones (if the measurements are sensitive enough). Namely, all the symmetry group parameters (being uniquely related to the chiral indices of a nanotube) can be gathered from the pattern while numerical simulations have proved to be satisfactory fast. Precise determination of the tube parameters, like chirality and number of walls is discussed.     

Valleytronics in transition metal dichalcogenides materials

Nano Research - Valley degree of freedom in the first Brillouin zone of Bloch electrons offers an innovative approach to information storage and quantum computation. Broken inversion symmetry...