One-pot,one-step,and selective terpolymerization of ethylene oxide,propylene oxide,and COS to copoly(thioether)s with tunable thermal properties

Facile construction of sulfur-rich polymers using readily available raw chemicals is an area aggressively pursued but challenging. Herein we use common feedstocks of ethylene oxide (EO), propylene oxide (PO), and carbonyl sulfide (COS) to synthesize copoly(thioether)s which are traditionally produced from unpleasant and difficult to store episulfides. In this protocol, the EO/COS coupling selectively generates a pure poly(ethylene sulfide) (PES) with melting temperature (T_m) values up to 172°C and high yields up to 98%. The EO/PO/COS terpolymerization leads to the incorporation of soft poly(propylene sulfide) (PPS) and hard PES segments together, affording a random PES-co-PPS copoly(thioether) with the complete consumption of EO and PO. Additionally, by simply varying the EO/PO feeding ratio, the obtained copoly(thioether)s possess tunable thermal properties, T_m values in the range of 76–144°C, and excellent solubility. These copolymerizations are conducted in one-pot/one-step at industrially favored reaction temperatures of 100–120°C using catalysts of common organic bases, suggesting a facile and practical manner. Especially, the copoly(thioether) exhibits high refractive indices up to 1.68 owing to its high sulfur content, suggesting a broad application prospect in optical materials.     

MCNOs/CdS双效光催化剂的制备及其性能研究

水热合成法制备了不同磁性纳米洋葱碳(MCNOs)负载量(0%、1%、3%、5%)的MCNOs/CdS光催化剂。并通过X射线衍射分析(XRD)、扫描电子显微镜(SEM)、傅里叶红外光谱(FT-IR)、X射线光电子能谱(XPS)、紫外可见光光谱(UV-Vis)、磁滞回线测定仪(VSM)对其进行表征,探究了MCNOs负载比例对催化剂在可见光下降解RhB性能及机理的影响。结果表明,MCNOs能有效提高CdS的光催化效果,复合3%MCNOs后降解率为96%,与纯CdS相比降解率提高了30%,磁性分析表明,其具有良好的顺磁性并能实现催化剂的有效回收。MCNOs/CdS在可见光下催化降解RhB的一级反应动力学直线有较好的拟合度,表明制备的催化剂有较好的催化活性。     

Synthesis and characterization of molybdenum incorporated mesoporous aluminophosphate

A synthesis of molybdenum incorporated mesoporous aluminophosphate with long-chain n-alkylamine as template material had been prepared under non-aqueous condition. These materials were extensively characterized by using X-ray diffraction (XRD), nitrogen sorption isotherms, nuclear magnetic resonance of ²⁷Al and ³¹P (NMR), inductive coupled plasma (ICP), electron spin resonance (ESR), Fourier transform infrared (FTIR) and thermogravimetric-differential thermal analysis (TG-DTA). Morphology of the materials had been observed by using transmission electron microscope (TEM) that revealed the mesoporous materials possessed wormhole-like structures. Alkaline solvent extraction using n-butylamine/ethanol had been efficiently removed the n-alkylamine from the mesoporous samples which yielded BET surface areas around 550-730 m²/g. BJH analysis showed a narrow pore size distribution which increased with increasing of the carbon chain length of alkylamine (template). Valence state and coordination of the molybdenum in the obtained samples were investigated by using ESR and FTIR where it was found that Mo⁴⁺ and Mo⁶⁺ molybdenum species existed in the molybdenum incorporated mesoporous aluminophosphate in tetrahedral coordination.     

Influence of radiation on thin ZnS-Tb films

Changes in thin zinc-sulfide films under the action of the γ-radiation of Co⁶⁰ are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component, and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to⁵D₃→⁷F_j transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred that irradiating the ZnS films with small radiation doses of 10⁴–10⁵ rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects. Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997.     

Heat-treatment studies of molybdenum oxide-monohydrate

The dehydration of molybdic acid, MoO₃---H₂O, was studied by thermal analysis, X-ray diffractometry and FTIR spectroscopy. The results show that an intermediate phase, MoO₃-2/3H₂O is formed at 216 °C and the monoclinic form of MoO₃ is grown above 350 °C. The mechanism of dehydration and structural rearrangement were confirmed by the features of the infrared spectra showing formation of corner-shared MoO₆ octahedra.     

Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

Synthese und Eigenschaften von Sr3Mo1.5Zn0.5O7‐δ, einer Phase mit perowskitverwandter Schichtstruktur

Synthesis and Properties of the Layered Perovskite Phase Sr₃Mo_1.5Zn_0.5O_7‐δ The new layered perovskite phase Sr₃Mo_1.5Zn_0.5O_7‐δ was synthesized by solid state reaction using a Zn/ZnO oxygen buffer. The crystal structure was refined from X‐ray powder pattern by the Rietveld method. The compound crystallizes tetragonal in the space group I4/mmm (no. 139) with the lattice parameters a = 3.9631(3) Å, c = 20.583(1) Å. An oxygen deficiency corresponding to δ ≈ 0.25 was determinated, indicating the presence of molybdenum in mixed valence (Mo⁴⁺ and Mo⁶⁺).     

Vapour and plasma ignition thresholds for visible pulsed-laser ablation of metallic targets

The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result.     

A photoemission study of molybdenum hexacarbonyl adsorption and decomposition on TiO2(1 1 0) surface

The adsorption and decomposition of molybdenum hexacarbonyl on (1 1 0) TiO₂ surfaces were studied using both core levels and valence band photoemission spectroscopies. It was found that after an adsorption at 140 K, when going back to room temperature, only a small part of molybdenum compounds, previously present at low temperature, remained on the TiO₂ surface. This indicates that the desorption temperature on such a surface is lower than the decomposition one. The use of photon irradiation to decompose the hexacarbonyl molecule was also studied. It was shown that during such a decomposition molecular fragments were chemisorbed on the surface allowing a higher amount of metal to remain on the surface. It was also shown that it was possible to get rid of adsorbed subcarbonyl groups and to organize the metal atoms by thermal treatments at temperatures as low as 400 K, i.e. much lower than the one needed to obtain the same structures using physical vapour deposition (PVD). Moreover, due to lower used temperatures, this chemical way of deposition allows a better control of the interface than during PVD growth.     

Scanning probe microscopy studies of PbS surfaces oxidized in air and etched in aqueous acid solutions

Natural n-type PbS single crystals have been studied using AFM, STM and STS after long-term oxidation in air at ambient temperatures and extensive etching in aqueous acid solutions, in contrast to previous work devoted to initial corrosion of fresh surfaces. The exposure of PbS to atmosphere at high relative humidity for several days yields widespread loose oxidation products; the process is much slower at low humidity. Surface morphologies diverge after the treatment in 1 M perchloric and hydrochloric acid solutions at room temperature and become widely different at elevated temperatures, displaying commonly etch pits up to several micrometers in size and depth along with rather uniformly distributed 20-100 nm protrusions of PbS phase. The changes both in topography and semiconducting properties of PbS found by tunneling spectroscopy have been explained in terms of the non-uniform distribution of donor- and acceptor-type defects D⁺/D⁻ in the metal depleted surface layer, which are generated by chemical reactions and, in turn, determine the rates of the PbS corrosion. In particular, the D⁻ centers exhibit a self-catalyzing effect on the non-oxidative local dissolution of PbS in HCl media, resulting in the deep etch pits.