乙炔氢氯化反应中的负载金-离子液体催化剂:离子态金物种的稳定机制

聚氯乙烯(PVC)作为世界通用工程塑料之一,具有优异的物理、化学和机械性能,在工业、农业、建筑、包装、电力等行业中应用广泛.氯乙烯是生产聚氯乙烯的重要单体.氯乙烯的生产主要有电石法和乙烯法两种工艺路线,由于我国“贫油、富煤、少气”的资源现状,电石法产能占全部产能的83%以上.电石法生产氯乙烯的原理是在氯化汞催化剂存在下,将电石水解精制后的乙炔气与氯化氢加成直接合成氯乙烯.随着节能减排及环保要求的逐渐提高和国际涉汞公约的实施,开发新一代绿色无汞催化剂具有重要的战略意义.近年来,金基催化剂是无汞催化剂基础研究和技术开发中最重要的方向.在之前的工作中,我们课题组首先报道了负载离子液体-金催化剂体系(Au-SILP)在电石法生产氯乙烯工艺中的应用,并发现离子液体的存在可以显著提高金活性物种在载体表面的分散度和稳定其化学价态.在后续研究中,我们在负载离子液体-金催化体系中引入金属铜离子(Cu^2+),利用反应过程中Au-Cu之间的氧化还原循环,设计并制备了金属铜基配位离子液体,构建了负载离子液体-金-铜催化剂体系.铜离子的引入形成了一个催化剂自身维持氧化态的微环境,实现了被还原金物种的原位氧化再生.本文在上述研究基础上,利用配位离子液体[Bmim][N(CN)2]中[N(CN)2^–]阴离子和阳离子金之间的强配位作用,构建出比Au-Cl键更稳定的Au–N键,并通过X射线光电子能谱(XPS)、球差校正-扫描透射电镜(AC-STEM)和扩展X射线吸收精细结构(EXAFS)表征证明了Au以单原子状态存在于载体表面.制备的Au-N(CN)2/AC催化剂在乙炔氢氯化反应中表现出比Au-Cl/AC和Au/AC催化剂更高的稳定性和催化活性以及更短的诱导期.进一步表征分析发现,[N(CN)2^–]配体促进了阳离子金和配体之间的电子转移,提高了阳离子金的电子云密度,削弱了乙炔在阳离子金上的吸附强度,抑制了其还原,提高了催化剂的稳定性.更重要的是,与阳离子金配位的[N(CN)2^–]配体使得反应过程中的氯化氢在氮位点发生化学解离,促进了氯化氢活化,同时降低了反应能垒.对负载配位离子液体-金催化体系反应诱导期的分析结果表明,反应诱导期与反应物(乙炔、氯化氢)分子在离子液体层中的溶解度无关,而主要取决于催化剂中Au(Ⅲ)物种的含量和反应物分子在离子液体中的扩散速率.上述研究结果进一步深化了离子液体和活性金物种之间电子的作用机理,建立了负载离子液体-金催化剂体系对反应物的活化机制和反应机理,为进一步开发具有工业应用价值的乙炔氢氯化反应无汞催化剂提供了科学基础和参考.     

A Conjugated Copolymer Bearing Imidazolium-based Ionic Liquid:Electrochemical Synthesis and Electrochromic Properties

An imidazolium-based ionic liquid(IL) modified triphenylamine derivative,namely 1-(4-((4-(diphenylamino)benzoyl) oxy)butyl)-3-methyl imidazole tetrafluoroborate(TPAC_6 IL-BF_4),was designed and synthesized,and further applied with 3,4-ethylene dioxythiophene(EDOT)to prepare conjugated copolymer P(EDOT:TPAC_6 IL-BF_4) via electrochemical polymerization.The cyclic voltammetry curves show that the copolymer P(EDOT:TPAC_6 IL-BF_4) possesses two pairs of redox peaks,which should be ascribed to the redox behaviors of EDOT and triphenylamine.The ultraviolet-visible(UV-Vis) absorption spectrum of P(EDOT:TPAC_6 IL-BF_4) exhibits one maximum absorption peak at 580 nm and a small shoulder characteristic peak at 385 nm under neutral state which are assigned to π-π~* conjugated structure of EDOT and triphenylamine.After being applied at the positive voltage,the copolymer color changes from dark blue to light blue,which is close to the color of poly(3,4-ethylenedioxythiophene)(PEDOT).Surprisingly,the copolymer P(EDOT:TPAC_6 IL-BF_4) shows shorter switching time of 0.37 s,0.30 s at 580 nm and 0.38 s,0.45 s at 1100 nm compared with PEDOT.It is more intriguing that the copolymer P(EDOT:TPAC_6 IL-BF_4) exhibits electrochromism even in free supporting electrolyte.The results confirm that the existence of imidazolium-based ionic liquid has an improvement on the ion diffusion properties and the switching time of conjugated polymer,which may provide a potential direction for the preparation of high-performance electrochromic materials.     

Isoselective Ring-opening Polymerization of Racemic Lactide Catalyzed by N-heterocyclic Olefin/(Thio)urea Organocatalysts

The isoselective ring-opening polymerization of racemic lactide was achieved by combining N-heterocyclic olefin(NHO) with mono(thio)ureas or bis(thio)ureas as catalytic systems. The polymerization process shows high stereoselectivity, controllability and reactivity,delivering multi-block isotactic polylactides with high chain-end fidelity and narrow molecular weight distributions. The enhancement of catalytic performance was observed in the following order: bisthiourea(DTU) monothiourea(TU) bisurea(DU) urea(U). The highest Pm(probability of forming a meso dyad) = 0.91 was observed at-70 °C when using NHO/U1 catalytic system and the high stereoselectivity was attributed to chain-end control mechanism.     

A cosolvent pretreatment: effect of solvent–water on enzymatic hydrolysis of glucan,lignin structure,and dynamics

Cellulose - In this study, a biomass pretreatment strategy with a recyclable cosolvent (toluene sulfonic acid/ethanol) was developed. The low boiling point solvent (78.15 °C),...     

Rapid and label-free classification of pathogens based on light scattering,reduced power spectral features and support vector machine

The rapid identification of pathogens is crucial in controlling the food quality and safety. The proposed system for the rapid and label-free identification of pathogens is based on the principle of laser scattering from the bacterial microbes. The clinical prototype consists of three parts: the laser beam, photodetectors, and the data acquisition system. The bacterial testing sample was mixed with 10 mL distilled water and placed inside the machine chamber. When the bacterial microbes pass by the laser beam, the scattering of light occurs due to variation in size, shape, and morphology. Due to this reason, different types of pathogens show their unique light scattering patterns. The photo-detectors were arranged at the surroundings of the sample at different angles to collect the scattered light. The photodetectors convert the scattered light intensity into a voltage waveform. The waveform features were acquired by using the power spectral characteristics, and the dimensionality of extracted features was reduced by applying minimal-redundancy-maximal-relevance criterion (mRMR). A support vector machine (SVM) classifier was developed by training the selected power spectral features for the classification of three different bacterial microbes. The resulting average identification accuracies of E. faecalis,E. coli and S. aureus were 99%, 87%, and 94%, respectively. The overall experimental results yield a higher accuracy of 93.6%, indicating that the proposed device has the potential for label-free identification of pathogens with simplicity, rapidity, and cost-effectiveness.     

Simultaneous photoelectrochemical detection of dual microRNAs by capturing CdS quantum dots and methylene blue based on target-initiated strand displaced amplification

Herein,we propose a novel photoelectrochemical(PEC) biosensor for dual microRNAs(miRNAs) highly sensitive and simultaneous biosensing based on strand displaced amplification(SDA) reaction.The recognition of H_(miR-21) and H_(let-7 a) by microRNA-21 and let-7 a leads to their change in hairpin structures,subsequently initiating the immobilization of abundant CdS quantum dots(CdS QD s) and methylene blue(MB) based on SDA reaction.The immobilized CdS QDs and MB produce both high PEC currents under430 nm light and 627 nm light illumination,respectively,and the generated PEC currents are closely relied on target miRNAs amounts.Thus,highly sensitive and simultaneous detection of microRNA-21 and let-7 a was readily achieved with detection limit at 6.6 fmol/L and 15.4 fmol/L based on 3σ,respectively.Further,this PEC biosensor was applied in simultaneous analysis of miRNA-21 and let-7 a in breast cancer patient's serum with acceptable results.We expect this biosensor will find more useful application in diagnosis of miRNA-related diseases.     

粘土担载的钼基催化剂的制备、结构及CO加氢合成醇性能

采用溶胶凝胶法与等体积浸渍相结合制备了一系列以粘土为载体的K-Co-Mo催化剂. 采用XRD、N₂等温吸脱附、H_{26+的还原,但对Mo⁴⁺和Co²⁺的还原没有明显的影响. 催化剂经还原后,在其表面生成了一种更低价态的Mo^δ+(1<δ<4)物种,被认为是合成醇的活性中心. 与非负载催化剂相比,粘土担载的K-Co-Mo具有更高的合成醇性能. 负载型催化剂具有较高的活性物种分散度,并且其介孔结构在一定程度上延长了合成醇反应中间体的滞留时间,从而促进了低碳醇的生成. 经773 K还原的催化剂具有较高的活性,其原因可为催化剂表面具有较高含量的Mo^δ+物种.}     

Characterization of Cr‐doped Sb2Te3 films and their application to phase‐change memory

Phase‐change memory (PCM) is regarded as one of the most promising candidates for the next‐generation nonvolatile memory. Its storage medium, phase‐change material, has attracted continuous exploration. Along the traditional GeTe–Sb₂Te₃ tie line, the binary compound Sb₂Te₃ is a high‐speed phase‐change material matrix. However, the low crystallization temperature prevents its practical application in PCM. Here, Cr is doped into Sb₂Te₃, called Cr–Sb₂Te₃ (CST), to improve the thermal stability. We find that, with increase of the Cr concentration, grains are obviously refined. However, all the CST films exhibit a single hexagonal phase as Sb₂Te₃ without phase separation. Also, the Cr helps to inhibit oxidation of Sb atoms. For the selected film CST_10.5, the resistance ratio between amorphous and crystalline states is more than two orders of magnitude; the temperature for 10‐year data retention is 120.8 °C, which indicates better thermal stability than GST and pure Sb₂Te₃. PCM cells based on CST_10.5 present small threshold current/voltage (4 μA/0.67 V). In addition, the cell can be operated by a low SET/RESET voltage pulse (1.1 V/2.4 V) with 50 ns width. Thus, Cr–Sb₂Te₃ with suitable composition is a promising novel phase‐change material used for PCM with high speed and good thermal stability performances. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)