C/C,C/C-SiC梯度基、纳米基、双元基复合材料微观结构特征

采用C和SiC共沉积的CVI技术制备了C/C ,C/C SiC梯度基、纳米基和双元基复合材料 .用光学显微镜、电子探针微观分析、透射电子显微镜和扫描电子显微镜观察了各种材料微观结构 .结果表明 ,SiC加入到碳基体里改变了热解碳的微观结构并导致了C/C复合材料性能的改善 .每种材料都各具特点 .由于它们密度低、良好的力学性能和抗氧化性能使得这些材料成为很有希望的热结构复合材料     

甲醇在Pt/C和Pt/WO_3/C电极上的电氧化

用液相还原法制备碳载Pt(Pt/C)和碳载Pt/WO3(Pt/WO3/C)催化剂.实验表明该催化剂中加入一定量的WO3后,其对甲醇的催化氧化活性和稳定性都有一定提高,并以Pt、W原子比为1∶1的催化剂性能最好.这是由于Pt催化剂中加入了WO3后,其电化学活性比表面积增大,并且降低了对CO吸附强度.     

低铂催化剂Pd@Pt/C及PdPt@Pt/C在燃料电池中的应用

采用分步高压有机溶剂法制备了金属含量为20%(w)的低铂核壳结构催化剂Pd12%Pt3%@Pt5%/C(记为:PdPt@Pt/C)和Pd12%@Pt8%/C(记为:Pd@Pt/C),其中金属钯、铂的含量分别为12%和8%(w)。研究表明:对于甲醇的阳极氧化过程,催化剂PdPt@Pt/C甲醇氧化峰电流密度是Pd@Pt/C的1. 87倍;且催化剂PdPt@Pt/C氧还原催化具有较大的扩散电流密度,比Pd@Pt/C具有较好的氧还原催化能力。采用X射线衍射(XRD)、透射电镜(TEM)、循环伏安法(CV)等方法对催化剂进行表征的结果表明:催化剂采用PdPt为核,Pt为壳的催化剂PdPt@Pt/C,其分散性及电化学活性均比Pd为核,Pt为壳制得的催化剂Pd@Pt/C好。     

Synthesis of bicyclic lactones via I2-mediated intramolecular tandem C–C/C–O bond formation

The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results.     

基于ZIF-8/C制备ZnO/C复合材料及光催化性能的研究

本文采用常温搅拌法将Zn(NO_3)2·6H_2O、活性炭粉和2-甲基咪唑溶于甲醇中,得到一系列含不同质量分数活性炭粉的ZIF-8/C材料,500℃下煅烧,得到ZnO/C复合材料。利用傅里叶红外光谱(Fourier transform infrared spectroscopy,FT-IR)、孔径分布分析仪(Pore diameter analysis apparatus)、紫外-可见吸收光谱(UV-visible absorption spectra)、场发射扫描电子显微镜(Field emission scanning electron microscopy,FE-SEM)和X射线粉末衍射(Powder X-ray diffraction,PXRD)对前驱体和目标产品进行表征分析。这些结果表明前驱体和目标产品中分别含有ZIF-8和ZnO,加入活性炭粉可以拓展ZnO光催化剂的吸收光谱范围。目标产品具有介孔和大孔结构,其中ZnO/C-2的粒径更为均一。另外,在可见光和紫外光下考察目标产品对有机染色剂亚甲基蓝的光催化降解性能和稳定性。实验结果表明:目标产品ZnO/C-2的光催化性能最佳。     

Formation of active phases of Fe/C,Cr/C and Fe–Cr/C catalysts in oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane into ethylene using CO₂ as an oxidant at temperatures of 650–750 °C was carried out over Fe/C, Cr/C and Fe–Cr/C catalysts deposited on a carbon support. Before and after the reaction the catalysts were investigated by X-ray powder diffraction (XRD), in situ magnetometry and transmission electron microscopy methods. The correlation between activity of Fe/C, Cr/C and Fe–Cr/C catalytic systems and their phase composition was established.     

新方法合成LiFePO4/C

以Fe(NO3)3·9H2O、LiNO3、NH4H2PO4和蔗糖为原料,在超临界CO2流体中反应合成,进而经二次焙烧制得LiFePO4/C。 结果表明,在超临界CO2流体中经50 ℃反应24 h,在350和600 ℃焙烧后制得粒径分布在0.5~1.0 μm的纯LiFePO4/C,该材料作为锂离子电池正极的放电比容量达156.6 mA·h/g,经50次循环后容量几乎没有衰减。     

生物质转化中C―O/C―C键的活化断裂

生物质作为自然界中唯一可持续的有机碳来源,在解决环境和能源问题、创建一个碳中和的社会方面展现出巨大的潜力。木质生物质是由具有C―O/C―C键的基本结构单元构成的高分子化合物,活化、断裂这些C―O/C―C键是生物质高值化利用的关键,因此在过去十年中受到了广泛的关注。本文首先简要综述了生物质转化中C―O/C―C键催化断裂的现状,主要关注C―O/C―C键断裂的关键挑战和现有策略。我们的目标不是全面概述C―O/C―C键活化断裂的现况,而是提出与C―O/C―C键断裂相关的核心问题并且对未来的研究作出展望。我们选择了碳水化合物和木质素中几种具有代表性的C―O/C―C键来讨论它们在不同情况下协同催化断裂的机理,然后对未来的研究提出自己的见解。     

生物质转化中C―O/C―C键的活化断裂

Sustainable fuels and chemicals are receiving unprecedented attention worldwide in the context of achieving global carbon neutrality. Biomass, as the only natural and sustainable carbon-based source, shows great potential in addressing our current environmental/energy problems and in creating a carbon-neutral society. Lignocellulosic biomass is made up of basic structural units containing C―O/C―C bonds, and the catalytic cleavage of these C―O/C―C bonds is the key for biomass valorization; thus, garnering considerable attention in the past decade. This viewpoint begins with a brief report on the current status of catalytic activation/cleavage of C―O/C―C bonds during biomass conversion, and then goes on to discuss the key challenges experienced and possible strategies that can be implemented using cooperative catalysis. Our goal is not to provide a comprehensive overview of the activation/cleavage of the C―O/C―C bonds in biomass, but rather to highlight the core questions and challenges related to this process and the requirements for future investigations. We selected several representative C―O/C―C bonds in carbohydrates and lignin to discuss their catalytic mechanism in terms of total/selective bond cleavage, and then present our own insights for future studies. Therefore, this article mainly discusses the following two aspects: (1) The activation and cleavage of C―O bonds, which includes total and selective C―O bond cleavage in furan-based fuel precursors and lignin. When aiming to produce liquid fuels, including alkanes and arenes from biomass, the total cleavage of C―O bonds is essential. During the hydrodeoxygenation (HDO) of furan-based fuel precursors, various C―O bonds need to be cleaved, especially the C―O bond of each tetrahydrofuran ring, which has the highest bond energy. When compared with the total HDO of fuel precursors, the removal of the phenolic hydroxyl groups in lignin to produce arenes is more challenging because of the competition between the over-hydrogenation of the benzene rings and the cleavage of phenolic C―O bonds. The selective or partial cleavage of C―O/C―C bonds to form highly functionalized chemicals has recently attracted great interest and is believed to be a dynamic future research avenue. For example, the production of phenol from lignin or lignin-model compounds, through the selective removal of methoxy groups and para-side-chain groups, while preserving the phenolic hydroxyl groups, has been extensively explored in the past few years. (2) The other important aspect of this article is the cleavage of the C―C bonds in carbohydrates and lignin. The cleavage of carbohydrate C―C bonds occurs via retro-aldol condensation, which produces propylene glycol, ethylene glycol, ethanol, and lactic acid. The cleavage of C―C bonds in lignin is challenging because the bond energy of the C―C bonds is generally higher than that of the C―O bonds in lignin. Therefore, in this section, we discuss the cleavage of the strongest 5―5' bond in lignin. Finally, some subjective perspectives and future directions are provided, also highlighting several major challenges in this field.      

C440/C540/Saf-T三元混合染料体系的荧光光谱研究

选择适当的混合染料溶液作为染料激光器的工作物质,近年来,已有一些文献报导,但大都局限于二元混合染料体系。对于三元混合染料体系国外也曾有过少量报导,诸如C102/R110/RB,C102/RB/CV,C2/C6/R6G,R6G/CV/NB等。或多或少地得到了三个波长     

Rh6G-DMTC分子间能量转移的荧光光谱研究

利用N_2激光器作为激发光源, 测量若丹明6G(Rh6G)和N,N′-二甲基噻碳菁碘盐(DMTC)不同浓度混合的乙醇溶液的荧光光谱, 证明 Rh6G-DMTC组成施主-受主对, 存在着分子间能量转移效应。通过对DMTC荧光强度与Rh6G浓度的关系的测量, 讨论了Rh6G-DMTC能量转移的机制, 并且导出了辐射转移和Förster转移两种典型过程中受主荧光强度与施主浓度的关系式。     

Highly Branched Polymers with Layered Structures that Mimic Light‐Harvesting Processes

Hyperbranched polymers (HBPs) with decorated donor and acceptor chromophores in different domains were constructed to demonstrate the function of light harvesting in a polymeric nanostructure. Taking advantage of our recently developed chain‐growth copper‐catalyzed azide–alkyne cycloaddition polymerization, two structural parameters in the HBPs, for example, the molar ratio of the acceptor Coumarin 343 in the core to the donor Coumarin 2 on the periphery, and the average distance between these two layers, could be independently varied in a one‐pot synthesis. The results demonstrated an efficient energy transfer from the excited Coumarin 2 to the ground‐state Coumarin 343 in the core, with the efficiency of the energy transfer reaching as high as 98 %. The excited Coumarin 343, after receiving energy from donor Coumarin 2 emitted higher fluorescence intensity than when directly excited, indicating an observed light concentration effect from the periphery dye to the central dye in one polymer structure.     

全合成双分子膜分子激发态能量转移的研究

研究了全合成双分子膜内的分子激发态能量转移行为,给体为囊泡双亲分子上的联苯生色基,受体是通过静电相互作用结合在囊泡表面上的荧光黄阴离子.荧光黄猝灭联苯的荧光强度符合Sern-Volmer猝灭定律.探讨了囊泡在能量转移过程中的组织作用、转移效率与机制.通过研究由静电作用结合在囊泡表面上的荧光黄给体和四苯基卟啉受体间的能量转移,改善了光的输出,扩展了光波的覆盖范围.全合成双分子膜是能量转移的有效介质和良好的膜模拟剂.     

A study of polymer blends by nonradiative energy transfer fluorescence spectroscopy

The nonradiative energy transfer (NRET) method has been used to study the miscibility of polymer blends in the solid state. This can be done by labeling the polymers with fluorescence donor and acceptor chromophores. The efficiency of energy transfer, which reveals the interpenetration of the chains, is measured by following changes in the fluorescence intensity ratio of the donor and acceptor as a function of the concentration of the polymer mixture and by comparison with reference values corresponding to totally miscible and totally immiscible systems. It is shown that the reference ratio corresponding to the absence of energy transfer must be determined by using donor-labeled and acceptor-labeled polymer films, instead of making measurements in chromophore solutions in organic solvents, as has usually been done. It is also shown that fluorescence quenching is important in such studies, since it can lead to variations of the fluorescence intensity ratio by more than an order of magnitude; this factor varies with blend concentration and is particularly sensitive to the presence of halogen atoms. The NRET technique has been applied to several PVC/CPVC binary blends and to PCL/PVC/CPVC ternary blends in which PVC and CPVC were labeled by naphthalene and anthracene, respectively [PCL is poly(ε-caprolactone), PVC is poly(vinyl chloride), and CPVC is chlorinated PVC]. For binary blends, the measured intensity ratios indicate the immiscibility of PVC with CPVC, although there is nonnegligible energy transfer between the two phases. For ternary blends, the intensity ratios indicate that the addition of up to 40 wt % of PCL to the immiscible PVC/CPVC binary system leads to the formation of two coexisting PCL/PVC and PCL/CPVC phases.     

Design and synthesis of core and peripherally functionalized with 1,8-naphthalimide units fluorescent PAMAM dendron as light harvesting antenna

This paper reports on the design, synthesis and spectral characteristics of a novel PAMAM dendron (7), core and peripherally functionalized with 1,8-naphthalimide fluorophores. The novel compound 7 was configured as light harvesting antenna where the system surface is functionalized with “donor” dyes (blue emitting 1,8-naphthalimides) that are capable of absorbing light and efficiently transferring the energy to a single “acceptor” dye (yellow-green emitting 1,8-naphthalimide) in the focal point of the dendron. The overlap between the emission of the donor and the absorbance of the acceptor was more than 95%. As a result of the energy transfer, the blue emission intensity of the periphery in the donor–acceptor system was decreased with 93%, while the yellow-green core fluorescence enhancement (λ_ex = 360 nm) of the system was more than 26 times with respect to the fluorescence intensity of the comparative yellow-green emitting 1,8-naphthalimide. This indicates efficient energy transfer between the donor and acceptor dye fragments and that the novel compound 7 would be able to act as a highly efficient light harvesting antenna.     

Transfer of electronic excitation energy between randomly mixed dye molecules in the channels of zeolite L

Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Fine-tuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10(-4) mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for F?rster energy transfer material.     

Construction of triblock copolymer-gold nanorod composites for fluorescence resonance energy transfer via pH-sensitive allosteric

To explore the effects of microenvironmental adjustments on fluorescence, a pH-sensitive nano-composite system based on fluorescence resonance energy transfer (FRET) was constructed. The model system included a modified triblock copolymer (polyhistidine-b-polyethylene glycol-b-polycaprolactone) and gold nanoparticles. A near-infrared dye was used as the donor, and spectrally matched gold nanorods, attached after C-terminus modification with α-lipoic acid, were used as the receptor to realize control of the FRET effect over the fluorescence intensity for two polymer configurational changes (i.e., “folded” and “stretched” states) in response to pH. After synthesis and characterization, we investigated the self-assembly behavior of the system. Analysis by quartz crystal microbalance revealed the pH sensitivity of the polymer, which exhibited “folding” and “stretching” states with changes in pH, providing a structural basis for the FRET effect. Fluorescence spectrophotometry investigations also revealed the regulatory impact of the assembled system on fluorescence.     

Photopolymerization reactions initiated by a visible light photoinitiating system: Cyanine dye/borate salt/1,3,5‐triazine

New three‐component photoinitiating systems consisting of a cyanine dye, borate salt, and a 1,3,5‐triazine derivative were investigated by measuring their photoinitiation activities and through fluorescence quenching experiments. Polymerization kinetic studies based on the microcalorimetric method revealed a significant increase in polymerization rate when the concentration of n‐butyltriphenylborate salt or the 1,3,5‐triazine derivative were increased. The photo‐induced electron transfer process between electron donor and electron acceptor was studied by means of fluorescence quenching and SrEt change of the fluorescence intensity. The experiments performed documented that an increase of the n‐butyltriphenylborate salt concentration dramatically increases the rate of dye fluorescence quenching, whereas the increasing of the 1,3,5‐triazine derivative concentration slows down the consumption of the dye. We conclude that the primary photochemical reaction involves an electron transfer from the n‐butyltriphenylborate anion to the excited singlet state of the dye, followed by the reaction of the 1,3,5‐triazine derivative with the resulting dye radical to regenerate the original dye. This reaction simultaneously produces a triazinyl radical anion derived from the 1,3,5‐triazine, which undergoes the carbon‐halogen bond cleavage yielding radicals active in initiation of a free radical polymerization chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3626–3636, 2007     

The synthesis and fluorescence of a methoxy-phenyl substituted C_60-pyrrolidine derivative

A new 4-methoxyphenyl substituted C60-pyrrolidine derivative, C60(C10H13NO) (1), was prepared and its room-temperature fluorescence was studied. Its fluorescence intensity is three times stronger than that of C60. Its singlet energy was estimated to be 25 kJ/mol lower than that of C60. The fluorescence lifetime was determined to be 2.1+0.3 ns by using the frequency domain method. The fluorescence quenching by concentration and aromatic electron donor: N, N-dimethyl aniline (DMA) was investigated. Data show that its fluorescence could not be quenched by DMA.     

MECHANISM OF CONCENTRATION QUENCHING OF A XANTHENE DYE ENCAPSULATED IN PHOSPHOLIPID VESICLES

Encapsulating a xanthene dye in phospholipid vesicles produces vesicle solutions that contain dye at very high microscopic concentrations, but have a low overall optical density, thereby eliminating reabsorption. Using this system, we have studied the effects of concentration on the fluorescence lifetime of one such dye, sulforhodamine 101. We have observed that the lifetime decreases as a function of encapsulated dye concentration, which is indicative of collisional quenching. The lifetime decreases from 4.5 nsec for sulforhodamine in dilute aqueous solution to 0.69 ns at an encapsulated concentration of 33 m M . The bimolecular rate constant for this event is 2.6 10¹⁰ M ^-1 s^-1, consistent with a diffusion controlled event. However, the quenching constant calculated from changes in intensity is 2.2 10¹¹ M ^-1 s^-1. Thus, collisional quenching is not the predominant mechanism of quenching. The absorption spectra of dye in vesicles indicate an important contribution from static complex formation. Förster distance calculations indicate that energy transfer can also occur to a significant extent, with a predicted efficiency of transfer of 34% at a dye concentration of only 1 m M