Wide characterisation to compare conventional and highly effective microwave purification and functionalization of multi-wall carbon nanotubes

Both microwave-assisted and conventional acidic treatments for the purification and functionalization of multi-wall carbon nanotubes were investigated. Impurities such as zeolite, catalyst particles and amorphous carbon were eliminated. In comparison to the harshness of the acidic treatment of a conventional technique, the microwave-assisted procedure makes it possible to obtain a material with a higher degree of purity (> 98%) and -COOH functionalization in a shorter time, at a lower temperature, with a smaller amount and lower concentration of acid, as well as without agitation. An extensive step-by-step characterization of the treated samples has shown that the microwave-assisted treatment has limited effects on the significant characteristics of the nanotubes.     

Characterization of carbon thin films prepared by the thermal decomposition of spin coated polyacrylonitrile layers containing metal acetates

Polyacrylonitrile (PAN) layers were cast from dimethyl-formamide solutions onto quartz substrates by spin coating and subsequently annealed at up to 1000 °C in N₂ atmosphere. Carbonization was catalyzed by nickel or cobalt added to the solution as acetate salts. The synthesized films were approx. 970 nm thick and were characterized by Raman and infrared spectroscopy as well as thermogravimetric and electrical conductance measurements. We discuss the effects of carbonization temperature and metal concentration on the morphology, composition and electrical properties of the formed carbon layer. Increasing the amount of catalyst and the pyrolysis temperature was beneficial for the process and resulted in carbonaceous films with a higher degree of structural order as evidenced by the decreasing Raman I_D/I_G ratio and the increasing electrical conductivity of the films. Cobalt is a better catalyst for PAN carbonization than nickel as far as the structure of the product film is concerned.     

Growth, structure and electronic properties of ultrathin cerium oxide films grown on Pt(111)

Ultrathin cerium oxide films have been prepared by oxidizing Ce-Pt/Pt(111) surface alloys with 65 L O₂ at 900 K. According to low electron energy diffraction data, phonon spectra recorded by high resolution electron energy loss spectroscopy and scanning tunneling microscopy measurements the films are of fluorite-type CeO₂(111) structure. They grow three dimensionally as islands, which are flat and up to several hundred square nanometers large. The film thickness varies between one and five layers. The band gap of the oxide films has been probed by scanning tunneling spectroscopy and turned out to be significantly smaller than for bulk CeO_2.     

Fe3O4 on ZnO: A spectroscopic study of film and interface properties

Magnetite (Fe₃O₄) thin films have been grown epitaxially on zinc oxide (ZnO) substrates, using reactive molecular beam epitaxy. The film quality was found to be strongly dependent on the oxygen partial pressure during growth. For a uniform Fe₃O₄ film a certain pressure variation was needed during growth. Structural, electronic, and magnetic properties were analyzed utilizing low energy electron diffraction, Hard X-ray Photoelectron Spectroscopy (HAXPES), Magneto-Optical Kerr Effect (MOKE), and X-ray Magnetic Circular Dichroism (XMCD). Diffraction patterns show clear indication for growth of Fe₃O₄ in the [111] direction on ZnO(0001). Non-destructive depth profiling by HAXPES revealed uniform magnetite thin films. Both, MOKE and XMCD measurements show easy in-plane magnetization. The dichroic spectra clearly support the formation of Fe₃O₄.     

Thermal annealing effect on the nanomechanical properties and structure of P3HT:PCBM thin films

Nanostructured polymer-fullerene thin films are among the most prominent materials for application in high efficient polymer solar cells. Specifically, poly(3-hexylthiophene) (P3HT) and fullerene derivatives (PCBM) blends are used as the donor/acceptor materials forming a bulk heterojunction. Although P3HT:PCBM properties have been extensively studied, less light has been set on its nanomechanical properties, which affect the device service life. In this work Atomic Force Acoustic Microscopy (AFAM), Atomic Force Spectroscopy and Nanoindentation were used to study the effect of the fullerene presence and the annealing on the P3HT:PCBM nanomechanical behavior. The P3HT:PCBM thin films were prepared by spin coating on glass substrates and then annealed at 100 °C and 145 °C for 30 min. Large phase separation was identified by optical and Atomic Force Microscopy (AFM) for the annealed samples. Needle-like PCBM crystals were formed and an increase of the polymer crystallinity degree with the increase of the annealing temperature was confirmed by X-ray diffraction. AFAM characterization revealed the presence of aggregates close to stiff PCBM crystals, possibly consisting of amorphous P3HT material. AFM force-distance curves showed a continuous change in stiffness in the vicinity of the PCBM crystals, due to the PCBM depletion near its crystals, and the AFM indentation provided qualitative results about the changes in P3HT nanomechanical response after annealing.     

A Quasi 2D Model of a High Temperature Polymer Fuel Cell for the Interpretation of Impedance Spectra

Electrochemical impedance spectroscopy is a widely recognized tool for in situ diagnostics of polymer fuel cells. The main drawback of this measurement is that it includes several features, which are not directly related to physical phenomena and the interpretation is often difficult. In this work, a physical quasi 2D model is applied to experimental data of a high temperature proton exchange fuel cell based on polybenzimidazole doped with phosphoric acid. The quasi 2D approach is applied in order to decrease the computational cost of the model, without decreasing the prediction capability. The model is able to simulate polarization curves and impedance spectra and it is fitted on six polarization data and impedance spectra recorded in different conditions. The model is able to capture the main features of a typical spectrum of a polybenzimidazole based high temperature polymer fuel cell. A sensitivity analysis is also performed on the model parameters to show the effect of each physical parameter.     

Electrochemical Impedance Modeling of a Solid Oxide Fuel Cell Anode

A simulation package for the impedance response of SOFC anodes is presented here. The model couples the gas transport in gas channels and within a porous electrode with the electrochemical kinetics. The gas phase mass transport is modeled using mass conservation equations. A transmission line model (TLM), which is suitably modified to account for the electrode microstructural details, is used for modeling the impedance arising from the electrochemical reactions. In order to solve the system of nonlinear equations, an in‐house code based on the finite difference method was developed. Some of the model constants have been calibrated against experimental data. It is demonstrated that the simulation tool is capable of predicting the impedance response of an experimental data set obtained on symmetrical cells with Ni/ScYSZ SOFC anodes. A parametric study is also carried out using the developed simulation tool and the results are further discussed.     

食用油脂掺伪鉴别技术研究进展

食用油脂既是人们膳食结构中不可缺少的重要组成部分,也是食品工业的重要基础原料,其品质和安全性对人类健康有着重要的影响。当前食用油市场较为混乱,各种掺伪现象层出不穷,其掺伪种类和方式多变且复杂,使得油脂掺伪检验已成为油脂安全监控领域的一项技术性难题,亟待建立一套科学、有效的食用油脂掺伪鉴别方法以保护消费者健康,保障食品安全,强化政府监管能力。本文重点综述了气相色谱、液相色谱和色质联用等色谱技术,红外光谱、近红外光谱和拉曼光谱等光谱技术,以及核磁共振法和电子鼻技术等现代分析技术在食用油脂掺伪鉴别中的最新研究进展和应用中存在的问题,并展望今后研究方向,旨在为食用油掺伪鉴别研究提供一定的思路和方法指导。     

中国酿酒行业中近红外光谱技术的应用进展

近红外光谱分析技术作为近几年一种新兴的检测技术,具有无需预处理、速度快、成本低、无污染、不破坏样品化学性质、结果重演性高、绿色环保、多成分可同时分析等优点。目前,我国的酿酒企业多以品评作为酒体质量检测与等级划分的标准,随着近红外光谱分析技术的引入,这为酒体的品评及成分分析提供了一种快速准确科学的分析方法。本文综述了近红外光谱分析技术在目前中国酿酒行业中的应用进展研究,涵盖了白酒、葡萄酒、啤酒、黄酒,并对红外光谱分析技术的进一步发展做了展望。     

High Yield Synthesis,Detailed Spectroscopic Characterization and Electrochemical Fate of Novel Cationic Surfactants

Two new cationic surfactants, N-(dodecanoyl(ethylammonio)carbonothioyl)-N-ethylbenzenaminium bromide and N-(dodecanoyl(ethylammonio)carbonothioyl)-N-ethyl-N-phenylbenzenaminium bromide were synthesized with a high yield by the reaction of appropriate amounts of lauryl chlorides, potassium thiocyanate, amine and alkyl halides. The structures were characterized by ¹H-NMR, ¹³C-NMR, FTIR and UV–Vis spectroscopy. Cyclic, square wave and differential pulse voltammetry were used to investigate the electrochemical fate of both surfactants over a wide pH range.