NaBF4对锂离子电池石墨负极性能的影响

利用恒流充放电、循环伏安、交流阻抗、SEM、EDS等测试技术研究了在锂离子电池石墨负极和浆过程中加入NaBF₄对其电化学性能的影响。结果表明:NaBF₄的最佳添加量为2%,可明显提高石墨电极的首次放电比容量和充放电效率;电极的自放电性能和循环稳定性得到明显改善。室温条件下,添加了2% NaBF₄的电极以放电容量计算的自放电率为0.87%·d^-1,比未添加时降低了15%;循环伏安、EDS以及SEM测试结果表明,四氟硼酸钠参与了石墨电极的成膜过程,改变了SEI膜的组分和形貌。     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(C_nTAB)对其进行插层处理;通过改变C_nTAB的链长、浓度,得到系列C_nTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及C_nTAB插入量进行表征。结果表明,随着C_nTAB链长的增长、C_nTAB浓度的增大,C_nTAB/GO插层复合物的最大底面间距逐渐增大。C_nTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即C_nTAB以单分子层吸附在GO片层上。根据C_nTAB/GO插层复合物最大底面间距及C_nTAB插入量的变化规律分析,得出C_nTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

镍锌铁氧体/膨胀石墨/聚苯胺复合物的电磁损耗性能

用化学共沉淀法和原位乳液聚合法分别制备了镍锌铁氧体(Ni_xZn_1-xFe₂O₄)、Ni_0.7Zn_0.3Fe₂O₄/膨胀石墨(NZF/EG)二元复合物及其聚苯胺(PANI)包覆的三元复合物(NZF/EG/PANI)。用现代测试技术表征了样品的组成、结构、形貌和电磁性能。结果表明,NZF粒子较好地嵌入到EG的层间,PANI对NZF/EG的包覆效果良好;三元复合物的磁性能随磁性组分含量的减小而减弱,而电导率与EG和PANI的导电性及其相对含量相关联;复合物的电磁损耗性能优良,其中三元复合物优于二元复合物。含PANI 70wt%的NZF/EG/PANI三元复合物,制样厚度分别为1.5、2.0和2.5 mm时,其反射损耗峰值(有效带宽)分别为-19.99 dB(5.82 GHz),-20.33 dB (4.08 GHz)和-25.28 dB(3.67 GHz),具有优良的电磁波吸收效果。     

锂硫电池膨胀氧化石墨/硫复合正极材料的制备及其性能

以棒状石墨为原料,采用改良的Hummers法与热处理制备得到膨胀氧化石墨(E-GO),利用在酸性水溶液中归中化学反应的方法合成纳米尺寸的硫颗粒,使其嵌入到膨胀氧化石墨的内部,制备了膨胀氧化石墨-硫复合材料。采用红外光谱,X-射线光电子能谱表征了膨胀氧化石墨表面官能团的存在和种类;X-射线衍射分析结果表明生成的硫属于斜方晶结构;扫描电子显微镜和透射电镜分析证明了材料中硫的均匀分布。恒电流充放电结果表明该复合正极材料的首次放电容量为1 020 mAh.g-1,100周循环之后其容量还保持在650 mAh.g-1左右;材料的倍率性能和库伦效率优异,这可能得益于小尺寸的硫在材料中均匀分布,以及表面官能团对硫的固定化作用。     

石墨炉原子吸收法测定PU材料中的铬

采用微波消解技术进行样品前处理,建立了石墨炉原子吸收法测定PU材料中铬含量的方法。在波长429.0 nm下,利用石墨炉程序升温测定,狭缝设为0.5 nm,塞曼效应作为背景校正。标准工作曲线线性良好,相关系数r=0.9986,方法检出限为0.051μg/L,测定结果的相对标准偏差为3.78%,加标回收率为92%～120%(n=6)。该方法简便、可行,适用于PU材料中铬的测定。     

微波消解–石墨炉原子吸收法测定化妆品中的铅

建立了微波消解–石墨炉原子吸收光谱法测定化妆品中铅的方法。探讨了样品前处理条件、基体改性剂的选择和优化、石墨炉升温条件等对测定结果的影响。在优化的试验条件下,铅的质量浓度在0~100 ng/mL范围内与吸光度具有良好的线性关系,线性相关系数r=0.9991,检出限为0.33 ng/mL。用该法对5种化妆品中的铅进行测定,加标回收率在95.0%~106.1%之间,测定结果的相对标准偏差不大于3.6%。该方法可应用于化妆品中痕量铅的分析。     

C K‐edge NEXAFS study of fluorocarbon formation on carbon anodes in molten NaF–AlF3–CaF2

Operational instability from processes occurring at the anode during the production of aluminum in the commercial Hall‐Héroult process may lead to an increase in undesirable fluorocarbon emissions, higher energy use, and shorter plant life. One contribution to this instability may be the possible formation of a fluorocarbon film at the electrode interface. Here, the surface composition of graphite anodes after electrolysis in molten NaF–AlF₃–CaF₂ at 990 °C is investigated for evidence of fluorocarbon formation using C K‐edge near edge X‐ray absorption fine structure. Fluorocarbon is identified on an anode surface after prolonged anode effect (very high overpotential with increased cell resistance) and also on an anode surface after normal electrolysis without anode effect. This provides evidence that fluorocarbon formation may occur prior to anode effect lowering the surface tension of the anode and therefore resulting in dewetting to contribute to the onset of the anode effect. Confirmation that such compounds form furthers our understanding of electrochemical reactions of graphite with fluoride and of the fundamental processes that occur in an aluminum smelter cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry using Pd/Mg chemical modifier and slurry sampling

Effectiveness of Pd/Mg chemical modifier for the accurate direct determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry (GF-AAS) using slurry samples was evaluated. A calibration curve prepared by aqueous zinc standard solution with addition of Pd/Mg chemical modifier is used to determine the zinc concentration in the sediment. The accuracy of the proposed method was confirmed using Certified Reference Materials, NMIJ CRM 7303-a (lacustrine sediment) from National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Japan, and MESS-3 (marine sediment) and PACS-2 (marine sediment) from National Research Council, Canada. The analytical results obtained by employing Pd/Mg modifier are in good agreement with the certified values of all the reference sediment materials. Although for NRC MESS-3 an accurate determination of zinc is achieved even without the chemical modifier, the use of Pd/Mg chemical modifier is recommended as it leads to establishment of a reliable and accurate direct analytical method. One quantitative analysis takes less than 15 minutes after we obtain dried sediment samples, which is several tens of times faster than conventional analytical methods using acid digested sample solutions. The detection limits are 0.13?µg?g^?1 (213.9?nm) and 16?µg?g^?1 (307.6?nm), respectively, in sediment samples, when 40?mg of dried powdered samples are suspended in 20?mL of 0.1?mol?L^?1 nitric acid and a 10?µl portion of the slurry sample is measured. The precision of the proposed method is 8–15% (RSD).     

Phase Systems and Post-Column Dithizone Reaction Detection for the Analysis of Organo-Mercurials by HPLC

Abstract

The suitability of HPLC (normal and reversed phase adsorption) with UV or post-column reaction detection for the analysis of organomercurials was investigated systematically. The separation of organomercurials is best carried out on a reversed phase system with a C-8 bonded phase material as the stationary phase and acetonitrile-aqueous sodium bromide mixtures as the mobile phase.

The precision and detection limit of the method and the efficiency of the extraction procedure were established. For the alkylmercury compounds the lowest limit of detection (80ppb) was obtained with the dithizone reaction detection and for the phenylmercury compounds with UV detection (60ppb). A chromatogram of a spiked fish (2ppmHg) and a river water sample (50ppbHg) is shown.     

Anodic stripping voltammetry of antimony at unmodified carbon electrodes

Antimony is an element of significant environmental concern, yet has been neglected relative to other heavy metals in electroanalysis. As such very little research has been reported on the electroanalytical determination of antimony at unmodified carbon electrodes. In this paper we report the electrochemical determination of Sb(III) in HCl solutions using unmodified carbon substrates, with focus on non-classical carbon materials namely edge plane pyrolytic graphite (EPPG), boron doped diamond (BDD) and screen-printed electrodes (SPE). Using differential pulse anodic stripping voltammetry, EPPG was found to give a considerably greater response towards antimony than other unmodified carbon electrodes, allowing highly linear ranges in nanomolar concentrations and a detection limit of 3.9?nM in 0.25?M HCl. Furthermore, the sensitivity of the response from EPPG was 100 times greater than for glassy carbon (GC). Unmodified GC gave a comparable response to previous results using the bare substrate, and BDD gave an improved, yet still very high limit of detection of 320?nM compared to previous analysis using an iridium oxide modified BDD electrode. SPEs gave a very poor response to antimony, even at high concentrations, observing no linearity from standard additions, as well as a major interference from the ink intrinsic to the working electrode carbon material. Owing to its superior performance relative to other carbon electrodes, the EPPG electrode was subjected to further analytical testing with antimony. The response of the electrode for a 40?nM concentration of Sb(III) was reproducible with a mean peak current of 1.07?µA and variation of 8.4% (n?=?8). The effect of metals copper, bismuth and arsenic were investigated at the electrode, as they are common interferences for stripping analysis of antimony.