A Stable Porphyrin Functionalized Graphite Electrode Used at the Oxygen Evolution Reaction Potential

Many researches have been devoted to rechargeable power generators that can store (but also release) energy. This availability is ensured through (e. g.) the oxygen evolution reaction (OER). However, (i) large values of the overpotentials and (ii) a progressive detriment of the anode (graphite) electrode limit the ultimate device. In view of enhancing the electrode performances, graphite was protected by following different strategies, which oblige to follow precise preparation protocols. Here, we prove that a thin layer of free-base porphyrin molecules is able to protect the underneath graphite electrode from detriment even if many (about 100) electrochemical cycles are performed.     

Graphene to graphite; a layer by layer experimental measurements and density function theory calculations of electric conductivity

ABSTRACT

We measured the electric conductivity of large (25?×?50?mm) graphene films as a function of number of layers in the range of 1–20 layers. We also calculated the energy gap for such samples using density function theory. Our results showed a conductivity slightly above that of ITO for monolayer graphene and an exponential decrease as the number of graphene layers increased. Both experimental and simulation results showed a convergence of graphene into graphite at as little as 18–20 layers.     

基于拉曼热测量技术的铜基复合物法兰GaN基晶体管的热阻分析

采用拉曼热测量技术结合有限元热仿真模型,分析比较新型铜/石墨复合物法兰封装与传统铜钼法兰封装的GaN器件的结温与热阻,发现前者的整体热阻比铜钼法兰器件的整体热阻低18.7%,器件内部各层材料的温度分布显示铜/石墨复合物法兰在器件中的热阻占比相比铜钼法兰在器件中的热阻占比低13%,这证明使用高热导率铜/石墨复合物法兰封装提高GaN器件热扩散性能的有效性.通过对两种GaN器件热阻占比的测量与分析,发现除了封装法兰以外,热阻占比最高的是GaN外延与衬底材料之间的界面热阻,降低界面热阻是进一步提高器件热性能的关键.同时,详细阐述了使用拉曼光热技术测量GaN器件结温和热阻的原理和过程,展示了拉曼光热技术作为一种GaN器件热特性表征方法的有效性.     

自动石墨消解–电感耦合等离子体质谱法同时测定左氧氟沙星胶囊中7种金属元素

建立自动石墨消解-电感耦合等离子体质谱法(ICP-MS)同时测定左氧氟沙星胶囊中铅、铬、砷、镉、锡、铝、铁7种金属元素含量的方法。以HNO3-H2O2()体积比为1∶1为消解体系,采用自动石墨消解法消解左氧氟沙星胶囊样品,消解液除酸后,用5%硝酸溶液定容至50 mL,采用电感耦合等离子体质谱法对消解液进行测定,以内标法定量。铅、铬、砷、镉、锡、铝、铁的质量浓度在0.05~20.0μg/mL范围内与质谱响应值成良好的线性关系,相关系数均大于0.998,方法检出限为0.119~1.323μg/kg。样品加标回收率为91.2%~105.5%,测定结果的相对标准偏差为1.67%~3.46%(n=6)。该方法样品前处理简单,检出限低,测定结果准确,适用于左氧氟沙星胶囊等沙星类抗生素中多种金属元素残留的测定。     

Chemical-Reductant-Free Electrochemical Deuteration Reaction using Deuterium Oxide

We report a method for the electrochemical deuteration of α,β-unsaturated carbonyl compounds under catalyst- and external-reductant-free conditions, with deuteration rates as high as 99 % and yields up to 91 % in 2 h. The use of graphite felt for both the cathode and the anode was key to ensuring chemoselectivity and high deuterium incorporation under neutral conditions without the need for an external reductant. This method has a number of advantages over previously reported deuteration reactions that use stoichiometric metallic reductants. Mechanistic experiments showed that O₂ evolution at the anode not only eliminates the need for an external reductant but also regulates the pH of the reaction mixture, keeping it approximately neutral.     

Reversible M−M Bonding by Alkaline Earth Metals (Mg,Ca, Sr,Ba) in Graphite Intercalation Compounds

The alkaline earth metals (M=Mg, Ca, Sr, and Ba) exhibit a +2 oxidation state in nearly all known stable compounds, but M^I dimeric complexes with M−M bonding, [M₂(en)₂]²⁺, (en=ethylenediamine) of all these metals can be stabilized within the galleries of donor-type graphite intercalation compounds (GICs). These metals can also form GICs with more conventional metal (II) ion complexes, [M(en)₂]²⁺. Here, the facile interconversion between dimeric-M^I and monomeric-M^II intercalates upon the addition/removal of en are reported. Thermogravimetry, powder X-ray diffraction, and pair distribution function analysis of total scattering data support the presence of either [M₂(en)₂]²⁺ or [M(en)₂]²⁺ guests. This phase conversion requires coupling graphene and metal redox centers, with associated reversible M−M bond formation within graphene galleries. This chemistry allows the facile isolation of unusual oxidation states, reveals M⁰→M²⁺ reaction pathways, and present new opportunities in the design of hybrid conversion/intercalation materials for applications such as charge storage.     

Voltammetric Determination of Favipiravir Used as an Antiviral Drug for the Treatment of Covid-19 at Pencil Graphite Electrode

This work describes the sensitive voltammetric determination of favipiravir (FAV) based on its reduction for the first time with a low-cost and disposable pencil graphite electrode (PGE). In addition, the determination of FAV was also performed based on its oxidation. Differential pulse (DP) voltammograms recorded in 0.5 M H₂SO₄ for the reduction of FAV show that peak currents increase linearly in the range of 1.0 to 600.0 μM with a limit of detection of 0.35 μM. The acceptable recovery values (98.9–106.0 %) obtained from a pharmaceutical tablet, real human urine, and artificial blood serum samples spiked with FAV confirm the high accuracy of the proposed method.     

超级微波消解－石墨炉原子吸收光谱法测定香菇中的镉

为建立一种快速批量检测香菇中镉的方法,建立了超级微波消解－石墨炉原子吸收光谱法测定香菇中镉含量的方法。分别采用湿法消解、普通微波消解和超级微波、传统微波和湿法消解技术前处理香菇标准物质样品,对比消解效果,优化超级微波消解技术的酸体系和消解最终温度。;采用石墨炉原子吸收光谱仪法测定,优化基体改进剂、灰化温度等工作参数,确定仪器最佳检测条件,验证分析方法的准确性和稳定性。结果表明,超级微波消解优于湿法消解和传统微波消解技术,准确性和重复性最佳,大幅减少用酸量的同时更加安全、高效,避免样品污染。在最优分析方法条件下,镉在0~4.0 μg/L范围内所得回归方程线性关系良好,相关系数(R)为0.9994,方法检出限为0.001 mg/kg,精密度RSD为1.4%~2.5%。超级微波消解－石墨炉原子吸收光谱法检测的探索与应用超级微波消解优于湿法消解和传统微波消解技术,大幅减少用酸量的同时更加安全、高效,避免样品污染,为农产品镉含量批量检测提供可靠的方法支撑。     

机械剥离石墨烯修饰电极检测食品接触材料中双酚A的迁移量

采用机械剥离石墨烯修饰电极快速检测食品接触材料中双酚A的迁移量。X射线电子衍射表征显示机械剥离石墨烯表面不存在含氧官能团,与化学还原石墨烯相比,机械剥离石墨烯对双酚A具有更好的电催化性能,降低了双酚A的氧化过电位,提高了电流响应。在优化的试验条件下,双酚A的浓度在1.0×10-7~1.5×10-5mol·L-1范围内与氧化峰电流呈线性关系,检出限(3S/N)为3.0×10-8mol·L-1。采用该电极对食品模拟物中的双酚A进行检测,加标回收率在85.1%~104%之间,测定值的相对标准偏差(n=6)在2.7%~5.9%之间。