Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CN_x) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CN_x electrode. Thus, an a-CN_x film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L⁻¹ KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CN_x electrode were 0.0656 μmol L⁻¹ for DA and 1.05 μmol L⁻¹ for AA, whereas with the BDD electrode these values were 0.283 μmol L⁻¹ and 0.968 μmol L⁻¹, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CN_x electrode in electroanalysis.     

酸性AlCl3-BMIC离子液体中的铝阳极溶解

采用线性扫描伏安法研究了Lewis 酸性AlCl₃-BMIC (BMIC: 1-butyl-3-methylimidazolium chloride)离子液体中铝电极的溶解. 铝电极在阳极极化时出现了钝化现象, 钝化是由于在铝电极表面形成了固体AlCl₃钝化膜造成的. 铝的电化学溶解过程可以依次分为三个区: 电化学控制区、过渡区和钝化区. 在电化学控制区, 铝的电化学溶解速率随着电位的正移而逐渐增加; 在过渡区, 由于电极表面AlCl₄^-和Al₂Cl₇^-浓度发生改变而析出固体AlCl₃使得铝电化学溶解速率随着电位的正移而逐渐减小; 当钝化膜形成之后, 铝的电化学溶解速率不再随着电位的正移而发生改变, 铝溶解进入钝化区. 增加搅拌、升高温度、降低离子液体AlCl₃摩尔分数都可以增加铝溶解阳极极限电流密度.     

Molecular Dynamics in 1- and 2-D Confinement as Studied for the Case of Poly(Cis-1,4-Isoprene)

Broadband Dielectric Spectroscopy (BDS) is used to probe the molecular dynamics of Type A polymer, poly(cis-1,4-isoprene), when confined in the 1-dimensional (1D) exploring space of thin layers and the 2-dimensional (2D) constraining geometry of unidirectional anodic aluminum oxide (AAO) nanopores. For both cases, it was observed that the structural relaxation remains bulk-like in its mean relaxation rate, although the distribution of its relaxation times is broadened in 2D confinement. Furthermore, the fluctuation of the end-to-end vector is interrupted, with the 1D case being relatively less pronounced. By this clear-cut comparison, it is demonstrated that the effects of confinement on molecular dynamics depend, inter alia, on the dimensionality of the restricting space.     

Electrochemical synthesis of selenocyanated imidazo[1,5-a]quinolines under metal catalyst-and chemical oxidant-free conditions

Reported herein is the first example of electrochemical selenocyanation of imidazo[1,5-a]quinolines with KSeCN under metal catalyst-and chemical oxidant-free conditions.This sustainable strategy shows a broad scope and great compatibility with functional groups,and affords synthetically and biologically important selenocyanated imidazo[1,5-a]quinolines in good to excellent yields with cheap graphite and Ni plates as the electrodes.The gram-scale synthesis was also successfully conducted,which might demonstrate the potential value of this electrochemical protocol.     

Pd催化的配体导向C—H键乙酰化反应的理论研究

Pd催化的配体导向C-H键官能化反应已经成为有机化学中一种重要的合成手段. 我们用B3PW91密度泛函方法研究了Pd催化的配体导向C-H键乙酰化反应中催化剂和底物配合步骤以及C-H键活化步骤中的热力学性质. 研究发现, 具有不同导向基团的反应物之间竞争反应的选择性取决于导向基团与Pd(OAc)₂的配合步骤, 配合反应稳定常数大的较容易生成乙酰化的产物. 另一方面, 反应的选择性与C-H键的活化步骤无关, 并且与导向基团的配位原子的气相碱性、原子上的电荷密度以及最高占据轨道能量都没有相关性.     

一种新型铅钐锡正极板栅合金

目前,铅钙锡合金已广泛用作阀控式铅酸蓄电池(VRLAB)的板栅材料.由于钙的存在,使铅钙锡合金阳极氧化时易形成高阻抗的阳极腐蚀层,并出现晶间腐蚀,电池循环充放电能力仍不理想.为克服铅钙锡合金作为正极板栅材料的不利因素.     

强度调制光电流谱研究TiO2悬浮体系光催化机理

用强度调制光电流谱在光电化学电池中研究TiO2粒子悬浮液体系中的光催化反应机理,将强度按正弦变化的调制光照射TiO2粒子悬浮液,产生随频率变化的光电流响应,收集在Pt电极上,得到了光电流响应复数平面图,其上半圆和下半圆分别代表光生空穴和光生电子的阴极还原和阳极氧化反应过程.根据阴极和阳极光电流的幅度及上下半圆的特征频率分析讨论了光催化反应的机理及外加电压和H2O2添加物的影响.     

金、铜金属纳米棒或纳米线的AFM和SERS的研究(英文)

通过电化学氧化法制备具有不同孔径氧化铝模板 ,利用交流电镀的方法在模板中沉积金属 ,再用酸溶解模板可以得到相应尺度的金属纳米线或纳米棒的阵列 .本文利用原子力显微镜和表面增强拉曼技术分别表征了金和铜两种金属纳米线阵列 .研究结果表明 ,作为探针分子的硫氰(SCN )在金属纳米线上的碳氮三键的振动频率随纳米线直径的增大而蓝移 .这一现象可能是因为尺寸效应对纳米线的费米能级造成影响 ,使不同直径的金属纳米线电子结构存在微小的差别 .     

DNA在纳米金标上的组装、杂交、检测与银增强

利用电化学方法进行DNA的杂交检测.将目标ss-DNA固定在玻碳电极表面, 使其与纳米金标记的互补DNA发生杂化反应, 通过银增强试剂（该种试剂可以使银在纳米金表面沉积, 达到信号增强的效果）在纳米金上沉积银, 形成银包金的核壳结构.在酸性介质中沉积的银被氧化释放, 以离子状态存在于溶液中.用阳极溶出伏安法(ASV)检测银离子从而达到间接检测目标DNA的目的.测定结果表明，ss-DNA的浓度在100～1 000 pmol•L－1 范围内有非常好的线性关系, 检测限为10 pmol•L－1.     

甘油氧化的光谱电化学傅里叶变换衰减全反射谱红外光谱薄膜流动池中硼酸镍层厚度的优化

在碱性甘油电氧化反应中,利用电化学傅里叶变换衰减全反射谱红外光谱法,研究了薄膜流动池中滴注硼酸镍催化剂负载量对玻碳电极性能的影响.连续操作的径向流动池包括一个位于内反射元件上方50μm的钻孔电极,可实现红外光谱分析.这是在确定条件下对电催化剂进行简便和可重复筛选的一个适合的方法,同时还提供了对复杂反应(如甘油氧化)产物选择性的检测.通过对泵送电解液进行更耗时的定量高效液相色谱分析,结果表明,衰减全反射红外光谱法可快速鉴定产物.在层流条件下,水中使用0.1 M甘油和1 M KOH,流速为5μL min-1时,甘油转化率较高.转化率和选择性取决于催化剂的负载量,负载量又决定了催化剂层的厚度和粗糙度.由于在更粗糙的膜中停留时间更长有利于再吸附和C-C键断裂,因此当负载量最高达210μg cm-2时,甘油转化率为73％且甲酸选择性接近80％.当最低负载量为13μg cm-2时,甘油转化率达到63％,甲酸选择性降至60％,相应地,C2物种(如乙醇酸盐)选择性较高,为8％.因此,只有催化剂负载量较低时才能形成几微米厚度范围内的薄膜,此时才适合进行优质催化剂的筛选.