Effects of Adsorbed Polyaniline on Redox Processes on As(2)O(3) Surfaces

Polyaniline deposited on As(2)O(3) surface resulted in a new material, which was characterized by infrared spectoscopy, thermogravimetry, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and cyclic voltammetry. The mass percentage of polymer deposited on oxide surface is approximately 13%. The scanning electron microscopy images as well as the X-ray diffraction patterns provided conclusive evidence that the oxide surface is coated by the polymer. The cyclic voltammograms of the polyaniline adsorbed on As(2)O(3) surface showed that the adsorbate exerts remarkable effects on redox processes on this oxide. The pure oxide exhibited two oxidation/reduction peaks at 0.25/-0.06 and 0.47/-0.25 V attributed tentatively to the processes As(2)O(3)(s)+6H(+)+6e(-)=2As(s)+3H(2)O and As(s)+3H(+)+3e(-)=AsH(3)(g), respectively. The polyaniline-coated sample exhibited a better-defined voltammogram in which the first oxidation peak of the oxide had its intensity increased about four times. Copyright 2000 Academic Press.     

Characterization of the Surface Redox Process of Adsorbed Cercosporin (CER) at Glassy Carbon Electrodes by Anodic Stripping Square‐Wave Voltammetry

The adsorptive accumulation of cercosporin (CER) at glassy carbon electrodes is studied by square‐wave voltammetry (SWV). The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of CER with glassy carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the CER bulk concentration (c*_CER). SWV was also used to generate Q vs. c*_CER and I_{p, n}. vs. c*_CER calibration plots from pure commercial reagent solutions. Theoretical detection limits of 1.8×10^?7 and 9.7×10^?8 M were calculated from Q. vs. c*_CER and I_{p, n} vs. c*_CER plots, respectively. The lowest concentration value measured experimentally from calibration plots performed at a f =40 Hz for a signal to noise ratio of 2 : 1 was 3.7×10^?8 M, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled CER reduction peak. I_{p, n}./f vs. f plots from SW voltammograms performed at different c*_CER as well as different accumulation times showed the so‐called “quasi‐reversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (?0.260±0.011) V was determined for the formal potential of the adsorbed redox couple from the split voltammetric peak. A full characterization of the surface redox process was obtained by applying the methods of the “quasi‐reversible maximum” and the “split SW peak”. In 1 M HClO₄ aqueous solution, the formal rate constant and the anodic transfer coefficient were (3.5±0.5)×10² s^?1 and (0.50±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1.     

水蒸汽在Pd表面吸附的热力学

用密度泛函方法和相对论有效原子实势分别对PdOH2、PdOH 及PdO 的几何构型进行了优化, 得到PdOH2分子为Cs构型, Pd 与H2O 分子不在同一平面, RPdO=0.2283 nm; PdOH 分子为2A'态, RPdO=0.1965 nm, ROH=0.0968 nm, ∠PdOH=110.186°; PdO分子基态为3Π, RPdO=0.1858 nm. 根据电子-振动近似理论计算了不同温度下金属Pd与H2O、OH及游离态O原子反应的生成热力学函数, 导出了反应平衡压力随温度的变化关系, 分析认为水蒸汽引起Pd合金膜中毒是由于H2O分子的离解产物OH和O原子吸附在膜表面所致.     

Surface structure and catalytic properties of MoO3/CeO2 and CuO/MoO3/CeO2

XRD, LRS, TPR and in situ NH(3) adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO(3)/CeO(2) and CuO/MoO(3)/CeO(2) catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH(3) adsorption FT-IR, the relationships between the activities for 'NO + NH(3) + O(2)' reaction and surface acid properties (Br?nsted and Lewis acid sites) of the catalysts were discussed.     

Redox Reaction of Disulfide/Polyaniline in Aqueous Solution

Introductionlthasbeensh0wnthat0rganodisulfidesIikeDMcTc0uldbep0lymerizedanddepolymerizedreversibly,correspondingtotheirchemical0reIectr0chemicaloxidati0nandreductionreactions.Thisisduetothereversibletbrmationandscissi0nofthedisulfidebond,atw0-electr0ntransferpr0cess(Schemel).LithiumsecondarybatterieswithatheoreticalenergydensityoflO7OWhjkgwereset-upusingtheabovedisulfidecompoundasthean0dicmaterial.H0wever,theredoxreacti0n0fdisulfidewasveryslowatr0omtemperature,thus,thechargeanddischargepro…     

Friction of MoO3 Nanoflakes on Graphite Surface with an Ace-like Intercalation Layer

How water layer adsorbed on solid surface under ambient conditions affects the interfacial friction is a fundamental question for understanding the friction and lubrication phenomena in practical system. We investigate the formation of ice-like(IL) water layers on the hydrophobic surface of graphite with partially covered MoO₃ nanoflakes(NFs) using atomic force microscopy(AFM) based techniques. The IL water layers are found surrounding the MoO₃ NFs and also intercalated at the MoO₃/graphite interface, as proved by thickness measurements as well as local adhesion force and surface potential mappings. AFM manipulations carried out on MoO₃ NFs on graphite show that the presence of the IL water layers increases the frictional resistance of the interface. Comparing the results on continuous and discontinuous IL water layers, we can identify the different sliding interfaces in the two scenarios. The increased friction for MoO₃ NFs sliding on graphite with an intercalated water layer is attributed to the energy dissipation originated from the metastable nature of the IL layers.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为, 在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响. 根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为, 解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因: (1) 相比PDMS涂层, 蛋白质与PEG涂层的结合能量较低, 使其结合更加疏松; (2) 蛋白质吸附到材料表面要克服表面水化层分子引起的能障, PEG表面与水分子之间结合紧密, 结合水难于脱附, 造成蛋白质在其表面的吸附需要克服更高的能量, 不利于蛋白质的吸附.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为,在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响.根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为,解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因:(1)相比PDMS涂层,蛋白质与PEG涂层的结合能量较低,使其结合更加疏松;(2)蛋白质吸附到材料表面要克服表面水化层分子引起的能障,PEG表面与水分子之间结合紧密,结合水难于脱附,造成蛋白质在其表面的吸附需要克服更高的能量,不利于蛋白质的吸附.     

Heterogeneous Kinetics of Metal- and Ligand-Based Redox Reactions within Adsorbed Monolayers

Dense monolayers of [Os(bpy)(2)py(p3p)](2+), where bpy is 2,2'-bipyridyl, py is pyridine, and p3p is 4,4'-trimethylenedipyridine, have been formed by spontaneous adsorption onto clean platinum microelectrodes. Three well-defined waves, corresponding to osmium- and bipyridyl-based redox reactions, are observed in cyclic voltammetry of these monolayers, where the supporting electrolyte is tetrabutylammonium tetrafluoroborate (TBABF(4)) dissolved in acetonitrile. These reactions correspond to the charge states 3+/2+, 2+/1+, and 1+/0, respectively. Chronoamperometry, conducted on a microsecond time scale, has been used to measure the heterogeneous electron transfer rate constant, k/s(-1), for all three redox processes. For concentrations of TBABF(4) above 0.1 M, heterogeneous electron transfer is characterized by a single unimolecular rate constant. Standard heterogeneous electron transfer rate constants, k degrees, have been evaluated by extrapolating Tafel plots of ln k vs overpotential, eta, to zero driving force to yield values of (4.8 +/- 0.3) x 10(4) s(-1), (2.5 +/- 0.2) x 10(5) s(-1), and (3.3 +/- 0.3) x 10(4) s(-1) for k degrees (3+/2+), k degrees (2+/1+), and k degrees (1+/0), respectively. For large values of eta, these Tafel plots are curved for all three redox reactions, and while those corresponding to metal-based electron transfer are asymmetric with respect to eta, those corresponding to ligand-based reactions are symmetric. Temperature-resolved measurements of k reveal that the electrochemical activation enthalpy, DeltaH(), decreases from 43.1 +/- 2.8 kJ mol(-1) for the 3+/2+ reaction to 25.8 +/- 1.9 kJ mol(-1) for the 1+/0 process. Probing the temperature dependence of the formal potential gives the reaction entropy, DeltaS(rc) degrees. The reaction entropy depends on the state of charge of the monolayer with values of 212 +/- 18, 119 +/- 9, and 41 +/- 5 J mol(-1) K(-1) being observed for the 3+/2+, 2+/1+, and 1+/0, redox transformations, respectively. The electronic transmission coefficient, kappa(el), describing the probability of electron transfer once the nuclear transition state has been reached, is considerably less than unity for all three redox processes. However, kappa(el) is larger for the bipyridyl-based reductions, (2.4 +/- 0.9) x 10(-5), than for the metal-based reaction, (1.5 +/- 0.7) x 10(-6). This large difference in electronic transmission coefficients may be a consequence of the redox potentials of the bridging ligand and the remote redox sites being comparable, so that the electronic states of the bridging ligand contribute to the electron tunneling pathway.     

聚苯胺纳米点的氧化还原态与其库仑台阶效应

应用电化学恒电位法结合模板法制备聚苯胺纳米点阵列,导电原子力显微镜研究处于不同氧化还原态的聚苯胺纳米点的I～V特性,发现只有处于部分氧化态(导电态)的聚苯胺纳米点才出现库仑台阶效应,还原和全氧化态聚苯胺纳米点不显示库仑台阶.初步探讨了上述现象.     

氧化钼表面不同氧位对氢吸附性能的从头计算研究

 用从头计算Hartree－Fock方法研究了MoO3（010）和（100）晶面上几种结构不等价氧的成键特征和电子结构,并考察了H＋在不同氧位上的吸附性能以及吸附后形成的OH从表面脱附的性质．结果表明,在氧化钼晶体中,钼氧原子间的成键具有离子性和共价性相结合的特性,且几种不等价氧与钼之间的成键性质各不相同：端氧或不对称桥氧与钼的成键具有较强的共价性,而对称桥氧具有较强的离子性;H＋在MoO3（010）和（100）晶面上几种不等价氧位都能形成稳定的吸附,而在端氧位的吸附最稳定;H＋吸附形成的OH都与表面有较强的作用,端氧位的OH最难脱附,而桥氧位的OH在表面的活动性较大,故桥氧位很可能是丙烯选择氧化过程中脱氢反应的活性中心．     

光电子调控的聚苯胺氧化还原反应用于铜离子可视化检测

构建了由中间价态聚苯胺(ES-PANI)和二氧化钛(TiO2)纳米粒子组成的光致变色检测平台,用于痕量铜可视化检测.在紫外光激发下,ES-PANI(墨绿色)会被TiO2产生光生空穴氧化为完全氧化态聚苯胺(深蓝色);随着Cu2+的加入,ES-PANI生成还原态聚苯胺(浅黄色),导致一系列可由肉眼观测到的颜色变化.光致变色过程中的颜色转变取决于Cu2+调控的不同价态聚苯胺.本方法结合了光电化学和可视化检测的优点,在Cu2+的检测中表现出了高选择性和灵敏度,检出限为0.4μmol/L.采用Photoshop软件读取绿通道平均强度值和用酶标仪记录紫外吸收值,发展了另外两种定量检测方法.此外,将本方法用于人类头发实际样品中Cu2+的定量检测,回收率令人满意.所建立的检测平台简单、成本低廉,无需复杂的仪器即可在几分钟内同时检测多种样品.这种光电子调控的比色策略为设计新型比色检测平台提供了新思路,并且可望应用于临床快速诊断便携试剂盒的开发.     

Methods of Numerical Analysis of a Voltammogram for an Adsorbed Redox System

Methods of analysis of voltammograms for redox systems adsorbed on an electrode are analyzed. The methods allow for the interaction between species in the adsorption layer. An approximate equation of the adsorption peak, suitable for performing numerical calculations on a computer using standard programs, is proposed. The accuracy of the equation and conditions of its application are discussed.     

基体表面性质对原位聚合沉积导电聚苯胺薄膜性能的影响

以水溶性高分子聚乙烯吡咯烷酮(PVP)为空间稳定剂,在经十八烷基三氯硅烷(OTS)改性的玻璃表面进行原位聚合,沉积得到导电聚苯胺(PANI)薄膜。采用表面界面张力仪、扫描电镜(SEM)、紫外可见光谱(UV-Vis)、红外光谱(FT-IR)、四探针电导率测试仪及光学显微镜对不同基体表面的接触角、PANI膜的形貌、厚度、结构、导电性及其在亲/憎水表面选择性沉积性能进行测定。结果表明:OTS对玻璃表面的改性促进了聚苯胺的沉积且提高了薄膜厚度,薄膜饱和厚度达到200 nm;缩短了溶液中苯胺分散聚合的诱导期,反应速率增大;与未改性玻璃表面沉积的薄膜相比,改性的玻璃表面得到的聚苯胺薄膜更加细密均匀,聚苯胺颗粒尺寸小,堆积紧密;薄膜的电导率达到7.5×10-3S/cm;OTS改性对基体表面的薄膜生长和溶液中的苯胺聚合具有催化作用。     

MoO3在介孔分子筛MCM—41上分散状况的研究

采用XPS和XRD方法,测定了MoO3在未经改性的MCM－41及用Al2O3和TiO2改性后的MCM－41上的单层分散阈值,发现,MoO3在用Al2O3和TiO2改性后的MCM－41上的单层分散阈值比未经改性的MCM－41上的要提高三分之二。另外,借助MoO3/MCM-41、MoO3/Al2O3-MCM-41、MoO3/TiO2-MCM-41系列样品的比表面积和孔分布测定,研究了MoO3在未经改性的MCM－41及用Al2O3和TiO2改性后的MCM－41上的分散状况。     

表面增强拉曼光谱研究吸附态的变化

测量了吡啶分子在电化学处理的银表面和亚甲基蓝分子在硝酸刻蚀银表面的表面增强拉曼光谱（ＳＥＲＳ）．对ＳＥＲＳ谱线的分析结果表明，吡啶分子在较低的表面吸附分子密度时倾向于平躺方式；而在较高的表面分子密度时，则倾向于向垂直吸附态转化．亚甲基蓝分子在较低浓度时主要是平躺吸附，随Ｃｌ－浓度的增加，亚甲基蓝从“平躺”吸附态转向“站立”吸附态．     

Composite Material Based on Macroporous Polyaniline and Osmium Redox Complex for Biosensor Development

Here the feasibility of layers based on the conducting polymer polyaniline (PANI) as component of glucose biosensors using glucose oxidase (GOx) as enzyme and [Os(bpy)₂(4‐aminomethylpyridine)Cl]PF₆ (OsCmplx) as electrochemical mediator, is evaluated. Particularly, PANI was employed to obtain a nanostructured macroporous material (m‐PANI) around polystyrene nanoparticles taken as template and the mediator was co‐immobilized during the polymerizing procedure. The GOx biosensor based on OsCmplx modified m‐PANI provides a linear response to glucose concentration in the range 5 up to 65 mM with a sensitivity of 3.54 µA/mM/cm² (on a projected geometric area=0.07 cm²), an LOD of 0.8 mM and a good precision (%RSD≤7, n=5); the biosensor is stable showing a decrease of 10% to the value of the sensitivity after 15 days of use and of about 50% after 40 days.     

添加金属对MoO3/Al2O3 碳化过程的影响

The investigation on MoO3 / Al2O3 sample or its modifiers with nickel,copper or potassium was performed using temperature programmed surface reaction（TPSR）technique and measurements of BET surface area. The results indicate that addition of nickel promotes the methane reduction,further the carburization,of MoO3,and addition of nickel also promotes the activation of methane over the surface of oxycarbide or carbide due to the increase of active sites per unit area and intrinsic activity of catalytic centers. This is favorable to the conversion of methane. The addition of copper promotes the methane reduction,further the carburization,of MoO3 to some extent,while the introduction of copper also accelerates the sintering of catalyst to a degree. Thus copper doped carbide catalyst exhibits its exceptionally catalytic performance. However,potassium prevents the MoO3 from reduction with methane,which is unfavorable to the carburization. Potassium also restrains methane from being activated over the surface of oxycarbide or carbide. MoO3 / Al2O3 doped with potassium is of lower specific area,which originates from its boosting sintering of catalyst. This caauses the inferior methane conversion over potassium doped carbide catalyst.     

吸附于AgCl溶胶表面的单羟基四苯基卟啉的电子吸收光谱

研究了两种单取代羟基四苯基卟啉——— 5 - (4-羟基苯基 ) - 10 ,15 ,2 0 -三苯基卟啉 (H2 POH)和 5 - (4-羟基苯基 ) - 10 ,15 ,2 0 -三氯苯基卟啉 (H2 (p -Cl) 3 POH)在冰醋酸中和吸附于AgCl溶胶表面的电子吸收光谱(UVA)和化学反应 .结果表明 ,在冰醋酸中H2 POH和H2 (p -Cl) 3 POH均以二酸和游离碱的形式存在 ;在乙醇中 ,pH值为 10 .5 - 11.5时 ,H2 POH与H2 (p -Cl) 3 POH在AgCl表面发生配位反应 ,生成了Ag(Ⅱ )POH和Ag(Ⅱ ) (p -Cl) 3 POH ,并且溶液的酸度越低 ,配位反应的速度越大