阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附动力学的影响

运用电化学循环伏安和程序电位阶跃方法研究了阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附反应动力学的影响. 结果表明, 阴离子特性吸附显著影响乙二醇的解离吸附, 在高氯酸介质中(无特性吸附)测得乙二醇解离吸附反应的初始速率vi以及解离吸附物种(DA)的饱和覆盖度均明显大于硫酸溶液(发生SO2-4/HSO-4特性吸附)中的相应值; 其平均速率v随电极电位的变化呈类似火山型分布, 最大值位于0.22 V(vs SCE)附近. 还发现通过不同处理获得的Pt(111)电极的不同表面结构对这一表面过程也具有显著的影响.     

酸性溶液中苯并三氮唑和3-巯基-1-丙烷磺酸钠在铜电极表面的电化学SERS研究

利用原位电化学表面增强拉曼光谱技术(EC-SERS)研究了酸性溶液中苯并三氮唑(BTAH)、 3-巯基-1-丙烷磺酸钠(MPS)及Cl^-在铜电极表面的竞争吸附行为。在较正电位区间,BTAH分子在铜电极表面的吸附主要是通过三唑环在铜电极表面形成[Cu(BTA)]_n聚合物膜;随着电位负移,聚合物膜逐渐转化为BTAH分子形式吸附在铜电极表面。而MPS主要是以巯基端吸附在铜电极表面,其吸附方向的改变使得其在铜表面的拉曼信号呈现出先强后弱的趋势。Cl^-主要是以Cu-Cl的形式存在,占据电极表面的活性位点与MPS产生协同作用。当三者复配时是以BTAH在电极表面的强吸附性为主导,且随着电位的负移,BTAH的拉曼信号呈现出先增强再减弱的趋势,相较于BTAH的强吸附作用,MPS与Cl^-在电极表面的吸附强度较弱但依旧可以监测到两者参与竞争吸附的过程。     

Pt/巯基乙酸/玻碳电极的表面形貌与电催化性能

以巯基乙酸为偶联层在玻碳(GC)电极上组装 Pt纳米颗粒, 得到Pt /巯基乙酸/GC电极, 利用扫描电镜(SEM)和循环伏安法(CV)研究了不同条件下复合电极的表面形貌和电化学性能. 研究结果表明, 巯基乙酸在GC电极表面具有特性吸附, 形成了具有一定致密性的吸附层. 在0.5 mol/L H2SO4+1.0 mol/L CH3OH溶液中, 组装19 h的复合电极对甲醇氧化表现出较好的电催化性能.     

铜-金属有机框架物修饰电极的制备及甲硝唑测定

在玻碳电极表面聚合一层对氨基苯甲酸导电膜,通过羧基配位作用将具有优良导电性及催化能力的铜金属有机框架化合物(Cu-MOFs)自组装在对氨基苯甲酸修饰电极表面,制备了铜-金属有机框架物修饰电极。对Cu-MOFs进行了表征,研究了修饰电极的伏安特征及对甲硝唑(MNZ)的电催化特性,建立了一种高灵敏度的测定甲硝唑的电化学分析方法。在1.0~100.0μmol/L浓度范围内,MNZ的还原电流与其浓度呈良好的线性关系,检出限达0.23μmol/L,方法已用于蜂蜜样品中MNZ的测定。     

铜-真空-铜金属隧道结转变电压的理论研究

利用非平衡格林函数与密度泛函理论相结合方法研究了电极表面具有原子级突起的铜-真空-铜隧道结的转变电压.计算结果表明,铜电极真空隧道结的转变电压主要决定于电极表面尖端铜原子4p轨道的局域态密度,因而对电极取向和表面局域原子构型非常敏感.对于电极取向沿(111)方向的铜电极真空隧道结,当电极表面原子级突起取为铜吸附原子和金字塔型铜纳米粒子两种构型时,转变电压的计算值分别约为1.40和2.40 V.当电极取向沿(100)方向时,电极表面原子级突起分别为铜吸附原子和金字塔型铜纳米粒子两种构型的铜电极真空隧道结,其转变电压的差异更为显著.具体而言,电极表面有一金字塔型铜纳米粒子的铜电极真空隧道结的转变电压值减小至1.70 V,而电极表面原子级突起为铜吸附原子的铜电极真空隧道结却因铜吸附原子4p轨道的局域态密度过于扩展,即使在偏压超过1.80 V时仍然没有出现转变电压.这些结果表明转变电压谱可用作分析金属电极真空隧道结电子输运特性的有力工具.     

苯甲醛缩氨基脲铜（II）配合物为载体的高选择性硫氰酸根离子电极的研究

首次研究以苯甲醛缩氨基脲铜（II）[Cu(II)-BASA]为中性载体的PVC膜电极， 该电极对硫氰酸根离子（SCN~-）具有优良的电位响应特性并呈现出反Hofmeister 选择性行为，其选择性次序为：SCN~- > ClO_4~- > I~- > Sal~- > Br~- > NO_3~- > Cl~- > NO_2~- > SO_3~(2-) > SO_4~(2-) > H_2PO_4~-。电极在pH 6. 0的磷酸盐缓冲体系中，对SCN~-在1.0 * 10~(-1)～8.0 * 10~(-6) mol/L浓度范围 内呈近能斯特响应，斜率为56.0 mV/sSCN~- (28 ℃)，检测下限为3.0 * 10~(-6) mol/L。采用交流阻抗技术和紫外可见光谱技术初步研究了阴离子与载体的作用机 理，结果表明配合物中心金属原子的结构以及载体本身的结构与电极的响应行为之 间有非常密切的构效关系。该电极具有响应快、重现性好、检测限低、制备简单等 优点。将电极初步应用于实际样品废水分析，结果与HPLC法一致。     

苯甲醛缩氨基脲铜（II）配合物为载体的高选择性硫氰酸根离子电极的研究

首次研究以苯甲醛缩氨基脲铜（II）[Cu(II)-BASA]为中性载体的PVC膜电极， 该电极对硫氰酸根离子（SCN~-）具有优良的电位响应特性并呈现出反Hofmeister 选择性行为，其选择性次序为：SCN~- > ClO_4~- > I~- > Sal~- > Br~- > NO_3~- > Cl~- > NO_2~- > SO_3~(2-) > SO_4~(2-) > H_2PO_4~-。电极在pH 6. 0的磷酸盐缓冲体系中，对SCN~-在1.0 * 10~(-1)～8.0 * 10~(-6) mol/L浓度范围 内呈近能斯特响应，斜率为56.0 mV/sSCN~- (28 ℃)，检测下限为3.0 * 10~(-6) mol/L。采用交流阻抗技术和紫外可见光谱技术初步研究了阴离子与载体的作用机 理，结果表明配合物中心金属原子的结构以及载体本身的结构与电极的响应行为之 间有非常密切的构效关系。该电极具有响应快、重现性好、检测限低、制备简单等 优点。将电极初步应用于实际样品废水分析，结果与HPLC法一致。     

多相光催化分解H2S中阴离子表面活性剂对半导体催化剂CdS表面的影响

研究了在H₂S碱性溶液中,CdS粉末催化剂存在时,光催化分解H₂S释氢和生成硫反应。考察了阴离子表面活性剂——十二烷基硫酸钠(SDS)对催化剂的表面性质和催化活性的影响。通过模拟该反应体系,用电化学方法测定了单晶CdS电极在上述反应体系中加入SDS(浓度低于临界胶团浓度CMC值)后的平带电位的变化。结果表明:单晶CdS电极的平带电位,由于该体系加入SDS而正移,与n型多晶半导体CdS在加入SDS的H₂S碱性溶液中,光催化分解H₂S的释氢量减少相一致。并探讨了在该体系中,由于表面活性剂的阴离子与S^2-在单晶CdS电极表面上的竞争吸附,而引起单晶CdS电极的平带电位正移。     

用石英晶体微天平研究表面活性剂在银固态表面上的动态吸附

吸附是表面活性剂的一个重要特征.迄今用于原位监测表面活性剂在固体表面上吸附重量变化的方法尚不多见.近年来压电石英晶体作为一种高灵敏的质量传感器(石英晶体微天平)已被用于大气和溶液中多种微量成分的监测.用石英晶体微天平研究I~-、Br~-和表面活性剂在金电极上的吸附行为亦有报道.本文研究了十六烷基三甲基溴化铵(CTAB)、十二烷基磺酸钠(SDSO)、十二烷基硫酸钠(SDS)在银固态表面上的吸附平衡动力学特性及其吸附机制.     

多晶n-CdSe电极在K4Fe(CN)6-EDTA溶液中稳定性的研究

旋转环盘电极(RRDE)研究表明,多晶n-CdSe电极表面经金属离子溶液处理,提高溶液的pH及增加溶液中还原剂K₄Fe(CN)₆的浓度均使该电极在K₄Fe(CN)₆-FDTA体系中的稳定因子S提高。用Au、Ru、Pt及Pb等离子溶液处理电极表面时,S值增大。Ru离子处理使S增大几乎可达1。从X射线荧光光谱和Mott-Schottky关系图分析证明,处理后的CdSe多晶电极表面沉积了一层金属薄层。本文对电极表面沉积的金属薄层、溶液pH等的影响、稳定因子S提高的原因也作了初步讨论。     

Increased interfacial thickness of the NaF, NaCl and NaBr salt aqueous solutions probed with non-resonant surface second harmonic generation (SHG)

Specific ion effects on the nonlinear optical response from the water molecules at the air/sodium halide solution interfaces are measured using non-resonant surface second harmonic generation (SHG). Procedures have been developed to monitor and remove the impurities in the salt solution samples to ensure measurement of small changes in the SHG signal. Quantitative polarization analysis of the measured SHG data indicated that the average orientation of the interfacial water molecules changed only slightly around 40 degrees with the increase of the bulk concentration of the three sodium halides, namely NaF, NaCl and NaBr, from that of the neat air/water interface. The observed significant SHG signal increase with the bulk salt concentration is attributed to the overall increase of the thickness of the interfacial water molecular layer, following the order of NaBr > NaCl approximately NaF. The absence of the electric-field-induced SHG (EFISHG) effect indicated that the electric double layer at the salt aqueous solution interface is much weaker than that predicted from the molecular dynamics (MD) simulations. These results provided quantitative data to the specific anion effects on the interfacial water molecules of the electrolyte aqueous solution, not only for the larger and more polarizable Br(-) anion, but also for the smaller and less polarizable F(-) and Cl(-) anions.     

Adsorption of ions to the surface of dilute electrolyte solutions: the Jones-Ray effect revisited

The controversial observation of a minimum in the surface tension of dilute aqueous electrolyte solutions by Jones and Ray in the 1930s is confirmed by new resonance-enhanced second harmonic generation (SHG) experiments demonstrating surface enhancement of simple inorganic anions in the same concentration range. New experiments show that the quadruply charged ferrocyanide, Fe(CN)(6)(4-), anion is not surface active at high concentrations, as expected, but at dilute concentrations, the anion is strongly attracted to the interface with a Gibbs free energy of adsorption of -6.8 kcal/mol. Using this value, the original Jones and Ray data are fit to a simple model of the surface tension with qualitative agreement, although better agreement is found for all 13 Jones and Ray salts with an even stronger surface adsorption.     

Second harmonic generation at the interface of copper tetra-tert-butyl phthalocyanine Langmuir-Blodgett film/metal

As one of the most primitive nonlinear optical phenomena, optical second harmonic genera-tion (SHG) has been investigated for half a century and it has become a very useful spectroscopic tool in the study of surface and interface[1—3]. It was theoretically shown that the SH signal cannot be generated in a centrosymmetric system. However, the generation of SH signal from the centro-symmetric molecules such as fullerene (C60) and CuPc has been detected[4—7]. In our recent ex-periments, an …     

Quantum chemical studies of the chemisorption of water and of unhydrated and hydrated halide ions on mercury

Local structures on electrode interfaces can be explored by quantum chemical investigation of medium-sized systems consisting of a cluster of substrate (metal) atoms, one or several solvent molecules, and/or at least one ion to be adsorbed at the interface. For the study of water adsorption and halide ion adsorption (unhydrated as well as hydrated) on a mercury surface, we have used the standard CNDO method together with geometrical optimization of the atom positions.In this paper, the following topics have been treated: (a) adsorption of a single water molecule in different positions on a close-packed plane cluster of seven mercury atoms; (b) adsorption of unhydrated halide ions (Cl^?, Br^?, I^?) in the “on-top” or hollow position on the mercury surface; (c) adsorption of monohydrated halides on the mercury surface. Further studies including solvation by six water molecules are discussed.The calculations provide information about minimum-energy geometries, energetic data, and local charges. Furthermore, they allow some conclusions about water mobility and reorientation on a close-packed metal surface, water orientation under the combined influence of an adsorbed ion and the metal surface, and trends of charge distribution in the halide series to be drawn. Calculations are critically discussed in the light of experimental and other quantum chemical data.     

Contact electroresistance of metals in aqueous solutions during the anion adsorption involving charge transfer

Notions about charge transfer during adsorption of anions on metals in aqueous solutions are rendered. The role played by the electron tunneling on macrocontacts during the signal formation in the method of contact electroresistance (CER) is considered. It is shown that CER depends on the metal surface coverage by adsorbed species and their effective charge. Bell-like CER vs.E curves are obtained for copper, silver, and gold in solutions containing halide ions. Potentials of maximums in the curves,E _max, correspond to the charge transfer onset and depend on the nature of the metal and anion and on the anion concentration. AtE belowE _max, halides adsorb in the form of ions, involving no substantial charge transfer. At potentials exceedingE _max by 0.1 to 0.2 V, practically complete charge transfer occurs. With changing anion nature,E _max for a given metal rises in the series I^- < Br^- ≪ Cl^-. For a given anion (say, I^-),E _max increases with the metal nature in the series Cu ≤Ag ≪ Au. The link between the charge transfer during adsorption of anions and the surface reconstruction in single-crystal electrodes is discussed.     

Tracking oxytetracyline mobility across environmental interfaces by second harmonic generation

This work examines the binding behavior of the antibiotic oxytetracycline (OTC) to mineral oxide/water interfaces in the presence and absence of organic functional groups using the interface-specific technique second harmonic generation (SHG). Studies show that OTC binding to fused quartz, methyl ester, carboxylic acid, and alkyl interfaces is fully reversible and highly dependent on solution pH, with appreciable adsorption occurring only at pH 8. Relative surface coverage at pH 8 is highest for the polar organic-functionalized surfaces, and surface saturation occurs for the methyl ester-functionalized fused quartz/water interface at 2 x 10(-5) M. Adsorption isotherm measurements indicate that the binding process is controlled by hydrogen bonding and hydrophobic interactions, with free energies of adsorption on the order of -40 kJ/mol for all interfaces studied. The results indicate that OTC transport in the environment will depend heavily on soil pH and composition and have implications for the development of bacterial antibiotic resistance.     

酞菁铜/金属薄膜界面电位与光二次谐波特性分析

Using the Kelvin probe and the optical second harmonic generation (SHG) measurement, the Space charged phenomenon and the non-linear optical effects at the interfaces of the coppertetra-tert-butyl phthalocyanine (CuttbPc) Langmuir-Blodgett (LB) film deposited on a metal (AlorAu) coated glass slide substrate were in vestigated. The surface potentials decreaseas the film thickness increases and eventually approaches a saturated value. The SHG has been detected although there is a centro-symmetric systemin the Cuttb Pcmolecular, and avery strong SH signal can be investigated at 1260 nm band for Cuttb Pc/Al samples. According to a proposed physical model for Cuttb PcLB film/metal, the nonlinear mechanism were analyzed by using electromagnetic wave theory. It is considered that the enhanced SH peak of CuttbPc/Al is attributed to the strong surface potential aroused by SCIEF at the interface, and shows that the production of SH signal is correlated closely with the electrostatic phenomena at the interface.     

A second harmonic generation study of the oxidation of copper electrodes

The oxidation of copper in basic media has been studied by in situ second harmonic generation (SHG), where the SHG signal was recorded alongside the cyclic voltammogram. The SHG signal changes markedly as the copper surface is oxidised to first Cu₂O and then CuO in a duplex structure. The development of Cu₂O gives rise to a resonant SHG signal because of the band-gap of the material then the upper CuO layer produces an electric-field induced second harmonic (EFISH) response. A correlation of charge with the SHG signal is informative with regard to the mechanism of reduction of CuO and SHG is shown to be a useful method for the examination of oxidation of electrode surfaces.     

Behavior of β-amyloid 1-16 at the air-water interface at varying pH by nonlinear spectroscopy and molecular dynamics simulations

The adsorption and aggregation of β-amyloid (1-16) fragment at the air-water interface was investigated by the combination of second harmonic generation (SHG) spectroscopy, Brewster angle microscopy (BAM), and molecular dynamics simulations (MD). The Gibbs free energy of surface adsorption was measured to be -10.3 kcal/mol for bulk pHs of 7.4 and 3, but no adsorption was observed for pH 10-11. The 1-16 fragment is believed not to be involved in fibril formation of the β-amyloid protein, but it exhibits interesting behavior at the air-water interface, as manifested in two time scales for the observed SHG response. The shorter time scale (minutes) reflects the surface adsorption, and the longer time scale (hours) reflects rearrangement and aggregation of the peptide at the air-water interface. Both of these processes are also evidenced by BAM measurements. MD simulations confirm the pH dependence of surface behavior of the β-amyloid, with largest surface affinity found at pH = 7. It also follows from the simulations that phenylalanine is the most surface exposed residue, followed by tyrosine and histidine in their neutral form.