Investigation of Ig.G adsorption and the effect on electrochemical responses at titanium dioxide electrode

The adsorption of Immunoglobulin G on a titanium dioxide (TiO(2)) electrode surface was investigated using (125)I radiolabeling and electrochemical impedance spectroscopy (EIS). (125)I radiolabeling was used to determine the extent of protein adsorption, while EIS was used to ascertain the effect of the adsorbed protein layer on the electrode double layer capacitance and electron transfer between the TiO(2) electrode and the electrolyte. The adsorbed amounts of Ig.G agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential was applied to the electrode, while the application of a negative potential resulted in a decrease. Exposure to solutions of Ig.G resulted in a decrease of the double layer capacitance (C) and an increase in the charge-transfer resistance (R(2)) at the electrode solution interface. As more Ig.G adsorbed onto the electrode surface, the extent of C and R(2) variation increased. These capacitance and charge-transfer resistance variations were attributed to the formation of a proteinaceous layer on the electrode surface during exposure.     

Impact of porous electrode properties on the electrochemical transfer coefficient

The rate of an activation-controlled electrochemical reaction is determined by two key parameters, the exchange current density, io, and the transfer coefficient, alpha, which is inversely related to the Tafel slope. Assuming that the symmetry factor, beta, is 0.5, the minimum alpha value should be 0.5 for all standard reaction mechanisms, with alpha values larger than this indicating a better electrocatalytic mechanism. The primary goal of this paper is to better understand why alpha values of < 0.5 are often observed experimentally, with specific examples given for the oxygen reduction reaction. These low alpha values cannot be explained by adsorption behavior, but they can result when reactions occur within a porous electrode structure. Consistent with past literature related to Tafel slope predictions, we show that long and narrow pores, a low ionic or electronic conductivity of the electrode layer, and a high io value can cause alpha to be < 0.5, most typically 0.25. However, alpha values between 0.25 and 0.5 are also encountered in practice. We show here that such alpha values can be obtained for reactions occurring at porous films that have nonuniform properties. We also show that the overpotential range over which alpha changes from 0.5 to 0.25 can be quite broad, especially at high temperatures, and thus can be misinterpreted as a true Tafel region with a transfer coefficient between 0.25 and 0.5.     

Temperature dependences of electrical and electrochemical properties of titanium disulfide

The electrical conductivity and thermoelectric power of titanium disulfide were measured at temperatures ranging from 77 to 300 K on samples exhibiting different deviations from stoichiometry. It was found that Ti_1+yS₂ has metallic properties at the temperatures studied, the effective mass of the carriers varying with the deviation from stoichiometry. It was shown that the character of the discharge curve for the Li/Li⁺/Li_xTi_1+yS₂ cell was correlated with the electronic structure of titanium disulfide.The author is grateful to Prof. S. Mrowec and Dr. A. Stoklosa for helpful discussions.     

Investigation of protein adsorption and electrochemical behavior at a gold electrode

The adsorption of two model proteins, human serum albumin and immunoglobulin G, on a gold electrode surface was investigated using 125I radiolabeling and cyclic voltammetry (CV). 125I radiolabeling was used to determine the extent of protein adsorption, while CV was used to ascertain the effect of the adsorbed protein layer on the electron transfer between the gold electrode and an electroactive moiety in solution, namely, K3Fe(CN)6. The adsorbed amounts of HSA and IgG agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential (700 mV) was applied to the electrode, while the application of a negative potential (-800 mV) resulted in a decrease. When the solution pH was varied to alter the charge on the protein, the adsorption trends appeared to follow electrostatic interaction, namely, greater adsorption when the electrode and the protein possessed opposite charge and vice versa. The adsorbed protein layer had the effect of blocking the electron transfer. It was possible to correlate the degree of electron blocking with the amount of adsorbed protein to show that the greater the adsorption, the larger the blocking effect. Of the two proteins used, HSA proved to be more efficient at blocking the electron transfer.     

Investigation of the alumina properties with adsorbed polyvinyl alcohol

The influence of solution pH on the structure of polyvinyl alcohol adsorption layer on the alumina surface was investigated. The spectrophotometry, viscosimetry, thermogravimetry, potentiometric titration and microelectrophoresis were applied in experiments. These methods enable determination of the following parameters: adsorbed amount of PVA, stability of suspension without and with polymer, thickness of its adsorption layers, changes in thermal characteristics of Al₂O₃ surface with the adsorbed polymer, surface charge density and zeta potential of solid particles in the presence and absence of PVA, respectively. All measurements were carried out in the pH range 3–9. The obtained results indicate that pH has a great influence on the conformation of PVA chains adsorbed on the alumina surface. It is due to incomplete hydrolysis of acetate groups of polyvinyl alcohol macromolecules (degree of hydrolysis 97.5%), which dissociate with the increasing pH. Moreover, the polymer adsorption on the alumina surface causes changes in the course of thermogravimetric curves. The effect of weight loss for Al₂O₃–PVA systems is smaller than that of Al₂O₃ without polymer. It is due to elimination of water molecules from the solid surface by adsorbed polymer.     

光谱电化学方法研究: 茜素红S在玻碳电极上的电化学行为

本文首次用长光程光透薄层电解池, 以现场光谱电化学方法研究了茜素红S在酸性溶液中于玻碳电极上的电化学行为, 发现在1.00-0.60V电位范围内存在三个电化学反应过程和一个化学反应过程, 并根据电化学和光谱数据, 提出了电极过程的机理。     

NiO@CuO@Cu bilayered electrode: two-step electrochemical synthesis supercapacitor properties

Present work deals with a two-step synthesis and electrochemical properties of nickel oxide @copper oxide@copper (NiO@CuO@Cu) bilayered electrode. In the first step, anodization (40 V for 25 min) of Cu foil has been carried out for forming Cu-hydroxide@Cu which when annealed at 300 °C for 1 h produces CuO@Cu. In the second step, Ni-hydroxide is deposited onto CuO@Cu by applying current density of 0.03 A/cm² for 3 min which when re-annealed at 300 °C for 1 h gives out NiO@CuO@Cu bilayered electrode. Obtained NiO@CuO@Cu bilayered electrode demonstrates separate CuO and NiO phases. The electrochemical properties have obtained using cyclic voltammetry, galvonostatic charge-discharge, and Nyquist plot measurements that reveal an importance of NiO@CuO@Cu as a potential electrode material in the electrochemical supercapacitor application with 58.14, 51.25, and 4.73 F g^?1 values in 0.5 M, NaOH, KOH, and Na₂SO₄ electrolytes, respectively, measured at 2 mVs^?1 scan rate.     

Cyclic voltammetry of FAD adsorbed on graphite,glassy carbon,platinum and gold electrodes

The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10^?8 mol cm^?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k⁰≌1 s^?1. The pH dependence of E_1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.     

Photochemistry of iron pentacarbonyl adsorbed on titanium dioxide

The photolysis of iron carbonyl (Fe(CO)₅) adsorbed on titanium dioxide (TiO₂, anatase) was studied by FT-IR spectroscopy. When adsorbed Fe(CO)₅ is illuminated by visible and near-UV light, the IR spectrum of its photolysis products is hardly observed, indicating that most of the Fe(CO)₅ is photodecomposed to iron(0) or iron oxides on TiO₂. The carbon monoxide (CO) evolution rate upon illumination depends on the wavelength of light; 433 nm light is more effective for CO evolution than 366 nm light. This result implies that the band-gap excitation of TiO₂ has little effect on the photolysis of adsorbed Fe(CO)₅, since the absorption edge of TiO₂ (anatase) lies at around 400 nm. The effects of substrates on the photolysis of adsorbed Fe(CO)₅ are discussed with reference to previous results obtained for aluminium oxide (Al₂O₃) and silicon dioxide (SiO₂), on which the photolysis leads to the formation of Fe₂(CO)₉ or Fe₃(CO)₁₂.     

329 - Investigation on the electrochemical properties of catecholmines and melanins

The melanization process was investigated using electrochemical methods.On the a.c. and multisweep curves the particular stages occur as separated, consecutively rising and decreasing peaks, corresponding to gradual association of precursor molecules.An interesting effect is the rise of d.c. waves at potentials characteristic for H₂O₂ (appearing usually if O₂ is present in the solution) in deoxygenated solutions of melanins. The differences in the curves of catechol-melanin and indole-melanin permit to ditinguish these compounds using polarographic methods.The result of practical importance is the possibility of a fast determination of small amounts of adrenaline and noradrenaline by use of multisweep methods.     

Synthesis,characterization and electrochemical properties of a compact titanium dioxide layer

In this paper, we report on the synthesis, characterization, and electrochemical properties of a compact titanium dioxide layer as well as its application in dye-sensitized solar cells (DSCs). The compact TiO₂ layer, which was prepared via a facile approach by the hydrolysis of TiCl₄ aqueous solution, has been characterized by XRD, SEM, UV–vis absorption spectroscopy, voltammetry, and electrochemical impedance spectroscopy (EIS). Experimental results show that the compact TiO₂ layer with the thickness of about 100 nm is composed of anatase-phase nanoparticles with the particle size of 10–15 nm. Impedance measurements display that the compact layer of TiO₂ can prevent the back reaction of electrons with tri-iodide ions under low applied potentials, increase the open circuit voltage (V_oc) and fill factor (FF), and finally improve the conversion efficiency (η) for the DSCs from 7.5 to 8.1%.     

The effect of ionic and electronic properties of titanium oxide on the electrochemical growth and redox behavior of polyaniline on titanium surfaces

Polyaniline (PANI) was electrodeposited directly from aniline (ANI)-containing sulfuric acid media on Ti|TiO₂ electrodes, which were prepared in ANI-free 0.5 M H₂SO₄ solution by applying suitable anodization conditions in order to control the donor density (N _D) in the oxide layer of a fixed thickness. By using the suggested procedure, reproducible conditions for the cyclic voltammetric growth of PANI on Ti can be achieved, and most importantly, the properties of Ti|TiO₂|PANI electrodes can be modulated to meet the requirements for specific applications. The polymerization rate and the deposited amount of PANI were found to depend strongly on the N _D estimated by Mott-Schottky analysis. The redox behavior of the resulted Ti|TiO₂|PANI electrodes indicated differences in acid solutions as compared with the corresponding behavior of other PANI-modified metal surfaces. Analysis of the anodic and cathodic electrochemical response of the prepared Ti|TiO₂|PANI electrodes discloses the significant role of ionic and electronic properties of the intervening oxide between the metal support and PANI.     

对乙酰氨基酚在纳米金/十二烷基苯磺酸钠修饰电极上的电化学行为研究

基于电化学沉积法制备了纳米金/十二烷基苯磺酸钠修饰玻碳电极(Nano-Au/SDBS/GCE),并采用扫描电子显微镜、X-射线光电子能谱和电化学方法进行表征。研究了对乙酰氨基酚在Nano-Au/SDBS/GCE上的伏安行为,结果表明,对乙酰氨基酚由在裸玻碳电极上的不可逆氧化过程变为准可逆过程,氧化峰峰电位由0.60 V负移至0.50 V,且在0.42 V处产生一个新的还原峰,表明nano-Au/SDBS膜能催化对乙酰氨基酚的电化学反应。在优化条件下,氧化峰峰电流与对乙酰氨基酚浓度在1.0×10-6mol/L～9.0×10-6mol.L–1和1.0×10-5～1.0×10-4mol.L–1间有良好的线性关系,检出限为8.0×10-7mol.L–1(S/N=3)。     

Preparation of a mercury film electrode modified by tri-n-octylphosphine oxide and the electrochemical properties of this electrode

Mercury film electrodes have been prepared on silver metal and silver-coated glassy-carbon supports and have been modified by a film of tri-n-octylphosphine oxide (TOPO) in a poly(vinyl chloride) matrix. The electrodes have been characterized in detail and the effects of the modifying film parameters on their electrochemical properties have been studied. It has been shown that these electrodes permit selective and sensitive determinations of many metals. The most important parameters are the thickness of the modifying film, the modifier-to-matrix ratio in the modifying film and the base electrolyte composition. Data concerning the reactions of a number of metal ions on the modified electrode are given.     

Effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of nanoporous titanium dioxide electrodes

Titanium dioxide is a widely used photocatalyst whose properties can be modified by fluoride adsorption. This work is focused on the effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of TiO(2) nanoporous thin films. Surface fluorination was achieved by simple addition of HF to the working solution (pH 3.5). Open circuit potential as well as ex situ XPS measurements verify that surface modification takes place. Fluorination triggers a significant capacitance increase in the accumulation potential region, as revealed by dark voltammetric measurements for all the TiO(2) samples studied. The photoelectrocatalytic properties (measured as photocurrents under white light illumination) depend on the substrate being oxidized and, in some cases, on the nature of the TiO(2) sample. In particular, the results obtained for electrodes prepared with a mixed phase (rutile + anatase) commercial nanopowder (PI-KEM) indicate that the processes mediated by surface trapped holes, such as the photooxidation of water or methanol, are accelerated while those occurring by direct hole capture from the adsorbed state (formic acid) are retarded. The photooxidation of catechol and phenol is also enhanced upon fluorination. In such a case, the effect can be rationalized on the basis of a diminished recombination and a surface displacement of both the oxidizable organic substrates and the poisoning species formed as a result of the organics oxidation. Photoelectrochemical and in situ infrared spectroscopic measurements support these ideas. In a more general vein, the results pave the way toward a better understanding of the photocatalysis phenomena, unravelling the importance of the reactant adsorption processes.     

Improvement in reflective-emissive dual-mode properties of electrochemical displays by electrode modification

We studied the electrochromic (EC) and electrochemiluminescent (ECL) properties of a novel dual-mode display (DMD) cell that was enabled for reflective and emissive modes of representation by introducing both EC and ECL materials into an electrochemical cell. We fabricated EC, ECL, and DMD cells based on a simple-mixture solution or modified electrodes and compared their properties to clarify the advantage of a DMD system based on modified electrodes. Both the solution- and modified electrode-based DMDs showed EC properties in the reflective mode under dc bias application and ECL properties in the emissive mode under ac bias application. Although the solution-based DMD cell featured a very simple structure, some improvements related to side reaction and quenching reaction were required. The modified electrode-based DMD cell was fabricated to improve these aspects. The advantage of the DMD model based on the modified electrodes was certainly suggested by comparisons of the results with those of EC, ECL, and DMD cells based on a simple-mixture solution.     

Raman spectra of pyridine adsorbed on a copper electrode

The surface enhanced Raman scattering (SERS) of pyridine adsorbed on a copper electrode was observed with 647.1 nm excitation and the dependence of the Raman intensity as a function of electrode potential was obtained for the most intense bands. The results are compared with reported intensity and frequency values for the silver/pyridine system.