Stripping voltammetry of copper and lead using gold electrodes modified with self-assembled monolayers

One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes. Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes. The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed. Received: 29 May 1997 / Accepted: 24 June 1997     

锑(III)在铂电极上的欠电位沉积行为

由于经欠电位沉积（UPD）形成的吸附金属原子居可以改变电极表面的结构和组成，从而达到增强电祝活性的目的，因此欠电位沉积在电化学领域中颇受重视．对于梯（Ⅲ）的欠电位沉积行为，自1953年Mills和Wills发现锑（Ⅲ）可在AS电极上形成单电子层[1]以后，Schimide等人和Motoo等人分别研究证实梯（Ⅲ）可在Au电极上[2]和Pt电极上[3]发生火电位沉积，并且Motoo等人使用梯（V）化合物测定了每个吸附梯原子占据的铂原子数[4]．本文试图用电位扫描法、微分电容法、电位阶跃法等实验方法对锑（Ⅲ）在柏电极上的大电位沉积并为进行系统的研究…     

铅在铜上电沉积的原位椭圆偏振法

采用循环伏安法(CV)和原位椭圆偏振法(SE)研究铅在铜电极上的电沉积行为。 原位椭圆偏振参数Ψ和Δ值的变化率在CV图峰电位处同时出现极值。 通过建立单层膜模型描述“电极-溶液”界面的结构并对椭圆偏振光谱数据进行拟合得到铅沉积层厚度随电位的变化规律。 拟合结果显示,铅在铜电极上的电沉积有3个不同的沉积速率,-0.20～-0.35 V之间沉积速率为0.003 nm/mV,-0.35～-0.48 V之间沉积速率为0.025 nm/mV,-0.48～-0.60 V之间沉积速率为0.116 nm/mV,由此表明铅的电沉积分为3个不同阶段：欠电位沉积阶段、欠电位沉积向本体沉积的过渡阶段和本体沉积阶段。     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

Catalytic effect of Pd nanoparticles on electroless copper deposition

This study elucidates the application of Pd nanoparticles as catalysts of electroless copper deposition and their catalytic effect on the deposition kinetics and microstructure in an electroless copper bath. Quartz crystal microgravimetry (QCM) and high-resolution field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray spectroscopy (EDX) demonstrated that the kinetic changes associated with electroless copper deposition (ECD) comprised two stages—the incubation period and the acceleration period. In the incubation period, small copper particles were deposited. In the acceleration period, the ECD rate increased rapidly and continuously conducting films with large grains were formed. Leaner sweep voltammetry (LSV) and mixed potential theory (MPT) were applied to examine the catalytic powers of the prepared Pd nanoparticles and the related electrochemical kinetics in the ECD bath.     

离子液体中Au(111)和Pt(111)表面Ge欠电位沉积的现场STM研究

本文研究BMIPF₆离子液体中Au(111)和Pt(111)表面Ge的电沉积行为. 循环伏安法测试结果表明,在含0.1 mol·L^-1 GeCl₄的BMIPF₆溶液Au(111)和Pt(111)表面均有两个与Ge沉积过程相关的还原峰. 第一个还原峰包含了Ge⁴⁺还原成Ge²⁺及Ge的欠电位沉积,第二个还原峰对应Ge的本体沉积. 现场扫描隧道显微镜研究结果表明,Ge在Au(111)和Pt(111)表面均有两层欠电位沉积. 第一层欠电位沉积厚度约为0.25 nm、形貌平整、带有缝隙的亚单层结构. 第二层欠电位沉积形貌相对粗糙的点状团簇结构. 该欠电位沉积过程伴随表面合金化.     

Anodic-stripping voltammetric determination of arsenic at a copper-coated glassy-carbon electrode

The anodic-stripping voltammetric behaviour of arsenic(III) at a glassy-carbon electrode copper-coated in situ has been investigated. The effects of copper concentration, acidity, deposition potential and sweep rate on the stripping peak have been examined and criteria are given for the choice of experimental conditions. The procedure is applicable to the determination of 7.5-750 ng/ml of arsenic levels and is useful for the analysis of various types of water sample.     

Underpotential Deposition and Stripping of Lead at Disorganized Monolayer‐Modified Gold Electrodes

Underpotential deposition (UPD) and stripping of Pb²⁺ at thiol‐based disorganized monolayer‐modified gold electrodes was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry (EQCM). Electrodes modified with mercaptoacetic acid or mercaptoethane sulfonic acid were studied. Due to the proximity of the potentials for the Pb UPD and thiol reductive desorption, achievement of a UPD‐stripping voltammetry methodology for determination of low concentrations of Pb²⁺ was not successful. However by comparison of the CV and EQCM data and consideration of the possible mass changes per mole electrons transferred in light of the other species present in solution, possible mechanisms are put forward for the deposition and stripping of Pb²⁺ at thiol‐modified electrodes.     

Self-assembling Process of Alkanethiol Monolayers on Gold Surface via Underpotential Deposition

IntroductionThe measurement of the effective surface area(i.e.unoccupied area) of a given substrate is of fun-damental importance in the characterization of interfa-cial modification processes. Several methods, such asiodine chemisorption[1], cyclic volta…     

Open circuit stability of underpotentially deposited Pb monolayer on Cu(1 1 1)

The stability of underpotentially deposited (UPD) Pb layer on Cu(1 1 1) is investigated by conventional electrochemical techniques in perchlorate solution at open circuit potential (OCP). In situ scanning tunneling microscopy (STM) is employed to monitor and ascertain structural and morphological changes at characteristic potentials. A corrosion-like mechanism associated with UPD layer stripping powered by reduction processes is found to operate in the system of interest in absence of potential control. OCP transients suggest strong dependence of the Pb layer stability upon the concentration of oxidizing agents, such as oxygen and/or nitrate ions, present in the solution. It is found that the increase of the oxidizing agent concentration results in a proportional decrease of the Pb UPD layer stripping time at OCP. The concentration of the dissolved oxygen is found to affect the UPD layer behavior in the entire range of underpotentials in accordance with the strong affinity of the Pb²⁺/Cu(1 1 1) system to the oxygen reduction reaction (ORR). In contrast to oxygen, nitrate ions appear to play active role only in the potential range positive to the UPD peaks where mostly bare Cu surface is in contact with the solution. Specifically adsorbing Cl⁻ ions are examined as a possible inhibitor of the reduction processes operating in the Pb underpotential range. Concentrations of Cl⁻ ions as low as 1 × 10⁻⁴ M are found to stabilize the Pb UPD layer by a factor of 2.5.     

Electrochemistry in ultrahigh vacuum: underpotential deposition of Al on polycrystalline W and Au from room temperature AlCl(3)/1-ethyl-3-methylimidazolium chloride melts

The voltammetric characteristics of polycrystalline Au and W electrodes cleaned (thermal annealing at 1100 K) and characterized (Auger electron spectroscopy) in ultrahigh vacuum (UHV) have been examined in ultrapure AlCl(3)/1-ethyl-3-methylimidazolium chloride (EtMeImCl) melts in UHV. These experiments were performed using a custom-designed transfer system that allows for the all-Al electrochemical cell to be filled with EtMeImCl in an auxiliary UHV chamber and later transferred under UHV to the main UHV chamber that houses the Auger electron spectrometer. The results obtained for the underpotential (UPD) and bulk deposition of Al on Au were found to be very similar to those reported in the literature for measurements carried out under 1 atm of an inert gas in a glovebox. For the far more reactive W surfaces, voltammetric features ascribed to the stripping of underpotential-deposited Al could be observed following a single scan from 1.0 V vs Al(3+)/Al to a potential negative enough for bulk deposition of Al to ensue. This behavior is unlike that reported in the literature for experiments performed in a glovebox, which required either extensive potential cycling in the Al bulk deposition and stripping region or excursions to potentials positive enough for chlorine evolution to ensue for Al UPD features to be clearly discerned. These observations open new prospects for fundamental electrochemical studies of well-characterized, highly reactive metals, including single crystals, in a variety of low vapor pressure ionic liquids.     

The detection of nitrate using in-situ copper nanoparticle deposition at a boron doped diamond electrode.

Electrochemical deposition from a 0.1 M sodium sulphate solution, containing Cu2+ (adjusted to pH 3 with hydrochloric acid) produced a well defined copper nanoparticle deposit on the surface of a boron doped diamond electrode. Changing conditions such as potential (-0.8, -1.0 and -1.2 V), time (5, 2 and 0.5 s) and concentration of Cu2+ (500, 250 and 100 microM) was found to give copper nanoparticles of varying size and particle density. The electrocatalytic properties of the copper surface towards nitrate reduction were explored. An in-situ copper nanoparticle production method was developed for the detection of nitrate; this involves electrodeposition, followed by linear sweep voltammetry for the reduction of nitrate and then application of a stripping potential to renew the electrode surface. The linear sweep was discovered to have homogenised the size of the nanoparticles but their number density was still dependant on the initial conditions of deposition. Some particles were still present at the surface after the stripping potential had been applied but repetitions of the procedure showed these did not have an effect on subsequent deposits. Optimisation of the method lead to applying a deposition potential of -0.8 V, at a BDD electrode for 5 s in a 0.1 M sodium sulphate solution (pH 3) containing 100 microM Cu2+ followed by a linear sweep at 1 V/s; this yielded a limit of detection of 1.5 microM nitrate. The analytical applicability of the technique was evaluated for nitrate detection in a natural mineral water sample and was found to agree well with that stated by the manufacturer.     

Parameters affecting the determination of mercury by anodic stripping voltammetry using a gold electrode

The electrochemical determination of aqueous Hg(II) by anodic stripping voltammetry (ASV) at a solid gold electrode is described. The aim of this work is to optimise all factors that can influence this determination. Potential wave forms (linear sweep, differential pulse, square wave), potential scan parameters, deposition time, deposition potential and surface cleaning procedures were examined for their effect on the mercury peak shape and intensity. Five supporting electrolytes were tested. The best responses were obtained with square wave potential wave form and diluted HCl as supporting electrolyte. Electrochemical and mechanical surface cleaning, aimed at removing the amount of mercury deposited onto the gold surface, were necessary for obtaining a good performance of the electrode. Response linearity, repeatability, accuracy and detection limit were also evaluated.     

A Modulation QCM Applied to Copper Electrodeposition and Stripping

A fast electrochemical quartz crystal microbalance with dissipation monitoring (EQCM−D) was applied to copper electrodeposition and subsequent stripping. Accumulation brings the frequency noise down to the mHz range, corresponding to 0.1 % of a monolayer. With this precision, the apparent mass transfer rate as determined from the time-derivative of the frequency shift can be directly compared to the current. Small but systematic deviations between the two can be attributed to nanoscale roughness. In the voltage range of underpotential deposition (UPD), the apparent mass transfer rate shows peaks and shoulders. The plating additive benzotriazole (BTA) leaves the magnitude of electrogravimetric signals unchanged, but shifts the UPD onset potential. The additive thiourea (TU) promotes UPD and strongly increases the bandwidth.     

Underpotential deposition of Cu on partially oxidized Rh electrodes

The underpotential deposition (UPD) of copper on partially oxidized rhodium electrodes was studied in acid medium using potentiodynamic techniques. The process was analyzed as a function of the potential and time of deposition. The potentiodynamic I-E patterns for the oxidative dissolution of Cu provide evidence for the existence of a chemical reaction between Cu and oxygen existing on the electrode surface. Redistribution of the active sites is also possible when appreciable quantities of oxidized species are simultaneously reduced by the UPD process. The partially oxidized rhodium electrodes were prepared by cyclic voltammetry and anodic polarization. The later method provided the most oxidized surfaces, but, even in this case, the degree of oxygen surface coverage was lower than that corresponding to a monolayer. Received: 11 July 1997 / Accepted: 10 February 1998     

Electrodeposition of Se on carbon-supported Pt nanoparticles by cyclic voltammetry

Cyclic voltammetry (CV) is a powerful and popular electrochemical technique widely used to study the surface structure of materials through the electrochemical behaviors. Herein CV is utilized to study the electrochemical deposition of selenium (Se) on carbon black-supported Pt nanostructures. We synthesized carbon-loaded platinum nanoparticles (Pt/C) by microwave method and studied the electrochemical behavior of selenium on them. Through the experiment of changing the reverse potential, the corresponding relationship between the Se deposition peak and stripping peak was clarified and the deposition and stripping process of Se was proposed. Meanwhile, we synthesized cubic and octahedral nanocrystals of Pt, and used CV to study the Se deposition on these nanosctructures supported by carbon. It was found that the relative intensity of UPD peaks on Pt is different, as Pt_cube@C is dominated by (100) and Pt_oct@C electrode is dominated by (111) while Pt@C falls in between.

     

Sensitive Anodic Stripping Voltammetric Copper Ions Determination Performed in Double Deposition and Double Stripping Steps System for Real Water Samples Analysis

The article reports on utilization of double deposition and stripping steps for increasing sensitivity of Cu(II) determination by anodic stripping voltammetry (ASV) at two lead film working electrodes. A significant preconcentration of copper was achieved thanks to utilization of a simple design of four electrodes system that gives possibility to perform one measurement cycle consisting of two deposition and two stripping steps. Due to the fact that deposition step is doubled, the concentration of Pb(II) needed to lead film electrodes formation was significantly reduced as compared to traditional procedures using three electrodes system. The analytical procedure of Cu(II) determination was optimized. The experimental factors: supporting electrolyte's pH and its concentration, lead ions concentration, potential and time of deposition at both working electrodes were studied. The Cu(II) peak current was linearly dependent on its concentration from 5×10^?10 to 2×10^?8 mol L^?1 (deposition time of 270 and 160 s at the first and the second working electrode, respectively). The obtained detection limit for copper ions determination was 2.1×10^?10 mol L^?1. The described procedure was validated by analysis of two water certified reference materials. The described procedure was also utilized for real water sample analysis.     

A Study on the Suitability of Carbon Disk Microelectrodes for Trace Analysis of Lead and Copper by ASV

The performance of carbon microdisk electrodes for the simultaneous trace analysis of lead and copper by anodic stripping voltammetry is investigated. The evaluation of the two metal ions in a single step, i.e., by employing a plating potential at which both cations are reduced simultaneously, gives unpredictable results due to the interaction between lead and copper deposited onto the electrode surface. In particular, the calibration plots of lead are not linear, while the copper stripping peak is quite broad and irreproducible. A two-steps deposition procedure, based on a preelectrolysis of copper performed at a potential at which lead ion is not reduced, followed by a simultaneous reduction of the two cations at large enough negative potentials, provides, instead, linear calibration graphs for lead. Copper can be determined without interference by plating the metal at a negative potential where lead ion is not reduced. The reliability of the two-steps procedure for the determination of lead and copper is verified in rain and wine samples.     

Anodic stripping voltammetry and chronopotentiometry of copper at a rotating carbosital disk electrode

The use of a new carbon material — carbosital — for electrodes is reviewed. The behaviour of copper deposited on the carbosital electrode surface in anodic stripping voltammetry and chronopotentiometry is discussed. In anodic stripping voltammetry with a rotating carbosital disk electrode, the peak current and the number of coulombs involved in stripping copper are directly proportional to the square root of the electrode rotation rate during preelectroiysis; the peak current is directly proportional to the potential scan rate during stripping. For anodic stripping voltammetry and anodic stripping chronopotentiometry, linear calibration graphs are obtained in the range 1 X 10^-3–1 x 10^-6 M copper(II). The method is applicable to analysis of high-purity cadmium for copper.     

Comparative investigation of underpotential deposition of Ag from aqueous and ionic electrolytes: An electrochemical and in situ STM study

Underpotential deposition (UPD) of Ag on Au(111) has been studied with two different electrolytes: aqueous 0.1 M H2SO4 solution in comparison with the ionic liquid 1-butyl-3-methylimidazolium chloride BMICl + AlCl3. Of particular interest is the distinct behavior of 2D phase formation at both interfaces, which has been investigated by cyclic and linear sweep voltammetry in combination with in situ electrochemical scanning tunneling microscopy (STM). It is found that one monolayer (ML) of Ag is formed in the UPD region in both electrolytes. In aqueous solution, atomically resolved STM images at 500 mV versus Ag/Ag+ show a (3 x 3) adlayer of Ag, whereas after sweeping the potential just before the commencement of the bulk Ag deposition, a transition from expanded (3 x 3) to pseudomorphic ML of Ag on Au(111) occurs. In BMICl-AlCl3, the first UPD process of Ag exhibits two peaks at 410 and 230 mV indicating that two distinct processes on the surface take place. For the first time, STM images with atomic resolution reveal a transition from an inhomogeneous to an ordered phase with a (square root of 3 x square root of 3)R30 degrees structure and an adsorption of AlCl4- anions having a superlattice of (1.65 x square root of 3)R30 degrees preceding the deposition of Ag.