Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria

The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm?3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.     

Selective copper–iron dissolution from a molybdenite concentrate using bacterial leaching

The present research reports on the selective dissolution of copper and iron from a Chilean molybdenite concentrate using mesophilic, moderate and extreme thermophilic culture bacteria. From the results obtained it is deduced that molybdenite is not attacked by any of the above mentioned microorganisms, whereas the attack of the copper–iron species is dependent on various experimental conditions: pH, potential, pulp density, or addition of silver as catalyst. Optimal copper–iron dissolution is obtained using extreme thermophilic microorganisms and low pulp density (2% w/v). Total selective dissolution of chalcopyrite is achieved which leads to a pure molybdenite concentrate being obtained. © 2001 Society of Chemical Industry     

The electrochemical behaviour of silver sulphide in sulphuric acid solutions

The electrochemical behaviour of synthetic silver sulphide (acanthite) electrodes in sulphuric acid solutions has been investigated using several techniques including cyclic voltammetry, anodic polarization and constant potential experiments. Under anodic polarization the dissolution has been attributed to the reaction Ag₂S=2Ag⁺+S+2e which occurs in two sequential, single electron transfer steps. A kinetic model for this stepwise anodic dissolution process at lower overpotential, where the current is a function of potential, is provided. At high dissolution rates (i.e. high currents) the slightly soluble silver sulphate salt is formed on the surface due to the saturation of the electrolyte near the Ag₂S interface. This observation is supported by the influence of electrolyte composition on the cyclic voltammetry and the polarization curve. A paralinear film growth model has been found to describe the formation and growth of the silver sulphate product layer indicating an initial region of parabolic kinetics which gradually changes to linear kinetics as the rate of film dissolution approaches that of film formation.     

Influence of surface chemical structure of active carbon on its electrochemical behaviour in the presence of silver

Cyclic voltammetric studies of the influence of surface chemistry on the electrochemical behaviour of powdered active carbon electrodes were carried out in the presence of silver both in bulk solution and pre-adsorbed on carbon. Surfaces with a variety of chemical properties were obtained through the modification of carbon samples by heat treatment under vacuum, oxidation with concentrated nitric acid and annealing in an ammonia atmosphere. The surface area (BET), acid–base neutralization capacities and sorption capacity towards Ag+ ions were estimated in the samples obtained. The states and relative amounts of deposited Ag species were estimated using XPS. The influence of the surface chemistry of the powdered carbon material in terms of its electrochemical properties and the mechanism of silver adsorption and deposition is discussed.     

1—苯基—5—巯基四氮唑和苯并三氮唑在胶态银和硫化银上的阳极抑制效应

为了研究抑制剂对银核和硫化银核的不同作用，本工作考察了1－苯基－5－巯基四氮唑（PMT）和苯并三氮唑（BTA)作为抑制剂在银核和硫化银核上物理显影的阳极抑制和解抑制效应。实验结果表明：1）PMT和BTA对Ag核和银离子过量时制得的硫化银核，Ag2S(Ag)，的显影催化活性都有不同程度的抑制作用，而对硫离子过量时制得的硫化银核，Ag2S(S)，无明显的抑制作用，这可能是由于过量硫离子在硫化银核上的吸附要强于这两种抑制剂；2）S2O3^2-或I^-离子的存在对BTA在Ag核上有解抑制作用，不仅可恢复甚至提高Ag核的显影催化活性，而对Ag2S核的抑制作用无明显影响；3）与BTA不同，S2O3^2-或I^-离子对PMT在Ag核上没有解抑制作用，对Ag2S(Ag)核的抑制作用还稍有增强，而对Ag2S(S)核稍有减弱；4）银溶胶中的表面增强拉曼谱（SERS）测量证实：BTA在Ag核上的吸附导致Ag核显影催化活性的下降，加入S2O3^2-或I^-离子后致使BTA的SERS信号消失则意味着BTA在银核表面的脱附。以上这些结果说明阳极抑制机理在抑制效应中有重要作用。     

Catalytic mechanism of manganese ions and visible light on chalcopyrite bioleaching in the presence of Acidithiobacillus ferrooxidans

The bioleaching of chalcopyrite is low cost and environmentally friendly,but the leaching rate is low.To explore the mechanism of chalcopyrite bioleaching and improve its leaching rate,the effect and mechanism of manganese ions(Mn²⁺) and visible light on chalcopyrite mediated by Acidithiobacillus ferrooxidans(A.ferrooxidans) were discussed.Bioleaching experiments showed that when both Mn²⁺ and visible light were present,the copper extraction was 14.38% higher than that of t...     

The electrochemistry of silver in sulphide and tetrasulphide solutions

A cyclic voltammetric and rotating disc study of the sulphide and tetrasulphide ions on glassy carbon and silver electrodes is described. Oxidation of the tetrasulphide ion on glassy carbon produces a thin film of sulphur. In the case of the sulphide or hydrosulphide ion on silver, two sets of peaks were observed. The set with the more negative potential was shown to be due to the electrochemical formation and decomposition of α- and β-silver sulphide (Ag₂S). The silver sulphide formation was limited by diffusion of HS^? in solution, the diffusion coefficient being (11.9 ± 0.5) × 10^?10 m² s^?1. The more anodic set of peaks was shown to be due to the silver dissolution reaction, followed by the chemical precipitation of silver sulphide. The tetrasulphide ion—silver system showed similar behaviour, but with two additional features. One was an extra silver sulphidation peak which was ascribed to the direct electrochemical reaction between silver and the tetrasulphide ion. The other was the reduction of the tetrasulphide ion to sulphide at large negative potentials. Under rotation, a diffusion plateau for this reaction was observed, from which a diffusion coefficient for S₄^2? of (5.9 ± 0.2) × 10^?10 m² s^?1 was determined.     

Highly sensitive and selective electrochemical determination of dopamine and ascorbic acid at Ag/Ag2S modified electrode

A biosensor electrode possessing highly sensitive and selective determination of dopamine (DA) is fabricated. This electrode, a silver (Ag) thin film on indium-tin-oxide glass, is treated with a silver sulfide (Ag₂S) film using electrochemical deposition. Active Ag ion is easier to form on Ag₂S than on pristine Ag, which prefers to attract ascorbic acid (AA). The Ag₂S layer reduces the oxidation potential of AA due to the electrostatic interaction, which results in well-separation of mixed oxidation responses to both of DA and AA. Besides, the Ag₂S-modified electrode exhibits dramatic electrocatalytic effect on the oxidation of DA in the presence of AA. In 0.1 M phosphate buffer solution at pH ∼ 7.0, the differential pulse voltammetric peak intensity linearly correlates with DA concentration in two regions, viz. 1.0–10, and 10–100 μM, with correlation coefficient of 0.998 and 0.995, respectively. The lowest concentration limit of 1.0 μM DA can be detected. The interference of AA effectively diminishes in the mixed solution. These features make the Ag₂S significant for selective and sensitive measurement of DA in the presence of excess AA.     

Photocatalysts for reagentless disinfection on the basis of titanium dioxide films modified by silver nanoparticles

Using the test cultures of Pseudomonas fluorescens and Lactococcus lactis bacteria, photoinduced pathophysiological properties of film titanium dioxide photocatalysts modified by silver nanoparticles are investigated. It is shown that the deposition of silver leads to an increase in the adsorption of microorganisms from the solution and to a rise in the efficiency of photogeneration of hydroxyl radicals and superoxide ions, which provides the attainment of a high level of antimicrobial activity. In particular, the survival rate of P. fluorescens eubacteria under the UV irradiation in contact with the TiO₂/Ag catalyst decreases by a factor of more than 70 compared with irradiation in the absence of the photocatalyst. The developed photocatalysts allow the manifold increase in the efficiency of the disinfection of aqueous media with the use of ultraviolet.     

Adsorption and antibacterial activity of silver‐dispersed carbon aerogels

Silver‐dispersed carbon aerogels (Ag/CAs) were obtained by the direct immersion of organic aerogels in aqueous AgNO₃ solutions and then carbonization of the resulting material under a nitrogen atmosphere. The adsorption and antibacterial activity of Escherichia coli and Staphylococcus aureus on Ag/CAs were studied by the measurement of the amount of viable bacteria in suspensions and scanning electron microscopy (SEM) observations. The adsorbed amount of bacteria on samples without silver increased with an increase in the carbonization temperature and contact time. SEM studies showed that the adsorption capacity of Ag/CAs decreased with an increase in the silver content; this was considered to be mainly due to the dissolution behavior of bacteria by silver ions. The antibacterial test showed that 2.5 mg of Ag/CAs with more than 3.6% Ag could inhibit the growth of 10⁵ cfu/mL E. coli in 10 mL of a Mueller–Hinton broth culture, but in the case of S. aureus, 10‐mg samples just got the same antibacterial effect. An antibacterial persistency test showed that 25 mg of Ag/CAs with 6.5% Ag could kill 50 mL of 10⁵ cfu/mL E. coli eight times. These results indicate that Ag/CAs possess strong and long‐term antibacterial activity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1030–1037, 2006     

Hollow mesoporous silica capsules loaded with copper,silver, and zinc oxide nanoclusters for sustained antibacterial efficacy

Intensive and overuse of antibiotics during the last years has triggered a distinct rise in antibiotic resistance worldwide. In addition to the newly developed antimicrobials, there is a high demand for alternative treatment options against persistent bacterial infections. The biocidal impact of metal ions like copper (Cu²⁺), silver (Ag⁺), and zinc (Zn²⁺), also known as the oligodynamic effect has been used for ages to kill or inhibit the growth of microorganisms and to employ long-term prevention strategies against their biological antagonists. Herein, we report on the synthesis of Cu, Ag, and Zn metal and corresponding oxide nanoparticles immobilized on hollow mesoporous silica capsules (HMSCs) obtained by a hard-template assisted sol-gel synthesis followed by reduction of appropriate metal salts in the presence of HMSCs. Compartmentalization of nanosized metal and oxide clusters in Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles prevented their agglomeration and offered high release kinetics of metal ions between 2.0 and 3.7 mM during 24 h, as monitored by UV-vis analyses. The distribution and morphology of pristine and metal functionalized HMSCs were evaluated by transmission electron microscopy analysis revealing the successful synthesis of Ag, Cu, and ZnO nanoparticles supported on HMSCs. X-ray photoelectron spectroscopy revealed that mainly Cu(II), Ag(0), and Zn(II) species were present in the modified HMSCs. In addition to the surface attachment of preformed metal (Ag and Cu) and metal oxide (ZnO) cluster, nucleation of metal nanoparticles inside the void of HMSCs provided an internal reservoir which allowed for a time-dependent release of metal ions through slower dissolution rates leading to a long-term and sustained bacterial inhibition over several hours. The high antimicrobial efficiency of Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles was investigated toward both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria by INT assays showing a complete growth inhibition for both bacteria types after 24 h. While Ag@HMSCs and Cu@HMSCs showed a higher susceptibility against Gram-negative bacteria, ZnO@HMSCs showed a higher susceptibility against Gram-positive bacteria. This demonstrates the promise of metal-loaded capsules as antibacterial delivery vehicles with dual-mode time-release profiles being potential alternatives for antibiotic drugs.     

银离子交换的沸石修饰电极的循环伏安新特性

银离子交换沸石Y修饰电极（Ag^ -沸石Y）的循环伏安（CV）行为，不同于溶液中的银离子在固体银电极表面上的CV行为。Ag^ －沸石电极中银离子还原电位明显受沸石体内银簇影响。依据Ag^ -沸石修饰电极在含有能够与银离子形成难溶盐的电解质中的CV行为，本文发现了沸石对溶液中阴离子具有尺寸选择效应，并解释了银离子交换沸石修饰电极的循环伏安反应特性。     

On the capacity fading of LiCoO2 intercalation electrodes:: the effect of cycling, storage, temperature, and surface film forming additives

The electrochemical behavior and surface chemistry of LiCoO₂ intercalation cathodes as a function of cycling and storage at 25, 45, and 60 °C was studied. The standard solutions for this work comprised ethylene carbonate (EC), ethyl-methyl carbonate (EMC), (1:2) and 1 M LiPF₆. The effect of two surface film-forming additives, vinylene carbonate (VC) and an organo-borate complex (denoted as Merck's AD25) in solutions was also explored. We analyzed temperature-dependent processes of surface film formation on the cathodes, which increase their impedance upon cycling and storage, thus making their electrochemical kinetics sluggish. We also analyzed cobalt dissolution from the cathodes at 25, 45 and 60 °C. The apparent capacity fading of the LiCoO₂ electrodes is attributed mostly to changes on their surface, rather than to bulk degradation. There are signs that the presence of HF in solutions may play a major negative role. Hence, as the electrode's surface/solution volume ratio is higher, the capacity fading of the LiCoO₂ electrodes should be lower. The main tools for this study were cyclic voltammetry, chronopotentiometry, impedance spectroscopy, electrochemical quartz crystal microbalance (EQCM), IR-spectroscopy, XRD, XPS, and SEM.     

Studying the localized deposition of Ag nanoparticles on self-assembled monolayers by scanning electrochemical microscopy (SECM)

The local deposition of Ag nanoparticles (NPs) on ω-mercaptoalkanoic acid, HS(CH₂)_nCO₂H, (n = 2, 10) self-assembled monolayers (SAMs) by scanning electrochemical microscopy (SECM) is reported. We found that the presence of a SAM had a pronounced effect on Ag deposition. Experiments were conducted by applying different potentials to an Au(1 1 1) substrate either in the presence of a constant concentration of Ag⁺ ions in solution (bulk deposition) or by generating a flux of Ag⁺ from an Ag microelectrode that was positioned close to the Au(1 1 1) substrate (SECM deposition). SECM was used for generating a controlled flux of silver ions by anodic dissolution of an Ag microelectrode close to the SAMs modified Au(1 1 1). We found that the shape of the NPs was affected by the length of the carbon-chain of the SAM. Tetrahedral NPs were obtained on bare Au(1 1 1) surfaces while rod like and cubic Ag NPs were deposited onto 3-mercaptopropanoic acid (MPA) and 11-mercaptoundecanoic acid (MUA) SAMs, respectively. The size and shape of the deposited NPs were influenced by the deposition potential.We conclude that the shape and distribution of locally deposited Ag NPs on Au(1 1 1) can be controlled by modification of the substrate with a SAM and through controlling the Ag⁺ flux generated by SECM.     

Development of a Ag/Ag micro-reference electrode for electrochemical measurements in ionic liquids

We report on a novel miniaturized Ag/Ag⁺ reference electrode (RE) design suitable for electrochemical measurements in room temperature ionic liquids (RTILs). The electrode is based on capillaries with an outer diameter of 365 μm and contains a 10 mmol/l solution of a silver salt in a RTIL. The silver salt bears the same type of anion as the RTIL. While potential shifts of several hundred millivolts have been observed for common platinum or silver pseudo-reference electrodes, our Ag/Ag⁺ micro electrode provides a stable and reliable reference potential over a period of more than two weeks, if protected from light and stored in a nitrogen atmosphere. Due to the small dimensions of the RE, it can be placed close to the working electrode (WE) and it is well-suited for application in electrochemical micro cells as well as for potential-controlled in situ AFM, STM or electrochemical impedance measurements. The electrode characteristics were determined by voltammetric measurements on ferrocene and cobaltocenium hexafluorophosphate dissolved in a RTIL. The highest expected contamination of the sample with Ag⁺ ions was calculated and found to be below 4 ppm.     

纳米银修饰电极的电化学性能初探

在圆柱形电解槽中,采用直流电沉积方法在导电玻璃上沉积银纳米材料,制备了Ag/I-TO、Ag/CNTs/ITO复合电极,并以制得的复合电极做工作电极,测定两种电极在磷酸缓冲溶液中的循环伏安响应曲线。CNTs具有很高的比表面积,除了对银离子的反应具有催化作用外,还可能对带有负电荷的SCN-离子具有吸附作用。实验结果表明：银修饰的碳纳米管导电玻璃电极具有很好的电化学活性,可用于检测SCN^-。     

Inherent emf relaxation of electrochemical cells with nanocrystalline Ag electrodes

The open circuit voltage of the electrochemical cell Ag (nano)|solid silver electrolyte|Ag (macro) is found to be inherently unstable. Even under conditions which support the morphological stability of the arrangement of nanocrystalline silver, the particles grow significantly as soon as they function as electrodes; i.e. when they are in contact with a silver electrolyte and connected electronically at the same time. The process is shown to be due to electrochemical Ostwald ripening with the interfacial transfer of Ag⁺ through the Ag/electrolyte interface being the rate limiting step. Its activation energy is 0.01 eV. The decay is in good agreement with modelling results.     

Electrochemical recovery of silver from waste aqueous Ag(I)/Ag(II) redox mediator solution used in mediated electro oxidation process

The paper presents a process for the electrochemical recovery of silver(Ag) by electro deposition on the electrode surface from the waste solutions of Ag(I)/Ag(II) redox system in nitric acid medium used for the mediated electrochemical process. Electrochemical recovery was carried out in an undivided cell with DSA-O₂ electrodes at room temperature condition. At an optimized current density of 12 A/dm², 99% of Ag recovery efficiency was achieved with high yield and low energy consumption. Experimental runs were made in order to observe the performance of the Ag recovery process. The operating conditions like current density, temperature and Ag(I) concentration of the electrolyte, the acid concentrations, agitation rate and inter-electrode distance were optimized.     

纳米银修饰电极的制备

在圆柱形电解槽中,采用直流电沉积方法在导电玻璃上沉积银纳米材料,制备了Ag／ITO、Ag／CNTs／ITO复合电极,并以制得的复合电极作工作电极,测定两种电极在磷酸缓冲溶液中的循环伏安响应曲线。实验结果表明,纳米银修饰的电极具有很好的电化学活性。     

Characterization of solid embeddable reference electrodes for corrosion monitoring in reinforced concrete structures

Metal-metal oxide (MMO), graphite and laboratory-made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarization behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of 2 years. It was found that the MMO pseudo-reference electrode is pH-sensitive, the graphite pseudo-reference electrode is oxygen sensitive and the Ag/AgCl pseudo-reference electrode is chloride sensitive. In spite of the fact that any of them can be used to determine the corrosion rates of rebars because they do not depend on the absolute potential and/or the long-term stability of the reference electrode when using traditional electrochemical techniques, long-term drifts in the electrode potentials may lead to misinterpretations of the rebar state. In this context graphite electrodes are recommended because they provide conservative results regarding the active/passive state of the rebars.