Effect of thiourea on copper dissolution and deposition (original) (raw)
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Journal of the Chemical Society: Faraday Transactions, 1996, 92, 2725-2729., 1996
Electrochemical data recorded for copper electrodes immersed in a solution containing thiourea indicates that thiourea is adsorbed at potentials more negative than the onset of copper oxide formation, and the passive layer is built upon a layer of adsorbed thiourea. Thus, anodization of the specimens leads to the establishment of a competition between the formation of an anodic layer containing thiourea and the oxides layer, and the electrodissolution of the metal through the anodic film.
Journal of Applied Electrochemistry, 2008
We investigated the effect of allyl thiourea (ATU) on both the electrodeposition and electrodissolution of copper in aqueous sulfuric acid by combining cyclic voltammetry (CV) with electrochemical quartz crystal microbalance (EQCM) studies and surface enhanced Raman spectroscopy (SERS). The results demonstrated that the two-electron transfer reaction is the predominant process for the copper dissolution-deposition process in 1.0 M H 2 SO 4 solution not containing ATU in the potential range-0.65 to 0.05 V versus SCE. In comparison, the copper dissolution-deposition process in 1.0 M H 2 SO 4 solution containing ATU corresponds to a one-electron transfer reaction. The spectral features observed from the SERS studies showed at molecular level that ATU can be adsorbed tilted to the copper electrode surface and that coordination occurs via the sulfur atom. The secondary amino group is nearer to the surface than the primary amino group. SO 4 2and HSO 4 can be coadsorbed on the protonated-NH (CH 2 CHCH 2) groups.
Journal of the Chilean Chemical Society, 2009
The effect of thiourea (TU) concentration on copper electrodeposition was studied employing cyclic voltammetry and electrochemical crystal quartz microbalance techniques. It was found that the polarization effects are related to the type of species generated in the electrode interface. Due to formation of formamidine disulfide (FDS) at concentrations greater than 10-4 mol dm-3 , the electrode surface is blocked, and copper electrodeposition shifts towards more negative potential values (polarizing effect). Lower concentrations favors the formation of Cu(I)-TU contributing to the de-polarization of copper electrodeposition reaction.
Anodisation of copper in thiourea- and formamidine disulphide-containing acid solution
Journal of Electroanalytical Chemistry, 2001
The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV-vis spectroscopy, XPS and EDAX analysis, and structural information on copper-thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range − 0.305 E5 0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)-thiourea soluble complexes, and Cu(I)-thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E] 0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced.
Journal of Electroanalytical Chemistry, 2001
The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV–vis spectroscopy, XPS and EDAX analysis, and structural information on copper–thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range −0.30≤E≤0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)–thiourea soluble complexes, and Cu(I)–thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E≥0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced.
Journal of Electroanalytical Chemistry, 2001
The electrochemical behaviour of copper anodes in aqueous thiourea (TU)-containing sulphuric acid was followed from open circuit potential measurements, voltammetry and rotating disk and ring-disk electrode data. The open circuit potential of copper is controlled by equilibria involving different Cu(I)-TU complex species. The thiourea electro-oxidation which yields formamidine disulphide and Cu(I)-TU complex species can be described as a process under intermediate kinetics taking place on a partially blocked copper anode. The degree of copper surface coverage and the type of predominant adsorbate depend on the concentration of thiourea and applied electric potential. Depending on the potential range adsorbates can be formed directly from either a strong TU-copper interaction or a relatively weaker formamidine disulphide interaction. The passivating layer can be related to the formation of polymer-like Cu(I)-TU layers and residues resulting both from thiourea and formamidine disulphide electro-oxidation. A previously proposed complex reaction pathway can explain the general behaviour of these systems, including adsorbate formation and the influence of the electrolyte solution constituents.
X-ray diffraction study of copper(I) thiourea complexes formed in sulfate-containing acid solutions
Acta Crystallographica Section B Structural Science, 2000
The formation of three different copper(I) thiourea complexes in sulfate-containing acid solutions was observed. The ratio between CuI and thiourea (tu) in these complexes depends on the amount of thiourea and copper sulfate in the solution. The crystal and molecular structure of a new complex, [Cu_2(tu)_6](SO_4)\cdotH_2O, was determined, and the formation and structures of [Cu_2(tu)_5](SO_4)\cdot3H_2O and [Cu_4(tu)_7](SO_4)_2\cdotH_2O were confirmed. The compound [Cu_2(tu)_6](SO_4)\cdotH_2O crystallizes in the P\overline 1 space group, with a = 11.079 (2), b = 11.262 (1), c = 12.195 (2) Å, \alpha = 64.84 (1), \beta = 76.12 (1), \gamma = 66.06 (1)°, and Z = 2. The Cu-thiourea complex is arranged as a CuI tetranuclear ion, [Cu_4(tu)_{12}]^{4+}, sited on a crystallographic inversion center. All copper ions are in a tetrahedral coordination with thiourea ligands and located at alternate sites on an eight-membered, crown-like ring.
Electrochemical properties of copper(I) halides and substituted thiourea complexes
2007
The complexes between copper(I) halides and N,N 0 -diphenylthiourea have been investigated by cyclic voltammetry to compare their structure and behaviour in solid state with those in solution. The halides under investigation include chloride, bromide, and iodide. Chloride and bromide complexes did not show the redox reaction, suggesting that they formed the strongest bond with the metal and hence the oxidation was inhibited. In contrast, iodide behaved differently because of the two peaks of halide and trihalide oxidations. One peak disappeared, leaving the other halide-oxidized peak shifted to a more positive voltage due to the bonding with the metal. In solution, all complexes of N,N 0 -diphenylthiourea were derived from the oxidation process and exhibited oxidation potentials shifted to positive values.
Electrodialysis of copper-thiourea solutions
Hydrometallurgy, 1993
Thiourea is used as a complexing agent for the treatment of precious metal ores and manufacturing and thiourea is sometimes present in aqueous solutions containing copper ions. The purpose of this work is to determine if electrodialysis can be used for the recovery of Cu 2 + ions from solutions containing thiourea. The solutions studied contained sodium and copper ions as well as thiourea. The transmembrane fluxes ofNa + and Cu 2÷ are measured under a constant current. For the transport of the two cations, the current efficiency is decreased when thiourea is present in the solution. This is due to the formation of Cu (I) thiourea complexes, which create several positively charged species as a product of thiourea oxidation and which remain irreversibly bound inside the membrane material.
Electrochemical sensor for thiourea focused on metallurgical applications of copper
Sensors and Actuators B: Chemical, 2016
A simple and reliable device is presented for the direct monitoring of thiourea in copper electrorefinery baths as a tool for reconditioning of industrial baths, and so reducing its environmental impact. For this purpose, a screen-printed graphite electrode is modified with silver nanoparticles (AgNPs) contained in a polyelectrolyte-surfactant matrix. The AgNPs are able to adsorb the thiourea, improving the sensitivity of the electrode toward this analyte, even in the presence of usual additives (Avitone ® and glue). The system allows the determination of thiourea in a range of 1-10 mg/L. A coupled electrochemical and IR analysis is proposed to evaluate the involved mechanism.