Monovalent copper aqueous solutions

The last step is dominated by the metallic-copper cluster formation. We assume that in the initial process, all the accessible sulfur sites of PMeT are saturated. Then, in the absence of a stabilizing agent in aqueous solution, the monovalent copper ions undergo disproportionation to produce Cu2+ ions and metallic copper. Additional Cu2+ is then drained from the solution, resulting in an increase in the absolute copper content. 

This reaction was studied in the presence of acetonitrile, NH3 or as ligands to monovalent copper in aqueous solutions (30,151). Each ligand has a imique effect on the redox potential of the Cud) complex and stabilizes Cu(I) in a different way as was mentioned in Section 11. The addition of a ligand increases the Cud) concentration in the solution, but it also influences the reactivity of the Cud) as a catalyst (30,151). 

Copper cyanide complexes are usually present as monovalent (Cu(CN)2 ), divalent (Cu(CN)3 ), and trivalent (Cu(CN)4 ) species in aqueous solutions, as shown in Figure 7.4. Computations for copper cyanide speciation show that for ratios of total copper cyanide to total copper greater than 16, speciation at any given pH does not depend on the [CN]j/[Cu]x ratio. The solution pH, however, greatly affects the speciation of complexes (see Figure 7.4). The fraction of monovalent species decreases whereas the fraction of the divalent species increases as pH increases. Concentrations of trivalent species are negligible below pH 7.5. These results show the need to consider pH dependency of speciation in the adsorption isotherm expression. 

Copper acetate was used in Ref. 38 it was noted that if chloride was used instead of acetate, no deposition occurred, and this was attributed to adsorption of chloride on the substrate (Pt). The berzelianite phase with a small amount of umangite impurity was obtained. The composition and phase of the film could be altered by electrochemical cathodic polarization (in an aqueous K2SO4 solution). Initially, there occurred an increase in lattice parameters and decrease in x (Cu2-A Se). With continued polarization, a phase change occurred until eventually only orthorhombic Cui xSe was present in the film. The umangite phase also disappeared, and it was believed that this impurity phase catalyzed the phase transformation. The change in composition during cathodic polarization was attributed to reduction of zerovalent Se to Se, which was dissolved in the solution. Based on the study of Fohner and JeUinek [41] discussed earlier, this explanation can be interpreted as reduction of Sei ( monovalent Se) to Se (divalent Se). 

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