| Abstract
| - In the present work we studied, for the first time, the kinetics of adsorption of the Co(H2O)62+ species on the“electrolytic solution/γ-Al2O3” interface at pH = 7 and 25 °C for a very broad range of Co(II) surfaceconcentrations ranged from 0.03 to 6 theoretical Co(H2O)62+ surface layers. Moreover, we studied the surfacedissolution of γ-alumina in the presence of the Co(H2O)62+ ions in the impregnating solution, the contributionof the Co(II) desorption on the whole deposition process and the deposition isotherm. It was found that underthe conditions where the deposition has taken place, the dissolution of the γ-alumina surface is negligibleeven in the presence of the Co(H2O)62+ species in the impregnating solution. It was, moreover, inferred thatthe Co(II) desorption does not participate significantly to the whole deposition process. It was found that thedeposition kinetics may be described by the following kinetic expression rCo,bulk = k‘CCo,bulk2, which relatesthe rate of disappearance of the Co(H2O)62+ ions from the impregnating solution, rCo,bulk, with their concentrationCCo,bulk. This kinetic expression may be derived assuming the following deposition scheme: nS + 2[Co(H2O)62+] → Sn − [Co(H2O)x,x<62+]2, where S represents the surface reception sites. The above expressionsindicated that two Co(H2O)62+ ions are involved, from the side of the interface, in the reaction with thereception sites. It seems probable that the deposition step involves the simultaneous adsorption and dimerizationof the two interfacial Co(H2O)62+ ions through (hydr)oxobridges. On the other hand, the sigmoidal form ofthe deposition isotherm and the dependence of the apparent rate constant, k‘, on the interfacial Co(II)concentration suggested that the already deposited Co(II) species may be involved in the reception sites, S,promoting the adsorption and resulting to the formation of multinuclear complexes and Co(II) surfaceprecipitates. Finally, reasonable interface potential values for oxides were determined for the first time usingkinetic results.
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