Sorption of Iodide on Cuprite (Cu₂O)

The interactions of iodide ions with cuprite (Cu2O) surfaces were studied by combining batch experiments and surface analyses. The evolution of iodide uptake with pH was investigated. The thermodynamical calculations and surface analyses (X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and electrochemistry) were used to show that two different pH-dependent mechanisms are responsible for the accumulation of the iodide species on Cu2O. At pH values lower than 6.5, the precipitation of CuI occurs on the cuprite surface, while in more alkaline medium, the iodide adsorption takes place by substituting the surface hydroxyl groups of Cu2O. The sorption processes were not affected by a 1000-fold excess of chloride ions, but they were limited to the potential range corresponding to the stability domain of Cu2O (i.e., between −10 and +190 mV/ENH at pH 8); thus no accumulation was observed either on metallic copper or on CuO.

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