**3.1. Solutions**

Both metal ions and chalcogenides solutions for the process are prepared with analytical reagent grade without further purification. Buffer solutions are prepared with double-distilled water and analytical reagent-grade acid and bases. Commonly, a buffer of HClO4 (65%) and NH4 OH (33%) is used to freshly prepare solutions of the metal and chalcogenides ions at very small concentration (typically 0.5 mM).
