1. Chemistry Department, Faculty of Science, Alexandria University, P. O. Box 426, Ibrahimia, 21321 Alexandria, Egypt, Fax: +2‐03‐3911794
2. Departament de Química Inorgànica and Institut de Nanociència i Nanotecnologia de la Universitat de Barcelona (UN2UB), Martí I Franqués 1–11, 08028 Barcelona, Spain, Fax: +34‐934907725
3. Environmental Inorganic Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden, Fax: +46‐31‐7722853