ULTRAVIOLET-VISIBLE-NEAR-INFRARED AND EXAFS STUDY OF CO-II COORDINATION CHEMISTRY IN POST-DOPED SILICA SOL-GEL GLASSES

UV-VIS-NIR and EXAFS spectroscopies have been used to probe the coordi nation chemistry of cobalt(II) in post-doped silica sol-gel glasses. M aterials doped with cobalt(II) chloride, nitrate and acetate were prep ared and the cobalt(II) coordination chemistry was studied in relation to post-doping treatments such as dehydration, rehydration and densif ication. Both octahedral and tetrahedral coordination geometries were observed for the hydrated and dehydrated get glasses with pronounced a nion coordination present in all dehydrated samples. The presence of s alts in the gel-glass pore structure provided additional absorbing cen tres for water. The extent of associated water adsorption (hydrogen bo nded to silanol groups and hydrogen bonded to other water molecules) i n the pores varied in the order nitrate > chloride > acetate. When the sample was sintered cobalt was incorporated in the glass framework an d anions and water were lost.