he silica sols were prepared by the acid-catalyzed hydrolysis and condensation process. TEOS and MTES were used as the silica precursors mixed with ethanol (EtOH), nitric acid (HNO3), cobalt nitrate, as metal salt, and distilled water. To avoid the partial hydrolysis while mixing H2O/HNO3 mixture with TEOS/EtOH mixture, the latter was placed in an ice bath and then H2O/HNO3 mixture was added drop wise under continuous stirring [16]. The different molar compositions investigated in this work as well as the sample notations are listed in Table 1. For the cobalt-doping within the hybrid silica matrix, a solution of cobalt nitrate in eth- anol was prepared. Ethanol was chosen as the solvent for the salt solution because it was the same solvent used in the sols prepara- tion. Moreover, the nitrate salt was used because it is compatible with the silica sol which was catalyzed by nitric acid [28].