Low temperature synthesis of Co2SiO4/SiO2 nanocomposite using a modified sol-gel method

The paper presents a study on the preparation of Co2SiO4/SiO2 nanocomposites by a new modified sol-gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC2H5)(4)), cobalt nitrate Co(NO3)(2)center dot 6H(2)O and some diols: ethylene glycol (C2H6O2), 1,2propanediol (C3H8O2) and 1,3propanediol (C3H8O2), for a final composition: 30% CoO/70% SiO2. During the heating of the gels at 140 A degrees C, a redox reaction takes place between NO3 (-) ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250-300 A degrees C to the corresponding oxides: CoO and/or Co3O4 inside the matrices pores. When CoO results, it reacts with SiO2 at low temperature leading to Co2SiO4, which crystallizes at 700 A degrees C. XRD patterns of the samples annealed at temperatures lower than 700 A degrees C were characteristic to amorphous phases. The samples annealed at temperatures a parts per thousand yen700 A degrees C, contain Co2SiO4 (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co2SiO4 nanoparticles are homogenously dispersed inside the silica matrix.