Structural investigation of cobalt-doped silica derived from sol-gel synthesis

This work investigates the structural properties of cobalt doped silica samples prepared by sol-gel synthesis. Air calcination led to the formation of Co3O4 particles as evidenced by XRD and FTIR tests, although these features were no longer apparent for hydrogen-reduced samples. This behavior suggests the formation of metallic Co and CoO in the reduced samples. The variation of the cobalt content embedded in the silica matrix resulted in a change in texture of the prepared materials from microporous to mesoporous. This was attributed to the agglomeration of particles as observed in TEM micrographs, which led to larger particles and pores. The latter was associated with the formation of hysteresis loop in the nitrogen adsorption isotherms as a function of the [Co/(Si + Co)] molar ratio. This effect was more remarkable for reduced samples, leading to a further broadening of the hysteresis loop that stemmed from the reduction or loss of oxygen from cobalt oxide particles.