Cobalt-Doped Silica Organic-Inorganic Materials by Sol-Gel Method: Preparation and Thermal Stability Calcined under N₂ Atmosphere

Abstract

Cobalt-doped silica organic-inorganic (Co/SiO₂) materials were prepared by sol-gel technique using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as silicon precursors and Co(NO₃)₂·6H₂O as cobalt source. The influence of calcination temperature on the microstructure of Co/SiO₂ material under N₂ atmosphere was discussed by X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectrum (EDS) and thermogravimetric-differential thermogravimetric (TG-DTG) measurements. The results showed that, when calcined at N₂ atmosphere, the Co element in the Co/SiO₂ material exists not only as the Si-O-Co bond, but also the crystals containing the cobalt element. In the calcing process of 25 ∼ 800 °C, the crystals containing the cobalt element have successively undergone four phase transitions from Co(NO₃)₂·6H₂O to Co₃O₄, CoO and elemental Co⁰. The Si-O-Co bonds were formed in the calcined Co/SiO₂ materials. The water contact angle on the Co/SiO₂ film surface achieved the maximum value of 95.6° when the calcination temperature is at 400 °C. In order to keep the hydrophobicity of Co/SiO₂ membrane materials for gas separation, the optimal calcination temperature should be 350 ∼ 400 °C. The Co/SiO₂ membrane material calcined at 400 °C has a larger specific surface area, pore volume and mean pore diameter than the SiO₂ sample.

Keywords:

• Co-doped SiO₂ materials
• sol-gel method
• hydrophobicity
• thermal stability

Additional information

Funding

This work was supported by the Scientific Research Project of Shaanxi Education Department, China [No.19JC017], the Xi’an Municipal Science and Technology Project, China [No. 2020KJRC0025] and the Scientific Research Project of Shaanxi province of China [2020SF-421 and 2021GY-147].