Synthesis of Non-Al-Containing Hydrotalcite-like Compound Mg0.3CoII0.6CoIII0.2(OH)2(NO3)0.2·H2O

Abstract

Hydrotalcite-like compound (HTlc) of Mg0.3CoII0.6CoIII0.2(OH)2(NO3)0.2·H2O has been synthesized for the first-time by coprecipitation in an ammoniacal solution and hydrothermal treatments under various O2:N2 atmospheres. Using elemental analysis and redox titration, it is found that about 23% of the original Co2+ is oxidized to Co3+, resulting in formation of HTl structure. Related to the Co3+ content, intercalation of NO3- anion is observed. The X-ray diffraction pattern shows a conversion from brucite-like to HTl structures with increase of O2 partial pressure. Using different drying schemes (25 and 60 °C) and differential scanning calorimetry analysis, it is found that the thermal stability of the HTlcs is proportional to the Mg content. Higher specific surface areas are observed for decomposed products with low Co/Mg ratio. A trace amount of Co3O4 is also detected by FTIR for samples synthesized under high O2 partial pressures, which can be attributed to a deeper oxidation of Co2+. Thermodynamic considerations are also given to the redox reactions in both aqueous and solid phases.