Ozonation:  A Unique Route To Prepare Nickel Oxyhydroxides. Synthesis Optimization and Reaction Mechanism Study

This paper details the reacting paths involved during the oxidation of αII-Ni(OH)2 and βII-Ni(OH)2 with ozone, which is compared to the oxidation process conducted in aqueous solution. The main advantage of the ozone method lies in the control of the reaction medium steps owing to the feasibility of operating in the presence or absence of alkaline cations. This enables the preparation of the pure βIII-NiOOH phase, well-known to be difficult to obtain in aqueous media without γIII-NiOOH traces. The reaction mechanisms for both oxidation processes were found to be similar, and to yield the same final products, except for αII-Ni(OH)2, where ozonation allowed the preparation of a new oxidized phase that was isolated and characterized by means of complementary techniques such as X-ray diffraction, chemical analysis, HRTEM, TGA, and FT-IR. A mechanism to account for the formation of this phase is proposed.