Effect of Mg2+ ions on the formation of todorokite type manganese oxide octahedral molecular sieves

The readily available permanganate, KMnO4, was successfully utilized in the synthesis of manganese oxide octahedral molecular sieve (OMS-1) with the todorokite type structure. The magnesium concentration in the starting materials was systematically varied to study the synthetic chemistry of Mg-OMS-1. The techniques such as powder XRD, ICP, TGA, TPD, and redox titrations were all applied to characterize the as-synthesized Mg-OMS-1 samples. The correlation between the amount of magnesium in the starting materials and the properties of Mg-OMS-1 results in differences in (1) colors, (2) crystalline purity, and (3) thermal stabilities. Magnesium(II) ions are believed to be doped into the framework of the OMS-1 structure, but the major amount of Mg2+ mainly behaves as a template and is located in the tunnels of OMS-1. Two interesting Mg2+ concentration windows have been observed, one for the starting materials and another for the Mg2+ ions in the framework of Mg-OMS-1 which cover the magnesium concentration range where good quality Mg-OMS-1 can be formed.