Effect of Mg2+ Ions on the Formation of Todorokite Type Manganese Oxide Octahedral Molecular Sieves

The readily available permanganate, KMnO 4, 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 Mg 2+ mainly behaves as a template and is located in the tunnels of OMS-1. Two interesting Mg 2+ concentration windows have been observed, one for the starting materials and another for the Mg 2+ ions in the framework of Mg−OMS-1 which cover the magnesium concentration range where good quality Mg−OMS-1 can be formed.