Title

A Facile One-Step Template-Free Synthesis of Uniform Hollow Microstructures of Non-doped and Iron-doped Cryptomelane-Type Manganese Oxide K-OMS-2

Date of Completion

January 2011

Keywords

Chemistry, Inorganic|Engineering, Materials Science

Degree

Ph.D.

Abstract

Hierarchical hollow microstructures of non-doped and iron-doped cryptomelane-type manganese oxide were produced in a template-free one-step process based on the fine-tuning of the oxidation rate of manganese species during the synthesis. The tuning of the reaction rate brought about by a mixture of the oxidants oxone and potassium nitrate becomes apparent from the gradual physical changes taking place in the reaction medium at early times of the synthesis. The successful synthesis of the hollow uniform structures could be performed in the ranges 120-160 °C and 8.2 -10.7 for temperature and mass ratio oxone to potassium nitrate, respectively. Independent of presence of the doping metal, all of the complex microstructures showed the same high order pattern for the array of long nanofibers in the case of non-doped materials and nanoneedles in the case of the doped materials. These nanofibers and nanoneedles displayed a crystal growth pointing outward from the empty cavities. A mechanism based on the secondary nucleation of the cryptomelane phase on the surface of an amorphous precursor and the growth of the nanoscale particles by processes such as dissolution-crystallization and lateral attachment of the primary nanocrystalline fibers and nanoneedles is proposed to explain the formation of the hollow structures. ^