Synthesis of Manganese Oxides by Reduction of KMnO4with KBH4in Aqueous Solutions

✍ Scribed by C. Tsang; J. Kim; A. Manthiram

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 388 KB
• Volume: 137
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7656

✦ Synopsis

Reduction of KMnO 4 with KBH 4 in aqueous solutions has been investigated systematically at ambient temperatures as a function of reaction pH and the volume of borohydride. The products are characterized by X-ray diffraction, transmission electron microscopy, atomic absorption spectroscopy, redox titrations to determine the oxidation state of manganese, and thermogravimetric analysis. The reduction gives both binary MnO 2؊ and ternary K x Mn y O z oxides that are hydrated and nanocrystalline. The composition of the reduction products is influenced by the reaction pH as well as the volume of borohydride. While acidic conditions tend to stabilize products with predominantly Mn 4؉ due to a disproportionation of Mn 3؉ , nearly neutral conditions could access Mn 3؉ with +0.5 in MnO 2؊ . While no potassium-containing K x Mn y O z is obtained in highly acidic solutions with pH +1, the compound becomes accessible with increasing pH, and a maximum x+0.5 could be obtained in highly basic solutions with pH +11. The as-prepared samples lose most of the water below 200°C and tend to lose oxygen at higher temperatures.