ESCA and Vibrational Spectroscopy of Alkali Cation Exchanged Manganic Acids with the 2X2 type Tunnel Structure Synthesized via Different Chemical Routes

摘要

Manganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of 'dioxide' is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H~+ for alkali cations incorporated in 'hydrous manganese dioxides'. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO_4 and MnSO_4, and thermal decomposition of (CH_3)_3COK and MnCO_3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.