Redox-driven formation of hausmannite-type manganese oxide and its catalytic performance

Abstract

Various manganese oxides have been reported to be an active catalyst for degradation of a dye. The synthetic manganese oxides can be conducted by several methods with the products having the different physicochemical properties and structures. This research focused on the synthesis of  hausmanite-type manganese oxide (Mn₂O₃)  by hydrothermal method with different mole  ratio  of  KMnO₄/glucose (3:1 and 2:3) and its application as a Fenton catalyst   for the degradation of methylene blue (MB). The as-synthesized manganese oxides were then characterized  by XRD for their structure and crystallinity and FTIR and Raman spectroscopy for the lattice vibrations. The average oxide state (AOS) of manganese in the as-synthesized manganese oxide was determined by the back titration method. The XRD results indicated  the presence of mixed phases with hausmanite  phase as major component and  cryptomelane and birnessite phases as minor ones. FTIR spectroscopy results showed the presence of O-Mn vibrations at wavelengths of 468 cm^-1, 487cm^-1, and 726 cm^-1. In addition, Raman spectroscopy results clearly showed the  specific vibrations of hausmanite at 655 cm^-1 and 653 cm^-1, respectively. The low value of  Mn AOS was obtained when the oxide was prepared in low ratio KMnO4/glucose and short reaction time. The as-synthesized hausmanite was  tested  as the Fenton catalyt for the degradation of MB.  The as-synthesized hausmanite synthesized with different mole rasio and reaction time showed similar catalytic activity for the degradation of MB with the highest MB degradation of 90.76%