Robust iron-doped manganese oxide nanoparticles from facile fabrication to photo-catalytic degradation application of binary dyes mixture

Abstract

The manganese oxide (MnO₂ and iron-doped manganese oxide (Fe-MnO₂) nanoparticles (NPs) with reduced band gap (Eg) were fabricated through the co-precipitation process. They used to degrade Indigo Carmine (IC) and Rhodamine B (RB) binary mixture in an aqueous medium under solar light irradiation. From FT-IR, the twisting modes of the Mn-O bond and the stretching vibrations of the Fe-Mn-O₂ bond were confirmed from the peaks observed at 480 cm^-1,584 cm^-1,675 cm^-1, and 900 cm^-1, 1150 cm^-1, and 1200 cm^-1 respectively. The MnO₂ has an optical band gap of 3.2 eV, which was decreased to 3 eV in Fe-MnO₂. The zero charge (PZC) point was 8 for Fe-MnO₂ and 7 for MnO₂. The BET surface area for Fe-MnO2 was 398 m²/g, relatively higher than MnO2 particles, having a surface area of 384 m²/g. The average crystallite sizes calculated from Scherer formulae were 37 nm for MnO₂ and 31 nm for Fe-MnO₂ NPs. SEM confirmed the irregular morphology of the prepared particles. It was analyzed that agglomeration occurs in MnO₂ than the Fe-MnO₂. The maximum degradation of IC dye was 99%, and that of RB was 98% at the optimum conditions. The data were best fitted to second-order kinetics.

Keywords: Degradation; Indigo carmine; MnO(2); Photo-catalysis; Rhodamine B.