Photo-catalytic activity of highly efficient binary Mn–Fe nano composite oxides for degradation of cresol fast violet: phase formation and band gap study

Abstract

Binary Mn–Fe nano composite oxides as highly efficient photo-catalyst was prepared and applied for photo-catalytic degradation of cresol fast violet. The binary Mn–Fe nano composite oxides were prepared by precipitation pyrolysis technique using nitrate precursors with calcination temperature of 400 °C. Phase formation and band gap properties of nano-particles in the course of the preparation method were studied by FTIR, XRD, EDX, FESEM and DRS analyses for conversion of Mn–Fe nitrates to binary Mn–Fe oxides. The XRD data revealed a rhombohedral iron oxide (hematite) and tetragonal manganese oxide MnO₂ as nano composite without any impurity phases. The absorption peaks attained from 539 to 610 cm⁻¹ in FTIR spectra for manganese dioxide are corresponded to the characteristic stretching collision of oxygen–manganese–oxygen, which confirmed the existence of the tetragonal manganese oxide. The characteristic absorption bands at 539 and 473 cm⁻¹ are related to Fe–O stretching and bending vibration mode of α-Fe₂O₃ respectively. The broad band appeared at 473 cm⁻¹ is due to the presence of Fe–O–Mn linkage in the binary Mn–Fe nano composite oxide. FESEM results showed that the surface morphology of the nano composite was regular shape agglomeration of grain-like particles with rough surface morphology with an average size of 23 nm which is also comparable with the size obtained by XRD data analysis. The value of band gap for binary Mn–Fe nano composite oxide was 1.66 eV with a red shift compared with α-Fe₂O₃ (2.3 eV) and MnO₂ (2.41 eV) attributed to coupling of α-Fe₂O₃ with MnO₂. The coupling between α-Fe₂O₃ with MnO₂ with different band gaps to form heterojunctions in photocatalytic systems significantly enhanced the optical absorption of photocatalysts. The coupling between α-Fe₂O₃ with MnO₂ can also effectly reduces the recombination rate of the photogenerated charge carriers. The photocatalytic activity of nano-composite showed maximum degradation of 95% for degradation of cresol fast violet dye solution using the binary Mn–Fe nano composite oxide photocatalyst coated on glass.