Chromium and copper substituted lanthanum nano-ferrites: Their synthesis, characterization and application studies

Nano-crystalline lanthanum ferrites substituted by chromium and copper having formula LaM Fe1-xO3 (M = Cr, Cu; 0.0 <= x <= 0.5) were synthesized using sal-gel auto-combustion method. The formation of ferrite particles was confirmed using Fourier Transform Infra-Red (FT-IR) spectra and powder X-ray Diffraction (XRD) techniques. The entire ferrite compositions were found to be pure phased with same symmetry as LaFe03. The average crystallite size was calculated to be similar to 60 nm. The ferrite compositions were observed to behave as semi-conductors, as their resistivity decreased with increasing temperature. These ferrite compositions were employed as catalysts in the decomposition of hydrogen peroxide solution (0.17 M). Pure LaFeO3 was found to have a very low catalytic activity towards the decomposition of hydrogen peroxide solution, while presence of copper in the lanthanum ferrite lattice was found to significantly enhance its catalytic activity. The rate constant in case of reactions catalysed by LaCuO5Fe0.3O3 was nearly 25 times larger than that obtained from reactions catalysed by pure LaFeO3. However, chromium substitution was not found to influence the catalytic activity of lanthanum ferrites as chromium substituted lanthanum ferrites exhibited very low catalytic activity. This was explained on the basis of relative stability of oxidation states of the substituent ions and the presence of defects in the crystal lattice. (C) 2014 Elsevier B.V. All rights reserved.