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

• LaMxFe1−xO4 (M = Cr3+, Cu2+; x = 0.0–0.5) prepared by sol–gel auto-combustion method.
• Ferrites had same symmetry as LaFeO3.
• Ferrites employed for catalytic decomposition of hydrogen peroxide solution.
• Cu2+ substituted ferrites exhibit much higher catalytic activity than pure ferrites.
• Cr3+ ions have little effect on catalytic activity of lanthanum ferrites.

Nano-crystalline lanthanum ferrites substituted by chromium and copper having formula LaMxFe1−xO3 (M = Cr, Cu; 0.0 ⩽ x ⩽ 0.5) were synthesized using sol–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 LaFeO3. The average crystallite size was calculated to be ∼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 LaCu0.5Fe0.5O3 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.

Concentration vs time graph for decomposition of hydrogen peroxide catalysed by LaCuxFe1−xO3 annealed at 400 °C.Figure optionsDownload as PowerPoint slide