Augmenting the catalytic activity of CoFe2O4 by substituting rare earth cations into the spinel structure

Abstract

The current research work evaluates enhancement in photo-Fenton activity of pristine CoFe₂O₄ by inserting a very small quantity of rare earth (RE) cations into its spinel structure. For this purpose, RE metal (Ce³⁺ and La³⁺) doped CoFe₂O₄ (having compositions CoLa_xFe_2−xO₄; x = 0.1, 0.2, 0.3, 0.4, 0.5 and CoCe_xFe_2−xO₄; x = 0.1, 0.2, 0.3) was synthesized by employing a sol–gel methodology. The samples were well characterized using diverse techniques (FTIR, powder XRD, HR-TEM, VSM, UV-DRS, BET surface area analyzer). The photo-Fenton reactions were performed using five probe molecules i.e. textile dyes (reactive black 5 and remazol brilliant yellow) and phenolic analogues (o-nitrophenol, m-nitrophenol and p-nitrophenol) using two inorganic oxidizing agents (hydrogen peroxide and potassium peroxymonosulphate). Interestingly, significant enhancement in photo-Fenton activity was noticed for RE metal (La/Ce) substituted samples in comparison with pristine parent CoFe₂O₄ irrespective of the nature of the inorganic oxidant used. The maximum photo-Fenton activity was observed for compositions CoCe_0.1Fe_1.9O₄ and CoLa_0.4Fe_1.6O₄. The enhancement in activity of x = 0.1 and x = 0.4 for Ce and La doped CoFe₂O₄ respectively was correlated to the octahedral site preference of RE metal ions, reduced band gap and enhanced surface area. This work announces the prominent role of RE metal ions in photo-Fenton activity enhancement. In addition, the magnetic nature of CoFe₂O₄ means that the RE metal (Ce³⁺ and La³⁺) doped CoFe₂O₄ could be efficiently recovered from reaction mixtures.