Preparation, characterization and photocatalytic activity of nickel-substituted CoFe2O4: exploration of changes in the micro structural parameters and distribution of cations in the lattice

Abstract

NixCo1−x Fe2O4 (x = 0.0, 0.3, 0.6 and 0.9) samples were prepared by sol-gel combustion method and were characterized by various analytical techniques. The tetrahedral (A) and octahedral (B) radius permits one to calculate the edge length and bond length of M–O at A and B sites. Cation distribution is used to calculate the ionic radius of tetrahedral and octahedral sites and oxygen positional parameter. We investigated the effects of Ni+2 substitutions on structural and electrochemical properties of CoFe2O4. Due to difference in the ionic radius of Ni2+ and Fe3+ for tetrahedral site and Co2+ and Fe3+ for octahedral site the changes are observed in the structural parameter like hopping length at tetrahedral (LA) site and octahedral (LB) and x-ray density. Ni0.6Co0.4 Fe2O4 shows lower charge transfer resistivity compared to other composition. UV-visible spectra of CoFe2O4, Ni0.3Co0.7Fe2O4, Ni0.6Co 0.4Fe2O4 and Ni 0.9Co 0.1Fe2O4 shows wide absorption and the calculated band gap values were found to be 2.59, 2.24, 2.17 and 2.41 eV respectively. The continue absorption implies active d-d transitions involving transition metals present in the composite. The PL spectra show lesser recombination of photogenerated charge carriers for Ni0.6Co 0.4Fe2O4 catalyst compared to other catalysts. Lower intensity peak represents the lower recombination rate. The chemical environment and elemental binding states of Co, Ni, Fe and O were confirmed by XPS analysis. Photocatalytic activity follows in the decreasing order Ni0.6Co0.4Fe2O4 > Ni0.9Co0.1 Fe2O4 > Ni0.3Co0.7 Fe2O4 > CoFe2O4. Superoxide, perhydroxy radical and hydroxyl free radicals are involved in the degradation of Alizarin Red S (ARS).