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

Ni x Co 1−x Fe 2 O 4 (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 CoFe 2 O 4 . Due to difference in the ionic radius of Ni 2+ and Fe 3+ for tetrahedral site and Co 2+ and Fe 3+ for octahedral site the changes are observed in the structural parameter like hopping length at tetrahedral (L A ) site and octahedral (L B ) and x-ray density. Ni 0.6 Co 0.4 Fe 2 O 4 shows lower charge transfer resistivity compared to other composition. UV-visible spectra of CoFe 2 O 4 , Ni 0.3 Co 0.7 Fe 2 O 4 , Ni 0.6 Co 0.4 Fe 2 O 4 and Ni 0.9 Co 0.1 Fe 2 O 4 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 Ni 0.6 Co 0.4 Fe 2 O 4 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 Ni 0.6 Co 0.4 Fe 2 O 4 > Ni 0.9 Co 0.1 Fe 2 O 4 > Ni 0.3 Co 0.7 Fe 2 O 4 > CoFe 2 O 4 . Superoxide, perhydroxy radical and hydroxyl free radicals are involved in the degradation of Alizarin Red S (ARS).