Nickel-doped cobalt ferrite nanoparticles: efficient catalysts for the reduction of nitroaromatic compounds and photo-oxidative degradation of toxic dyes

This study deals with the exploration of Ni x Co 1− x Fe 2 O 4 ( x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrite nanoparticles as catalysts for reduction of 4-nitrophenol and photo-oxidative degradation of Rhodamine B. The ferrite samples with uniform size distribution were synthesized using the reverse micelle technique. The structural investigation was performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray and scanning tunneling microscopy. The spherical particles with ordered cubic spinel structure were found to have the crystallite size of 4-6 nm. Diffused UV-visible reflectance spectroscopy was employed to investigate the optical properties of the synthesized ferrite nanoparticles. The surface area calculated using BET method was found to be highest for Co 0.4 Ni 0.6 Fe 2 O 4 (154.02 m 2 g −1 ). Co 0.4 Ni 0.6 Fe 2 O 4 showed the best catalytic activity for reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH 4 as reducing agent, whereas CoFe 2 O 4 was found to be catalytically inactive. The reduction reaction followed pseudo-first order kinetics. The effect of varying the concentration of catalyst and NaBH 4 on the reaction rates was also scrutinized. The photo-oxidative degradation of Rhodamine B, enhanced oxidation efficacy was observed with the introduction of Ni 2+ in to the cobalt ferrite lattice due to octahedral site preference of Ni 2+ . Almost 99% degradation was achieved in 20 min using NiFe 2 O 4 nanoparticles as catalyst. Catalytic efficiency enhanced tremendously with the introduction of Ni 2+ ions into the cobalt ferrite lattice.