Synthesis, characterization of Mg/Mn substituted Ni-Zn ferrites and mechanism of their visible light photo catalysis of Methylene Blue and Rhodamine B dyes under magnetic influence

Abstract

Rare earth doped spinel ferrites belonging to the series Ni0.6Zn0.2Me0.2GdxFe2-xO4 (where Me = Mg/Mn, x = 0/0.06) were synthesized by sol-gel method. The characterizations of the prepared samples were performed using X-rayDiffraction (XRD), High Resolution Transmission Electron (HRTEM) Microscopy, Vibrating Sample Magnetometry (VSM), X-ray Photoelectron Spectroscopy (XPS) and Open aperture z-scan technique. The XRD patterns confirm the crystallization of the ferrites in cubic form with spinel structure. The average crystallite size calculated using Debye-Scherrer's equation is in 10-20 nm range. The HRTEM images reveal the formation of spherically shaped agglomerated nanoparticles. The magnetic parameters such as remanence magnetization (Mr), coercivity (Hc) and saturation magnetization (Ms) were obtained from the hysteresis curves. The samples show better optical limiting parameters than reported which make them promising materials for non-linear applications requiring low limiting thresholds. Owing to their low band gaps ferrites can be efficiently used for the photo catalysis of organic dyes with visible solar energy which constitutes a major portion of sunlight. Ferrites have an added advantage by virtue of their spinel lattice which makes available extra catalytic sites. In the present work, the photocatalytic activity under visible sunlight irradiation was explored from the degradation of Methylene Blue (MB) and Rhodamine B (RhB) dyes. Higher photocatalytic efficiency was exhibited by magnesium containing samples. Near total decolouration of dye solution subjected to magnetic separation has not been reported before. The improvement in photocatalytic degradation efficiency is due to the adsorption followed by effective separation and prevention of photo generated electron-hole pair recombination for a longer period by these ferrites. To further aid the degradation, H2O2 was added as precursor to the reactive mixture which increases the formation of hydroxyl radical (OH•).