Enhanced Fenton-Photocatalytic Degradation of Rhodamine B over Cobalt Ferrite Nanoparticles Synthesized by a Polyvinylpyrrolidone-Assisted Grinding Method

A simple grinding method using polyvinylpyrrolidone (PVP) as a capping agent is introduced to synthesize CoFe₂O₄ nanoparticles. The effects of calcination temperature (ranging from 450 to 850 °C) on the structural, morphological, physical, and optical properties of the materials are investigated using various techniques, including thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), N₂ adsorption isotherm, ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), and vibrating sample magnetometry (VSM). The presence of PVP significantly suppresses the agglomeration of the materials, resulting in a nanocrystalline size of 18 nm for a sample calcined at 650 °C, which is approximately 38% smaller than that of the sample synthesized without PVP. Among the materials studied, the sample calcined at 650 °C exhibits unique properties, including optimal average pore size, specific surface area, and band gap energy, contributing to its superior photocatalytic degradation of rhodamine B via the Fenton reaction. Systematic experiments are performed to investigate the effects of pH, catalyst dosage, dye, and H₂O₂ concentrations and competitive anions on the rhodamine B degradation. Additionally, the Fenton photodegradation of RhB on CoFe₂O₄ is well-fitted to the first-order kinetic model. The redox pairs of Co(III)/Co(II) and Fe(III)/Fe(II) in the CoFe₂O₄ spinel structure might facilitate the formation of Fenton radicals, contributing to the decomposition of RhB through a proposed four-step mechanism. Notably, the material exhibits a strong magnetic response and maintains its excellent performance over five cycles, demonstrating the high potential for reusability as a photocatalyst.