Enhanced Fenton-Photocatalytic\nDegradation of Rhodamine\nB over Cobalt Ferrite Nanoparticles Synthesized by a Polyvinylpyrrolidone-Assisted\nGrinding Method

A simple grinding method using polyvinylpyrrolidone (PVP)\nas a\ncapping agent is introduced to synthesize CoFe<sub>2</sub>O<sub>4</sub> nanoparticles. The effects of calcination temperature (ranging from\n450 to 850 °C) on the structural, morphological, physical, and\noptical properties of the materials are investigated using various\ntechniques, including thermogravimetric analysis/differential scanning\ncalorimetry (TGA/DSC), powder X-ray diffraction (PXRD), transmission\nelectron microscopy (TEM), N<sub>2</sub> adsorption isotherm, ultraviolet–visible\ndiffuse reflectance spectroscopy (UV–vis DRS), and vibrating\nsample magnetometry (VSM). The presence of PVP significantly suppresses\nthe agglomeration of the materials, resulting in a nanocrystalline\nsize of 18 nm for a sample calcined at 650 °C, which is approximately\n38% smaller than that of the sample synthesized without PVP. Among\nthe materials studied, the sample calcined at 650 °C exhibits\nunique properties, including optimal average pore size, specific surface\narea, and band gap energy, contributing to its superior photocatalytic\ndegradation of rhodamine B <i>via</i> the Fenton reaction.\nSystematic experiments are performed to investigate the effects of\npH, catalyst dosage, dye, and H<sub>2</sub>O<sub>2</sub> concentrations\nand competitive anions on the rhodamine B degradation. Additionally,\nthe Fenton photodegradation of RhB on CoFe<sub>2</sub>O<sub>4</sub> is well-fitted to the first-order kinetic model. The redox pairs\nof Co(III)/Co(II) and Fe(III)/Fe(II) in the CoFe<sub>2</sub>O<sub>4</sub> spinel structure might facilitate the formation of Fenton\nradicals, contributing to the decomposition of RhB through a proposed\nfour-step mechanism. Notably, the material exhibits a strong magnetic\nresponse and maintains its excellent performance over five cycles,\ndemonstrating the high potential for reusability as a photocatalyst.