Thermal, Structural, and Morphological Analysis of ZnFe2O4 Embedded and Non-Embedded in a SiO2 Matrix for Magnetic and Photocatalytic Applications

This study compares the structural, morphological, magnetic, and photocatalytic properties of a pure SiO2 matrix, a ZnFe2O4-doped SiO2 nanocomposite (both synthesized via the sol-gel method), and bulk ZnFe2O4 produced by thermal decomposition. Thermogravimetric analysis (TGA) reveals that metal oxalates form below 200 °C and decompose into metal oxides, which subsequently form ferrite. Fourier-transform infrared (FTIR) spectroscopy confirms the embedding of both undoped and ZnFe2O4-doped nanoparticles into the SiO2 matrix at all investigated annealing temperatures. X-ray diffraction (XRD) consistently reveals the formation of crystalline ZnFe2O4, with the crystallite size increasing from 48 to 93 nm upon annealing. Atomic force microscopy (AFM) shows spherical ferrite nanoparticles surrounded by an amorphous layer, with particle growth observed at higher temperatures. Structural parameters derived from XRD (e.g., crystallite size, density, porosity, lattice constant, unit cell volume) and AFM (e.g., particle size, coating thickness) as well as magnetic parameters (saturation magnetization, remanence, anisotropy, coercivity) demonstrate clear dependence on both dopant presence and annealing temperature. Magnetic measurements reveal enhanced properties with increasing ferrite content and heat treatment, with a transition from superparamagnetic behavior at 700 °C to ferrimagnetic behavior above 1000 °C. Scavenger experiments confirmed the involvement of holes, hydroxyl radicals, and superoxide radicals in the photocatalytic process. The photocatalytic efficiency, as evaluated by the Rhodamine B degradation under visible light, highlights the promising potential of the obtained nanocomposite for advanced environmental and technological applications.