Probing the spectroscopic effects of Indium (In3+)-doped Ni-Zn spinel ferrites and visible-light driven methylene blue degradation

This study examines effects of In 3+ on the thermal, structural, cationic, Raman, morphological, and optical properties of sol–gel auto-combusted Ni 0.65 Zn 0.35 Fe 2-x In ₓ O 4 (x = 0.00, 0.08, 0.16, and 0.24) nanoparticles. X-ray diffraction (XRD) confirmed the formation of single-phase cubic spinel structure, with an enhanced lattice parameter attributed to the larger ionic radius of In 3+ . In the cation distribution derived from the XRD data, at lower concentrations In 3+ primarily occupied tetrahedral sites, whereas at higher concentrations (x ≥ 0.16), it distributed over both tetrahedral and octahedral sites. Raman spectra revealed consistent vibrational modes that remained intact even with In 3+ doping. Field-emission scanning electron microscopy (FE-SEM) demonstrated spherical grains with few agglomerations, whereas transmission electron microscopy (TEM) indicated a decrease in the average particle size from 25.4 nm to 17.9 nm with In 3+ doping. The selected area electron diffraction (SAED) pattern validated the polycrystalline nature by the presence of concentric diffraction rings corresponding to the allowed crystal planes of the cubic structure. X-ray photoelectron spectroscopy (XPS) provided the oxidation states and changes in the chemical environment of the elements in the composition. Moreover, diffuse reflectance spectroscopy (DRS) revealed an enhanced optical band gap with In 3+ varying in the range of 2.23–2.56 eV. Additionally, the photoluminescence (PL) spectra exhibited a wide emission band suggesting the presence of multiple sub-bands, indicating numerous energy levels. The photocatalytic degradation of four dyes, namely, congo red, rhodamine B, methylene blue, and crystal violet, was studied under visible light. The highest efficiency (72.3%) for methylene blue degradation over 180 min was shown by the 10-mg catalyst dosage of sample x = 0.16.