Enhancing dye degradation with Li–Ni ferrite: A sol-gel auto-combustion synthesis strategy with temperature tunable properties

In this study, ${Li}_{0.5-\frac{x}{2}}{Ni}_x{Fe}_{2.5-\frac{x}{2}}{O}_4$ (X = 0.6) ferrites were synthesized via the sol-gel method, with a detailed investigation into the effects of annealing temperatures (400, 500, 600, and 700 °C) on their properties. X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and Raman spectroscopy confirmed the formation of a cubic spinel structure in the synthesized ferrites. The comprehensive crystalline analysis is carried out using the Williamson-Hall plot and Nelson-Riley function plot. FTIR confirmed two characteristic absorption peaks for cubic spinel ferrite around 460 cm⁻¹ and 580 cm⁻¹. X-ray photoelectron spectroscopy (XPS) confirmed the chemical states of each element in the Li–Ni ferrite. UV–Vis diffuse reflectance spectroscopy (UV-DRS) revealed the bandgap energies of samples. The photocatalytic activity of Li–Ni ferrite for the degradation of rhodamine B, methylene blue, and methyl orange dyes was also studied, with samples annealed at 600 °C showing significant degradation efficiency. This high performance is attributed to enhanced crystallinity, favorable defect characteristics, and optimal optical properties. Overall, this work highlights Li–Ni ferrite as a highly effective photocatalyst for dye removal applications.