The impact of Cd substitution on the microstructural, vibrational magnetic, optical and efficient photocatalytic properties of spinel materials for dye degradation

\(\begin{gathered} Ni_{0.7 - x} Cd_{0.3 + x} Cr_{2} O_{4} \left( {x = 0,\,0.4} \right) \hfill \\ \hfill \\ \end{gathered}\) spinel chromites were successfully synthesized via the sol–gel method. Scanning Electron Microscopy (SEM) revealed the particle size and morphology, while Fourier Transform Infrared (FTIR) spectroscopy confirmed the spinel structure through characteristic absorption bands at ~ 568 cm⁻¹ (x = 0) and ~ 618 cm⁻¹ (x = 0.4). Magnetic measurements at 300 K reveal ed paramagnetic behavior for both samples, with temperature-dependent magnetization showing antiferromagnetic–paramagnetic transitions at Neel temperatures (T_N) of 52 K (x = 0) and 37 K (x = 0.4). The decrease in T_N with Cd substitution is attributed to the dilution of magnetic interactions. Optical analysis indicated that both the band gap energy (E_g) and Urbach energy (E_u) decreased significantly with increasing Cd content. Photocatalytic activity, assessed through the degradation of methylene blue, was notably enhanced in the Cd-rich sample, likely due to improved charge carrier separation. These results demonstrate that Cd substitution effectively tunes the structural, magnetic, optical, and photocatalytic properties of Ni–Cd–Cr spinel chromites, underscoring their potential for environmental remediation applications.