In this research, Mg0.5Ni0.5AlxFe2-xO4 (x = 0.5, 1, 1.5) spinel ferrites were synthesized by facile sol-gel technique. The effects of the aluminum ion as a dopant on structural, morphological, optical, magnetic properties, and photocatalytic activity of spinel ferrites have been investigated using various analytical techniques. The XRD results approve the formation of a single-phase cubic spinel structure. It is also observed that the crystallite size decreases as Al3+ concentration increases. The FESEM and TEM analyses indicate a nanosized particle morphology. According to the VSM results, the saturation magnetization (Ms) decreases by the increase of Al content. Optical band gap energy studies of samples express that Eg value increases from 2.55 to 2.67 eV by increasing Al3+ dopant, which is confirmed by UV–vis DRS. The photocatalytic activity of the catalysts was evaluated for the degradation of DB129 as a model reaction under visible light irradiation. Based on our results, there is a direct correlation between photocatalytic activity and the amount of Al. Hence, the catalyst with x = 1.5 illustrates better degradation than the catalyst with x = 1 and 0.5. The catalyst with x = 1.5 is also capable to degrade the direct blue 129 up to 94%.
