A sol-gel fabrication, characterization, and boosted photocatalytic activity of a zinc-substituted nickel ferrite: RSM optimization study

• Efficient easy sol-gel synthesis of Zn 0.75 Ni 0.25 Fe 2 O 4 . • Boosted photocatalytic activity of Zn 0.75 Ni 0.25 Fe 2 O 4 concerning the individual ferrites. • A red shift in Eg of the heterostructure system concerning zinc ferrite . In the current project, to degrade metronidazole aqueous solution, NiFe2O4 and ZnFe 2 O 4 nanophotocatalysts have been used individually and in combination. The sol-gel method was used for the synthesis of single and combined photocatalysts. To identify them, XRD, DRS, EDX, SEM, VSM, FT-IR and X-ray mapping methods were used. The Scherrer and Williamson-Hall models were used to calculate crystallite size. The values for the Scherrer formula are 20.5, 25.2 and 14.8 nm for zinc ferrite, nickel ferrite and zinc-substituted nickel ferrite, respectively, and 27.3, 26.5 and 20.4 nm by the Williamson-Hall formula. Band gap energies obtained from DRS are 1.59, 1.39 and 1.79 eV for Zn 0.75 Ni 0.25 Fe 2 O 4 , NiFe 2 O 4 and ZnFe 2 O 4, respectively. The proposed mechanism, due to the DRS result, is a p-n junction. EDX results showed that the distribution of components is homogeneous, also confirming the mole ratio of 1:3 for Zn: Ni in Zn x Ni 1-x Fe 2 O 4 . VSM results confirm that all of the photocatalysts have magnetic properties. The magnetic properties, crystallite size, and lattice parameters were systematically analyzed, revealing that Zn substitution reduces saturation magnetization while influencing microstructural features. Among the photocatalysts tested, Zn 0.75 Ni 0.25 Fe 2 O 4 showed the highest MZ degradation efficiency, attributed to enhanced e − /h + separation. An acceptable value of R 2 (0.9816) for the quadratic model indicates good regression for the plot of predicted and experimental data. The highest degradation rate of metronidazole solution (86.4%) was achieved under the following conditions: irradiation time: 70 min, pH: 5, metronidazole concentration: 5 mg/L, and dose of catalyst: 0.8 g/L.