Dyes, being potential pollutants, need alarming attention for their degradation from wastewater. Advanced oxidation processes (AOPs) are among the most effective methodology for the degradation of pollutants. In the present study, the heterogeneous photo-Fenton catalysts (ZnFe₂O₄ and graphene oxide based ZnFe₂O₄ composite) were prepared and used to study the degradation of synzol red reactive dye. The prepared catalysts were well characterized by using SEM, FTIR and XRD analysis. The effect of various parameters like pH, catalysts dosage, H₂O₂ dosage, effect of dye concentration and irradiation time during heterogeneous photo-Fenton processes was studied. The results showed 57% and 94% degradation of dye under optimized conditions (e.g. pH = 3, Catalysts dose = 75 mg l⁻¹ for ZnFe₂O₄ and 50 mg l⁻¹ for GO- ZnFe₂O₄, H₂O₂ dose = 27 mM and irradiation time of 60 min) was observed for ZnFe₂O₄ and GO-ZnFe₂O₄, respectively. A comparison of degradation potential of catalysts using various light sources like UV-254 nm, ambient solar light and white LED, was studied. The current findings support the application of solar and LED light for the degradation of organic pollutants in wastewater. The stability and reusability of these catalysts for the degradation of the dye were also studied. The GO- ZnFe₂O₄ composite showed negligible iron leaching and no considerable reduction in degradation efficiency upto six consecutive cycles of reusability. It has been found that the composite (GO–ZnFe₂O₄) showed enhanced degradation of dye as compared to ZnFe₂O₄.

Pesticides are one of the main organic pollutants as they are highly toxic and extensively used worldwide. The reclamation of wastewater containing pesticides is of utmost importance. For this purpose, GO-doped metal ferrites (GO-Fe₃O₄ and GO-CoFe₂O₄) were prepared and characterized using scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopic techniques. Photocatalytic potentials of catalysts were investigated against acetamiprid’s degradation. A detailed review of the parametric study revealed that efficiency of overall Fenton’s process relies on the combined effects of contributing factors, i.e., pH, initial oxidant concentration, catalyst dose, contact time, and acetamiprid load. ~97 and ~90% degradation of the acetamiprid was achieved by GO-CoFe₂O₄ and GO-Fe₃O₄, respectively during the first hour under UV radiations at optimized reaction conditions. At optimized conditions (i.e., pH:3, [H₂O₂]: 14.5 mM (for Fe₃O₄, GO-Fe₃O_4, and GO-CoFe₂O₄) and 21.75 mM (for CoFe₂O₄), catalysts: 100 mgL⁻¹, time: 60min) the catalysts exhibited excellent performance, with high degradation rate, magnetic power, easy recovery at the end, and efficient reusability (up to 5 cycles without any considerable loss in catalytic activity). A high magnetic character offers its easy separation from aqueous systems using an external magnet. Moreover, the combined effects of experimental variables were assessed simultaneously and justified using response surface methodology (RSM).