Enhanced photocatalytic degradation of organic pollutants using cu-doped spinel ferrites synthesized via sol-gel auto-combustion: a study of structural, optical, and catalytic properties

CR dye, a toxic industrial pollutant discharged at 280,000 tons annually, poses severe environmental risks. In this study, we developed Cu-doped Sr₁₋₂Al₀.₄Fe₁.₆O₄ (x = 0.0, 0.4) spinel ferrites via sol-gel auto-combustion method as efficient photocatalysts for dye degradation. Cu-doping induced significant structural modifications: the crystallite size decreased from 28.011 to 20.438 nm, the lattice parameter contracted from 8.4679 to 8.3801 Å, and the BET surface area increased 3.7-fold (from 6.63 to 24.45 m²/g). The optical bandgap narrows from 2.6 to 2.3 eV, enhancing visible-light absorption. Under optimised conditions (pH 7, 30 °C, 10 mg catalyst, 10 ppm dye, 100 W visible light), Cu₀.₄Sr₀.₄Mn₀.₂Al₀.₄Fe₁.₆O₄ achieved 99.70% CR degradation in 100 min, compared to 52.45% for the undoped catalyst. Performance metrics showed a quantum yield of 2.77 × 10⁻⁶ molecules/photon and space-time yield of 1.39 × 10⁻⁷ molecules/photon. Hydroxyl radicals were identified as the primary reactive species in scavenger studies. The catalyst demonstrated versatility by degrading multiple dyes: Rhodamine B (84.23%), Alizarin Yellow (71.83%), and Methylene Blue (53.10%). The addition of H₂O₂ (6 mM) accelerated the complete degradation to 65 min. The catalyst maintained an efficiency of 91.34% after five cycles, confirming its stability. This Cu-doped spinel ferrite system presents a sustainable solution for the treatment of industrial wastewater. Graphical Abstract