Ultrasound-assisted visible-light photo-Fenton degradation of tetracycline over surface-engineered Ag/MgFe2O4 heterointerfaces: mechanistic and DFT insights.

The integration of ultrasound with visible-light photo-Fenton catalysis provides an attractive route for accelerating the degradation of persistent antibiotic pollutants. In this work, pristine MgFe2O4 (MFO) together with surface-engineered Zr(3 wt%)/MFO, Co(3 wt%)/MFO, and Ag(3 wt%)/MFO photocatalysts were synthesized to investigate the influence of surface engineering on tetracycline (TCH) degradation under ultrasound-assisted visible-light (US/VL) photo-Fenton conditions. Structural, morphological, and surface analyses confirmed that the deposited metal species formed stable heterointerfaces while preserving the spinel MFO framework. Among the prepared photocatalysts, Ag(3 wt%)/MFO exhibited the highest activity, achieving 98.4 % TCH degradation within 120 min under the optimized reaction conditions. The enhanced performance originates from improved interfacial charge migration, efficient H2O2 activation, and accelerated Fe2+/Fe3+ redox cycling under the combined action of ultrasonic cavitation and VL irradiation, resulting in enhanced ROS generation. Radical quenching experiments identified •OH radicals as the dominant oxidative species, while •O2- radicals and photogenerated electrons contributed synergistically to the degradation process. The optimized photocatalyst maintained over 94 % degradation efficiency after four consecutive cycles, while post-reaction XRD and XPS analyses confirmed excellent structural and chemical stability. LC-MS analysis identified the degradation intermediates of TCH, while DFT calculations revealed the preferential ROS attack sites, supporting the proposed degradation mechanism. Overall, this work establishes surface-engineered Ag(3 wt%)/MFO as an efficient US/VL-photo-Fenton photocatalyst for sustainable wastewater remediation.