Enhanced ultrasound-assisted pore-adjustable spherical imma-Fe3O4 catalytic-activated piezoelectric Fenton reaction for PDE-5i degradation

The focus of this study was the ultrasound-assisted degradation of sildenafil by three-dimensional (3D) mesoporous Fe3O4 with large surface undulations. The influence of various factors, such as pH, H2O2 dosage, and ultrasonic (US) power, on sildenafil decomposition was examined. The maximum difference in the undulations of Fe3O4 was observed with a synthesis time of 8 h (40 nm). The optimal experimental conditions were 10 mmol H2O2, pH 3, and US intensity of 300 W, and the maximum kinetic constant (0.23903 min−1) was achieved under these experimental conditions. The 3D spherical Fe3O4 (8 h) catalyst almost completely removed 50 mg L−1 of sildenafil within 120 min, and AFM characterizations revealed that the Fe3O4 catalyst had a piezoelectric response of 33 pm/V. These data demonstrate that a piezoelectric catalyst with large surface undulations can substantially enhance the US cavitation effect. Free-radical experiments indicated that •OH radicals were the main active species during the process. Based on the quantitative structure–activity relationship results obtained under neutral conditions, the US–Fenton–piezoelectric process reduced the ecotoxicity and improved the biodegradability of sildenafil.