Intensified photo-decontamination of tetracycline antibiotic by S-scheme spinel manganese ferrite-grafted ZIF-8 heterojunction photocatalyst: Mechanism conception, degradation pathway and DFT studies

The enhancing outbreaks of refractory pharmaceutical compounds in aquatic bodies and subsequent adverse influences on the ecosystem have resulted in great environmental aggravation for living creatures throughout the world. In response to this issue, constructing a step-scheme (S-scheme) for pharmaceuticals elimination is of great importance. In this contribution, a robust MnFe₂O₄/ZIF-8 S-scheme heterojunction was constructed via an environmentally benign green approach. The physicochemical properties of the MnFe₂O₄/ZIF-8 heterojunction were verified utilizing multiple characterization techniques. The as-designed MnFe₂O₄/ZIF-8 nanomaterial was applied as a photocatalyst for decontaminating tetracycline (TC) by irradiation with simulated sunlight. The purification experiments demonstrated that the complete removal of TC was achieved at the pH of 9.0, catalyst quantity of 0.5 g/L, and TC dosage of 5 mg/L in the presence of simulated sunlight for 200 min. Besides, HO^• radicals were inferred to be the primary oxidizing agents in the photo-decontamination of TC by MnFe₂O₄/ZIF-8 and exhibited unique photocatalytic reactivity for TC after the six-succeeding recycle experiment. EIS, Mott-Schottky, radical capture experiment, and transient photo-current were used to elucidate the probable photocatalytic degradation mechanism of the S-scheme systematically. Furthermore, the possible decontamination pathways of TC were deduced through intermediate analysis and density functional theory (DFT) computations. Concomitantly, the biodegradation ability of the MnFe₂O₄/ZIF-8/xenon system was evaluated from pharmaceutical wastewater purification. These experiments showed that the AOS and COS levels of the wastewater sample elevated from 1.7 to 2.4 and 3.1, respectively, under simulated sunlight irradiation, manifesting the robust oxidation of stubborn organic substances by employing the investigated system.