Microbubble-Assisted Catalytic Ozonation of Tetracycline-Class Antibiotics Using Granular MIL-101(Fe)/γ-Al2O3

Tetracycline-class antibiotics are persistent contaminants in aquatic environments and are difficult to remove by conventional treatment processes. In this study, a recoverable granular MIL-101(Fe)/γ-Al2O3 catalyst was prepared through ligand anchoring followed by secondary Fe-MOF growth on spherical γ-Al2O3 and applied to catalytic ozonation of tetracycline (TC) under ordinary-bubble and microbubble-assisted operation. Structural characterization supported the formation of Fe-containing MOF domains on the alumina support, accompanied by an increase in BET surface area from 164.28 to 210.05 m2 g−1 and enhanced Lewis-acid-related pyridine-IR signals. Under conventional bubbling ozonation, the optimized catalyst achieved 67.93% apparent UV–Vis-based TC removal during an overall 50 min run consisting of 30 min dark adsorption followed by 20 min ozonation. In a 12 L microbubble reactor, the catalyst-assisted system reached 93.74% apparent UV–Vis-based TC removal at pH 6 with 100 g catalyst and 6 mg min−1 fed ozone, showing higher apparent removal than ordinary ozonation, microbubble ozonation, and ordinary-bubble catalytic ozonation under the tested configuration. Phosphate-blocking and radical-quenching experiments were consistent with the involvement of Lewis-acid-related sites, hydroxyl radicals, and superoxide-related pathways, but these tests are interpreted as indirect mechanistic evidence. LC-MS analysis suggested possible hydroxylation, demethylation, deamidation, ring opening, and low-molecular-weight product formation. The system also transformed chlortetracycline, oxytetracycline, and doxycycline and reduced COD and TOC in a simulated mixed-antibiotic matrix. Because parent-compound HPLC/LC-MS time-series quantification, ozone utilization/off-gas ozone measurement, bubble-size/kLa analysis, and ICP-based Fe loading/leaching data were not available, the present work is positioned as an apparent catalyst–reactor coupling study rather than a complete catalytic, hydrodynamic, or process-level demonstration.