Hierarchical 0D/3D BaTiO3/MgIn2S4 S-Scheme Piezo-Photocatalyst for Enhanced Visible-Light/Ultrasound Mineralization of Norfloxacin

A hierarchical BaTiO 3 /MgIn 2 S 4 (BTO/MIS) heterostructure was synthesized via a one‑step solvothermal route to couple the strong piezoelectric potential of BaTiO 3 with the visible‑light activity of MgIn 2 S 4 . X-ray diffraction, electron microscopy, and XPS confirm the intimate interfacial contact between BTO and MIS nanosheets, establishing an n–n S-scheme junction that promotes internal band bending and an intrinsic electric field for vectorial charge migration. Under simultaneous 70 W simulated solar irradiation and low‑power (20 kHz, 20 W) ultrasonication, the optimized 2.0‑BTO/MIS composite decomposed 95 % of the fluoroquinolone antibiotic norfloxacin (10 mg L -1 ) within 90 min, nearly an order of magnitude faster than either photocatalysis or piezocatalysis alone and corresponding to a synergy factor of 6.9 and 89.6 %. Electrochemical impedance and photoluminescence analyses revealed markedly lower charge-transfer resistance and suppressed electron–hole recombination compared to the parent phases, while transient piezocurrent measurements demonstrated an efficient conversion of mechanical energy into reactive charge carriers. Degradation proceeded most effectively in acidic solution (optimum pH ≈ 3), where the positively charged antibiotic was strongly adsorbed onto the negatively polarised surface. Radical‑quenching experiments identified valence‑band holes and •OH as the dominant oxidants, consistent with the S‑scheme mechanism. Collectively, these results demonstrate that integrating piezoelectric BaTiO 3 with visible‑light‑responsive MgIn 2 S 4 in an S‑scheme configuration affords a robust piezo‑photocatalyst capable of harvesting both solar and low‑frequency mechanical energies to drive rapid, mineralization-level removal of persistent pharmaceutical pollutants from water