New insights into XSnO₃ (X = Ca, Ba) photocatalysts for ciprofloxacin degradation based on theoretical defect formation and surface morphology

In this work, CaSnO 3 (CSO) and BaSnO 3 (BSO) perovskite oxides were synthesized via a solid-state reaction route. Their photocatalytic response was systematically evaluated towards rhodamine B dye – as a reference model – and the antibiotic ciprofloxacin (CIP). CSO exhibited superior activity, achieving 96.4% RhB and CIP (over 90%) degradation within 15 min and 20 min, respectively. BSO also demonstrated high efficiency - over 90% CIP removal in 60 min. Atomistic simulations reveal that these distinct photocatalytic responses originate from intrinsic defect chemistry and surface energetic state: CSO is dominated by Ca/Sn antisite defects and a combination of stable surfaces - (010) and (001), (212), (122), (211), and (221) – with mixed Ca–O/Sn–O or Ca–Sn–O terminations. On the other hand, BSO preferentially forms BaO Schottky defects and Ba–O and O–Sn terminations in lower surface area facets, which enhance carrier trapping and recombination, hindering photocatalysis. Scavenger and probe experiments confirm that photocatalytic degradation proceeds predominantly through •OH, •O 2 - , and ¹O 2 reactive oxygen species generated by photoinduced redistribution of electronic density across the valence and conduction bands. This work’s results positions XSnO 3 (X=Ca, Ba) as efficient photocatalysts for the removal not only of organic dyes – as extensive research shows – but also towards pharmaceuticals ( i.e., CIP), and even more so, considering the solid-state reaction method of synthesis, which allows scaling up, making it suitable for large-scale production. • CSO and BSO reached over 90% CIP degradation over 60 min UV irradiation. • Ca/Sn antisite defects and surface stabilization (CSO) optimize charge separation. • BaO Schottky defects and Ba–O terminations (BSO) favor traps and recombination. • •OH, •O 2 H, and 1 O 2 drive degradation. • Non-toxic effluents confirmed by L. sativa phytotoxicity assays.