Crystal-phase-dependent interfacial lattice matching in BiOBr/Bi₂O₃ S-scheme heterojunctions for efficient charge...

Interfacial lattice commensurability is an underexplored design dimension in heterojunction photocatalysis, despite its centrality to charge-carrier dynamics at solid-solid interfaces. Here, we report the fabrication of BiOBr with vacancy oxygen employing three Bi₂O₃ polymorphs (α, β, γ) and systematically elucidate the role of interfacial lattice commensurability on photocatalytic performance. The α-Bi₂O₃ polymorph (space group P2₁/c; a = 7.79 Å, b = 7.87 Å, c = 5.48 Å) exhibits near-ideal lattice commensurability with the tetragonal BiOBr (102) plane with a lattice mismatch of 3.1% along the x direction. High-resolution transmission electron microscopy (HRTEM) provides a direct view of a coherent heterointerface with uninterrupted crystallographic registry between α-Bi₂O₃ (121) (d = 0.329 nm) and BiOBr (102) (d = 0.285 nm). The shifts in X-ray photoelectron spectroscopy (XPS) binding energy and density functional theory (DFT) calculations together confirm an S-scheme charge-transfer route, which is driven by an internal electric field resulting from the difference in work functions (Φ_BiOBr = 5.39 eV compared to Φ_α-Bi2O3 = 5.06 eV). The optimized α-BOB composite achieves pseudo-first-order levofloxacin (LEV) degradation with a rate constant of k = 0.0207 min^-1 under visible-light irradiation, representing a 5.2-fold improvement over BiOBr. The total organic carbon (TOC) removal efficiency of 68.3% after 120 min irradiation confirms that a significant portion of the LEV carbon skeleton is mineralized to CO₂. Radical scavenging experiments establish a dominant reactive species hierarchy of •O₂^- > h⁺ > ¹O₂ > •OH. The average carrier lifetime for α-BOB, as revealed by time-resolved photoluminescence, is 4.13 ns, compared to 3.85 ns for β-BOB and 3.68 ns for γ-BOB, suggesting less defect-mediated recombination at the coherent interface. Liquid chromatography-mass spectrometry (LC-MS) analysis reveals ten degradation intermediates along three mineralization pathways, and Ecological Structure Activity Relationships (ECOSAR) verification shows a gradual detoxification to harmless metabolites. The study demonstrates that lattice matching based on crystal phase is a sensible design principle for developing efficient S-scheme photocatalysts.