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

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 (ΦBiOBr = 5.39 eV compared to Φα-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.