S-scheme Bi6O5(OH)3(NO3)5·3H2O/BiOBr0.8I0.2 Heterojunction Photocatalyst: Synthesis and Visible-Light Degradation Mechanism of Rhodamine B

• • Optimal mass ratio (BON:BI = 2:8) yields BON@BIOPT with 99.8% RhB degradation in 30 min visible light, a 1.9-fold improvement over pristine BI (52.2%), and an apparent rate constant (Kapp) of 0.20617 min⁻¹—8.64 times higher than BI (0.02385 min⁻¹). This performance leap addresses the bottleneck of slow kinetics in single-phase photocatalysts, enabling faster treatment cycles in industrial wastewater. • • BON@BIOPT exhibits a 37.4% increase in specific surface area (44.7 vs. 32.54 m²·g⁻¹) and a 20 nm red-shift in absorption edge (580 vs. 560 nm), narrowing the bandgap from 2.55 to 2.43 eV. Enhanced light harvesting and more active sites directly translate to higher quantum efficiency and lower energy consumption for visible-light-driven water treatment. • • The S-scheme heterojunction with internal electric field suppresses charge recombination, as evidenced by the dominant reactive species (O₂•⁻ and h⁺). This mechanistic design ensures efficient spatial separation of redox-active carriers, a critical factor for achieving sustained high mineralization rates in complex effluents. • • BON@BIOPT retains 88.6% degradation efficiency after 7 cycles and maintains 85–98% efficiency under pH variations and in the presence of common anions (HCO₃⁻, Cl⁻, SO₄²⁻, H₂PO₄⁻, NO₃⁻). This robustness indicates operational longevity and resilience to real-world water matrices, reducing catalyst replacement frequency and operational costs.