The sandwich-shaped double S-scheme heterojuction OCN/BiOCl/Bi24O31Cl10 efficiently degrades levofloxacin and its charge transfer mechanism

Abstract

The rapid recombination rate of photogenerated charges presents considerable challenges for the rational design of high-performance, stable photocatalysts. In this study, we integrated the characteristics of oxygen doping and heterojunctions into oxygen-doped g-C₃N₄/BiOCl/Bi₂₄O₃₁Cl₁₀ (OCN/BiOCl/Bi₂₄O₃₁Cl₁₀) using a straightforward impregnation-calcination method. Oxygen doping disrupts the symmetric atomic arrangement in pure-phase samples, optimizing the electronic configuration of active sites at the reaction interface and enhancing the coupling between anions and cations. The introduction of BiOCl, which offers an excellent coordination environment, in conjunction with Bi₂₄O₃₁Cl₁₀, creates a dual-S heterojunction. This structure establishes dual reaction interfaces that facilitate efficient dual electron ’transport channels,’ promoting the rapid transfer of charge carriers among OCN, BiOCl, and Bi₂₄O₃₁Cl₁₀. Experimental results demonstrate that the OCN/BiOCl/Bi₂₄O₃₁Cl₁₀ heterojunction material achieves a degradation efficiency of 96.1 % for 10 mg·L⁻¹ levofloxacin under visible light. Notably, in situ measurements obtained through Kelvin probe force microscopy (KPFM) and density functional theory (DFT) calculations jointly reveal a unique chemical environment and electronic structure arising from the formation of an internal electric field among OCN, BiOCl, and Bi₂₄O₃₁Cl₁₀, thereby providing enhanced pathways for the migration of photogenerated charge carriers. Furthermore, the heterostructure significantly reduces the transport distance of photogenically induced charges and decreases internal transport resistance, thereby improving the separation efficiency of photogenerated electron-hole pairs. This mechanism is crucial for the markedly enhanced photocatalytic degradation performance of OCN, BiOCl, and Bi₂₄O₃₁Cl₁₀ materials. In summary, this work explores the synergistic effects among multiple modifications, providing insights for the precise design of efficient and stable photocatalytic degradation systems.