Enhanced synergistic photocatalysis: a thorough investigation of Bi2Sn2O7/C3N5 heterojunctions

Abstract

The close bandgap alignment between graphitic-C₃N₅ (g-CN) and Bi₂Sn₂O₇ (BSN) facilitates effective heterojunction formation, enhancing charge separation and transport. This study explores the photocatalytic degradation of ortho-dichlorobenzene (o-DCB) using a series of Bi₂Sn₂O₇–g-C₃N₅ (BSN–CN) heterojunctions, which were synthesized hydrothermally with various dispersions of Bi₂Sn₂O₇ (BSN) on graphitic-C₃N₅ (g-CN). A thorough characterization was carried out using different techniques, including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS-UV-Vis), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL), time-resolved photoluminescence (TRPL), and cyclic voltammetry (CV). These analyses not only confirmed the formation of the heterojunctions but also revealed the effect of structural parameters that significantly influenced their photocatalytic behavior. These structural parameters mainly affected the kinetics, lifetime, and migration pathways of photogenerated electron–hole (e⁻/h⁺) pairs. The photocatalytic activity of these heterojunctions was tested for o-DCB degradation, representing dioxin and furan analogues, under visible light and ambient, liquid-phase conditions. The BSN–CN composites demonstrated superior photocatalytic performance compared to the individual components and their physical mixtures. Notably, the BSN–CN-15 (with 15% BSN dispersed over CN) sample, which had the highest BSN content, achieved almost complete mineralization of o-DCB at one of the fastest rates reported to date. A detailed structure–activity relationship was established, highlighting the roles of bandgap energy, valence band position, and surface charge in governing photocatalytic efficiency. Post-reaction XPS analysis further revealed changes in surface chemistry, shedding light on the degradation mechanism. Additionally, the formation of surface intermediates was investigated to better understand the photocatalytic pathway and guide future improvements in catalyst design.