SubPc-Br/BiOI S-scheme heterojunctions: efficient charge separation for enhanced photocatalytic degradation of tetracycline

Abstract

Constructing S-scheme heterojunctions is an effective strategy to enhance charge separation efficiency. In this study, for the first time, boron subphthalocyanine bromide (SubPc-Br) was formed by self-assembly on the surface of layer BiOI to form an S-scheme heterojunction (SubPc-Br/BiOI) through halogen bonding and π–π stacking interactions. Experimental results demonstrate that the SubPc-Br/BiOI composite enhances tetracycline removal efficiency by a factor of 1.6 compared to pure BiOI. Notably, after five cycles, the composite still maintains a high tetracycline removal rate, which is 2.62 times that of pure BiOI. DFT and TDDFT theoretical calculations, combined with synchrotron X-ray photoelectron spectroscopy (XPS) under simultaneous illumination, indicate that the internal electric field generated between the [Bi₂O₂] layer and the SubPc-Br macrocycle plays a dominant role in charge separation, while interfacial electron transfer contributes to the constitution of the S-scheme heterojunction. Moreover, the combination of molecular dynamics simulations (MD), Fukui function calculations, and HPLC-MS detection reveals the mechanism of pollutant degradation. This study introduces an innovative strategy for the construction of BiOI-based S-scheme heterojunctions.