Role of Interfacial Built-In Electric Field Induced by Fluorine Selective Substitution-Doped g-C3N4 in Photocatalysis of the g-C3N4/TiO2-B(001) Heterostructure: Type-II or Z-Scheme Photocatalytic Mechanism?

Abstract

Nonmetallic doping is considered to be an effective method to regulate the electronic property and improve the photocatalytic activity of heterostructures. Herein, we investigate the photocatalytic mechanism of F-doped g-C3N4 supported by TiO2-B(001) substrate, that is, F@g-C3N4/TiO2-B(001) heterostructures. It is found that if the dopant F atom substitutes pyridine N with lone pair electrons (N2), the induced interfacial charge transfer is from g-C3N4 to TiO2-B(001), whereas the induced interfacial charge transfer is from TiO2-B(001) to g-C3N4 if the dopant F atom substitutes the sp2-hybridized C atom (C1). Thus, the built-in electric field induced by reverse charge transfer between g-C3N4 and the TiO2-B(001) interface plays a completely different role in the directional migration of photocarriers. The FN2@g-C3N4/TiO2-B(001) heterostructure follows a direct Z-scheme photocatalytic mechanism. Differently, the FC1@g-C3N4/TiO2-B(001) heterostructure is a type-II photocatalyst. Although the photocatalytic mechanism of these two heterostructures is different, their optical absorption edge is obviously expanded to the infrared region, and they would become full-spectrum solar light-activated photocatalysts. We believe our findings may provide a reference for regulating the charge transfer direction and the photocatalytic mechanism of heterostructures in the experiment.