Role of Interfacial Built-In Electric Field Induced by Fluorine Selective Substitution-Doped g-C<sub>3</sub>N<sub>4</sub> in Photocatalysis of the g-C<sub>3</sub>N<sub>4</sub>/TiO<sub>2</sub>-B(001) Heterostructure: Type-II or Z-Scheme Photocatalytic Mechanism?
Xiaojia Yuan, Shuhan Tang, Shuang Qiu, Xiaojie Liu
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-C 3 N 4 supported by TiO 2 -B(001) substrate, that is, F@g-C 3 N 4 /TiO 2 -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-C 3 N 4 to TiO 2 -B(001), whereas the induced interfacial charge transfer is from TiO 2 -B(001) to g-C 3 N 4 if the dopant F atom substitutes the sp 2 -hybridized C atom (C1). Thus, the built-in electric field induced by reverse charge transfer between g-C 3 N 4 and the TiO 2 -B(001) interface plays a completely different role in the directional migration of photocarriers. The F N2 @g-C 3 N 4 /TiO 2 -B(001) heterostructure follows a direct Z-scheme photocatalytic mechanism. Differently, the F C1 @g-C 3 N 4 /TiO 2 -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.