Infiltration of C-ring into crystalline carbon nitride S-scheme homojunction for photocatalytic hydrogen evolution

Enhancing the carrier separation in graphitized carbon nitride (g-C3N4) is advantageous for improving its photocatalytic activity. Herein, we propose a feasible method for preparing CN-C by thermal polymerization to gradually infiltrate carbon rings (C-rings) into the surface of crystalline carbon nitride (CN), enabling photogenerated electrons to be transferred rapidly between the CN inner layers and the CN/C outer layer. Successful penetration and distribution of carbon rings into carbon nitride were confirmed by secondary ion mass spectroscopy using ratio analysis of C and N elements at various depths of the prepared photocatalyst. Theoretical calculations indicated that CN and CN/C in the molecule generated different Fermi levels to form an S-scheme homojunction, establishing appropriate built-in electric fields and thus enabling interlayer charge migration. Moreover, the overlap of the conjugate plane of C-rings with carbon nitride led to the formation of photogenerated in-plane charge transfer tunnels. The two-electron transfer tunnels greatly improved the dissociation efficiency of photogenerated electrons. The prepared sample loaded with 3 wt% Pt as a co-catalyst for hydrogen production under visible light irradiation, and the prepared optimal sample CN-C showed a maximum quantum efficiency of 15.56% for photocatalytic H2 evolution at 385 nm. This research introduces a new idea for constructing a directional transfer path for charge carriers in-plane and intralayer.