Direct Z-scheme porous g-C3N4/BiOI heterojunction for enhanced visible-light photocatalytic activity

Constructing direct Z-scheme heterojunction photocatalysts is a highly efficient pathway to completely utilize the high redox ability of photogenerated charge carriers. Herein, a direct Z-scheme porous g-C3N4 (Pg-C3N4)/BiOI heterojunction was constructed through the in-situ growth of BiOI on the surface of Pg-C3N4. First principle density functional theory calculations indicated that charge transfer would occur from Pg-C3N4 to BiOI due to the difference in their Fermi energies, resulting in a strong internal electric field (IEF) at the interface between Pg-C3N4 and BiOI. Under photoexcitation, the electrons in the conduction band (CB) of BiOI combine with the holes in the valance band (VB) of Pg-C3N4 with the help of IEF at the interface. A possible Z-scheme type charge transfer can be achieved. This special charge transfer mechanism greatly improved the separation efficiency of photogenerated charge carriers and maintained the high redox ability of photogenerated electrons in the CB of Pg-C3N4 and photogenerated holes in the VB of BiOI. Photocatalytic activities were estimated by the photodegradation of methylene blue under visible light. Results indicated that Pg-C3N4/BiOI exhibited higher photocatalytic performance than pure Pg-C3N4 and BiOI, which can be attributed to the Z-scheme type charge transfer between Pg-C3N4 and BiOI. This work provides new insights into the high photocatalytic activities of g C3N4 based heterojunction photocatalysts.