BACKGROUNDPreparing catalysts with heterojunction structures is a strategy to achieve efficient charge separation and transfer of charges to enhance photocatalytic activity of photocatalysts. To optimize the graphitic carbon nitride (g‐C3N4)‐based photocatalysts, Bi2MoO6@ 2D g‐C3N4 catalyst was prepared.RESULTS2D Bi2MoO6 nanopiece@2D g‐C3N4 nanoflake composites in different proportions were prepared by the hydrothermal method. The prepared materials were characterized by various modern instrumental analyses, and their photocatalytic ability to decompose water and degrade rhodamine B under visible light irradiation was tested. Compared with pure Bi2MoO6 nanopiece and g‐C3N4 nanoflake, the hydrogen evolution rate of Bi2MoO6 nanopiece@g‐C3N4 nanoflake (1:10) composite was highest, at 4847 μmol h−1 g−1. The composite (3:10) exhibited significantly enhanced photocatalytic rhodamine B degradation for organic dye removal due to the formation of an excellent heterojunction to improve the separation and migration efficiency of photogenerated carriers.CONCLUSIONO2− and •OH were the two main active species in the photocatalytic degradation of rhodamine B. Bi2MoO6 formed a heterojunction with g‐C3N4, which accelerated separation and migration efficiency, thereby enhancing the photocatalytic activity. © 2023 Society of Chemical Industry (SCI).