BACKGROUND Photocatalytic hydrogen (H-2) production using sunlight is a promising solution for obtaining clean renewable energy. Therefore, the study of efficient, nontoxic and stable photocatalysts is very important. RESULTS A novel ternary carbon dots/cobalt monoxide/graphitic carbon nitride (CDs/CoO/g-C3N4) composite photocatalyst was prepared by a simple solvothermal method for photocatalytic H-2 production under visible light irradiation (lambda > 420 nm). Compared with single semiconductors CoO and g-C3N4, and binary composite CoO/g-C3N4, the ternary CDs/CoO/g-C3N4 nanocomposite exhibited higher photocatalytic performance. The optimal photocatalytic H-2 rate of CDs/CoO/g-C3N4 photocatalyst was 987.4 mu mol g(-1)center dot h(-1) with the apparent quantum efficiency of 2.39% at 420 nm. This enhanced photocatalytic activity can be attributed to the synergy effect of strong absorption and electron buffer property of CDs as well as the merits of the internal heterojunction formed between CoO and g-C3N4. CONCLUSIONS This work provides a new approach to the design of a high-efficiency composite photocatalyst for converting solar energy into chemical fuel. (c) 2020 Society of Chemical Industry