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• The S + K-codoped g-C 3 N 4 presents excellent H 2 production (8.78 mmol g−1 h−1) under visible light. • The S + K-codoped g-C 3 N 4 inhibits the recombination of photogenerated carriers. • The S + K-codoped g-C 3 N 4 photocatalyst shows apparent quantum efficiency of 70 % at 420 nm for H 2 production. Modifying the structure of a photocatalyst to tailor its electronic and physicochemical properties is an effective approach for efficient photocatalysis. Herein, we demonstrate that co-doping non-metal (S) and metal (K) atoms into graphitic carbon nitride (g-C 3 N 4) provides excellent visible-light photocatalytic hydrogen production activity of 8.78 mmol g−1 h−1, which is 98 times higher than that of pristine g-C 3 N 4 (0.09 mmol g−1 h−1). The apparent quantum efficiency of the S+K-co-doped g-C 3 N 4 reaches 70 % at 420 nm. This outstanding photocatalytic performance attributed to an increased specific surface area from 6.78 to 74.23 cm3 g−1, which reduced the recombination of photogenerated charge carriers and enhanced conductivity. Various characterizations are undertaken to elucidate the S+K-co-doped g-C 3 N 4 photocatalytic mechanism. Our work not only demonstrates a facile, eco-friendly and scalable strategy for the synthesis of S+K-co-doped g-C 3 N 4 photocatalysts, but also opens a new avenue for the design of co-doped photocatalysts. [ABSTRACT FROM AUTHOR]