The preparation of nanoscale molybdenum sulfide (MoS2)-modified graphitic carbon nitride (g-C3N4) nanosheets usually contains complex and multiple-step operations, including the separate synthesis of nanoscale MoS2 and g-C3N4 nanosheet, and their subsequent composite process. To effectively overcome the above drawbacks, herein, a facile one-step trifunctional ammonium tetrathiomolybdate ((NH4)(2)MoS4)-assisted approach has been designed to produce ultra-small MoSx nanodot-coupled g-C3N4 nanosheet photocatalyst, including the first addition of ammonium chloride (NH4Cl) and (NH4)(2)MoS4 into melamine precursors and their following one-step calcination. During high-temperature calcination, except for the promoting generation of the g-C3N4 nanosheets by produced ammonia (NH3) and hydrogen sulfide (H2S) gases, the above (NH4)(2)MoS4 decomposition not only can efficiently clip the s-heptazine framework to produce more terminal amino groups and cyano groups, but also can produce ultra-small MoSx nanodots on the resultant g-C3N4 nanosheet surface, resulting in the final production of ultra-small MoSx nanodot-coupled g-C3N4 nanosheets. The resultant MoSx nanodot-coupled g-C3N4 nanosheets evidently exhibit increased photocatalytic hydrogen (H-2)-generation rate, about 8-fold increase to the traditional MoS2-modified g-C3N4 photocatalyst. The ncreased H-2 -generation rate can be mainly attributed to the synergism of MoS x nanodots and cyano group on the g-C3N4 nanosheet surface. The current facile technology could open the sights for the preparation of other high-efficiency photocatalysts. (C) 2020 Elsevier Inc. All rights reserved.