This work synthesized a novel Ag2S/K-g-C3N4 photocatalyst which was effective in photocatalytic hydrogen production under simulated sunlight and visible light. Systematic investigation including TG, XRD, FT-IR, DRS, XPS, N-2-adsorption, SEM, TEM, PL, and photoelectrochemical analyses was executed to examine the structure, optical property and charge separation efficiency of the as-prepared photocatalysts. Result indicated that potassium was successfully doped into the g-C3N4 framework via direct heating the mixture of melamine and potassium iodide at 520 degrees C, which increases the BET surface area, broadens the visible light response region, and elevates the separation efficiency of electron-hole pairs. The modification of Ag2S nanoparticles on the optimal K-g-C3N4 sample further improves the surface charge separation efficiency via a type-II mechanism, which was believed to be the key role in photocatalytic reaction. The best Ag2S/K-g-C3N4 hybrid shows a photocatalytic H-2 generation rate of 868 and 96 mu mol.g(-1).h(-1) under simulated sunlight and visible light, respectively. This value is 2.7 and 1.3 times greater than that of g-C3N4 and K-g-C3N4, respectively. Meanwhile, the Ag2S/K-g-C3N4 displayed high photocatalytic stability. A probable mechanism of the synthesized photocatalyst was also suggested. (C) 2020 Elsevier Inc. All rights reserved.