By means of density functional theory (DFT) computations, we investigated the functionalization effects of relatively non-toxic organic molecules (C6H5COOH and C6H5OCH3) on the photocatalytic performance of monolayer MoS2. It is found that C6H5COOH and C6H5OCH3 both are physically adsorbed on the surface of MoS2. The functionalization of C6H5COOH and C6H5OCH3 on monolayer MoS2 not only facilitate the separation of photoinduced carriers and improve the optical adsorption ability, but also make the band positions enough to drive water split into H-2 and O-2. Thus, we propose that the C6H5COOH/MoS2 and C6H5OCH3/MoS2 can be potential photocatalysts for overall water splitting under visible light. (C) 2017 Elsevier B.V. All rights reserved.