Hydrogen (H-2) production and sulfur (S) recovery by hydrogen sulfide (H2S) photo-splitting is an ideal strategy to remove the hazardous gas and simultaneously turn the waste into clean energy and industrial resources. For this purpose, the highly photocatalytic activity of heterojunctions has attracted worldwide attention in H2S splitting. However, the intricate mechanism of interfacial coupling effect on the whole process of H2S photo-splitting, including light absorption, photoinduced carrier separation and surface reactions, restricts the design and construction of highly efficient heterojunctions. This work devotes to illuminating the interfacial coupling effect from these three aspects by constructing g-C3N4/r-TiO2 heterojunction based on the density functional theory (DFT). The reduced band gap of g-C3N4/r-TiO2 is beneficial to enhance the visible-light absorption. Photoinduced carriers could be efficiently separated in the staggered type II g-C3N4/r-TiO2 heterojunction which possesses sufficient redox potentials for H2S splitting into H-2 and S. Particularly, the r-TiO2 (1 1 0) and g-C3N4 (0 01) are the active surfaces of g-C3N4/r-TiO2 for H2S dissociation and H-2 production, respectively. More importantly, the interfacial coupling effect of g-C3N4/r-TiO2 could facilitate H2S dissociation by reducing the reaction energy barriers and promote the desorption of S to avoid the deactivation of g-C3N4/r-TiO2. Given the different functions of rTiO(2) (1 1 0) and g-C3N4 (0 0 1), the exposure of r-TiO2 (1 1 0) is crucial to the activity of g-C3N4/r-TiO2 during the design and fabrication of g-C3N4/r-TiO2 for H2S splitting. This work could provide novel insights into the interfacial coupling effect on the surface reactions and offer helpful guidance for constructing efficient heterojunctions. (C) 2019 Elsevier Inc. All rights reserved.