The combination of graphene and semiconductor photocatalysts such as graphitic carbon nitride (g-C3N4) has been widely demonstrated as an effective strategy to improve the H-2-evolution performance of photocatalysts. However, owing to the hydrophobicity of graphene, the green synthesis of well-suspended grapheneig-C3N4 in the absence of surfactant or additives is still a challenge. In this study, the suspended reduced-graphene-oxide-modified g-C3N4 (rGO/g-C3N4) photocatalysts were fabricated through an in situ hydrothermal synthesis route, which includes a facile preparation of well-coupled GO/g-C3N4 precursor and its following in situ transformation to form the rGO/g-C3N4 by a hydrothermal reduction method. It was found that the obtained rGO/g-C3N4 photocatalysts showed a cotton-like structure and could be well suspended in water owing to the well coupling between rGO and g-C3N4 nanosheets, which is quite favorable for the photocatalytic reactions in an aqueous solution system. After loading Pt cocatalyst as the active site for H-2 evolution reaction, the rGO/g-C3N4 composite photocatalysts exhibited an obviously improved performance (ca. 23.7%) by the addition of a small amount of rGO (0.08%), compared with the pure g-C3N4. The improved photocatalytic H-2-evolution performance of rGO/g-C3N4 composite can be attributed the synergistic effect of rGO nanosheets and Pt nanoparticles, namely, rGO nanosheet acts as an electron-transfer mediator to rapidly capture the photogenerated electrons from the g-C3N4 and then transfer to the Pt cocatalyst, while the Pt nanoparticle functions as a reduction active site to promote the H-2-evolution reaction effectively. Considering its green preparation and high photocatalytic performance, the present synthesis route of suspended rGO/g-C3N4 may provide new insights into design and fabrication for other composite materials with various potential applications. (C) 2016 Elsevier B.V. All rights reserved: