The coupling of semiconductor photocatalysts with graphene quantum dots (GQDs) has been proven to be an effective strategy to enhance the photocatalytic and photoelectrical conversion performances of the resulted composites; however, the preparation of semiconductor/GQDs composites usually involves several time-inefficient and tedious post-treatment steps. Herein, we present a facile one-step hydrothermal route for the preparation of GQDs coupled TiO₂ (TiO₂/GQDs) photocatalysts using 1,3,6-trinitropyrene (TNP) as the sole precursor of GQDs. During the hydrothermal process, TNP molecules undergo an intramolecular fusion to form GQDs, which simultaneously decorate on the surface of TiO₂ nanoparticles, leading to a strong surface interaction between the two components. The effective coupling of GQDs on TiO₂ can effectively extend the light absorption of the TiO₂ to visible region and enhance the charge separation efficiency of TiO₂/GQDs composites as a result of GQDs acting as a photosensitizer and an excellent electron acceptor. These key advances make the TiO₂/GQDs photocatalyst highly active towards the H₂ evolution reaction, resulting in 7 and 3 times higher H₂ evolution rate and photocurrent response at optimal GQDs content than TiO₂ alone, respectively. This study provides a new methodology for the development of high-performance GQDs modified semiconductor photocatalysts for energy conversion applications.