摘要： Two-dimensional (2D) nanosheet-based nanocomposites have attracted intensive interest owing to the unique electronic and optical properties from their constituent phases and the synergistic effect from the heterojunctions. In this study, an interfacial coupled TiO2/g-C3N4 2D-2D heterostructure has been prepared via in situ growth of ultrathin 2D-TiO2 on dispersed g-C3N4 nanosheets. This strongly coupled 2D-2D TiO2/g-C3N4, different from the weakly bonded 2D-TiO2/g-C3N4 heterostructures produced by mechanical mixing, has unique electronic structures and chemical states due to strong interlayer charge transfer, confirmed by both experimental and theoretical analyses. Significantly enhanced visible-light responses have been observed, indicating a great potential for visible-light induced photosynthesis and photocatalysis. For benzylamine coupling reactions under visible-light irradiation, 80% yield rate has been achieved, superior to ~30% yield rate when adopting either 2D-TiO2 or g-C3N4 structure. The enhanced photocatalytic activity can be attributed to the adequate separation of photo-generated electrons at the strongly coupled 2D-2D heterojunction interfaces.