As rapidly growing environmental pollution demands the development of efficient photocatalytic materials, tremendous attention has been drawn to TiO2, a widely used photocatalytic material with cost-effectiveness, stability, and outstanding reactivity. To maximize its photocatalytic efficiency by enhancing the photogenerated charge separation, lowering the intrinsically large bandgap (3.2 eV) of TiO2 is a key problem to be overcome. Herein, a new design is reported for an efficient photocatalyst realized by heterostructuring a 3D nanostructured TiO2 monolith (3D TiO2) and graphene quantum dots (GQDs) through using 3-aminopropyltriethoxysilane (APTES) as a linker. The incorporation of APTES between the TiO2/GQD interface enables the formation of a charge injection-type heterostructure, as confirmed by transient absorption spectroscopy, providing improvement of both visible absorption and charge separation. As a result, the heterostructure exhibits a 242% enhanced photocatalytic performance compared to that of nonheterostructured 3D TiO2 under visible irradiation, demonstrating its promising potential for practical photocatalytic applications in environmental remediation.