The use of solar energy is a promising means for pollution abatement or environmental remediation. In the present work, we report the design and fabrication of Bi2WO6 QDs/g-C3N4 binary heterojunction photocatalysts with highly efficient solar light response, wherein the Bi2WO6 QDs were in situ uniformly immobilized on porous g-C3N4 ultrathin nanosheets (NSs) by one-pot hydrothermal strategy. The photocatalytic performance of the Bi2WO6 QDs/g-C3N4 NSs hybrid composites was evaluated for the photodegradation of Rhodamine B (RhB). It was found that the mass ratio of Bi2WO6 QDs to g-C3N4 nanosheets in the composites significantly affects the photocatalytic activity. Higher amounts of g-C3N4 nanosheets in Bi2WO6 QDs/g-C3N4 composites showed lower photocatalytic activity. The composite with 10 mg g-C3N4 nanosheets exhibited the highest photocatalytic activity, with nearly 11-fold enhancement in photocatalytic efficiency over pure Bi2WO6 QDs. Different from previous reports, a novel Z-scheme photocatalytic mechanism was proposed to explain the enhanced the photocatalytic efficiency. (c) 2015 Elsevier B.V. All rights reserved.