Constructing Z-scheme photocatalysts is an effective approach to enhance the conversion efficiency of solar to chemical energy. Herein, W18O49/g-C3N4 heterostructures have been synthesized by growing W18O49 ultrathin nanowires on g-C3N4 nanosheets via a convenient solvothermal process. Various characterizations were performed on the materials to understand the structure-performance relationship. The photocatalytic properties of the W18O49/g-C3N4 heterostructures were evaluated by the two oxidation reactions, phenol degradation and oxidative N-C coupling of benzylamines, under a simulated sunlight (360 <= lambda <= 780 nm). With tuning the W18O49/g-C3N4 mass ratio, the optimal photocatalyst of W18O49(30)/g-C3N4 containing 30 wt% W18O49 nanowires exhibited the highest activity in both the photocatalytic reactions. The generations and contributions of the active species in the photocatalytic reactions were identified by electron spin resonance (ESR) spectra and active-species-eliminating experiments. Accordingly, the photocatalytic mechanism of W18O49/g-C3N4 heterostructures has been expounded based on the direct Z-scheme electron transfer between the two semiconductors as well as the synergistic actions of active sites on W18O49 nanowires and g-C3N4 nanosheets. This work demonstrates a rational paradigm to construct 1D/2D semiconductor heterostructures and provides further insights into Z-scheme photocatalytic mechanism for boosting solar-driven pollutant degradation and organic transformation. (C) 2019 Elsevier Inc. All rights reserved.