In this study, a newly-designed Z-scheme g-C3N4@ZnO heterostructure was synthesized by 3D ZnO controllable deposition on 2D g-C3N4 nanosheets using thermal atomic layer deposition. The activity of 2D/3D g-C3N4@ZnO was evaluated by photocatalytic degradation of cephalexin under simulated sunlight. Results showed that the g-C3N4@ZnO photocatalyst achieved 98.9% degradation and 72.8% mineralization of cephalexin within 60 min of illumination. This degradation process fitted to the pseudo first order dynamic model with reaction rate constant of 0.0735 min(-1), 5.4 and 8.1 times higher than that of pure g-C3N4 and ZnO, respectively. Consecutive degradation experiments revealed the excellent stability and recyclability of 2D/3D g-C3N4@ZnO photocatalyst. Mechanism exploration found the enhanced photocatalytic activity was mainly ascribed to the strong oxidizability of active species generated on Z-scheme g-C3N4@ZnO. Besides, the oxidative species, especially h(+) and center dot OHplayed significant roles in the degradation process. Moreover, the degradation intermediates were identified through HPLC/MS/MS analysis and the possible pathway of cephalexin decomposition was proposed accordingly. The Z-scheme 2D/3D g-C3N4@ZnO was also proved effective for contaminants removal in real sewage. This study provided a new platform for controllable creation of Z-scheme photocatalysts with broad application prospects in contaminants remediation from aquatic environment under solar light