▎ 摘　　要

An upstanding graphene/ZnO/graphene sandwich heterojunction synthesized by coating vertical ZnO nanowalls with two-dimensional (2D) graphene sheets is characterized and used for NO2 detection at room temperature. The integration of graphene coatings and ZnO nanowalls yields improved NO2 sensing properties with the few layer graphene providing high electrical conductivity and the ZnO nanowalls providing high sensitivity and selectivity to NO2. At room temperature, the upstanding graphene/ZnO/graphene sandwich heterojunction sensor also exhibits a rapid response recovery time (25 s, 10 s) and good selectivity for NO2 against CH4, CO, SO2, NH3, and CH3CH2OH. The enhanced sensing performance of this hybrid structure suggests that the combinations of other 2D materials may yield further improvement in sensing properties.