Hexagonal ZnO nanoplates/graphene composites with excellent sensing performance to NO₂ at room temperature

Metal oxides with high-energy facets usually have more active surface sites to facilitate gas adsorption. In this work, the ZnO/graphene composites are synthesized hydrothermally and the morphology of ZnO nanoparticles can be changed from nanorods to nanoplates with the high-energy {0001} polar surface exposed by changing the density of sodium citrate in the reaction. The ZnO{0001}/graphene composites have better sensing properties to NO₂ at room temperature (RT). Based on first-principles calculation, the adsorption energy of NO₂ on the ZnO{0001} facet is more negative than that on the {011¯0} surface indicating stronger interactions between the former and NO₂. Furthermore, the ZnO{011¯0} surface shows semiconducting characteristics, whereas the ZnO{0001} polar surface is metallic. The metallic characteristics promote charge transfer at the interface between ZnO and graphene and enhance the NO₂ detection sensitivity.