The coupling of graphene, graphitic carbon nitride and cellulose to fabricate zinc oxide-based sensors and their enhanced activity towards air pollutant nitrogen dioxide.

It is desirable but challenging to sense toxic nitrogen dioxide (NO2) for it has become one of the most prominent air pollutants. Zinc oxide-based gas sensors are known to detect NO2 gas efficiently, however, the sensing mechanism and involved intermediates structures remain underexplored. In the work, a series of sensitive materials, including zinc oxide (ZnO) and its composites ZnO/X [X = Cel (cellulose), CN (g-C3N4) and Gr (graphene)] have been comprehensively examined by density functional theory. It is found that ZnO favors adsorbing NO2 over ambient O2, and produces nitrate intermediates; and H2O is chemically held by zinc oxide, in line with the non-negligible impact of humidity on the sensitivity. Of the formed composites, ZnO/Gr exhibits the best NO2 gas-sensing performance, which is proved by the calculated thermodynamics and geometrical/electronic structures of reactants, intermediates and products. The interfacial interaction has been elaborated on for composites (ZnO/X) as well as their complexes (ZnO- and ZnO/X-adsorbates). The current study well explains experimental findings and opens up a way to design and unearth novel NO2 sensing materials.