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

Abstract

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.

Keywords: DFT calculation; Environmental pollutant NO(2); Gas-sensing mechanism; Graphene; Thermodynamics; Zinc oxide-based sensor; g-C(3)N(4) and Cellulose.