An enhanced optoelectronic NO2 gas sensors based on direct growth ZnO nanowalls in situ on porous rGO

ZnO nanowalls were grown in situ on the surface of porous reduced graphene oxide (PG) films using spray, thermal reduction and facile solution method in this work. The products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy. The results showed that the highly developed interconnected 3-D ZnO nanowall networks were anchored homogeneously on the surface of PG films to construct 3D ZnO/PG hybrid nanocomposites. This 3D hybrid nanostructure provided many channels for gas diffusion. The fabricated sensor based on ZnO/PG composites showed good photo sensing response (7.4) to 365 nm UV light and an enhanced gas sensitivity (35.31) to 50 ppm NO2 with irradiation of UV light of 1.2 mW/cm2 in the air at room temperature, which was 2.24 fold higher than that of pure ZnO, and the response-recovery times were (∼37s, and 2s) when exposed to 50 ppm NO2. The optoelectronic gas sensing mechanisms of ZnO/PG composites were proposed in detail to understand the effect of UV irradiation in the NO2 detection process.