Flexible NO 2 gas sensors based on sheet-like hierarchical ZnO 1− x coatings deposited on polypropylene papers by suspension flame spraying

Abstract

Abstract 2D sheet-like ZnO coatings composed of nanoparticles were deposited on flexible polypropylene papers equipped with gold electrodes in three steps. Firstly, sheet-like ZnO powder was synthesized by direct precipitation method. Then, the as-synthesized powders were dispersed in anhydrous ethanol to form feedstock suspension. At last, the feedstock suspension was injected into the acetylene-oxygen flame to deposit ZnO coatings. X-ray diffraction and field-emission microscopy results revealed that the coatings were hexagonal phase and porous hierarchical structure. With an increase in spray distance, the coatings exhibited a morphology with smaller particle size and sheet thickness. Photoluminescence and X-ray photoelectron spectra indicated that large amounts of oxygen vacancies were introduced into the coatings, and oxygen vacancy concentration increased with the spray distance. UV–vis spectra showed that the light absorption of the coatings was extended to visible light region, and wider absorption range was obtained when the spray distance was increased. The ZnO coatings exhibited good responses to sub-ppm level NO2 at room temperature under white LED light illumination, and the coating deposited with longer spray distance presented a better NO2 sensing performance.