Graphene oxide-templated hierarchically structured metal oxide toward superior chemiresistive-type gas sensors

Abstract

Metal oxide nanosheets have been widely used due to their intriguing properties, such as super-high surface-to-volume ratio, ultra-thin thickness, high ratio of mesopores, and small grain size. However, two dimensional nanostructures have the tendency to restack, so they can induce the decrease of accessible surface area and the pores. To solve these problems, herein, a facile synthesis of crumpled metal oxide nanosheets is reported, using graphene oxide (GO) as a template and via spray pyrolysis process with subsequent heat treatment. Also, this general synthetic method is extended to crumpled two different metal oxide nanosheets composites, which can control the composition as desired. Crumpled $SnO_2$, ZnO, and $Co_3O_4$ nanosheets (Crumpled 2D MO) were synthesized in this work, showing the high surface area to volume ratio with highly enhanced pores, and crumpled $SnO_2/ZnO$ and $SnO_2/Co_3O_4$ nanosheets (crumpled 2D MO/M’O) were haracterized by the existence of heterojunctions. Due to the large reaction site with high gas accessibility as well as functionalization of heterojunctions, crumpled 2D $SnO_2/ZnO$ and $SnO_2/Co_3O_4$ exhibited enhanced sensing performances ($R_{air}/R_{gas}$ = 20.25 at 5 ppm formaldehyde, and $R_{air}/R_{gas}$ = 14.13 at 5 ppm acetone, respectively).