A General Synthesis of Crumpled Metal Oxide Nanosheets as Superior Chemiresistive Sensing Layers

Metal oxide nanosheets having high mesoporosity, grain size distribution of 5-10 nm, and ultrathin thickness have attracted much attention due to their intriguing properties such as high surface-to-volume ratio and superior chemical activities. However, 2D nanostructures tend to restack, inducing a decrease in accessible surface area and a number of pores. To solve this problem, herein, a unique synthetic method of crumpled metal oxide nanosheets using spray pyrolysis of metal ion-coated graphene oxide, followed by heat treatment, is reported. This method is applicable not only to single-component metal oxides but also to heterogeneous multicomponent metal oxides in which composition can be controlled. Crumpled SnO2, ZnO, and Co3O4 as well as SnO2/ZnO and SnO2/Co3O4 nanosheets with heterogeneous interfaces are successfully synthesized and used as superior gas sensing layers. Because of the abundant reaction sites, well-developed porosity for high gas accessibility, the formation of heterojunctions, the crumpled SnO2/ZnO and SnO2/Co3O4 nanosheets exhibit outstanding sensing performance (R-air/R-gas = 20.25 toward 5 ppm formaldehyde, and R-air/R-gas = 14.13 toward 5 ppm acetone, respectively). This study can contribute to the realization of a family of heterogeneous crumpled metal oxide nanosheets that can be applied to various research fields.