Highly sensitive and ultra-fast responding gas sensors using self-assembled hierarchical SnO2 spheres

The Sn3O4 hierarchical microspheres self-assembled from nanosheets were prepared by a hydrothermal reaction of aqueous solution containing SnCl2·2H2O, H2C2O4, HCl, and N2H4·H2O, which were successfully transformed into nano-porous SnO2 hierarchical microspheres for gas sensor applications by heat treatment at 600 °C. The morphology of building blocks within the SnO2 hierarchical spheres could be manipulated from 0-dimensional nanoparticles to 2-dimensional nanosheets by varying the amount of H2C2O4 and N2H4·H2O. The SnO2 hierarchical spheres showed both the ultra-fast response (∼1 s) and high sensitivity to 50 ppm C2H5OH. The dramatic improvement in gas sensing characteristics was explained by the rapid diffusion of the target gas onto the entire sensing materials through the nano-porous network of nanosheets.