Ultra-fast and highly-sensitive gas sensing arising from thin SnO2 inner wall supported hierarchical bilayer oxide hollow spheres

Hierarchical SnO2/α-Fe2O3 bilayer hollow spheres with thin inner shell were successfully synthesized by using SnO2 contained carbon spheres as sacrificial templates. The heterojunction formed at the interface as well as the hierarchical structures which provide an effective gas diffusion path resulted in significant enhancement in sensing response to ethanol and acetone as compared to pristine urchin-like α-Fe2O3. Response values of the hollow spheres based sensors towards 100 ppm acetone and ethanol could reach to 47.1 and 29.5. Moreover, in contrast to many other types of α-Fe2O3/SnO2 composites reported previously, gas sensors based on the bilayer hollow spheres here exhibited ultra-fast response and recovery speed. The dynamic transients of the sensors demonstrated both their fast response (3-4 s) and fast recovery (6-9 s) towards acetone in the concentration of 10-100 ppm. The unique hierarchical hollow structure with thin inner shell might be responsible for the ultra-fast gas sensing properties. This simple template based strategy is expected to be extended for the fabrication of similar hollow structure semiconductor oxide composites, and this work might provide an effective principle for designing high performance hybrid gas sensing materials.