Hollow, porous, and yttrium functionalized ZnO nanospheres with enhanced gas-sensing performances

We report the synthesis of a hierarchical nanostructure of hollow and porous ZnO nanospheres with a high specific surface area as a novel sensing material to toxic formaldehyde by a simple template-free hydrothermal technique in organic solution. We demonstrate that the liquid mixture ratio and hydrothermal time play a pivotal role in forming such unique morphology and propose a growth mechanism of Ostwald ripening coupled with grain rotation induced grain coalescence. Comparison investigations reveal that yttrium allows resistance reduction of sensors and enhances significantly gas-sensing performances of ZnO nanospheres toward the formaldehyde over the commonly used undecorated ZnO nanoparticles. Such hollow, porous, and yttrium functionalized ZnO nanospheres could therefore serve as hybrid functional materials for chemical gas sensors. The results represent an advance of hierarchical nanostructures in enhancing further the functionality of gas sensors, and the facile method presented could be applicable to many other sensing materials.