Hierarchical NiO hollow microspheres assembled from nanosheet-stacked nanoparticles and their application in a gas sensor†
A facile and robust route for the mass preparation of hollow NiO microspheres assembled from nanosheet-stacked nanoparticles is developed. The Ni(HCO3)2 precursor with a hollow spherical structure was firstly prepared by a hydrothermal reaction without any surfactants or organic additives. The reaction generated gas bubble may act as a template for the formation of Ni(HCO3)2 hollow microspheres. These are converted into hierarchical NiO hollow microspheres assembled from nanoparticles (with diameter of ∼25 nm) upon calcination, which are further assembled by the stacking of ultrathin nanosheets. The hierarchical NiO hollow structures are attractive for catalyst, sensor and environmental applications, benefiting from their large surfaces. The sensing properties of the hierarchical NiO hollow microspheres were evaluated. They show high sensitivity, short response and recovery times, and good response and recovery characteristics to n-butanol. As compared with NiO nanoparticles with similar dimensions (∼20–35 nm), the nanoparticle assembled NiO hollow microspheres exhibit enhanced gas sensing properties. The effective integration of several nanostructures in one microunit would provide a novel way to design new materials for nanodevices.