Highly Porous Double-Shelled Hollow Hematite Nanoparticles for Gas Sensing

Multishelled hollow micro/nanostructures hold great potential for a variety of important applications due to their fascinating properties. However, the synthesis of multishelled hollow micro/nanostructures mainly relies on template-involved methods. A template-free protocol for multishelled hollow structures remains quite challenging. In this work, a solution strategy based on inside-out and outside-in Ostwald ripening is developed to manipulate hematite hollow spheres with single or double shells without using any hard or soft templates. The structure evolution of the hematite hollow spheres is comprehensively studied to reveal the formation mechanism. As a potential application, the hematite hollow spheres have been utilized for chemical gas sensors to investigate the structure–property correlations. Results demonstrate that the double-shelled hematite spheres exhibit much higher response than the single-shelled ones due to structure sensitization. An improved sensor response is further obtained by catalytic sensitization from Au nanoparticles. Outstanding sensing performances in terms of response speed, sensitivity, and detection limit toward acetone have been obtained by combining the dual sensitization effects. This work provides an alternative approach for the production of multishelled functional materials and a demonstration of the materials for application in high performance gas sensors.