Cementing Mesoporous ZnO with Silica for Controllable and Switchable Gas Sensing Selectivity

Abstract

Nanostructured ZnO semiconductors as gas sensing materials have attracted great attention due to their high sensitivities, especially to reducing gases. However, ZnO based gas sensors lack controllable sensing selectivity. Herein, for the first time novel silica-cemented mesoporous ZnO materials with different contents of silica, high surface areas, and well-interconnected pores (∼29 nm) are synthesized through the evaporation-induced co-assembly (EICA) approach, and these amorphous ZnO materials exhibit controlled selectivity to ethanol or acetone. Strikingly, pure ZnO is found to exhibit better sensitivity to ethanol than that of acetone, while 2 wt % silica cemented mesoporous ZnO exhibits oppositely a selectively higher response to acetone than that of ethanol. In situ gas chromatograph–mass spectrum (GC-MS) analysis during the sensing process, in combination with intelligent gravimetric analyzer (IGA) measurement, reveals that such a preferential enhancement of acetone sensitivity by silica modification is mainly attributed to the dramatically improved adsorption of polar acetone molecules with a larger dipole moment of 2.88 D on the silica-cemented ZnO materials with higher surface polarity imparted by rich Zn–O–Si–OH bonds, and the acetone sensing process on pure ZnO and silica-cemented ZnO is found to experience a different reaction pathway.