Core-double shell ZnO@In2O3@ZnO hollow microspheres for superior ethanol gas sensing

Abstract

• ZnO@In 2 O 3 @ZnO hollow microspheres have been prepared. • The heterojunctions were created at the interface of In 2 O 3 and both inner and outer ZnO. • The sensor exhibits enhanced gas-sensing properties toward ethanol. • The sensing mechanism is appropriately speculated. Core-double shell-structured ZnO@In 2 O 3 @ZnO microspheres consisting of ZnO hollow microspheres, an In 2 O 3 interlayer, and a ZnO outer layer were synthesized by decorating In 2 O 3 and ZnO on the surface of ZnO hollow microspheres. The ZnO hollow microspheres with a size of 1.4 μm provided a good matrix for the adhesion of In 2 O 3 and ZnO. Both In 2 O 3 and the ZnO shells have a loose microstructure, which provided numerous gas diffusion channels and active sites for gas diffusion and gas sensing reaction. The surface defects and electronic structure of ZnO and ZnO@In 2 O 3 @ZnO were examined by photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS). The gas sensing properties of the ZnO hollow microspheres, ZnO@In 2 O 3 core-shell microspheres, and ZnO@In 2 O 3 @ZnO core-double shell microspheres were compared using ethanol as the target gas. The response of ZnO@In 2 O 3 @ZnO toward 100 ppm ethanol was 453.2 at the optimum operating temperature of 200 °C, which was 2 and 30 times higher than that of ZnO@In 2 O 3 and ZnO. Even at a concentration of 1 ppm, the response of ZnO@In 2 O 3 @ZnO reached 53.2, indicating its excellent gas-sensing performance at low concentrations. The superior gas sensing properties of ZnO@In 2 O 3 @ZnO were attributed to its high specific surface area, abundant surface defects, and radial electronic modulation mechanism.