P-N heterointerface-determined acetone sensing characteristics of α-MoO3@NiO core@shell nanobelts

Constructing P-N heterojunctions is a well-known strategy to improve the gas-sensing performances of metal oxides. However, it remains a great challenge to design well-defined P-N heterojunctions, which hinders the achievement of high-performance P-N heterojunction gas sensors as well as the recognition of the P-N-heterojunction-enhanced gas-sensing mechanism. In this work, an alpha-MoO3@NiO nanocomposite with well-defined core@shell P-N heterojunction nanobelts was prepared via a facile method. Benefitting from a well-defined P-N heterojunction construction, the alpha-MoO3@NiO nanocomposite exhibited the highest response (R-g/R-a = 20.3) towards 100 ppm acetone, which was 17.2 times higher than that of pristine alpha-MoO3 (R-a/R-g = 1.18) and 6.6 times higher than that of pristine NiO (R-g/R-a = 3.07). Gas-sensing measurement revealed that the response of n-type alpha-MoO3 could be greatly improved by anchoring p-type NiO nanosheets. The main mechanism for the enhanced acetone sensing properties of the alpha-MoO3@NiO nanocomposite was investigated. The well-defined alpha-MoO3@NiO P-N nanocomposite offered abundant Mo-O-Ni bonds at the heterointerfaces, which could induce the large hole depletion regions in p-type NiO and hence benefit oxygen adsorption and gas-sensing reactions at the interfaces. This work not only demonstrates that the alpha-MoO3@NiO nanocomposite is a promising material for fabricating acetone sensors but also provides useful guidance for designing well-defined core@shell P-N heterojunctions in gas-sensing applications.