Diversiform metal oxide-based hybrid nanostructures for gas sensing with versatile prospects

Metal oxide semiconductors (MOS) have attracted much attention in constructing various gas sensors because of their low cost, portability, easy to manufacture, and high sensitivity. In this review, the gas-sensing mechanism of the MOS-based gas sensor and the factors affecting the gas sensitivity are summarized, in which the light excitation provides a promising potential to enhance the sensitivity of MOS-based gas sensors. This review focuses on providing various strategies to enhance their gas-sensing performance by specific functionalization of MOS with various materials such as metal oxides, metal nanoparticles (NPs), two-dimensional (2D) materials, conductive polymers, etc. We also discussed the metal-organic frameworks (MOFs)-derived MOS render them as an excellent gas-sensing material in detail, the MOS@MOFs nanostructures are able to effectively improve the selectivity of MOS sensors due to the adjustable pore size of MOFs. In addition, as an emerging application, wearable gas sensors are increasingly used in environmental monitoring and medical diagnosis. Electronic nose (E-nose), as an intelligent electronic instrument for distinguishing and identifying various odors, is introduced for the multi-component analysis. Self-powered gas sensing technologies have been developed by coupling piezoelectric or triboelectric devices with MOS-based sensors. Furthermore, the perspectives and challenges on the MOS-based sensors are discussed. (C) 2020 Elsevier B.V. All rights reserved.