The development of a high-performance sensing material for the detection of ammonia gas is of significant importance due to its wide industrial presence and potential hazard risks. In this article, we report the synthesis of porous and hollow MoO ₃ (p-h-MoO ₃ ) microspheres via the oxidation of MoS ₂ microsphere templates, which are obtained via self-assembly of MoS ₂ nanosheets under hydrothermal conditions. The composition and morphology of the p-h-MoO ₃ microspheres are systematically characterized via microscopic and spectroscopic techniques, and our sensing tests reveals that p-h-MoO ₃ possesses ultrahigh responsiveness to ammonia gas, which can be further optimized via the selection of a suitable oxidation temperature and time. Additionally, the p-h-MoO ₃ shows minimal responses to other gaseous molecules, thereby demonstrating significant selectivity toward ammonia. The sensing mechanism of p-h-MoO ₃ toward ammonia is further investigated to identify the origin of its ultrahigh sensitivity and selectivity via X-ray photoelectron spectroscopy and diffuse reflectance Fourier transform infrared spectroscopy.

A gas nanosensor is an instrument that converts the information of an unknown gas (species, concentration, etc.) into other signals (for example, an electrical signal) according to certain principles, combining detection principles, material science, and processing technology. As an effective application for detecting a large number of dangerous gases, gas nanosensors have attracted extensive interest. However, their development and application are restricted because of issues such as a low response, poor selectivity, and high operation temperature, etc. To tackle these issues, various measures have been studied and will be introduced in this review, mainly including controlling the nanostructure, doping with 2D nanomaterials, decorating with noble metal nanoparticles, and forming the heterojunction. In every section, recent advances and typical research, as well mechanisms, will also be demonstrated.