Advances in the designs and mechanisms of MoO3 nanostructures for gas sensors: a holistic review

The rapid expansion and development of industrial sectors and corridors pose a significant threat to the world today owing to the deteriorating air quality resulting from the release of harmful and toxic gases into the atmosphere. To combat and tackle air pollution, reliable and precise sub-ppm detection of these gases is highly desirable for human safety and the environment. For a gas sensor to perform its level best, the choice of nanomaterials is a critical factor that can significantly impact the robustness, stability, cost-effectiveness, sensitivity, and selectivity of the sensing device. Molybdenum trioxide (MoO3), as an n-type semiconducting metal oxide, has been rated as a research hotpot material in recent years due to its utility in a wide range of important technological applications. Owing to the advancement of synthetic techniques, it has been made possible to explore numerous novel nanostructures and integrate them into smart gas sensing devices. In this quest, this review is an effort to highlight the various nanostructures of MoO3 and the influence of these morphologies on the gas sensing performance. A detailed morphological overview of pristine MoO3 nanomaterials ranging from one-dimensional (1-D) to three-dimensional (3-D) nanostructure formation, followed by the preparation of different heterostructures including MoO3/metal oxides (p-type and n-type), MoO3/noble metal decoration, and MoO3/2D materials in the thematic domain of gas sensing, has been presented. Finally, a future outlook on the further progress of MoO3 gas sensors based on the current scenario is also suggested.