Review on the synthesis of metal sulfides gas sensors and their performances at room temperature

Toxic gases like hydrogen sulfide (H2S), ammonia (NH3), nitrogen dioxide (NO2), and VOCs like benzene, toluene, xylene, acetone, ethanol, and methanol are emitted from industries due to storage or as byproducts. They create health hazards for humans by inhalation of these gases. Monitoring of the concentration of different gases or VOCs is needed to control the air quality of the surrounding environment. Therefore, sensing these harmful gases or VOCs at a low level of concentration is the primary requirement for using sensors to maintain the air quality. Metal oxide gas sensors are immensely used for these types of applications. But fundamentally, these sensors are suffering from high operating temperatures, stability problems, etc. Recently metal sulfide (MS) based sensors have earned much attention to avoid these problems for sensing toxic gases and VOCs. Lots of experiments have been performed on various types of metal sulfides like lead sulfide (PbS), copper sulfide (CuxS), cadmium sulfide (CdS), tin (IV) sulfide (SnS2), zinc sulfide (ZnS), tungsten disulfide (WS2) and molybdenum disulfide (MoS2) for preparing gas sensors. The present article aims to review the recent developments in the synthesis of metal sulfide for gas sensors followed by gas sensing mechanisms. Sensitivity, response time and recovery time of these sensors have also been reviewed to evaluate the sensing performances toward toxic gases. Realizing the better metal sulfides for gas sensing applications with better sensing performances among the reported metal sulfides, the future scopes of research are also elucidated in this review.