Hazardous gases sensors based on conducting polymer composites: Review

[Display omitted] •An overview of the most toxic gases in the environment.•Gas sensing mechanism of the composites are investigated.•The parameters of the composites that govern the efficiency of gas sensors are discussed. This article reviews application of conducting polymers and their composites as promising candidates for detection of the most environmentally hazardous gases, including NH3, NO2, H2S, and CO. The gases properties, harmfulness, and permissible Exposure Limit (PEL) of environmentally hazardous gases have been comprehensively elaborated. Promising materials for selective and sensitive detection of environmentally harmful gases have been reviewed in the present communication. For example, polyaniline composites are the supreme promising materials for NH3 and CO detecting while Polypyrrole, Poly (3,4-thylenedioxythiophene), and polythiophene sensors are the utmost active for NO2 and H2S monitoring, respectively. The gas sensing mechanism of differently prepared conducting polymers and its composites towards hazardous gases (viz. NH3, NO2, H2S, and CO) has also been comprehensively reviewed.