Semiconductor metal oxide compounds based gas sensors： A literature review

This paper gives a statistical view about important contributions and advances on semiconductor metal oxide （SMO） compounds based gas sensors developed to detect the air pollutants such as liquefied petroleum gas （LPG）, H2S, NH3, CO2, acetone, ethanol, other volatile compounds and hazardous gases. Moreover, it is revealed that the alloy/composite made up of SMO gas sensors show better gas response than their counterpart single component gas sensors, i.e., they are found to enhance the 4S characteristics namely speed, sensitivity, selectivity and stability. Improvement of such types of sensors used for detection of various air pollutants, which are reported in last two decades, is highlighted herein.