Development of engineering and novel materials based chemiresistive sensors for detection of air pollutants

Abstract

The awareness of the population about the importance of Air Quality Monitoring (AQM) is increasing. This is because, the pollutants are toxic in nature and are causing several health hazards as has been indicated by agencies like World Health Organization (WHO). Air pollution is caused due to the toxic gases emitted by the industries, automobile emissions, and fossil fuel burning. Hence, developing portable and inexpensive sensors for these obnoxious and toxic gases is critical as they need to be mounted abundantly at multiple locations. This work focuses on sensing three air pollutants such as nitrogen dioxide (NO2), ammonia (NH3), newlineand carbon monoxide (CO). newlineResistive sensors can be miniaturized, are CMOS compatible, and with emergence of chemical routes of synthesis of sensing layers, can be developed in cost-effective way. In this research, seven different types resistive sensing layers were synthesized and tested for three air pollutants - NO2, CO, and NH3. The research began by developing three different types of intrinsic materials (transition metal dichalcogenides (TMDs), MXenes, and semiconducting polymers) based sensors. Two TMDs, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) were synthesized using liquid exfoliation methods. MoS2 was observed to exhibit 2.82 to 39.8% response for 3 to 150 ppm of the NO2 at room temperature. The TMD was found to be highly selective and very fast with response time and recovery times found to be not more than 10 seconds for any concentration of NO2. WS2, another TMD was found to exhibit good sensitivity towards NO2 and CO at room temperature and its response varied from -11.9 and -27.4% and -3.4 and -35.3%, for 2 to 10 ppm of CO and NO2, respectively. The number of layers present in WS2 was found to modulate the response, selectivity, speed, and reusability of the sensor. MXenes are emerging as an excellent sensing material. Hence, this research an attempt to synthesize Mo2C nanoflakes using a simple technique was made. newline