2D NANOMATERIALS ENABLED - CHEMIRESISTIVE GAS SENSORS FOR DETECTION OF ENVIRONMENTAL HAZARDS

Abstract

In the backdrop of rapid development in science and technology, air pollution has gradually emerged as a major challenge before the entire world. The continuous emission of toxic gases and VOCs into the atmosphere not only worsens air quality but also creates severe human health hazards. The carbon-based compounds comprising VOCs undergo easy evaporation and disperse into the atmosphere at ambient condition due to their low boiling points. Air pollution stands out as one of the leading causes of premature mortality and a wide range of health disorders, according to the World Health Organization. Detection and control of such pollutants are necessary to minimize their adverse impacts on both the environment and human health. Among many VOCs, ethanol is one of the most commonly encountered compounds in everyday life. It is true that, though very useful, continuous exposure to ethanol vapor may cause serious health effects such as irritation to the respiratory system, nausea, vomiting, headaches, kidney dysfunction, and damage to the central nervous system; it may even lead to carcinogenic effects in the human body. Further, ethanol is flammable; the explosion-concentration range of ethanol is 3.3-19%, and it may thus be a root cause of industrial and vehicular accidents. Its vapor can easily form an explosive mixture with other gases, increasing the safety risks. Given this, the rapid and reliable detection of ethanol gas, especially at room temperature, assumes great importance in the context of both environmental and occupational safety. In pursuit of this objective, a room-temperature chemiresistive ethanol gas sensor based on hydrothermally synthesized tin sulfide (SnS) incorporated with molybdenum diselenide (MoSe2) nanosheets was developed and systematically studied. The gas- sensing behavior of the SnS/MoSe2 nanocomposite was evaluated by exposing the sensor to varying concentrations of ethanol (50–400 ppm) in dry air. The incorporation Ph.D. Thesis (Sunil Kumar) vi of MoSe2 nanosheets into SnS nanoplates generated a synergistic effect that significantly enhanced the sensor’s response, leading to superior response and recovery times of 9.1 s and 15.7 s, respectively, along with excellent selectivity, reproducibility, and long-term stability. The nanocomposite sensor exhibited a high sensing response (Rg/Ra) of 26.8 toward 400 ppm ethanol in dry air and demonstrated typical p-type semiconducting behavior. Remarkably, the sensor operated efficiently at room temperature and was capable of detecting ethanol concentrations as low as 50 ppm. In addition, the device maintained stable performance over a 30-day testing period, confirming its durability. The improved sensing characteristics are attributed to the formation of a p-p heterojunction at the SnS/MoSe2 interface, which facilitates effective charge transfer. Furthermore, modulation of the potential barrier at this interface played a key role in enhancing the overall sensitivity of the sensor. Building on the enhanced sensing performance of the SnS/MoSe2 nanocomposite, where the presence of the p-p heterojunction at the SnS-MoSe2 interface was beneficial, a binary nanocomposite system comprising SnS and SnS2 has been further explored to exploit the advantages afforded by p-n heterojunctions. In this paper, a highly stable, selective, and reproducible ethanol gas sensor based on the SnS/SnS2 nanocomposite was successfully fabricated and exhibited excellent long-term operational stability. The sensor showed an outstanding response value of 35.7 toward 500 ppm ethanol gas and could detect ethanol as low as 10 ppm at room temperature. Besides, the device exhibited fast dynamic behavior, including a response time of 6.1 s and a recovery time of 18.3 s for 500 ppm ethanol. The sensor also exhibited excellent stability during a testing period of 40 days. The excellent sensing performance of the SnS/SnS2 nanocomposite could be primarily attributed to the formation of multiple p-n heterojunctions between SnS and SnS2 nanosheets. The intimate interfacial contact between the two phases not only facilitates good charge transfer but also increases the density of active sites available for ethanol adsorption and desorption. This synergistic effect significantly enhances the gas-sensing response, thereby making the developed nanocomposite a promising candidate for high-performance, room-temperature ethanol detection.In the backdrop of rapid development in science and technology, air pollution has gradually emerged as a major challenge before the entire world. The continuous emission of toxic gases and VOCs into the atmosphere not only worsens air quality but also creates severe human health hazards. The carbon-based compounds comprising VOCs undergo easy evaporation and disperse into the atmosphere at ambient condition due to their low boiling points. Air pollution stands out as one of the leading causes of premature mortality and a wide range of health disorders, according to the World Health Organization. Detection and control of such pollutants are necessary to minimize their adverse impacts on both the environment and human health. Among many VOCs, ethanol is one of the most commonly encountered compounds in everyday life. It is true that, though very useful, continuous exposure to ethanol vapor may cause serious health effects such as irritation to the respiratory system, nausea, vomiting, headaches, kidney dysfunction, and damage to the central nervous system; it may even lead to carcinogenic effects in the human body. Further, ethanol is flammable; the explosion-concentration range of ethanol is 3.3-19%, and it may thus be a root cause of industrial and vehicular accidents. Its vapor can easily form an explosive mixture with other gases, increasing the safety risks. Given this, the rapid and reliable detection of ethanol gas, especially at room temperature, assumes great importance in the context of both environmental and occupational safety. In pursuit of this objective, a room-temperature chemiresistive ethanol gas sensor based on hydrothermally synthesized tin sulfide (SnS) incorporated with molybdenum diselenide (MoSe2) nanosheets was developed and systematically studied. The gas- sensing behavior of the SnS/MoSe2 nanocomposite was evaluated by exposing the sensor to varying concentrations of ethanol (50–400 ppm) in dry air. The incorporation Ph.D. Thesis (Sunil Kumar) vi of MoSe2 nanosheets into SnS nanoplates generated a synergistic effect that significantly enhanced the sensor’s response, leading to superior response and recovery times of 9.1 s and 15.7 s, respectively, along with excellent selectivity, reproducibility, and long-term stability. The nanocomposite sensor exhibited a high sensing response (Rg/Ra) of 26.8 toward 400 ppm ethanol in dry air and demonstrated typical p-type semiconducting behavior. Remarkably, the sensor operated efficiently at room temperature and was capable of detecting ethanol concentrations as low as 50 ppm. In addition, the device maintained stable performance over a 30-day testing period, confirming its durability. The improved sensing characteristics are attributed to the formation of a p-p heterojunction at the SnS/MoSe2 interface, which facilitates effective charge transfer. Furthermore, modulation of the potential barrier at this interface played a key role in enhancing the overall sensitivity of the sensor. Building on the enhanced sensing performance of the SnS/MoSe2 nanocomposite, where the presence of the p-p heterojunction at the SnS-MoSe2 interface was beneficial, a binary nanocomposite system comprising SnS and SnS2 has been further explored to exploit the advantages afforded by p-n heterojunctions. In this paper, a highly stable, selective, and reproducible ethanol gas sensor based on the SnS/SnS2 nanocomposite was successfully fabricated and exhibited excellent long-term operational stability. The sensor showed an outstanding response value of 35.7 toward 500 ppm ethanol gas and could detect ethanol as low as 10 ppm at room temperature. Besides, the device exhibited fast dynamic behavior, including a response time of 6.1 s and a recovery time of 18.3 s for 500 ppm ethanol. The sensor also exhibited excellent stability during a testing period of 40 days. The excellent sensing performance of the SnS/SnS2 nanocomposite could be primarily attributed to the formation of multiple p-n heterojunctions between SnS and SnS2 nanosheets. The intimate interfacial contact between the two phases not only facilitates good charge transfer but also increases the density of active sites available for ethanol adsorption and desorption. This synergistic effect significantly enhances the gas-sensing response, thereby making the developed nanocomposite a promising candidate for high-performance, room-temperature ethanol detection.