Air quality is a growing concern in today’s world, especially in urban areas and workplaces. Whereas the continuous expansion of industries has led to poor air quality. While this deterioration in air quality has serious implications for human health, with an estimated seven million deaths annually attributed to air pollution. Alarmingly, 91% of the global population resides in areas that exceed the air quality limits established by the World Health Organization (WHO). To combat this issue, it is crucial to understand the sources of urban air pollution and its impact on health. However, to use modern nanotechnology for making electrochemical sensors to analyze air pollutants.
The most common air pollutants in urban environments include nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter from fossil fuel and biomass combustion. Whereas hydrogen sulfide (H₂S) from decaying organic matter and ammonia from industrial and automotive sources. Monitoring these pollutants is essential for identifying their sources and implementing effective mitigation strategies. While precise analytical devices like mass spectrometers and infrared spectroscopy exist, their high cost limits widespread deployment in growing cities. Affordable and reliable sensors are the solution to this problem, and electrochemical sensors have emerged as a promising technology.
Amperometric sensors
Amperometric sensors, which produce a current response when exposed to gases, have been widely adopted in the commercial market. They offer a linear response to gas concentrations, typically detecting toxic gases. The range is 1 to 10,000 parts per million (ppm), with recent advancements enabling detection at parts per billion (ppb) levels. Recent studies in Europe and the United States have tested these amperometric sensors for real-time air quality monitoring.
Additionally, chemiresistive sensors, which measure changes in resistance upon gas exposure, have shown potential for detecting gases at very low concentrations. These technological advancements are crucial for effective and widespread air quality monitoring efforts. Electrochemical sensors have been developed for various gases. These include nitrogen oxides (NOₓ), sulfur dioxide (SO₂), hydrogen sulfide (H₂S), ammonia (NH₃), and volatile organic compounds (VOCs).
NOx, SO₂, and H₂S Sensors
The Environmental Protection Agency (EPA) has set strict standards for acceptable exposure levels of NOx and SO₂. Chemiresistive sensors based on graphene and its derivatives have demonstrated potential in measuring NOx concentrations at the required ppb levels for environmental monitoring. These sensors can be further enhanced by depositing metal or metal oxide nanoparticles on graphene, resulting in improved sensitivity.
For SO₂ detection, sensors based on a layer-by-layer assembly of titanium dioxide (TiO₂) and reduced graphene oxide (rGO) have shown promise. Because an alternative approach involves ruthenium on alumina (Ru/Al₂O₃) deposited on zinc oxide (ZnO), which detects SO₂ by breaking it into detectable SO₂ radicals.
Ammonia
Ammonia and volatile organic compounds (VOCs) pose significant threats to air quality due to their industrial use. However, chemiresistive sensors employing materials like Ag/ZnO composites and MoS₂/ZnO have demonstrated excellent selectivity for ammonia detection in the range of 10 ppm to 100 ppm, even at room temperature. Conducting polymers doped with metal oxides, such as PANI-CeO₂ composites, have shown sensitivity to ammonia from 16 ppb to 50 ppm. Doping agents like hexachlorocyclotriphosphazene (HCHA) have been effective in lowering detection limits for ammonia sensors.
VOC Detection
Monitoring VOCs is a significant challenge, and traditional methods were expensive. However, mixed potential electrochemical sensors (MPES) with La₀.₈Sr₀.₂CrO₃ sensing electrodes have been developed to detect BTEX compounds (benzene, toluene, ethylbenzene, and xylene) down to 0.5 ppm, surpassing previous electrodes. Selectivity among different BTEX constituents remains a challenge, as their toxicity levels can vary significantly.
The expansion of industries has led to poor air quality, impacting human health and necessitating effective air quality monitoring. Electrochemical sensors, including amperometric and chemiresistive sensors, have emerged as affordable and reliable solutions. They offer sensitivity to ppb-level concentrations of various gases, addressing the challenges associated with urban air pollution. These sensors play a main role in monitoring air quality and identifying pollution sources. While implementing mitigation strategies, ultimately contributing to a healthier environment.
The sensor industry has come a long way and is expected to continue growing, with a focus on biosensors. While smart chemical sensors for applications in automotive, environmental monitoring, industrial settings, and IoT-based smart homes. These advancements in sensor technology are crucial for safeguarding human health. However, the environment is in the face of worsening air quality in urban areas.