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Industrial Expansion and Advancement in Electrochemical Sensors
Industrial Expansion and Advancement in Electrochemical Sensors

The ongoing growth of contemporary industries has led to poor air quality, especially in cities and in places of employment, which is a major threat to people's quality of life generally. The World Health Organization (WHO) estimates that air pollution causes seven million deaths yearly, and 91% of the world's population lives in locations where air quality is above acceptable levels.

For the benefit of human health, city planners and governments must comprehend the causes of urban air pollution. Nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter from burning biomass and fossil fuels are the most common air pollutants in metropolitan areas.


Hydrogen sulfide (H2S) is easily inhaled, it can have a rapid negative impact on human health. H2S is typically found in sewer systems or around decomposing organic materials. Due to its extensive use in agriculture and as a catalyst to lower NOx emissions from automobiles, ammonia has recently gained attention.

Volatile Organic Compounds

Health hazards are associated with volatile organic compounds (VOCs), especially aromatic chemicals including benzene, toluene, ethylbenzene, and xylene (BTEX). In the past, commercial gas sensors had difficulty detecting benzene concentrations below 100 parts per billion (ppb), which is only ten times lower than the permitted exposure limit.

EPA Environmental Monitoring

Monitoring pollutants at several sites in order to pinpoint their sources and create efficient mitigation plans is the first stage in reducing ambient air pollution. The EPA's air quality monitoring roadmap indicates that although accurate analytical tools such as mass spectrometers and infrared spectroscopy are available, their cost makes them unfeasible for broad use in fast expanding cities.

Thus, the development of robust and reasonably priced sensors is crucial for large-scale air quality monitoring. A variety of electrochemical sensors have been created, especially amperometric sensors, which provide a current response when exposed to analyte gasses. In the commercial industry, amperometric sensors are preferred because of their linear response to increasing gas concentrations. Toxic gases are normally detected in the parts per million (ppm) range, however recent improvements have allowed for detection as low as parts per billion (ppb).

Many of these amperometric sensors have been tried for real-time air quality monitoring in recent research conducted in the United States and Europe.
Furthermore, there has been promise in the detection of gases at very low concentrations using chemiresistive sensors, which identify dangerous chemicals by monitoring notable changes in resistance upon exposure. These developments in sensor technology are essential for widespread and successful air quality monitoring programs.

Electrochemical Sensors for NOx, SOx, and H2S

The allowable limit of nitrogen dioxide (NO2) exposure, as defined by the Environmental Protection Agency (EPA), is 100 parts per billion (ppb) for an hour and 53 ppb on an annual average. The European Commission, on the other hand, recommends a lower figure of 21 ppb over a year. This suggests that NOx sensors that can identify NO2 at ppb levels—much lower concentrations—are necessary.

Chemiresistive sensors, which are electrochemical sensors, have demonstrated the ability to detect NOx concentrations at the necessary levels for environmental monitoring. These sensors are based on graphene and its derivatives.
One example is single-layer graphene grown on silicon carbide (SiC), which responds linearly to NO2 in the 10–150 ppb range and responds 20% at 10 ppb of NO2. Metal or metal oxide nanoparticles are deposited atop reduced graphene oxide (rGO) to increase sensitivity. Pd and SnO2 nanoparticles on rGO, for instance, have a linear response in the range of 50–2000 ppb and can detect 50 ppb of NO2 with a 25% resistance change. In a similar vein, adding an In2O3-based NOx sensor to rGO makes it seven times more sensitive.

Though it hasn't been documented, the possible effect of metal or metal oxide nanoparticles on single-layer graphene at even lower NOx concentrations has the potential to greatly improve NOx detection.

Sensors for Sulphur

The EPA standard for sulfur dioxide (SO2) permits up to 75 parts per billion (ppb) over an hour. To detect SO2, researchers have investigated a variety of sensing techniques. One technique is layer-by-layer assembly of rGO and titanium dioxide (TiO2), which is effective in sensing SO2 in the 1 ppb to 5 ppm range. In this instance, SO2 adsorption results in a decrease in resistivity. In the TiO2/rGO hybrid, TiO2 reacts with SO2 gas to generate SO3, which lowers resistance and increases electron concentration. A growing recovery period is a problem at higher SO2 concentrations.

As an alternative, a sensor that use ruthenium on alumina (Ru/Al2O3) coated on zinc oxide (ZnO) breaks down SO2 into detectable SO• radicals, which are then detected through adsorption and a change in resistivity. The reaction between SO• and negatively charged adsorbed O2 is responsible for the electron donation to the ZnO substrate, which results in the decrease in resistance.

Among the many frequent interfering gases, the Ru/Al2O3/ZnO sensors demonstrate an outstanding degree of selectivity for detecting sulfur dioxide (SO2). It's crucial to remember that the study did not test for selectivity against ammonia (NH3) and nitrogen dioxide (NO2). The stated linear detection range of this sensor, which ranges from 5 parts per million (ppm) to 115 ppm, may not be sufficient for environmental monitoring even with its selectivity.

https://www.sciencedirect.com/topics/materials-science/electrochemical-sensor#:~:text=Electrochemical%20sensors%20detect%20the%20electrochemical,based%20on%20amperometry%2C%20potentiometry%20and

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