Editorial Feature

Chemical Sensors: Hydrogen Sulfide Gas Detection Sensor

A hydrogen sulfide (H2S) sensor is a gas sensor employed for measuring hydrogen sulfide. This sensor is a metal oxide semiconductor that changes the resistance that is normally produced by desorption and adsorption of hydrogen sulfide in a film.

The film can be a gold thin film or tin oxide film that is sensitive to hydrogen sulfide. The current response time of hydrogen sulfide sensor ranges from 25 ppb to 10 ppm, which is less than 1 minute.

Commonly, an ultra-high sensitive hydrogen sulfide sensor is used currently which employs micromachined nanocrystalline SnO2-Ag.

SnO2–Ag nanocomposite is fabricated by a polymeric sol–gel process, so that the sensor exhibits excellent sensing characteristics upon exposure to H2S of just 1 ppm at temperatures as low as 70°C (158°F). This sensor is less sensitive to gases like C6H14, SO2, HCl, Cl2, etc.

Research

The function of nitric oxide in the redox cell signaling mechanism is widely known. However, the function of another important biological signaling molecule, hydrogen sulfide, is less commonly known.

Accurate measurement of H2S in real time at low micromolar or nanomolar concentrations has been a long-term challenge.

In 2005, researchers from the University of Alabama at Birmingham have developed a novel polarographic H2S sensor that detects rapid changes in concentration of H2S in biological solutions having a detection limit of 10 nm.

This new sensor combines NO and O2 in multi-sensor respirometry. The sensor was found to display high signal specificity to H2S and the potential to provide a continuous record of H2S concentration under biologically relevant conditions, which is difficult to achieve using other existing sensors.

In 2012, Chen et al from the University of California developed genetically encoded fluorescent protein (FP)-based probes for selectively detecting H2S. This research involved taking the genetic codes of mammalian cells and E. coli and manipulating the FP chromophores with the sulfide-reactive azide functional group.

The modified chromophores were reduced by H2S thereby emitting sensitive fluorescence that can be detected by microscopic and spectroscopic methods. Experimental results showed that a circularly permuted FP exhibits faster responses, which makes it feasible for monitoring H2S in living mammalian cells.

Mickelson et al from the University of California at Berkeley proposed a small, inexpensive, selective nanomaterials-based gas sensor in 2012. The sensor employs an on-chip micro-hotplate for heating tungsten oxide nanoparticle network whose conductance was continuously monitored.

The device was heated with short pulses thereby drastically reducing the power consumption without altering the sensor response. The sensor was found to have high sensitivity to hydrogen sulfide. It does not have cross sensitivities to methane, water or hydrogen.

Current Applications

Some of the recent applications of hydrogen sulfide gas sensor include the following:

  • Sewage and water treatment plants
  • Gas turbines
  • Compressor stations
  • Gas storage and loading facilities
  • Battery rooms
  • Parking garages
  • Oil and gas exploration and production
  • Sulfur recovery plants
  • Offshore platforms and drilling rigs
  • Solvent monitoring
  • Sterilizing rooms in hospitals.

Hydrogen Sulfide sensors are  commonly used in offshore operations.

Future Developments

Hydrogen sulfide gas is highly toxic and one among the most common contaminants in natural gas and crude oil. In high concentrations, this gas can cause nausea, unconsciousness and even death. It is still dangerous in lower concentrations resulting in headaches and skin and eye irritations.

The oil and gas industries struggle to detect this deadly substance to save lives, and hence several safety system manufacturers have developed sensor technologies for quickly sensing H2S.

Toxic detection technologies are rapidly advancing. Some fixed-detector technologies like electrochemical sensors, metal oxide semiconductor (MOS) detectors and optical detectors are indeed the current proven detection technologies.

However, the electrochemical detectors are not suitable for high heat and prolonged high or low humidity conditions. In addition, they have to be frequently calibrated to ensure proper functioning.

MOS detectors, on the other hand, are sensitive to high humidity and changes in oxygen levels. The output of the MOS detectors may sometimes drift more than other sensor technologies.

In recent years, manufacturers have enhanced MOS sensors with the addition of nano-films that can be operated at high humidity and temperature ranges. However, choosing an appropriate detection technology based on the environment and conditions is required for an effective gas detection plan.

References

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