Detection of carbon dioxide (CO2) is very important for environmental, health, safety, and space applications. Carbon dioxide is a harmful pollutant at higher concentrations due to its ability to displace oxygen in large concentrations. Current commercial sensors for CO2 have issues and shortcomings, particularly with precision at different temperatures, pressures, and high humidity levels. NASA Ames has developed a patent-pending solid-state sensor configured for detection of CO2 having a concentration within the range of about 100 parts per million (ppm) and 10,000 ppm in both dry conditions and high-humidity conditions.
The solid-state sensor achieves detection of high concentrations of CO2 without saturation and in both dynamic flow mode and static diffusion mode conditions. The composite sensing material comprises oxidized multi-walled carbon nanotubes (O-MWCNT) and a metal oxide; for example, O-MWCNT and iron oxide (Fe2O3) nanoparticles. The composite sensing material has an inherent resistance and corresponding conductivity that is chemically modulated as the level of CO2 increases.
The CO2 gas molecules absorbed into the carbon nanotube composites cause charge-transfer and changes in the conductive pathway such that the conductivity of the composite sensing material is changed. This change in conductivity provides a sensor response for the CO2 detection. The sensor is well suited for automated manufacturing using robotics and software-controlled operations.
The sensor does not utilize consumable components or materials and does not require calibration as often as conventional CO2 sensors. Since the technology can be easily integrated into existing programmable electronic systems or hardware systems, the calibration of the sensor can be automated. The sensor can be easily integrated into existing electronic circuitry and hardware configurations including the hardware of a mobile computing device such as a smartphone or tablet device.