Development of carbon nanotubes ionization-based sensor for measuring concentration of ammonia

N.M. Mohamed
Universiti Teknologi PETRONAS, MY

Keywords: aligned multiwalled carbon nanotubes, ionization, breakdown voltage, electrode gap

Summary:

In developing the ionization-based gas sensor, the most important issue to be addressed is lowering the voltage breakdown for safe operation. The approach is to reduce the electrode gap between the electrodes. Further reduction can be obtained by using vertically aligned multiwalled carbon nanotubes (MWCNT) array. The lowest voltage breakdown was 18 V for the 7 µm-electrode gap. The significant reduction is attributed to the narrow gap achieved by controlling the thickness of MWCNT grown. Narrow electrode gap combined with protrusions of nanotips can create a high, non-uniform electric field that produces massive field emission electrons, resulting in ionization of neutral molecules.The ionization rate also depends strongly on the concentration such that it can be used to measure the concentration of ammonia over a wide range. The developed ionization-based sensor using aligned MWCNTs array allows for battery operation with fast response time, good selectivity and sensitivity, and operating over a full range (beyond 1,000 ppm) required to make decision on the appropriate Personal Protective Equipment necessary for proper protection from ammonia. It has an advantage over the electrochemical sensor which has fixed life expectancy and low maximum range and the photoionization detector that requires a replacement lamp and other attachments.