Electrochemical Sensing of H2S Gas in Air by Carboxylated Multi-walled Carbon Nanotubes

Abstract

<em>The electrochemical sensor for detecting hydrogen sulfide was fabricated. H₂S gas molecules pass through polytetrafluoroethylene membrane with 0.22 mm pore size. Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were used to fabricate working and counter electrodes. It can be seen from Field Emission Scanning Electron Microscopy (FESEM) images of the working electrode that MWCNTs-COOH is distributed fairly uniform on the hydrophobic membrane. Quantitative results of Energy Dispersive X-ray (EDX) analysis show the presence of carbon (85.95 wt %) and oxygen (12.95 wt %) on the working electrode. The cyclic voltammetry results show the MWCNTs-COOH responds to H₂S. The sensor response up to 56 ppm of H₂S gas was measured by chronoamperometry. The sensor showed linear behavior up to 16 ppm. The detection limit of the sensor is 310 ppb and its sensitivity 48 hours after assembling is 0.1436 µA/ ppm. The averages of response and recovery times for 10 ppm of H₂S were obtained 6.06 and 4.13 minutes respectively. The sensor with functionalized carbon nanotubes has many advantages than the sensor with raw carbon nanotubes; include more uniformity of fabricated electrodes, greater response, and less noise. Using functionalized carbon nanotubes concerning raw nanotubes increases the response of the sensor by 14.8 times at 10 ppm of H₂S.</em> <em>Also, the response of the sensor to 250 ppm concentration of carbon monoxide gas was 4.35 nA which is very low concerning sensor response for hydrogen sulfide (1.64 µA for 10 ppm of H₂S).</em>