Feasibility of using spiral MWCNT-COOH@DBSA-PANI to measure ammonia concentration and non-contact gap

A single spiral sensing unit based on carboxylated multi-walled carbon nanotubes composite dodecylbenzene sulfonic acid-doped polyaniline (MWCNT-COOH@DBSA-PANI) is shown in this research to be capable of detecting both NH 3 concentration and non-contact gap. The sensing unit effectively detects NH 3 concentrations (0–50 ppm) and non-contact gap (0–5 mm), showing a 46.740 % relative change in resistance at 20 ppm NH 3 and superior selectivity (greater relative change in resistance/impedance amplitude/impedance angle to NH 3 than to HCHO/DMF/ethanol/n-hexane). Additionally, within the non-contact gap range of 0–5 mm, it achieves impedance amplitude/angle sensitivity of 1.5652 %/mm (NH 3 : 50 ppm) and 2.2110 %/mm (NH 3 : 0 ppm), respectively. Stability test over 30 days shows relative standard deviations (RSD) of relative change in resistance, impedance amplitude and impedance angle to NH 3 remain below 10.7 %, 9.6 %, and 8.4 %, respectively. Furthermore, the RSD values for its impedance amplitude/angle sensitivity to gap (0–5 mm) do not exceed 8.0 %/7.6 %, correspondingly. When humidity increases from 31 % RH to 75 % RH, the relative change in resistance to 20 ppm NH 3 decreases from 46.740 % to 40.248 %. Finally, by employing the variable separation strategy, the feasibility of dual-function detection is further validated. At a known humidity, NH 3 concentration is determined by the relative change in resistance of sensing unit to NH 3 adsorption. Gap variation is perceived by detecting electromagnetic field disturbances from an approaching target object, manifested as change in the impedance amplitude/angle of the sensing unit. The work establishes a methodological foundation for environmental safety monitoring in confined spaces and real-time operational safety of precision equipment.