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. 2024 Dec 20;24(24):8154.
doi: 10.3390/s24248154.

Humidity-Activated Ammonia Sensor Based on Carboxylic Functionalized Cross-Linked Hydrogel

Yaping Song  1 , Yihan Xia  1 , Wei Zhang  1 , Yunlong Yu  1 , Yanyu Cui  1 , Lichao Liu  2 , Tong Zhang  1 , Sen Liu  1 , Hongran Zhao  1 , Teng Fei  1
Affiliations

Humidity-Activated Ammonia Sensor Based on Carboxylic Functionalized Cross-Linked Hydrogel

Yaping Song et al. Sensors (Basel). .

Abstract

Owing to its extensive use and intrinsic toxicity, NH3 detection is very crucial. Moisture can cause significant interference in the performance of sensors, and detecting NH3 in high humidity is still a challenge. In this work, a humidity-activated NH3 sensor was prepared by urocanic acid (URA) modifying poly (ethylene glycol) diacrylate (PEGDA) via a thiol-ene click cross-linking reaction. The optimized sensor achieved a response of 70% to 50 ppm NH3 at 80% RH, with a response time of 105.6 s and a recovery time of 346.8 s. The sensor was improved for response and recovery speed. In addition, the prepared sensor showed excellent selectivity to NH3 in high-humidity environments, making it suitable for use in some areas with high humidity all the year round or in high-humidity areas such as the detection of respiratory gas. A detailed investigation of the humidity-activated NH3-sensing mechanism was conducted using complex impedance plot (CIP) measurements.

Keywords: fast recovery; humidity-activated ammonia sensor; urocanic acid.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic diagram for the preparation of NH3 sensors and the structure of monomers.
Figure 2
Figure 2
Response and recovery curves of the (a) S1 sensor, (b) S2 sensor and (c) S3 sensor to NH3 with concentrations of 3 ppm, 5 ppm, 10 ppm, 20 ppm, 30 ppm, 40 ppm, and 50 ppm at 80% RH; the relationship between the impedance modulus and ammonia concentration of the (d) S1 sensor, (e) S2 sensor, and (f) S3 sensor (the red line is the fitted curve of the relationship between impedance modulus and ammonia concentration).
Figure 3
Figure 3
(a) The impedance modulus of the S2 sensor at with and without 50 ppm NH3 in 10–80% RH. (b) The response of the S2 sensor to 50 ppm NH3 in 10–80% RH. (c) The dynamic response curve of the S2 sensor to 50 ppm NH3 at 20% RH, 50% RH, and 80% RH.
Figure 4
Figure 4
Response and recovery curve of S2 sensor upon exposure to 50 ppm NH3 at 80% RH.
Figure 5
Figure 5
Complex impedance plots of S2 sensor without NH3 (gray) or 50 ppm NH3 (red) at (a) 20% RH, (b) 50% RH, and (c) 80% RH.
Figure 6
Figure 6
Proposed conduction mechanisms in the S2 sensor in the presence of humidity and NH3: (a) at low relative humidity (RH), (b) at moderate RH, and (c) at high RH.
Figure 7
Figure 7
(a) The response of the S2 sensor to 10 ppm NH3, CH3OH, CH3COCH3, and C2H4 at 25 °C at 80% RH. (b) The impedance modulus (black) of the S2 sensor at 80% RH and the response (red) of the S2 sensor to 50 ppm NH3 at 80% RH over 15 days.
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