Conductive polymers, such as polyaniline (PANI), Polythiophene (PTh), polypyrrole (PPy), etc., are widely used for gas sensors due to their excellent electrical conductivity and low cost to manufacture [1]. In particular, PANI has attracted more attention due to its ease of synthesis, high environmental stability, and high reactivity with ammonia gas. In addition, the selection of acid-base dopant during the preparation process of polyaniline can adjust carrier concentrations for the change in electrical conduction or resistance to improve sensing properties. There have been many reports on the fabrication of flexible gas sensors using PANI [2-4]. Bandgar et al. [5] synthesized a low-temperature flexible polyaniline gas sensor by in-situ chemical oxidation polymerization of aniline on a polyethylene terephthalate (PET) substrate, showing 99% reproducibility, rapid response and recovery. Still, the response value was only 26% in 100 ppm ammonia atmosphere. Qi et al. [6] prepared a gas sensor by in-situ polymerization of aniline on non-woven fabric. The high air permeability of the fabric effectively improved the performance of the polyaniline-based gas sensor. Due to the outbreak of the COVID-19 pandemic, the use of face masks in public has become essential to reduce the spread of the virus. Some reports claim that the increased carbon dioxide in the mask over time may cause medical issues related to the respiratory system. Therefore, monitoring breathing air quality can help detect the wearer's vital conditions.

In this study, we used a disposable mask as a flexible substrate to prepare polypropylene/carbon nanotube/polyaniline composite film through a layer-by-layer method. The polypropylene/carbon nanotube composite films were prepared by applying the carbon nanotube aqueous solution with surfactants evenly on the surface of a mask filter layer by a drop-coating method. Then, the in-situ polyaniline polymerization was performed on the surface of the polypropylene/carbon nanotube composite film through ammonium sulfate. The polypropylene/carbon nanotube /polyaniline composite film exhibits high sensitivity, fast sensing response/recovery time, room temperature operation, reliable flexibility, and cycle stability. The synthesized and wearable masks have demonstrated real-time detection respiratory rate and other breathing conditions such as CO2 and humidity. The ammonia gas sensing can also be used as a potential biomarker for health screening. The design and integration of multiple gas sensing materials in masks will help wearers better understand their own body conditions.

References

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[2] T.F. Wu, E. Gray, B.Q. Chen, A self-healing, adaptive and conductive polymer composite ink for 3D printing of gas sensors, J Mater Chem C, 6(2018) 6200-7.

[3] D.Z. Zhang, Z.L. Wu, X.Q. Zong, et al., Flexible and highly sensitive H₂S gas sensor based on in-situ polymerized SnO₂/rGO/PANI ternary nanocomposite with application in halitosis diagnosis, Sensor Actuators B: Chem, 289(2019) 32-41.

[4] C.H. Liu, H.L. Tai, P. Zhang, Z. Yuan, X.S. Du, G.Z. Xie, et al., A high-performance flexible gas sensor based on self-assembled PANI-CeO₂ nanocomposite thin film for trace-level NH3 detection at room temperature, Sensor Actuators B: Chem, 261(2018) 587-97.

[5] D.K. Bandgar, S.T. Navale, S.R. Nalage, R.S. Mane, F.J. Stadler, D.K. Aswal, et al., Simple and low-temperature polyaniline-based flexible ammonia sensor: a step towards laboratory synthesis to economical device design, J Mater Chem C, 3(2015) 9461-8.

[6] J. Qi, X. Xu, X. Liu, K.T. Lau, Fabrication of textile based conductometric polyaniline gas sensor, Sensors and Actuators B: Chemical, 202(2014) 732-40.