Poly (5-Carboxyindole)–β-Cyclodextrin Composite Material for Enhanced Formaldehyde Gas Sensing

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Journal of Materials Science

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Formaldehyde, a compound commonly employed in many construction materials, paints, and plastics, has been linked to deleterious health effects. Thus, monitoring the presence of formaldehyde in interior locations is increasingly important when it comes to public health. Currently, there is a crucial need for a low-cost, small-scale, selective, and sensitive indoor sensor capable of real-time formaldehyde detection. To meet these performance metrics, materials need to be incorporated onto existing gas sensor platforms to act as chemically selective recognition layers. A main challenge when addressing this issue is creating a material that can remain easily processable, can be easily synthesized, and can operate in practical environments (i.e., at common temperatures, humidity values, and in the presence of distractant analytes). Here, we show the unique properties of poly(5-carboxyindole) (P5C), an easily synthesized polymer, for practical indoor air monitoring of formaldehyde gas at concentrations as low as 25 ppm with rapid response and recovery times characterized by time constants of 27 s and 16 s, respectively. Importantly, we demonstrate that β-cyclodextrin (BCD), when blended into P5C to create a poly(5-carboxyindole) with β-cyclodextrin composite (P5C–BCD), offers distinct properties that enhance the response to formaldehyde gas in common operational conditions. Specifically, BCD adds features into the P5C such as its ability to form strong host–guest interactions with formaldehyde, its ability to buffer P5C protonation states to allow for more protonated carboxylic acid moieties on P5C which can hydrogen bond more effectively with formaldehyde, as well as creating a cylindrical morphology with the polymer film to assist the diffusion of formaldehyde into the polymer matrix. Additionally, these materials provide for chemically selective adsorption to formaldehyde gas in environments where interfering analytes exist. Due to the practical advantages these materials offer, they have the potential to unlock new avenues for future formaldehyde sensor materials.


Journal of Materials Science, Vol. 57, No. 24 (June 2022): 11460-11474. DOI.