Role and impact of differently charged polypyrrole on formaldehyde sensing behavior

- A negatively charged polypyrrole shows the highest sensitivity and selectivity for formaldehyde.
- A polaron peak in UV spectrum of PPy− is invisible with exposed to formaldehyde.
- The PPy− form is a potential sensing material for formaldehyde biomarker detection.

Structural and electronic properties of polypyrrole in neutral (nPy), cationic (nPy+), and anionic (nPy−) states exposed to formaldehyde were studied using density functional theory (DFT) and time dependent-DFT (TD-DFT) methods The strongest adsorption energy was found for nPy− with a greater change in conductive property than other states. For optical analysis, polaron band simulated in UV-VIS-NIR spectrum of nPy− was vanished upon sensing with formaldehyde, corresponding to electron transferred from polaron state of nPy− to adsorbed molecule. In contrast, the π → polaron bands of nPy+ complexes were all blue-shifted. With respected to human exhaled breath, interferences of carbon dioxide and humidity were studied, showing a minor contribution in terms of conductive properties. Our results revealed that negatively charged polypyrrole is a potential state of polypyrrole for formaldehyde measurement.

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