In situ chemical deposition of PPy/NDSA and PPy/DBSA layers on QCM electrodes: synthesis, structural, morphological and ammonia sensing performances study
Aiming to detect ammonia vapor, polypyrrole (PPy) thin layers were in situ coated on AT-cut 10 MHz quartz crystal microbalance QCM electrode by a facile chemical polymerization process using two organic acids as dopants, i.e. dodecylbenzene sulfonic acid (BDSA) and 1–5 naphthalene disulfonic acid (NDSA). Then after, polymers structural and morphological features were determined by FTIR, Raman spectroscopy and Scanning Electron Microscopy (SEM) techniques. Ammonia vapor sensing tests were related to QCM frequency changes recorded upon vapor adsorption and desorption on PPy films, it was found that frequency shifts varied linearly with both vapor concentration expressed in part per million (ppm) and polymer’s thin layer thickness given in nanometer (nm). This fact has been assumed to be mainly related to the electrostatic interactions established between ammonia vapor molecules and the polymer dopant agents. Tests have shown that films based PPy/NDSA exhibit high sensitivity around 3 ppm and detection limit of 4 ppm over films based PPy/DBSA. Interestingly, an excellent recovery time less than 3 min has been also recorded with PPy/NDSA thin layers. Moreover, when applying Fick’s second law, they have also shown a high diffusion constant.
KeywordsPolypyrrole Organic acids dopant (NDSA/DBSA) Ammonia sensing QCM sensors Gas diffusion constant
Authors are grateful to both of Military Polytechnic School and Université Hassiba Ben Bouali Chlef, Algeria, for financial support granted to the preparation of B. Mettai PhD thesis under the project number 55 Dept. GP/CSD/2015. The thankfulness is also extended to Macromolecular Chemistry Laboratory member’s, for their precious contribution and insightful discussions. The National Institute for Criminality is acknowledged for providing the assistance with FTIR, Raman and SEM measurements.
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