Abstract
Polypyrrole (PPy) nanorods (NRs) and nanoparticles (NPs) are synthesized via electrochemical and chemical methods, respectively, and tested upon ammonia exposure using Raman and X-ray photoelectron spectroscopy (XPS). Characterization of both nanomaterials via Raman spectroscopy demonstrates the formation of PPy, displaying vibration bands consistent with the literature. Additionally, XPS reveals the presence of neutral PPy species as major components in PPy NRs and PPy NPs, and other species including polarons and bipolarons. Raman and XPS analysis after ammonia exposure show changes in the physical/chemical properties of PPy, confirming the potential of both samples for ammonia sensing. Results demonstrate that the electrochemically synthesized NRs involve both proton and electron transfer mechanisms during ammonia exposure, as opposed to the chemically synthesized NPs, which show a mechanism dominated by electron transfer. Thus, the different detection mechanisms in PPy NRs and PPy NPs appear to be connected to the particular morphological and chemical composition of each film. These results contribute to elucidate the mechanisms involved in ammonia detection and the influence of the synthesis routes and the physical/chemical characteristics of PPy.
Highlights
Nanomaterials belong to one of the most active research areas of science and technology due to their size dependant properties, which are beneficial in different applications including medicine, environment, energy and various industries
Polarons form upon oxidation, when a π-electron is removed from the neutral PPy chain, whereas bipolarons appear upon further oxidation, when a second electron is removed from the PPy chain[25]
Raman facilitates the analysis of the intermolecular interactions and X-ray photoelectron spectroscopy (XPS) provides a semi-quantitative analysis of surface chemical composition
Summary
Nanomaterials belong to one of the most active research areas of science and technology due to their size dependant properties, which are beneficial in different applications including medicine, environment, energy and various industries. Electrical, and mechanical properties of PPy originate from its hetero-atomic and conjugated backbone structure (σ and π bonds)[11], which contains polarons and/or bipolarons These are oxidized states of PPy, associated with intermediate energy levels arose within the electronic band gap region of the polymer due to oxidation[24]). The sensing properties of PPy are influenced in part by its morphology as well as its oxidation level, which is readily affected by chemical or electrochemical doping/de-doping (oxidation/reduction) mechanisms during the exposure of PPy to the gas analyte. Spectroscopy techniques such as Raman and X-ray photoelectron spectroscopy (XPS) allow for the characterization of these chemical or electrochemical properties. Here we get an insight using spectroscopy techniques such as Raman and XPS into the dominant gas detection mechanisms of PPy NRs and PPy NPs synthesized electrochemically and chemically, respectively, towards ammonia as a model gas molecule
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