Comparison of Optical Ammonia-Sensing Properties of Conducting Polymer Complexes with Polysulfonic Acids

Abstract

Thin films of conducting polymer complexes with polysulfonic acids of various structures were electrochemically deposited onto transparent FTO electrodes. The behavior of the polymer-based optical ammonia vapor sensors in response to various concentrations of ammonia vapors, ranging from 5 to 135 ppm, was investigated, including the response time and response amplitude. It was found that the nature of the conducting polymers (poly (3,4-ethylenedioxythiophene), polypyrrole, polyaniline), as well as the structure of the polyacids, affected the sensing performance of the obtained complexes.

Poly(3,4-ethylenedioxythiophene) Electrosynthesis in the Presence of Mixtures of Flexible-Chain and Rigid-Chain Polyelectrolytes

“…The charter of changes in the electronic absorption spectra for PEDOT-t-PASA film shows significant differences (Figure 6c) from this one for traditional PEDOT films [30][31][32]. The maximum of the characteristic absorption bands of reduced (~500 nm) and polaron fragments (~700 nm) of PEDOT is shifted hypsochromically compared to that for PEDOT films obtained in the presence of PAMPSA and salt forms of all PEs and the mixtures (Table 2).…”

“…All calculate values of the sensor responses for all investigated films are presented in Table 3. The influence of ammonia on the PEDOT films leads to their reduction [30][31][32], as evidenced by an increase in the absorption in the region of the reduced form (450-500 nm) and a decrease in the absorption in the region of polarons (800-850 nm). For the PEDOT films obtained in the presence of PAMPSA, salt forms of PEs and their mixtures, much smaller changes in the absorption are observed than those in the case of PEDOT films with the rigid-chain t-PASA and the PAMPSA/t-PASA mixture (Figure 8a).…”

“…All calculated values of the sensor responses for all investigated films are presented in Table 3. The influence of ammonia on the PEDOT films leads to their reduction [30][31][32], as evidenced by an increase in the absorption in the region of the reduced form (450-500 nm) and a decrease in the absorption in the region of polarons (800-850 nm).…”

“…Further growth in the potential causes an increase in absorption in the NIR region of the spectrum (transition from polaronic to bipolaronic form) [40][41][42][43] and the second isosbestic point (i.p.2) can be observed. In reality, the transitions from the neutral form to the polaronic form and then to the bipolaronic form occur in wider ranges of potential, but optical phenomena occurring during PEDOT doping/dedoping due to changes in the film thickness and its refractive index introduce some uncertainty in the isosbestic points' positions (sometimes called "isosbestic range") [32].…”

“…At the moment, the sensing properties of PEDOT films in relation to ammonia have been insufficiently studied [21,[27][28][29][30][31][32], despite their high sensitivity to the effect of a reducing gas (a wide range of changes in resistance and optical density at a certain wavelength). Most often, optical sensors based on the films cast from commercially available chemically synthesized water dispersion of PEDOT:PSS are used [28][29][30][31].…”