Figure - available from: Journal of Solid State Electrochemistry
This content is subject to copyright. Terms and conditions apply.
Raman spectra of polyaniline layer at a gold electrode, as obtained in pH 2.0 solution at electrode potential of 0.0 V with different wavelengths of laser line excitation (as indicated)
Source publication
A comparative Raman spectroelectrochemical study on polyaniline electrodeposited at a gold electrode was performed within the broad range of spectra excitation wavelengths from UV (325 nm) through blue (442 nm), green (532 nm), red (633 nm) to NIR (785 nm) laser lines. Two solutions of pH 2.0 and 8.0 were selected for protonated and deprotonated fo...
Citations
... The structure, electrical properties, intermediates produced, and sensitive C-C vibrations of the polymer chain are investigated using RRS. The RRS of PANI hydrochloride films, and other doped PAni, as well as its basic forms, with different laser wavelengths and laser strengths, is documented in the literature [15,16]. The sample exhibits several peaks for phenazine-like cross-linkage vibrations, radical segment vibrations, polaron vibrations, and benzenoid and quinoid unit vibrations, along with other polymer chain vibrations with lower laser power at 638 nm laser wavelength. ...
Background
Polymeric nanocomposites containing metal oxides are of interest to researchers because these materials show hybrid properties that are generated from both components. Due to the control and design of structural properties at the nanoscale scale, they have specialized properties for a range of applications. Researchers have tried to improve the desirable characteristics and thus increase their application by reinforcing them with nanoscale materials to provide them with better properties than conventional micro composites.
Objective
In our present work we have used 5-sulphosalicylic acid doped polyaniline-γ-Fe2O3 composite (Fe-SPAni) to detect explosives using fluorescence quenching method. Along with ease of synthesis and low cost, Fe-SPAni possesses a variable oxidation state which is important for trace detection of the analytes.
Methods
We used the fluorophore Fe-SPAni to detect High Energy Materials (HEMs) using the fluorescence quenching approach, which is still difficult to achieve. UV-Vis spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM/EDAX) were used to determine the molecular structure of the Fe-SPAni composite produced by oxidative chemical polymerization; CV studies were performed to investigate the electrochemical properties. HEMs such as dinitrobenzene (DNB), pentaerythritol tetranitrate (PETN), trinitrotoulene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and hexanitrohexaazaisowurtzitane(CL-20) were used as quenchers.The fluorescence quenching process was determined using the Stern-Volmer graph.
Results
The Stern-Volmer(S-V) plot and limit of detection (LOD) data showed that PETN had the greatest results for the quenching constant value (Ksv) (Ksv =1.33 x 106 M-1 and 1.4x 10-6M, respectively).
Conclusion
The research points to Fe-SPAni as a promising contender for sensing explosives.
... Emeraldine appears blue when in the form of a base [7][8][9]. The different oxidation states of PANI may be modified through the processes of protonation and deprotonation [10][11][12]. Therefore, the oxidation states of PANI could be affected by changes in pH, leading to a colour change in PANI, thus making it a suitable colourimetric pH sensor [13]. ...
Intrinsically conducting polymers (ICPs) have been widely studied in various applications, such as sensors, tissue engineering, drug delivery, and semiconductors. Specifically, polyaniline (PANI) stands out in food industry applications due to its advantageous reversible redox properties, electrical conductivity, and simple modification. The rising concerns about food safety and security have encouraged the development of PANI as an antioxidant, antimicrobial agent, food freshness indicator, and electronic nose. At the same time, it plays an important role in food safety control to ensure the quality of food. This study reviews the emerging applications of PANI in the food industry. It has been found that the versatile applications of PANI allow the advancement of modern active and intelligent food packaging and better food quality monitoring systems.
... Due to its high electrical conductivity, biocompatibility, low toxicity, and good environmental stability, polyaniline (PANI) is one of the most studied conducting polymers [13]. Three redox forms of polyaniline are usually distinguished: leucoemeraldine (reduced), emeraldine (half-oxidized), and pernigraniline (fully oxidized), differing in color and electrical conductivity [14,15]. Traditionally, PANI layers are designed onto various substrates by electrochemical treatment in acidic solutions containing aniline. ...
... Resonance Raman spectroscopy provides rich molecular level information on the structure, oxidation and protonation states of polyaniline (PANI) [14,[40][41][42][43][44]. Figure 4 compares 632.8-nm excited Raman spectra of Ti/TiOx/PANI and Ti/TiO2/PANI samples. Two strong bands at 1169 and 1589 cm −1 belong to C−H bending and C=C stretching vibrations of quinone rings, respectively, whereas the broad feature at 1487 cm −1 is associated with C=N stretching vibration of an emeraldine base (imine sites) [14,40]. ...
... Resonance Raman spectroscopy provides rich molecular level information on the structure, oxidation and protonation states of polyaniline (PANI) [14,[40][41][42][43][44]. Figure 4 compares 632.8-nm excited Raman spectra of Ti/TiOx/PANI and Ti/TiO2/PANI samples. Two strong bands at 1169 and 1589 cm −1 belong to C−H bending and C=C stretching vibrations of quinone rings, respectively, whereas the broad feature at 1487 cm −1 is associated with C=N stretching vibration of an emeraldine base (imine sites) [14,40]. The shoulder near 1618 cm −1 is related to the stretching vibration of the benzene ring. ...
The fabrication of nanostructured composite materials is an active field of materials chemistry. However, the ensembles of nanostructured titanium monoxide and suboxide species decorated with polyaniline (PANI) species have not been deeply investigated up to now. In this study, such composites were formed on both hydrothermally oxidized and anodized Ti substrates via oxidative polymerization of aniline. In this way, highly porous nanotube-shaped titanium dioxide (TiO2) and nano leaflet-shaped titanium monoxide (TiOx) species films loaded with electrically conductive PANI in an emeraldine salt form were designed. Apart from compositional and structural characterization with Field Emission Scanning Electron Microscopy (FESEM) and Raman techniques, the electrochemical properties were identified for each layer using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Based on the experimentally determined EIS parameters, it is envisaged that TiO-based nanomaterials decorated with PANI could find prospective applications in supercapacitors and biosensing.
... The Raman spectra of PAni, PAni-CNT, and GA@PAni-CNT are compared in Figure 1b. From the spectra, the in-plane C-H contribution of quinoid and benzenoid rings, the C-N stretching vibration, and the C=C stretching vibrations of quinoid and benzene rings for both PAni and PAni-CNT are clearly seen at wavenumbers ~1166, ~1254, ~1335, ~1488, and ~1592 cm −1 , respectively [49,50]. Consistent with the UV-visible spectroscopy results, the mild blueshift of the quinoid stretching vibration of PAni-CNT was due to the weaker interactions between PAni and CNT, indicating a smaller charge carrier ability of PAni-CNT than that of pure PAni [51,52]. ...
... The Raman spectra of PAni, PAni-CNT, and GA@PAni-CNT are compared in Figure 1b. From the spectra, the in-plane C-H contribution of quinoid and benzenoid rings, the C-N stretching vibration, and the C=C stretching vibrations of quinoid and benzene rings for both PAni and PAni-CNT are clearly seen at wavenumbers~1166,~1254,~1335,~1488, and~1592 cm −1 , respectively [49,50]. Consistent with the UV-visible spectroscopy results, the mild blueshift of the quinoid stretching vibration of PAni-CNT was due to the weaker interactions between PAni and CNT, indicating a smaller charge carrier ability of PAni-CNT than that of pure PAni [51,52]. ...
Significant agricultural and industrial activities necessitate the regular monitoring of
nitrate (NO3−) ions levels in feed and groundwater. The current comparative study discloses an innovative user-friendly electrochemical approach for the determination of NO3− over polyaniline (PAni)-based modified electrodes. The electrochemical sensors concocted with PAni, multi-walled carbon nanotubes (CNT), and gum arabic (GA). The unique electrode material GA@PAni-CNT was synthesized by facile one-pot catalytic polymerization of aniline (Ani) with FeCl3/H2O2 in the presence of CNT and GA as integral components. As revealed by cyclic voltammetry (CV), the anchoring/retention of NO3− followed by reduction is proposed to occur when a GA@PAniCNT electrode is immersed in phosphate buffer electrolyte containing NO3− that eventually results
in a significantly higher redox activity of the GA@PAni-CNT electrode upon potential scan. The mechanism of NO3− anchoring may be associated with the non-redox transition of leucomeraldine salt (LS) into emeraldine salt (ES) and the generation of nitrite (NO2−) ions. As a result, the oxidation current produced by CV for redox transition of ES to pernigraniline (PN) was ~9 times of that obtained with GA@PAni-CNT electrode and phosphate buffer electrolyte, thus achieving indirect NO3− voltammetric determination of the GA@PAni-CNT electrode. The prepared GA@PAni-CNT electrode displayed a higher charge transfer ability as compared to that of PAni-CNT and PAni electrodes. The optimum square wave voltammetric (SWV) response resulted in two linear concentration ranges of 1–10 (R2 = 0.9995) and 15–50 µM (R2 = 0.9988) with a detection limit of 0.42 µM, which is significantly lower. The GA@PAni-CNT electrode demonstrated the best detection, sensitivity, and performance among the investigated electrodes for indirect voltammetric determination of NO3− that portrayed the possibility of utilizing GA—stabilized PAni and CNT nanocomposite materials in additional electrochemical sensing applications.
Citation: Kosa, S.A.M.; Khan, A.N.; Ahmed, S.; Aslam, M.; Bawazir, W.A.; Hameed, A.; Soomro, M.T. Strategic Electrochemical Determination of Nitrate over Polyaniline/Multi-Walled Carbon Nanotubes-Gum Arabic Architecture. Nanomaterials 2022, 12, 3542. https://doi.org/10.3390/nano12193542
... The functionality of PANI can be different by doping with different acids and has many applications. The electrical conductivity of the polymer also varies according to the degree of oxidation by doping and protonation 13 . PANI has different structures which have different physical and chemical properties. ...
... Imine positions in the open form of emeraldine are easily protonated by doping. This trait leads to a significant increase in conductivity and the formation of positive charges in the polymer network 13 . This, while the number of electrons in the polymer structure remains constant. ...
Over the last decade, nanotechnology and nanomaterials have attracted enormous interest due to the rising number of their applications in solar cells. A fascinating strategy to increase the efficiency of organic solar cells is the use of tailor-designed buffer layers to improve the charge transport process. High-efficiency bulk heterojunction (BHJ) solar cells have been obtained by introducing hollow core polyaniline (PANI) nanofibers as a buffer layer. An improved power conversion efficiency in polymer solar cells (PSCs) was demonstrated through the incorporation of electrospun hollow core PANI nanofibers positioned between the active layer and the electrode. PANI hollow nanofibers improved buffer layer structural properties, enhanced optical absorption, and induced a more balanced charge transfer process. Solar cell photovoltaic parameters also showed higher open-circuit voltage (+ 40.3%) and higher power conversion efficiency (+ 48.5%) than conventional architecture BHJ solar cells. Furthermore, the photovoltaic cell developed achieved the highest reported efficiency value ever reached for an electrospun fiber-based solar cell (PCE = 6.85%). Our results indicated that PANI hollow core nanostructures may be considered an effective material for high-performance PSCs and potentially applicable to other fields, such as fuel cells and sensors.
... Raman spectroscopy is a valuable analytical tool for further elucidating the surface structure of the synthesized Cys-PANi@FAU-50 composite ( Fig. 2(d)). The bands at around 1588 and 1472 cm − 1 are attributed respectively to the C--C and C--N vibrations, reflecting the formation of PANi emeraldine form (Mažeikienė et al., 2019). The peak near 1331 cm − 1 corresponds to the C-N +• stretching vibration of delocalized polaronic charges on the PANi chains, which is characteristic of the protonated imine groups of Cys-PANi (emeraldine salt form) (Mažeikienė et al., 2019). ...
... The bands at around 1588 and 1472 cm − 1 are attributed respectively to the C--C and C--N vibrations, reflecting the formation of PANi emeraldine form (Mažeikienė et al., 2019). The peak near 1331 cm − 1 corresponds to the C-N +• stretching vibration of delocalized polaronic charges on the PANi chains, which is characteristic of the protonated imine groups of Cys-PANi (emeraldine salt form) (Mažeikienė et al., 2019). The bands at 1216, 1163 and 774 cm − 1 , due to C-N stretching of amine groups, C-H bending in benzenoid units and deformation of quinoid units, further confirm the successful deposition of the PANi emeraldine salt (Mažeikienė et al., 2019). ...
... The peak near 1331 cm − 1 corresponds to the C-N +• stretching vibration of delocalized polaronic charges on the PANi chains, which is characteristic of the protonated imine groups of Cys-PANi (emeraldine salt form) (Mažeikienė et al., 2019). The bands at 1216, 1163 and 774 cm − 1 , due to C-N stretching of amine groups, C-H bending in benzenoid units and deformation of quinoid units, further confirm the successful deposition of the PANi emeraldine salt (Mažeikienė et al., 2019). The peak located at 941 cm − 1 is characteristic of the S-H bending mode of cysteine (Bazylewski et al., 2017). ...
Nowadays, the global spreading of hazardous heavy metals becomes a top-priority environmental challenge, owing to its serious detrimental health outcomes. Herein, a novel cysteine-doped polyaniline@faujasite hybrid composite (Cys-PANi@FAU) was synthesized via a facile in-situ polymerization route for the effective detoxification of Cr(VI)-bearing wastewaters. The Cys-PANi@FAU-50 composite displayed an open mesoporous structure richly decorated with nitrogen/oxygen-containing functional groups, which consequently boosted the diffusion, adsorption and reduction of Cr(VI) oxyanions. The Cr(VI) adsorption behavior was satisfactorily tailored via pseudo-second-order law and Langmuir model with a maximum uptake capacity of 384.6 mg/g. Based on the advanced statistical physics theory, the monolayer model with two distinct receptor sites provided a reliable microscopic and macroscopic prediction of the Cr(VI) adsorption process. Stereographically, the Cr(VI) ions were adsorbed through horizontal multi-anchorage and vertical multi-molecular mechanisms on the amine and hydroxyl groups of Cys-PANi@FAU-50, respectively. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. XPS analysis proved that Cr(VI) ions were electrostatically adsorbed, and subsequently reduced to Cr(III), which in turn immobilized by chelation with imine/sulfonate groups and electrostatic interactions with carboxylate groups. The Cys-PANi@FAU-50 featured an effortless regenerability and good reusability. Overall, the Cys-PANi@FAU-50 composite owns outstanding potentiality for detoxifying Cr(VI)-laden effluents.
... In the case of non-SERS-active (platinum) or weakly SERS-active (polished gold) substrates, a contribution to the enhancement of the Raman intensity by resonance effect occurs. The presence of absorption bands in the red and NIR domains of the optical spectrum, characteristic of partially or totally oxidized states of PAni (emeraldine salt and pernigraniline salt) [58][59][60][61] leads to a resonance Raman effect when the laser excitation wavelength overlaps with one of these bands. ...
... The drop in intensity of the spectrum with oxidation at pH 5 might reflect degradation of the polymer as a result of its overoxidation when subjected to more positive potentials in relatively high pH solutions [58,[84][85][86]. ...
Electropolymerization of aniline on suitably roughened gold electrodes enabled us to record in situ surface-enhanced Raman scattering (SERS) spectra of polyaniline (PAni) during the doping-undoping process. Indeed, SERS-activation pretreatment of gold working electrode, using a specific electrochemical oxidation-reduction procedure, leads to the formation of countless surface asperities. The intergranular sites, known as “hot spots”, thus generated by the surface roughness are the seat of a strong electromagnetic coupling which leads to a huge SERS effect. Contrary to the case of platinum or mirror-polished gold electrodes, the use of roughened gold leads to high quality in situ SERS spectra of PAni, allowing the observation of important changes in the spectral features of its different oxidation states. In this study, we relied on spectral decomposition procedures to monitor and try to quantify these transformations accompanying the variation in the oxidation state of the polymer in different acidic aqueous solutions. In particular, the transition between the different forms of PAni (leucoemeraldine → emeraldine → pernigraniline), the drastic passage from benzenoid to quinoid structures of some aniline nuclei and the evolution of the charge-carrying structural defects are investigated despite the limitations imposed by the challenging conditions of the in situ analysis.
... There is another vibration near 1424 cm −1 , which is absent in the spectra of PANI-H 2 SO 4 film. The authors of [48,49] attributed it to phenazine structures in the PANI macromolecule. There is some possibility that association of aniline monomers with the sulfonic groups of the polyacid creates preconditions for the formation of PANI in very limited molecular volume. ...
... org/10.1016/j.jelechem.2020.114415. [48,49] or C-N + stretching in radical-cation π-dimers [6] or C\C stretching in the main chain of the polyacids [ ...
Application of back-scattering geometry in Raman spectroelectrochemistry of laser-absorbing polymer films on reflective metallic electrodes results in different degrees of doubling of excitation (by the incident and reflected beams) of the electrode/film/solution interfaces. Taking this into account, this method was first applied to study in situ galvanostatic polymerization of aniline on Pt-electrode in aqueous solutions of polymeric sulfonic acids distinguished by different rigidity of the main chain. Firstly, it was found that 532 nm laser radiation caused fluorescence in the solutions of phenyl-containing polyacids resulted in the Raman spectrometer overload. One can reduce fluorescence by increasing the incident angle of the laser beam on the electrode up to 20° (perpendicular direction is taken as 0°). Secondly, some of the polyacids were found to have intensive Raman bands in the range of characteristic Raman frequencies (1000–1800 cm⁻¹) of polyaniline (PANI). In this case, subtraction of the solution background spectrum before starting the electropolymerization monitoring causes appearance of ever-growing negative Raman signals as the laser-absorbing PANI film grows on the reflective electrode. The above two issues are due to the double excitation of the thin solution layer before the electrode by the incident and reflected laser beams, the degree of this doubling decreasing as (1) the incident angle is increased and (2) the PANI film thickness grows. The distortive influence of the solution Raman spectrum on the real shape of PANI spectrum may be estimated and diminished by using the amplitude of ever-growing negative Raman signal in the area of water OH vibration (near 3440 cm⁻¹) as a measure of the ever-decreasing reflectance of the working electrode. Using the developed approach, it was shown that evolutions of the relative portions of the imine nitrogen (near 1490 cm⁻¹) and the radical-cation nitrogen (near 1340 cm⁻¹) fragments in the Raman spectra of PANI recorded in the course of electropolymerization can be used as informative criteria for the explanation of the differences in the aniline polymerization rate in the presence of polyacids of different chemical structure.
... The cell moves together with the electrode in a linear path with respect to the Raman light source, reducing the time for which a single spot on the electrode is exposed to the Raman source. The linear moving electrode was first developed by Niaura et al. 140 and is mostly used by Mažeikienė et al. to study polyaniline [141][142][143][144][145][146] , dyes [147][148][149][150] and hexacyanoferrates 151,152 . ...
... Another popular application of Raman-SEC within material science is to get more insight on conductive polymers, studied by the group of Malinauskas [141][142][143][144][145][146]191 and others [192][193][194][195][196][197][198][199][200][201][202] . A number of applications are reported on the investigation of dyes [147][148][149][150]203,204 , small organic molecules that can form monolayers on the electrode material [205][206][207][208][209] and protein / cell studies 140,210-212 . ...
The combination of electrochemistry and spectroscopy, known as spectroelectrochemistry (SEC), is an established technique. By combining these two techniques, the relevance of the data obtained is greater than what it would be when using them independently. A number of review papers have been published on this subject, mostly written for experts in the field and focused on recent advances. In this review, written for both the novice in the field and the more experienced reader, the focus is not on the past but on the future. The scope is narrowed down to four techniques the authors claim to have most potential for the future, namely: infrared spectroelectrochemistry (IR-SEC), Raman spectroelectrochemistry (Raman-SEC), nuclear magnetic resonance spectroelectrochemistry (NMR-SEC) and perhaps slightly more controversial, but certainly promising, electrochemistry mass-spectrometry (EC-MS).
... The ChP measured in the process of PANI synthesis during the longest time of modification (60 min) is shown in Fig. 3. Electronic absorption spectra of the composites (Fig. 4) have been obtained right after membrane modification. The analysis of the electronic absorption spectra of the composites shows that the spectra of all samples contain characteristic absorption peaks for the emeraldine form of PANI (not oligomers): about 350 nm, due to π -π * electron transitions in the benzene rings of PANI, and a wide band at 800 nm corresponding to radical cations (Fig. 4) [31,32]. ...
A series of composites based on the perfluorinated MF-4SK membrane and polyaniline was obtained under electrodiffusion of monomer and oxidizer. Aniline was used as monomer and potassium dichromate as oxidizer. Chronopotentiometry was proposed as the method of monitoring the formation of polyaniline in the near-surface layer of the membrane. The electronic absorption spectra of the composites and optical microphotographs of the surfaces were obtained right after membrane modification. A combined interpretation of results revealed the following stages: the accumulation of monomer in the reaction space accompanied by the onset of polymerization, the polymerization with a subsequent increase in rate, and the formation of modifier layer on the membrane surface. The polarization behavior of composite membranes was studied using voltammetry. It was shown that the presence of two limiting currents (pseudo-limiting and limiting) on the current-voltage curves when the composite was oriented with a polyaniline layer to the counterion flow but only for membranes obtained at synthesis times more than 35 min. Also for these composite membranes, no plateau of the limiting current on the current-voltage curve was observed in the case of reverse membrane orientation. But at the same time, the fluctuations of potential drop on the current-voltage curve indicated the overlimiting state of electromembrane system. A correlation between the shape of the chronopotentiogram recorded during membrane modification and the polarization behavior of the obtained composites was found.
