Study of polaron and bipolaron states in polypyrrole by in situ Raman spectroelectrochemistry

Nitrogen-Containing Carbon Tubes Fabricated by Light Irradiation

Cotton-core/polypyrrole (PPy)-sheath fibers (cotton/PPy fibers) were synthesized by aqueous chemical oxidative seeded polymerization and were utilized as precursors for nitrogen-containing carbon (NCC) tubes. Irradiation of the cotton/PPy fibers with a near-infrared (NIR) laser heated them to approximately 300 °C due to light-to-heat photothermal conversion by the PPy, and the cotton core was thermally decomposed and vaporized. Scanning electron microscopy studies revealed the formation of tubes with monodispersed diameters, and elemental microanalysis, Fourier transform infrared spectroscopy, and Raman spectroscopy confirmed that the PPy sheath was converted into NCC. Furthermore, sunlight also worked as the light source in fabricating the NCC tubes. The thicknesses of the tubes were controlled between 410 nm and 2.30 μm by tuning the PPy sheath thickness. The method developed in this study can be extended to other polymeric fibers, including acrylic and wool fibers. The shapes of the cross sections and surface nanomorphologies of the NCC tubes can be reflected in those of the polymer/PPy fibers.

Electrical Conductivity Boost: In Situ Polypyrrole Polymerization in Monolithically Integrated Surface-Supported Metal-Organic Framework Templates

Recent progress in synthesizing and integrating surface-supported metal-organic frameworks (SURMOFs) has highlighted their potential in developing hybrid electronic devices with exceptional mechanical flexibility, film processability, and cost-effectiveness. However, the low electrical conductivity of SURMOFs has limited their use in devices. To address this, researchers have utilized the porosity of SURMOFs to enhance electrical conductivity by incorporating conductive materials. This study introduces a method to improve the electrical conductivity of HKUST-1 templates by in situ polymerization of conductive polypyrrole (PPy) chains within the SURMOF pores (named as PPy@HKUST-1). Nanomembrane-origami technology is employed for integration, allowing a rolled-up metallic nanomembrane to contact the HKUST-1 films without causing damage. After a 24 h loading period, the electrical conductivity at room temperature reaches approximately 5.10-6 S m-1 . The nanomembrane-based contact enables reliable electrical characterization even at low temperatures. Key parameters of PPy@HKUST-1 films, such as trap barrier height, dielectric constant, and tunneling barrier height, are determined using established conduction mechanisms. These findings represent a significant advancement in real-time control of SURMOF conductivity, opening pathways for innovative electronic-optoelectronic device development. This study demonstrates the potential of SURMOFs to revolutionize hybrid electronic devices by enhancing electrical conductivity through intelligent integration strategies.

Study of Chemical Polymerization of Polypyrrole with SDS Soft Template: Physical, Chemical, and Electrical Properties

Polypyrrole (PPy) is a conductive polymer known for its biocompatibility and ease of synthesis. Chemically polymerized PPy was synthesized in the presence of sodium dodecyl sulfate (SDS), showing correlations among chemical properties, physical morphology, and electrical properties. Focused synthesis parameters included the pyrrole (Py) concentration, SDS concentration, and ammonium persulfate (APS)/Py ratio. The addition of SDS during chemical polymerization influenced the physical morphology of PPy by altering the self-assembling process via micelle formation, yielding sheet-like morphologies. However, the phenomenon also relied heavily on other synthesis parameters. Varying SDS concentrations within the 0.01 to 0.30 M window produced PPy sheets with no significant difference in optical band gap or physical size. While using 0.10 M SDS, an increase in Py concentration from 0.10 to 0.30 M yielded a larger size of PPy as the morphology changed from sheet-like to irregular shape. The band gap dropped from 2.35 to 1.10 eV, and the conductivity rose from 6.80 × 10-1 to 9.40 × 10-1 S/m. With an increase in the APS/Py ratio, the PPy product changed from a random to a sheet-like form. The product provided a larger average size, a decreased band gap, and increased electrical conductivity. Py polymerization in the absence of SDS revealed no significant change in shape or size as the Py concentration increased from 0.10 to 0.30 M; only a sphere-like form was observed, with a large band gap and small conductivity. Results from Raman spectral analysis indicated a correlation between optical band gap, physical morphology, and bipolaron/polaron ratio, mainly at the wavelengths associated with C-C stretching and C-H deformation. The increase in average size was associated with a decrease in band gap and resistance as well as an increase in the bipolaron/polaron ratio. This work indicates a strong correlation between size, morphology, electrical properties, and the bipolaron/polaron ratio of PPy in the presence of SDS.

Contact Piezoresistive Sensors Based on Electro-Polymerized Polypyrrole and a Regulated Conductive Pathway

The performance of contact resistive pressure sensors heavily relies on the intrinsic characteristics of the active layers, including the mechanical surface structure, conductivity, and elastic properties. However, efficiently and simply regulating the conductivity, morphology, and modulus of the active layers has remained a challenge. In this study, we introduced electro-polymerized polypyrrole (ePPy) to design flexible contact piezoresistive sensors with tailored intrinsic properties. The customizable intrinsic property of ePPy was comprehensively illustrated on the chemical and electronic structure scale, and the impact of ePPy's intrinsic properties on the sensing performance of the device was investigated by determining the correlation between resistivity, roughness, and device sensitivity. Due to the synergistic effects of roughness, conductivity, and elastic properties of the active layers, the flexible ePPy-based pressure sensor exhibited high sensitivity (3.19 kPa-1, 1-10 kPa, R2 = 0.97), fast response time, good durability, and low power consumption. These advantages allowed the sensor to offer an immediate response to human motion such as finger-bending and grasping movements, demonstrating the promising potential of tailorable ePPy-based contact piezoresistive sensors for wearable electronic applications.

Hybrid Polypyrrole and Polydopamine Nanosheets for Precise Raman/Photoacoustic Imaging and Photothermal Therapy

The development of near-infrared light responsive conductive polymers provides a useful theranostic platform for malignant tumors by maximizing spatial resolution with deep tissue penetration for diagnosis and photothermal therapy. Herein, the self-assembly of ultrathin 2D polypyrrole nanosheets utilizing dopamine as a capping agent and a monolayer of octadecylamine as a template is demonstrated. The 2D polypyrrole-polydopamine nanostructure has tunable size distribution which shows strong absorption in the first and second near-infrared windows, enabling photoacoustic imaging and photothermal therapy. The hybrid double-layer is demonstrated to increase Raman intensity for 3D Raman imaging (up to two orders of magnitude enhancement and spatial resolution up to 1 µm). The acidic environment drives reversible doping of polypyrrole, which can be detected by Raman spectroscopy. The combined properties of the nanosheets can substantially enhance performance in dual-mode Raman and photoacoustic guided photothermal therapy, as shown by the 69% light to heat conversion efficiency and higher cytotoxicity against cancer spheroids. These pH-responsive features highlight the potential of 2D conductive polymers for applications in accurate, highly efficient theranostics.

In-Situ Spectro-Electrochemistry of Conductive Polymers Using Plasmonics to Reveal Doping Mechanisms

Conducting polymers are a key component for developing wearable organic electronics, but tracking their redox processes at the nanoscale to understand their doping mechanism remains challenging. Here we present an in-situ spectro-electrochemical technique to observe redox dynamics of conductive polymers in an extremely localized volume (<100 nm³). Plasmonic nanoparticles encapsulated by thin shells of different conductive polymers provide actively tuned scattering color through switching their refractive index. Surface-enhanced Raman scattering in combination with cyclic voltammetry enables detailed studies of the redox/doping process. Our data intriguingly show that the doping mechanism varies with polymer conductivity: a disproportionation mechanism dominates in more conductive polymers, while sequential electron transfer prevails in less conductive polymers.

Recent advancement in conjugated polymers based photocatalytic technology for air pollutants abatement: Cases of CO2, NOx, and VOCs

According to World Health Organization (WHO) survey, air pollution has become the major reason of several fatal diseases, which had led to the death of 7 million peoples around the globe. The 9 people out of 10 breathe air, which exceeds WHO recommendations. Several strategies are in practice to reduce the emission of pollutants into the air, and also strict industrial, scientific, and health recommendations to use sustainable green technologies to reduce the emission of contaminants into the air. Photocatalysis technology recently has been raised as a green technology to be in practice towards the removal of air pollutants. The scientific community has passed a long pathway to develop such technology from the material, and reactor points of view. Many classes of photoactive materials have been suggested to achieve such a target. In this context, the contribution of conjugated polymers (CPs), and their modification with some common inorganic semiconductors as novel photocatalysts, has never been addressed in literature till now for said application, and is critically evaluated in this review. As we know that CPs have unique characteristics compared to inorganic semiconductors, because of their conductivity, excellent light response, good sorption ability, better redox charge generation, and separation along with a delocalized π-electrons system. The advances in photocatalytic removal/reduction of three primary air-polluting compounds such as CO₂, NO_X, and VOCs using CPs based photocatalysts are discussed in detail. Furthermore, the synergetic effects, obtained in CPs after combining with inorganic semiconductors are also comprehensively summarized in this review. However, such a combined system, on to better charges generation and separation, may make the Adsorb & Shuttle process into action, wherein, CPs may play the sorbing area. And, we hope that, the critical discussion on the further enhancement of photoactivity and future recommendations will open the doors for up-to-date technology transfer in modern research.

Polypyrrole-based nanomaterials: A novel strategy for reducing toxic chemicals and others related to environmental sustainability applications

Aqueous contaminants such as pharmaceuticals, dyes, personal care products, etc., are the common water contaminants that show adverse health effects. Photocatalysis is one of the well-known techniques to treat these water contaminants. Currently, most inorganic photocatalysts show a poor balance between adsorption and photocatalytic activity. In addition, heavy metal pollution and low biosafety are significant concerns in photocatalysis. Thus, environmentally friendly photocatalysts are required to avoid the secondary pollution caused by some inorganic semiconductor-photocatalysts. Organic polymer-based photocatalysts are low-cost, stable, non-toxic, and can utilize visible and NIR light for photocatalysis. In this review, we have discussed polypyrrole as a photocatalyst. Polypyrrole is a conducting organic polymer photocatalyst that is highly stable with high charge mobility and strong binding sites for photocatalytic reactions. Besides these advantages, polypyrrole has limitations, such as high charge recombination due to a small bandgap and poor dispersity. So we have explored the modifications to polypyrrole photocatalysts, such as doping and heterojunctions. Further, we have explained the applications of polypyrrole in photocatalysis as an adsorbent, sensitizer, degradation of pollutants, and energy production. Finally, the future aspects of polypyrrole photocatalysis are also explored to improve the path of future research.

A Comparative Study of Biomimetic Synthesis of EDOT-Pyrrole and EDOT-Aniline Copolymers by Peroxidase-like Catalysts: Towards Tunable Semiconductive Organic Materials

It has been two decades since biomimetic synthesis of conducting polymers were first reported, however, the systematic investigation of how catalysts influence the properties of the conducting polymers has not been reported yet. In this paper, we report a comparative study between peroxidase-like catalyst, dopants, and their effect on the properties of poly (3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). We also investigate the EDOT-Pyrrole and EDOT-Aniline copolymerization by enzymomimetic synthesis using two catalysts (Ferrocene and Hematin). It was found that, chemically, there are no detectable effects, only having small contributions in molar ratios greater than 0.7–0.3. Spectroscopic data provide solid evidence concerning the effect in the variation of the molar fractions, finding that, as the molar fraction of EDOT decreases, changes associated with loss of the conjugation of the structure and the oxidation state of the chains were observed. The electrical conductivity was considerably modified depending on the type of catalyst. Hematin produces conductive homopolymers and copolymers when doped with p-toluene sulfonic acid (TSA), while ferrocene produces low conductive copolymers under the same conditions. The mole fraction affects conductivity significantly, showing that as the EDOT fraction decreases, the conductivity drops drastically for both EDOT-PY and EDOT-ANI copolymers. The type of dopant also notably affects conductivity; the best values were obtained by doping with TSA, while the lowest were obtained when doping with polystyrene sulfonate (PSS). We also draw a biomimetic route to tailor the fundamental properties of conducting homopolymers and copolymers for their design and scaled-up production, as they have recently been found to have use in a broad range of applications.

Statistical Study of the Influence of Electrosynthesis Conditions on the Capacitance of Polypyrrole

Polypyrrole (PPy) is a promising material for the fabrication of flexible energy storage devices and much research has been published. However, no statistical tools have been used to relate PPy synthesis conditions to its energy storage performance, considering not only the main synthesis factors but also their interactions. In this work, we use a factorial design of experiments to evaluate the influence of two electropolymerization methods and three synthesis parameters on the energy storage capacity of PPy coatings. The polymers were characterized by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and scanning electron microscopy (SEM). Statistical tests showed that ClO₄ ^--doped PPy exhibits higher capacitances than p-toluenesulfonate (pTS)-doped PPy, with a maximum capacitance of 353.75 ± 1.6 F g^-1 at 1 A g^-1. However, the pTS-doped PPy had better cycling stability, losing only 10% of its original energy storage capability after 5000 charge-discharge cycles at 1 A g^-1. The best energy densities and power densities were 49.1 ± 0.2 Wh kg^-1 and 2297 ± 15 W kg^-1 (ClO₄ ^--doped PPy) and 47.8 ± 1.5 Wh kg^-1 and 2191 ± 91 W kg^-1 (pTS-doped PPy), respectively, which indicates that through statistical tools, the optimal synthesis conditions are refined to take advantage of the energy storage properties of this polymer.

Non-metallic T2-MRI agents based on conjugated polymers

Developing non-metallic contrast agents of clinically applied magnetic resonance imaging (MRI) is an alternative strategy to reduce the toxicity of heavy metal elements in current MRI agents. These non-metallic MRI agents usually generate contrasts by unpaired electrons, which are prone to be deactivated by in vivo radical scavenging pathways. Since the unpaired electrons in conjugated polymers exhibit satisfying stability for in vivo imaging, developing conjugated polymers based MRI agents may solve the in vivo stability problem of current non-metallic agents. However, MRI-active properties have not been reported in existing conjugated polymers yet. Herein we report on MRI-active conjugated polymer nanoparticles based on polypyrrole (PPy), which can be used for in vivo imaging. Our method not only introduce a kind of non-metallic MRI agents but extends the applications of conjugated polymers from optical imagings to MRI.

The toxicity of heavy metals for MRI contrast agents is an issue. Here, the authors report on the development of conjugated polymers nanoparticles based on paramagnetic polypyrrole to generate T2 MRI contrast effects by changing the interactions between polarons and water protons.

Dual-template rectangular nanotube molecularly imprinted polypyrrole for label-free impedimetric sensing of AFP and CEA as lung cancer biomarkers

A high-performance sensing layer based on dual-template molecularly imprinted polymer (DMIP) was fabricated and successfully applied for one-by-one detection of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) as lung cancer biomarkers. The plastic antibodies of AFP and CEA were created into the electropolymerized polypyrrole (PPy) on a fluorine-doped tin oxide (FTO) electrode. Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests were performed to pursue the formation and characterization of the sensing layer. Methyl orange (MO) increased the conductivity of PPy and induced the formation of MO doped PPy (PPy-MO) rectangular-shaped nanotubes. Using impedimetric detection, the rebinding of the template antigens was evaluated, the charge transfer resistance increased as the concentration of AFP and CEA increased. The linear dynamic ranges of 5-10⁴ and 10-10⁴ pg mL^-1 and detection limits of 1.6 and 3.3 pg mL^-1 were obtained for CEA and AFP, respectively. Given satisfactory results in the determination of AFP and CEA in the human serum samples, high sensitivity, and good stability of DMIP sensor made it a promising method for sensing of AFP and CEA in serum samples.

Facile fabrication of a conductive polypyrrole membrane for anti-fouling enhancement by electrical repulsion and in situ oxidation

Conductive membranes provide a promising method to alleviate membrane fouling, but their cost-effective fabrication, which is urgently needed, is still a challenge. This paper describes the facile fabrication of an ultrafiltration conductive polypyrrole (PPy)-modified membrane (PMM) by in situ chemical polymerization of FeCl₃ and monomer pyrrole vapor on a commercial membrane surface. The resulting membrane had a high electrical conductivity and an outstanding water flux of 2766.55 L m^-2 h^-1 bar^-1. The preparation cost of the PPy deposition was $2.22/m², which was ∼8% of the commercial ultrafiltration membrane cost. Once the PMM was charged at -1 V as a membrane electrode, the normalized water flux was maintained at 92.48 ± 1.14% after fouling by bovine serum albumin (BSA) solutions, which was 18.82% higher than that when the PMM was not charged. The reduced membrane fouling was ascribed to the electrical repulsion between the negatively charged BSA and the PMM cathode. In addition, hydroxyl and sulfate radicals were generated by peroxymonosulfate (PMS) activation on the PMM surface through electron transfer by PPy, which facilitated foulant oxidation. The PPy on the PMM surface was oxidized after catalysis and electrochemically reduced when the PMM was charged as a cathode, exhibiting continuous catalytic ability for PMS activation. These findings provide an alternative method for the facile fabrication of cost-effective conductive membranes to mitigate membrane fouling.

Monodispersed Nitrogen-Containing Carbon Capsules Fabricated from Conjugated Polymer-Coated Particles via Light Irradiation

Near-infrared (NIR) light irradiation induced the transformation of polypyrrole (PPy) to nitrogen-containing carbon (NCC) material due to its light-to-heat photothermal property. The temperature of the PPy increased over 700 °C within a few seconds by the NIR laser irradiation, and elemental microanalysis confirmed the decreases of hydrogen and chloride contents and increases of carbon and nitrogen contents. Monodispersed polystyrene (PS)-core/PPy shell particles (PS/PPy particles) synthesized by aqueous chemical oxidative seeded polymerization were utilized as a precursor toward monodispersed NCC capsules. When the NIR laser was irradiated to the PS/PPy particles, the temperature rose to approximately 300 °C and smoke was generated, indicating that the PS component forming the core was thermally decomposed and vaporized. Scanning electron microscopy studies revealed the successful formation of spherical and highly monodispersed capsules, and Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy studies confirmed the capsules consisted of NCC materials. Furthermore, sunlight was also demonstrated to work as a light source to fabricate NCC capsules. The size and thickness of the capsules can be controlled between 1 and 80 μm and 146 and 231 nm, respectively, by tuning the size of the original PS/PPy particles and PPy shell thickness.

Spatial distribution of active sites for plasmon-induced chemical reactions triggered by well-defined plasmon modes

Plasmon-induced chemical reactions triggered by near-infrared light illumination might enable efficient photo energy conversion. Here, electrochemical oxidative polymerization of a conductive polymer was conducted on plasmonic photoconversion electrodes. The absolute electrochemical potential of the generated holes was estimated from the redox potentials of the monomers. In addition, well-defined plasmonic structures were examined to better understand the relationship between the excited plasmon mode and spatial distribution of reaction active sites. Rod structures with various lengths had distinct spatial distributions of reaction active sites that depended on the higher plasmon modes, as visualized by Raman measurements.

Coaxial Ni-S@N-Doped Carbon Nanofibers Derived Hierarchical Electrodes for Efficient H2 Production via Urea Electrolysis

Electrochemical water splitting into hydrogen is a promising strategy for hydrogen production powered by solar energy. However, the cell voltage of an electrolyzer is still too high for practical application, which is mainly limited by the sluggish oxygen evolution reaction process. To this end, hybrid water electrolyzers have drawn tremendous attention. Herein, coaxial Ni/Ni₃S₂@N-doped nanofibers are directly grown on nickel foam (NF), which is highly active for hydrogen evolution reaction. Meanwhile, the Ni₃S₂@N-doped nanofibers on NF prepared in an Ar atmosphere display superior urea oxidation reaction performance to previously reported catalysts. The cell voltage is about 1.50 V in urea electrolysis to deliver a current density of 20 mA cm^-2, lower than that of a traditional water electrolyzer (1.82 V). The current density is around 77% relative to its initial value of 20 mA cm^-2 after 20 h, superior to Pt/C|Ir/C-based urea electrolysis (14%). It is found that the synergistic effect between metallic Ni and Ni₃S₂, as well as the interfacial effect between metal centers and N-doped carbon, favors the initial dissociation of H₂O and the adsorption/desorption of H* with thermal neutral Gibbs free energy. Meanwhile, the in-situ generated NiOOH on the outer surface of Ni₃S₂ possessed lower electrochemical activation energy for urea decomposition. Meanwhile, the abundant oxygen vacancies in electrodes could expose more active sites for the adsorption of intermediates, including H* and OOH*. It is also found that the hierarchical nanostructure of densely packed nanowires provides ideal electronic and ionic transport paths for fast electrocatalytic kinetics. The present work indicated that the modulation of compositions and hierarchical nanostructure is effective to prepare efficient catalysts for H₂ production via urea electrolysis.

Nanodiamond surface chemistry controls assembly of polypyrrole and generation of photovoltage

Nanoscale composite of detonation nanodiamond (DND) and polypyrrole (PPy) as a representative of organic light-harvesting polymers is explored for energy generation, using nanodiamond as an inorganic electron acceptor. We present a technology for the composite layer-by-layer synthesis that is suitable for solar cell fabrication. The formation, pronounced material interaction, and photovoltaic properties of DND-PPy composites are characterized down to nanoscale by atomic force microscopy, infrared spectroscopy, Kelvin probe, and electronic transport measurements. The data show that DNDs with different surface terminations (hydrogenated, oxidized, poly-functional) assemble PPy oligomers in different ways. This leads to composites with different optoelectronic properties. Tight material interaction results in significantly enhanced photovoltage and broadband (1–3.5 eV) optical absorption in DND/PPy composites compared to pristine materials. Combination of both oxygen and hydrogen functional groups on the nanodiamond surface appears to be the most favorable for the optoelectronic effects. Theoretical DFT calculations corroborate the experimental data. Test solar cells demonstrate the functionality of the concept.

Spectroelectrochemistry: A Powerful Tool for Studying Fundamental Properties and Emerging Applications of Solid-State Materials Including Metal–Organic Frameworks

Spectroelectrochemistry (SEC) encompasses a broad suite of electroanalytical techniques where electrochemistry is coupled with various spectroscopic methods. This powerful and versatile array of methods is characterised as in situ, where a fundamental property is measured in real time as the redox state is varied through an applied voltage. SEC has a long and rich history and has proved highly valuable for discerning mechanistic aspects of redox reactions that underpin the function of biological, chemical, and physical systems in the solid and solution states, as well as in thin films and even in single molecules. This perspective article highlights the state of the art in solid-state SEC (ultraviolet–visible–near-infrared, infrared, Raman, photoluminescence, electron paramagnetic resonance, and X-ray absorption spectroscopy) relevant to interrogating solid state materials, particularly those in the burgeoning field of metal–organic frameworks (MOFs). Emphasis is on developments in the field over the past 10 years and prospects for application of SEC techniques to probing fundamental aspects of MOFs and MOF-derived materials, along with their emerging applications in next-generation technologies for energy storage and transformation. Along with informing the already expert practitioner of SEC, this article provides some guidance for researchers interested in entering the field.

Comparative Study on the Effect of Protonation Control for Resistive Gas Sensor Based on Close-Packed Polypyrrole Nanoparticles

Conducting polymers are often used as sensor electrodes due to their conjugated chain structure, which leads to high sensitivity and rapid response at room temperature. Numerous studies have been conducted on the structures of conducting polymer nanomaterials to increase the active surface area for the target materials. However, studies on the control of the chemical state of conducting polymer chains and the modification of the sensing signal transfer with these changes have not been reported. In this work, polypyrrole nanoparticles (PPyNPs), where is PPy is a conducting polymer, are applied as a sensor transducer to analyze the chemical sensing ability of the electrode. In particular, the protonation of PPy is adjusted by chemical methods to modify the transfer sensing signals with changes in the polymer chain structure. The PPyNPs that were modified at pH 1 exhibit high sensitivity to the target analyte (down to 1 ppb of NH3) with short response and recovery times of less than 20 s and 50 s, respectively, at 25 °C.

Mechanism of Zn-Ion Intercalation/Deintercalation in a Zn-Polypyrrole Secondary Battery in Aqueous and Bio-Ionic liquid Electrolytes

Zn-ion batteries(ZIB) have recently emerged as a promising and rather cheap alternative to Li-ion batteries. However, the divalent charge of Zn limits the choice of cathode materials, whereas the choice of electrolyte is limited by hydrogen-evolution reaction. Polymer cathodes have been shown to be a promising material for ZIB. In this paper, we have studied in detail a Zn/polypyrrole battery in both aqueous and bio-ionic liquid-water mixture electrolytes. From in situ Raman spectroelectrochemistry, it was observed that in aqueous solution, Zn intercalation/deintercalation takes place by a two-step mechanism, whereas a single-step mechanism for Zn storage was involved in bio-ionic liquid-water mixture electrolytes. The charge-discharge measurements showed a higher Zn-storage capacity in the mixture of bio-ionic liquid-water electrolyte compared to the aqueous electrolyte. However, with cycling, a capacity loss was observed. Post analysis of the polymer after cycling showed that a phase transformation has taken place in the polymer with Zn ions trapped in the polymer matrix that decreased the Zn-storage capacity. Furthermore, the Zn anode showed the formation of Zn nanoflakes from aqueous electrolytes that might lead to dendritic growth, whereas dendrite-free Zn nanoparticles were observed on using the bio-ionic liquid-water electrolyte.

Raman and XPS studies of ammonia sensitive polypyrrole nanorods and nanoparticles

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.

Polypyrrole nanotubes for electrochemically controlled extraction of atrazine, caffeine and progesterone

Polypyrrole (PPy) was electrochemically synthesized with charge control on the surface of a steel mesh. Two different morphologies (globular and nanotubular) were created and characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The modified electrodes were used as extraction phases in solid-phase extraction (SPE) and electrochemically controlled solid-phase extraction (EC-SPE) of atrazine, caffeine and progesterone. Raman spectroscopy was employed for the structural characterization of PPy after long exposure to the analytes. The electrochemical behavior was studied by cyclic voltammetry which revealed the higher capacitive behavior of polypyrrole nanotubes because of the huge superficial area, also no electrocatalytical behavior was observed evidencing the strong adsorption of the analytes on the PPy surface. The effects of the PPy oxidation state on the extraction performance were evaluated by in-situ electrochemical sorption experiments. The sorption capacity was evaluated by gas chromatography coupled to mass spectrometry (GC-MS). The method displays good stability, repeatability and reproducibility. The limits of detection range between 1.7-16.7 μg L^-1. Following the extraction of river water samples, it was possible to identify the presence of other endogenous organic compounds besides the analytes of interest. This indicates the potential of the method and material developed in this work. Graphical abstract Schematic representation of a steel mesh electrode covered with polypyrrole nanotubes used as extraction phase for separation of contaminants from aqueous samples. The oxidation level of polypyrrole was electrochemically tuned by which the adsorption of analytes is deeply affected.

Superior cycling performance of a novel NKVO@polypyrrole composite anode for aqueous rechargeable lithium-ion batteries

An aqueous rechargeable lithium-ion battery (ARLB) system has been assembled using as-prepared polypyrrole (PPy) to coat Na_0.8K_0.2K₆O₁₅ (NKVO) anode coupled with LiMn₂O₄ cathode, both immersed in an aqueous LiNO₃ solution.

Resonance Raman Spectroscopy of Conducting Polypyrrole Nanotubes: Disordered Surface versus Ordered Body

Polypyrrole nanotubes rank among the most conducting forms of organic semiconductors. They are prepared by the oxidation of pyrrole in the presence of methyl orange. Other organic dyes, viz. ethyl orange, Acid Blue 25, and Acid Blue 129, have been used in the present study to prepare globules or nanofibers. The resulting polypyrroles were studied in detail by Raman spectroscopy. The apparent paradox when a dye contribution to spectra is absent with 785 nm excitation line and present with shorter wavelengths is explained by the resonance character of the Raman scattering, which allows the separation of the contributions from the polypyrrole surface and from the bulk. These differ depending on the laser excitation wavelength and the position of absorption maximum of the individual dyes in ultraviolet-visible spectra and affect both the laser-penetration depth and observation of the resonance effect. The spectra are discussed in terms of different ordering of polymer chains in individual morphologies. The correlation between conductivity, surface areas, and the proportions of ordered and disordered polypyrrole phases at the surface and in the interior of nanostructures is proposed and established using resonance Raman spectroscopy.