Characterization of Reaction Intermediate Aggregates in Aniline Oxidative Polymerization at Low Proton Concentration

An approach to enhance carbon/polymer interface compatibility for lithium-ion supercapacitors

Developing high-efficiency and easy machining components, as well as high-performance energy storage components, is a pressing issue on the road to economic and social progress. Optimizing the interface compatibility between composites and promoting the efficient utilization of the electrochemical active sites are crucial factors in improving the electrochemical performance of composite electrode materials. To address this challenge, a carbon-based flexible lithium-ion supercapacitor positive material (Polyaniline @ Carbon Foam-Supercritical carbon dioxide (P@C-SC)) is synthesized using commercial melamine foam and aniline monomer. The synthesis process utilizes supercritical fluid technology, effectively solving the interface compatibility problem between the composite materials. Consequently, the electrochemical performance of the composite electrode materials is significantly improved. The supercapacitive properties of this material are investigated in 1 mol/L sulfuric acid (H2SO4) and lithium sulfate (Li2SO4) electrolytes using a three-electrode system. In H2SO4 electrolyte, the material exhibits a working voltage of up to 2.2 V and a specific capacitance of 898F/g (at 1 A/g), resulting in a maximum energy density of 50.8 Wh kg-1. Furthermore, this electrode demonstrates superior lithium storage performance, with a specific capacity of approximately 900 mAh/g (at 1 A/g) and a retention of about 400 mAh/g after 200 cycles, along with a coulomb efficiency of 100%. This work offers insights into the integrated design of composite materials with improved electrochemical properties and interface compatibility, thus providing potential applicability of supercritical fluids in the field of lithium-ion supercapacitors.

Reuse of PANI wastewater treated by anodic oxidation/electro-Fenton for the preparation of PANI

The present work investigated the treatment of the polyaniline (PANI) wastewater by anodic oxidation/electro-Fenton and reusing the treated PANI wastewater for the preparation of PANI. Organics were degraded by hydroxyl radical (OH) and sulfate radical (SO₄^-) formed simultaneously in the wastewater from electro-Fenton reaction and the anode surface. Under the conditions of 160 mL min^-1 oxygen flow rate, constant current density 14 mA cm^-2 and Fe²⁺ concentration 0.2 mM, 89% COD can be removed from the PANI wastewater after 360 min treatment. The energy consumption was 50 kWh (kg COD)^-1 and the current efficiency was 27.8%. After the PANI wastewater treatment, the aniline, aniline derivatives and aniline oligomers were removed from the wastewater. The PANI obtained using fresh solution, treated PANI wastewater and untreated PANI wastewater were recorded PANI-F, PANI-T and PANI-U, respectively. In the preparation of PANI-U, the reaction of p-benzoquinone with aniline or aniline oligomers could change the nucleation and growth, leading to the production of aggregated nanoparticles and low specific capacitance. However, the morphology and specific capacitance of PANI-T were similar to that of PANI-F. The PANI-T is three-dimensional sphere of nanofibers with high specific capacitance about 446.7 F g^-1. The yield of PANI-T using treated PANI wastewater could reach to 92.1%. These results demonstrate that the PANI wastewater treatment approach is efficient and environmentally friendly.

The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

There are several types of aniline oligomers that can be formed in the early stages of aniline oxidation: linear oligomers with repeating units joined in para positions, and various branched and polycyclic oligomers, being the two most important groups. The fraction of these different oligomeric groups depends upon the reaction conditions of aniline oxidation. The aim of this study was to analyze the first products of the chemical and electrochemical oxidation of aniline at the (starting) pH 1 and 7, in order to specify the conditions of the formation of phenazine-like oligomers, and to test the theory that they have an important role in polyaniline film formation. We have confirmed that phenazine-like oligomers do not form at pH 1, neither in the chemical nor the electrochemical oxidation of aniline; however, they form in both chemical and electrochemical oxidation of aniline at pH 7. Phenazine-like oligomers are thus definitely not necessary intermediates for PANI film formation, not even in the chemical polymerization of aniline. Finally, the redox behavior of phenazine-like oligomers was demonstrated in a medium at pH 1.

The non-stationary case of the Maxwell-Garnett theory: growth of nanomaterials (2D gold flakes) in solution

The solution-based growth mechanism is a common process for nanomaterials. The Maxwell-Garnett theory (for light-matter interactions) describes the solution growth in an effective medium, homogenized by a mean electromagnetic field, which applies when materials are in a stationary phase. However, the charge transitions (inter- and intra-transitions) during the growth of nanomaterials lead to a non-stationary phase and are associated with time-dependent permittivity constant transitions (for nanomaterials). Therefore, time-independence in the standard Maxwell-Garnett theory is lost, resulting in time dependence, ε i(t). This becomes important when the optical spectrum of a solution needs to be deconvoluted at different reaction times since each peak represents a specific charge/energy transfer with a specific permittivity constant. Based on this, we developed a time-resolved deconvolution approach, f(t) ∝ ε i(t), which led us to identify the transitions (inter- and intra-transitions) with their dominated growth regimes. Two gold ion peaks were precisely measured (322 nm and 367 nm) for the inter-transition, and three different polyaniline oxidation states (PAOS) for the intra-transition, including A (372 nm), B (680 nm), and C (530 nm). In the initial reaction time regime (0-90 min), the permittivity constant of gold was found to be highly dependent on time, i.e. f E ∝ ε i(t), since charge transfer takes place from the PAOS to gold ions (i.e. inter-transition leads to a reduction reaction). In the second time regime (90-180 min), the permittivity constant of gold changes as the material deforms from 3D to 2D (f S ∝ ε 3D-2D), i.e. intra-transition (combined with thermal reduction). Our approach provides a new framework for the time-dependent modelling of (an)isotropic solutions of other nanomaterials and their syntheses.

Influence of polaron doping and concentration dependent FRET on luminescence of PAni-PMMA blends for application in PLEDs

The role of quantum mechanical phenomena such as polaron-exciton quenching interaction and concentration-dependent FRET in determining the luminescence efficiency of PAni-PMMA polymer blends has been investigated. PAni samples prepared in different environments using different acids and bases show different absorbance and emission profiles indicating a direct relation between generated polarons in PAni by acid-base doping-dedoping and photoluminescence spectra of PAni. The observed low luminescence in PAni has been modeled using exciton quenching by polarons through charge transfer. The investigation also reveals that the effect of exciton quenching by polarons becomes pronounced when the polaron concentration in PAni reaches a density of ∼1017-1018 polarons cm-3. To overcome the low emission efficiency of PAni, poly(methyl methacrylate) (PMMA) has been blended with PAni. The blending of donor PMMA (D) with acceptor PAni (A) gives rise to another quantum phenomenon - donor PMMA concentration dependent FRET between PAni (A) and PMMA (D). It is experimentally observed from the photoluminescence measurements of blends that at high donor PMMA concentration above a critical value in the PAni-PMMA polymer blend the emission profile of blends drops sharply. Donor concentration dependent FRET is a contradictory observation with respect to standard concentration independent FRET theory due to competition between inter-layer donor-acceptor and donor-donor intra-layer energy transfer within the donor layer. At high donor concentration intra-donor interaction gradually overtakes inter-layer donor-acceptor FRET which modifies the lifetime of the donor. The modification decreases the quantum yield of the donor and hence emission efficiency of blends above a critical concentration of PMMA by reducing inter donor-acceptor FRET. Thus, polaron exciton quenching and concentration dependent FRET are two dominant physical phenomena controlling luminescence in PAni-PMMA polymer blends. Therefore, optimization of luminescence of PAni-PMMA should be achieved by tuning the factors like reduction of spectral overlap between polarons and excitons in PAni, the density of PAni, diffusion of excitons in blends, and intra donor FRET within the PMMA layer before consideration of the blend being used as an emissive layer in PLEDs.

The biocompatibility of polyaniline and polypyrrole: A comparative study of their cytotoxicity, embryotoxicity and impurity profile

Conducting polymers (CP), namely polyaniline (PANI) and polypyrrole (PPy), are promising materials applicable for the use as biointerfaces as they intrinsically combine electronic and ionic conductivity. Although a number of works have employed PANI or PPy in the preparation of copolymers, composites, and blends with other polymers, there is no systematic study dealing with the comparison of their fundamental biological properties. The present study, therefore, compares the biocompatibility of PANI and PPy in terms of cytotoxicity (using NIH/3T3 fibroblasts and embryonic stem cells) and embryotoxicity (their impact on erythropoiesis and cardiomyogenesis within embryonic bodies). The novelty of the study lies not only in the fact that embryotoxicity is presented for the first time for both studied polymers, but also in the elimination of inter-laboratory variations within the testing, such variation making the comparison of previously published works difficult. The results clearly show that there is a bigger difference between the biocompatibility of the respective polymers in their salt and base forms than between PANI and PPy as such. PANI and PPy can, therefore, be similarly applied in biomedicine when solely their biological properties are considered. Impurity content detected by mass spectroscopy is presented. These results can change the generally accepted opinion of the scientific community on better biocompatibility of PPy in comparison with PANI.

Enzymatic oligomerization and polymerization of arylamines: state of the art and perspectives

The literature concerning the oxidative oligomerization and polymerization of various arylamines, e.g., aniline, substituted anilines, aminonaphthalene and its derivatives, catalyzed by oxidoreductases, such as laccases and peroxidases, in aqueous, organic, and mixed aqueous organic monophasic or biphasic media, is reviewed. An overview of template-free as well as template-assisted enzymatic syntheses of oligomers and polymers of arylamines is given. Special attention is paid to mechanistic aspects of these biocatalytic processes. Because of the nontoxicity of oxidoreductases and their high catalytic efficiency, as well as high selectivity of enzymatic oligomerizations/polymerizations under mild conditions-using mainly water as a solvent and often resulting in minimal byproduct formation-enzymatic oligomerizations and polymerizations of arylamines are environmentally friendly and significantly contribute to a "green" chemistry of conducting and redox-active oligomers and polymers. Current and potential future applications of enzymatic polymerization processes and enzymatically synthesized oligo/polyarylamines are discussed.

Spectroscopic study of the highly homogeneous polyaniline film formation on gold support

The oxidation of aniline with ammonium peroxydisulfate in the aqueous solution of acetic acid has two subsequent phases: the oxidation of the neutral aniline molecules at low acidity, which was followed by the oxidation of the anilinium cations after the acidity became higher. The final polyaniline film deposited on immersed surfaces is usually contaminated with semi-crystalline oligomers which precipitated during induction period from the reaction medium. To obtain a homogeneous film, which is important in the fabrication of many molecular electronic devices, we have studied the course of aniline oxidation in a view of new experimental evidence. In the unique series of experiments, the silicon or gold supports have been immersed in the reaction mixture at crucial stages of oxidation reaction, and the deposits at the end of the reaction were analyzed. The growth of a highly homogenous film on the gold-coated glass substrate immersed in the reaction mixture at the end of the polymerization period has been observed. The molecular structure of the products was monitored with UV-visible, infrared, and Raman spectroscopies. The possible mechanism of the film formation and the molecular mechanism of the surface interaction of chemisorbed aniline oligomers with gold support are proposed.

Interfacial Synthesis of Gold-Polyaniline Nanocomposite and Its Electrocatalytic Application

Gold-polyaniline (Au-PANI) nanocomposite was prepared using a simple interfacial polymerization method, performed in an immiscible water/toluene biphasic system using tetrachloroaurate, AuCl4(-) as an oxidant. The formation of Au nanoparticles (AuNPs) or Au-PANI nanocomposite can be controlled to a certain degree by varying the ratio of initial Au(+) and aniline concentrations. Under optimal condition (HAuCl4/aniline ratio is 1:2), green dispersion of Au-PANI nanocomposite is produced in aqueous phase, whose morphology, structure and physicochemical properties are investigated in details. The nanocomposite shows granular morphology with mostly rodlike AuNPs embedded in polymer. It was found that polyaniline in the composite is in the conducting emeraldine salt form, containing high amount of Au (28.85 wt %). Furthermore, the electrical conductivity of the nanocomposite was found to be four-fold higher than that of the polymer itself. In addition, the nanocomposite powder, isolated from the as-prepared aqueous dispersion, can later be easily redispersed in water and further used for various applications. Moreover, the obtained Au-PANI nanocomposite showed excellent electrocatalytic performance toward the electrochemical oxygen reduction reaction (ORR), with high ORR onset potential and good selectivity. This makes it a promising candidate for a new class of Pt-free ORR catalyst.

Ethanol-guided synthesis of (flower-on-leaf)-like aniline oligomers with excellent adsorption properties

A novel oligoaniline with hierarchical flower-on-leaf microstructures and excellent adsorption properties has been fabricated via the oxidation of aniline in EtOH/water (3 : 7, v/v) mixtures.

In Situ Infrared Spectroscopy of Oligoaniline Intermediates Created under Alkaline Conditions

The progress of the oxidation of aniline with ammonium peroxydisulfate in an alkaline aqueous medium has been monitored in situ by attenuated total reflection (ATR) Fourier transform infrared spectroscopy. The growth of the microspheres and of the film at the ATR crystal surface, as well as the changes proceeding in the surrounding aqueous medium, are reflected in the spectra. The evolution of the spectra and the changes in the molecular structure occurring during aniline oxidation in alkaline medium are discussed with the help of differential spectra. Several processes connected with the various stages of aniline oxidation were distinguished. The progress of hydrolysis of the aniline in water and further an oxidation of aminophenol to benzoquinone imines in the presence of peroxydisulfate in alkaline medium have been detected in the spectra in real time. The precipitated solid oxidation product was analyzed by mass spectrometry. It is composed of oligomers, mainly trimers to octamers, of various molecular structures incorporating in addition to aniline constitutional units also p-benzoquinone or p-benzoquinoneimine moieties.