Effect of Oxidants on Properties of Electroactive Ultrathin Polyazulene Films Synthesized by Vapor Phase Polymerization at Atmospheric Pressure

A non-benzenoid aromatic hydrocarbon azulene, naturally found in plants and mushrooms, is known for its derivatives applications in medicines. However, the processability of its chemically synthesized high-capacitance polymer is constrained by the sparingly soluble nature of its polymeric form. Oxidative chemical synthesis on a desirable substrate overcomes this difficulty. In this report, polyazulene (PAz) thin films are synthesized by vapor phase polymerization at atmospheric pressure using oxidants, such as CuCl2, CuBr2, FeCl3, and FeTOS. The effect of oxidants on morphologies of PAz films is studied using atomic force microscopy and microscope imaging. Each oxidant produced distinct microstructures in the films. The films synthesized using Cu(II) salts showed organized and knitted structures, whereas Fe(III) salts formed casted sheet-like disordered arrangements. The films synthesized using CuCl2 created uniform porous film assemblies. The pre-peak formations and their splitting observed in the cyclic voltammograms revealed phase segregations in the films. Oxidant-dependent structural and chemical differences such as charge carrier formation, doping levels, and polymer chain length in the PAz films are studied by using UV-Vis and FTIR spectroscopy. The results indicated that 240 and 180 mM are the optimum concentration of CuCl2 to produce high capacitance and well-organized single-and triple-layered PAz films, respectively.</p

Improved long term cycling of polyazulene/reduced graphene oxide composites fabricated in a choline based ionic liquid

To improve the energy density of supercapacitors, novel electronically conducting polymers should be introduced to the research field. Polyazulene is a well-suitable candidate as it exhibits good capacitive behavior both in organic solvents as well as in various ionic liquids, but especially its long term cycling stability should be improved. Previously, enhanced properties have been obtained by combining conducting polymers with carbon nanomaterials to fabricate composites. This work presents an ionic liquid assisted electrochemical polymerization and characterization of polyazulene-reduced graphene oxide composites. The ionic liquid of our choice is choline-based liquid salt. We prepared stable dispersions of graphene oxide in this ionic liquid and performed potentiodynamic electropolymerization of azulene in the mixture. Changing the concentration of graphene oxide between 0.1 and 2 mg mL(-1) had no remarkable effect on the polymerization or electrochemical behavior of the composite materials. The composites exhibit higher capacitances compared to neat polymer films determined by cyclic voltammetry and electrochemical impedance spectroscopy. The obtained films also exhibit excellent cycling stabilities retaining over 90% of their initial capacitance with tendency towards improved cycling stability when combined with reduced graphene oxide. The successful incorporation and reduction of graphene oxide was determined by several spectroscopic techniques

Fabrication of electroactive multi-layered polyazulene thin films by atmospheric pressure-vapor phase polymerization

Thin films of polyazulene (PAz) are produced by using an optimized atmospheric pressure–vapor phase polymerization (AP-VPP) method. Method optimization is carried out by studying the effect of cell temperature, substrate temperature, polymerization time, and washing-solvent on film properties like optical bandgap, sheet resistance, surface roughness, and % transmittance (%T). Multi-layered PAz films were produced by layer-by-layer engineering. The effects of thin, electroactive multiple layers on film properties are investigated. UV–Vis, IR, and Raman analysis are utilized to understand the extended conjugation length and nature of the charge carriers. The spectroscopic data revealed the anomalous behaviour of PAz at a high level of doping. The proportion and amount of quinoid conformation is discussed. The addition of layers changes the transport of ions across the electroactive PAz films, which is studied using cyclic voltammetry at various scan rates. AFM and SEM images reveal a change in structural properties which is further correlated with a deviation of capacitance values at elevated scan rate. Comparison with earlier reported literature on electrochemically and chemically synthesized PAz is also provided. The conductivity, transparency and high capacitance show a promising application of AP-VPP PAz in various fields.</p

Exploring amide linkage in a polyviologen derivative towards simultaneous voltammetric determination of Pb(II), Cu(II) and Hg(II) ions

In this study, we report reductive electrosynthesis of a polyviologen derivative bearing amide linkage in its side chain, derived from a cyanopyridinium based monomer with amide functionality. The as grown film was characterized by cyclic voltammetry which displays a well-defined and reversible two step redox response characteristic of viologen. FTIR analysis show evidence of amide linkage and successful reduction of cyanopyridinium moieties to polyviologen. In situ multi ESR/UV-Vis-NIR spectroelectrochemistry show a single line in ESR signal, thereby suggesting polarons as the only charge carrier involved during charging/discharging process. Furthermore, a characteristic UV&ndash;Vis absorption spectra confirms viologen formation. Finally, the polyviologen film is subjected to simultaneous voltammetric determination of heavy metal ions, Pb(II), Cu(II) and Hg(II). The amide linkage in the polyviologen derivative is supposedly complexing these divalent metal ions, enabling their sensitive and simultaneous determination with low detection limits.</div

Synthesis of Layered Double Hydroxides and TiO2 Supported Metal Nanoparticles for Electrocatalysis

In the present work, solution-phase synthesis was employed to prepare two sets of catalysts with different transition metals as active sites. One set contained Au or Pd supported on TiO2 (Au-TiO2, Pd-TiO2), whereas the other set contained layered double hydroxides (NiFe-LDH and CuFe-LDH). The electrocatalytic performance of these composite materials was investigated by cyclic voltammetry (CV) using a model compound 4-nitrophenol (4-NP). Composite materials were characterized by various analytical techniques to gain insight into the catalysts active sites. The morphology and structure of the prepared samples were investigated by X-ray diffraction, attenuated total reflectance Fourier transform infrared, X-ray photoelectron spectroscopy, transmission scanning electron microscope, and field emission scanning electron microscope. Metal nanoparticles loading on TiO2 was measured by inductively coupled plasma - optical emission spectrometry. CV measurements were performed in acetonitrile solution containing 0.1 m tetrabutylammonium hexafluorophosphate (TBAPF(6)) and 1 mm 4-NP. Among all dioxides (Au-TiO2, Pd-TiO2) and hydroxides (NiFe-LDH and CuFe-LDH) studied, Pd-TiO2 shows the lowest onset potential (-0.32 V vs. Ag/AgCl) for the electrocatalytic reduction of 4-NP. This is the first comparative study of such materials for 4-NP electrocatalysis in aprotic solvent, thus demonstrating the suitability of dioxide and hydroxide based materials as electrocatalysts

Study of the sterile conk of Inonotus obliquus using 13C CPMAS NMR and FTIR spectroscopies coupled with multivariate analysis

The sterile conk caused by the infection of the basidiomycete Inonotus obliquus (Chaga) is an important source of bioactive compounds. However, its structure and biochemistry are only generally understood. Solid state 13C NMR and FTIR spectroscopy have been utilized for the first time to investigate the sterile conk with non-invasive methods. The application of multivariate data analysis techniques and spectral distance algorithm to the obtained datasets showed clear distinction between the outer and inner layers of the sterile conk. Moreover, the sterile conk bark, compared to the inner layers, was spectroscopically more similar to wood tissues. The fungal tissue was proven to be concentrated below the bark. The similarity of the sterile conk inner layers to both decayed wood and hyphae of I. obliquus was shown by the multivariate data analysis of both spectra datasets. The spectroscopic data indicated lack of lignin degradation in the heart rot, except for demethoxylation, and a slight preference for hemicellulose degradation. Therefore, the results obtained suggest that the classification of I. obliquus as preferential lignin degrader (white-rot fungus) should be revised and clarified by further studies.</p

J-like aggregation of a cationic polythiophene with hydrogen-bonding capabilities due to 1,4-dioxane: Solution excitation spectra and fluorescence, morphology and surface free energy of films

This work presents solution- and solid-state evidence of the enhancement of J-like aggregation of a cationic polythiophene (CPT) with isothiouronium functionalities (PT1), caused by a decrease in the polarity and hydrogen-bonding (H-bonding) capacity of the solvent, generated by using a 50:50 v/v 1,4-dioxane-water mixture (W-DI) instead of water. In solution, the presence of 1,4-dioxane (DI) seems to generate selective solvation, tuning the energy transfer within PT1 from inter-chain into intra-chain, enhancing J-like aggregation. On the other hand, during the casting process, the presence of DI directs the interaction with solid-substrates, generating an increase in the solid-state fluorescence, modifying the morphology from one similar to ballistic-aggregation (BA) into one similar to attachment limited aggregation (ALA), DI also modifies the SFE by increasing slightly its polar contribution (γSp) and decreasing the dispersive one (γSd). These results can be explained to be caused by a "coating" effect in presence of DI (as proposed before experimentally and computationally). Our results show a clear correlation between the solution- and solid-state properties of PT1 in each solvent, further validating the use of the fluorescence excitation spectra to trace J-like aggregation of water-soluble conjugated polymeric fluorophores in solution. This information could be useful for predicting and designing specific mesoscopic architectures of CPTs (and conjugated polyelectrolytes in general), which are molecules lacking of clear structure-function guidelines for designing high-performance polythiophene-based interlayer materials, especially for CPTs (and conjugated polyelectrolytes (CPEs) in general), particularly those with H-bonding capabilities. To the best of our knowledge the use of solution-state fluorescence excitation spectra to identify J-like aggregation of water-soluble conjugated polymers (CPs) has been scarcely used/discussed in literature and no correlation with solid-state properties was reported previously

Cationic Imidazolium Polythiophenes: Effects of Imidazolium-Methylation on Solution Concentration-Driven Aggregation and Surface Free Energy of Films Processed from Solvents with Different Polarity

Cationic imidazolium-functionalized polythiophenes with single- or double-methylation of the imidazolium ring were used to study the impact of imidazolium-methylation on (i) the solution concentration-driven aggregation in the presence of paramagnetic probes with different ionic and hydrophobic constituents and (ii) their surface free energy (SFE) as spin-coated films deposited on plasma-activated glass. Electron paramagnetic resonance spectroscopy shows that the differences in film structuration between the polymers with different methylations originate from the early stages of aggregation. In the solid state, higher degree of imidazolium-methylation generates smaller values of total SFE, gamma S, (by around 2 mN/m), which could be relevant in optoelectronic applications. Methylation also causes a decrease in the polar contribution of gamma S (gamma Sp), suggesting that methylation decreases the polar nature of the imidazolium ring, probably due to the blocking of its H-bonding capabilities. The values of gamma S obtained in the present work are similar to the values obtained for doped films of neutral conjugated polymers, such as polyaniline, poly(3-hexylthiophene), and polypyrrole. However, imidazolium-polythiophenes generate films with a larger predominance of the dispersive component of gamma S (gamma Sd), probably due to the motion restriction in the ionic functionalities in a conjugated polyelectrolyte, in comparison to regular dopants. The presence of 1,4-dioxane increases gamma Sp, especially, in the polymer with larger imidazolium-methylation (and therefore unable to interact through H-bonding), probably by a decrease of the imidazolium-glass interactions. Singly-methylated imidazolium polythiophenes have been applied as electrode selective ("buffer") interlayers in conventional and inverted organic solar cells, improving their performance. However, clear structure-function guidelines are still needed for designing high-performance polythiophene-based interlayer materials. Therefore, the information reported in this work could be useful for such applications

Characterization of Hardwood-Derived Carboxymethylcellulose by High pH Anion Chromatography Using Pulsed Amperometric Detection

An approach for the quantitative analysis of substituent distribution in carboxymethylcellulose (CMC) is presented. In short, the high-pH anion-exchange chromatography method, coupled to pulsed amperometric detection (PAD), is introduced. Each of the seven derivatives in CMC is presented by a single peak on the PAD trace, thus enabling an easy quantification. New inside information on monomer composition is obtained by this novel method, which is essential for understanding the structure versus property relationships in the CMC samples

Effect of Oxidants on Properties of Electroactive Ultrathin Polyazulene Films Synthesized by Vapor Phase Polymerization at Atmospheric Pressure

A non-benzenoid aromatic hydrocarbon azulene, naturally found in plants and mushrooms, is known for its derivatives applications in medicines. However, the processability of its chemically synthesized high-capacitance polymer is constrained by the sparingly soluble nature of its polymeric form. Oxidative chemical synthesis on a desirable substrate overcomes this difficulty. In this report, polyazulene (PAz) thin films are synthesized by vapor phase polymerization at atmospheric pressure using oxidants, such as CuCl2, CuBr2, FeCl3, and FeTOS. The effect of oxidants on morphologies of PAz films is studied using atomic force microscopy and microscope imaging. Each oxidant produced distinct microstructures in the films. The films synthesized using Cu(II) salts showed organized and knitted structures, whereas Fe(III) salts formed casted sheet-like disordered arrangements. The films synthesized using CuCl2 created uniform porous film assemblies. The pre-peak formations and their splitting observed in the cyclic voltammograms revealed phase segregations in the films. Oxidant-dependent structural and chemical differences such as charge carrier formation, doping levels, and polymer chain length in the PAz films are studied by using UV–Vis and FTIR spectroscopy. The results indicated that 240 and 180 mM are the optimum concentration of CuCl2 to produce high capacitance and well-organized single- and triple-layered PAz films, respectively