Quinoid Ring Research Articles

Effect of drying temperature on polyaniline electrode for polyaniline|Zn battery performance

ABSTRACT . Here, we report the effect of various drying temperature of Polyaniline (PAni) on battery PAni|Zn performance. PAni was synthesized using the electrodeposition method on the surface of the graphite sheets (GS), at 0.7 V relative to the saturated Ag/AgCl. PAni is dried with various temperature, 25, 80, 120, and 180 o C, respectively. PAni was characterized by Raman spectroscopy; then the performance Pani battery was studied in a rechargeable battery system. The measurement results found the PAni|Zn battery with 25 o C temperature drying of PAni was a good performance which the capacity density stable at 175–105 mAh g -1 until 100 cycles. Raman study showed that high-temperature drying resulted in a cleavage peak at 1188 cm -1 and increased peak intensity at 1495 cm -1 . This vibrational mode appears as a stretching ν(C-C) on the semi quinonoid ring and ν(C=N) on the quinoid ring. This phenomenon indicated the changing structure of PAni to be Emeraldine base form. KEY WORDS : Aniline, Annealing, Polyaniline, Rechargeable battery, Temperature effect Bull. Chem. Soc. Ethiop. 2019 , 33(3), 551-559. DOI: https://dx.doi.org/10.4314/bcse.v33i3.15

Spectral and thermal studies on polyaniline–titanium dioxide nanocomposites by inverted emulsion techniques

Inverted emulsion polymerization technique using benzoyl peroxide, as an initiator, was used to prepare conducting polyaniline (PANI)/nano titanium dioxide (TiO2) composites. Polyaniline ratio was varied between 10 and 90% based on the yield percentage. The prepared nanocomposites were analyzed further by Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and four probe conductivity. The FTIR spectrum of pure PANI and its composites with nano-TiO2 shows the vibrational bands due to benzenoid, quinoid ring stretching etc. Conductivity of pure polyaniline was observed to be 1.6 S cm−1 and upon the addition of nano-TiO2 the conductivity decreases. X-ray diffraction of PANI–nano TiO2 composites reveals that the crystalline nature of TiO2 is retained. TGA thermogram of nanocomposites monitored the thermal stability of pure PANI which improved by the addition of TiO2 in different ratios. SEM image reveal that nano-TiO2 particles are uniformly distributed in the PANI matrix.

Hybrid Nickel Ferrite Nanotubes Doped Polyaniline Nanocomposite and Its Dielectric Properties

Nanotubes of nickel ferrite were prepared by the citrate method and were used in nanocomposite synthesis via in situ polymerization technique. The structural and surface morphology characterizations were carried out by Fourier-transform infrared spectroscopy (FTIR), x-ray powder diffraction (XRD), and scanning electron microscopy (SEM) techniques. FTIR spectra show the characteristic peaks of benzenoid ring, quinoid ring, and nickel ferrite stretching of tetrahedral and octahedral sites. XRD pattern shows the cubic spinal structure of NiFe2O4 nanotubes and it remaining undistorted even after dispersion in a polyaniline matrix. The SEM image of 15 wt.% nanocomposite shows that the polyaniline coated nickel ferrite nanotubes form a length about 100 nm. Furthermore, the DC conductivity shows three steps conductivity feature and among all prepared nanocomposites, the 15 wt.% shows high conductivity of 1.89 S/cm. This is due to high absorption at activation energy of 0.213 × 10−2 J/mol and elongation of nanocomposites chain length which is confirmed from the negative thermal coefficient (NTC) graph. The vibrating sample magnetometer (VSM) study shows the saturation magnetization decrease after formation of polyaniline nanocomposite. The dielectric properties were analyzed by impedance analyzer, and it was found that 15 wt.% nanocomposite shows the lowest dielectric constant and dielectric loss as a result of high ac conductivity of about 1.32 S/cm which is due to the sharp drop in bulk resistance and low relaxation time of 0.1375 μs as evidenced from the cole-cole plot.

Imine-Rich Poly( o -phenylenediamine) as High-Capacity Trifunctional Organic Electrode for Alkali-Ion Batteries

Alkali-ion batteries, including potassium-ion batteries, lithium-ion batteries, and sodium-ion batteries are important energy storage devices; however, with the cation size increased, there exists ...

Single-walled carbon nanotubes–polyaniline composites: Synthesis and field-emission analysis

In this article, we report a facile synthesis and comparative analysis of field emission behavior of polyaniline (PANI)-coated as-received and annealed single-walled carbon nanotube (SWCNT) films by in-situ polymerization and ex-situ synthesis routes, respectively. Amongst all the samples, the sample prepared by in-situ polymerization method with more fraction of annealed SWCNTs in the composite gave an enhanced field emission characteristics with E to = 3 V/μm and β = 1.2 × 104 probably because of good formation of pi-pi non-covalent bonds between the SWCNTs and PANI represented by pi-pi interaction between the quinoid rings of PANI and π bond of the SWCNTs lattice. A significant increase in the threshold field is observed after annealing and doping of nanocomposite films. Field emission behavior of as-prepared nanocomposite samples are also analyzed and discussed with two PANI forms: micro-PANI particles and PANI nanofibers. It is also speculated that PANI may have helped in lowering the overall work function of the composite structure which gave an enhanced field emission. The stability of all the samples are also presented and it is analyzed that nanocomposite sample films synthesized by in-situ polymerization method showed a stability for at least 8 h. The surface morphology analysis by field emission scanning electron microscopy of nanocomposite sample films reveal an increase in SWCNTs diameter upon PANI wrapping. The high-resolution transmission electron microscopy and Raman spectra and X-ray diffraction analysis are also presented.

The Role of Polyaniline Molecular Structure in Producing High‐Performance Fe‐N‐C Catalysts for Oxygen Reduction Reaction

AbstractThe precise control of nano‐structure and increase active sites density are of crucial importance for the pyrolyzed Fe‐N−C catalysts′ performance optimization. Herein, the relationship between molecular structures of PANI precursors and the activity for oxygen reduction reaction (ORR) of the derived Fe‐N−C catalysts is investigated. The PANI molecular structure, especially the content of quinoid rings (QR), is controlled by varying molar ratios of ammonium persulfate (APS) to aniline monomers (AN). With the increase of APS/AN ratio from 0.5 to 4, the oxidation degree together with the QR content of PANI increases. Accordingly, the produced catalysts’ morphology experiences an evolution from bulk, nanotube to flower‐like structure. And the ORR activity shows volcano‐relationship with the increase of the QR content in PANI precursors. Specifically, when APS/AN=2.5, the derived PANI with moderate QR content benefits to produce Fe‐N−C catalyst which shows the maximum ORR activity with a half‐wave potential of 0.74 V (vs RHE) in acidic electrolyte among the produced catalysts. Moreover, two opposite effects with the increasing QR content are revealed; i) the QR benefits the Fe coordination and Fe−Nx active sites formation which enhances the activity, and ii) the accompanying formed oligomers decrease the thermal stability and thus decrease the number of active sites.

Chitosan/Polyaniline Conductive Blends for Developing Packaging: Electrical, Morphological, Structural and Thermal Properties

The present study aim to evaluate the development of electrical conducting blends made from the biodegradable polymer, chitosan (Cs), and polyaniline (PANI) doped with dodecylbenzene sulfonic acid dissolved in acid solution chitosan, to enable development of conductive and smart packages that help to monitor exposure conditions of food aimed to reduce food waste. Concentration of Cs is fixed (2%), and PANI (80, 100 mg mL−1) and glutaraldehyde (Glut) (0.625 × 10−3 μL) concentrations are alter. Morphological (SEM), structural (FTIR, RAMAN), thermal (TGA) and electrical (Hall effect) properties are evaluate. Blends were predominantly negative carriers, with conductivity in order of 10−1 S cm−1. Best formulations are those make without of Glut. Analyses show an interaction between components. FTIR show bands characteristic of benzene and quinoid rings of PANI, and RAMAN exhibit a band related to PANI’s protonation. TGA show maintenance of maximum degradation temperature of PANI. This results evidence maintenance of PANI’s conducting structures even after blends synthesis.

Synthesis of polyaniline-modified graphene oxide for obtaining a high performance epoxy nanocomposite film with excellent UV blocking/anti-oxidant/ anti-corrosion capabilities

This paper focuses on the synthesis and modification of graphene oxide nanosheets with polyaniline. The main aim is to take the advantages of both graphene oxide and polyaniline in enhancing the long-term performance (including weathering and corrosion) of exterior nanocomposites. For this purpose, the synthesized graphene oxide was treated via an in-situ polymerization process. The modified hybrid nanosheets were characterized by Fourier transform infrared spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction analysis (XRD), Ultraviolet–visible spectrophotometry (UV–Vis) and Raman spectroscopy. It was approved that the emeraldine base form of polyaniline has been successfully polymerized on the graphene oxide nanosheets in two forms of non-covalent bonding through π-π interactions between quinoid ring of PANI and basal plane of graphene oxide, and covalent bonding through reaction with epoxide group. The modified nanosheets were introduced into a typical epoxy matrix and then subjected to accelerated weathering and corrosion cycles. The results revealed that a considerable improvement in both weathering (42% reduction in ΔE) and corrosion resistance was achieved which was mainly attributed to the considerable enhancement in UV shielding, radical scavenging as well as better dispersion of graphene oxide modified with polyaniline.

Polyaniline-Modified Hydrolyzed Polyethylene Separators for High-Performance Lithium-Sulfur Batteries

The practical application of lithium-sulfur battery (LSB) is limited owing to its poor cycling stability stemming from the ‘shuttle effect’ or the migration of soluble polysulfide intermediates (Li2Sn, 4 ≤ n ≤ 8). Numerous strategies have been proposed to solve this issue by designing host materials to control polysulfides within the cathode, developing electrolytes to be able to reduce polysulfide solubility, and adding interlayers to block polysulfide migration to the anode.[1] However, these concepts are far from practical operation. Herein, we introduce the modified polyethylene separator with an objective for reducing the ‘shuttle effect’. The commercial hydrolyzed polyethylene (HyPE) separator was firstly functionalized with carboxylic acid (-COOH) groups before grafting polyaniline (PANI) molecules on its surface via an amide coupling process for which the -COOH on the HyPE surface can chemically react with imine groups (-N=) of the PANI structure. Interestingly, the battery with the modified PANI separator can enhance the specific capacity and coulombic efficiency for 10 and 15%, respectively, as compared with the conventional cell configuration using the PE seperator. Owing to the chemical interaction between the imine group of the quinoid ring in the structure of PANI and the lithium polysulfide molecules, the polysulfide species are retained on the PANI/HyPE surface until Li2S is fully formed.[2] This idea can improve the sulfur utilization and enhance the stability of the lithium-sulfur batteries.

Malleable Electronic Structure of Chloranilic Acid and Its Species Determined by X-ray Charge Density Studies

Herein, we present a detailed X-ray charge density study of the electron delocalization in five species of chloranilic acid: neutral molecule, mono- and dianion, and two chelating modes: bidendate and (bis)bidentate. The experiments provide the electron density at the bond critical points, which yields an accurate measure of bond order (and therefore electron delocalization), and complement previous literature and our data on bond lengths extracted from crystal structures and infrared spectra. Mapping of the electrostatic potential indicates electron-rich and electron-poor areas in the molecule, corresponding to single (electron-poor), double, and delocalized bonds (electron-rich) that can explain stacking interactions of quinoid rings in crystal packing.

Synthesis and characterization of polyaniline-drug conjugates as effective antituberculosis agents

Polyaniline (PANI) and its drug composites with some drugs like Neomycin (NM), Trimethoprim (TMP) and Streptomycin (ST) have been prepared by oxidative polymerization of aniline using hydrochloric acid (HA) and ammonium persulfate (APS) as a dopant and as an oxidant, respectively. The structures of PANI and PANI-drug composites were elucidated by FTIR and NMR spectroscopy, which confirmed the presence of benzenoid and quinoid rings in the synthesized compound. Molecular weight and thermal stability were determined by gel permeation chromatography (GPC) and thermogarvimetric analysis, respectively. From the GPC, PDI values of PANI-NM, PANI-TMP and PANI-ST were found to be 1.37, 1.23 and 1.56, respectively. For the study of antibacterial behavior of the synthesized PANI and PANI-drug composites, different micro-organisms, namely, four Gram positive (S. aureus MTCC 96, B. subtilis MTCC 441, S. pyogenes MTCC 442 and S. mutans MTCC 890) and four Gram negative (S. typhi MTCC 98, KL. pneumoniae MTCC 109, E. coli MTCC 443 and P. aeruginosa MTCC 1688) bacteria were selected due to their pharmacological importance. Some of the PANI-drug composites were found to show excellent results as compared to components polyaniline and drugs used for composite formation. Antituberculosis activity of the PANI and its drug composites against Mycobacterium tuberculosisH37RV (acid fast Bacilli) was determined. MIC values for PANI-NM and PANI-TMP were found to be 0.12 and 0.20 µg/mL, respectively. Results suggested that some of the drug composites may be tried as potential candidates for use as an antituberculoid agent to reduce TB transmission.

Towards understanding π-stacking interactions between non-aromatic rings.

The first systematic study of π interactions between non-aromatic rings, based on the authors' own results from an experimental X-ray charge-density analysis assisted by quantum chemical calculations, is presented. The landmark (non-aromatic) examples include quinoid rings, planar radicals and metal-chelate rings. The results can be summarized as: (i) non-aromatic planar polyenic rings can be stacked, (ii) interactions are more pronounced between systems or rings with little or no π-electron delocalization (e.g. quinones) than those involving delocalized systems (e.g. aromatics), and (iii) the main component of the interaction is electrostatic/multipolar between closed-shell rings, whereas (iv) interactions between radicals involve a significant covalent contribution (multicentric bonding). Thus, stacking covers a wide range of interactions and energies, ranging from weak dispersion to unlocalized two-electron multicentric covalent bonding ('pancake bonding'), allowing a face-to-face stacking arrangement in some chemical species (quinone anions). The predominant interaction in a particular stacked system modulates the physical properties and defines a strategy for crystal engineering of functional materials.

Synthesis of a Polyaniline Nanoparticle Using a Solution Plasma Process with an Ar Gas Bubble Channel.

This work researched polymerization of liquid aniline monomer by solution plasma with a gas bubble channel and investigated characteristics of solution plasma and polyaniline (PANI). The injected gas bubble channel in the proposed solution plasma process (SPP) played a significant role in producing a stable discharge in liquid aniline monomer at a low voltage and furthermore enhancing the contact surface area between liquid aniline monomer and plasma, thereby achieving polymerization on the boundary of the liquid aniline monomer and plasma. Solution plasma properties were analyzed with voltage–current, optical emission spectroscopy, and high-speed camera. Conductivity, percentage yield, and firing voltage of PANI nanoparticle dispersed solution were measured. To investigate the characteristics of synthesized PANI nanoparticles, field emission scanning electron microscopy, dynamic light scattering, transmission electron microscopy, selective area electron diffraction (SAED) pattern, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography, 1H-nuclear magnetic resonance (1H-NMR), and X-ray photo spectroscopy (XPS) were examined. The FTIR, 1H-NMR, and XPS analysis showed the PANI characteristic peaks with evidence that some quinoid and benzene rings were broken by the solution plasma process with a gas bubble channel. The results indicate that PANI nanoparticles have a spherical shape with a size between 25 and 35 nm. The SAED pattern shows the amorphous pattern.

Supramolecular Architecture of Chloranilate Salts with Organic Cations

Four novel salts of chloranilic acid (H2CA; 3,6-dichloro-2,5-dihydroxy-1,4-quinone) with organic cations pyridinium (Hpy+), piperazinediium (H2ppz2+), 4,4'-bipyridinediium (H2bpy2+) and 1,10-phenanthrolinium (Hphen+) were prepared and structurally characterised: (Hpy)2CA (1), (H2ppz)CA (2), (H2bpy)CA·4H2O (3) and (Hphen)HCA·MeOH (4). Supramolecular architecture is based on extensive hydrogen bonding and π-stacking. The central motive is chloranilate dianion which acts as an acceptor of two bifurcated hydrogen bonds. Topology and dimensionality of hydrogen bonded networks can be tuned by use of different cations: thus discrete motives, 1D chains and 2D layers were observed. Three different types of π-stacks are present: aromatic stacks, quinoid stacks and stacks of alternating quinoid and aromatic rings.

Polyaniline-grafted hydrolysed polyethylene as a dual functional interlayer/separator for high-performance Li-S@C core-shell batteries.

A modified hydrolysed polyethylene with polyaniline was used as a dual functional interlayer/separator for high-performance lithium-sulphur batteries (LSBs) to reduce the migration of soluble polysulphide intermediates. Also, the sulphur cathode was encapsulated with carbon nanoparticles with a S@C core-shell structure using a solvent-free coating process. The chemical interaction between the imine group of the quinoid ring in the PANI structure and the polysulphides reducing the shuttle effect as well as the high electrical conductivity and less volume change of the carbon encapsulated sulphur can provide high-performance Li-S@C core-shell batteries.

Effect of dopant on the properties of polyaniline/carbon nanofiber composites

Polyaniline-modified carbon nanofibers were prepared in the presence of five different dopant acids, namely toluene sulfonic acid (TSA), hydrochloric acid (HCl), sulfuric acid (H2SO4), phosphoric acid (H3PO4) and camphor sulfonic acid (CSA), by oxidative polymerization. A comparative study on the effect of various types of dopants on the properties of PANI/CNF composite was performed. The electrical, dielectric and thermal properties of PANI/CNF composites were studied in contrast to pure PANI. Unlike polyaniline, all polyaniline/carbon nanofiber combination resulted in enhanced electrical and dielectric properties. Higher conductivity and thermal dependence of DC conductivity were obtained for toluene sulfonic acid-doped composite. UV–Vis analysis of the composites showed that the appreciable increase in conductivity of TSA-doped PANI/CNF composite is due to the extensive electron transfer. Further, thermogravimetric analysis showed improved thermal stability compared to PANI. A significant improvement is observed for organic acid-doped composites which suggest the presence of strong interaction between π orbitals of CNF and the quinoid rings of PANI. Hence, the study indicated that the dopants had a remarkable effect on the properties of PANI/CNF composites.

Itaconic acid–doped polyaniline/MWCNTs nanocomposites for microwave absorbing materials

Itaconic acid–doped polyaniline (PANI)/multiwalled carbon nanotubes (MWCNTs) nanocomposites were prepared via in situ polymerization for microwave absorbing materials. The interaction between PANI and MWCNTs and the influence of MWCNTs loadings on the properties of their nanocomposites were investigated by various measurements, such as Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, thermogravimetric analysis, and network analyzer. The electron delocalization in the composites is associated with the π–π* interaction between the surface of MWCNTs and the quinoid rings of PANI. The conductivity, crystallinity, and thermal stability of the nanocomposites with different morphologies have been increased due to the introduction of different MWCNTs loadings. Moreover, the microwave-absorbing property of itaconic acid-doped PANI in the reflection loss value and in different frequency areas is improved by the incorporation of MWCNTs. The nanocomposites are promising candidates in microwave absorption applications.

Crossflow electrochemical filtration for elimination of ibuprofen and bisphenol a from pure and competing electrolytic solution conditions.

For the first time, a crossflow electrochemical filtration system containing multiwalled carbon nanotubes (MWNTs) blended with buckypaper as a flat sheet dual membrane electrode was investigated for the removal of two contaminants of emerging concern, Ibuprofen and Bisphenol A. Breakthrough experiments revealed that a crossflow configuration could be highly efficient in eliminating both contaminants at applied DC potentials of 2 and 3 V over an extended period, from pure salt electrolyte as well as from synthetic secondary wastewater effluent. The shear flow provided consistent surface coverage resulting in excellent sorption performance. The long residence time of the two contaminants within the membrane (18.3 s) was sufficient enough to allow for almost complete degradation of phenolic aromatic products and quinoid rings and the resulting formation of aliphatic carboxylic acids, which was more evident at a higher applied potential (3 V). The formation of the non-toxic aliphatic carboxylic acids is a clear indication of the superior electrochemical performance of the crossflow mode over the dead-end flow-through system. Moreover, this study provides an in-depth understanding of different factors such as filter surface area and residence time that can greatly affect the removal of the contaminants considered.

Effect of Different Electrolytes on the Supercapacitor Behavior of Single and Multilayered Electrode Materials Based on Multiwalled Carbon Nanotube/Polyaniline Composite

AbstractIn the present study, the electropolymerization (template synthesis) and then fabrication of symmetrical supercapacitors based on single and multilayered multiwalled carbon nanotube/polyaniline (MWCNT/PA) is achieved. It is found that the morphology and capacitance values depend strongly on the nature and concentration of electrolytes. The presence of micro and mesopores on the MWCNTs provides the space for the deposition of PA on them. The extended conjugation results due to the overlapping of π electron cloud of sp2 hybridized carbon network of MWCNT with quinoid rings of three layers of PA doped with three dopants. This leads to the highest capacitance of 333 F g−1 and good charge–discharge cycling behavior with 85% charge retention at 1000 cycles for the symmetrical supercapacitor based on the multilayered composite material.

Iodide···π Interactions of Perhalogenated Quinoid Rings in Co-crystals with Organic Bases

First anion···π contacts with quinoid rings have been described in novel co-crystals of tetrabromo- and tetrachloroquinone with iodide salts of substituted N-methylpyridinium cations. In seven crys...