Polyaniline Backbone Research Articles

Impedance study of thiolated polyaniline

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H2SO4. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.

Single-walled carbon nanotubes and polyaniline composites for capacitive deionization

Single-walled carbon nanotubes (SWCNTs) and polyaniline (PANI) composites with different proportions of SWCNTs were synthesized by in situ polymerization. The resultant composites were characterized by Fourier Transform Infrared (FTIR) spectroscopy and their morphology was studied by transmission electron microscopy (TEM). Their specific surface areas were determined by N2 adsorption/desorption tests and the mesoporous structure of the composites was analyzed using the Barrett–Joyner–Halenda (BJH) method. A band shift in the FTIR spectrum indicates a strong interaction between PANI and SWCNTs. The mesopore volume was increased by introducing PANI into the SWCNTs. Cyclic voltammetry (CV) was carried out to study their electrochemical properties. The SWCNT/PANI composites obtained exhibited reversible electrochemical and faster ion transport properties, even in a neutral aqueous environment. This is probably due to \\pi - \\pi interaction between the PANI backbone and the graphite-like structure of carbon nanotubes. Finally, a capacitive deionization (CDI) test was conducted in a batch mode bench-scale cell. The electrodes made from SWCNT/PANI composites showed a higher ion electrosorption capacity than those made from SWCNTs alone and the composite electrodes can be easily regenerated, indicating excellent recyclability.

Cobalt ferrite–polyaniline heteroarchitecture: a magnetically recyclable photocatalyst with highly enhanced performances

A cobalt ferrite–polyaniline photocatalyst is successfully prepared by in situ oxidative polymerization. The excellent magnetic properties of CoFe2O4 are maintained in the composite to some extent, and therefore the photocatalyst can be separated easily by an external magnetic field. A significant adsorption can be observed in the case of the anionic dyes and neutral dyes because the negatively charged groups or the electron-rich groups of these dyes undergo chemical interactions with the positively charged backbone of polyaniline (PANI). Such an adsorption helps in promoting the photodegradation of the dyes. It is interesting that although CoFe2O4 alone is an inactive visible-light-driven photocatalyst, the combination of CoFe2O4 nanoparticles with PANI leads to high photocatalytic activity for the degradation of the dyes under visible light irradiation. The dramatic enhancement in photoactivity can be attributed to the excited state electrons in PANI which can migrate to the conduction band (CB) of CoFe2O4, and the photogenerated holes in the valence band (VB) of CoFe2O4 which can directly transfer to the HOMO of PANI, effectively preventing a direct recombination of electrons and holes. Due to electrostatic repulsion, the cationic dyes containing positively charged groups cannot easily gain access to the positively charged backbone of PANI, giving very low photodegradation rates.

Enhanced thermoelectric properties of CNT/PANI composite nanofibers by highly orienting the arrangement of polymer chains

Carbon nanotube (CNT)/Polyaniline (PANI) thermoelectric composite nanofibers were prepared by a combination of in situ polymerization and electro-spinning processes. The obtained composite nanofibers were macroscopically aligned, while the CNTs were embedded in the nanofibers and oriented along the fiber axis. Polarized Raman spectra and X-ray diffraction (XRD) studies verified that the PANI backbone chains were orientated along the CNT axis and therefore along the fiber axis due to the strong chemical interactions between PANI and CNTs. The highly ordered arrangement of the PANI backbone chains not only reduces the π–π conjugated defects in the polymer backbone, but also increases the effective degree of electron delocalization and therefore enhances the carrier mobility in PANI, which results in the anisotropic thermoelectric properties especially with more than a doubled improvement of power factor in the orientation direction. This study not only provides an effective route to orient the conducting polymer chains at the molecular level but also demonstrates a possibility to design a conducting polymer with high thermoelectric performance through constructing a highly extended and orderly aligned backbone chain structure by chemical routes.

Identification of Aspartic Acid Enantiomers Based on Molecularly Imprinted Polyaniline

AbstractAffinity sites for L‐aspartic acid (L‐Asp) in polyaniline (PAn) were created by two successive processes: first, L‐Asp was simply added as template molecules during the polymerization of aniline; second, L‐Asp incorporated in PAn backbone was extracted by solvent. PAn with cavities complementary to L‐Asp template molecules has been utilized for enantioselective recognition of L‐ and D‐Asp. Enantioselectivity of the imprinted PAn could be attributed to the cavities in the imprinted PAn which was complementary to L‐Asp templates both in shape and in positioning of groups. Also in this paper, the structural changes before and after extraction of L‐Asp templates were revealed by Fourier‐transform infrared (FTIR) spectrum.

Synthesis, Electrical Conductivity, Spectral and Thermal Stability Studies on Poly(aniline-co-o-nitroaniline)

o-Nitroaniline units were incorporated in the polyaniline backbone through copolymerization with aniline. The copolymers were synthesized for 1:3 and 1:1 molar ratios of aniline and o-nitroaniline in acidic medium using potassium persulphate as oxidant and their properties were compared with that of polyaniline. The polymers showed less electrical conductivity than polyaniline. Unlike polyaniline, the presence of nitro group caused higher frequency dependence of electrical conductivity. Electronic spectra showed a blue shift in both the band of the copolymers due to the decrease in the extent of conjugation leading to lower conductivity, which could also be explained in terms of a decrease of delocalization of electron as evinced from electron para magnetic resonance (EPR) data. Thermo gravimetric analysis (TGA) revealed that copolymer derived from 1:1 molar ratio showed comparable thermal stability with polyaniline and the one derived from 1:3 molar ratios is thermally less stable than polyaniline. Activation energies for thermal degradation were estimated using Broido equation. The temperature dependence of electrical conductivity suggested charge transport is mainly through variable range hopping.

Synthesis of water‐soluble and conducting polyaniline by growing of poly (N‐isopropylacrylamide) brushes via atom transfer radical polymerization method

AbstractPolyaniline‐graft‐Poly(N‐isopropylacrylamide) copolymers were synthesized by atom‐transfer radical polymerization (ATRP) of N‐isopropylacrylamide using polyaniline macro‐initiators. Polyaniline‐chloroacetylchloride and polyaniline‐chloropropionylchloride macroinitiators were obtained by the reaction of amine nitrogens of polyaniline with chloroacetyl chloride and 2‐choloropropionyl choloride, respectively. Both macroinitiators and graft copolymers were characterized by FT‐IR and 1H‐NMR spectroscopy. The cyclic voltammetry (CV) and UV‐Vis spectroscopy studies showed that these copolymers are electroactive. The solubility test revealed that the polyaniline‐graft‐poly (N‐isopropylacrylamide) copolymers are water soluble or water/methanol soluble. The Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) images showed the growing of poly (N‐isopropylacrylamide) chains on polyaniline backbone. Investigation of thermal behavior of graft copolymers by thermal gravimetry analysis (TGA) confirmed the results obtained from AFM and SEM images. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A facile route to hollow microspherical polyaniline

A facile method to prepare polyaniline hollow microsphere was developed using potassium hexacyanoferrate (III) as oxidant for polymerization of aniline in aqueous condition without acid or alkali or organic solvent, and doped polyaniline with electrical conductivity of Ca. 10−3 S/cm was directly obtained with hexacyanoferrate (II) anion surrounding imine and amine atoms in polyaniline backbone, which was seven orders of magnitude higher than that of polyaniline hollow spheres synthesized in alkaline medium (Ca. 10−10 S/cm). The hollow spherical structure was formed by a self-assembly process of spherical aniline micelles as shell and inner aniline droplet as core, and nanoscale polydispersed hollow spheres whose diameter varied from 380 nm to 700 nm with a shell thickness from 50 nm to 78 nm were readily obtained.

Interaction of polyaniline with hydroxyl-ions in N-methylpyrrolidinone

Interaction of emeraldine base (EB) of polyaniline (PANI) with tetraalkylammonium hydroxides (TAAHs) has been studied in N-methylpyrrolidinone solutions and complex films. The spectral changes in the solutions at the early stage of the interaction showed features typical of the increased intramolecular conductivity in PANI backbone, which has been assigned to a “pseudo” doping effect upon interaction of EB with TAAHs. Conductivity of films was found to also increase, however, intrinsic electronic conductivity of the films was completely masked by the ionic one. The above effect has been compared with that of the conventional inorganic base KOH in the same medium. It has been found that similar changes in electronic absorption spectra of EB take place within some range of concentrations of KOH in the mixture. The conclusion on strong interaction of EB and the above bases was supported by IR spectra of the complex films, which evidenced in favor of the chemical transformation of the polymer backbone. The final product was found to be unstable and degrades readily. Based on the above results the interaction of PANI and the bases used is discussed. A scheme of the possible PANI transformations is suggested.

Imidazole functionalized polyaniline: Synthesis, characterization, and Cu (II) coordination studies

AbstractPolyaniline functionalized with imidazole as strategically designed receptor group in its backbone was synthesized for copper binding. The synthesized polymer has been characterized using FTIR, NMR, and UV‐Vis spectroscopic techniques. The addition of copper (II) to the polymer distinctly changes the properties such as crystallinity, molecular weight, aggregation, and electronic properties. XRD, DLS, SEM, and four‐point probe techniques have been used for study of these changes. It is observed that the secondary ion generated as a result of copper coordination results in the doping of the polyaniline backbone, which enhances the conductivity by one order of magnitude. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Cooperative doping in polyaniline-poly(ethylene-3,4-dioxythiophene): poly(styrenesulfonic acid) composite system

Interaction of emeraldine base of polyaniline (PANI) and poly(ethylene-3,4-dioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) in a complex solution is shown to lead to a new polymer complex whose components act to each other to favor an increase in intramolecular conductivity in both PANI and PEDOT backbones. Asymmetric changes in intramolecular conductivity of the polymer mixture have been demonstrated upon addition of PANI to PEDOT:PSS dispersion and vise versa. Complex films cast from the solution revealed a specific spherulite-like morphology and increased conductivity up to one order of magnitude as compared to films of the net PEDOT:PSS, which allowed us to conclude on formation of a qualitatively new system rather than a simple blend of the polymers and the effect of cooperative doping of the components by each other, respectively. The doping efficiency was shown to be strongly dependent on the solvent environment and concentration of the polymers in solutions. It is discussed that the increase in conductivity of the composite system is controlled not only by the direct doping of PANI with PSS, but also by weakening of interaction of PSS with the PEDOT backbone itself as a result of the above doping process.

Polyaniline Nanoscaffolds for Colorimetric Sensing of Biomolecules via Electron Transfer Process

Biologically important analytes such as cysteine and vitamin-C were detected by electron transfer (ET) via naked eye colorimetric sensing using a tailor-made water-soluble self-doped polyaniline (PSPANa) as a substrate. Monomer (N-3-sulfopropylaniline) was synthesized via ring-opening of propane sultone with excess aniline and polymerized in water using ammonium persulfate to obtain green water-soluble polymer. Vitamin-C (ascorbic acid) and cysteine showed unexpected sharp and instantaneous color change from blue to colorless sensing action. The stoichiometry of the analyte to polymer was determined as 3:2 and 4:1 with association (or binding) constants of K = 2.1 × 10(3) and 1.5 × 10(3) M(-1) for vitamin-C and cysteine, respectively. Efficient electron transfer from vitamin-C (also cysteine) to the quinoid unit of the polyaniline base occurred in solution; as a result, the color of the solution changed from deep blue to colorless. Cyclic voltammetry analysis of PSPANa showed the disappearance of the cathodic peak at -0.21 V upon the addition of analytes (vitamin-C and cysteine) and confirms the electron transfer from the analyte to the polymer backbone. Dynamic light scattering (DLS) and zeta potential techniques were utilized to trace the molecular interactions in the electron transfer process. DLS histograms of the polymer samples confirmed the existence of nanoaggregates of 8-10 nm in diameter. The polymers possessed typical amphiphilic structure to produce micellar aggregates which facilitate the efficient electron transfer occurred between the analyte and polyaniline backbone.

Effect of chemical functionalization on the electrochemical properties of conducting polymers. Modification of polyaniline by diazonium ion coupling and subsequent reductive degradation

The electrochemical properties of polyaniline (PANI) can be altered by coupling the polymer with aryldiazonium ions. The ions are synthesized by diazotization of aromatic primary amines (1-aminoanthraquinone, sulphadiazine and 4-cyanoaniline) bearing functional groups which are then linked to the polyaniline backbone. All materials produced are electroactive, suggesting that the reaction involves coupling of the diazonium ion with the aromatic rings and not nucleophilic substitution by the aminic nitrogen of PANI on the aryl cations. The electrochemical properties of the modified polymers are different to those of PANI, likely due to electronic and steric effects of the attached groups. Reductive degradation of the azo linkages, using dithionite ion, removes the attached moieties leaving primary amino groups attached to the polyaniline backbone. In that way, the effect of the attached groups on the electrochemical properties of PANI is eliminated. FTIR spectroscopy measurement of the different polymers supports the proposed mechanism. Using the method a polymer containing redox (anthraquinone) groups, which could be used for charge storage, is obtained. Additionally a material containing sulphadiazine moieties, which can be released in vivo by bacterial activity, is also produced. The molecule is a well-known sulfa drug with bacteriostatic activity. The reaction sequence seems to be of general application to modify polyanilines, by attaching functional groups, and then to produce a PANI backbone bearing primary amino groups. Evidence is presented on the kinetic control of attached group removal.

Enhanced electrical conductivity of polyaniline film by a low magnetic field

We report the enhanced electrical conductivity of polyaniline (PANI) films produced in a low magnetic field using polyaniline that was synthesized by a self-stabilized dispersion polymerization (SSDP). The sample PANI film prepared with a low magnetic field of 1.4 T showed a 1.85-fold increase in electrical conductivity. Moreover, the film using the polyaniline prepared using the SSDP method showed greater conductivity enhancement than the conventionally prepared sample. In addition, the PANI films exhibited considerable anisotropy of the electrical conductivity depending on the direction of the applied magnetic field. This was attributed to the non-negligible contribution of the orientation of the polyaniline backbone segment and the face-to-face π–π stacking of the main-chains by the magnetic field.

Synthesis and chemical properties of photoluminescent self-doped polyanilines

Fluorescent self-doped polyanilines (PAS-AntPy-a and PAS-AntPy-b) were obtained by the pyridinium sulfonation of poly(2-methoxyaniline-5-sulfonic acid) (PAS) with 4-(2-anthracene-9-yl-vinyl)pyridine (AntPy). The degrees of pyridinium sulfonation in PAS-AntPy-a and PAS-AntPy-b were 0.70 and 0.97, respectively. A neutral polyaniline with an AntPy side unit (PANI-AntPy) was synthesized by the oxidative polymerization of N-(2-aminophenyl)-4-(2-anthracene-9-yl-vinyl)pyridinium chloride. The UV-vis spectra of PAS-AntPy-a and PAS-AntPy-b exhibited an absorption due to the polaron band that was derived from the protonation of amine groups in the polyaniline backbone with the remaining sulfonic acid proton. In contrast, PANI-AntPy did not exhibit absorption due to the polaron band. PAS-AntPy-a, PAS-AntPy-b, and PANI-AntPy were photoluminescent in a solution. The electric conductivity of PAS-AntPy-a was σ = 1.5 × 10−7 S cm−1, which was higher than that of H2SO4 doped PANI (4.2 × 10−9 S cm−1) reported previously.

A Serendipitous C−C Bond Formation Reaction between Michael Donors and Diiminoquinoid Ring Assisted by Quaternary Ammonium Fluoride

An efficient C-C bond formation reaction assisted by a fluoride ion has been identified for N,N'-diphenyl-1,4-phenylenediimine with the compounds having an active methylene group. The reaction follows the typical Michael addition fashion and proceeds to completion within 1 h at 70 degrees C in acetonitrile in the presence of tetrabutylammonium fluoride (TBAF), while the same reaction failed to proceed in the absence of a fluoride anion. The new finding reported herein also offers an unprecedented method for a direct functionalization of polyaniline backbone with versatile functional alkyl groups.

Electrochemical quartz crystal microbalance study of covalent tethering of carboxylated thiol to polyaniline for electrocatalyzed oxidation of ascorbic acid in neutral aqueous solution

The electrochemical quartz crystal microbalance (EQCM) was used to study the electrosyntheses and electrochemical properties of two kinds of polyaniline (PANI)-thiol composite films in aqueous solutions, which were prepared by covalent binding of a thiol to the oxidized forms of PANI (PANI(post)-thiol, protocol A), and electropolymerization of aniline in the presence of a thiol (PANI(poly)-thiol, protocol B), respectively. The thiols involved were mercaptosuccinic acid (MSA), thioglycolic acid (TGA) and beta-mercaptoethanol (ME). The PANI(post)-thiol binding processes were monitored in situ with the EQCM, giving molar binding ratios (r, thiol vs. aniline unit of the polymer) of ca. 0.50 at saturation for these thiols. Both PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols showed a controllable electroactivity of the PANI moiety in neutral even weakly alkaline phosphate buffer solutions (PBS), with maximum electroactivity roughly at r = 0.11 for PANI(post)-MSA or at r = 0.21 for PANI(post)-TGA. The PANI-thiol interaction was also supported by experiments of scanning electron microscopy, electrochemical surface plasmon resonance, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the interaction mechanism is briefly discussed. The PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols effectively electrocatalyzed the oxidation of ascorbic acid in pH = 7.3 PBS, and the PANI(post)-thiol exhibited electrocatalytic activity higher than the relevant PANI(poly)-thiol under our experimental conditions. The covalent anchoring of anionic thiol groups on the PANI backbone to prepare electroactive PANI in neutral solutions is conceptually new and may be extended to the development of new functional materials from many other conducting polymers and thiols for wide applications in catalysis, biosensing, molecular electronics, and so on.

Methane Interactions with Polyaniline/Butylmethylimidazolium Camphorsulfonate Ionic Liquid Composite

In our previous report, a polyaniline (PAn) and ionic liquid butylmethylimidazolium camphorsulfonate (BMICS) composite was used as a methane sensing material which significantly increased the sensitivity for methane detection using quartz crystal microbalance (QCM) transducers. In this paper, we focus on the interactions within the PAn/BMICS composite and between the composite and methane. UV-vis and Fourier transform infrared (FTIR) spectroscopic results indicated that the anion of BMICS, camphorsulfonate, could form hydrogen bonds with the "nitrogen" sites of protic acid doped PAn. These hydrogen bonds align the camphorsulfonate anions in a comblike manner along the PAn backbone and therefore enhance the long-range pi-orbital conjugation of PAn. Methane molecules absorbed into the PAn/BMICS may sit in the "space" between the aligned anions and cations of BMICS. By measuring the methane absorption in PAn/BMICS at a temperature range of 25-65 degrees C, the entropy and enthalpy of dissolution were obtained following the van't Hoff equation. They are -163.2 +/- 30.1 J/mol.K and -50.5 +/- 8.7 kJ/mol, respectively, which are relatively higher than those in pure BMICS and in PAn only. These thermodynamic parameters further support that the absorbed methane molecules might exist in PAn/BMICS in a relatively ordered manner. Molecular mechanics simulation results agree with the spectroscopic and thermodynamic results.

Adsorption of Sulfonated Dyes by Polyaniline Emeraldine Salt and Its Kinetics

A method for the removal of anionic (sulfonated) dyes from aqueous dye solutions using the chemical interaction of dye molecules with polyaniline is reported. Polyaniline (PANI) emeraldine salt was synthesized by chemical oxidation. Sulfonated dyes undergo chemical interactions with the charged backbone of PANI, leading to significant adsorption of the dyes. This phenomenon of selective adsorption of the dyes by PANI is reported for the first time and promises a green method for removal of sulfonated organics from wastewater. The experimental observations from UV-vis spectroscopy, X-ray diffraction, and conductivity measurements rule out the possibility of secondary doping of polyaniline salt by sulfonated dye molecules. A possible mechanism for the chemical interaction between the polymer and the sulfonated dye molecules is proposed. The kinetic parameters for the adsorption of sulfonated dyes on PANI are also reported.

Formation mechanism of a nanotubular polyanilines prepared by an emulsion polymerization without organic solvent

A nanotubular polyaniline (PANINT) was prepared from a simple emulsified polymerization method without oil solvent present. A mechanism of the formation of the nano-fibers/tubes was proposed to show that it started with the connecting arrangement of the neighboring anilinium micelles before and during polymerization, which resulted in the formation of the intermediate morphology of centipedes converting into rod-like nanofibers later. The obtained PANINTs displayed not only nanofibrous structure but owned an unusual dispersing behavior in toluene. SEM and TEM showed the dendrite-like networks of nanofibers connected and glued together by the free (not complexed to polyaniline backbone) n-dodecylbenzene sulfonic acid (DBSA) molecules. After removing the free DBSA by acetone, the clear/well-defined empty nanotubes can be seen from TEM in the magnified micrograph. The Atomic force microscopic (AFM) microgaphs demonstrated the cottage like surface morphology of the un-perturbed PANINTs and the morphology was converted to an anisotropic/oriented rods after rubbing on the wet/cast PANINTs' dispersion of toluene before entire evaporation.