Composite layers consisting of polyaniline and poly(o-phenylenediamine): Electrochemical deposition, electrochromic and electrocatalytic properties

The composite polymer layers consisting of polyaniline (PANI) and poly(o-phenylenediamine) (poly(o-PDA)) were electrodeposited on a platinum electrode by simultaneous electrochemical oxidation of corresponding monomers from aquaeous hydrochloric solutions. The growth of PANI and poly(o-PDA) occurs separately resulting in layers with two distinct, finely distributed phases. The first deposited layers are composed mainly of poly(o-PDA) and become richer in PANI as the electropolymerization proceeds. The aniline/o-PDA copolymer was not formed during electrodeposition, as evidenced by cyclic voltammetry and Fourier-transformed IR spectroscopy. It was demonstrated that the electrochromic properties of resulting composite layers are the combination of yellow/brown-reddish and green/dark blue observable color transitions which are characteristics of poly(o-PDA) and PANI, respectively. Electrocatalytic properties of the electrosynthesized composite layers were investigated on quinone/hydroquinone (Q/H₂Q) redox system and it was shown that the composite layers increase the heterogeneous electron transfer rate with a magnitudes ranging from those obtained on pure poly(o-PDA) to those obtained on pure PANI layer.     

Synthesis of poly(o-phenylenediamine) hollow spheres and nanofibers using different oxidizing agents

Poly(o-phenylenediamine) (PoPD) hollow spheres (ca. 800 nm in outer diameter) were synthesized by a simple solution route using ammonium persulfate (APS) as the oxidizing agent, whereas PoPD nanofibers (0.5-2 μm in width and more than 100 μm in length) and gold nanoparticles (200-500 nm) were obtained when changing the oxidizing agent of APS to chlorauric acid (HAuCl₄). The chemical structures of PoPD hollow spheres and nanofibers were characterized by FTIR and XRD spectra. When using HAuCl₄ as the oxidizing agent, the products of PoPD nanofibers and gold nanoparticles could be separated by chemical methods. The monomer droplets were proposed to act as template to the formation of polymer hollow spheres while the oriented growth of polymer nanofibers might be catalyzed by gold nanoparticles.     

A novel voltammetric sensor for ascorbic acid based on molecularly imprinted poly(o-phenylenediamine-co-o-aminophenol)

A molecularly imprinted copolymer, poly(o-phenylenediamine-co-o-aminophenol) (PoPDoAP), was prepared as a new ascorbic acid (AA) sensor. The copolymer was synthesized by incorporation of AA as template molecules during the electrochemical copolymerization of o-phenylenediamine and o-aminophenol, and complementary sites were formed after the copolymer was electrochemically reduced in ammonium aqueous solution. The molecularly imprinted copolymer sensor exhibited a high sensitivity and selectivity toward AA. Differential pulse voltammograms (DPVs) showed a linear concentration range of AA from 0.1 to 10 mM, and the detection limit was calculated to be 36.4 μM. Compared to conventional polyaniline-based AA sensors, the analytical performance of the imprinted copolymer sensor was improved due to the broadened usable pH range of PoPDoAP (from pH 1.0 to pH 8.0). The sensor also exhibited a good reproducibility and stability. And it has been successfully applied in the determination of AA in real samples, including vitamin C tablet and orange juices, with satisfactory results.     

Copolymers and two-layered composites of poly(<Emphasis Type="Italic">o</Emphasis>-aminophenol) and polyaniline

Electroactive conducting copolymers of aniline (ANI) and o-aminophenol (OAP) and two-layered poly(o-aminophenol) (POAP)/polyaniline (PANI) composites were prepared in aqueous acidic solution by electrode potential cycling. Copolymerization was carried out at different feed concentrations of OAP and ANI on a gold electrode. A strong inhibition of electropolymerization was found at a high molar fraction of OAP in the feed. The copolymers showed good adherence on the electrode surface and gave a redox response up to pH=10.0. Two transitions were observed in the in situ conductivities of the copolymers (as with PANI), but the conductivities were lower by 2.5–3 orders of magnitude as compared to PANI. Electrosynthesis of PANI on POAP modified electrodes showed copolymer formation after reaction initiation and finally formation of a PANI layer at the copolymer/solution interface. The ‘memory effect’ of the bilayer structures of both polymers was discussed in terms of protonation/deprotonation and anion consumption taking place during redox processes of both polymers.     

Graphene/poly(ortho-phenylenediamine) nanocomposite material for electrochemical supercapacitor

Reduced graphene oxide was synthesized by simple chemical processing of graphite. Electron microscopy investigations of synthesized graphene showed slightly folded transparent sheets with a few square micrometers dimension. Poly(ortho-phenylenediamine)/graphene/Pt electrode was electrochemically fabricated in a 2.0-M H₂SO₄ solution by means of multiple potential cycling. Due to the catalytic effect of graphene on the oxidative electropolymerization of ortho-phenylenediamine, the ortho-phenylenediamine/graphene (PoPD/GR) nanocomposite showed greatly enhanced electrical properties and excellent capacitive behavior. Electrochemical impedance spectroscopy, galvanostatic charge/discharge curves, and voltammetric investigations revealed that PoPD/GR nanocomposite represented good capacitive behavior with a specific capacitance as high as 308.3 F g^?1 at 0.1 A g^?1. It is almost three times higher than that of pure graphene (111.7 F g^?1). In addition, the nanocomposite electrode retained more than 99 % of the initial capacity after 1,500 cycles at a current density of 1 A g^?1.     

Polymer types regulation strategy toward the synthesis of carbonized polymer dots with excitation-wavelength dependent or independent fluorescence

Three kinds of carbonized polymer dots (CPDs) synthesized via a one-pot process from o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD) exhibit excitation-wavelength independent yellow, green and red emissions, respectively. In sharp contrast, two kinds of CPDs prepared via a hydrothermal process from citric acid (CA) and diethylenetriamine (DETA) exhibit obvious excitation-wavelength dependent emissions. Through the characterization and comparison of the two types of CPDs, it is concretely revealed that the polymer structure types during the formation of CPDs can effectively control the fluorescence excitation-wavelength independence/dependence. The homogeneous polymer structures contained in CPDs contribute to excitation-wavelength independence, whereas random copolymer structures contribute to excitation-wavelength dependence. These studies are of great significance for further understanding the polymer structures and designing unique optical properties of CPDs.     

Electrocatalytic performance of poly(o-phenylenediamine)-Pt–Ru nanocomposite for methanol oxidation

The electrocatalytic properties of poly(o-phenylenediamine) (PoPD)-Pt–Ru nanocomposite electrode for methanol oxidation have been investigated by linear sweep and cyclic voltammetry. The Pt–Ru ion concentration ratio in the electrodeposition bath is varied in the ratios of 1:0.25, 1:0.5, 1:1, 1:2, and 1:4. The morphology and particle size of the nanocomposites are obtained from the scanning electron microscopy data. The onset potential for the oxidation of methanol is found to be effectively reduced by 220 mV for the (PoPD)-Pt–Ru (1:1) nanocomposite compared to PoPD-Pt electrode. Also, the PoPD-Pt–Ru (1:1) composite shows a value of 4.2 for the ratio of forward to reverse peak current which is relatively a high value that can be observed among the conducting polymer-based catalysts used for methanol oxidation. The results are substantiated by the polarization and stability data.     

In situ oxidative copolymerization and characterization of new poly(benzidine-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">o</Emphasis>-phenylenediamine)/kaolinite microcomposites

Copolymers of benzidine and o-phenylenediamine/kaolinite clay composites with different percentages of kaolinite clay particles were synthesized via in situ oxidative copolymerization. The spectral characteristics upon incorporation of o-phenylenediamine units into the polybenzidine backbone in presence of kaolinite clay were investigated by means of UV–Vis and FTIR spectroscopy. The copolymer in the absence and in the presence of kaolinite clay was studied by thermal gravimetric analysis under non-oxidative conditions. The morphology of the copolymer kaolinite composites system was investigated by the scanning electron microscopy.     

Spectroelectrochemical studies of poly-o-phenylenediamine Part 2. In situ UV—vis subtractive reflectance spectroscopy

In our previous paper, the phenazine-like structure of the poly-o-phenylenediamine (PoPD) and its three steady redox states have been revealed mainly by using in situ resonance Raman spectroscopy. It has also been shown that the semi-oxidized state of PoPD is the most stable state of PoPD, while the totally-oxidized state of PoPD is chemically unstable and can exist only at certain electrode potentials. In the present work, the more detailed reaction mechanism of a PoPD film in strong acid solution has been studied by using in situ UV—vis substractive reflectance spectroscopy. The semi-oxidized state and the totally-oxidized state of PoPD have electronic absorption bands around 300 nm, 430 nm, 500 nm and 300 nm, 450 nm, 530 nm, 735 nm respectively in the in situ steady state UV—vis subtractive reflectance spectra with respect to the reduced state of PoPD, which verifies once again that three redox states of PoPD exist in the redox process of PoPD. Moreover, the relative intensity between two oxidized states of PoPD at the maximum absorption wavelength (λ_max) reveals that only about one third of the semi-oxidized state of PoPD can be oxidized to the totally-oxidized state of PoPD. The in situ resonance Raman spectra and the cyclic voltammograms of PoPD display the same quantitative relationship. New absorption bands were observed in the in situ time-resolved UV—vis subtractive reflectance spectra with appropriate time resolutions, which illustrate the dynamic structure changes of PoPD in its redox process. These intermediate states of PoPD are more unstable than its three redox states.     

Morphology studies of polyaniline lengthy nanofibers formed via dimers copolymerization approach

In this paper, two different aniline dimers, N-phenyl-1,2-phenylenediamine (2-PPD) and N-phenyl-1,4-phenylenediamine (4-PPD) were used as starting monomers in polyaniline (PANI) synthesis. It was found that 2-PPD dimer alone produced only an amorphous PANI oligomer with a flaky morphology, while the 4-PPD provided either linear nanofiber or a spaghetti-like hollow nanofiber structures comprising of worm-like fibril subunits. By adjusting the molar fed ratio of 4-PPD to 2-PPD in the copolymerization, long PANI nanofibers with length up to tens of microns, bundled together by single PANI fibrils with diameter ca. 3-5 nm, was formed. A possible formation mechanism was proposed taking account of the reactivity difference at positions 4 and 2 on the 4-PPD and 2-PPD, respectively.     

The interaction of fluorinated 2-arylhydrazono-1,3-dicarbonyl compounds with o-phenylenediamine

2-Arylhydrazono-3-fluoroaklyl-3-oxo esters react with o-phenylenediamine under neutral conditions to form mainly o-aminoanilides, from which can be obtained 1,5-benzodiazepin-2-ones. Ethyl-2-(benzimidazol-2-yl)-2-(4-methylphenyl)hydrazonoethanoate was isolated also from the reaction of di(tri)fluoromethyl-containing 2-arylhydrazono-3-oxo esters. The reactions of o-phenylenediamine with 1,2,3-triketone 2-arylhydrazones containing alkyl substituents result in the formation of 1-(benzimidazol-2-yl)-1,2-dioxoalkane arylhydrazones, whereas phenylsubstituted analogues afford 2-phenylbenzimidazole. Nickel(II) chelates of N,N′-phenylene-bis(2-arylazo-1,3-aminovinylketones) were obtained from 1,2,3-triketone 2-arylhydrazones and o-phenylenediamine using a template method.     

Chemical oxidative polymerization of m-phenylenediamine and its derivatives using aluminium triflate as a co-catalyst

Aromatic diamine monomers, including m-phenylenediamine (mPD), 2-methyl-m-phenylenediamine (2Me-mPD), 4-methyl-m-phenylenediamine (4Me-mPD) and trimethyl-m-phenylenediamine (tMe-mPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co-catalyst under various polymerization conditions. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The poly(2-methyl-m-phenylenediamine) (P(2Me-mPD)), poly(4-methyl-m-phenylenediamine) (P(4Me-mPD)) and poly(trimethyl-m-phenylenediamine) (P(tMe-mPD)) polymers exhibited better solubility than poly(m-phenylenediamine) (P(mPD)) polymers in most common solvents. The homopolymers obtained were characterized by FT-IR, ¹H and ¹³C NMR, WAXD and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. TGA measurements indicated that the polymers have good thermal stability and decompose above 400 °C in nitrogen.     

Estimating the thickness of hydrated ultrathin poly(o-phenylenediamine) film by atomic force microscopy

A novel method to measure ultrathin poly(o-phenylenediamine) (PPD) film electropolymerized on gold electrode in liquid was developed. It is based on the force versus distance curve (force curve) of atomic force microscopy (AFM). When 1-0.25 μm/s was chosen as the rising rate of the scanner, and 50% of the confidence interval (CI) as the qualifying threshold value, the thickness of the hydrated polymer film could be calculated. This result was compared with one obtained from an AFM image. A step-like electrode fabricated by a photolithographic process was used. The height difference of the electrode before and after the PPD coating was imaged in liquid, and then the real thickness, 19.6±5.2 nm, was obtained. The sample was also measured by estimating the transition range of the force curve of hydrated PPD film, and the thickness of the hydrated PPD film was determined to be 19.3±8.2 nm. However, the results calculated by integrating the electropolymerized charge for the oxidation process of o-phenylenediamine (o-PD) was only one-third as large as it was when using the two previously described methods. This indicated that the structure of hydrated PPD film might have been swollen.     

Electro-oxidation of o-phenylenediamine at platinum electrodes in acetonitrile solutions

The study of o-phenylenediamine electro-oxidation at platinum electrodes in acetonitrile solutions under different experimental conditions is presented. Cyclic voltammograms show 4 oxidation peaks, which are assigned to o-phenylenediamine, o,o′-diamineazobenzene and protonated o-phenylenediamine anodic oxidation. An additional prepeak system is apparent at potentials less anodic than the first peak in successive scans. This prepeak system evidences the presence of two redox systems diphenylamine and H⁺, derived from the initial oxidation product o-phenylenediamine cation radical. The effect of base and acid addition is also studied. o,o′-Diamineazobenzene was identified as one of the principal soluble products in preparative scale electrolysis and a general mechanism for o-phenylenediamine oxidation is proposed.     

Formation of 2,3-diaminophenazines and their self-assembly into nanobelts in aqueous medium

One-dimensional (1D) nanobelts of several hundred micrometers in length, several hundred nanometers in width and several hundred nanometers in height are obtained by direct mixing of ortho-phenylenediamine (oPD) and FeCl₃ aqueous solution at room temperature. The nanobelts were characterized by elemental analysis, liquid chromatography/mass spectrometry (LC/MS), NMR (¹H and ¹³C), FT-IR, UV-vis, thermogravimetric (TG) and conductivity measurement. The nanobelts are identified as 2,3-diaminophenazine assemblies. The formation of the nanobelts involves two stages: (1) oxidation of oPD by FeCl₃, yielding individual 2,3-diaminophenazine molecules; and (2) self-assembly of the 2,3-diaminophenazine, forming the 1D nanobelts. The nanobelts exhibit fairly high thermal stability and show conductivity at the level of semiconductors.     

Surface modification of a reactive metal or alloy by polyaniline for electrooxidation of iodide

Generally, an inert metal such as platinum is used for studying electrooxidation reactions. As a non-platinum metal or alloy undergoes corrosion and oxidation, it is not useful for this purpose. In the present study, surface modification of non-platinum metals by coating electronically conducting polymers for electrooxidation reactions was investigated. Polyaniline (PANI) was electrochemically deposited on stainless steel (SS) substrate by potentiodynamic method. The oxidation of I⁻ was studied by cyclic voltammetry and amperometry experiments. The I⁻/I₂ reaction couple was found to be quasireversible on the PANI/SS electrode. The amperometry study, conducted under fast mass transport conditions, has provided linear relationship between current and concentration of I⁻. The data were analyzed and rate constant of the reaction was evaluated. Thus the oxidation of I⁻, which does not occur on bare SS electrode, was shown to occur through electron transfer mediated by polyaniline.     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of block copolymer of poly(trimethylene carbonate) with oligo(ethylene glycol) and the surface properties of the dip coated film

To persuade the stent coating materials for the better sustainable development, a block copolymer composed of hydrophobicity of poly(trimethylene carbonate) (PTMC) and hydrophilicity of PTMC bearing ethylene glycol chains was synthesized as a potential candidate. The result of thermal stability of the polymer was analyzed which reached up to 206 °C (T₁₀) and it is considered that sufficient for sterilization during the treatment. Moreover, the dip coated films of polymer were coated on polyethylene (PE) and stainless steel (SS) substrates in order to stimulate the stability upon the physiological environment. In addition, the preliminary in vitro test of the films were evaluated by protein adsorption and blood platelet adhesion tests. Hence, this study tends to convince that the synthetic block copolymer based on PTMC derivatives were approached for stent coating materials.     

Intercalation chemistry of aluminium dihydrogentriphosphate with weak bases and polymerization of aniline between its layers

Weak bases such as 2-aminopyridine, 4-aminopyridine,o-phenylenediamine,p-phenylenediamine and aniline were intercalated into aluminium dihydrogentriphosphate (ADHP) using ultrasonic wave irradiation. The interlayer spacing of ADHP increased from 8.1 Å to 12.4–20.0 Å. From the values of the layer expansions and host/guest ratios, bilayer or monolayer structures were considered. Chemical oxidation of the aniline resulted in the formation of polyaniline in the ADHP layers.Author for correspondence.     

Features of the reactions of β-aryl(heteryl)-α-nitroacrylates with N,N-, N,O-, and N,S-binucleophiles

The reactions of ??-aryl(heteryl)-??-nitroacrylates with N,N-, N,O-, and N,S-binucleophiles proceed regiospecifically through the initial formation of the Ad_N products, among which only the product from o-aminothiophenol was isolated. The conditions of converting the S-adducts into 2-aryl(heteryl)benzothiazole were found. The N-adducts formed in the reaction with hydrazine, o-phenylenediamine, and o-aminophenol undergo immediately the spontaneous transformation into the linear (azine, azomethine) or heterocyclic (benzimidazole) structures.