Electrochemical recognition and trace-level detection of bactericide carbendazim using carboxylic group functionalized poly(3,4-ethylenedioxythiophene) mimic electrode

The electrochemical recognition and trace-level detection of bactericide carbendazim (MBC) in paddy water and commercial juice were realized using carboxylic group functionalized poly(3,4-ethylenedioxythiophene) (PC4-EDOT-COOH) film electrode. PC4-EDOT-COOH film was prepared by one step, low-cost, and green electrosynthesis in aqueous microemulsion system and characterized by FT-IR, cyclic voltammetry, UV–vis and SEM. In comparison with poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(hydroxymethylated-3,4-ethylenedioxylthiophene) (PEDTM), PC4-EDOT-COOH exhibited the best electrochemical recognition towards MBC and the recognition mechanism was proved by quantitative calculation. Sensing parameters such as pH values, accumulation potential, accumulation time, supporting electrolyte, and scan rate on the current response of MBC were discussed. In addition, the sensor can be applied to quantification of MBC in the concentration range of 0.012–0.35 μM with a low detection limit of 3.5 nM (S/N = 3). Moreover, PC4-EDOT-COOH film electrode showed good stability, high selectivity, and satisfactory anti-interference ability. Satisfactory results indicated that PC4-EDOT-COOH film is a promising sensing platform for the trace-level analysis of bactericide residue carbendazim in agricultural crops and environment.     

Electrochemical behaviour of poly(3,4-ethylenedioxythiophene) in a room-temperature ionic liquid

The cyclic voltammetry responses and the redox switching dynamics of poly(3,4-ethylenedioxythiophene) (PEDOT) in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMImTf₂N), were investigated. The shape of the cyclic voltammograms showed two anodic and two cathodic peaks. These peak currents varied linearly with the scan rate indicating a thin-layer behaviour. No memory effects were observed during the cyclic voltammetry experiments in this ionic liquid. On the other hand, the redox switching dynamics of PEDOT were studied by means of potential step experiments. The analysis of chronocoulograms in term of RC-circuits indicated that the time dependence of the charge transferred during the potential step showed two time constants. These results were consistent with the postulated structure or morphology of the PEDOT film which contained two types of coexisting zones: a compact and an open structures.     

Electrochemical sensor for nitrobenzene based on carbon paste electrode modified with a poly(3,4-ethylenedioxythiophene) and carbon nanotube nanocomposite

A sensitive and selective electrochemical sensor for the determination of nitrobenzene (NB) was developed based on a carbon paste electrode (CPE) modified with a nanocomposite prepared from the conducting polymer poly(3,4-ethylenedioxythiophene) and carbon nanotubes. The modified CPE exhibits good conductivity, a large surface area, and excellent catalytic activity towards the electrochemical reduction of NB. Under optimal conditions, the modified CPE is capable of detecting NB in the 0.25 to 43 μM concentration range and with a detection limit at 83 nM. Moreover, the sensor is highly stable and reusable, and free of interferences by other commonly present nitro compounds. It was used to determine NB in wastewater samples.

Electrochemical deposition of molybdenum oxide into films of poly(3,4-ethylenedioxythiophene) conducting polymer on glassy carbon substrates

Electrochemical deposition of molybdenum oxides from molybdate-containing solutions onto glassy carbon electrodes and the same electrodes coated with a film of poly(3,4-ethylenedioxythiophene) conducting polymer was studied. The morphology of the deposited molybdenum oxides was examined by scanning electron microscopy. The method of X-ray photoelectron spectroscopy was used to determine the state of molybdenum in surface molybdenum oxides and a conclusion was made that the oxide MoO₂ is mostly present.     

Surface area measurement of functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes have been functionalized and the specific surface areas of the functionalized nanotubes measured. Contrary to expectations, functionalization leads to a decrease in specific surface area compared to that of the unfunctionalized nanotubes. Treatment with a concentrated 1:1 nitric/sulfuric acid mixture followed by high-temperature baking at 1000 degrees C was found to increase the specific surface area of the nanotubes. For the unfunctionalized SWNTs, this treatment increases the specific surface area (SSA) by 20%. In the case of SWNTs functionalized by n-butyl groups the increase in the SSA was nearly 2-fold with the value increasing from 410 (drying at 110 degrees C) to 770 m2/gm (acid and bake treatment followed by drying at 110 degrees C). For the ozonized SWNTs, the SSA increases more than 3-fold from 381 (drying at 110 degrees C) to 1068 m2/gm (acid and bake treatment followed by drying at 110 degrees C). SEM images indicate that the nanotubes rebundle in the solid state with an average bundle size of 10-30 nm. AFM studies show that the ozonized tubes have been cut to short bundles after ozonolysis. Hydrogen uptake studies carried out on the baked ozonized tubes led to a 3 wt % hydrogen uptake at 77 K and 30 bar.     

DNA functionalized single-walled carbon nanotubes for electrochemical detection

Single-walled carbon nanotubes (SWNTs) were effectively dispersed and functionalized by wrapping with single-stranded DNA (ssDNA). The ssDNA-SWNTs attach strongly on glass substrate and easily form a uniform film, making it possible for electrochemical analysis and sensing. The film was fabricated into a working electrode, which exhibited good electrochemical voltammetric properties, such as flat and wide potential window, well-defined quasi-reversible voltammetric responses, and quick electron transfer for a Fe(CN)6(3-)/Fe(CN)6(4) system, indicating that the ssDNA-SWNTs film should be a good analytical electrode for electrochemical detection or sensing. This was demonstrated by highly selective and sensitive detection of a low concentration of dopamine in the presence of excess ascorbic acid.     

Click-functionalization of conducting poly(3,4-ethylenedioxythiophene) (PEDOT)

Efficient post-functionalization of conductive polymer films was achieved by Cu(+)-catalyzed "click"-cycloaddition of novel poly(azidomethyl-EDOT) and various functionalized terminal alkynes under mild heterogeneous conditions with high conversion efficiencies.     

ESR spectroelectrochemistry of poly(3,4-ethylenedioxythiophene) (PEDOT)

In situ ESR spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) (PEDOT) have been performed, in an attempt to take a closer look at species responsible for the conductivity of the polymer in the doped state. A series of ESR spectra at progressively changed potentials applied to the polymer film in the oxidation and subsequently, reduction half-cycles were recorded. The results reveal distinct ESR lines with a noteworthy concentration of spins in the reduced state of the polymer and marked changes in both the intensities and ΔB_pp widths of the ESR signal across the studied potential range, indicating non-trivial changes in the character of charge carriers with changing potential. Also, interesting phenomena like the potential hysteresis of the spin concentration and of ΔB_pp linewidths between the oxidation and reduction cycles of the polymer are observed. The presence of residual spins in the polymer in the reduced state may indicate that at least to some partial extent, PEDOT chains exist in the quinoid rather than benzoid configuration in the dedoped state. Hysteresis of spectroscopic parameters may imply that certain hindrance factors like slow anion expulsion speed accompany the dedoping process of the polymer.     

Synthesis and characterization of perfluorohexylated poly(3,4-ethylenedioxythiophene)

The perfluorohexylated 3,4-ethylenedioxythiophene 5 was prepared via Mitsunobu reaction of perfluorohexylatyed diol 2 with diethyl 3,4-dihydroxythiophenedicarboxylate followed by decarboxylation. The polymerization of 5 was conducted with both oxidative chemical and electrochemical polymerizations. The polymers were characterized by cyclic voltammogram, UV, IR, TGA and DSC.     

Understanding interactions between poly(styrene-co-sodium styrene sulfonate) and single-walled carbon nanotubes

Understanding formation mechanisms of hybrids of carbon nanotubes (CNTs) wrapped by polymers and their interactions is critical in modifying solubility of CNTs in aqueous solution and developing new nanotube-based polymer materials. In the present work, we investigate the structural details of poly(styrene-co-sodium styrene sulfonate) (PSS) wrapping around the CNT and the interactions between the PSS chain and the CNT using molecular dynamics (MD) simulations. The fraction of sulfonated groups significantly influences the wrapping conformations of the PSS chain. Due to limited time scale in the MD simulations, two different initial conformations of the chains are introduced to explore the effect of the initial state on the wrapping behavior. When the chains initially wrap around the CNT in a perfect helix manner, more compact pseudo-helical conformations are obtained. For initial straight line arrangement of the chain monomers, the chains adopt looser wrapping conformations. The free-energy analysis and binding interaction of the PSS chain on the CNT surface take a glance on the relationship between the conformational transition of the chain and the energy evolution.     

Conductimetric immunosensor based on poly(3,4-ethylenedioxythiophene)

A conductimetric reagentless immunosensor using the biospecific binding pair of goat antirabbit IgG and rabbit IgG has been designed and fabricated using poly (3,4-ethylenedioxythiophene) as the immobilization matrix-cumtransducer.     

"Click"-modification of a functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) soluble in organic solvents

A PEDOT-based conductive copolymer soluble in organic solvents was synthesized electrochemically using dihexyl-EDOT and azidomethyl-EDOT as monomers and was successfully post-functionalized by "click"-cycloaddition reaction with a functionalized terminal alkyne under mild heterogeneous conditions.     

Conducting poly(3,4-ethylenedioxythiophene)-montmorillonite exfoliated nanocomposites

Exfoliated nanocomposites formed by poly(3,4-ethylenedioxythiophene) and different concentrations of non-modified montmorillonite (bentonite), which range from 1% to 10% w/w, have been prepared by anodic electropolymerization in aqueous solution. Analyses of the electrochemical and electrical properties reveal that the electroactivity of the nanocomposites is higher than that of the individual homopolymer, while the electrical conductivity of the two systems is practically identical. On the other hand, the exfoliated distribution of the clay in the polymeric matrix and the morphology of the prepared materials have been characterized using transmission electron microscopy, X-ray diffraction and atomic force microscopy. The overall of the results represents a significant improvement with respect to other nanocomposites constituted by conducting polymers and clays, including those involving poly(3,4-ethylenedioxythiophene), and evidences the reliability of the preparation procedure employed in this work.     

Multicolor and fast electrochromism of nanoporous NiO/poly(3,4-ethylenedioxythiophene) composite thin film

We report a nanoporous NiO/poly(3,4-ethylenedioxythiophene) (PEDOT) composite film using a highly porous NiO film as a template by the combination of chemical bath deposition and electro-polymerization methods. The as-prepared NiO/PEDOT composite film has an interconnecting reticular morphology with nanometer sized pores ranging from 20–150 nm. The NiO/PEDOT composite film exhibits multicolor electrochromism with reversible color changes from purple to light blue brown and presents a transmittance variation of 31% at 600 nm. Fast switching speed is achieved in this composite film, and the response time for oxidation and reduction is 500 and 600 ms, respectively.     

Rheology of polycarbonate reinforcedwith functionalized and unfunctionalized single-walled carbon nanotubes

Nanocomposites of polycarbonate (PC) containing low concentrations of pristine and COOH and OH functionalized single-walled carbon nanotubes (SWNTs, COOH-SWNTs and OH-SWNTs) were prepared by melt-mixing and analyzed using rheology and scanning electron microscopy (SEM). The steady state and linear viscoelastic behavior of each nanocomposite material is presented and compared to that of the neat PC. SEM analysis revealed that samples containing functionalized SWNTs were more dispersible than samples containing the pristine SWNTs.     

Potential-modulated, attenuated total reflectance spectroscopy of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene methanol) copolymer films on indium-tin oxide

We report the first application of a potential-modulated spectroelectrochemical ATR (PM-ATR) instrument utilizing multiple internal reflections at an optically transparent electrode to study the charge-transfer kinetics and electrochromic response of adsorbed films. A sinusoidally modulated potential waveform was applied to an indium-tin oxide (ITO) electrode while simultaneously monitoring the optical reflectivity of thin (2-6 equivalent monolayers) copolymer films of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene methanol) (PEDTM), previously characterized in our laboratory. At high modulation frequencies the measured response of the polymer film is selective toward the fastest electrochromic processes in the film, presumably those occurring within the first adsorbed monolayer. Quantitative determination of the electrochromic switching rate, derived from the frequency response of the attenuated reflectivity, shows a linear decrease in the rate, from 11 x 10(3) s(-1) to 3 x 10(3) s(-1), with increasing proportions of PEDTM in the copolymer, suggesting that interactions between the methanol substituent on EDTM and the ITO surface slow the switching process by limiting the rate of conformational change in the polymer film.     

Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene) in ionic liquids with bulky organic anions

The electrochemistry of poly(3,4-ethylenedioxythiophene) (PEDOT) was studied in two ionic liquids with bulky organic anions, i.e., 1-butyl-3-methylimidazolium (BMIM) diethylene glycol monomethyl ether sulfate (MDEGSO₄) and BMIM octyl sulfate (OctSO₄). BMIM-MDEGSO₄ is a liquid, while BMIM-OctSO₄ is in solid form at room temperature. Electrosynthesis of PEDOT in BMIM-MDEGSO₄ with an EDOT concentration of 0.1 M and in BMIM-MDEGSO₄/EDOT 1/1 (w/w) solution resulted in no polymer at all or a very limited amount of polymer on the electrode surface, as determined by cyclic voltammetry in 0.1 M KCl(aq) solution. In contrast, electrosynthesis of PEDOT in BMIM-OctSO₄/EDOT 1/1 (w/w) resulted in a high yield of electroactive material on the electrode surface. Furthermore, electrosynthesis of PEDOT in ionic liquid–water solution (C_{ionic liquid}=1.5 M) containing 0.1 M EDOT was also found to give a relatively high yield of electroactive material on the electrode surface, both for 1.5 M BMIM-MDEGSO₄(aq) and 1.5 M BMIM-OctSO₄(aq). The PEDOT electrodes showed an anionic potentiometric response in 10^–5–10^–1 M KCl(aq) solution, indicating a predominant anion transfer at the polymer–solution interface despite the relatively bulky anions (MDEGSO₄^– or OctSO₄^–) incorporated as counterions in PEDOT during electropolymerization. On the basis of electrochemical impedance spectroscopy, the charge (ion) transport properties of the polymer film were strongly influenced by the water content of the ionic liquid (C_{ionic liquid}=0.05–2.0 M).Dedicated to Zbigniew Galus on the occasion of his 70th birthday     

Interaction of single-walled carbon nanotubes with poly(propyl ether imine) dendrimers

We study the complexation of nontoxic, native poly(propyl ether imine) dendrimers with single-walled carbon nanotubes (SWNTs). The interaction was monitored by measuring the quenching of inherent fluorescence of the dendrimer. The dendrimer-nanotube binding also resulted in the increased electrical resistance of the hole doped SWNT, due to charge-transfer interaction between dendrimer and nanotube. This charge-transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. We also report the effect of acidic and neutral pH conditions on the binding affinities. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer-nanotube complex. The complexation was achieved through charge transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen, and n-propyl moieties of the dendrimer.