Nafion Polymer Film Research Articles

On-site detection of heavy metals in agriculture land by a disposable sensor based virtual instrument

A field-based detection system was designed and implemented for the simultaneous determination of heavy metals in soil samples. The detection principle is based on electrochemical differential pulse anodic stripping voltammetry (DPASV). In order to fulfill the requirements of field screening usage, a fast soil pretreatment process using ultrasonic-assisted extraction was applied. A disposable and integrated sensor, incorporating a three-electrode configuration (working electrode, reference electrode and counter electrode), was fabricated by the screen-printing technology and further modified with Nafion polymer and bismuth film. Coupled with the portable and flexible analysis instrument which was developed by virtual instrument technology, this system was used for trace determination of cadmium and lead content in soil. For accurate qualitative and quantitative analysis of heavy metals, the detection methodology based on the statistical algorithm and chemometrics method was proposed. The results showed that the system was sensitive, reliable and effective, which might hold great promise for its on-site analysis applications.

Crystal facet engineering of ZnO photoanode for the higher water splitting efficiency with proton transferable nafion film

Zinc oxide (ZnO) is considered as an extraordinary photoanode with direct band gap and high charge mobility for solar light water splitting reaction, but it suffers from proton (H+) produced by the photo-oxidation reaction. In the current work, we demonstrate that the long term-stability of ZnO photoanode with the introduction of proton transfer media. Proton transferable polymer such as nafion allows favorable transport of the generated H+ ions from the surface of ZnO photoanode to electrolyte and results in an enhanced its stability. Nafion polymer film was coated on the surface of ZnO thin film photoanode with each selectively exposed (002), (100) and (101) facet. Especially, nafion film with (002) crystal facet ZnO photoanode showed 3.9mA/cm2 of the high photocurrent density and 0.3–0.6μmol/cm2 of high oxygen and hydrogen gas evolution for 2h. The photoelectrochemical performance of nafion coated (002), (100) and (101) facet oriented ZnO thin film photoanode increase the performance of water splitting reaction and stability of ZnO thin film were demonstrated as a development of high efficient ZnO photoelectrode. Present work suggests the strategy to fabricate the stable metal oxide photoelectrode with the high photoelectrochemical performance.

Electrochemical sensing of mesalazine and its N-acetylated metabolite in biological samples using functionalized carbon nanotubes

A rapid analytical method without the time-consuming separation step was developed to simultaneously determine mesalazine and its N-acetylated metabolite. A simply designed electrochemical sensor with functionalized carbon nanotubes in a Nafion matrix was constructed for this purpose. The presence of the nanocomposite modifier on the electrode surface significantly affects the voltammetric response of target analytes. The morphology of the modified surface was investigated by scanning electron microscopy. The effect of modifier amount on the sensor performance was investigated in order to obtain the most favorable response of mesalazine since it was found in lower concentration limits in real samples then its metabolite due to the rapid drug elimination and the slightly slower renal metabolite excretion. Under optimal conditions, the anodic peak currents measured by square-wave voltammetry increased linearly after short accumulation of 30s in the range of 5.0×10−8–2.5×10−6M and 1.0×10−7−5.0×10−6M for drug and metabolite, respectively. In addition to stable response, the sensor has excellent performance associated with high sensitivity (2.33×107 and 8.37×106µAM−1 for drug and metabolite, respectively). The synergistic effect of the carbon nanotubes and Nafion polymer film yielded detection limit of 1.2×10−8M for mesalazine and 2.6×10−8M for its metabolite that is comparable to known chromatographic methods. Due to the easy preparation and regeneration, the proposed sensor opens new opportunity for fast, simple and sensitive analysis of drug and its metabolite in human serum samples as well as direct quantification of mesalazine in delayed-release formulations.

Electroless synthesis of multibranched gold nanostructures encapsulated by poly( o-phenylenediamine) in Nafion

Multibranched gold (Au) nanocomposite materials encapsulated by poly( o-phenylenediamine) (P oPD) (Au@P oPD) were synthesized in a Nafion polymer film through the electroless synthetic route. The micro-heterogeneous structured Nafion film acted as a reaction vessel and as the template for the formation of Au@P oPD nanocomposite materials leading to the formation of highly uniform distribution of high density of the polymer–gold nanocomposite material. The formation of Au@P oPD nanomaterials at the GP/Nf surface was scrutinized by recording in situ absorption spectra and was characterized. The formation of the (1 1 1) plane of gold was dominant at the Au@P oPD nanocomposite. The ratio of the benzenoid and quinoid units of the P oPD (ca. 1.65) observed for the Au@P oPD confirmed that the micro-heterogeneous structure of Nf film acted as a reaction vessel and as template for the formation of Au@P oPD nanocomposite material. Both P oPD and Au at the Au@P oPD nanocomposite showed electrochemical activities at the GC/Nf–Au@P oPD modified electrode. The electrocatalytic activity of the GC/Nf–Au@PoPD modified electrode was studied for oxygen reduction reaction (ORR).

Electrochemical preparation, characterization, and electrocatalytic studies of Nafion–ruthenium oxide modified glassy carbon electrode

Electrochemical synthesis of ruthenium oxide (RuOx) onto Nafion-coated glassy carbon (GC) electrode and naked GC electrode were carried out by using cyclic voltammetry. Electrochemical deposition of RuOx onto Nafion-coated electrode was monitored by in situ electro- chemical quartz crystal microbalance (EQCM). Surface characterizations were performed by scanning electron microscope (SEM) and atomic force microscope (AFM). SEM and AFM images revealed that ruthenium oxide particles incorporated onto the Nafion polymer film. In addition, a GC electrode modified with ruthenium oxide- Nafion film (RuOx-Nf-GC) was shown excellent electro- catalytic activity towards dopamine (DA) and ascorbic acid (AA). The anodic peak current increases linearly over the concentration range of 50 μM-1.1 mM for DA with the correlation coefficient of 0.999, and the detection limit was found to be (S/N=3) 5 μM. Owing to the catalytic effect of the modified film towards DA, the modified electrode resolved the overlapped voltammetric responses of AA and DA into two well-defined voltammetric peaks with peak-to- peak separation about 300 mV. Here, RuOx-Nf-GC electrode employed for determination of DA in the presence of AA. This modified electrode showed good stability and antifouling properties.

Development and Interfacial Properties of Novel Polymer-Modified Carbon Film Electrodes

The surface properties of carbon film electrode sensors covered by coating with Nafion polymer film, before and after electrochemical analysis of sub-micromolar traces of lead and cadmium ions, were investigated. These protective polymer films are applied to the electrode surfaces to prevent the irreversible adsorption of chemical species, such as proteins and surfactants present in natural media, which leads to a decrease in response. Electrochemical impedance spectroscopy and voltammetric techniques were used for characterisation. The effect of non-ionic surfactant molecules in solution on the behaviour of the polymer-coated electrode was also investigated. It is shown that permanent changes to the structure and morphology of the Nafion film and of the carbon-Nafion interface occur after deposition of the trace metal ions, an effect which is lessened in the presence of surfactant.

Determination of Diquat at a Nafion Film Modified Glassy Carbon Electrode Using Electrocatalytic Voltammetry

A Nafion polymer film modified glassy carbon electrode (NFGCE) was used for the determination of diquat. Diquat was preconcentrated onto NFGCE by the cation-exchange feature of Nafion at open circuit potential and determined by cathodic differential pulse voltammetry (DPV) in a medium containing permanganate. Good sensitivity was achieved through the good cation-exchange property of Nafion and the catalytic process between diquat and permanganate. With 4 min accumulation, the analytical signal versus concentration dependence was linear from 3×10–9 M (0.55 ppb) to 4×10–7 M (73 ppb), and the detection limit was 0.21 ppb. The interferences from metal ions could be reduced by adding ethylenediaminetetraacetate (EDTA) into the sample solutions. The use of Nafion also improves the resistance to interferences from surfactants.

Determination of Diquat at a Nafion Film Modified Glassy Carbon Electrode Using Electrocatalytic Voltammetry

A Nafion polymer film modified glassy carbon electrode (NFGCE) was used for the determination of diquat. Diquat was preconcentrated onto NFGCE by the cation-exchange feature of Nafion at open circuit potential and determined by cathodic differential pulse voltammetry (DPV) in a medium containing permanganate. Good sensitivity was achieved through the good cation-exchange property of Nafion and the catalytic process between diquat and permanganate. With 4 min accumulation, the analytical signal versus concentration dependence was linear from 3×10–9 M (0.55 ppb) to 4×10–7 M (73 ppb), and the detection limit was 0.21 ppb. The interferences from metal ions could be reduced by adding ethylenediaminetetraacetate (EDTA) into the sample solutions. The use of Nafion also improves the resistance to interferences from surfactants.

Electroactive coatings of dicyano‐bis(1,10‐phenanthroline)iron(II) attached to Nafion polymer film modified electrodes via adsorption

AbstractA dicyano‐bis(1,10‐phenanthroline)iron(II)/Nafion modified elecrode was prepared. The voltammetric and the spectroelectrochemical behavior of this electrode were investigated. The influence of pH and the amount of Nafion and dicyano‐bis(1,10‐phenanthroline)iron(II) (DBPI) used in the electrode preparation on the electrochemical behavior is presented.

Influence of polymer structure on the electrochemistry of phenothiazine dyes incorporated into Nafion films

Electrochemical properties of phenothiazine dyes, thionine (TH+) and methylene blue (MB+), incorporated into Nafion films have been studied at different acid concentrations. The TH+ and MB+ dyes adsorbed by Nafion films gave an unusual redox wave at more positive potentials in addition to the usual redox wave at less positive potentials in 0.05 mol dm–3 H2SO4. Upon continuous cycling for 45 min the unusual redox wave disappeared. The two redox waves observed at 0.05 mol dm–3 H2SO4 were accounted for by the distribution of electroactive species in different domains of the Nafion polymer film, i.e. the lower void volume of the interfacial region and the higher void volume of the ionic cluster region. The same dyes incorporated into Nafion films in 0.5 mol dm–3 H2SO4 gave only the usual redox wave, which was accounted for by the molecules residing only in the ionic cluster region of the swelled Nafion film. The same electrochemical behaviour was also observed in Na+- and H+-Nafion film. The effects of different concentrations of dyes in the Nafion films were also studied in order to understand the influence of the polymer film structure on the electrochemical properties of phenothiazine dyes.

An optical waveguide acid vapor sensor

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.

Preparation and electrochemical behaviour of a methylene blue-modified electrode based on a Nafion polymer film

A methylene blue (MB) chemically modified electrode has been prepared by incorporating MB molecules into a Nafion polymer film on a glassy carbon surface. The electrochemical behaviour of the MB-modified polymer film electrode is discussed in detail. The electrode reaction of MB bound to the polymer film shows a reversible, two-electron transfer process with good stability and reproducibility. The equation of half-wave potential E1/2vs. pH was deduced theoretically and was proved to be reasonable experimentally by the effect of solution pH on the MB-modified polymer-film electrode. The influence of supporting electrolytes on the electrode is discussed.

Researches on chemically modified electrodes: Part XXIV. Preparation and characterization of nafion polymer film modified electrodes containing Fe(II)-phen complex

A Nafion polymer film modified electrode containing Fe(II)-phen complex has been prepared successfully. The process was studied by cyclic voltammetry. Fe(II) in aqueous solution was coordinated with phen on a glassy carbon (GC) electrode to form a complex Fe(phen) 2+ 3; the latter was attached to the Nafion polymer film electrode surface by association with SO − 3 sites in the Nafion. The electrochemical behavior and spectral properties of the Fe(phen) 2+ 3 -Nafion polymer film electrode was characterized and compared with those of the complex in the solution. The results show that the half-wave potential E 1/2 and the visible absorption spectrum for Fe(phen) 2+ 3 attached on the polymer film electrode are similar to those in the solution. The preparation of the polymer film electrode is discussed.