Diffusion regimes at nanoelectrode ensembles in different ionic liquids

The electrochemical and diffusion behaviour of different redox probes in different ionic liquids is studied at gold nanoelectrode ensembles (NEEs) in comparison with millimetre sized gold (Au-macro) and glassy carbon (GC) disk electrodes. The redox probes are neutral ferrocene (Fc), the ferrocenylmethyltrimetylammonium cation (FA⁺) and the ferrocenylmonocarboxylate anion (FcCOO⁻). The ILs are the dicyanamide, [N(CN)₂] or bis(trifluoromethylsulfonyl)amide), [N(Tf)₂] salts of the following cations: 1-butyl-3-methylimidazolium, [BMIm], 1-butyl-3-methylpyrrolidonium, [BMPy], or tris(n-hexyl)tetradecylphosphonium [P_14,666]. These ILs are characterized by different viscosities, ranging from 32 to 277 cP. The cyclic voltammetric behaviour of the redox probes is reversible and diffusion controlled at GC electrodes. Diffusion coefficients (D) calculated by the Randles-Sevcik equation scales inversely with the IL viscosity, ranging from 2 × 10⁻⁸ to 3 × 10⁻⁷ cm² s⁻¹. Ionic solutes, namely FA⁺ and FcCOO⁻, present slightly lower D values than neutral Fc. At the Au-macro the electrochemical behaviour of the redox probes is diffusion controlled in the ILs containing the [N(Tf)₂] anion, while it involves relevant adsorption processes in the [N(CN)₂] containing electrolyte. For this reason the diffusion at gold NEEs is studied only in the former ILs.The CVs of the redox probes at the NEEs are peak shaped at low scan rate (v), while they are sigmoidally shaped at high v, but with some shift between forward and backward patterns. This is indicative of the occurrence of a total overlap (TO) diffusion condition when v is low which becomes a mixed diffusion layers (MDL) regime, with only a partial overlapping of individual diffusion layers, at high v values. In the most viscous IL, namely [P_14,666] [N(Tf)₂], at v higher than 0.8 V s⁻¹, a plateau current independent on the scan rate is achieved, indicating the tendency to reach the pure radial regime in this IL. The v values at which the transition between TO and MDL is observed scales directly with D and inversely with the IL viscosity. This behaviour is interpreted on the basis of the dependence of individual diffusion layers at each nanoelectrode on redox probe/IL interaction which fits with existing theoretical models very recently developed for nanoelectrode arrays.     

Molecular characteristics of poly(1-trimethylsilyl-1-propyne) in dilute solutions

Samples and fractions of a membrane-forming polymer, poly(1-trimethylsilyl-1-propyne) (PTMSP), were studied by methods of molecular hydrodynamics (velocity sedimentation, translational isothermal diffusion and viscometry) in cyclohexane in the molecular mass range 60<M×10⁻³ g mol⁻¹<430. The following molecular-mass dependencies of the hydrodynamic characteristics (intrinsic viscosity [η] (cm³ g⁻¹), sedimentation coefficient s₀(s) and translational diffusion coefficient D₀ (cm² s⁻¹)) were established: [η]=0.198 M^0.50±0.06; s₀=8.66×10⁻¹⁶M^0.50±0.04; D₀=9.30×10⁻⁵M^{−0.50±0.04}. On the basis of the hydrodynamics data the equilibrium rigidity and hydrodynamic diameter of PTMSP chains were evaluated. The equilibrium properties of the different disubstituted polyacetylenes molecules are compared on the base of the normalised scaling plots.     

Interaction between promethazine hydrochloride and DNA and its application in electrochemical detection of DNA hybridization

The interactions of promethazine hydrochloride (PZH) with thiolated single-stranded DNA (HS-ssDNA) and double-stranded DNA (HS-dsDNA) self-assembled on gold electrodes have been studied electrochemically. The binding of PZH with ssDNA shows a mechanism containing an electrostatic interaction, while the mode of PZH interaction with dsDNA contains both electrostatic and intercalative bindings. The redox system belongs to the category of diffusion control approved by cyclic voltammetry (CV). The diffusion coefficients of PZH at the bare, HS-dsDNA and HS-ssDNA modified gold electrodes decrease regularly as 1.34 × 10⁻³ cm² s⁻¹, 1.04 × 10⁻³ cm² s⁻¹, 7.47 × 10⁻⁴ cm² s⁻¹, respectively. The electron transfer standard rate constant k_s of PZH at bare gold, HS-ssDNA and HS-dsDNA modified electrodes are 0.419 s⁻¹, 0.131 s⁻¹, and 0.154 s⁻¹, respectively. The presence of adsorbed dsDNA results in a great increase in the peak currents of PZH in comparison with those obtained at a bare or ssDNA adsorbed gold electrode. The difference between interactions of PZH with HS-ssDNA and HS-dsDNA has been used for hybridization recognition of 14-mer DNA oligonucleotide. The peak current (i_pa) of PZH is linearly proportional to the logarithmic concentration of complementary target DNA in the range from 2.0 × 10⁻⁹ mol L⁻¹ to 5.0 × 10⁻⁷ mol L⁻¹ with the detection limit of 3.8 × 10⁻¹⁰ mol L⁻¹.     

Investigation of water diffusion in poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by generalized two-dimensional correlation ATR-FTIR spectroscopy

Water diffusion process in biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx, HHx = 12 mol%) was investigated by generalized 2D correlation time-resolved ATR-FTIR spectroscopy based on the analysis of v(OH) stretching and δ(OH) bending bands of water as well as v(CO) and v(C-O-C) stretching bands of PHBHHx. Three states of water were figured out during water diffusion process. They are bulk water, bound water and free water. The water diffusion mechanism was suggested as: water molecules firstly diffuse into the micro-voids in bulk water form or are dispersed on the surface in free water form, and then penetrate into the polymer matrix in hydrogen bound water with the hydrophilic groups of PHBHHx. Moreover, water molecules diffuse into the loose amorphous phase and then into compact crystalline phase. Water diffusion coefficient in PHBHHx was thus evaluated as 7.8 ± 0.7 × 10⁻⁸ cm² s⁻¹ for the PHBHHx with crystallinity of 16.2 ± 0.3% at 293 K.     

Studies on the electrochemical behavior of 3-nitrobenzaldehyde thiosemicarbazone at glass carbon electrode modified with nano-γ-Al2O3

Nano-γ-Al₂O₃ is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10⁻⁶ M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10⁻⁵ M to 1.0 × 10⁻⁴ M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10⁻⁹ mol cm⁻² was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10⁻³ cm² s⁻¹, 2.03 × 10⁻³ cm² s⁻¹) and reaction rate constant k_s (5.9573 s⁻¹, 7.15 × 10⁻² cm s⁻¹) were obtained for quasi-reversible system I and irreversible system II, respectively.     

Synergistic gelation of solutions of isotactic polypropylene and bis-(3,4-dimethyl benzylidene) sorbitol and its use in gel-processing

We report the synergistic, rapid gelation of solutions of isotactic polypropylene (i-PP) and the nucleating agent 1,3:2,4-bis-(3,4-dimethyl benzylidene) sorbitol (DMDBS) in decalin. Cooling to room temperature of a solution comprising, for instance, 3.0 wt% of a moderately high molecular weight i-PP (M_v=1.3×10⁶ g/mol) and as little as 0.0075 wt% DMDBS (0.25 wt% based on the polymer) resulted in the fast formation of highly ductile gels. In reference experiments without DMDBS, often ‘mud-cracked’, brittle polymer films were obtained, and decaline solutions of DMDBS alone at the above concentration did not form macroscopically coherent gels. In the present work we employed this useful occurrence for gel-processing/drawing of i-PP, yielding material with Young's moduli of 35 GPa, tensile strengths of approximately 1 GPa and melting temperatures measured for constrained samples as high as 228 °C.     

Insight into the electroreduction of nitrate ions at a copper electrode, in neutral solution, after determination of their diffusion coefficient by electrochemical impedance spectroscopy

The electrochemical reduction of nitrate ions at a copper electrode in an unbuffered neutral aqueous solution is studied. Using a two compartment electrochemical cell, three stationary cathodic waves, noted P1, P2 and P3, were evidenced by cyclic voltammetry at −0.9, −1.2 and −1.3 V/SCE, respectively. By comparing the electrochemical response of nitrate and nitrite containing solutions, P1 was attributed to the reduction of nitrate to nitrite. In order to assign P2 and P3 features by determining the number of electrons involved at the corresponding potential, rotating disk electrode experiments at various rotation speeds, combined with linear sweep voltammetry, were performed. Current data analysis at a given potential was carried out using Koutecky-Levich treatment taking into account water reduction. Confident values of the diffusion coefficient D of nitrate ions were assessed by electrochemical impedance spectroscopy for nitrate concentrations of 10⁻³, 10⁻² and 10⁻¹ M. For a nitrate concentration of 10⁻² M, D was found to be 1.31 × 10⁻⁵ cm² s⁻¹ allowing the number of electrons to be determined as 6 for P2 and 8 for P3, in accordance with nitrate reduction into hydroxylamine and ammonia, respectively. The formation of hydroxylamine was confirmed by the observation of its reoxidation at a Pt microelectrode present at the Cu electrode/nitrate solution interface.     

Analysis of the chemical diffusion coefficient of lithium ions in Li3V2(PO4)3 cathode material

The chemical diffusion coefficients of lithium ions (DLi⁺) in Li₃V₂(PO₄)₃ between 3.0 and 4.8 V are systematically determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The DLi⁺ values are found to be dependent on the voltage state of charge and discharge. Based on the results from all the three techniques, the true diffusion coefficients measured in single-phase region are in the range of 10⁻⁹ to 10⁻¹⁰ cm² s⁻¹. Its apparent diffusion coefficients measured in two-phase regions by CV and GITT range from 10⁻¹⁰ to 10⁻¹¹ cm² s⁻¹ and 10⁻⁸ to 10⁻¹³ cm² s⁻¹, respectively, depending on the potentials. By the GITT, the DLi⁺ varies non-linearly in a “W” shape with the charge-discharge voltage, which is ascribed to the strong interactions of Li⁺ with surrounding ions. Finally, the chemical diffusion coefficients of lithium ions measured by CV, EIS and GITT are compared to each other.     

Synthesis and characterization of highly soluble 9,10-diphenyl-substituted poly(2,6-anthracenevinylene)

We report the synthesis and optoelectronic properties of highly soluble poly(9,10-bis(3′,4′-di(2″-ethylhexyloxy))phenyl)-2,6-anthracenevinylene) (HSM-PAV). The key intermediate for the synthesis of HSM-PAV is 2,6-dimethyl-9,10-dibromoanthracene, and the high solubility of HSM-PAV is from the incorporation of lateral 3,4-di(2-ethylhexyloxy)phenyl moieties into the 9,10-positions of anthracene units. The increase of side alkyloxy groups endows HSM-PAV with higher molecular weight (M_n = 3.2 × 10⁴) and better electroluminescence performances (L_max = 590 cd/m², LE_max = 0.27 cd/A) compared with the poly(2,6-anthracenevinylene) with lateral monoalkyoxy moieties (M_n = 1.9 × 10⁴, L_max = 340 cd/m², LE_max = 0.17 cd/A). The electrical conductivity of doped HSM-PAV film with iodine is 5 × 10⁻² S cm⁻¹ that is several order higher than that of doped 9,10-anthracene-based polymers, further demonstrating that linkage position has a dramatic effect on the optoelectronic properties of anthracene-based conjugated polymers.     

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite and its application for electrochemical supercapacitor

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO₂/P(An-co-oAs)] was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the MnO₂/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The MnO₂/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near 100 times greater than that of its pristine MnO₂ (3.5 × 10⁻⁷ S cm⁻¹). The specific capacitance of the MnO₂/P(An-co-oAs) nanocomposite reached 262 F g⁻¹ in 1 M Na₂SO₄ at a current density of 1 A g⁻¹, which was significantly higher than that of either of its two pristine materials [MnO₂ (182 F g⁻¹) or P(An-co-oAs) (127 F g⁻¹)] owing to the synergic effect between the two pristine components. The fabrication mechanism of the nanocomposite was also proposed and discussed in this paper.     

Estimation of the compositional gradient in a PVC/PMMA graded blend prepared by the dissolution-diffusion method

We reported a new preparation method in the previous paper, by which an excellent graded polymer blend was simply prepared. In this report, we propose a new model for the dissolution-diffusion process. The model was derived by obeying Fick's second law for diffusion and by assuming that the evaporation of the solvent in PMMA solution during the diffusion could be neglected. We then proved that this model was applicable to the graded structure of a PVC/PMMA graded blend. Further, it was confirmed that the dissolution rate of PVC into PMMA solution remained constant during preparation. Thus, our model was found to be reliable. However, while the apparent diffusion coefficients (D_ABs) of PVC in 0.183 and 0.274 ml/cm² of the initial solution volumes were equal to each other, they were larger than the D_AB in 0.091 ml/cm² of the initial solution volume. Thus, the effects of PVC concentration dependency of D_AB and changing of PMMA concentration in the solution on D_AB were discussed, because all of the D_ABs should be equal to each other. Then, our model was modified as follows. We considered that PVC finished diffusing below a PMMA concentration of 0.18 g/ml, because the diffusion coefficient of PVC immediately increased at a higher PMMA concentration. Then, the solution layer was shrunk to about 1/6, in order to form a blend film. Thus, it was found that the D_AB in each of the initial solution volumes was 4.2 ± 0.25 × 10⁻⁸ cm²/s. Further, the D_ABs estimated by diffusion thickness method, were from 1.5 to 3.5 times larger than those estimated by our model. Therefore, it was proved that our modified model was applicable to the experimental data.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

Mechanism of formation and growth of sunflower-shaped imperfections in anodic oxide films on niobium

Anodizing of niobium has been investigated to develop niobium solid electrolytic capacitors. Chemically polished niobium specimens were anodized in a diluted phosphoric acid solution, initially galvanostatically at i_a = 4 A m⁻² up to E_a = 100 V, and then potentiostatically at E_a = 100 V for t_pa = 43.2 ks. During the galvanostatic anodizing, the anode potential increased almost linearly with time, while, during potentiostatic anodizing, the anodic current decreased up to t_pa = 3.6 ks, and then increased slowly before decreasing again after t_pa = 30.0 ks. Images of FE-SEM and in situ AFM showed that nuclei of imperfections were formed at the ridge of cell structures before t_pa = 3.6 ks. After formation, the imperfection nuclei grew, showing cracking and rolling-up of the anodic oxide film, and crystalline oxide was formed at the center of imperfections after t_pa = 3.6 ks. The growth of imperfections caused increases in the anodic current between t_pa = 3.6 and 30.0 ks. Long-term anodizing caused a coalescence of the imperfections, leading to decreases in the anodic current after t_pa = 30.0 ks. As the imperfections grew, the dielectric dispersion of the anodic oxide films became serious, showing a bias voltage dependence of the parallel equivalent capacitance, C_p, and a dielectric dissipation factor, tan δ. The mechanism of formation and growth of the imperfections, and the correlation between the structure and dielectric properties of anodic oxide films is discussed.     

Reduction process of uranium(IV) and uranium(III) in molten fluorides

This study focused on the electroreduction process of uranium cations in molten fluorides. It involved cyclic voltammetry, chronopotentiometry with and without current reversal, and square wave voltammetry.The results indicate a two-step reduction process for uranium(IV). The first step U(IV)/U(III) exchanging one electron corresponds to a soluble/soluble system and is limited by U(IV) diffusion with D_U(IV) = 1.25 ± 0.35 × 10⁻⁵ cm² s⁻¹ in LiF-NaF at 720 °C.In order to perform a thorough study of the second step U(III)/U(0) in the reduction process, the melt was chemically reduced in U(III) with U metal as reducing agent. Alternatively to the use of LiF-NaF where U metal is unstable at 720 °C, the chemical reduction of U(IV) in U(III) was performed in a LiF-CaF₂-UF₄ solution containing U metal at 810 °C. It has been confirmed that the reduction of U(III) proceeds in one step exchanging three electrons and by a diffusion controlled process with D_U(III) = 2.2 ± 0.7 × 10⁻⁵ cm² s⁻¹ in LiF-CaF₂ at 810 °C.     

Novel chemosensory materials based on polyfluorenes with 2-(2′-pyridyl)-benzimidazole and 5-methyl-3-(pyridin-2-yl)-1,2,4-triazole groups in the side chain

Polyfluorenes with 2-(2′-pyridyl)-benzimidazole (P1, P2 and P4) and 5-methyl-3-(pyridin-2-yl)-1,2,4-triazole (P3) groups in the side chain were synthesized by Suzuki polycondensation. The responsive properties of polymers on metal ions and H⁺ were investigated by absorption and emission spectra. The fluorescences of polymers (P1-P4) were completely quenched upon the transition metal ions such as Co²⁺, Ni²⁺, Fe³⁺ and Ag⁺ due to the enhanced electronic communication properties of conjugated polymers. The obvious differences to Ni²⁺ ion responsive sensitivity were observed between P1 and P4 polymers. The fluorescences of P1 and P4 were quenched to 50 (I₀/I) and to 22 (I₀/I) upon the addition of a Ni²⁺ solution of 3.2 × 10⁻⁶ M, as well as 5.0 × 10⁻⁶ M, respectively, owing to the different conjugated backbone. The fluorescences of P2 and P3 were completely and hardly quenched upon the addition of a Al³⁺ solution of 1.0 × 10⁻⁴ M, respectively, owing to the different receptors in the side chain. P2 showed good selectivity to Ni²⁺ ion in the range of quencher concentration as low as 5 ppm, owing to the different chelating abilities of receptor with ions. Cu²⁺ and Mn²⁺ ions hardly quenched the fluorescences of polymers (P1-P4), which were different from the oligopyridyl-functionalized conjugated polymers. The results further opened the opportunities to develop the tailored sensory materials through the appropriate alteration of receptors in the side chain and the conjugated backbone.     

Effect of surface-modified zinc oxide nanowires on solution crystallization kinetics of poly(3-hexylthiophene)

Interfacial interactions between donor and acceptor molecules are determinative to the device performance of hybrid photovoltaics. However, the dynamic process of such interactions remains largely obscure. In this work, we report the kinetic behavior of solution crystallization of poly(3-hexylthiophene) (P3HT) in anisole in the presence of ZnO nanowires by means of ultraviolet-visible absorption spectroscopy. ZnO nanowires are surface-modified by covalently attaching aliphatic and aromatic ligands to enhance the miscibility and interfacial interactions between P3HT and ZnO nanowires. Upon cooling the hot solution to room temperature, a significant time-dependent chromism occurs spontaneously. Analysis of the kinetics of isothermal solution crystallization across a range of crystallization temperature displays that the growth rate of the crystals scales with polymer concentration as R ∝ C^1.6 for both the control P3HT and P3HT with ZnO nanowires. The Lauritzen–Hoffman theory of secondary nucleation is utilized to analyze the kinetic behavior of crystallization, and the fold surface free energies of the crystals of P3HT in anisole are calculated to be 6.6–10.3 × 10⁻² J m⁻². It is found that the addition of surface-modified ZnO nanowires decreases the fold surface free energy by 21.5% and 43.8%, respectively, for aliphatic and aromatic ligands.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Electrooxidation of sulfide by cobalt pentacyanonitrosylferrate film on glassy carbon electrode by cyclic voltammetry

A glassy carbon (GC) electrode was modified with cobalt pentacyanonitrosylferrate (CoPCNF) film. Cyclic voltammetry (CV) of the CoPCNF onto the GC (CoPCNF/GC) shows a redox couple (Fe^III/Fe^II) with a standard potential (E^0′) of 580 mV. The current ratio I_pa/I_pc remains almost 1, and a peak separation (ΔE_p) of 106 mV is observed in 0.5 M KNO₃ as the supporting electrolyte. Anodic peak currents were found to be linearly proportional to the scan rate between 10 and 200 mV s⁻¹, indicating an adsorption-controlled process. The redox couple of the CoPCNF film presents an electrocatalytic response to sulfide in aqueous solution. The analytical curve was linear in the concentration range of 7.5 × 10⁻⁵ to 7.7 × 10⁻⁴ M with a detection limit of 4.6 × 10⁻⁵ M for sulfide ions in 0.5 M KNO₃ solution.     

Synthesis and characterization of controlled molecular weight disulfonated poly(arylene ether sulfone) copolymers and their applications to proton exchange membranes

tert-Butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers with controlled molecular weights (M_n), 20-50 kg mol⁻¹, were successfully prepared by direct copolymerization of the two activated halides, biphenol and the endcapper, 4-tert-butylphenol. The high molecular weight copolymer (molecular weight over 80 kg mol⁻¹) was also synthesized with 1:1 stoichiometry without an endcapping reagent. The chemical compositions and the molecular weights of the endcapped copolymers were characterized by their ¹H NMR spectra utilizing the 18 unique protons at the chain ends. Modified intrinsic viscosity measurements in 0.05 M LiBr/NMP solution further correlated well with NMR results. Combining the endcapping chemistry with proton NMR end group analysis and intrinsic viscosity measurements, one can demonstrate a powerful tool for characterizing molecular weight of sulfonated poly(arylene ether sulfone) random copolymers. This enables one to further investigate the influence of molecular weight on several critical parameters important for proton exchange membranes, including water uptake, in-plane protonic conductivity and selected mechanical properties. These are briefly discussed herein and will be more fully described in subsequent publications.