Electrochemical Responses and Sensitivities of Films Based on Multi-Walled Carbon Nanotubes in Aqueous Solutions

Novel films consisting of multi-walled carbon nanotubes (MWCNTs) were fabricated by means of chemical vapor deposition with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene as catalyst. The electrochemical responses of MWCNT-based films towards the ferrocyanide/ferricyanide, [Fe(CN)₆]^3?/4? redox couple were probed by means of cyclic voltammetry and electrochemical impedance spectroscopy at 25.0?±?0.5?°C. Both MWCNT-based films exhibit Nernstian response towards [Fe(CN)₆]^3?/4? with some slight kinetic differences. Namely, heterogeneous electron transfer rate constants lying in ranges of 2.69?×?10^?2?C1.7?×?10^?3 and 9.0?×?10^?3?C2.6?×?10^?3?cm·s^?1 were obtained at v?=?0.05?V·s^?1 for MWCNT_ACN and MWCNT_BZ, respectively. The detection limit of MWCNT_ACN, estimated to be about 4.70?×?10^?7?mol·L^?1 at v?=?0.05?V·s^?1, tends to become slightly poorer with the increase of the scan rate, namely at v?=?0.10?V·s^?1 the detection limit of 1.70?×?10^?6?mol·L^?1 was determined. Slightly poorer response ability was exhibited by MWCNT_BZ; specifically the detection limits of 1.57?×?10^?6 and 4.35?×?10^?6?mol·L^?1 were determined at v?=?0.05 and v?=?0.10?V·s^?1, respectively. The sensitivities of MWCNT_ACN and MWCNT_BZ towards [Fe(CN)₆]^3?/4? were determined as 1.60?×?10^?7 and 1.51?×?10^?7?A·L·mol^?1·cm^?2, respectively. The excellent electrochemical performance of MWCNT_ACN is attributed to the presence of incorporated nitrogen in the nanotube??s structure.     

Electrochemical Oxidation of Methionine Mediated by a Fullerene‐C60 Modified Gold Electrode

The usefulness of a C₆₀‐fullerene modified gold (Au) electrode in mediating the oxidation of methionine in the presence of potassium ions electrolyte has been demonstrated. During cyclic voltammetry, an oxidation peak of methionine appearing at +1.0 V vs. Ag/AgCl was observed. The oxidation current of methionine is enhanced by about 2 times using a C₆₀ modified gold electrode. The current enhancement is significantly dependent on pH, temperature and C₆₀ dosage. Calibration plot reveals linearity of up to 0.1 mM with a current sensitivity of close to 50 mA L mol^?1 and detection limit of 8.2×10^?6 M. The variation of scan rate study shows that the system undergoes diffusion‐controlled process. Diffusion coefficient and rate constant of methionine were determined using hydrodynamic method (rotating disk electrode) with values of 1.11×10^?5 cm² s^?1 and 0.0026 cm s^?1 respectively for unmodified electrode while the values of diffusion coefficient and rate constant of methionine using C₆₀ modified Au electrode are 5.7×10^?6 cm² s^?1 and 0.0021 cm s^?1 respectively.     

Comparison of Electrochemical Synthesis of Ammonia by Using Sulfonated Polysulfone and Nafion Membrane with Sm1.5Sr0.5NiO4

Polysulfone (PSF) and sulfonated polysulfone (SPSF) were synthesized and characterized by IR spectrum. Sm_1.5Sr_0.5NiO₄ (SSN) and Ni‐Ce_0.8Sm_0.2O_2?δ (Ni‐SDC, Ni‐samarium doped ceria) were prepared and characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Ammonia was synthesized from wet hydrogen and dry nitrogen with applied voltage, using SSN as cathode, Ni‐SDC as anode, Nafion and SPSF as proton membrane respectively. The performances of Nafion and SPSF membranes in ammonia synthesis were investigated and compared at atmospheric pressure and low temperature (25–100°C). The results demonstrated that the proton conducting performances of Nafion and SPSF membranes were similar and the highest rates of evolution of ammonia were up to 1.05×10^?8 and 1.03×10^?8 mol·cm^?2·s^?1 respectively at 80°C and 2.5 V.     

牛磺酸双核铜络合物为载体的高选择性硫氰酸根离子电极的研究

本文报道了一种以牛磺酸双核铜络合物为中性载体的硫氰酸根PVC膜电极。该电极对硫氰酸根有良好的电位响应并呈现出anti-Hofmeister行为,其选择性顺序SCN^->I^->ClO₄^->Sal^->NO₃^-> NO₂^-> Br^- > Cl^- > SO₃^-> SO₄ ^2-。在20℃ pH 5.0的磷酸缓冲溶液中,其线性范围为1.0´10 ^-1~ 1.0´10^-6mol×L-1,检测线为8.0×10 ^-7mol•L^-1,斜率为 -56.5 mV/pcSCN^-。紫外、红外和交流阻抗研究表明电极的高选择性与载体的立体结构和分析物与中心金属离子的作用相关。将该电极用于废水和人体尿液中硫氰酸根的测定,获得了较满意的结果。     

New insights on the Cd UPD on Au(111)

The Cd underpotential deposition (UPD) process on Au(111) was analyzed by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). In the underpotential range 300?ΔE (mV) ?400, 2D Cd islands are formed on the fcc regions of the Au(111)‐(√3 × 22) reconstructed surface without lifting the reconstruction. At lower underpotentials, the 2D Cd islands grow and, simultaneously, new 2D islands nucleate and coalesce with the previous ones forming a complete condensed Cd monolayer (ML). STM images and long time polarization experiments performed at ΔE = 70 mV demonstrate the formation of an Au? Cd surface alloy. At ΔE = 10 mV, the formation of the complete Cd ML is accompanied by a significant Au? Cd surface alloying and the kinetic results reveal two different solid‐state diffusion processes. The first one, with a diffusion coefficient D₁ = 4 × 10^?17 cm² s^?1, could be ascribed to the mutual diffusion of Au and Cd atoms through a highly distorted (vacancy‐rich) Au? Cd alloy layer. The second and faster diffusion process (D₂ = 7 × 10^?16 cm² s^?1) is associated with the appearance of an additional peak in the anodic stripping curves and could be attributed to the formation of another Cd_zAu_x alloy phase. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on Dynamic Interfacial Tension of 3‐Dodecyloxy‐2‐hydroxypropyl Trimethyl Ammonium Chloride at n‐Decane/Water Interface

Dynamic interfacial tension (DIT) and interface adsorption kinetics at the n‐decane/water interface of 3‐dodecyloxy‐2‐hydroxypropyl trimethyl ammonium chloride (R₁₂TAC) were measured using spinning drop method. The effects of R_nTAC concentration and temperature on DIT have been investigated, the reason of the change of DIT with time has been discussed. The effective diffusion coefficient, D _a, and the adsorption barrier, ?_a, have been obtained with extended Word‐Tordai equation. The results show that the higher the concentration of surfactants is, and the smaller will be the DIT and the lower will be the curve of the DIT, and the R₁₂TAC solutions follow a mixed diffusion‐activation adsorption mechanism in this investigation. With increase of concentration in bulk solution of R₁₂TAC from 8×10^?4 mol · dm^?3 to 4×10^?3 mol · dm^?3, D _a decreases from 2.02×10^?10 m^?2 · s^?1 to 1.4×10^?11 m^?2 · s^?1 and ? _a increases from 2.60 kJ · mol^?1 to 9.32 kJ · mol^?1, while with increase of temperature from 30°C to 50°C, D _a increases from 2.02×10^?10 m^?2 · s^?1 to 5.86×10^?10 m^?2 · s^?1 and ε_a decreases from 2.60 kJ · mol^?1 to 0.73 kJ · mol^?1. This indicates that the diffusion tendency becomes weak with increase strength of the interaction between surfactant molecules and that the thermo‐motion of molecules favors interface adsorption.     

Electrosynthesis of Poly(azure B) from Sulfuric Acid Solution

Electrochemical polymerization of azure B from sulfuric acid solution was carried out by using cyclic voltammetry. The electrolytic solution consisted of 5.0 mmol · dm^?3 azure B and 0.3 mol · dm^?3 H₂SO₄. The temperature for polymerization was controlled at 20°C. A blue film, i.e., poly(azure B) was formed on a platinum foil and had a electrochemical reversibility, stability and a fast charge transfer ability in the 0.5 mol · dm^?3 Na₂SO₄ with pH ≤4.0 solution. The currents of both anodic and cathodic peaks are proportional to υ^1/2 at the scan rate (υ) region of 25 and 600 mV · s^?1 on the cyclic voltammograms. The conductivity of poly(azure B) is 2.8×10^?6 S · cm^?1 at 20°C. The UV‐visible spectrum and Raman spectrum of the polymer are different from those of the monomer. A possible polymerization mechanism of azure B was also proposed.     

Amperometric Biosensor for Hydrogen Peroxide Based on Electrodeposited Sub-micrometer Gold Modified Glassy Carbon Electrode

IntroductionAmperometricbiosensorofhydrogenperoxideisofpracticalimportancebecauseofitswideapplicationsinchemical,biological,clinical,environmentalandmanyotherfields.Forimprovementofsensor抯quality,vari-ouskindsofchemicalmodificationmethodshavebeendevelopedforreducingredoxoverpotentialsofH2O2atelectrodesurfaces,increasingthedetectionsensitivity,linearrange,stabilityandlivetime.Ithasbeenshownthattheuseofsub-micrometersizedmetalparticlessuchasPt-blackcansignificantlyimprovethequalityofthebiosens…     

Rate constants for hydrogen abstraction reactions of the sulfate radical,SO4−. Alkanes and ethers

Rate constants have been determined for the reactions of SO₄^? with a series of alkanes and ethers. The SO₄^? radical was produced by the laser-flash photolysis of persulfate, S₂O₈^2?. For methane, only an upper limit of 1 × 10⁶ M^?1 s^?1 could be determined. For ethane, propane, and 2-methylpropane, rate constants of 0.44, 4.0, and 10.5 × 10⁷ M^?1 s^?1 were found. For ethyl and n-propyl ether, rate constants of 1.3 × 10⁸ and 2.2 × 10⁸ M^?1 s^?1 were found and for 1,4-dioxane and tetrahydrofuran, rate constants of 7.2 × 10⁷ and 2.8 × 10⁸ were obtained. The reaction of SO₄^? with allyl alcohol was also studied and found to have a rate constant of 1.4 × 10⁹ M^?1 s^?1.     

Intermolecular interaction between squarylium cyanine and porphyrin

In this paper, the interaction between squarylium cyanine and porphyrin in chloroform is investigated by absorption and fluorescence spectroscopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of squarylium cyanine and the fluorescence spectrum of porphyrin was calculated, which reveals that the singlet-singlet energy transfer may occur from porphyrin to squarylium cyanine in solution. In comparison of the observed rate constant [kqII=6.1 ×1013 (mol/L)-1·s-1] for fluorescence quenching of porphyrin by squarylium cyanine with the diffusion rate constant in chloroform [kdif=1.1×1010 (mol/L)-1·s-1] and the rate of energy transfer [ket≤6.7×104 (mol/L)-1·s-1 in the experimentally dilute solutions] estimated from Forster formula, the possibility of energy transfer by electron exchange or/and coulombic mechanism could be excluded. So it has been definitely convinced that the intermolecuiar energy transfer between them is     

Ozone–olefin reactions in the gas phase 1. Rate constants and activation energies

Reactions of ozone with simple olefins have been studied between 6 and 800 mtorr total pressure in a 220-m³ reactor. Rate constants for the removal of ozone by an excess of olefin in the presence of 150 mtorr oxygen were determined over the temperature range 280 to 360° K by continuous optical absorption measurements at 2537 Å. The technique was tested by measuring the rate constants k₁ and k₂ of the reactions (1) NO + O₃ → NO₂ + O₂ and (2) NO₂ + O₃ rarr; NO₃ + O₂ which are known from the literature. The results for NO, NO₂, C₂H₄, C₃H₆, 2-butene (mixture of the isomers), 1,3→butadiene, isobutene, and 1,1 -difluoro-ethylene are 1.7 × 10^{?1 4} (290°K), 3.24 × 10^?17 (289°K), 1.2 × 10^{?1 4} exp (–4.95 ± 0.20/RT), 1.1 × 10^{?1 4} exp (–3.91 ± 0.20/RT), 0.94 × 10^{?1 4} exp ( –2.28 ± 0.15/RT), 5.45 ± 10^{?1 4} exp ( –5.33 ± 0.20/RT), 1.8 ×10^?17 (283°K), and 8 × 10^?20 cm³/molecule ·s(290°K). Productformation from the ozone–propylene reaction was studied by a mass spectrometric technique. The stoichiometry of the reaction is near unity in the presence of molecular oxygen.     

Micro-determination of gold using N-cyanoacylacetaldehyde hydrazone

A reliable and rapid procedure for the flotation and micro-determination of Au(III) using N-cyanoacylacetaldehyde hydrazone (CyAH) is proposed. CyAH forms a blue 1:1 complex (K_f=4.1×10⁵ mol^?1l^?1) with Au(III) at pH 3–7. The maximum absorbance is obtained after 7 min; instantaneously by adding 3.3×10^?3 mol/l H₃PO₄ or by heating to 55°C. Beer's law is obeyed for 1–30 ppm of Au(III) with a molar absorptivity of 0.3×10⁴ l mol^?1 cm^?1 at 550 nm.     

Flash photolysis study for reactions of NO3· with sulfur compounds in acetonitrile solution

The rate constants for the reaction of NO₃· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 10⁴ M^?1s^?1 at ?10°C) is larger than that of the deuterium derivative, indicating that NO₃· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 10⁹ M^?1 s^?1 at ?10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO₃·, suggesting the electron transfer reaction from the sulfide to NO₃·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 10⁹ M^?1 s^?1 (at ?10°C) was not practically affected by the deuterium substitution, suggesting that NO₃· adds to sulfur atom forming (CH₃)₂?(O)-ONO₂. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.     

Polybromostryl macromers and their anionic polymerization

The decomposition of polybromostyryl carbanions (PBS^?), obtained by anionic polymerization of 4-bromostyrene in tetrahydrofuran (THF), was investigated in the dark in a temperature range of ?6–?21°C. It was accompanied by the evolution of bromine anions and by the formation of polymeric allylic carbanions (λ_max = 575 nm; ε_max = 6800 eq^?1·L·cm^?1). The reaction mechanism was elucidated. The rate constant of the unimolecular rate-determining step of the process was 1.3 × 10^?5 s^?1 and 9.7 × 10^?5 s^?1 at ?21 and ?6°C, respectively. Its apparent energy of activation E_app = 18.38 Kcal/mol. The polybromostyrenes with allylic carbanions at their ends may decompose further. Their “dark” decomposition yielded 1,3-butadiene-1,3-diphenyl-macromers. The mechanisms of decomposition of the PBS^? carbanions and the dark decomposition of the polybromostyryl allylic carbanions are analogous. The rate constant of the latter process was 2.5 × 10^?6 s^?1 at ?6°C. The anionic polymerization of prepared macromers can be initiated in THF at ?78°C by α-methylstyryl carbanions, which do not react, however, with PBS^? carbanions. “Comblike” polymacromers were prepared in which each branch had a molecular weight of about 50,000. The overall molecular weight of the polymacromer was estimated to be about 1 × 10⁶. It has been assumed that the 2–1 mode of addition to the diene group of the macromer is predominant during its polymerization. The 3–4 mode of addition followed by proton shift represents the termination step. The 4–3 mode of addition was ruled out on the basis of spectroscopic evidence.     

Sol—Gel Derived Carbon Ceramic Electrode Bulk—Modified with Tris（1,10—phenanthroline—5,6—dione） iron （Ⅱ）Hexafluorophosphate and Its Use as an Amperometric Iodate Sensor

A surface‐renewable tris(1, 10‐phenanthroline‐5, 6‐dione) iron (D) hexafluorophosphate (FePD) modified carbon ceramic electrode was constructed by dispersing FePD and graphite powder in methyltrimethoxysilane (MTMOS) based gels. The FePD‐modified electrode presented pH‐dependent voltammetric behavior, and its peak currents were diffusion‐controlled in 0.1 mol/L Na₂SO₄ + H₂SO₄ solution (pH = 0.4). In the presence of iodate, dear electrocatalytic reduction waves were observed and thus the chemically modified electrode was used as an amperometric sensor for iodate in common salt. The linear range, sensitivity, detection limit and response time of the iodate sensor were 5 × 10^?6–1 × 10^?2 mol/L, 7.448 μA·L/ mmol, 1.2 × 10^?6 mol/L and 5 s, respectively. A distinct advantage of this sensor is its good reproducibility of surface‐renewal by simple mechanical polishing.     

Study on the determination of trace rhenium (VII) by the adsorption differential pulse polarography

The determination of trace rhenium (VII) by differential pulse polarography in the system of H₂SO₄-(NH_sOH)₂ · H₂SO₄-TeO^2?₄ is markedly improved by the addition of Nitron, which is adsorbed on the surface of mercury electrode. The limit of detection is down to 2 × 10¹⁰ M. The adsorptive peak potential is ?0.80 V (vs. SCE). In the ranges of 5 × 10¹⁰—10^?8, 1 × 10^?5—10^?7 and 1 × 10^?7—10^?6M, there are good linear relationships between the peak current increment and the concentration, of which the relative standard deviations are 9.5, 6.6, 1.8% respectively with the correlation coefficients of linear regression of 0.995–0.999. The results relating to this polarographic wave show that it is an adsorption-catalytic wave. The mechanism of the electrode reaction is discussed.     

Modeling the reversible addition–fragmentation chain transfer process in cumyl dithiobenzoate‐mediated styrene homopolymerizations: Assessing rate coefficients for the addition–fragmentation equilibrium

A full kinetic scheme for the free‐radical reversible addition–fragmentation chain transfer (RAFT) process is presented and implemented into the program package PREDICI®. With the cumyl dithiobenzoate‐mediated bulk polymerization of styrene at 60 °C as an example, the rate coefficients associated with the addition–fragmentation equilibrium are deduced by the careful modeling of the time‐dependent evolution of experimental molecular weight distributions. The rate coefficient for the addition reaction of a free macroradical to a polymeric RAFT species (k_β) is approximately 5 · 10⁵ L mol^?1 s^?1, whereas the fragmentation rate coefficient of the formed macroradical RAFT species is close to 3 · 10^?2 s^?1. These values give an equilibrium constant of K = k_β/k_?β = 1.6 · 10⁷ L mol^?1. Conclusive evidence is given that the equilibrium lies well on the side of the macroradical RAFT species. The high value of k_β is comparable in size to the propagation rate coefficients reported for acrylates. The transfer rate coefficient to cumyl dithiobenzoate is close to 3.5 · 10⁵ L mol^?1 s^?1. A careful sensitivity analysis was performed, which indicated that the reported rate coefficients are accurate to a factor of 2. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1353–1365, 2001     

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

Swelling Characterization of the Superabsorbent Copolymer in the Petroleum-Based Solvent-Water Mixtures

The crosslinked and porous copolymer grains were synthesized by inverse suspension polymerization of acrylamide. The synthesized copolymer was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). It was achieved to absorbed 418 g water by 1 g copolymer after 5 min waiting time. Moreover, it was seen that about 99% of water was absorbed by 1 g copolymer in the solvent water mixtures (300 mL solvent–200 mL distilled water) after 2.5 min waiting time. The diffusion coefficients of the copolymer in the solvent-water mixtures were found between 8.87 · 10⁴ and 10.64 · 10⁴ cm²s^?1. Furthermore, the copolymer in distilled water achieved to reach a high value of the diffusion coefficient (13.2 · 10⁴ cm²s^?1).     

Electrochemical and kinetic study of oxygen in a perfluorotributylamine emulsion

Oxygen can be determined in a perfluorotributylamine emulsion used as a blood substitute by coulometry and polarography. The oxygen uptake of the emulsion (4.3 × 10^?3 mol l^?1 or 11 ml-% at 25°C and P_O2 = 760 mm Hg) is about three times greater than that of water. The adsorption of surfactant on a dropping mercury electrode changes the electrochemical parameters E_{$\text{1}\text{2}$}, α and k₃. The marked difference between the diffusion coefficients of oxygen and hydrogen peroxide (ratio 2.6) seems to be proceed from the ejection of oxygen molecules from the perfluorotributylamine droplets and from the insolubility of hydrogen peroxide molecules in the droplets. The constant rate of oxygen release by these droplets was estimated to be 10⁴ s^?1 by a stopped-flow spectrophotometric method. This constant rate seems to be linked with the particle diameter (0.2 μm) and the diffusion coefficient in the perfluorotributylamine droplets (1.6 × 10^?6 cm² s^?1).