Shunitz Tanaka

Electrochemical oxidation of bisphenol A. Application to the removal of bisphenol A using a carbon fiber electrode.

The electrochemical behavior of bisphenol A was investigated by voltammetric techniques. The electrochemical oxidation of bisphenol A led to the inactivation of the glassy carbon electrode as the result of the deposition of the electropolymerized films. Although phenolate is oxidized more easily than the neutral phenol, an electropolymerized film of bisphenol A was formed in neutral media rather than in alkaline media. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferrocyanide ion as the redox marker. The electrochemical removal of bisphenol A based on the formation of the electropolymerized film on an anode surface was also attempted using a carbon fiber electrode with a very large surface area. The high removal efficiency for bisphenol A was obtained in a dilute solution of bisphenol A. The maximum surface coverage (gamma) of electropolymerized bisphenol A on the carbon fiber was about 2 x 10(-9) mol/cm2.

Electrochemical decomposition of bisphenol A using Pt/Ti and SnO2/Ti anodes

Methodology for the electrochemical decomposition of bisphenol A is described. The electrochemical behaviour of bisphenol A at a Pt electrode was investigated by means of cyclic voltammetric techniques. The electrochemical oxidation of bisphenol A led to the deactivation of the electrode as a result of the deposition of an electropolymerized film. However the electrochemical decomposition of bisphenol A could be achieved by the use of a platinum coated titanium (Pt/Ti) electrode and a tin dioxide coated (SnO2/Ti) electrode. The electrolysis was carried out galvanostatically at a constant current of 0.3 A. The mineralization of bisphenol A was monitored by determining the amount of total organic carbon. Furthermore, the generation and nature of intermediates produced in the electrochemical reactions was investigated. Although large amounts of aliphatic acids were generated by electrolysis with the Pt/Ti anode, they were produced only to a small extent in at the SnO2/Ti anode. In the case of the SnO2/Ti anode, bisphenol A is rapidly oxidized to carbon dioxide and water, compared to the Pt/Ti anode.

Chromium(III) binding abilities of humic acids

The abilities of the humic acids (HAs) to bind Cr(III) were evaluated by a model on the basis of binding between Cr3+ and CrOH2+ species and the HAs. This model equation denotes the relationship between the concentration of unbound ([Cr(III)]ub) and bound ([Cr(III)]b) species. The aqueous solution containing Cr(III) and HA was equilibrated, and then [Cr(III)]b was determined by flame atomic absorption spectrometry after a pre-separation with the cation-exchanger, sulphopropyl Sephadex C-25 (C-25), in which the cationic unbound Cr(III) species retained on the C-25 could be calculated by subtracting [Cr(III)]b in the effluent from the total concentration of Cr(III) added initially ([Cr(III)]t). An excellent curve-fitting was obtained in the range of pH 3.2–4.3 by the non-linear least square regression analyses of the proposed model equation to the experimental data set ([Cr(III)]ub, [Cr(III)]b). The calculated conditional binding constants (K′Cr3+, K′CrOH2+) and the binding capacities (N) were as follows: log K′Cr3+, 3.4-4.9; log K′ in 4.9-5.3; N, 0.8-2.4 (mmol g−1 of C), and these values increased with increasing pH. The conditional binding constants of the Cr(III)-HA complex (pH 3.25, I = 0.01) were compared with those of other metal-HA complexes in the literature (pH 3.00, I = 0.01). The logK′Cr3+ value was comparable to those of metal ions as Ca2+, Zn2+ and the logK′CrOH2+ value was comparable to those of Pb2+, and Cu2+ and Ni2+. The N values were larger than those in the case of copper(II) ions. The Cr(III) binding abilities of the peat HAs were also evaluated by the present model. It was found that the N values of the HAs correlated to the carboxylic contents. Comparison of FTIR (Fourier transform infrared) spectra between the protonated HA and Cr(III)-HA complex suggested the existence of Cr(III)-carboxylate binding.

Improvement of resolution in the capillary electrophoretic separation of catecholamines by complex formation with boric acid and control of electroosmosis with a cationic surfactant

Abstract In order to improve the resolution of catecholamines, the control of both the electroosmotic and the electrophoretic mobilites were carried out. The former was controlled by the addition of borate ion and a change in pH. The control of the latter was carried out by addition of a cationic surfactant. Ten catecholamines were sufficiently separated.

Acid-base characterization of molecular weight fractionated humic acid

Acid-base properties of molecular weight fractionated humic acids (HAs) were investigated by the acid-base potentiometric titration. The acidic group contents (C(A(t))) and the average values of apparent pK (pK(app)) were evaluated by applying a modified Henderson-Hasselbalch equation to the experimental titration curves. The average values of pK(app) of the fractionated and unfractionated HAs were about 4.1-4.4, and the distribution of pK(app) values could be represented by the relationships between alpha and pK(app) plots in the range 2-8. The C(A(t)) values increased with a decrease in molecular size, as did the aromaticity. This suggests that the acidic group contents are related to the aromaticity of the HA.

Removal of Cr(VI) from contaminated soil by electrokinetic remediation

A new process for the removal of hexavalent chromium [Cr(VI)] contaminated soil is described. The process provides for an efficient removal of anionic chemicals from contaminated soils. Chromate anions were removed from the soil to the anodic reservoir by the moving force of electromigration. In this process, the chromate anions that accumulate in the anodic reservoir are simultaneously eliminated by using a column packed adsorbent. The adsorbent (immobilized tannin) used was chemically incorporated into cellulose. Cr(VI) was found to be adsorbed to this adsorbent efficiently. In the electrokinetic process, the pH of the aqueous solution in the anodic reservoir was decreased by the electrolysis of water. In the present study, the pH of the solution in the anodic reservoir is maintained at pH 6 by the addition of an aqueous alkaline solution during the electrokinetic process. The advantage of pH control is that it promotes the release of Cr(VI) from the soil by electromigration, thus permitting the maximum adsorption of Cr(VI) on the immobilized tannin. Simultaneous collection of Cr(VI) from the anodic reservoir leads to the protection from secondary contamination with Cr(VI).

Interpretation of the acid-base equilibrium of humic acid by a continuous pK distribution and electrostatic model

Acid-base equilibria of a humic acid were characterized by considering ionic group heterogeneity and electrostatic effects. The continuous pK distribution model, in which acidic functional groups having two centers of distribution were assumed in the humic molecule, was adapted to the experimental titration data by non-linear least square regression analysis. Excellent curve-fitting was obtained, and two centers of pK distribution (μ1 and μ2) and the total amounts of functional groups (CA1 and CA2) were evaluated. It was suggested that there are strong and weak acidic groups in the humic molecule and that they continuously deprotonate according to their pK distribution. The μ values were evaluated in media of various ionic strength (I = 0.004−1); μ1 (strong groups): 3.4–5.1, μ2 (weak groups): 6.0–7.9, and the ratio of CA1 to CA2 was ca. 5:2. The electrostatic model including the Debye-Huckel theory was adapted to evaluate the intrinsic dissociation constants, pKi,int. From the relationship between the μ values and I12, the intrinsic pKi values of two centers of distributions, μint, could be evaluated; μ1,int: 3.03, μ2,int: 5.12. The intrinsic pK distribution and the species distribution curves were calculated under electrostatic-free conditions. Investigation of Fourier transform infrared spectra and the species distribution curves suggested that the two different types of carboxylic groups would contribute to the pK distribution of each functional group.

Electrochemical removal of p-nonylphenol from dilute solutions using a carbon fiber anode

p-Nonylphenol, which is widely used as raw material in industrial activities has been regarded as an environmental endocrine disrupter. In an effort to develop a new treatment method for p-nonylphenol, we initially investigated the electrochemical behavior of p-nonylphenol by voltammetric techniques. The electrochemical oxidation of p-nonylphenol led to the formation of electropolymerized film on the glassy carbon electrode surface. The fouling on the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferrocyanide ions as the redox marker. The electrochemical removal of p-nonylphenol based on the formation of the electropolymerized film on an anode surface was performed using a carbon fiber (CF) with a very large surface area. The high removal efficiency for p-nonylphenol was obtained by applying a potential at 0.7 V. The maximum surface coverage of electropolymerized p-nonylphenol on the CF was about 5 x 10(-9) mol/cm2. The presence of humic acid hardly inhibited the removal of p-nonylphenol. Furthermore, the application to the removal of phenol, o-chlorophenol, p-chlorophenol, 2,4-dichlorophenol, and 2,4,5-trichlorophenol was attempted by using this method.

Stripping voltammetry of silver(I) with a carbon-paste electrode modified with thiacrown compounds

The accumulation behaviour and stripping voltammetry of silver(I) was investigated with a carbon-paste electrode modified with a thiacrown compound. Silver could be accumulated at the electrode in the absence of an applied potential by immersing the electrode in a solution of sodium perchlorate containing silver(I), then reduced at constant potential in 0.1M acetate buffer solution. Finally a well-defined stripping peak could be obtained by scanning the potential in a positive direction. The calibration curve for silver was linear over the range 0.5-2.5 muM with accumulation for 5 min. Studies of the effect of other metal ions showed that the silver was selectively accumulated at the electrode.

Effect of cetyltrimethylammonium chloride on electroosmotic and electrophoretic mobilities in capillary zone electrophoresis

Abstract The effect of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), on the electroosmotic mobility and the electrophoretic mobility of organic anions in capillary zone electrophoresis was investigated. The electroosmotic mobility showed four stepwise changes, including a reversal, with increasing CTAC concentration. The behaviour, especially the reversal of the electroosmotic mobility, was explained by assuming the formation of hemimicelles on the capillary wall. That is, CTAC first adsorbs individually by electrostatic interactions and then begins to associate into hemimicelles by Van der Waals attraction. The formation of hemimicelles changes the surface charge of the capillary wall from negative to positive and causes the reversal of the electroosmotic mobility. The effective electrophoretic mobilities of organic anions such as benzoic acid analogues were also influenced by the CTAC concentration. It was concluded that the behaviour was due to the interaction with hemimicelles on the capillary wall and also ion association with the monomer of CTAC and the interaction of micelles in bulk solution.