Biosorption of uranium by chemically modified Rhodotorula glutinis

The present paper reports the biosorption of uranium onto chemically modified yeast cells, Rhodotorula glutinis, in order to study the role played by various functional groups in the cell wall. Esterification of the carboxyl groups and methylation of the amino groups present in the cells were carried out by methanol and formaldehyde treatment, respectively. The uranium sorption capacity increased 31% for the methanol-treated biomass and 11% for the formaldehyde-treated biomass at an initial uranium concentration of 140 mg/L The enhancement of uranium sorption capacity was investigated by Fourier transform infrared (FTIR) spectroscopy analysis, with amino and carboxyl groups were determined to be the important functional groups involved in uranium binding. The biosorption isotherms of uranium onto the raw and chemically modified biomass were also investigated with varying uranium concentrations. Langmuir and Freundlich models were well able to explain the sorption equilibrium data with satisfactory correlation coefficients higher than 0.9. (C) 2010 Elsevier Ltd. All rights reserved.

Activated carbons chemically modified by concentrated H2SO4 for the adsorption of the pollutants from wastewater and the dibenzothiophene from fuel oils

The surface properties, porosities, and adsorption capacities of activated carbons (AC) are modified by the oxidation treatment using concentrated H2SO4 at temperatures 150-270 degreesC. The modified AC was characterized by N-2 adsorption, base titration, FTIR, and the adsorption of iodine, chlorophenol, methylene blue, and dibenzothiophene. The treatment of AC with concentrated H2SO4 at 250 degreesC greatly increases the mesoporous volume from 0.243 mL/g to 0.452 mL/g, specific surface areas from 393 m(2)/g to 745 m(2)/g, and acidic surface oxygen complexes from 0.071 meq/g to 1.986 meq/g as compared with the unmodified AC. The base titration results indicate that the amount of acidic surface oxygen groups on the modified AC increases with increasing the treatment temperatures and carboxyls and phenols are the most abundant carbon-oxygen functional groups. The carboxyl groups, COO- species, and hydroxyl groups are detected mainly for the sample treated at 250 degreesC. The mesoporous properties of the AC modified by concentrated H2SO4 were further tested by the adsorption of methylene blue and dibenzothiophene. The AC modified by concentrated H2SO4 at 250 degreesC has much higher adsorption capacities for large molecules (e.g., methylene blue and dibenzothiophene) than the unmodified AC but less adsorption capacities for small molecules (e.g., iodine). The adsorption results from aqueous solutions have been interpreted using Freundlich adsorption models.

Study on the lifetime of M-intermediate of bacteriorhodopsin film chemically modified with CeO2 nanoparticles

The characteristics of intermediates of bacteriorhodopsin (bR) can be verified by chemical modification of its surroundings. CeO2 nanoparticles, which were obtained using water-in-oil (W/O) microemulsion and calcined at various temperatures, were used as chemical additive for the modification of bR. X-ray diffraction (XRD) shows that the mean particle sizes for the samples calcined at 500 and 800 degrees C are approximately 10 and 30 nm, respectively. We prepared CeO2 nanoparticle modified poly(vinyl alcohol) (bR-PVA) films with an optical density of about 1.5 at the ground state. It is observed that the lifetime of the Wintermediate for the modified films is prolonged compared with that of the unmodified ones, and the lifetime increases with decreasing particle size. A probable mechanism, which is likely to involve effective molecular interactions between the CeO2 nanoparticles and the bR molecules, is discussed. The hydroxyl groups, which might arise from the interaction between the nanoparticles and the surrounding water molecules, help to lower the ability of the Schiff base of uptaking protons in the Wintermediate. The results indicate that controlling the interactions between biomolecules and various nanomaterials would enlarge the functionality and the range of the application of nanoparticles.

Direct electrochemistry and surface plasmon resonance characterization of alternate layer-by-layer self-assembled DNA-myoglobin thin films on chemically modified gold surfaces

Alternate layer-by-layer (L-by-L) polyion adsorption onto gold electrodes coated with chemisorbed cysteamine gave stable, electroactive multilayer films containing calf thymus double stranded DNA (CT ds-DNA) and myoglobin (Mb). Direct, quasi-reversible electron exchange between gold electrodes and proteins involved the Mb heme Fe2+/Fe3+ redox couple. The formation of L-by-L (DNA/Mb), films was characterized by both in situ surface plasmon resonance (SPR) monitoring and cyclic voltammetry (CV). The effective thickness of DNA and Mb monolayers in the (DNA/Mb)l bilayer were 1.0 +/- 0.1 and 2.5 +/- 0.1 mn, corresponding to the surface coverage of similar to65% and similar to89% of its full packed monolayer, respectively. A linear increase of film thickness with increasing number of layers was confirmed by SPR characterizations. At pH 5.5, the electroactive Mb in films are those closest to the electrode surface; additional protein layers did not communicate with the electrode. CV studies showed that electrical communication might occur through hopping conduction via the electrode/base pair/Mb channel, thanks to the DNA-Mb interaction. After the uptake of Zn2+, a special electrochemical behavior, where MbFe(2+) acts as a DNA-binding reduction catalyst in the Zn2+-DNA/Mb assembly, takes place.

Multilayer assembly of Bis-Keggin-type heteropoly compound on chemically modified glassy carbon electrode and its electrocatalysis

Through layer-by-layer assembly, the bis-Keggin-type heteropolyanion K10H3 [Nd(SiMo7W4O39)(2)] XH2O was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of the heteropolyanion was investigated. Cyclic voltammetry proved the uniform growth of the film. However, the characteristic redox peaks of the heteropolyanion in the film were deformed with increasing of the number of the multilayer film. The effect of pH on the redox behaviors of [Nd(SiMo7W4)(2)](13-) in the film was discussed. The multilayer film electrodes have excellent electrocatalytic activities to the reduction of BrO3-, HNO2 and H2O2.

Multilayer assembly of Mn-substituted Keggin-type [ZnW11O39Mn(H2O)](8-) on chemically modified glassy carbon electrode and its electrocatalytic properties

Through layer-by-layer assembly, undecatungstozincates monosubstituted by transition metals Mn, ZnW11 Mn (H2O) O-39(8-) was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of these polyoxometalates was investigated. Cyclic voltammetry proves the uniform growth of the film. They exhibit some special electrochemical properties in the films, different from those in homogeneous aqueous solution. The effect of pH on the redox behavior of ZnW11Mn(H2O)O-39(8-) in the film was discussed in detail. The multilayer film electrodes have an excellent electrocatalytic response to the reduction of H2O2 and BrO3-, and to the oxidation of ascorbic acid.

In-situ Fourier transform infrared spectroelectrochemistry as a probe of the glassy carbon electrode chemically modified by nickel (II)-cyanometallates

A new nickel (II)-cyanometallates modified on glassy carbon electrode was prepared by a new method and studied by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroelectrochemistry. It was found that the NiHCF film existed in two forms: Ni2Fe(II)-(CN)(6) and M2NiFe(II)(CN)(6), Fe(CN)(3)(6-) codeposited in the NiHCF film existing in free cation or bridged-bond state depended on the property of the cations in electrolyte: in NaCl and LiCl solution, it is in bridges-bonded, but in HCl and KCl, it is free.

SENSITIVE AMPEROMETRIC DETECTION OF GLUCOSE BY REVERSED PHASE LIQUID-CHROMATOGRAPHY AT A PRUSSIAN BLUE CHEMICALLY MODIFIED ELECTRODE OF NOVEL CONSTRUCTION

A new liquid chromatography electrochemical (LCEC) scheme for glucose sensing has been developed on the basis of a Prussian Blue chemically modified electrode (CME) of novel construction and characterized in terms of various experimental parameters by the flow injection analysis (FIA) technique. Unique hydrodynamic voltammograms were obtained for the first time at the CME in the flow-through amperometric detection of glucose, and subsequently both anodic and cathodic peaks could be expected on monitoring the operating potential in the modest positive or negative region. The unique pH dependence on the CME response towards glucose makes it perfectly compatible with conventional reversed phase liquid chromatography systems. On the basis of these features, practical application in glucose LCEC detection has been effectively performed; a linear response range over three orders of magnitude and a detection limit of subpicomole level were readily obtained. The capability of the established LCEC mode in the direct sensing of urinary glucose has been demonstrated.

A STUDY ABOUT PH CHEMICALLY MODIFIED ELECTRODES BASED ON AMINO-DERIVATIVES OF NAPHTHALENE

The electrochemical polymerization of amino-derivatives of naphthalene has been studied on the platinum wire electrodes. The effects of acidity of the modifying media and the potential scan rate on the cyclic voltammograms are verified. As potentiometric pH sensors, the electrodes prepared from 1-naphthylamine and 2,3-diaminonaphthalene showed performance characteristics superior to some other electrodes tested. The electrode modified with 1-naphthylamine in the optimum medium showed a nearly Nernstian response of 4.20-13.70 pH and a slope of -54.8 mV/pH, while the linear range of the electrode prepared by 2,3-diaminonaphthalene was 4.00-13.60 pH, with a slope of -52.4 mV/pH.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CATECHOL, RESORCINOL, AND HYDROQUINONE WITH A COPPER-BASED CHEMICALLY MODIFIED ELECTRODE

A copper-based chemically modified electrode (CME) has been constructed and characterized for flow-through amperometric detection of catechol, resorcinol, and hydroquinone. Novel potential dependence of the detector response was first obtained for these analytes at the Cu CME, where negative peaks together with positive ones were observed in one definite chromatogram using amperometric detection. Its advantages in chromatographic applications were demonstrated. From these observations it is proposed that the detector response was governed by formation of copper complexes with the solutes. A dynamic linear range over two orders of magnitude was obtained, when operating the detector at +0.10 V vs. SCE, from which ng detection limits were achieved.

CATALYTIC REDUCTION OF HEMOGLOBIN AT THIONINE CHEMICALLY MODIFIED ELECTRODE AND FIA APPLICATIONS

Thionine-containing chemically modified electrode (cme) was constructed with glassy carbon substrate by potential sweep oxidation, electrodeposition and adsorption procedures, and electrocatalytic reduction of hemoglobin was carried out and characterized at the cme under batch and flow conditions. Comparison of the catalytic response toward hemoglobir obtained at the cme was made mainly in terms of the potential dependence, the detectability and long-term stability. When used in flow injection analysis (FIA) experiments with the detector monitored at a constant potential applied at -0.35 V vs sce, detection limit of 0.15-1.5 pmol level of hemoglobin injected was achieved at the cme, with linear response range over 2 orders of magnitude. All the cme s retained more than 70% of their initial hemoglobin response level over 8 h of continuous service in the flow-through system.

AMPEROMETRIC DETECTION OF CATECHOLAMINES WITH LIQUID-CHROMATOGRAPHY AT A NOVELLY CONSTRUCTED PRUSSIAN BLUE CHEMICALLY MODIFIED ELECTRODE

A novel Prussian blue chemically modified electrode (CME) was constructed and characterized for liquid chromatography electrochemical detection (LCEC) of catecholamines. Both anodic and cathodic peaks could be obtained by monitoring at constant applied potential at anodic and slightly cathodic potential ranges (0.3-0.7 and -0.2-0.1 V vs. SCE), respectively. When arranged in a series configuration, using the modified electrodes as generating and collecting detectors, extremely high effective collection efficiencies of 0.91 (for norepinephrine) and 0.58 (for dihydroxyphenylacetic acid) were achieved in dual-electrode LCEC for catecholamines; and a linear response range over 3 orders of magnitude and a detection limit of 10 pg were obtained with a downstream CME as the indicating detector.

POLYANILINE CHEMICALLY MODIFIED ELECTRODE FOR DETECTION OF ANIONS IN FLOW-INJECTION ANALYSIS AND ION CHROMATOGRAPHY

An electrochemical detector based on a polyaniline conducting polymer chemically modified electrode (PAn CME) was developed for use in flow-injection analysis and ion chromatography. Iodide, bromide, thiocyanate and thiosulphate are detected by using ion chromatography with a PAn CME electrochemical detector. The detection limits are 1, 5, 10 and 10 mgl-1, respectively. The CME response for electroinactive anions varies selectively with the mobile phase composition in flow-injection analysis. By this approach, perchlorate, sulphate, nitrate, iodide, acetate and oxalate can be detected conveniently and reproducibly over a linear concentration range of at least 3 orders of magnitude. The electrode is stable for over 2 weeks with no evidence of chemical or mechanical deterioration.