Electrochemical characterization of adsorbed bilirubin oxidase on Vulcan XC 72R for the biocathode preparation in a glucose/O2 biofuel cell

A new biocathode was built and tested. It consisted of bilirubin oxidase adsorbed on Vulcan XC 72 R and immobilized into a Nafion^® matrix. The possibility of direct electron transfer between bilirubin oxidase and Vulcan XC 72 R was also demonstrated. The kinetics on biocathode were enhanced by including 2,2′-azinobis-3-ethylbenzothiazoline-5-sulfonic acid in the catalytic film. A first order reaction rate was observed for oxygen concentrations lower than 22%. A complete kinetic investigation of the system was shown. A biofuel cell test performed with this biocathode and Au₇₀Pt₃₀ nanoparticles as anode catalyst permitted to reach a power density of 170 μW cm⁻² at a cell voltage of 0.6 V, which is superior to what can be obtained with the concentric design.     

Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

Hydroxyl radical-related electrogenerated chemiluminescence reaction for a ruthenium tris(2,2′)bipyridyl/co-reactants system at boron-doped diamond electrodes

An electrogenerated chemiluminescence (ECL) reaction of the Ru(bpy)₃²⁺ (2,2′-bipyridyl, bpy)/co-reactant system in the extremely high-potential region (over 2.6 V versus Ag/AgCl) was probed using a boron-doped diamond (BDD) electrode. At the BDD electrode, three ECL waves (1.25, 2.30 and 3.72 V) were observed in cyclic voltammograms for 20 mM ascorbic acid (AA). For the ECL peaks observed at 1.25 V corresponding to the oxidation potential for Ru(bpy)₃²⁺ (1.15 V), the light intensities and current densities were found to depend on the square root of the AA concentration. This suggests that AA oxidation, followed by the formation of the reducing radical that is necessary for generating the excited state of Ru(bpy)₃^2+* occurred through homogeneous electron-transfer between Ru(bpy)₃³⁺ and the AA species. However, for the ECL peaks at 2.30 V, the current densities and light intensities linearly increased with increasing AA concentration, suggesting that the reducing radical was formed through the direct oxidation at the electrode surface. The ECL reaction at 3.72 V was observed only at the BDD electrode and not at other electrodes. The onset potentials for the light intensity were approximately 2.6 V, independently of the type of the co-reactants (e.g. 2-propanol and AA). The peak potentials exhibited linear relation with the co-reactant concentration. In the analysis of the ECL intensity for various co-reactants (alcohols) that show different reactivity for the hydrogen abstraction reaction, the order of the light intensities at the peaks for alcohols was found to be consistent with that for the rate constants of the hydrogen abstraction reaction. These results indicate that the co-reactant radical was formed through the hydrogen abstraction reaction with the hydroxyl radical (HO) generated during the oxygen evolution reaction.     

Influence of nature, concentration and pH of buffer acid-base system on rate determining step of the electrochemiluminescence of Ru(bpy)3 with tertiary aliphatic amines

The electrogenerated chemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′-bipyridyl) with tertiary aliphatic amines as co-reactants, was theoretically and experimentally studied as a function of the pre-equilibria involved in the ammonium proton lost and in relation to the nature of the rate determining step. Transient potential steps were used with a 3-mm glassy carbon disk electrode or carbon fiber ultramicroelectrodes array to investigate emission behavior in a variety of aqueous solution types, containing phosphate, tartrate and phthalate acid-base systems at differing pH values. The emission of Ru(bpy)₃²⁺ resulting from the reaction with n-tripropylamine (TPrA), tri-isobutylamine (TisoBuA), n-tributylamine (TBuA), methyl-di-n-propylamine (MeDPrA) and triethylamine (TEtA) in varying acid-base media was interpreted on the basis of the quoted pre-equilibria, ammonium pK_a being known. The nature of the rate determining steps changes depending on pH. Above pH ≈ 5 the amine neutral radical formation is the rate determining step and, is independent of pH with rate constant close to 10³ s⁻¹; below pH ≈ 5 the rate determining step becomes the deprotonation of the ammonium ion, operated by different bases present in solution. Different amines in the same acid-base system showed analogous ECL behavior, conditioned by the chosen acid base system. A single amine in different acid-base systems showed different kinetic behaviors, due to the dissociation constants of the chosen buffers. The concentration of the acid-base system also played an important role and influenced emission intensity and shape. ECL emission were simulated by finite difference methods, implementing a previously proposed mechanism by including the relevant pre-equilibria. Simulation may also give estimates of the pK_a values of the ammonium ions. An ion pair formation between R₃N⁺ and the mostly charged species present in solution is hypothesized to explain the contradictory experimental results concerning the reaction mechanism of the proton lost of the radical cation.     

Nafion掺杂多壁碳纳米管固定Ru（bpy）32+的电致化学发光法检测壮观霉素的研究

利用Nafion掺杂多壁碳纳米管形成复合膜将Ru(bpy)32+固定于玻碳电极表面形成Ru(bpy)32+-N-C。基于壮观霉素对该电极电致化学发光信号的增强作用,建立了一种新的壮观霉素电致化学发光检测方法,方法的线性范围为1.0×10-5～2.0×10-4 mol.L-1,检测限为2.5×10-6 mol.L-1。该方法用于尿样中壮观霉素的测定,加标回收率在87.1%～120.2%之间。     

An enzyme-based microfluidic biofuel cell using vitamin K3-mediated glucose oxidation

Viamin K₃-modified poly-l-lysine (PLL-VK₃) was synthesized and used as the electron transfer mediator during catalytic oxidation of NADH by diaphorase (Dp) at the anode of biofuel cell. PLL-VK₃ and Dp were co-immobilized on an electrode and then coated with NAD⁺-dependent glucose dehydrogenase (GDH). The resulting enzymatic bilayer (abbreviated PLL-VK₃/Dp/GDH) catalyzed glucose oxidation. Addition of carbon black (Ketjenblack, KB) into the bilayer enlarged the effective surface area of the electrode and consequentially increased the catalytic activity. An oxidation current of ca. 2 mA cm⁻² was observed when the electrochemical cell contained a stirred 30 mM glucose, 1.0 mM NAD⁺, pH 7.0 phosphate-buffered electrolyte solution. The performance of glucose/O₂ biofuel cells, constructed as fluidic chips with controllable fuel flow and containing a KB/PLL-VK₃/Dp/GDH-coated anode and an Ag/AgCl or a polydimethylsiloxane-coated Pt cathode, were evaluated. The open circuit voltage of the cell with the PDMS-coated Pt cathode was 0.55 V and its maximum power density was 32 μW cm⁻² at 0.29 V when a pH 7.0-buffered fuel containing 5.0 mM glucose and 1.0 mM NAD⁺ was introduced into the cell at a flow rate of 1.0 mL min⁻¹. The cell's output increased as the flow rate increased. During 18 h of continuous operation of the cell with a load of 100 kΩ, the output current density declined by ca. 50%, probably due to swelling of the enzyme bilayer.     

Layer-by-layer assembly of functional silica and Au nanoparticles for fabricating electrogenerated chemiluminescence sensor

We described the use of silica nanoparticles as building blocks for the immobilization of electrogenerated chemiluminescence (ECL) reagent Ru(bpy)₃²⁺ and the fabrication of layer-by-layer assembly film by alternating the deposition of the Ru(bpy)₃²⁺-doped silica nanoparticles and Au nanoparticles. UV-vis absorption spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry and ECL were used to characterize the uniform growth of the multilayer film. Since Ru(bpy)₃²⁺ could still maintain its ECL property when doped into the silica nanoparticles, the as-prepared multilayer film could be used as an effective ECL sensor, and the sensor showed high sensitivity and good stability.     

Facile functionalization by π-stacking of macroscopic substrates made of vertically aligned carbon nanotubes: Tracing reactive groups by electrochemiluminescence

We report a simple, fast and reliable non-covalent route of functionalization of macroscopic carbon nanotubes (CNTs) surfaces based on the π-stacking of CNTs sidewall with fluorescein derivatives (i.e., amino- and isothiocyanate-). The electrochemiluminescent emission of Ru(bpy)₃²⁺ labels bearing –COOH and –NH₂ side groups coupled with colorimetric and XPS measurements allowed to estimate the quantity of –NH₂ and –NCS functions obtained. The evaluation of reactivity suggests that functionalized CNTs substrates, in particular those carrying –NCS groups, are suitable to covalently bind probe molecules such as proteins and oligonucleotides, thus opening up the possibility of future application in genomics and proteomics fields.     

联吡啶钌体系电致化学发光测定精胺的研究

基于精胺对Ru（bpy）32＋电化学发光的显著增强效应,利用池内停流技术,建立了精胺的电化学发光测定法。本方法具有灵敏度高,线性范围宽和分析速度快的特点。在最优条件下,相对电化学发光值与精胺浓度在5×10-8~5×10-5mol/L范围内呈现良好的线性关系,对5×10-8mol/L浓度的精胺进行11次平行测定,其相对标准偏差为3.03%,检出限为2.31×10-8mol/L。     

Luminescent properties of a novel afterglow phosphor Sr3Al2O5Cl2:Eu,Ce

A series of Eu²⁺ and Ce³⁺ doped/co-doped Sr₃Al₂O₅Cl₂ afterglow phosphors that presented various bright colors were successfully synthesized via high temperature solid state reaction. The structure and luminescence properties of the obtained samples were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) spectra and decay curves as well as the thermoluminescence (TL) glow curves. The XRD results showed that all the phase could be indexed to the orthorhombic structure with the space group P2₁2₁2₁. After being exposed to a 254 nm or 365 nm mercury lamp, blue/yellow-orange afterglow emissions with broad bands peaking around 620 nm/435 nm, which were ascribed to the characteristic 4f⁶5d–4f⁷/5d¹–4f¹ transitions of Eu²⁺/Ce³⁺, could be observed in phosphors of Sr₃Al₂O₅Cl₂:Eu²⁺/Sr₃Al₂O₅Cl₂:Ce³⁺, respectively. Because of the overlap spectral range between the Sr₃Al₂O₅Cl₂:Eu²⁺ and Sr₃Al₂O₅Cl₂:Ce³⁺ phosphors, the energy transfer (ET) from Ce³⁺ to Eu²⁺ occurred. The related ET process was discussed in detail. Moreover, the incorporation of Ce³⁺ could significantly prolong the afterglow duration of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor, which was due to the increase of trap concentration. Consequently, 6 h of the afterglow duration could be observed in Sr₃Al₂O₅Cl₂:1.0%Eu²⁺, 0.5%Ce³⁺ sample, exhibiting much longer than that of Sr₃Al₂O₅Cl₂: 1.0%Eu²⁺ (3 h). From the afterglow decay curves and the fitting results, the optimal concentration of Ce³⁺ for the enhanced afterglow property was experimentally determined to be 0.5%.     

Estimation of the effectiveness factor of an outer-sphere redox couple (Fe3+/Fe2+) using rotating disk Ti/IrO2 electrodes of different loading

The effectiveness factor; E _f , defined as the fraction of the surface that participates effectively in a given reaction, is an important parameter when operating three-dimensional (3D) electrodes. The rotating disk electrode (RDE) technique with the Fe³⁺/Fe²⁺ redox couple as a probe reaction has been used for the evaluation of the effectiveness factor of 3D Ti/IrO₂ electrodes with different IrO₂ loading. For this purpose, steady-state polarization measurements using Ti/IrO₂ rotating disk electrodes in 0.5 M Fe³⁺/Fe²⁺ in 1 M HCl were carried out under well-defined hydrodynamic conditions. The low-field approximation relation has been used for the estimation of the exchange current densities j ₀, of the Fe³⁺/Fe²⁺ redox couple. It was found for this redox couple that the effectiveness factor is very low (<2%) and essentially the 2D electrode surface area works effectively in the steady-state polarization measurements.     

Evaluation of electrolytes for redox flow battery applications

A number of redox systems have been investigated in this work with the aim of identifying electrolytes suitable for testing redox flow battery cell designs. The criteria for the selection of suitable systems were fast electrochemical kinetics and minimal cross-contamination of active electrolytes. Possible electrolyte systems were initially selected based on cyclic voltammetry data. Selected systems were then compared by charge/discharge experiments using a simple H-type cell. The all-vanadium electrolyte system has been developed as a commercial system and was used as the starting point in this study. The performance of the all-vanadium system was significantly better than an all-chromium system which has recently been reported. Some metal-organic and organic redox systems have been reported as possible systems for redox flow batteries, with cyclic voltammetry data suggesting that they could offer near reversible kinetics. However, Ru(acac)₃ in acetonitrile could only be charged efficiently to 9.5% of theoretical charge, after which irreversible side reactions occurred and [Fe(bpy)₃](ClO₄)₂ in acetonitrile was found to exhibit poor charge/discharge performance.     

Influence of precursor Bi/Fe ion concentration on hydrothermal synthesis of BiFeO3 crystallites

In this study we investigated the effect of precursor Bi³⁺/Fe³⁺ ion concentration on the hydrothermal synthesis of BiFeO₃ crystallites. It is demonstrated that the phase-purity and morphology of the products is highly dependent on the metal ion concentration. Phase-pure BiFeO₃ crystals can be prepared at the Bi³⁺/Fe³⁺ ion concentration ranging from 0.025 to 0.0625 M. The samples prepared at n(Bi³⁺/Fe³⁺)=0.025, 0.0375, 0.05, and 0.0625 M, are composed, respectively, of cuboid-like particles (100–200 nm), regular spherical agglomerates (30–40 μm) made up of irregular grains with size about several hundred nanometers, irregular flower-like clusters formed from irregular grains of several hundred nanometers in size, and octahedron-shaped particles (500–600 nm). These samples have a similar bandgap energy of 2.20 eV and exhibit a typical antiferromagnetic behavior at room temperature.     

测试——聚乙烯亚胺改性磁性膨润土对Pb2+和Cu2+的吸附性能(测试稿件)

在磁性膨润土(MBent)表面接枝聚乙烯亚胺(PEI)制备了聚乙烯亚胺改性磁性膨润土(PEI/KH560/MBent),采用FTIR、VSM、XRD、TGA、EA、SEM和EDS对其进行了表征,考察了其对水溶液中Pb_²⁺和Cu_²⁺的吸附性能。结果表明,聚乙烯亚胺已成功接枝于磁性膨润土表面,并有效提高其对Pb_²⁺和Cu_²⁺吸附量；溶液初始pH对吸附量影响较大,随着pH的增大,吸附量增加。在pH=5,溶液初始质量浓度为300 mg/L,PEI/KH560/MBent对Pb_²⁺和Cu_²⁺吸附量分别为96.21和61.08 mg/g；吸附过程符合准二级动力学模型,吸附行为符合Langmuir吸附等温模型。热力学研究表明,吸附为自发吸热过程。经过5次循环利用后,其吸附容量仍保持初始的60%以上,表明PEI/KH560/MBent具有一定的重复利用性。     

Homogenous photocatalytic decomposition of acetic acid using UV-Fe/Fe system in the absence of oxygen

Photocatalysis is a promising way to eliminate organic pollution. Here a novel homogenous non-oxygen photocatalytic system was studied. Acetic acid was used as a model substrate to be decomposed into hydrogen, methane, ethane and carbon dioxide continuously by photo-excited Fe²⁺ and Fe³⁺ ions. Fluorescence spectra and ultraviolet visible spectra showed that Fe²⁺ and Fe³⁺ were excited by ultraviolet light. The rate of acetic acid decomposition increased along with the increase of temperature, Fe²⁺ and acetic acid concentration. The photocatalytic mechanism and kinetics were proposed and the effects of pH value, reaction temperature, concentration of FeSO₄ and CH₃COOH were investigated.     

Enhanced photoluminescence property of Dy co-doped BaAl2O4:Eu green phosphors

Eu²⁺-doped BaAl₂O₄ green phosphors were prepared by a conventional solid-state reaction and the effects of Dy³⁺ co-doping on the photoluminescence property were investigated. The phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD showed that all prepared samples exhibited a hexagonal BaAl₂O₄ phase. Fluorescence spectroscopy showed that the photoluminescence efficiency increased with increasing Eu²⁺ concentration until 3 mol% then decreased at higher concentrations due to concentration quenching effect. Moreover, Dy³⁺ co-doping increased the photoluminescence efficiency of the Eu²⁺-doped BaAl₂O₄ phosphor.     

Ozonation of Reactive Orange 122 Using La3+-Doped WO3/TiO2/Sep Photocatalyst

La³⁺/WO₃/TiO₂/sep composites have been prepared by the sol–gel method. The degradation of dye was studied under the influence of various operational parameters such as initial pH, amounts of catalyst, concentrations of the dye, and ozone flow rate. The mineralization of Reactive Orange 122 has been confirmed by chemical oxygen demand measurements. The color removal of dye was found to follow a pseudo–first-order kinetics. Maximum color and chemical oxygen demand removal were 99.9% and 90% respectively, at a dye concentration of 200 mg/L, ozone flow rate of 2.0 L/min., 0.05 g/L weight of catalyst, and pH of 6.9 in 4 h. In addition, the catalyst was characterized by X-ray diffraction spectra, Fourier-Transform Infrared Spectroscopy, scanning electron microscopy, and a transmission electron microscope. This work could be a good candidate as a practical application for photocatalytic dye degradation.     

Synthesis and photoluminescence properties of MgAl(PO4)O:Eu red phosphor for white LEDs

Eu³⁺-activated MgAl(PO₄)O:phosphor has been synthesized by a high temperature solid state reaction and efficient red emission under near-ultraviolet excitation is observed. The emission spectrum shows a dominant peak at 594 nm due to the ⁵D₀→⁷F₁ transition of Eu³⁺. The excitation spectrum is coupled well with the emission of UV LED (350–410 nm). The effect of Eu³⁺ concentration on the luminescent properties of MgAl(PO₄)O:Eu³⁺ and the mechanism of concentration quenching of Eu³⁺ are studied. The results show that MgAl(PO₄)O:Eu³⁺ is a promising red-emitting phosphor for white LEDs.     

Voltammetric study of interaction of Co(phen)3 with DNA at gold nanoparticle self-assembly electrode

Modifying electrode surfaces on the molecule scale allow developing new electrochemical biosensors. A new strategy for the immobilization of calf thymus DNA on the surface of gold nanoparticles which are co-immobilized at a gold electrode through 4,4^′-bis(methanethiol) biphenyl (MTP) molecule by assembly process is demonstrated. The DNA modified electrode was incubated in Co(phen)₃³⁺ solution of an aqueous buffer or an acetonitrile (AN) solution, then it was rinsed and placed in a Co(phen)₃³⁺ free buffer solution or AN solution, followed by cyclic voltammetric experiments. Clear redox peaks of Co(phen)₃³⁺ were observed both in an aqueous and AN solutions. The concentration of supporting electrolyte on electrochemical behavior was discussed. It was found that the surface coverage value of DNA molecules on modified gold nanoparticle and the redox current of adsorbed Co(phen)₃³⁺ were decrease with increasing the size of gold nanoparticles (6, 25, 42, 73, and 93 nm). In aqueous solution, the electron transfer rate constant of Co(phen)₃^3+/2+ redox couple became slow with increasing the diameter of gold nanoparticle, and the speed almost had nothing to do with the diameter in nonaqueous solution. The surface concentration of Co(phen)₃³⁺ adsorption on DNA modified electrode decreased and rate constant of adsorption kinetics increased with increasing the interactive temperature. In AN solution, the electrostatic interaction between DNA and Co(phen)₃^3+/2+ was greatly reduced, however, compare with in aqueous solution the interaction between DNA and reduced form of Co(phen)₃²⁺ was more strongly than oxidized form Co(phen)₃³⁺. The surface concentration of Co(phen)₃³⁺ adsorption on DNA modified electrode reach maximum value when the interactive temperature about 20 °C, and rate constant of adsorption kinetics nearly independent of the interactive temperature. The results show that the DNA can adsorb on the modified electrode firmly and the Co(phen)₃^3+/2+ adsorbed on DNA give good electrochemical response both in aqueous and nonaqueous solutions. It was confirmed that the DNA modified electrode can be applied in a nonaqueous system and the modified electrode can be used to investigate the interaction between DNA and electroactive species both in aqueous and nonaqueous systems.     

Development and operation of a 150 W air-feed direct methanol fuel cell stack

A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117^® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm² geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm^–2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm²) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm^–2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.