Electrochemical behavior of hydrogen peroxide sensor based on new methylene blue as mediator

A novel amperometric hydrogen peroxide sensor was proposed by co-immobilizing new methylene blue (NMB) and Horseradish peroxidase (HRP) on glassy carbon electrode through covalent binding. The electrochemical behavior of the sensor was studied extensively in 0.1 mol/L phosphate buffering solution (pH = 7.0). The experiments showed NMB could effectively transfer electrons between hydrogen peroxide and glassy carbon electrode. The electron transfer coefficient and apparent reaction rate constant were determined to be 0.861 and 1.27 s⁻¹. The kinetic characteristics and responses of sensor on H₂O₂ were investigated. The Michaelis constant is 8.27 mol/L and the linear dependence of current on H₂O₂ is in the range of 2.5–100 μmol/L. At the same time, the effects of solution pH, buffer capacity, and temperature on the sensor were examined. Translated from Chemistry, 2006, 23(8): 916–920 [译自: 化学通报]     

LaNi<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based sensor for sensitive determination of paracetamol

A novel electrochemical sensor based on LaNi_0.5Ti_0.5O₃/CoFe₂O₄ nanoparticle-modified electrode (LNT–CFO/GCE) for sensitive determination of paracetamol (PAR) was presented. Experimental conditions such as the concentration of LNT–CFO, pH value, and applied potential were investigated. Under the optimum conditions, the electrochemical performances of LNT–CFO/GCE have been researched on the oxidation of PAR. The electrochemical behaviors of PAR on LNT–CFO/GCE were investigated by cyclic voltammetry. The results showed that LNT–CFO/GCE exhibited excellent promotion to the oxidation of PAR. The over-potential of PAR decreased significantly on the modified electrode compared with that on bare GCE. Furthermore, the sensor exhibits good reproducibility, stability, and selectivity in PAR determination. Linear response was obtained in the range of 0.5 to 901 μM with a detection limit of 0.19 μM for PAR.     

Acerate ZnO whiskers and sodium alginate films: preparation and application in bioelectrochemistry of hemoglobin

A novel biocompatible acerate ZnO whiskers (AZW) has been prepared. We explored AZW and sodium alginate for the construction of electrochemical biosensors. The composition, morphology, and size were studied by scanning electron microscopy. UV–vis spectra revealed that hemoglobin (Hb) adsorbed in the acerate ZnO whiskers and sodium alginate retained its native structure. The amperometric response was measured as a function of H₂O₂ concentration at a fixed potential of −0.25 V in phosphate-buffered saline (pH 7.0). The electrochemical parameters of Hb in acerate ZnO whiskers and sodium alginate were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k _s) as 0.5 and 2.5 s⁻¹, respectively, indicating good facilitation of the electron transfer between Hb and the modified electrode, which may result from the unique nanostructures and larger surface area of acerate ZnO whiskers. The hydrogen peroxide biosensor showed a fast response of <5 s of linear range 2.1 μM–4.8 mM, with a detection of 0.7 μM (S/N = 3). The apparent Michaelis–Menten constant K_m^app K_m^{{app}} is 0.8 mM. The biosensor possesses high sensitivity, good reproducibility, and long-term stability.     

Synthesis and characterization of vanadium oxide/hexadecylamine membrane and its application as pH-EGFET sensor

Vanadium oxide/hexadecylamine (V₂O₅/HDA) sensing membrane was deposited on the glassy carbon substrate and used as the sensing layer of the extended gate H⁺-ion sensitive field effect transistor (EGFET) device. The structural and morphological features of V₂O₅/HDA were studied by X-ray diffraction, Fourier transformed-infrared spectroscopy and Scanning electronic microscopy images; and the electrochemical behavior was analyzed by cyclic voltammogram. V₂O₅/HDA presents a lamellar structure as well as several rod formations. The material stabilizes electrochemically after several cycles and leads to reproducibility of Li⁺ ion insertion/de-insertion into the vanadium oxide structure. The material was investigated as a pH sensor in the pH range 2–12 and presented a sensitivity of 38.1 mV/pH. The sensitive membrane structure is simple to fabricate and the measurement is fast for application as a disposable sensor.     

Sol–gel process of ZnO and ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> coated aluminum borate whiskers

Zinc nitrate and citric acid were used to prepare ZnO sol. ZnO and ZnAl₂O₄ coated aluminum borate whiskers were separately prepared by a sol–gel process. The results show that ZnO forms when ZnO xerogel is calcined at 500 °C and it does not undergo any phase transformation in the range of 500 and 1000 °C during calcinations. In ZnO xerogel coated aluminum borate whiskers system, a large amount of heat, gas and pores are produced during the heating process. When ZnO xerogel coated aluminum borate whiskers are calcined at 500 °C, ZnO can be uniformly coated on the surface of the whikers and the coated whiskers can be easily dispersed in distilled water through an ultrasonic vibration apparatus. During the calcination of ZnO coated whiskers at 1000 °C, ZnO reacts with the whiskers and ZnAl₂O₄ forms on the surface of aluminum borate whiskers.     

Thermoelectric power and electrochemical studies on CdI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

A quaternary super-ion-conducting system, 20CdI₂ − 80[xAg₂O − y(0.7V₂O₅ − 0.3B₂O₃)] where 1 ≤ x/y ≤ 3, has been prepared by melt quenching technique. The electrical conductivity measured was the order of 10⁻⁴  S/cm at room temperature. The values of silver-ion transport number obtained by electromotive force technique are nearly unity. The thermoelectric power and electrochemical studies were done on the CdI₂–Ag₂O–V₂O₅–B₂O₃ system. The discharge and polarization characteristics were examined for different cathodes to evaluate the utility of these cells as power sources for low energy applications.     

Synthesis of LiCoO<Subscript>2</Subscript> by <Emphasis Type="SmallCaps">l</Emphasis>-apple acid assisted sol–gel method and its electrochemical behavior in aqueous lithium-ion battery

The synthesis process of LiCoO₂ prepared by l-apple acid (l-HOOCCH(OH)CH₂COOH) assisted sol–gel method is studied by using Fourier transforms infrared spectroscopy, mass spectroscopy, simultaneous thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and elemental analysis. The results show that lithium and cobalt ions are trapped homogeneously on an atomic scale throughout the precursor. Lithium carbonate and Co₃O₄ are intermediate products during heat treatment of the precursor. Moreover, the kinetics for formation of LiCoO₂ by l-apple acid assisted sol–gel method is faster than the case of the conventional solid-state reaction between lithium carbonate and Co₃O₄. In comparison with the solid-state reaction, the sol–gel method significantly shortens the required reaction time for synthesizing LiCoO₂, and also reduces the particle size. In the electrochemical test, it is found that the specific discharge/charge capacities as well as the coulomb efficiency substantially increase with increasing the calcination temperature. It is considered that LiCoO₂ with a good-layered structure facilitates the insertion and de-insertion of lithium ions in aqueous electrolyte. As a result, the combination of the sol–gel method with proper calcination processes is highly successful in producing LiCoO₂ powders with large specific capacity and good cycle performance in aqueous lithium-ion battery.     

Electrochemical characterization of praseodymium centers in Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> zirconias using electrocatalysis and photoelectrocatalysis

The voltammetry of nanoparticles and scanning electrochemical microscopy are applied to characterize praseodymium centers in tetragonal and monoclinic zirconias, doped with praseodymium ions (Pr _x Zr_1−x O₂), prepared via sol–gel routes. Doped zirconia nanoparticles were synthesized by a sol–gel liquid-phase route and characterized by different techniques, including X-ray diffraction powder pattern, ultraviolet–visible diffuse reflectance spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM). Gels annealed at around 400 °C yielded tetragonal Pr _x Zr_1−x O₂ phases. The monoclinic forms of Pr-doped ZrO₂ were obtained by annealing at temperatures higher than 1,100 °C. TEM micrographs proved that the size of the nanoparticles produced was dependent on their crystalline form, around 15 and 60 nm for tetragonal and monoclinic, respectively. The electrochemical study confirmed that a relatively high content of praseodymium cation was in the chemical state (IV), i.e., as Pr⁴⁺, in both zirconia host lattices. The catalytic and photocatalytic effects of Pr⁴⁺ centers located in the monoclinic zirconia lattice on nitrite reduction and oxygen evolution reaction were studied.     

Catalytic conversions of chloroolefins over iron oxide nanoparticles 2. Isomerization of dichlorobutenes over iron oxide nanoparticles stabilized on the surface of ultradispersed poly(tetrafluoroethylene)

Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene) (UPTFE) granules were synthesized by the thermal destruction of iron formate in boiling bed of UPTFE on the surface of heated mineral oil. The particle size of nanoparticles (∼6 nm) containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to polymer ratio. The metal state is determined by the synthesis conditions. The nanoparticles synthesized at 280 °C consist mainly of the Fe₃O₄ and Fe₂O₃ phases. The samples obtained at 320 °C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested in dichlorobutene isomerization. Unlike isomerization on the iron oxide nanoparticles supported on silica gel, reaction over the UPTFE supports proceeds without an induction period. The sample with 10 wt.% Fe containing magnetically ordered γ-Fe₂O₃ nanoparticles possesses the highest catalytic activity. Fast electron exchange between the iron ions in different oxidation states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic activity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1383–1390, June, 2005.     

Influence of the composition of carriers based on ZrO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of cobalt-containing catalysts on the selective reduction of NO with methane

A series of cobalt-containing granulated and structured catalysts based on zirconium and aluminum oxides has been studied. The optimum composition of binary oxide samples (80% ZrO₂ − 20% Al₂O₃) for the selective reduction of nitrogen monoxide with methane (84% conversion of NO achieved at 320 °C) has been determined. The activity of the structured catalysts depends on both the composition of the secondary carrier (ZrO₂, Al₂O₃, and their mixture) and on the nature of the skeleton of the cellular structure (cordierite, kaolin-aerosil). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 237–241, July–August, 2007.     

Investigations on the selectivity of catalytic no reduction by ammonia

The activity and selectivity of V₂O₅/γ-Al₂O₃ catalyst were studied in the catalytic reduction of nitrogen oxide by ammonia. The activity of the catalyst monotonically increases as a function of temperature, however, its selectivity decreases. The DeNOx reaction of nitrogen oxides with ammonia can be described well by a mathematical model, which considers selectivity-decreasing side reactions as well in a wide temperature range (220–420°C).     

Structural and electrochemical behavior of Mn–V oxide synthesized by a novel precipitation method

Manganese–vanadium oxide had been synthesized by a novel simple precipitation technique. Scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis/differential scanning calorimetry, and X-ray photoelectron spectroscopy were used to characterize Mn–V binary oxide and δ-MnO₂. Electrochemical capacitive behavior of the synthesized Mn–V binary oxide and δ-MnO₂ was investigated by cyclic voltammetry, galvanostic charge–discharge curve, and electrochemical impedance spectroscope methods. The results showed that, by introducing V into δ-MnO₂, the specific surface area of the mixed oxide increased due to a formation of small grain size. The specific capacitance increased from 166 F g⁻¹ estimated for MnO₂ to 251 F g⁻¹ for Mn–V binary oxide, and the applied potential window extended to −0.2–1.0 V (vs. saturated calomel electrode). Through analysis, it is suggested that the capacitance performance of Mn–V binary oxide materials may be improved by changing the following three factors: (1) small grain and particle size and large activity surface area, (2) appropriate amount of lattice water, and (3) chemical state on the surface of MnO₂ material.     

New class of carbohydrate-based nonionic surfactants: diblock co-oligomers of tri-<Emphasis Type="Italic">O</Emphasis>-methylated and unmodified cello-oligosaccharides

Mixtures of diblock co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides have been found to be amphiphilic, as reported before. In order to clarify their accurate amphiphilic property, diblock co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides with monodispersity, methyl β-d-glucopyranosyl-(1→4)-2,3,6–tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6–tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranoside (1, pentamer), methyl β-d-glucopyranosyl-(1→4)- β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranoside (2, hexamer), and methyl β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)- 2,3,6-tri-O-methyl-d-glucopyranoside (3, trimer) were synthesized independently. These compounds had higher surface activities compared to the mixture of diblock co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides and commercially available methylcellulose (MC) SM-4. This paper describes the methods of synthesis of these compounds, and the influence of amphiphilic character on their surface activity. A new class of carbohydrate-based nonionic surfactant without long alkyl chain was discovered.     

Controllable solvo-hydrothermal electrodeposition of lithium vanadate uniform carnation-like nanostructure and their electrochemical performance

In this paper, we successfully developed a novel method to synthesize uniform carnation-like lithium vanadate nanostructures by combining electrochemical deposition and solvo-hydrothermal method. The samples were characterized by field emission scanning electron microscopy, power X-ray diffraction, and thermogravimetric analysis. The results show that the LiV₃O₈·H₂O carnation-like nanostructure is 2–3 μm in diameter and assembled from nanosheets with thickness of 10–20 nm. Based on a series of experiments, we proposed a possible growth mechanism, in which the supersaturation derived from electric field and high conductivity under solvo-hydrothermal conditions due to the successive growth of lithium vanadate. In our work, we have discussed three different solvo-hydrothermal systems. It is proved that the morphology of coating materials could be conveniently controlled by selecting alcohols with different chain of alkyl. Compared with short-chain alcohol, CH₃–(CH₂)₆–CH₂–OH was beneficial to promote the oriented growth of nanosheets. Electrochemical performances of lithium vanadate cathode materials were characterized by galvanostatic charge–discharge, and LiV₃O₈ synthesized in n-octanol aqueous solution exhibits the highest capacity of 357 mAh g⁻¹ and best cycle stability. Furthermore, the influence of solvo-hydrothermal conditions on the morphology and electrochemical performance of products has also been studied.     

Indirect electrochemical oxidation of N -methyl- n -aminophenol by active oxygen species generated in situ from O2, H2O, and H2O2

Indirect electrochemical oxidation of N-methyl-n-aminophenol by active oxygen species was studied. The active species were in situ generated from O₂, H₂O₂, and H₂O in aqueous solutions with various pH values by using a gas-diffusion cathode in a diaphragmless electrolyzer with anodes made of platinum, lea dioxide, and ruthenium-titanium oxide (RTO). Original Russian Text ? G.V. Kornienko, N.V. Chaenko, V.L. Kornienko, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 8, pp. 1285–1289.     

Influence of H<Subscript>2</Subscript>O and SO<Subscript>2</Subscript> on the activity of deposited cobalt oxide catalysts in the processes of reduction of nitrogen(I), (II) oxides with carbon monoxide and C<Subscript>3</Subscript>-C<Subscript>4</Subscript> alkanes

It is shown that palladium–cobalt oxide–cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt–iron catalysts in simultaneous reduction of NO + N₂O with C₃-C₄ alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-Co₃O₄/cordierite catalyst exceeds the Pt-Co₃O₄/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O₂ + H₂O + SO₂. Modification of the Pd-Co₃O₄/cordierite with cerium oxide considerably increases its sulfur resistance.     

Recovery and Reduction of Spent Alumina-Supported Cobalt–Molybdenum Oxide Catalyst via Plasma Sintering Technique

A thermal plasma process for the recovery and reduction of the spent alumina-supported cobalt–molybdenum oxide catalyst (Co₃O₄–MoO₂/Al₂O₃) was developed. The spent catalyst was sintered at >1,500 K under plasma condition and the cobalt–molybdenum oxide therein was reduced to cobalt–molybdenum, which was proven by XRD and EDX. By application of SEM and GC technique, the organic tar on the surface of the spent catalyst was found to decomposed and converted to syngas (CO, CO₂, and H₂), which might be the reducing agents in the process. A gasification mechanism for the generation of syngas and the reduction of cobalt–molybdenum oxide under plasma conditions was proposed.     

Selective and sensitive molecularly imprinted sol–gel film-based electrochemical sensor combining mercaptoacetic acid-modified PbS nanoparticles with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Au–multi-walled carbon nanotubes–chitosan

A sensitive molecularly imprinted electrochemical sensor was developed for selective detection of streptomycin by combination of mercaptoacetic acid-modified PbS nanoparticles with Au-coated Fe₃O₄ magnetic nanoparticles dispersed multi-walled carbon nanotubes doped chitosan film. The imprinted sensor was fabricated onto the Au electrode via stepwise modification of nanocomposites and an electrodeposited thin film of molecularly imprinted polymers via sol–gel technology. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, cyclic voltammetry, and differential pulse voltammetry, respectively. The prepared sensor showed very high recognition ability and selectivity for streptomycin. Under optimal conditions, the imprinted sensor displayed good electrocatalytic activity to the redox of streptomycin. And the differential voltammetric anodic peak current was linear to the logarithm of streptomycin concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻³ mol L⁻¹, and the detection limit obtained was 1.5 × 10⁻⁹ mol L⁻¹. This proposed imprinted sensor was used successfully for streptomycin determination in different injection solution samples.     

Application of mechanochemical activation for synthesis of uranium–lanthanoid mixed oxides

The applicability of mechanochemistry to produce uranium–lanthanoid mixed oxides is presented. Phase homogeneous uranium–cerium solid solutions of the type Ce _x U_1−x O₂ (x = 0.3 ÷ 0.95) and polyphase systems containing La _y U_1−y O_2+x (y = 0.12) were prepared by mechanochemical activation in air of sol–gel produced precursors. The possibility for synthesis of urania–lanthania solid solution by mechanochemical interaction of La₂O₃ with sol–gel produced U (IV,VI) oxide is established. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. The size of the crystallites (8–16 nm), lattice parameters, crystallite strains and densities of the oxides are calculated by BRASS program for Rietveld calculation.