Functionalized inorganic-organic composite material derivated by sol-gel for construction of mediated amperometric hydrogen peroxide biosensor

A novel functionalized inorganic-organic hybrid material with cation exchange property was prepared by sol-gel method. The H2O2 biosensor was fabricated by simply dipping the horseradish peroxidase-containing functionalized membrane modified electrode into Meldola's blue (MDB) solution. MDB was adsorbed and firmly immobilized within the membrane. The electrochemical behavior of MDB incorporated in the membrane was more reversible compared with that of the solution species and suitable as mediator for the horseradish peroxidase. The response time was less than 25 s. Linear range is up to 0.6 mM (COH. coeff. 0.9998) with detection Limit of 9 x 10(-7) M. High sensitivity of 75 nA mu M cm(-2) was obtained due to high MDB-loading. The biosensor exhibited a good stability. (C) 1999 Elsevier Science B.V. All rights reserved.

Electrochemistry of heteropolyanions in coulombically linked self-assembled monolayers

A composite film containing heteropolyanion was fabricated on gold by attaching the Keggin-type heteropolyanion, PMo12O403- on a 4-aminothiophenol SAM via Au-S bonding. Reflection FTIR, cyclic voltammetry and XPS were used for the characterization of the composite film. Reflection FTIR studies indicate that there is some Coulombic interaction between PMo12O403- and the surface amino group in the composite film, which greatly improves the film stability and prevents effectively the destructive intermolecular aggregation. The composite him shows three reversible redox couples within the pH range pH less than or equal to 7.0, attributed to three two-electron and two-proton electrochemical reduction-oxidation processes of PMo12O403-. Compared with PMo12O403- in the solution, the PMo12O403- of the composite film electrode can exist in a larger pH range, and shows smaller peak-to-peak separation, and more reversible reaction kinetics. Moreover, the composite him obtained shows a good catalytic activity for the reduction of BrO3-. (C) 1998 Elsevier Science S.A. All rights reserved.

Reactivity of Pt/Al2O3 and Pt/CeO2/Al2O3 catalysts for partial oxidation of methane to syngas

The ceria modified Pt/CeO2/Al2O3 and Pt/Al2O3 catalysts were studied in the partial oxidation of methane to syngas. The SEM, XRD, TPR and TPD techniques were used for the catalyst characterization. The addition of ceria could enhance the Pt dispersion and decrease the Pt crystallise size; the activity and selectivity of catalyst for partial oxidation were improved significantly, and the methane total oxidation was suppressed sharply. The ceria effect was also discussed in a detailed way.

Partial oxidation of methane to syngas over Pt-Ni/Al2O3 Catalyst

The catalytic partial oxidation of methane to syngas over Ni/Al2O3, Pt/Al2O3 and a series of Pt - Ni/Al2O3 catalysts was investigated. It was found that Pt - Ni/Al2O3 catalysts exhibit higher activity and stability than Ni/Al2O3 and Pt/Al2O3. TPR and TPD methods were used to characterize Pt - Ni bimetallic interactions in the catalysts. A series of Pt - Ni/Al2O3 catalysts and unsupported Pt - Ni samples were studied by XRD and XPS. It was found the formation of Pt - Ni alloy in the Pt - Ni/Al2O3 catalysts and the enrichment of platinum on the surface of the catalysts. It is concluded that the higher activity and stability of Pt - Ni/Al2O3 catalysts were caused by Pt - Ni bimetallic interactions.

Partial oxidation of methane to syngas over Pt/A(2)O(3) and Pt/CeO2/Al2O3

The catalytic oxidation of methane to syngas has been carried out over Pt/Al2O3 and Pt/CeO2/Al2O3. It was found that the catalysts with ceria exhibit a higher activity and selectivity than those without ceria. The catalysts were characterized by means of TPR, TPD, SEM-EDX and XRD. There is a strong interaction between ceria and platinum under the reaction condition, which increase the dispersion of platinum over catalysts, preventing the sinter of the Pt particles. As a result of the synergistic;effect between Pt and ceria, the activity of Pt/Al2O3 for combustion reaction was suppressed, the activity and selectivity :For partial oxidation were improved greatly. Another role of ceria in the catalyst is the enhancing of the WGSR, which leads to the increase of the selectivity of catalyst for hydrogen and accelerating the equilibrium of the reaction.

Electrocatalytic oxidation of methanol at the titanium oxide electrode modified with Pt microparticles

The electrocatalytic oxidation of methanol at the Titanium oxide (TiOx, x<2) film modified with Pt microparticles has been studied. The results show that the modified electrodes exhibit a significant electrocatalytic activity and good stability for the oxidation of methanol. Under the optimal conditions, the peak current density at 0.58 V for the oxidation of methanol in the positive-going sweep is about 526 mA/cm(2) at the scan rate of 5 mV/s in 0.5 mol/L CH3OH and 0.5 mol/L H2SO4 solution and the over potential of the methanol oxidation at the modified electrode increases about 30 similar to 40 mV after 70 minutes at the current density of 100 mA/cm(2) and 50 mA/cm(2). The enhanced electrocatalytic activity and good stability are ascribed to the high dispersion of Pt microparticles in and on the TiOx film and the synergistic effect between Pt microparticles and TiOx.

In situ microscopic FTIR spectroelectrochemistry study of oxidation of L-ascorbic acid in polymer electrolyte (PEG/LiClO4)

In situ microscopic FTIR spectroelectrochemistry behavior of L-ascorbic acid (H(2)A) in polymer electrolyte is reported for the first time. H(2)A undergoes a two-step oxidation, The oxidation waves shift towards more anodic potential values when the scan rate increases. The peak currents of the oxidation waves are proportional to the square roots of scan rate up to 100 mV/s, The in situ infrared spectra suggest that the product of the oxidation be dehydroascorbic acid, which may exist as a dimer.

Electrocatalytic oxidation of hydrazines at a 4-pyridyl hydroquinone self-assembled platinum electrode and its application to amperometric detection in capillary electrophoresis

4-Pyridyl hydroquinone on a platinum electrode adsorbs through the pyridine nitrogen forming stable self-assembled layers. The electrocatalytical oxidation of hydrazines was performed by the modified electrode. The overpotential of hydrazines was decreased markedly at the self-assembled monolayer (SAM) electrode. The mechanism of hydrazine oxidation was also investigated. Amperometric detection of hydrazine under zero potential (vs Ag\AgCI\sat. KCl) was exhibited by the SAM electrode used as an electrochemical detector in a flow system. (C) 1998 Elsevier Science S.A. All rights reserved.

Catalysis of hydrotalcite-like compounds in liquid phase oxidation: (II) - Oxidation of p-cresol to p-hydroxybenzaldehyde

Hydrotalcite-like compounds (HTLcs): CoMAlCO3-HTLcs (M=Cu2+, Ni2+, Mn2+, Cr3+, Fe3+), were synthesized by coprecipitation and characterized with XRD and IR. The catalysis of these HTLcs and their calcined products were studied in the p-cresol oxidation, and the effects of the temperature of HTLcs calcination, the ratio of Co/Cu, different promoters, reaction temperatures and reaction times on reaction activities were investigated. It has been found that calcined HTLcs have higher activity than uncalcined samples and mechanical mixed oxides in this reaction. The best yield was obtained from the CoCuAlCO3-HTLc (Co/Cu/Al=3:1:1) calcined at 450 degrees C. A tentative reaction mechanism was also proposed. (C) 1998 Elsevier Science B.V.

Partial oxidation of methane to synthesize gas over Ni/alpha-Al2O3 catalyst promoted by noble metals

The production of synthesis gas by partial oxidation bf methane in oxygen has been examined over Ni/alpha-Al2O3 catalyst promoted by noble metals(Rh, Ru, Pt and Pd), especially with Pt. The reactivity is considered in conjunction with the result of H-2-TPR, CO-TPD, SEM and XRD. It is found that small amount of Pt results in a great improvement of activity for the Ni/alpha-Al2O3 catalyst. The activity order is : Rh-Ni>Pt-Ni approximate to Ru-Ni>Pd-Ni, meantime the Pt improves the stability of Ni/alpha-Al2O3 catalyst except for Pd which is easy to he deactivated by carbon deposition. The results of TPD, SEM and XRD indicate that there is an interaction between Ni and Pt metals in the catalyst. The interaction increases the dispersions of Pt and Nit the presence of Pt suppresses the growth and the migration of Ni grains over the surface of the catalyst.

Catalysis of hydrotalcite-like compounds in liquid phase oxidation: (I) phenol hydroxylation

Hydrotalcite-like compounds (HTLcs): (CuMAlCO3)-Al-II-HTLcs, where M-II=Co2+, Ni2+, Cu2+, Zn2+ and Fe2+, were synthesized by coprecipitation and characterized with XRD and IR. The catalysis of these HTLcs was studied in the phenol hydroxylation by H2O2 in liquid phase; then the effects of the ratio of Cu/Al, reaction temperature, solvent and pH of medium were investigated. It has been found that the uncalcined HTLcs have higher activities than those of calcined samples in this reaction. The catalyst CuAlCO3-HTLcs having Cu/Al=3 efficiently oxidized phenol and gave high yields of the corresponding diphenols in appropriate reaction conditions. A tentative reaction mechanism is also proposed. (C) 1998 Elsevier Science B.V.

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)(2)/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and. cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyclohexene catalyzed by Pd(OAc)(2)/HQ/FePc was elucidated.

Electrocatalytic oxidation and flow amperometric detection of hydrazine at an electropolymerized 4-vinylpyridine/palladium film electrode

A poly(4-vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4-vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion-exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).

The electrochemical study of oxidation-reduction properties of horseradish peroxidase

Oxidation-reduction properties of horseradish peroxidase (HRP) have been investigated by using direct electrochemical methods. Two successive separated distinct one-electron processes of HRP were obtained and the related physiological processes were described. The monolayer coverage of HRP at the electrode surface is about 50 pmol/cm(2). UV-Vis spectrophotometry and stable amperometry prove that the enzyme electrode possesses catalytic activity for H2O2 in the absence of a mediator and it might offer an opportunity to build the third generation of biosensors for analytes, such as H2O2, glucose and cholesterol etc. (C) 1997 Elsevier Science S.A.