PMo12-doped carbon ceramic composite electrode based on sol-gel chemistry and its electrocatalytic reduction of bromate

A conductive carbon ceramic composite electrode (CCE) comprised of cc-type 1:12 phosphomolybdic acid (PMo12) and carbon powder in an organically modified silicate matrix was fabricated using a sol-gel method and characterized by scanning electron microscopy, cyclic voltammetry, and Osteryoung square-wave voltammetry. Osteryoung square-wave voltammograms of the modified electrode immersed in different acidic aqueous solutions present the dependence of current and redox potential on pH. The PMo12-doped CCE shows more reversible reaction kinetics, good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling or dopant leaching. Moreover, the modified electrode shows good catalytic activity for the electrochemical reduction of bromate.

Synthesis, characterization and crystal structure of a charge transfer salt based on 1.3-cyclopentadiene tetrabutylammoniumdodecamolybdosilicoate

A charge transfer salt, (Bu4N)(4) (C5H6)[(HSiMo11MoO40)-Mo-VI-O-V] has been photochemically synthesized from (Bu4N)(4)SiMo12O40 and 1.3-cyclopentadiene and Characterized, by elemental analysis, IR spectra, solid diffusion reflectance electronic spectra, CV and ESR. The X-ray crystal structure revealed that the title complex crystal data are as follows: triclinic, space group P (1) over bar, a = 14.347(3), b = 14.423(3), c = 27.158(5) Angstrom, alpha = 96.90(3), beta = 104.18(3), gamma = 98.20(3)degrees, V = 5322(2) Angstrom (3), Z = 2, M-r = 2855. 30, D-c = 1.782g.cm(-3), F(000) = 2860, R = 0.0719, wR = 0.198. The title compound is composed of 1.3-cyclopentadiene, four tetrabutylammonium and [(SiMo11MoO40)-Mo-VI-O-V](4-) anion.

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11 immobilized with Nafion film has been studied by means of cyclic voltammetry and rotating disk electrode techniques. The modified electrode shows high catalytic activity toward the reduction of both O-2 and H2O2. The rate constants of Oz and H2O2 reduction at the modified electrode have been measured and compared. It is found that O-2 undergoes a four-electron reduction at the modified electrode and the catalytic activity for the reduction of O-2 is dependent on the pH of the solutions.

The role of redox property of La2-x(Sr,Th)(x)CuO4 +/-lambda playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La2-xSrxCuO4 +/- lambda (0.0 less than or equal to x less than or equal to 1.0) and La(2-x)Tn(x)CuO(4 +/-) (lambda) (0.0 less than or equal to x less than or equal to 0.4), with K2NiF4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry (lambda) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO + CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, A and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO + CO reaction. For the NO + CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted). (C) 2000 Elsevier Science B.V. All rights reserved.

The application and a substitution defect model for Eu3+ -> Eu2+ reduction in non-reducing atmospheres in borates containing BO4 anion groups

The variations of emission intensities of SrB4O7:Eu2+ and Sr2B5O9Cl:Eu2+ prepared in different atmospheres are discussed in view of the structure of host compounds. A model of substitution defects is proposed to explain the abnormal reduction of Eu3+ --> Eu2+ in non-reducing atmospheres of N-2, air and O-2. Experiment results show that SrB4O7:Eu2+ phosphor sample prepared in N-2 atmosphere has an emission intensity of 94% as high as that of the sample prepared in H-2 gas. This implies that the reduction of Eu2+ --> Eu2+ in non-reducing atmospheres could be potentially used in preparing phosphors, such as SrB4O7:Eu2+. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthesis, structure characterization and biological activity of a novel amino acid salt (HAla)(8)(H3O)(10)[PMo12O40](6) center dot 22H(2)O

A novel compound was synthesized and characterized by means of elemental analysis, IR and UV spectra, TG, CV and single crystal X-ray diffraction. The compound crystallized in an orthorhombic space group C222 with a=1. 622 4(3) nm, b=3. 498 4(7) nm, c=1. 301 5(3) nm, V=7. 387 (3) nm(3), Z=6, R-1= 0. 037 3, wR(2)=0. 114 0. The Ala (Ala = alanine) molecules were protonated at the amino nitrogen N (1) and the C (2) of Ala group with the terminal oxygen atom O(15), O(14), O(26) and O(27) of the polyoxometalates participating in the hydrogen bond network. The anti-tumor activity of the title compound was estimated against Hela and Pc-3m cancer cells.

Sol-gel-derived carbon ceramic electrode containing 9,10-phenanthrenequinone, and its electrocatalytic activity toward iodate

9,10-Phenanthrenequinone (PQ) supported on graphite powder by adsorption was dispersed in propyltrimethoxysilane-derived gels to yield a conductive composite which was used as electrode material to fabricate a PQ-modified carbon ceramic electrode. In this configuration, PQ acts as a catalyst, graphite powder guarantees conductivity by percolation, the silicate provides a rigid porous backbone, and the propyl groups endow hydrophobicity and thus limit the wetting region of the modified electrode. Square-wave voltammetry was exploited to investigate the pH-dependent electrochemical behavior of the composite electrode and an almost Nernstian response was obtained from pH 0.42 to 6.84. Because the chemically modified electrode can electrocatalyze the reduction of iodate in acidic aqueous solution (pH 2.45), it was used as an amperometric sensor for the determination of iodate in table salt. The advantages of the electrode are that it can be polished in the event of surface fouling, it is simple to prepare, has excellent chemical and mechanical stability, and the reproducibility of surface-renewal is good.

Photochemical synthesis and crystal structure of a charge transfer salt [HMDH2][(H2PMoMo11O40)-Mo-v]center dot 2AA center dot 3H(2)O center dot DMF

The title supramolecular compound, [HMDH2][(H2PMoMo11O40)-Mo-V] . 2AA . 3H(2)O . DMF (HMD = hexamethylene diamine; AA=acetaldehyde; DMF=N,N-dimethyl formamide), has been photochemically synthesized by using elemental analysis, IR, solid diffusion reflectance, electronic spectra, ESR spectra and X-ray single-crystal analysis. The crystallographic data: triclinic, P (1) over bar, a=14.092(2), b=14.347(3), c=14.358(3)Angstrom, alpha = 75.10(3), beta = 80.70(3), gamma = 80.73(3)degrees, V = 2746.6(10)Angstrom (3), Z = 2, M-r = 2081.68, D-c=2.517g/cm(3), F(000) =1970, mu (MoK alpha) =2.766mm(-1). The structure has been refined to R =0.0832 and wR=0.2638, by full-matrix least-squares method. The title compound is composed of hexamethylene diamine, two acetaldehyde molecules, three water molecules, one N,N-dimethylformamide and [(H2PMoMo11O40)-Mo-V](2-) heteropoly anion.

Co-Cu-Al mixed oxides derived from hydrotalcite-like compound for NO reduction by CO

Various hydrotalcite based catalysts were prepared for catalytic removal of NO (NO reduction by CO). The general formula of hydrotalcite compounds (HTLc) was Co-Cu-Al-HTLc. Precalcination of these materials at 450 degrees C for NO reduction by CO, was necessary for catalytic activity. All catalysts except Co-A1 and Cu-Al have very good activity at lower temperature for NO reduction by CO. All samples were characterized by XRD and BET. The tentative reaction mechanism was also proposed.

The reduction of RE3+ in SrB6O10 prepared in air and the luminescence of SrB6O10 : RE2+ (RE=Eu, Sm, Tm)

The reduction of RE3+ to RE2+ (RE=Eu, Sm and Tm) in SrB6O10 prepared in air by high-temperature solid state reaction was observed. The luminescent properties of Eu2+ and Tm2+ show f-d transition and Sm2+ shows f-f transition at room temperature. Three crystallographic sites for Sm2+ in matrix are available. Vibronic transition of D-5(0)-F-7(0) of Sm2+ was studied. The coupled phonon energy about 108 cm(-1), was determined: from the vibronic transition. Due to the thermal population from D-5(0) level, (D1-FJ)-D-5-F-7 (J=0, 1, 2) transitions of Sm2+ were observed at room temperature. A charge compensation mechanism is proposed as a possible explanation.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.

Preparation, characterization of solid solution La4BaCu5-xMnxO13+lambda (x=0-5) and its catalytic activity in the reduction of NO by CO

A series of layered mixed oxides La4BaCu5-xMnxO13+lambda(x = 0-5) was prepared, characterized and used as catalysts for NO+CO reaction. It was found that all the samples were single phase having a structure with five-layered-perovskite. La4BaCu2Mn3O13+lambda showed the highest activity in the title reaction, this could be attributed to the synergetic effect between Cu and Mn. The results of TPR, TPD and excess oxygen investigations confirmed that the Cu ion would be the active center. The displacement of the Cu ion by Mn caused the Cu ion to be more easily reducible and more content of excess oxygen, and it was beneficial to the activity of the catalyst. The reaction mechanism was also proposed.

Photoinduced electrochemical reduction of nitrite at an electrochemically roughened silver surface

Photoelectrochemical reduction of nitrite and nitrate was studied on the surface of an electrochemically roughened silver electrode. The dependence of the photocurrent on photon energy, applied potential, and concentration of nitrite was determined. It was concluded that the photoelectrochemical reduction proceeds via a photoemission process followed by the capture of hydrated electrons by electron accepters. The excitation of plasmon resonances in nanosize metal structures produced during the roughening procedure resulted in the enhancement of the photoemission process. Ammonia was detected as one of the final products in this reaction. Mechanisms for the photoelectrochemical reduction of nitrite and nitrate are proposed.

A study on the mechanism of the abnormal reduction of Eu3+ -> Eu2+ in Sr2B5O9Cl prepared in air at high temperature

This paper reports a new observation of the abnormal reduction of Eu3+ --> Eu2+ in Sr2B5O9Cl when prepared in air at high temperature. A model based on the nature of substitution defects is proposed to explain this abnormal reduction. Electrons, which reduced the Eu3+ ions, are created by the substitution of cations first and then transferred to the target Eu3+ ions via tetrahedral berate anion groups. Codoping experiments are designed and performed. The results of these experiments support the model proposed. (C) 1999 Academic Press.

Catalytic reduction of NO by CO with hydrotalcite derived mixed oxides

Catalysts with spinel structure derived from Hydrotalcite-like Compounds (HTLcs) containing cobalt have been investigated in NO catalytic reduction by Co. It was found that catalysts with spinel structures derived from HTLcs had obviously higher activity than that prepared from general methods. A two-step reaction was observed during the reaction curse: NO was first reduced to N2O by Co, and with the increase of temperature, the N2O was reduced to N-2. The reactivity of the catalysts studied increased with the amount of cobalt-content in the catalyst, and decreased with the calcination temperature. The crystal defect would play an important role in the reaction.