磷钼钒类杂多酸—聚吡咯薄膜修饰电极及其电催化性能研究

合成了磷钼类杂多酸，采用电化学方法首次在导电基体玻碳电极上研制了磷钼钒类杂多酸－聚吡咯薄膜修饰电极，该电极性能稳定，经久耐用，对膜修饰电极的电化学行为进行了表征，研究了膜修饰电极酸性水溶液中的氯酸根、溴酸根，、磺酸根，亚硝酸根，三阶铁离子，     

Fabrication of Self‐Assembled Tris(1,10‐phenanthroline) ruthenium/12‐Molybdophosphoric Acid Films with Bifunctional Electrocatalytic and Photoluminescent Properties

The thin films containing transition metal complex tris(1,10‐phenanthroline) ruthenium(II) Ru(phen)₃Cl₂ (abbr Ru(phen)₃, phen=1,10‐phenanthroline), and 12‐molybdophosphoric acid [PMo₁₂O₄₀]_3? (abbr PMo₁₂) were fabricated on quartz, silicon and ITO substrates by layer‐by‐layer (LBL) method. The LBL films were characterized by the UV‐vis spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy and cyclic voltammetry. The films can catalyze both the reduction of ClO , BrO , IO , and the oxidation of C₂O due to the presence of bifunctional composite, and the redox potentials depend on pH as a result of protonation. The photoluminescence of films were also investigated. The films exhibited photoluminescence arising from π*–t_2g ligand‐to‐metal transition of Ru(phen)₃.     

Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Phosphomolybdate-modified multi-walled carbon nanotubes as effective mediating systems for electrocatalytic reduction of bromate

Electrocatalytic properties (towards reduction of bromate in 0.5 mol dm⁻³ H₂SO₄) of multi-walled carbon nanotubes (CNTs) modified with phosphododecamolybdate (PMo₁₂) monolayers have been diagnosed using cyclic voltammetry and amperometry. The ability of negatively charged PMo₁₂-modified CNTs to attract electrostatically ultra-thin, positively charged conducting polymer (PEDOT or polypyrrole) structures is explored to grow in controlled manner hybrid organic-inorganic network electrocatalytic films. Due to the presence of three-dimensionally distributed CNTs, the films’ conductivity and porosity are improved. The hybrid systems utilizing polypyrrole, rather than PEDOT, have produced fairly higher bromate electroreduction catalytic currents. Comparison is also made to Nafion-stabilized dispersion of PMo₁₂-modified CNTs inks. The latter system is characterized by good stability and relatively the highest sensitivities with respect to bromate concentration.     

Enhancement of oxygen reduction at Co-porphyrin catalyst by supporting onto hybrid multi-layered film of polypyrrole and polyoxometalate-modified gold nanoparticles

Three-dimensional multi-layered films (on glassy carbon) composed of networks of polyoxometallate (PMo₁₂O₄₀ ³⁻)-modified gold nanoparticles linked together through the alternately deposited ultra-thin layers of polypyrrole have served as active supports for Co-porphyrin catalytic centers. The hybrid organic-inorganic films (supports) have been prepared by using the layer-by-layer approach. The fact that polyanionic (phosphomolybdate) adsorbates on gold nanoparticles are attracted by positively charged sites of conducting polymer (polypyrrole) structures leads to the stabilizing effect and facilitates distribution of Au nanostructures. The systems have been characterized using scanning electron microscopy, as well as with chronoamperometric and voltammetric techniques. By supporting Co-porphyrin centers onto the hybrid film of the polymer-linked phosphomolybdate-stabilized gold nanoparticles, significant electrocatalytic enhancement effects (namely voltammetric current increases) have been observed during the electroreduction of oxygen in acid medium relative to a standard response of the simple porphyrin deposit on glassy carbon measured under analogous conditions. Among important issues is the high activity of the hybrid film (support) itself toward the reductive decomposition of hydrogen peroxide to water. When it comes to performance of the Co-porphyrin-containing system, it is reasonable to expect that the O₂ reduction process is initiated at Co-porphyrin catalytic sites (two-electron reduction to H₂O₂) and continued (two-electron reduction to H₂O) at the hybrid film containing gold nanoparticles dispersed within the highly porous cauliflower-like structures of polypyrrole multi-layers. While the gold networks facilitate charge distribution within the hybrid electrocatalytic film, non-covalent π-π interactions of porphyrin rings with polypyrrole interlayers and charge transfers between negatively charged (PMo₁₂O₄₀ ³⁻ modified) gold nanoparticles and positively charged nitrogen sites of polypyrrole could also cause synergism.

     

Intramolecular coupling of BrO stretching vibrations in solid bromates, infrared and Raman spectroscopic studies on M(BrO3)2.6H2O (M = Mg, Co, Ni, Zn) and Ni(ClO3)2.6H2O

Infrared and Raman spectra of the isostructural cubic halate hexahydrates M(BrO3)2.6H2O (M = Mg, Co, Ni, Zn) and Ni(ClO3)2.6H2O (space group, Pa3; Z = 4) are presented. They are discussed with respect to the strength of the O-H...OXO2 hydrogen bonds (hydrogen bond acceptor capability, synergetic effect) and the order of the BrO stretching modes. In the case of undistorted bromate ions, e.g. at C3 lattice sites, the order of the symmetric (v1) and asymmetric (v3) XO stretching modes is v1 < v3 as for ClO3- but in contrast to IO3- with v1 > v3. The relative order of v1 and v3 of halate ions is mainly governed by the specific masses of the halogen atoms and the angles of the XO3- ions. The latter decrease in the sequence ClO3- (107degrees) > BrO3-> IO3- (< 100 degrees). The Raman scattering intensities of the asymmetric XO stretching modes v3 of the title compounds are unusually low (< 5% those of v1).     

The electrocatalytic reactions of adenine, guanine, H2O, H2O2, N2H4, and l -cysteine catalyzed by poly(Ni(4-TMPyP)) film-modified electrodes

Electrochemical preparation of poly(nickel tetrakis(N-methyl-4-pyridyl)porphyrin) tetratosylate (poly-Ni(4-TMPyP)) produces stable and electrochemically active films in strong and weak basic aqueous solutions. These films were produced on glassy carbon and gold electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly(Ni(4-TMPyP)) films. The electrochemical properties of poly(Ni(4-TMPyP)) films indicate that the redox process was confined in to the immobilized film. The electrochemical quartz crystal microbalance results showed an ion exchange reaction for the redox couple. The polymer films showed one new redox couple when transferred to strong and weak basic aqueous solutions and the formal potential was found to be pH dependent. The electrocatalytic oxidation of H₂O by a nickel tetrakis(N-methyl-4-pyridyl)porphyrin film-modified electrode was also performed. The mechanism of oxygen evolution was determined by cyclic voltammetry, chronoamperometry and rotating ring disc electrode methods. The oxygen evolution was determined by a bicatalyst system using hemoglobin, and iron tetrakis (N-methyl-2-pyridyl)porphyrin as catalyst to detect the oxygen by electrocatalytic reduction. The electrocatalytic oxidations of adenine, guanine, H₂O₂, N₂H₄, NH₂OH, and l-cysteine by the film-modified electrode obtained from water-soluble nickel porphyrin were also investigated.     

Multilayer films of cationic surfactants incorporating polyoxometalate on electrodes

A new kind of multilayer of didodecyldimethylammonium bromide (DDAB) and 1:12 phosphomolybdic anions (PMo₁₂) was achieved on the surface of a wax-impregnated graphite (WIG) electrode by ion exchange and electrostatic interaction. The characterization and electrochemical behavior of the multilayer films of DDAB/PMo₁₂ is described in detail. The chemically modified electrode was shown to exhibit an excellent electrocatalytic activity toward the reduction of BrO₃ ^– anion in 0.5 M H₂SO₄ and possesses several attractive features, such as simple preparation, fast response, good stability, etc. Electronic Publication     

Kinetic studies of the reactions of IO,BrO, and ClO with dimethylsulfide

The kinetics of the reactions of IO, BrO, and ClO with DMS have been investigated at 298 K and total pressures of 0.5–6.8 mbar He using the discharge flow-mass spectrometry technique to monitor the halogen oxide radicals. Rate coefficients of (8.8 ± 2.1) × 10^?15, (2.7 ? 0.5) × 10^?13 and (9.5 ± 2.0) × 10^?15 cm³ molecule^?1 s^?1 have been obtained for the reactions of IO, BrO, and ClO with DMS, respectively. The result for IO with DMS is in good agreement with two other recent studies on this reaction but is nearly three orders of magnitude slower than two earlier studies, one of which was from this laboratory. The earlier studies are now thought to be in error because of heterogeneous and secondary chemistry occurring in the systems investigated. The rate coefficient for BrO with DMS is in excellent agreement with a previously reported preliminary value from this laboratory. However, the rate coefficient for ClO with DMS is a factor of 4 lower than our previously determined value. The new data are considered more reliable in view of the much improved experimental technique in the present study. DMSO was detected as a product in all of these reactions. A semi-quantitative determination of the DMSO yield was only possible in the case of the reaction of IO with DMS where a yield of 84 ± 40% was found.     

Isomeric organic ligand dominating polyoxometalate-based hybrid compounds: synthesis and as electrocatalysts and pH-sensitive probes

By introducing isomeric organic ligands into polyoxometalate (POM) systems, two new POM-based hybrid compounds, [Cu₆(m-pyttz)₂(H₂O)][HPMo₁₂O₄₀] (1) and [Ag₃(p-H₂pyttz)(p-Hpyttz)Cl][H₂PMo₁₂O₄₀]·6H₂O (2) (m-/p-H₂pyttz = 3-(pyrid-3/4-yl)-5(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), have been hydrothermally synthesized and characterized. Single-crystal structural analysis shows the m-pyttz ligands link Cu^I ions to generate a two-dimensional layer with hanger-like rhombus, which is pillared by the PMo₁₂ anions in 1. Compound 2 exhibits a three-dimensional supramolecular framework, in which PMo₁₂ anions are building blocks facilitating the extension of the whole structure. The influence of the coordination modes of m-/p-H₂pyttz on the structures is discussed in detail. Furthermore, electrochemical properties of 1 and 2 have been studied and they display excellent electrocatalytic activities toward the reduction of nitrite and hydrogen peroxide and pH-dependent electrochemical behaviors.     

Layer-by-layer assembly of silicotungstate multilayer films modified on glassy carbon electrode and their electrochemical behaviors

A new electrode was modified by multilayer films composed of heteropolyanion (SiW12) and cationic polymer poly(diallyldimethylammonium chloride) through electrochemical growth. The modified electrode electrochemical behavior, the effect of solution pH and electrocatalytic response to the reduction of BrO3- and NO2- have been investigated. The result shows that the electrochemical process of multilayer films modified electrode including SiW12 is a reversible process by electrochemical step. One-electron process has no proton participation in the first step, and one-electron process is accompanied by one proton participation in the second step and two-electron process is accompanied by two protons participation in the third step. The films grow uniformly, and the peak currents increase with increasing layer numbers. The peak currents increase with scan rate, and the reduced potentials of multilayer films shift negatively with increasing pH. The electrochemical mechanism of multilayer films was suggested.     

[SiCu(H2O)W11O39]6-在玻碳电极上的多层组装及电催化性能

The electrochemical behavior of SiCu W11 heteropolyacide in acidic aqueous solution was studied. The effect of solution pH on the electrochemical behavior of SiCu W11 was discussed and the mechanism was suggested. New electrode was modified by muhilayer films composed of heteropolyanion (SiCu W11 and cationic polymer poly (diallyldimethylammonium chloride). Cyclic vohammetry showed the uniform growth of the film. The modified electrodes exhibited some special electrochemical properties in the films, different from those in homogeneous aqueous solutions. The effect of pH on the redox behavior of SiCu W11 in the films was discussed in details. The muhilayer film electrodes have an excellent electrocatalytic response to the reduction of BrO3^- and NO2^-.     

ITO Electrode Modified by α‐K6[P2W18O62] Hybrid Nanofibers for Nitrite Determination

A promising nitrite sensor based on one‐dimensional polyoxometalate hybrid nanofibers was prepared and developed by electrospinning of a mixture of poly(vinyl alcohol) and α‐K₆[P₂W₁₈O₆₂]?14H₂O (P₂W₁₈) onto the surface of an indium tin oxide (ITO) electrode. After thermal crosslinking, the P₂W₁₈ hybrid nanofibers are insoluble in aqueous solutions even after a period of 24 hours, which ensures the electrochemical stability of the P₂W₁₈ hybrid nanofiber‐modified ITO electrode. The cyclic voltammetry results have demonstrated that the P₂W₁₈ hybrid nanofiber‐modified ITO electrode exhibits excellent electrocatalytic activity toward the reduction of nitrite in acidic solutions. Additionally, long‐term stability and reproducibility have been observed.     

Kinetic studies of free radical reactions by mass spectrometry. II. The reactions of SO + ClO,SO + OClO and SO + BrO

The rates of several novel elementary reactions involving ClO, BrO and SO free radicals in their ground states were studied in a discharge-flow system at 295 K, using mass spectrometry. The rate constant k₂ was determined from the decay of SO radicals in the presence of excess ClO radicals: The SO + OClO overall reaction has a complex mechanism, with the primary step having a rate constant k₅ equal to (1.9 ± 0.7) × 10^?12 cm³ sec^?1: A lower limit for the rate constant of the rapid reaction of SO radicals with BrO radicals was determined:      

Fabrication and room-temperature exciton photoluminescence stability studies of inorganic–organic hybrid (C12H25NH3)2SnI4 thin films

A new methodology has been developed to fabricate the thin films of Tin (II) iodide based inorganic–organic (IO) hybrid, (C₁₂H₂₅NH₃)₂SnI₄, from direct and cost-effective three-step processing. The fabrication is based on room-temperature electrochemical deposition followed by simple solution processing. These IO hybrid films show room-temperature exciton related photoluminescence at 616 nm due to quantum and dielectric confinement effects. Systematic X-ray diffraction and optical studies are performed to understand the structural modification due to oxidation and consequent emission degradation. Post-processing methods to avoid emission degradation are also been demonstrated. The simple solution processing methodology and unique highly red-emitting IO hybrids, would be of interest for many multi-functional optoelectronic applications.     

Degradation of methylene blue in aqueous dispersion of hollow titania photocatalyst: study of reaction enhancement by various electron scavengers

Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles (averaged diameter: 200 nm) as a template in conjunction with the sol-gel method. Utilization of 0.20 mol/L titanium tetrabutoxide and 25 g/L latex led to the formation of anatase particles having shell thickness of about 15 nm and void diameter of about 150 nm. Photocatalytic activity of the titania hollow spheres was examined by focusing on its enhancement by electron scavengers in the photocatalytic decomposition of methylene blue (MB). The electron scavengers employed were inorganic oxidants such as ClO*3, BrO*3, IO*4, H2O2, and S2O2*8. Differences in electronegativity, atomic radius of the halogens, and the number of highly reactive radical and nonradical intermediates were proven to be important criteria for an electron scavenger to yield high efficiency in the MB photodecomposition. Based on the results, the effect of the oxidants used were found to be in the order of S2O2*8 > IO*4 > BrO*3 > H2O2 > ClO*3.     

Raman spectra of hybrid materials based on carbon nanotubes and Cs3PMo12O40

A route for the synthesis of hybrid materials using multiwalled carbon nanotubes (MWCNTS) and Cs₃PMo₁₂O₄₀ was confirmed. The Cs₃PMo₁₂O₄₀ salt was synthesized from H₃PMo₁₂O₄₀·14H₂O and CsCl. All compounds were characterized by Raman spectroscopy. The synthesis method can produce a chemically stable Cs₃PMo₁₂O₄₀ molecule and pure and oxidized MWCNTS. Raman spectroscopy showed that the chemical interaction between MWCNTS and Cs₃PMo₁₂O₄₀ was essentially of electrostatic nature. Raman spectra obtained with different wavelengths showed thermal decomposition of H₃PMo₁₂O₄₀·14H₂O (raw materials) from laser heating process. On the contrary, the synthesized compound (i.e. Cs₃PMo₁₂O₄₀) was stable under the experimental conditions.     

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis,Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe³⁺, [Fe(CN)₆]^3? and KCl. Fourier transform infrared spectroscopy, UV‐vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe³⁺ to Fe²⁺ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer‐by‐layer technique. The thus‐prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H₂O₂ reduction.     

钒取代Keggin型杂多酸的多层组装和电催化性能研究

用层层组装的方法在4-氨基苯甲酸预修饰的玻碳电极上交替沉积过渡金属钒取代的杂多酸H₃PW₆V₆O₆-40(简称PW₆V₆)和联吡啶锇取代的聚乙烯吡啶(QPVP-Os).用表面等离子体共振(SPR)技术和循环伏安(CV)法对多层膜进行了表征.结果表明,多层膜的生长均匀,平均厚度为2.88nm.还研究了多层膜对亚硝酸根(NO₂^-)和溴酸根(BrO₃^-)的催化还原活性.     

PMo12-functionalized Graphene nanosheet-supported PtRu nanocatalysts for methanol electro-oxidation

Graphene nanosheets, synthesized by a modified Hummers method, have been functionalized by PMo₁₂, and used as the supports of the PtRu nanoparticles. The electrocatalytic properties of the resultant nanocatalysts (PtRu/PMo₁₂-Graphene) for methanol electro-oxidation have been evaluated by cyclic voltammetry and chronoamperometry. The micrograph and the elemental composition have also been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopy. The results suggest that the addition of PMo₁₂ benefits the high dispersion of graphene nanosheets in the water and the uniform dispersion of the PtRu nanoparticles on the graphene nanosheets, and the PtRu/PMo₁₂-Graphene catalysts have higher electrocatalytic activity and better electrochemical stability for methanol oxidation compared to the PtRu/Graphene catalysts.