Browsing by Subject "Coordination reactions"

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    Continuous mesoporous pd films by electrochemical deposition in nonionic micellar solution
    (American Chemical Society, 2017) Iqbal, M.; Li C.; Wood, K.; Jiang B.; Takei, T.; Dag, Ö.; Baba, D.; Nugraha, A. S.; Asahi, T.; Whitten, A. E.; Hossain, M. S. A.; Malgras, V.; Yamauchi, Y.
    Mesoporous metals that combine catalytic activity and high surface area can provide more opportunities for electrochemical applications. Various synthetic methods, including hard and soft templating, have been developed to prepare mesoporous/nanoporous metals. Micelle assembly, typically involved in soft-templates, is flexible and convenient for such purposes. It is, however, difficult to control, and the ordering is significantly destroyed during the metal deposition process, which is detrimental when it comes to designing precisely mesostructured materials. In the present work, mesoporous Pd films were uniformly electrodeposited using a nonionic surfactant, triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), as a pore-directing agent. The interaction between micelles and metal precursors greatly influences the metal growth and determines the final structure. The water-coordinated species interact with the ethylene oxide moiety of the micelles to effectively drive the Pd(II) species toward the working electrode surface. From small-angle neutron scattering data, it is found that spherical P123 micelles, with an average diameter of ∼14 nm, are formed in the electrolyte, and the addition of Pd ions does not significantly modify their structure, which is the essence of the micelle assembly approach. The uniformly sized mesopores are formed over the entire mesoporous Pd film and have an average pore diameter of 10.9 nm. Cross-sectional observation of the film also shows mesopores spanning continuously from the bottom to the top of the film. The crystallinity, crystal phase, and electronic coordination state of the Pd film are also confirmed. Through this study, it is found that the optimized surfactant concentration and applied deposition potential are the key factors to govern the formation of homogeneous and well-distributed pores over the entire film. Interestingly, the as-prepared mesoporous Pd films exhibit superior electrocatalytic activity toward the ethanol oxidation reaction by fully utilizing the accessible active surface area. Our approach combines electrochemistry with colloidal and coordination chemistry and is widely applicable to other promising metals and alloy electrocatalysts.
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    Effects of ions on the liquid crystalline mesophase of transition-metal salt: surfactant (CnEOm)
    (American Chemical Society, 2004) Dag, Ö.; Alayoǧlu, S.; Uysal, İ.
    The transition-metal aqua complex salts [M(H2O) x]Y2 (where M is some of the first- and second-row transitionmetal ions and Y is Cl-, NO3-, and ClO4- counteranions) form liquid crystalline (LC) mesophases with oligo(ethylene oxide) nonionic surfactants (CnH 2n+1(CH2CH2O)mOH, denoted as C nEOm). The structure of the [M(H2O) x]Y2:CnEOm mesophase is usually 2D hexagonal in nitrate systems, cubic in perchlorate systems, and absent in the chloride systems. The solubility of the metal aqua complex salt follows the Hofmeister series in a [M(H2O)x]Y2:C nEOm mesophase. However, the nitrate ion interacts with the metal center as a bidentate and/or unidentate ligand, therefore reducing the ion density (and/or ionic strength) of the LC medium and further enhancing the solubility of nitrate salt in the LC systems. The cobalt chloride salt is the only soluble chloride salt that undergoes ligand-exchange reactions in the [Co(H2O)6]Cl2:CnEOm system. In an LC mesophase, anions have a greater influence on the hydrophilicity of nonionic surfactants than do cations. The structure and stability of the LC mesophase can be controlled by controlling either the hydrophilicity of the nonionic surfactant (by choosing the right anion type) or the ion density of the medium (by either influencing the equilibrium between the free and coordinated anions or balancing between the coordinating and noncoordinating anions in the medium).