Differential pulse voltammetric determination of P(V) following adsorptive accumulation of alpha-[PMo(12)O(40)](3-) on a polypyrrole-modified glassy carbon electrode.
On the basis of the formation and pre-concentration of an alpha-Keggin-type [PMo(12)O(40)](3-) complex, a novel voltammetric method was developed for the determination of trace levels of P(V). The alpha-[PMo(12)O(40)](3-) complex was formed by heating a 5x10(-4) M Mo(VI)-0.2 M HCl-40% (v/v) CH(3)CN system containing a trace amount of P(V) at 70 degrees C for 30 min. During the electrochemical polymerization of pyrrole in the alpha-[PMo(12)O(40)](3-) solution, the alpha-[PMo(12)O(40)](3-) complex was accumulated into the polypyrrole film on a glassy carbon electrode. The differential pulse voltammetric peak current due to the alpha-[PMo(12)O(40)](3-) complex incorporated in the polypyrrole film was linearly dependent on the P(V) concentration in the range of 5x10(-9)-5x10(-7) M; a detection limit of 2x10(-9) M was achieved.
Corrosion protection of steel by bi-layered polypyrrole doped with molybdophosphate and naphthalenedisulfonate anions
Abstract Bi-layered polypyrrole (PPy) coating was investigated for corrosion prevention of steels. The PPy coating consisted of the inner layer doped with PMo12 O 40 3 - (PMo12) and HPO 4 2 - ions and the outer layer doped with naphthalenedisulfonate (NDS) ions. PMo12 ions doped in the inner layer make the passive oxide film on steel stabilized and the outer layer doped with large organic ions of NDS restricts decomposition and release of PMo12 ions in the inner layer. Corrosion tests were made in 3.5% NaCl aqueous solution for the steels covered by the single PPy–PMo12, single PPy–NDS, and bi-layered PPy–PMo12/PPy–NDS coatings. The single PPy–PMo12 and PPy–NDS coatings maintained the steel in passive state for 34 h and 24 h, respectively. The bi-layered coating kept the steel in passive state and prevented corrosion of the steels for the longer time period.
Electrochemistry and redox chemistry of aquaferrotungstosilicate, H2OFeIIISiW11O395- in the presence of hydrogen peroxide and hydroxyl
Heteropolytungstates in which one of the positions normally occupied by a tungsten cation is occupied instead by an iron cation are shown to be catalysts for the electroreduction of H{sub 2}O{sub 2}. The rate constant governing the reduction of H{sub 2}O{sub 2} by H{sub 2}OFe{sup II}SiW{sub 11}O{sub 39}{sup 6{minus}} was measured, and a catalytic mechanism involving an Fe(IV) intermediate generated from the reaction between the Fe(III) form of the heteropolytungstate anion and hydroxyl radicals is presented. The Fe(IV) intermediate can react with itself to produce H{sub 2}O{sub 2} and the Fe(III) form of the heteropolytungstate. Alternatively, the Fe(IV) intermediate can consume additional H{sub 2}O{sub 2} by oxidizing it to O{sub 2}. Competition between these two reaction pathways accounts for the nonintegral stoichiometry observed under some experimental conditions during the electroreduction of H{sub 2}O{sub 2} catalyzed by H{sub 2}OFe{sup II}SiW{sub 11}O{sub 39}{sup 6{minus}}. Pulse-radiolysis experiments were employed to detect the Fe(IV) intermediate, to evaluate rate constants for the reactions in which it is formed and decomposed, and to measure the rate of reduction of the Fe(III) form of the heteropolytungstate by O{sub 2}{sup {minus}}. 21 refs., 3 figs., 3 tabs.