Sequential Hydride Research Articles

Selenium Speciation of Soil/Sediment Determined with Sequential Extractions and Hydride Generation Atomic Absorption Spectrophotometry

Understanding the speciation of the multioxidation states of selenium is vital to predicting the mineralization, mobilization, and toxicity of the trace element in natural systems .Asequential extraction scheme (SES) was developed for identification of Se oxidation states that first employed 0.1 M (pH 7.0) K2HP04-KH2P0~ (P-buffer) to release soluble selenate (Se+“‘) and selenide (Se-“) and ligandexchangeable selenite (Se? The second step involved oxidation of organic materials with 0.1 M K&&08 (90 W to release Se-r’ and Se+r”associated or occluded with organic matter. The final step used HNOs (90 ‘C) to solubilize insoluble Se remaining in the sample. The solubilized Se compounds were speciated by a selective hydride generation atomic absorption spectrophotometry technique. Accuracyofthe developed SES method (96-103% recovery) was verified by use of prepared Se compounds of known speciation, NlSTstandard reference materials, and existing seleniferous soils. The average precision (relative standard deviation) for the P-buffer extraction ranged from 5.5 to 7.7% (n= 12);the precision of the persulfate extraction ranged from 2.6 to 8.4% (n = 12); and the precision of the nitric acid extraction ranged from 2.8 to 7.4% (n = 12) for three soils extracted at four different time periods. The method was applied to analyze Se species in seleniferous plant, soil, and sediment samples.

Visible-light-induced photocatalysis of poly(pyridine-2,5-diyl). Photoreduction of water, carbonyl compounds and alkenes with triethylamine

Poly(pyridine-2,5-diyl)(PPy) exhibits heterogeneous and visible-light-induced photocatalysis toward the reduction of water, carbonyl compounds and alkenes in the presence of triethylamine (TEA) as a sacrifical electron donor. The water reductive H2 evolution is ehnanced by colloidal noble metals concurrently photoformed from noble metal halides, and colloidal Ru gives the highest apparent quantum yield of H2, 0.21 at 450 nm. With regard to the reduction of carbonyl compounds and electron-deficient alkenes, noble-metal-free PPy leads to the efficient and selective reduction to the corresponding alcohols and dihydro compounds, respectively. Carbonyl compounds whose reduction potentials are as negative as –1.83 V vs. SCE in acetonitrile are photoreducible. Deuterium incorporation experiments with dimethyl maleate and/or dimethyl fumarate in [O-2H]methanol have revealed that the photocatalysis of PPy should proceed through sequential two-electron transfer reduction, affording dideuteriated dimethyl succinate. Sequential electron transfer and hydride transfer mechanisms are proposed.

Stepwise reduction of acetonitrile in [Tp'(CO)(PhC.tplbond.CMe)W(N.tplbond.CCH3)][BF4

We report stepwise reduction of coordinated acetonitrile by sequential hydride and proton addition reactions. Intermediate metal complexes have been isolated and characterized at each stage of the reduction

Hydrogen surface segregation on Si(111) by photon-stimulated desorption at the SiKedge

The photon-stimulated desorption of H/sup +/ from cleaved Si(111) using photon energies near the Si K excitation threshold is reported. The time dependence of the H surface segregation from the bulk following cleavage shows two or three sequential time regimes of growth kinetics suggesting multiple sequential hydride phase formations. Removal of the H from the H-saturated surface results in the subsequent observation of only the first time regime (which we interpret as being due to formation of a monohydride phase).