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Yoshiyuki Okamoto

Bio: Yoshiyuki Okamoto is an academic researcher from New York University. The author has contributed to research in topics: Glass transition & Copolymer. The author has an hindex of 22, co-authored 138 publications receiving 1530 citations. Previous affiliations of Yoshiyuki Okamoto include Keio University & University of Arizona.


Papers
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TL;DR: The results suggest that cellular redox status is a determinant of pulmonary arterial endothelial cell TPMET activity, with T PMET activity more highly correlated with the poise of the NADH/NAD(+) redox pair.
Abstract: Pulmonary arterial endothelial cells possess transplasma membrane electron transport (TPMET) systems that transfer intracellular reducing equivalents to extracellular electron acceptors. As one asp...

65 citations

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TL;DR: A novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone is presented, which reveals the potential for substantial performance improvement by incorporation of highly permeable ionomers as the functional catalyst binder.
Abstract: Rapid improvements in polymer-electrolyte fuel-cell (PEFC) performance have been driven by the development of commercially available ion-conducting polymers (ionomers) that are employed as membranes and catalyst binders in membrane-electrode assemblies. Commercially available ionomers are based on a perfluorinated chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low gas permeability and high mechanical strength but introduces significant mass-transport losses in the electrodes. These transport losses currently limit PEFC performance, especially for low Pt loadings. In this study, we present a novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel backbone chemistry induces structural changes in the ionomer, restricting ionomer domain swelling under hydration while disrupting matrix crystallinity. These structural changes slightly reduce proton conductivity while significantly improving gas permeability. The performance implications of this trade-off are assessed, which reveal the potential for substantial performance improvement by incorporation of highly permeable ionomers as the functional catalyst binder. These results underscore the significance of tailoring material chemistry to specific device requirements, where ionomer chemistry should be rationally designed to match the local transport requirements of the device architecture.

57 citations

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TL;DR: In this article, a new family of amorphous perfluorodioxolane copolymers that show permselectivities above the polymer upper bound for important gas pairs is presented.
Abstract: Separations using polymer membranes is a rapidly growing field due to membrane advantages such as energy efficiency, environmental friendliness, and compact size. Among the materials considered for membrane use are perfluoropolymers, which offer unprecedented stability for operation in challenging conditions such as those required in industrial gas separations. Despite this favorable attribute, the relative lack of material choices has hindered perfluoropolymer adoption as membranes. Here, we report gas transport properties in a new family of amorphous perfluorodioxolane copolymers that show permselectivities above the polymer upper bound for important gas pairs (e.g., He/CH4, H2/CH4, N2/CH4). For example, the most selective of these membranes has a He/CH4 selectivity more than 5 times higher than any previously reported for a perfluoropolymer. The new copolymer membranes exhibit tunable transport properties through variation in the amount of monomers that function as “selective enhancers”. Such monomers, which show a tendency to crystalize as homopolymers, improve chain packing in the copolymer, enhancing the membrane ability to sieve molecules by size. In this manner, these materials open a new route to achieving tailored performance with inherently stable membranes. Moreover, these copolymers are soluble in fluorinated solvents, and thus are solution processable making their scale-up and conversion to membrane devices straightforward using existing industry methods.

55 citations

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TL;DR: In this paper, the reaction of diphenyl diselenide with di-n-butylmercury in dioxane at refluxing temperature gave nbutyl phenyl selenide (80% yield) and metallic mercury.

55 citations

Journal ArticleDOI
TL;DR: In this paper, two perfluoropolymers based on dioxolanes were synthesized by radical polymerization and characterized thoroughly for physical properties such as glass transition temperature (Tg), d-spacing between polymer chains, and fractional free volume (FFV).
Abstract: Glassy perfluoropolymers have become an exciting materials platform for membrane gas separation as they define the upper bounds for some gas separations, such as He/H2, He/CH4, and N2/CH4. However, due to the difficulty in synthesis, only a few glassy perfluoropolymers are commercially available, including Teflon AF and Hyflon AD derived from dioxoles and Cytop derived from dihydrofuran. In this study, two perfluoropolymers based on dioxolanes, poly(perfluoro-2-methylene-1,3-dioxolane) (poly(PFMD)) and poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) (poly(PFMMD)), were synthesized by radical polymerization and characterized thoroughly for physical properties such as glass transition temperature (Tg), d-spacing between polymer chains, and fractional free volume (FFV). The gas permeability and solubility were determined at 35 °C for a series of pure gases in these perfluorodioxolanes and compared with the commercial perfluoropolymers. Poly(PFMD) and poly(PFMMD) exhibit separation properties of He/H2, He/...

51 citations


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2,877 citations

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TL;DR: Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts, but both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions.
Abstract: Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter- or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C(6)F(5))(2) components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H(+)/H(-) pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal-free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three-component reactions, offering new strategies for synthetic chemistry.

1,621 citations

01 Jan 2008
TL;DR: Biosorption is emerging as a potential alternative to the existing conventional technologies for the removal and/or recovery of metal ions from aqueous solutions for heavy metal remediation.
Abstract: Heavy metal remediation of aqueous streams is of special concern due to recalcitrant and persistency of heavy metals in environment. Conventional treatment technologies for the removal of these toxic heavy metals are not economical and further generate huge quantity of toxic chemical sludge. Biosorption is emerging as a potential alternative to the existing conventional technologies for the removal and/or recovery of metal ions from aqueous solutions. The major advantages of biosorption over conventional treatment methods include: low cost, high efficiency, minimization of chemical or biological sludge, regeneration of biosorbents and possibility of metal recovery. Cellulosic agricultural waste materials are an abundant source for significant metal biosorption. The functional groups present in agricultural waste biomass viz. acetamido, alcoholic, carbonyl, phenolic, amido, amino, sulphydryl groups etc. have affinity for heavy metal ions to form metal complexes or chelates. The mechanism of biosorption process includes chemisorption, complexation, adsorption on surface, diffusion through pores and ion exchange etc. The purpose of this review article is to provide the scattered available information on various aspects of utilization of the agricultural waste materials for heavy metal removal. Agricultural waste material being highly efficient, low cost and renewable source of biomass can be exploited for heavy metal remediation. Further these biosorbents can be modified for better efficiency and multiple reuses to enhance their applicability at industrial scale.

1,245 citations

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TL;DR: In this paper, a white light-emitting electroluminescent devices were fabricated using poly(Nvinylcarbazole) (PVK) as a hole-transporting emitter layer and a double layer of 1,2,4−triazole derivative (TAZ) and tris(8quinolinolato)aluminum(III) complex (Alq) as an electron transport layer.
Abstract: White light‐emitting electroluminescent devices were fabricated using poly(N‐vinylcarbazole) (PVK) as a hole‐transporting emitter layer and a double layer of 1,2,4‐triazole derivative (TAZ) and tris(8‐quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. The PVK layer was doped with fluorescent dyes such as blue‐emitting 1,1,4,4‐tetraphenyl‐1,3‐butadiene, green‐emitting coumarin 6, and orange‐emitting DCM 1. A cell structure of glass substrate/indium‐tin‐oxide/doped PVK/TAZ/Alq/Mg:Ag was employed. White emission covering a wide range of the visible region and a high luminance of 3400 cd/m2 were obtained at a drive voltage of 14 V.

778 citations