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Simultaneous control of the size and chemical composition is an advantageous strategy to obtain the desired photochemical properties of multinary semiconductor nanocrystals, ZnS-AgInS2 solid solution ((AgIn) x Zn2(1–x)S2, ZAIS) nanocrystals (NCs), being different from conventional binary nanocrystals. The energy gap (E g) of ZAIS NCs was enlarged with a decrease in particle size due to the quantum size effect or with an increase in ZnS content in the ZAIS solid solution. The levels of the conduction band edge and valence band edge, determined by photoelectron spectroscopy in air, were shifted more negatively and more positively, respectively, with an increase in E g. A volcano-type dependence was observed between the PL quantum yield (QY) and the size of ZAIS NCs, in which the optimal PL QY for each x value was obtained at a similar particle size around 5–6 nm, except for x = 1.0, and maximum QY was recorded to be 79% for ZAIS NCs prepared with x = 0.5. The photocatalytic activity for H2 evolution was also greatly dependent on both the size and the chemical composition of ZAIS NCs, and then the highest activity was observed for ZAIS NCs having an average diameter of about 4.2–5.5 nm and E g of 2.3–2.4 eV. This can be reasonably explained by the enlargement of the driving force to reduce protons in the solution with a negative shift of the conduction band edge of ZAIS NCs and by the quenching of photoexcited ZAIS NCs with an increase in the amount of surface defect sites and/or with the formation of deeper trap sites along with a decrease in the particle size.

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A novel strategy to prepare a bimetallic Au-Pt particle film was developed through sequential sputter deposition of Au and Pt on a room temperature ionic liquid (RTIL). Au sputter deposition onto an RTIL containing hydroxyl-functionalized cations produced a monolayer of Au particles 4.2 nm in size on the liquid surface. Subsequent Pt sputtering onto the original Au particle monolayer floating on the RTIL enabled decoration of individual Au particles with Pt metals, resulting in the formation of a bimetallic Au-Pt particle monolayer with a Pt-enriched particle surface. The particle size slightly increased to 4.8 nm with Pt deposition for 120 min. The shell layer of a bimetallic particle was composed of Au-Pt alloy, the composition of which was tunable by controlling the Pt sputter deposition time. The electrochemical surface area (ECSA) was determined by cyclic voltammetry of bimetallic Au-Pt particle monolayers transferred onto HOPG electrodes by a horizontal liftoff method. The Pt surface coverage, determined by ECSAs of Au and Pt, increased from 0 to 56 mol % with elapse of the Pt sputter deposition time up to 120 min. Thus-obtained Au-Pt particle films exhibited electrocatalytic activity for methanol oxidation reaction (MOR) superior to the activities of pure Au or Pt particles. Volcano-type dependence was observed between the MOR activity and Pt surface coverage on the particles. Maximum activity was obtained for Au-Pt particles with a Pt coverage of 49 mol %, being ca. 120 times higher than that of pure Pt particles. This method enables direct decoration of metal particles with different noble metal atoms, providing a novel strategy to develop highly efficient multinary particle catalysts.

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ABSTRACT:Thermal reactions of N-phenylmaleimide (PMI) and o-allylphenol (AP) or diallylbisphenol-A (DABA) were investigated using 13 C NMR and GPC in order to obtain information on the curing of bismaleimidodiphenylmethane (BMI) with DABA, widely used as thermosetting bismaleimide resins. In the thermal reactions of PMI and AP, I : I and 3: I adducts were generated through ene-reaction and sequential Diels-Alder reactions accompanying the polymer of PMI and AP. The products from PMI and DABA were the ene-adduct and polymer but the Diels-Alder adduct could not be detected, in contrast to PMI/AP system. This difference in reactivity for PMI-AP and PMI-DABA may be due to steric repulsion of DABA and is discussed briefly by AM I molecular orbital calculations.