Band Edge Dynamics in CdSe Nanocrystals Observed by Ultrafast Fluorescence Upconversion

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• 作者：Maria Danielle Garrett ; Michael J. Bowers ; II ; James R.McBride ; Rebecca L. Orndorff ; Stephen J. Pennycook ; and ; Sandra J. Rosenthal
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：April 17, 2008
• 年：2008
• 卷：112
• 期：15
• 页码：6212 - 6212
• 全文大小：9K
• 年卷期：v.112,no.15(April 17, 2008)
• ISSN：1932-7455

文摘

We present a modular approach to the synthesis of nanostructured catalysts for photochemical splitting ofwater into hydrogen and oxygen. The catalysts are built from exfoliated, semiconducting niobate nanosheetsderived from the layered perovskite HCa₂Nb₃O₁₀. The latter is a catalyst for photochemical evolution ofhydrogen from water under UV irradiation. After chemical modification with 3-aminopropyltrimethoxysilane(APS), IrO₂ or Pt particles can be attached to the nanosheets to produce various two-component nanostructuresthat were fully characterized with transmission electron microscopy and ultraviolet and infrared spectroscopy.Cyclic voltammetry was used to determine the onset potentials for O₂ and H₂ evolution. At pH = 14, theobserved values are in the range +0.61 to +1.24 V (NHE, water oxidation) and -1.36 to -1.62 V (NHE,water reduction). Under UV irradiation, all catalysts evolve hydrogen from water without any sign ofdeactivation for 5 h. The highest quantum efficiency of 3.49% is observed for a structure with Pt directlygrown onto the nanosheets. No O₂ is evolved, which we attribute to the adsorption of O₂ to the catalystsurface. For Pt-[HCa₂Nb₃O₁₀], this process starts to shut down H₂ evolution after 9 h of constant irradiation,but the activity can be restored to >60% by evacuating the catalyst dispersion and purging it with Ar. Catalystsassembled from preformed citrate-coated Pt nanoparticles are slightly less active for H₂ evolution and so arecatalysts that use the linker aminoethyl-aminoundecanetrimethoxysilane (AEAUS) instead of APS. The activityof IrO₂-APS-[Ca₂Nb₃O₁₀] is lowest among two component catalysts, near the activities of the pure or APS-modified nanosheets. On the basis of XPS data, IrO₂ in this catalyst undergoes photochemical reduction toIr(0) upon UV irradiation.