Final Technical Report

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Our research has as its primary objective the development and mechanistic investigation of suitable photocatalytic surfaces, as mediators of energy-efficient heterogeneous oxidation of aliphatic hydrocarbons. Particular emphasis is placed on mixed iron(III)/titanium(IV) oxide semiconductor particulates, featuring low %Fe content, for which a novel synthetic protocol has been developed in this laboratory, relying on sol-gel hydrolysis of high purity iron and titanium isopropoxide precursors, followed by thermal treatment to develop the active anatase phase. This methodology leads to replacement of Ti(IV) ions by Fe(III) sites in the TiO{sub 2} (anatase) lattice, and is contrasted to samples prepared by physical mixing of ... continued below

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13 pages

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Stavropoulos, Pericles March 4, 2004.

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Description

Our research has as its primary objective the development and mechanistic investigation of suitable photocatalytic surfaces, as mediators of energy-efficient heterogeneous oxidation of aliphatic hydrocarbons. Particular emphasis is placed on mixed iron(III)/titanium(IV) oxide semiconductor particulates, featuring low %Fe content, for which a novel synthetic protocol has been developed in this laboratory, relying on sol-gel hydrolysis of high purity iron and titanium isopropoxide precursors, followed by thermal treatment to develop the active anatase phase. This methodology leads to replacement of Ti(IV) ions by Fe(III) sites in the TiO{sub 2} (anatase) lattice, and is contrasted to samples prepared by physical mixing of nanometer-sized a-Fe{sub 2}O{sub 3} (gift from MACH I, Inc.) and TiO{sub 2} (Degussa P-25). Mechanistic understanding of these systems involves multifaceted approaches. Our unique ability to evaluate charge-carrier separation distances, as measured by time-resolved photocharge experiments (TRPC) on instrumentation pioneered by Dr. Levy, permits correlation of this important photophysical property to photocatalytic efficiency and reaction mechanism. A major redesign of our benchmark TRPC apparatus was recently undertaken, which provides for controlled environments during measurement, i.e., vacuum; controlled atmosphere (inert or reactive); and temperature control (-100 to +150 C). Operation of this new TRPC cell necessitated insulation from RF noise, which was achieved by employing a walk-in Faraday enclosure to house the apparatus and supporting instrumentation. Previous work has shown that charge-carrier separation distances (CCSD) for Pt dopped TiO{sub 2} pass through a maximum at very low %Pt content. A similar region of maximum CCSD has now been tentatively identified with samples of a-Fe{sub 2}O{sub 3}/TiO{sub 2} (0-0.02 %Fe) under ambient conditions. Interestingly, the decay portion of the TRPC waveform (charge recombination) exhibits significant delay, by an order of magnitude, under vacuum conditions. Under high vacuum (10{sup -7} torr), reversal of the signal sign is frequently observed, further underscoring the importance of the surface condition in controlling CCSD values. Experimentation with inert gas atmospheres is currently under way to assist in the interpretation of these observations. Surprisingly, maximum CCSD values have been shown not to correlate always with maximum photocatalytic activity in the oxidation of hydrocarbons. As the oxidation products derive from precursors that combine radical species generated via the action of both photoholes (organic peroxyl radicals) and photoelectrons (superoxide), it is postulated that the maximum in photocatalytic activity will occur at a balance point between maximum CCSD and minimum distance crossover for the resulting radicals. The generality of this premise with respect to the present iron-dopped TiO{sub 2} preparations remains to be verified.

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13 pages

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OSTI as DE00821786

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  • Other Information: PBD: 4 Mar 2004

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  • Report No.: DOE/ER/14978-1
  • Grant Number: FG02-99ER14978
  • DOI: 10.2172/821786 | External Link
  • Office of Scientific & Technical Information Report Number: 821786
  • Archival Resource Key: ark:/67531/metadc787645

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  • March 4, 2004

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • June 10, 2016, 6:23 p.m.

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Stavropoulos, Pericles. Final Technical Report, report, March 4, 2004; United States. (digital.library.unt.edu/ark:/67531/metadc787645/: accessed August 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.