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Synthesis and characterization of li...

Allen, Mark Ryan.

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Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting./
Author:	Allen, Mark Ryan.
Description:	152 p.
Notes:	Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6771.
Contained By:	Dissertation Abstracts International71-11B.
Subject:	Chemistry, Inorganic. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3426007
ISBN:	9781124260068

Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting.
Allen, Mark Ryan.

Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting. - 152 p.

Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6771.

Thesis (Ph.D.)--University of California, Davis, 2010.

This work describes both the fabrication of LiMo3Se3 nanowire films and assessment their ability to detect analytes in aqueous solution, and the construction of layered photocatalysts, including heterojunction multicomponent materials, from K2Ti4O9, KCa 2Nb3O10, and K4Nb6O 17 nanosheets, and the characterization of these for their photocatalytic water splitting properties.

ISBN: 9781124260068Subjects--Topical Terms:

517253
Chemistry, Inorganic.

Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting.
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020 $a 9781124260068
035 $a (MiAaPQ)AAI3426007
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100 1 $a Allen, Mark Ryan. $3 2098640
245 1 0 $a Synthesis and characterization of lithium molybdenum selenide nanowires for chemical sensing applications and of nanosheets derived from potassium tetratitanate, potassium calcium niobate, and potassium niobate for photocatalytic water splitting.
300 $a 152 p.
500 $a Source: Dissertation Abstracts International, Volume: 71-11, Section: B, page: 6771.
500 $a Adviser: Frank E. Osterloh.
502 $a Thesis (Ph.D.)--University of California, Davis, 2010.
520 $a This work describes both the fabrication of LiMo3Se3 nanowire films and assessment their ability to detect analytes in aqueous solution, and the construction of layered photocatalysts, including heterojunction multicomponent materials, from K2Ti4O9, KCa 2Nb3O10, and K4Nb6O 17 nanosheets, and the characterization of these for their photocatalytic water splitting properties.
520 $a The LiMo3Se3 nanowire film sensors were conceived by drop-coating a 0.05% (mass) aqueous nanowire solution onto microfabricated indium tin oxide electrode pairs. According to scanning electron microscopy (SEM) and atomic force microscopy (AFM), the films are made of a dense network of 3-7 nm thick nanowire bundles. Immersion of the films in 1.0 M aqueous solutions of group 1 or 2 metal halides or of Zn(II), Mn(II), Fe(II), or Co(II) chlorides results in an increase of the electrical resistance of the films. The resistance change is always positive and reaches up to 9% of the base resistance of the films. It occurs over the course of 30-240 s, and it is reversible for monovalent ions and partially reversible for divalent ions. The signal depends on the concentration of the electrolyte and on the size and charge of the metal cation. Anions do not play a significant role, presumably because they are repelled by the negatively charged nanowire strands. The magnitude of the electrical response and its sign suggest that it is due to analyte-induced scattering of conduction electrons in the nanowires. An ion-induced field effect can be excluded based on gated conductance measurements of the nanowire films.
520 $a The tetratitanate K2Ti4O9 has been known as a photocatalyst for the oxidation of methanol under UV irradiation. Here we study the evolution of the morphological, optical, and photocatalytic properties of this titanate as it is converted into H2Ti4O 9 and subsequently exfoliated into individual tetrabutylammonium (TBA)-supported [Ti4O9]-2 nanosheets. We find that proton exchange and exfoliation are accompanied by a red shift of the optical absorption edge and fluorescence maximum, suggesting a reduction of the bandgap in the series K2Ti4O9 (3.54 eV), H2Ti 4O9 (3.25 eV), (TBA)2[Ti4O9] (3.00 eV). Neither compound is active for photochemical water splitting, even after photochemical deposition of platinum nanoparticles. However, in aqueous methanol, all platinated compounds are moderately active for H2 evolution upon bandgap irradiation, and in 0.01 M AgNO3, they all produce moderate quantities of O2. From the onset potentials for photoelectrochemical methanol oxidation, the values for the valence band edges at pH 7 are deduced to be lie between -0.23 and -0.53 V (NHE) for the non-platinated compounds, and at +0.08 V and -0.30 V for the platinated compounds. This Pt-induced decrease of negative charge on the titanates is likely due to Fermi level equilibration of metal and semiconductor. Its effect can also be seen in a shift of the onset potentials for electrochemical water oxidation, as measured by cyclic voltammetry. Transient absorption data reveal that photogenerated electrons are trapped in mid band gap states, from which they decay exponentially with a time-constant of 43.67 +/- 0.28 ms, much slower than observed for 68 +/- 1 ns for TiO2 nanocrystals (Degussa, P25).
520 $a Heterojunction multicomponent photocatalysts have been shown to possess enhanced charge separation upon photoexcitation. Nanostructured heterojunctions were prepared through soft chemical routes from nanosheets derived from the parent vi compounds K2Ti4O9, KCa2Nb 3O10, and K4Nb6O17. Five composites in total, consisting of either one or two types of nanosheets, were synthesized by precipitation of the precursor nanosheets with KOH. Resultant stacked materials were confirmed with transmission electron microscopy and characterized via powder x-ray diffraction. The layered catalysts were found to be inactive for photocatalytic water splitting under illumination of ultraviolet light. However, when irradiated in aqueous methanol, all five materials did yield substantial amounts of H2 gas. Photochemical deposition of platinum nanoparticles onto the materials resulted in them all being active toward evolving H2 when irradiated in both water and in aqueous methanol. Photocatalytic activity of the restacked materials comprised of two types of nanosheets were compared to the single-component catalysts and discussed in context of experimentally determined valence band edges of the single-component catalysts.
590 $a School code: 0029.
650 4 $a Chemistry, Inorganic. $3 517253
650 4 $a Nanotechnology. $3 526235
690 $a 0488
690 $a 0652
710 2 $a University of California, Davis. $b Chemistry. $3 1679244
773 0 $t Dissertation Abstracts International $g 71-11B.
790 $a 0029
791 $a Ph.D.
792 $a 2010
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3426007