Reactions of hydroxyl radicals on titania, silica, alumina, and gold surfaces
Journal Article
·
· Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Reaction probabilities of OH{sup {sm_bullet}} radicals under steady state conditions were determined over TiO{sub 2} (anatase and rutile), SiO{sub 2} (fused quartz), {alpha}-Al{sub 2}O{sub 3}, and Au surfaces. The OH{sup {sm_bullet}} radicals were produced from water in a microwave cavity and were detected by laser-induced fluorescence spectroscopy. At 308 K the reaction probabilities were 2 x 10{sup {minus}4} for TiO{sub 2} (anatase and rutile), 2 x 10{sup {minus}3} for SiO{sub 2}, 5 x 10{sup {minus}3} for {alpha}-Al{sub 2}O{sub 3} and > 3 x 10{sup {minus}2} for Au. The relative rate of H{sub 2}O{sub 2}(aq) decomposition was found to follow the sequence Au > {alpha}-Al{sub 2}O{sub 3} > TiO{sub 2} {approx_equal} SiO{sub 2}, which, except for TiO{sub 2}, follows the sequence found for the OH{sup {sm_bullet}} radical reaction probability. For all of the materials except TiO{sub 2}, a radical mechanism is proposed which describes a common set of reactions for the removal of OH{sup {sm_bullet}} and the decomposition of H{sub 2}O{sub 2}. The first step in this mechanism is the coupling of OH{sup {sm_bullet}} radicals to form H{sub 2}O{sub 2}. The overall rate of reaction for both OH{sup {sm_bullet}} removal and H{sub 2}O{sub 2} decomposition depends on the concentration of OH on the surface. A theoretical analysis using a cluster model for an Au surface has shown that the OH-Au chemisorption bond is dominantly ionic with the OH radical becoming an OH{sup {minus}} anion. The adsorption energy may be as large as 155 kJ mol{sup {minus}1}. With TiO{sub 2} as a catalyst and H{sub 2}O{sub 2} as a reagent, an alternate mechanism that involves redox chemistry is believed to occur.
- Research Organization:
- Texas A and M Univ., College Station, TX (US)
- OSTI ID:
- 20026928
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 12 Vol. 104; ISSN 1089-5647; ISSN JPCBFK
- Country of Publication:
- United States
- Language:
- English
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