Photoreaction of Ethanol on TiO2(110) Single-Crystal Surface

P. M. Jayaweera, E. L. Quah, H. Idriss

Research output: Contribution to journalArticle

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Abstract

The adsorption, thermal, and UV reactions of ethanol over a TiO2(110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH3 and -CH2O- groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH3 and -CH2O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH3COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O-2(-) or O-2(2-) species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O-2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 x 10(-18) cm(-2) at 1 x 10(-6) Torr of O-2. This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.

Original languageEnglish
Pages (from-to)1764-1769
Number of pages6
JournalThe Journal of Physical Chemistry C
Volume111
Issue number4
Early online date4 Jan 2007
DOIs
Publication statusPublished - 1 Feb 2007

Cite this

Photoreaction of Ethanol on TiO2(110) Single-Crystal Surface. / Jayaweera, P. M.; Quah, E. L.; Idriss, H.

In: The Journal of Physical Chemistry C, Vol. 111, No. 4, 01.02.2007, p. 1764-1769.

Research output: Contribution to journalArticle

Jayaweera, P. M. ; Quah, E. L. ; Idriss, H. / Photoreaction of Ethanol on TiO2(110) Single-Crystal Surface. In: The Journal of Physical Chemistry C. 2007 ; Vol. 111, No. 4. pp. 1764-1769.
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title = "Photoreaction of Ethanol on TiO2(110) Single-Crystal Surface",
abstract = "The adsorption, thermal, and UV reactions of ethanol over a TiO2(110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH3 and -CH2O- groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH3 and -CH2O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH3COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O-2(-) or O-2(2-) species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O-2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 x 10(-18) cm(-2) at 1 x 10(-6) Torr of O-2. This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.",
author = "Jayaweera, {P. M.} and Quah, {E. L.} and H. Idriss",
note = "H.I. acknowledges a University of Auckland VC award no. 23229. P.M.J. acknowledges the University of Sri Jayewardenepura, Sri Lanka, for research leave at the University of Auckland.",
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T1 - Photoreaction of Ethanol on TiO2(110) Single-Crystal Surface

AU - Jayaweera, P. M.

AU - Quah, E. L.

AU - Idriss, H.

N1 - H.I. acknowledges a University of Auckland VC award no. 23229. P.M.J. acknowledges the University of Sri Jayewardenepura, Sri Lanka, for research leave at the University of Auckland.

PY - 2007/2/1

Y1 - 2007/2/1

N2 - The adsorption, thermal, and UV reactions of ethanol over a TiO2(110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH3 and -CH2O- groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH3 and -CH2O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH3COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O-2(-) or O-2(2-) species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O-2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 x 10(-18) cm(-2) at 1 x 10(-6) Torr of O-2. This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.

AB - The adsorption, thermal, and UV reactions of ethanol over a TiO2(110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH3 and -CH2O- groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH3 and -CH2O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH3COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O-2(-) or O-2(2-) species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O-2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 x 10(-18) cm(-2) at 1 x 10(-6) Torr of O-2. This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.

U2 - 10.1021/jp0657538

DO - 10.1021/jp0657538

M3 - Article

VL - 111

SP - 1764

EP - 1769

JO - The Journal of Physical Chemistry C

JF - The Journal of Physical Chemistry C

SN - 1932-7447

IS - 4

ER -