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Title: Role of Water in Methanol Photochemistry on Rutile TiO2(110)

Abstract

Photochemistry of the molecularly and dissociatively adsorbed forms of methanol on the vacuum-annealed rutile TiO2(110) surface was explored using temperature programmed desorption (TPD), both with and without coadsorbed water. Methoxy, and not methanol, was confirmed as the photochemically active form of adsorbed methanol on this surface. UV irradiation of methoxy-covered TiO2(110) lead to depletion of the methoxy coverage and formation of formaldehyde and a surface OH group. Coadsorbed water did not promote either molecular methanol photochemistry or thermal decomposition of methanol to methoxy. However, terminal OH groups (OHt), prepared by coadsorption of water and oxygen atoms, thermally converted molecularly adsorbed methanol to methoxy at 120 K, thus enabling photoactivity. While chemisorbed water molecules had no influence on methoxy photochemistry, water molecules hydrogen-bonded in the second layer to bridging oxygen (Obr) sites inhibited the methoxy photodecomposition to formaldehyde. From this we conclude that Obr sites accept protons from the hole-mediated conversion of methoxy to formaldehyde. These results provide new fundamental understanding of the hole-scavenging role of methanol in photochemical processes on TiO2-based materials and how water influences this photochemistry. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences.more » Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle under contract DEAC05-76RL01830. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.« less

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1052518
Report Number(s):
PNNL-SA-88003
47406; KC0302010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry C, 116(35):18788–18795
Additional Journal Information:
Journal Name: Journal of Physical Chemistry C, 116(35):18788–18795
Country of Publication:
United States
Language:
English
Subject:
TiO2; photochatalysis; methanol; Environmental Molecular Sciences Laboratory

Citation Formats

Shen, Mingmin, and Henderson, Michael A. Role of Water in Methanol Photochemistry on Rutile TiO2(110). United States: N. p., 2012. Web. doi:10.1021/jp3046774.
Shen, Mingmin, & Henderson, Michael A. Role of Water in Methanol Photochemistry on Rutile TiO2(110). United States. https://doi.org/10.1021/jp3046774
Shen, Mingmin, and Henderson, Michael A. 2012. "Role of Water in Methanol Photochemistry on Rutile TiO2(110)". United States. https://doi.org/10.1021/jp3046774.
@article{osti_1052518,
title = {Role of Water in Methanol Photochemistry on Rutile TiO2(110)},
author = {Shen, Mingmin and Henderson, Michael A},
abstractNote = {Photochemistry of the molecularly and dissociatively adsorbed forms of methanol on the vacuum-annealed rutile TiO2(110) surface was explored using temperature programmed desorption (TPD), both with and without coadsorbed water. Methoxy, and not methanol, was confirmed as the photochemically active form of adsorbed methanol on this surface. UV irradiation of methoxy-covered TiO2(110) lead to depletion of the methoxy coverage and formation of formaldehyde and a surface OH group. Coadsorbed water did not promote either molecular methanol photochemistry or thermal decomposition of methanol to methoxy. However, terminal OH groups (OHt), prepared by coadsorption of water and oxygen atoms, thermally converted molecularly adsorbed methanol to methoxy at 120 K, thus enabling photoactivity. While chemisorbed water molecules had no influence on methoxy photochemistry, water molecules hydrogen-bonded in the second layer to bridging oxygen (Obr) sites inhibited the methoxy photodecomposition to formaldehyde. From this we conclude that Obr sites accept protons from the hole-mediated conversion of methoxy to formaldehyde. These results provide new fundamental understanding of the hole-scavenging role of methanol in photochemical processes on TiO2-based materials and how water influences this photochemistry. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle under contract DEAC05-76RL01830. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.},
doi = {10.1021/jp3046774},
url = {https://www.osti.gov/biblio/1052518}, journal = {Journal of Physical Chemistry C, 116(35):18788–18795},
number = ,
volume = ,
place = {United States},
year = {Tue Aug 07 00:00:00 EDT 2012},
month = {Tue Aug 07 00:00:00 EDT 2012}
}