Methylene bromide chemistry and photochemistry on rutile TiO₂(110)

Journal Article · Sat Oct 01 04:00:00 EDT 2011 · Surface Science

DOI:https://doi.org/10.1016/j.susc.2011.06.020· OSTI ID:1025065

Henderson, Michael A.; Robbins, Matthew D.

The chemistry and photochemistry of methylene bromide (CD₂Br₂) on the rutile TiO₂(110) surface was probed using temperature programmed desorption (TPD). CD₂Br₂ desorbed in three desorption states at 145, 160 and 250 K tentatively assigned to desorption from the multilayer, from an η¹-CD₂Br₂ species and a bridging η²-CD₂Br₂ species, respectively. The latter two TPD states presumably involve binding of CD₂Br₂ molecules to the surface through Br coordination at five-coordinate Ti⁴⁺ surface sites. The 160 and 250 K TPD states saturated at coverages of 1.0 and 0.33 ML, respectively, where 1 ML is equivalent to the surface Ti⁴⁺ site density (5.2 × 10¹⁴ cm^{- 2}). No thermal decomposition of CD₂Br₂ was observed on either the clean surface or with preadsorbed O₂. UV irradiation of CD₂Br₂ on TiO₂(110) resulted in predominately photodesorption, with trace amounts of photodecomposition evidenced in TPD. The rate of CD₂Br₂ photodesorption from TiO₂(110) occurred with a low cross section (~ 2 × 10^{- 21} cm²) similar to that expected from direct optical excitation of CD₂Br₂. This observation suggests that charge carriers generated in TiO₂(110) were no more effective in activating adsorbed CD₂Br₂ molecules than would be expected through direct molecular excitation. Finally, these findings suggest that photocatalytic destruction of halocarbons such as CD₂Br₂ on TiO₂ may preferentially occur though indirect processes (such as OH radical attack) as opposed to direct electron transfer processes involving charge carriers generated in TiO₂ by bandgap excitation.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1025065
• Report Number(s): PNNL-SA-79403; 35219; KC0302010
• Journal Information: Surface Science, Journal Name: Surface Science Journal Issue: 19-20 Vol. 605; ISSN 0039-6028
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
BROMIDES
CHARGE CARRIERS
CHEMISTRY
CROSS SECTIONS
DESORPTION
EXCITATION
Environmental Molecular Sciences Laboratory
IRRADIATION
Methylene Bromide
PHOTOCHEMISTRY
PYROLYSIS
Photocatalysis
RADICALS
RUTILE
TRACE AMOUNTS
TiO2