C O M M U N I C A T I O N S
2
-
adsorbed on TiO
VB band edges. This results in an enhancement of hole transport
to O molecules upon excitation of the TiO , resulting in the
acceleration of the hole-mediated O desorption process (Figures
and 3, upper panels). Concomitantly, the upward band bending
produced by either Cl or O causes a diminution of the process
mediated by electrons, namely the CO oxidation reaction (Figures
and 3, lower panels).
2
(110), cause upward band bending at the CB and
agents for adsorbed CO as they are reduced to O . It is likely that
-
the electron-mediated process, leading to adsorbed O
2
excitation
2
2
to a peroxide, is also responsible for various photooxidation
reactions involving organic molecules on TiO under anhydrous
condition; more complex electron-mediated oxidation chemistry
2
2
2
2
5-27
2
2
occurs when water is present.
2
Figure 4. Schematic mechanism of O
TiO (110) during electronic excitation. Desorption of O
by holes; Reaction of O
created in the TiO
2
desorption and CO oxidation on
-
2
2
2
as O (g) is induced
-
2
to produce CO is induced by excited electrons
2
2
.
In summary, the production of electrons and holes can be tuned
using Cl and O as electron acceptors to cause upward band
bending of the VB and CB of TiO . A surface oxidation process
involving adsorbed oxygen), which depends on the excitation of
2
2
2
(
2
electrons in the bulk TiO , has been demonstrated, and it is shown
that adsorbed acceptor molecules may be used as surface modifiers
to modulate the rate of the oxidation process.
Acknowledgment. We acknowledge with thanks the support
of the Army Research Office (ARO) under Grant W911NF-09-1-
0371.
Figure 3. Plots of the initial yields of 18O
(upper panel) and C O O
2
lower panel) as a function of O exposure during electronic excitation of
16
18
2
1
8
(
16
16
14
-2
a C O layer. The preadsorbed C O exposure: 1.18 × 10 molecules cm
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2806 J. AM. CHEM. SOC. 9 VOL. 132, NO. 37, 2010