Adsorption States and Mobility of TMAA Molecules on Reduced TiO2(110) Surface
Combined scanning tunneling microscopy (STM), x-rays photoelectron spectroscopy (XPS) and density functional theory (DFT) studies have probed the bonding configurations and mobility of trimethylacetic acid (TMAA) molecules on TiO2(100) surface at RT. Upon TMAA dissociation through deprotonation, two distinctly different types of stable chemisorption configurations of the carboxylate group (TMA) have been identified accordingly to their position and appearance in STM images. In configuration A, two carboxylate O atoms bonds to two Ti4+ cations, while in configuration B one O atom fills the bridging oxygen vacancy (VO) with the other O bounded at an adjacent regular Ti4+ site. Calculated adsorption energies for the configurations A and B are comparable at 1.28 and 1.36 eV, respectively. DFT results also show that TMA may rotate at RT about its O atom that filled the VO (in configuration B), with a rotation barrier of ~0.65 eV. Both the observation of the constant initial sticking coefficient and preference for TMAA molecules to dissociate at selective sites indicate that TMAA adsorption is mediated by a mobile precursor state. Several possible molecular (physisorbed) states of TMAA have indeed been identified by DFT, all being a highly mobile at RT. In contrast, the TMA diffusion in chemisorbed (dissociative) state is a very slow with calculated barrier of 1.09 eV for diffusion along the Ti row.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 982562
- Report Number(s):
- PNNL-SA-68203; 30194; 35219; KP1704020; TRN: US201014%%385
- Journal Information:
- Physical Chemistry Chemical Physics. PCCP, 12(23):5986-5992, Vol. 12, Issue 23
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ADSORPTION
ATOMS
BONDING
CATIONS
CHEMISORPTION
CONFIGURATION
DIFFUSION
DISSOCIATION
FUNCTIONALS
OXYGEN
PHOTOELECTRON SPECTROSCOPY
PIVALIC ACID
PRECURSOR
ROTATION
SCANNING TUNNELING MICROSCOPY
X-RAY PHOTOELECTRON SPECTROSCOPY
TiO2
O2
H2O
STM
DFT
Environmental Molecular Sciences Laboratory