Wet electrons at metal oxide surfaces
EMSL Project ID
13894
Abstract
Recently we have undertaken a time-resolved two-photon photoemission study of primary processes in photocatalytic reactions on TiO2. In the course of this study we have discovered excited electronic states with energy of ~2.2-2.5 eV above the Fermi level that appear when water and methanol are adsorbed on reduced rutile TiO2 surfaces. Based on our DFT calculations of the same systems, we assign these states to partially solvated or ?wet? electrons, which are bound primarily to surface OH, and to lesser extent to other dangling (not hydrogen bonded) H atoms that exist on oxide surfaces in hydrous environments. Time resolved photoemission measurements indicate excited state lifetimes that extend from few femtoseconds to picoseconds, depending on the adsorbate and coverage. We expect that similar partially solvated electron states exist on most, if not all, hydroxylated metal and semiconductor oxide surfaces, and that their energy depends on material specific factors such as the distance and geometry of surface OH. Solvated electrons that are generated thermally or through electronic excitation (light, energetic particles) could play an important role in many problems of environmental and technological interest, such as photocatalysis, catalysis, corrosion, electrochemistry, atmospheric photochemistry, environmental remediation, etc.We propose to extend our theoretical studies to other surfaces and polymorphs of TiO2, e.g. anatase, and other environmentally and technologically important oxide surfaces (SiO2, Fe2O3, etc). We expect to obtain information on how the stabilization of the wet electron state depends on material specific factors such at the lattice parameters of the unit cell (OH ? OH distance), the dipole moment of the surface, and the angle of the OH bond with respect to the surface plane. With the computing resources at EMSL we plan to theoretically investigate the properties of the solvated state on the different hydroxylated oxide surfaces. For this extended electronic structure calculation, we may need to handle hundreds of atoms to describe unit cells with multiple adsorbates with different concentrations (e.g. partially dissociated water), which place significant demand on the computational resources at the DFT level. Furthermore, because the surface solvated electron is an excited state, we also need to perform time-dependent theory to get more reliable results, which will require more resources.
In parallel with studies of electronic structure for different materials, we also want to initiate a theoretical study the dynamical properties of partially solvated electrons. In particular, we believe that the solvated electrons present an experimentally and theoretically tractable model for interfacial electron transfer that is relevant to electrochemistry, catalysis, corrosion, etc. Therefore, we expect that systematic studies of the electronic structure and electron transfer rates from the solvated electron to the bulk oxide will provide substantial insight into these more complex phenomena. We will perform these dynamical simulations by linear time-dependent DFT and molecular dynamics. Accurate calculations of couplings between different electronic states require highly accurate wavefunctions and their derivatives with respect to coordinates. Due to the computational resource limitations, such calculations are not possible with the available resources at the Center for Molecular and Materials Simulations, at the University of Pittsburgh and will benefit from the more substantial resources at the EMSL.
Project Details
Project type
Capability Research
Start Date
2005-03-17
End Date
2007-06-26
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Self-energy and excitonic effects in the electronic and optical properties ofTiO2crystalline phases
L. Chiodo, J.-M. García-Lastra, A. Iacomino, S. Ossicini, J. Zhao, H. Petek and A. Rubio, 2010. "Self-Energy and Excitonic Effects in the Electronic and Optical Properties of TiO2 Crystalline Phases." Phys. Rev. B 82:045207. published 7/22/2010. DOI: 10.1103/PhysRevB.82.045207
Ultrafast Interfacial Proton-Coupled Electron Transfer
Petek H, and J Zhao. 2010. "Ultrafast Interfacial Proton-Coupled Electron Transfer." Chemical Reviews 110(12):7082-7099. doi:10.1021/cr1001595).
Theoretical study of the molecular and electronic structure of methanol on aTiO2(110)surface
Jin Zhao, Jinlong Yang and Hrvoje Petek. 2009. "Theoretical study of the molecular and electronic structure of methanol on a TiO2(110) surface." Phys. Rev. B 80(23):235416. DOI:10.1103/PhysRevB.80.235416
Published 12/10/2009.
Published 12/10/2009.