Ultraviolet and Visible Photochemistry of Methanol at 3D Mesoporous Networks: TiO2 and Au-TiO2
Abstract
Comparison of methanol photochemistry at three-dimensionally (3D) networked aerogels of TiO2 or Au-TiO2 reveals that incorporated Au nanoparticles strongly sensitize the oxide nanoarchitecture to visible light. Methanol dissociatively adsorbs at the surfaces of TiO2 and Au-TiO2 aerogels under dark, high-vacuum conditions. Upon irradiation of either ultraporous material with broadband UV light under anaerobic conditions, adsorbed methoxy groups act as hole-traps and extend conduction-band and shallow-trapped electron lifetimes. A higher excited-state electron density arises for UV-irradiated TiO2 aerogel relative to commercial nanoparticulate TiO2, indicating that 3D networked TiO2 more efficiently separates electron-hole pairs. Upon excitation with narrow-band visible light centered at 550 nm, long-lived excited-state electrons are evident on CH3OH-exposed Au-TiO2 aerogel--but not on identically dosed TiO2 aerogels--verifying that incorporated Au nanoparticles sensitize the networked oxide to visible light. Under aerobic conditions (20 Torr O2) and broadband UV illumination, surface-sited formates accumulate as adsorbed methoxy groups oxidize, at similar rates, on Au-TiO2 and TiO2 aerogels. Moving to excitation wavelengths longer than 400 nm (i.e., the low-energy range of UV light) dramatically decreases methoxy photoconversion for methanol-saturated TiO2 aerogel, while Au-TiO2 aerogel remains highly active for methanol photooxidation. The wavelength dependence of formate production on Au-TiO2 tracks the absorbance spectrum for this material, which peaks at = 550 nm due to resonance with the surface plasmon in the Au particles. The photooxidation rate for Au-TiO2 aerogel at 550 nm is comparable to that for TiO2 aerogel under broadband UV illumination, indicating efficient energy transfer from Au to TiO2 in the 3D mesoporous nanoarchitecture.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 23, 2013
- Accession Number
- ADA591306
Entities
People
- D. Panayotov
- Debra R. Rolison
- Jeremy J Pietron
- John R Morris
- Lindsey C Szymczak
- Paul A DeSario
- Todd Brintlinger
Organizations
- United States Naval Research Laboratory