title: Identification of binding sites for acetaldehyde adsorption on titania nanorod surfaces using CIMS.
abstract: The interaction of acetaldehyde with TiO(2) nanorods has been studied under low pressures (acetaldehyde partial pressure range 10(-4)-10(-8) Torr) using chemical ionization mass spectrometry (CIMS). We quantitatively separate irreversible adsorption, reversible adsorption, and an uptake of acetaldehyde assigned to a thermally activated surface reaction. We find that, at room temperature and 1.2 Torr total pressure, 2.1 ± 0.4 molecules/nm(2) adsorb irreversibly, but this value exhibits a sharp decrease as the analyte partial pressure is lowered below 4 × 10(-4) Torr, regardless of exposure time. The number of reversible binding sites at saturation amounts to 0.09 ± 0.02 molecules/nm(2) with a free energy of adsorption of 43.8 ± 0.2 kJ/mol. We complement our measurements with FTIR spectroscopy and identify the thermal dark reaction as a combination of an aldol condensation and an oxidative adsorption that converts acetaldehyde to acetate or formate and CO, at a measured combined initial rate of 7 ± 1 × 10(-4) molecules/nm(2) s. By characterizing binding to different types of sites under dark conditions in the absence of oxygen and gas phase water, we set the stage to analyze site-specific photoefficiencies involved in the light-assisted mineralization of acetaldehyde to CO(2).
authors: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors: Daniel
authors: D
authors: Finkelstein-Shapiro
authors: Avram M
authors: AM
authors: Buchbinder
authors: Baiju
authors: B
authors: Vijayan
authors: Kaustava
authors: K
authors: Bhattacharyya
authors: Eric
authors: E
authors: Weitz
authors: Franz M
authors: FM
authors: Geiger
authors: Kimberly A
authors: KA
authors: Gray
mesh_terms: D000079:Acetaldehyde / Q000737:chemistry*; D019342:Acetic Acid / Q000737:chemistry; D000327:Adsorption; D000393:Air Pollutants / Q000737:chemistry; D001665:Binding Sites; D002245:Carbon Dioxide / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry; D002384:Catalysis; D005561:Formates / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D043942:Nanotubes / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D018629:Spectrometry, Mass, Secondary Ion; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D005561:Formates; D014867:Water; C030544:formic acid; D002245:Carbon Dioxide; C009495:titanium dioxide; D002248:Carbon Monoxide; D014025:Titanium; D000079:Acetaldehyde; D019342:Acetic Acid; D010100:Oxygen