Photodestruction of CCl₄ on MgO Films with/without Water

Abstract

Ultrahigh-vacuum (UHV) studies show that UV irradiation (193 nm) of carbon tetrachloride adsorbed on a MgO surface produces phosgene both with/without coadsorbed water. Isotope studies show the oxygen required for the phosgene formation comes from the MgO lattice in the absence of water and from the water when coadsorbed. The reaction kinetics differ strongly between the wet and dry conditions. The observations suggest that UHV studies can reproduce important features seen in bulk studies of oxides for destruction of environmental hydrocarbons and that surface reactions may play a more important role in air or aqueous photocatalytic destruction of hydrocarbons than typically assumed.

Theoretical Studies of Solid−Liquid Interfaces: Molecular Interactions at the MgO(001)−Water Interface

“…The calculated binding energy of water at the clean MgO(001) surface (14.2 kcal/mol) agrees well with a number of experimental estimates ranging from 10 to 19 kcal/mol. [67][68][69][70][71] This is also consistent with results of ab initio periodic Hartree-Fock 37 (17.3 kcal/mol) and other embedded cluster 24 (14.3-14.8 The average structure of H 2 O adsorbed at the MgO-water interface (see Table 1) is slightly different from that at the MgO-vacuum interface. The noticeable difference is an increase in the tilt angle by 3.3°.…”

EPR study of spin-trapped free radical intermediates formed in the heterogeneously-assisted photodecomposition of acetaldehyde †

“…The observation that the production of all radical species is greatest in irradiated MgO suspensions demonstrates unequivocally that band gap transitions are not responsible for the observed photochemistry; the promotion of an electron across the MgO band gap (7.8 eV) requiring the absorption of a photon with λ р 160 nm. 29 A clear trend emerges in the relationship between extent of radical production/spin trap oxidation and surface basicity of the oxide studied; the production of both acetaldehyde derived radicals and PBN-Ox increasing along the series representing an increase in surface basicity; TiO 2 (AlPO 4 coat), TiO 2 , MgO. The relative changes in primary radical adduct signal intensity are 0.6 : 1 : 3 respectively.…”

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms

“…In contrast, many experimental studies performed under UHV conditions with low concentrations of water at the interface show little or no indication of surface hydroxylation. 15 The extensive number of experimental 15,65,100,[102][103][104][105][107][108][109][110][768][769][770][771][772][773][774][775][776][777][778][779] and theoretical studies [96][97][98]106,748,754,763,775,[780][781][782][783][784][785][786][787][788][789][790][791][792][793] that probed the structure and reactivity of MgO (100) and the chemistry of water on MgO illustrates the complexity of this "simple" system. Empirical observations of molecular adsorption and chemidissociation vary depending on the experimental m...…”