Abstract

The adsorption, thermo- and photo-reactions of CH2Br2 on powdered TiO2 as well as the effects of H2O and/or O2 have been studied by Fourier-transform infrared spectroscopy. CH2Br2 is adsorbed molecularly on the surface at 35∘C, interacting with the surface OH groups. It is completely desorbed or decomposes to form CH3O(a) and HCOO(a) in a vacuum by 250∘C, probably via dioxymethylene (-OCH2O-). The presence of adsorbed H2O accelerates the formation of CH3O(a) and HCOO(a) from CH2Br2 dissociation. Adsorbed CH2Br2 decomposes to form CO(a), HCOO(a), CO3(a), and/or CO2(a) under 400 nm irradiation, depending on whether the presence of H2O and/or O2. The presence of O2 increases the photoreaction rate of CH2Br2(a) and the photodecomposition is further accelerated with addition of H2O.