Photocatalytic Degradation of Some Methyl Perfluoroalkyl Ethers on TiO₂ Particles in Air:  The Dependence on the Dark-Adsorption, the Products, and the Implication for a Possible Tropospheric Sink

Fluorinated ethers are potential substitutes for hydrochlorofluorocarbons and hydrofluorocarbons. Their lifetime through each removal process should be evaluated to estimate their effects on the environment as GWP. Photocatalytic reactions on titanium dioxide particles were examined as a possible tropospheric sink through heterogeneous processes on particulate matters. Photocatalytic degradation of three kinds of methyl perfluoroalkyl ethers in air takes place on titanium dioxide particles at ambient temperature under illumination of light (>300 nm). Main products are carbon dioxide and carbonyl fluoride. The initial photodegradation rate is proportional to the square root of the amount of fluorinated ethers adsorbed in the dark, while the adsorption shows a Henry type adsorption curve. A tentative reaction scheme via H atom abstraction and a formic ester is proposed. The kinetic data indicates that the heterogeneous photodegradation could proceed with a rate enough to serve as a tropospheric sink of fluorinated ethers even in such low density of titanium dioxide particles as in the environment.