CH2I2adsorption and reactions on TiO2

Abstract

Fourier-transform infrared spectroscopy has been employed to study the adsorption, thermal transformation, and photoreactions of CH₂I₂ on powdered TiO₂. At 35 °C, CH₂I₂ is adsorbed molecularly or dissociatively to form a surface species with CH_x and C–O functional groups possibly derived from C–I bond scission of CH₂I₂. As the surface temperature is raised above 100 °C, the adsorbed CH₂I₂ is transformed into CH₃O_(a) and HCOO_(a) simultaneously, very likely via disproportionation of the reaction intermediate of dioxymethylene (–OCH₂O–). Under UV irradiation in the presence of O₂, adsorbed CH₂I₂ on TiO₂ decomposes to form CO_(a), HCOO_(a), H₂O_(a), and CO_2(g). But the CH₂I₂ photoreaction is almost terminated in the absence of O₂. The possible initiation species involved in the CH₂I₂ photodecomposition is discussed.