Pathways of photocatalytic gas phase destruction of HD simulant 2-chloroethyl ethyl sulfide

Photocatalytic oxidation of HD simulant, 2-chloroethyl ethyl sulfide (CEES), was studied in a specially designed coil and flow photocatalytic reactor by means of GC-MS and FTIR techniques. TiO₂ Hombikat UV 100 photocatalyst was deactivated after a few hours of operation, which was signaled by the appearance of incomplete oxidation products in the reactor effluent and accumulation of incomplete oxidation products on the TiO ₂ surface. Complete reactivation of the photocatalyst was achieved by washing the photocatalyst with water. Compared to diethyl sulfide, CEES showed lower reactivity in photocatalytic oxidation and was accumulated on the TiO₂ surface after catalyst deactivation. Without UV irradiation, hydrolysis of CEES proceeded on the TiO₂ surface. Major gaseous products of CEES incomplete photocatalytic oxidation are acetaldehyde, chloroacetaldehyde, SO₂, diethyl disulfide, and chloroethylene. Surface products extracted from the TiO₂ surface with acetonitrile and water include mainly 2-chloroethyl ethyl sulfoxide and ethanesulfinic and ethanesulfonic acids, as well as diethyl di-, tri-, and tetrasulfides mono and disubstituted in the β position with a chlorine or hydroxyl group. While surface monodentate sulfates can be removed upon washing, surface bidentate species stayed on the surface and possibly contribute to the permanent catalyst deactivation.