Adsorption and thermal decomposition of 2-chloroethyl ethyl sulfide on TiO2 surfaces

The adsorption, desorption, and oxidative decomposition of the 2-chloroethyl ethyl sulfide molecule (2-CEES) has been investigated on the TiO2(110) surface as well as on high area anatase and rutile powdered samples. A combination of measurement tools has been employed. It has been found that a monolayer of 2-CEES desorbs in the temperature range from 275 to 400 K with an activation energy of 105 kJ/mol. Weak repulsive interactions are measured in the monolayer. The molecule may be oxidized both by Ti-OH groups on anatase or rutile and by lattice oxygen in the TiO2. Attack at the C-S bonds occurs as chloroethoxy and ethoxy groups are produced. At about 570 K these species further oxidize to form adsorbed COO and CO3 species. The involvement of lattice oxygen in these reactions near 600 K has been observed by measurements of the background level in the infrared spectrum that may be used to measure the formation of trapped electron states at Ti3+ centers formed when adsorbate oxidation occurs by consumption of lattice oxygen. Upon heating to 900 K in vacuum, oxidation products on the TiO2 surface are completely removed. Little difference in the reactivity patterns for anatase and rutile is found in this work.