Substoichiometric titanium oxide Ti2O3 exhibits greater efficiency in enhancing hydrolysis of 1,1,2,2-tetrachloroethane than TiO2 nanomaterials

Oxygen-deficient substoichiometric titanium oxides, or “titanium suboxides,” are produced incidentally from coal combustion and are environmentally abundant. Additionally, titanium suboxide nanomaterials are promising new materials with likely future environmental release. How these materials may affect contaminant fate differently than stoichiometric TiO 2 (nano)materials is largely unknown. Here, we show that Ti 2 O 3 (selected as a model titanium suboxide) exhibits significantly greater efficiency in enhancing the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, than the stoichiometric anatase and rutile TiO 2 . At environmentally relevant pH (6.5–7.5), the surface area-normalized pseudo-first-order hydrolysis rate constant in the presence of Ti 2 O 3 is approximately an order of magnitude higher than those associated with TiO 2 . The superior catalytic efficiency of Ti 2 O 3 can be attributed to both its higher surface hydrophobicity , which renders higher adsorption affinity for TeCA, and its higher concentration of Lewis acid sites (mainly the Ti 3+ and the five-coordinated Ti 4+ ). Particularly, the deprotonated hydroxyl groups attached to Ti 3+ (a weaker Lewis acid than Ti 4+ ) exhibit higher basicity and thus, are more effective in catalyzing the base-promoted hydrolysis reaction. The findings call for further understanding of the environmental implications of titanium suboxide (nano)materials, which may not be readily predictable based on the knowledge acquired for TiO 2 .