Hydroxylation of TiO2-B: insights from density functional calculations

Density functional calculations are carried out to investigate the
interaction of water with the low-index stoichiometric surfaces of the
TiO2-B polymorph of titanium dioxide. Dissociative adsorption is
predicted for the (100) surface, whereas mixed dissociative/molecular
adsorption is favored on both the (010) and (110) surfaces. On the
(001) surface, water is able to stabilize the type-II termination,
which is metastable in a dry environment, by converting the oxo ions
into hydroxyls. At high temperature, water desorption is likely to
convert the hydroxylated type-II surface to a type-I termination,
whereas the reverse type-I -> type-II transition is not allowed when
re-adsorption occurs. This could explain the experimental observation
that surface hydroxyls on TiO2-B surfaces are not fully regenerated
upon successive heating and cooling cycles.