  Copper dopants are varyingly reported to enhance photocatalytic activity at
titanium dioxide surfaces through uncertain mechanisms. In order to interpret
how copper doping might alter the performance of titanium dioxide
photocatalysts in aqueous media we applied density functional theory methods to
simulate surface units of doped anatase (101) planes. By including van der
Waals interactions, we consider the energetics of adsorbed water at anatase
surfaces in pristine and copper doped systems. Simulation results indicate that
copper dopant at anatase (101) surfaces is most stable in a 2+ oxidation state
and a disperse configuration, suggesting the formation of secondary CuO phases
is energetically unfavourable. In agreement with previous reports, water at the
studied surface is predicted to exhibit molecular adsorption with this tendency
slightly enhanced by copper. Results imply that the enhancement of
photoactivity at anatase surfaces through Cu doping is more likely to arise
from electronic interactions mediated by charge transfer and inter-bandgap
states increasing photoexcitation and extending surface-hole lifetimes rather
than through the increased density of adsorbed hydroxyl groups.
