Carbon-doped anatase titania nanoparticles: similarities and differences with respect to bulk and extended surface models.

C-Doping of titania nanoparticles is analyzed by using all-electron density functional theory-based calculations considering the (TiO 2 ) 84 nanoparticle as a realistic representative of nanoparticles in the scalable regime. Several sites are evaluated including substituting oxygen (C O ) and titanium (C Ti ) sites as well as interstitial (C i ) situations. The formation energy of such a doped structure is studied as a function of the oxygen chemical potential (or oxygen partial pressure). Our calculations predict that low partial oxygen pressure favors the formation of C-doped (TiO 2 ) 84 NPs at oxygen and interstitial sites. For the former, the most stable situation is for O sites at the inner part of the nanoparticle. Interestingly, the substitution of O by C at facet sites requires formation energies as those reported in previous studies where the bulk anatase and surfaces models were considered. However, C-doping - at other low coordinated sites not presented in extended models - is even more favorable which shows the need to employ more realistic models for nanostructures involved in photocatalytic processes.