We synthesize p-type TiO2 nanotubes that allow band-gap adjustment by quantum confinement. These tubes therefore enable reductive photocatalytic reactions that are not thermodynamically possible on classic titania photocatalysts. Here, we demonstrate the direct photocatalytic nitrate reduction to ammonia without any need of hole scavengers. The quantum confinement effect (and thus the thermodynamic driving force) can be controlled by the thickness of the nanotube walls. Notably, the use of Pt single atoms as cocatalysts decorated on the TiO2 nanotubes additionally offers a superior ammonia production and a remarkable enhanced selectivity compared to Pt nanoparticles. Overall, the work not only highlights the potential of size-controlled modifications of electronic properties in extending the utility of a most classical photocatalyst but also exemplifies its use in technologically relevant reactions.

Department of Materials Science and Engineering WW4 LKO Friedrich Alexander Universität Erlangen Nürnberg Martensstraße 7 91058 Erlangen Germany

Institute of Micro and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy IZNF Friedrich Alexander Universität Erlangen Nürnberg Cauerstraße 3 91058 Erlangen Germany

Regional Centre of Advanced Technologies and Materials Palacký University Šlechtitelů 27 Olomouc 78371 Czech Republic

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