Strong Coupling of Cr and N in Cr-N-doped TiO2 and Its Effect on Photocatalytic Activity

In spite of extensive research on cationic and anionic doping of titania, only moderate progress in improving its photocatalytic activity has been achieved. In this article, we show that chromium and nitrogen form strong coupling inside the titanium dioxide (TiO2) anatase lattice resulting in a 10-fold increase of photocatalytic activity under ultraviolet irradiation compared with that of Cr or N doping alone. Extensive density functional theory (DFT) calculations show that both negatively charged defect centers (Cr-Ti(-) N-O(-)) form strong bonds rather than repel each other. The resulting Cr-N defect centers are found to decrease the concentration of trivalent titanium in heavily doped films, which may contribute to the observed increase in photocatalytic activity. The importance of this work lies far beyond simply the Cr and N doping because it opens the door for scientifically driven designs of codoped titania for various photocatalytic applications ranging from self-cleaning coatings to solar cells.