DFT calculations for single-atom confinement effects of noble metals on monolayer g-CN for photocatalytic applications.

Graphitic carbon nitride, as a very promising two-dimensional structure host for single atom catalysts (SACs), has been studied extensively due to its significant confinement effects of single atoms for photocatalytic applications. In this work, a systematic investigation of g-CN confining noble metal single atoms (NM@g-CN) will be performed by using DFT calculations. The geometric structure calculations indicate that the most favorable anchored sites for the NM is located in the six-fold cavity, and the deformed wrinkle space of g-CN helps the NM to be stabilized in the six-fold cavity. The electronic structure calculations show that the conduction band of NM@g-CN moved down and crossed through the Fermi level, resulting in narrowing the band gap of the NM@g-CN. Moreover, the confined NM provide a new channel of charge transport between adjacent heptazine units, resulting in a longer lifetime of photo-generated carriers except Ru, Rh, Os and Ir atoms. Furthermore, the d-band centres of NM in NM@g-CN show that Rh@, Pd@, Ir@ and Pt@g-CN SACs may have better photocatalytic performance than other NM@g-CN SACs. Finally, Pt@g-CN SACs are considered to have higher photocatalytic activity than other NM@g-CN SACs. These results demonstrate that the confinement effects of noble metals on monolayer g-CN not only makes the single atom more stable to be anchored on g-CN, but also enhances the photocatalytic activity of the system through the synergistic effect between the confined NM and the monolayer g-CN. These detailed research may provide theoretical support for engineers to prepare photocatalysts with higher activity.