Density functional theory study on a nitrogen-rich carbon nitride material C₃N₅ as photocatalyst for CO₂ reduction to...

A new-type nitrogen-rich carbon nitride material C₃N₅ has been synthesized recently, in which the C:N ratio increases from 3:4 in g-C₃N₄ to 3:5 due to the introduction of azo linkage (NN) connecting segments in two C₆N₇ units. Herein, C₃N₅ as a photocatalyst for CO₂ reduction was investigated by density functional theory methods. The electronic and optical properties indicate that C₃N₅ has a longer visible-light region with 2.0 eV of band gap in comparison with g-C₃N₄. The spatial distributions of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) show that the π network of C₃N₅ is extended by introducing -NN- linkage, which results in much higher photocatalytic efficiency than g-C₃N₄. The Gibbs free energies for possible CO₂ reaction paths on C₃N₅ were computed. The results show that CO₂ can be reduced to CH₄ with a low limiting potential of -0.54 V and to CH₃CH₂OH with a low limiting potential of -0.61 V, which all driven by solar energy. The present work is expected to provide useful guide for new-type nitrogen-rich C₃N₅ as promising photocatalyst for CO₂ reduction reaction (CO₂RR).