Fe3+ doping promoted N2 photofixation ability of honeycombed graphitic carbon nitride: The experimental and density functional theory simulation analysis

- By controlling the Fe3+ concentration, honeycombed Fe3+ doped g-C3N4 is synthesized.
- The Fe3+ doping sites serve as active sites to adsorb and activate N2 molecules.
- DFT simulation confirms the chemisorption and activation of N2 occur on the Fe3+ doping sites.

Honeycombed iron doped graphitic carbon nitride with outstanding N2 photofixation ability is synthesized in this work. Characterization results indicate that Fe3+ inserts at the interstitial position and is stabilized in the electron-rich g-C3N4 through the coordinative Fe-N bonds. Fe3+ sites can chemisorb and activate N2 molecules, then transfer the photogenerated electrons from the g-C3N4 to adsorbed N2 molecules. Fe0.05-CN displays the highest NH4+ generation rate, which is approximately 13.5-fold higher than that of neat g-C3N4. Density functional theory simulations prove the N2 activation effect of Fe3+ sites due to the high adsorption energy and prolonged NN bond. Charge density difference result confirms the electrons transfer process from the Fe3+ doping sites to N2 molecule. DOS results indicate that the electrons of σg2p orbital (HOMO) in nitrogen atom is delocalized significantly when N2 adsorbed on Fe3+ doping sites, leading to its orbital energy almost connects to that of πg*2p orbital (LUMO), which confirming that Fe3+ doping sites can activate the N2 molecule effectively. The Mulliken charge of nitrogen is −3.1 when the N2 adsorbed on Fe3+ doping sites, indicating that N2 molecule is enriched by large number of electrons, which is beneficial to the H+ attack to form NH4+.

230The experimental and density functional theory simulation results confirm that Fe3+ doping sites can chemisorb and activate N2 molecules, then promote the photogenerated electrons transfer from the g-C3N4 to adsorbed N2 molecules, leading to the improved N2 photofixation ability.