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Honeycombed iron doped graphitic carbon nitride with outstanding N"2 photofixation ability is synthesized in this work. Characterization results indicate that Fe^3^+ inserts at the interstitial position and is stabilized in the electron-rich g-C"3N"4 through the coordinative Fe-N bonds. Fe^3^+ sites can chemisorb and activate N"2 molecules, then transfer the photogenerated electrons from the g-C"3N"4 to adsorbed N"2 molecules. Fe0.05-CN displays the highest NH"4^+ generation rate, which is approximately 13.5-fold higher than that of neat g-C"3N"4. Density functional theory simulations prove the N"2 activation effect of Fe^3^+ sites due to the high adsorption energy and prolonged N?N bond. Charge density difference result confirms the electrons transfer process from the Fe^3^+ doping sites to N"2 molecule. DOS results indicate that the electrons of @s"g2p orbital (HOMO) in nitrogen atom is delocalized significantly when N"2 adsorbed on Fe^3^+ doping sites, leading to its orbital energy almost connects to that of @p"g^*2p orbital (LUMO), which confirming that Fe^3^+ doping sites can activate the N"2 molecule effectively. The Mulliken charge of nitrogen is -3.1 when the N"2 adsorbed on Fe^3^+ doping sites, indicating that N"2 molecule is enriched by large number of electrons, which is beneficial to the H^+ attack to form NH"4^+.
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