Spirulina-derived atomically dispersed Fe–N4 sites on g-C3N4 for efficient CO2 photoreduction

Developing single-atom catalysts for photocatalytic CO 2 reduction requires sustainable and scalable synthesis strategies. Herein, we report a green and metal-salt-free route to construct dispersed single atom Fe sites in graphitic carbon nitride (Fe-SA/g-C 3 N 4 ) via co-pyrolysis of Spirulina biomass and urea. Spirulina acts as both Fe source and structural/chemical template, enabling the modulation of C/N ratio and N functional groups for enhanced visible-light absorption and formation of isolated Fe N 4 sites without toxic reagents. The atomic dispersion of Fe N 4 sites modifies the local electronic structure of g-C 3 N 4 , and promotes charge separation via electronic metal-support interactions. Combined density functional theory and in situ spectroscopic analyses highlight how Fe N 4 coordination facilitates CO 2 activation, promotes charge transfer, and directs the formation of key intermediates for CO and CH 4 production. The optimized Fe-SA/g-C 3 N 4 achieves CO and CH 4 production rates of 25.74 and 3.4 μmol g −1 h −1 , respectively, with 88.3 % CO selectivity. This work provides a sustainable platform for biomass-derived single atom photocatalyst toward efficient solar-driven CO 2 conversion. • In situ co-pyrolysis of Spirulina and urea yields atomically dispersed Fe-N 4 sites on g-C 3 N 4 . • Spirulina biomass serves as a natural Fe source and structural/chemical template. • Electronic metal-support interactions promotes the spatial separation of electrons and holes. • The Fe-SA/g-C 3 N 4 achieves enhanced CO and CH 4 production and CO selectivity.