Ferrous Fumarate‐Assisted In‐Situ Synthesis of Interlayer Fe Single Atoms on C ₄ N ₂ ‐Ring‐Rich G‐C ₃ N ₄ for Superior Photo‐Fenton‐Like Removal of Antibiotics

ABSTRACT A bottom‐up strategy of ferrous fumarate‐assisted thermal polycondensation of molten urea is designed for the in‐situ synthesis of a C ₄ N ₂ ‐ring‐rich g‐C ₃ N ₄ ‐supported catalyst with interlayer Fe single atoms (Fe/FU‐CN). At an optimal Fe loading and a corresponding C doping level, 0.49% Fe/FU‐CN demonstrates superior visible‐light photo‐Fenton‐like catalytic performance against representative antibiotic pollutants. In the degradation of trimethoprim (TMP), the 0.49% Fe/FU‐CN/peroxymonosulfate (PMS) photo‐Fenton‐like system possesses superior apparent first‐order rate constants (0.148 min ⁻¹ ), which are 6.56 and 6.87 times higher than 0.49% Fe/FU‐CN Fenton‐like (0.023 min ⁻¹ ) and photocatalytic systems (0.022 min ⁻¹ ), respectively. Complete mineralization is achieved within 6 h. The excellent catalytic efficiency originates from the synergistic effect where C ₄ N ₂ rings suppress charge recombination, while interlayer Fe single atoms serve as electron capture and PMS activation centers. This synergy promotes directional electron transfer to Fe sites, accelerates ≡Fe(III) reduction, boosts PMS activation to generate abundant reactive species, thereby enabling deep oxidation of antibiotic pollutants. Furthermore, a custom‐designed continuous‐flow reactor fitted with the 0.49% Fe/FU‐CN/polyethersulfone catalytic membrane enables efficient and sustained TMP degradation, maintaining a 94.0% removal rate over 12 h. The combination of high activity and long‐term stability makes this catalytic system highly promising for practical wastewater treatment.