Atomically dispersed Fe boosting elimination performance of g-C3N4 towards refractory sulfonic azo compounds via catalyst-contaminant interaction

Herein, an oxygen-doped porous g-C 3 N 4 photocatalyst modified with atomically dispersed Fe (Fe 1 /OPCN) is successfully prepared and exhibits significant superiority in removing refractory sulfonic azo contaminants from water via catalyst-contaminant interaction. The elimination performance of Fe 1 /OPCN towards acid red 9, acid red 13 and amaranth containing similar azonaphthalene structure and increasing sulfonic acid groups increases gradually. The amaranth degradation rate of Fe 1 /OPCN is 17.7 and 6.1 times as that of homogeneous Fenton and OPCN, respectively. In addition, Fe 1 /OPCN also has more outstanding removal activities towards other contaminants with sulfonic acid and azo groups alone. The considerable enhancement for removing sulfonic azo contaminants of Fe 1 /OPCN is mainly ascribed to the following aspects: (1) The modified Fe could enhance the adsorption towards sulfonic azo compounds to accelerate the mass transfer, act as e - acceptor to promote interfacial charge separation, and trigger the self-Fenton reaction to convert in-situ generated H 2 O 2 into •OH. (2) Fe(Ⅲ) could coordinate with — N=N — to form d-π conjugation, which could attract e - transfer to attack — N=N — bond. Meanwhile, the inhibited charge recombination could release more free h + to oxidize sulfonic acid groups into SO 4 - •. (3) Under the cooperation of abundant multiple active species ( • O 2 - , h + , e - , • OH, SO 4 - •) formed during the degradation reaction, sulfonic azo compounds could be completely mineralized into harmless small molecules (CO 2 , H 2 O, etc.) by means of — N=N — cleavage, hydroxyl substitution, and aromatic ring opening. This work offers a novel approach for effectively eliminating refractory sulfonic azo compounds from wastewater. An oxygen-doped porous g-C 3 N 4 photocatalyst modified with atomically dispersed Fe (Fe 1 /OPCN) exhibited significant superiority in removing refractory sulfonic azo contaminants. The modified Fe acted as electron acceptors, triggered self-Fenton reaction, and accelerated mass transfer. The advanced catalyst-contaminant interaction produced abundant multiple active species ( • O 2 - , h + , e - , • OH, SO 4 - •) for mineralizing sulfonic azo contaminants into small molecules. • An oxygen-doped porous g-C 3 N 4 photocatalyst modified with atomically dispersed Fe exhibited significant superiority in removing refractory sulfonic azo contaminants. • The modified Fe improved charge separation, triggered self-Fenton reaction, and accelerated mass transfer. • The advanced catalyst-contaminant interaction produced abundant multiple active species for mineralizing sulfonic azo contaminants into small molecules.