FeO ultrasmall nanoparticles supported on carbon-rich graphitic carbon nitride for efficient removal of recalcitrant organic pollutants via photo-Fenton-like catalysis.

Barbituric acid-assisted supramolecular self-assembly of dicyandiamide in the presence of Fe source followed by thermal polymerization is designed to prepare FeO ultrasmall nanoparticles supported on carbon-rich g-CN (FeO/CCN). With an optimal Fe loading of 0.72 wt% and C doping level, 0.72%FeO/CCN exhibits remarkably high heterogeneous photo-Fenton-like catalytic oxidation activity, achieving 99.9% removal of DEP within 90 min, significantly outperforming its photocatalytic and Fenton-like systems. The superior photo-Fenton-like catalytic oxidation activity of the FeO/CCN is caused by the greatly boosted charge separation and transfer dynamics, contributing from the C atom doping-induced internal electric field in CCN and the established Fe-N coordination bonds at the interface between FeO and CCN. The as-generated abundant electrons and holes can directly activate peroxymonosulfate and promote the continuous ≡Fe(II)/≡Fe(III) redox cycle, leading to the formation of high concentration of reactive oxygen species, especially •OH, contributing to the deep oxidation of target organic pollutants. Notably, in a home-made continuous-flow reactor equipped with 0.72%FeO/CCN film-coated optical fibers, 68.0% COD and 67.9% UV removal are achieved from high-salinity leather wastewater under 6 h of simulated sunlight irradiation. Such high catalytic oxidation and long-term stability of the catalytic reactor further highlight its potential for practical wastewater treatment applications.