Mesoporous structure and amorphous Fe-N sites regulation in Fe-g-C₃N₄ for boosted visible-light-driven photo-Fenton reaction

Heterogeneous photo-Fenton catalysts prepared by doping metal ions in g-C₃N₄ are promising alternatives to traditional homogeneous Fenton catalysts, but are restricted by poor mesoporous structure and agglomerate of metal species. Recently, the highly uniformly dispersed metal-N active sites in various photocatalysts have been proved to be the critical reason for their enhanced catalytic activity. In this study based on reasonable control of mesoporous structure and metal-N active sites, mesoporous Fe-g-C₃N₄ was synthesized using a simple one-step thermal shrinkage polymerization method using ferrous oxalate as iron source and pore-forming agent. The Fe and N elements in the triazine ring skeleton of Fe-g-C₃N₄ form a σ-π bond, thus the photogenerated electrons can be quickly transferred to Fe³⁺ to form Fe²⁺ under the interaction of chemical bonds, accelerating the Fenton reaction rate. Density functional theory calculations results demonstrate that the energy band structure and electron cloud density distribution of Fe-Nx active structure are better than that of routine FeOx crystal structure with metal species agglomeration. In addition, the excellent mesoporous structure of Fe-g-C₃N₄ creates conditions for the high exposure of Fe-Nx active sites in the photo-Fenton reaction under visible light. The as-developed Fe-g-C₃N₄ system shows high recyclability and excellent photo-Fenton performance for removal of typical intractable pollutants (The degradation rate of dye and tetracycline reaches 98.2% and 98.7% at 60 and 120 min, respectively). This work provides a facile and sustainable route to develop mesoporous highly-active heterogeneous Fenton-like catalysts and even further general the design of general catalyst with ideal metal-N active sites, thereby promoting a feasible and efficient wastewater remediation solution.