Enhanced photo-Fenton catalysis via bandgap engineering of metalloporphyrin-based covalent organic framework shells on bimetallic metal–organic frameworks: accelerating Fe(III)/Fe(II) loop activation

Bimetallic iron-based metal organic frameworks (MFe-MOFs) exhibit promising photocatalytic properties but face challenges typical of pristine MOFs, including low photoresponsive activity, inadequate band gap regulation, and weak photoconductivity. Here, we designed porphyrin-based COFs (TpPAM-COFs) to serve as a shell grown on NH2-Fe-MIL-101 nanoparticles (NPs) using an in situ solvothermal approach. Subsequently, a ligand-anchoring full-range metallization process was applied to introduce hetero metal ions throughout the core–shell composites, establishing a type-II scheme heterojunction (Fe/Cu-M@PC-Cu) via covalent bonding between NH2-Fe/Cu-MIL-101 and Cu-TpPAM-COFs. The Cu-TpPAM-COF shell, with broad light absorption range, enhanced the generation of photogenerated electrons, facilitating the reduction of Cu2+ and Fe3+ within the Fe/Cu-M@PC-Cu heterojunction and promoting the regeneration of Cu+ and Fe2+ Fenton active sites. Moreover, rapid electron transfer between Fe3+ and Cu+ centers amplified the Fe3+/Fe2+ redox cycle, accelerating the catalytic decomposition of H2O2 and increasing ·OH radical production. Additionally, the optimized bandgap structure of Cu-TpPAM-COFs enhanced the oxidation capacity, as evidenced by the Fe/Cu-M@PC-Cu composite achieving exceptional photo-Fenton catalytic efficiency with 92.7% tetracycline hydrochloride (TCH) degradation in 35 minutes, surpassing that of most reported similar catalysts. Furthermore, the composite showed excellent stability, with only an 11.9% loss in photo-Fenton degradation efficiency after 8 cycles, highlighting its great potential for addressing challenging environmental pollutants.