Boosting Photo-Fenton reactions by amidoxime chelated ferrous iron (Fe(III)) catalyst for highly efficient pollutant control

[Display omitted] •Large-size and high-density Fe sites photo-Fenton catalysts were fabricated for H2O2 activation.•The chelated Fe(III) provides a well-defined reaction microenvironment with maximum atom efficiency.•The high loading Fe (III) catalyst can remove various model organic pollutants effectively.•U-g-PAO/Fe shows excellent catalytic activity in a wide range of pH, even in the process of multiple cycles.•XAFS and DFT revealed the coordination relationship of active sites and activation mechanism. The maximum exposure of active sites is the key to obtaining high reaction activity for supported metal catalysts. Single-atom metal sites and ultra-small metal clusters have received great attention because of their superior catalytic activities compared to their aggregated counterparts. However, developing high-density metal clusters with high activity and adequate stability remains a major challenge in practical applications. Herein, we demonstrate that highly dispersed and active Fe sites for heterogeneous Photo-Fenton systems can be chelated into graft chains on ultrahigh molecular weight polyethylene (UHMWPE) fibers via radiation-induced graft polymerization (RIGP) and subsequent modification, labeled as U-g-PAO/Fe. The amidoxime chelated Fe(III) catalyst, in which the loading amount of chelated Fe(III) is 24.04 wt%, exhibits remarkably efficient removal of ofloxacin within 35 min by activating H2O2 under visible light irradiation. The catalytic activities and stability of U-g-PAO/Fe were evaluated by the removal of various model organic pollutants and multiple recycles of degradation, demonstrating superior catalytic activities over a wide pH range (2–10) for the activation of H2O2 than a typical Fenton catalyst. Furthermore, the graft macromolecular chains of chelated Fe(III) provide a well-defined reaction microenvironment with maximum atom efficiency. X-ray absorption fine structure (XAFS) and density functional theory calculations (DFT) revealed that the unique active sites [Amidoxime-Fe(OH)(H2O)3]2+ of U-g-PAO/Fe considerably activated H2O2 decomposition under artificial sunlight irradiation. Our study presents a novel idea for the design and synthesis of highly dispersed and reactive Fe-based Photo-Fenton catalysts for practical applications in environmental remediation.