Defect‐Engineering‐Mediated Long‐Lived Charge‐Transfer Excited‐State in Fe–Gallate Complex Improves Iron Cycle and Enables Sustainable Fenton‐Like Reaction

Abstract Fenton reactions are inefficient because the Fe(II) catalyst cannot be recycled in time due to the lack of a rapid electron transport pathway. This results in huge H₂O₂ wastage in industrial applications. Here, it is shown that a sustainable heterogeneous Fenton system is attainable by enhancing the ligand‐to‐metal charge‐transfer (LMCT) excited‐state lifetime in Fe–gallate complex. By engineering oxygen defects in the complex, the lifetime is improved from 10–90 ps. The lengthened lifetime ensures sufficient concentrations of excited‐states for an efficient Fe cycle, realizing previously unattainable H₂O₂ activation kinetics and hydroxyl radical (^•OH) productivity. Spectroscopic and electrochemical studies show the cyclic reaction mechanism involves in situ Fe(II) regeneration and synchronous supply of oxygen atoms from water to recover dissociated Fe─O bonds. Trace amounts of this catalyst effectively destroy two drug‐resistant bacteria even after eight reaction cycles. This work reveals the link among LMCT excited‐state lifetime, Fe cycle, and catalytic activity and stability, with implications for de novo design of efficient and sustainable Fenton‐like processes.