Acyl Radicals in Environmental Chemistry: From Fundamental Mechanisms to Sustainable Water Treatment

ConspectusWhile acyl radicals have been harnessed in synthetic chemistry since their discovery in 1932, their environmental applications remain largely unexplored. Conventional water treatment predominantly utilizes inorganic radicals (^•OH, SO₄^•-, H^•) for their potent redox capabilities. Recent advances in peracetic acid (PAA)-based advanced oxidation processes (AOPs) have spotlighted the peroxyacetyl radical (AcOO^•), an oxidative derivative of the acetyl radical (Ac^•). Though PAA activation cannot directly generate Ac^•, the untapped capabilities of Ac^• merit dedicated investigation.Our work bridges this knowledge gap by establishing low-molecular-weight diketones (LDKs) as tunable precursors for targeted Ac^• generation. Through integrated electron paramagnetic resonance, laser flash photolysis, and mass spectrometry, we tracked the generation of Ac^• and its key derivatives─Ac^•(OH)₂ and AcOO^•─in UV/LDK systems. Crucially, dissolved oxygen (O₂) serves as a molecular switch: under oxic conditions, Ac^• reacts barrier-free with O₂ to form oxidative AcOO^•, whereas reductive species (Ac^• and Ac^•(OH)₂) dominate under anoxic conditions. This O₂-dependent speciation creates a unique dual-reactivity platform. Ac^• and its derivatives exhibit moderate yet selective reduction potentials, enabling tailored applications─from precision pollutant degradation and metal resource recovery to point-of-use disinfection─all controlled solely by O₂ modulation without additional chemicals.By unifying mechanistic insights with environmental innovation, this Account establishes acyl radicals as a transformative paradigm for advanced redox technologies. We invite chemists to expand radical selection criteria beyond conventional oxidants, prioritizing tunable, selective, and operationally simple systems enabled by Ac^• chemistry. Key priorities to advance this field include: (1) establishing systematic frameworks for reaction pathways, kinetics, and structure-reactivity relationships across Ac^• generating systems; (2) quantifying interconversion dynamics among Ac^•, Ac^•(OH)₂, and AcOO^• through combined computational and experimental approaches; and (3) investigating radical acetylation mechanisms and targeted biomolecule modification.