Malic acid-mediated photo-Fenton system for enhanced pharmaceuticals degradation at neutral pH

The Fenton reaction is widely utilized for degrading pollutants that resist conventional wastewater treatment methods. However, its application is often limited by the requirement for strict acidic conditions. This study investigates the potential of malic acid (MA), a biosafe ligand widely used in food processing industry and battery recycling, to enhance acetaminophen (APAP) degradation in a neutral photo-Fenton system under UVA irradiation. Results revealed that MA acts as an effective complexing ligand, stabilizing Fe(III) in photoactive complexes and enhancing OH generation. Under the conditions of 100 μM Fe(III), 1.5 mM MA and 1 mM H 2 O 2 at pH 6, over 90 % APAP was degraded within 10 mins, with an initial reaction rate nine times higher than without MA. The presence of PO 4 3− did not significantly affect the final degradation efficiency of APAP, revealing the strong complexation ability of MA. Validation in natural water matrices showed high APAP removal efficiency (>70 %), and sunlight-driven tests maintained effective processing performance, demonstrating the practical applicability of the MA-photo-Fenton system in realistic remediation scenarios. These results propose a novel ligand selection strategy for ligand-mediated iron-based redox cycles, and further validate the positive contribution of carboxylates to the photo-Fenton system in a neutral environment, providing a reliable pathway for the degradation of organic pollutants in the environment.