Tripolyphosphate-Mediated Interfacial Electronic Reconfiguration Boosts •OH Production and Redirects Mineral Evolution During FeS Oxygenation.

Oxygenation of mackinawite (FeS) at redox interfaces constitutes a key biogeochemical process that generates hydroxyl radicals (•OH) and facilitates contaminant attenuation. However, the influence of common inorganic ligands such as tripolyphosphate (TPP) on interfacial electron transfer in this process remains poorly understood. Herein, 1.0 mM TPP increased cumulative •OH production approximately 23.5-fold over 180 min of FeS oxygenation, with the electron utilization efficiency for •OH production increasing from 0.33% to 8.18%. TPP enhanced •OH generation by promoting Fe(II) dissolution, thereby driving homogeneous Fenton-like reactions, while facilitating Fe(III)/Fe(II) redox cycling through solid-liquid interactions. Additionally, TPP acted as an interfacial coordination modulator by rearranging the local Fe(II) environment, and the resulting surface Fe(II)-TPP complexes improved the utilization of structural electrons. Electrochemical measurements and DFT calculations indicated that this interfacial coordination suppressed structural Fe(II) oxidation and reduced unproductive electron consumption, while lowering the energy barrier for H2O2-forming O2 activation at TPP-modified FeS sites. XRD, FTIR, and EXAFS analyses showed that TPP adsorption inhibited lepidocrocite crystallization and redirected secondary mineral evolution toward ferrihydrite-rich products. These findings elucidate how ubiquitous ligands regulate mineral-water interfacial processes and •OH generation, providing a basis for optimizing FeS-based environmental remediation technologies.