Exploring the synergy between magnetic field and inorganic ligand for boosted O2 activation by microscale zero-valent iron

Abstract

Microscale zero valent iron (ZVI) is a promising material for in situ water purification through O₂ activation, but its activity is hindered by the slow electron transfer rate caused by the shielding effect of the surface passivation layer. Herein, we introduce a synergistic strategy that combines an inorganic ligand, i.e., tetrapolyphosphate (TPP), with magnetic field (MF) to boost the O₂ activation efficiency of ZVI under neutral conditions. This approach has resulted in a 4.7-fold increase in the degradation rate of diclofenac (DCF) compared to the MF-unassisted system and a remarkable 22.0-fold improvement over an analogous system with MF and EDTA. Multiphysics simulations, batch experiments, and characterizations revealed that the enhanced degradation rate was not only attributed to the elevated magnetic gradient on the ZVI surface to enrich the paramagnetic O₂ and Fe ions, but also to the functions of TPP to suppress the annihilation of •OH and reduce the redox potential of Fe²⁺/Fe³⁺. Furthermore, a synergistic mechanism between MF and TPP that facilitates the detachment of the surface-bound Fe³⁺-TPP complex into the aqueous phase, thereby regenerating the surface active sites was elucidated. This study underscores the potential of the MF-TPP synergy as an effective strategy to enhance ZVI-based Fenton-like catalysis for pollutant remediation.