Mechanism of Dissolved Organic Matter Constructing Zerovalent Iron Interfacial Mass-Transfer Channel Combined with <i>Shewanella oneidensis</i> MR-1 To Remove Cr(VI)

Nanoscale zerovalent iron (nZVI) is a promising remediation agent for the removal of heavy-metal wastewater. However, nZVI tends to agglomerate and be oxidatively deactivated during the reaction, which limits its application. To address the problem, this study develops a novel modification method to regulate the reaction interface of nZVI by introducing fulvic acid (FA), a naturally occurring environmental component, to the synthesis of nZVI. FA disrupts the circumferential-stress equilibrium of nZVI, enhances the Kirkendall effect, and establishes mass-transfer channels, facilitating the outward transfer of reducible Fe(II) and electrons and the inward transport of surface-adsorbed Cr(VI). The Cr(VI) removal is further enhanced by coupling FA-nZVI with Shewanella oneidensis MR-1, which reduces Fe(III) hydroxides to Fe(II) at the FA-nZVI interface, thereby preventing accumulation of the passivation layer that blocks the mass-transfer channels. The synergistic action of mass-transfer channels with MR-1 enhances the Cr(VI) removal rate by 4.7 times, ensuring a Cr(VI) removal rate of more than 60% under extreme conditions. By exploring the new functions of FA as an organic carbon component, this study provides a fresh perspective on carbon utilization in ecosystems. Leveraging environmental factors for the microstructural modulation of nZVI is an efficient and environmentally friendly approach for remediation of heavy-metal pollution.