Highly enhanced removal of Cr(VI) by nZVI in presence of myo-inositol hexakisphosphate: The depassivation performance and multiple electron transfer mechanisms.

The capability of traditional ligand in countering rapid passivation on nanoscale zero-valent iron (nZVI) surface is inadequate, and the precise electron transfer mechanism remains elusive. In this study, we reported that myo-inositol hexakisphosphate (IHP), a redox-inactive organophosphorus in soil, could highly enhance Cr(VI) reduction and immobilization in comparison with typical ligands (TPP, EDTA, oxalate and phosphate). And the effects of IHP concentration, Cr(VI) concentration and initial pH were systematically investigated. Cr K-edge XANES and XPS analysis revealed that Cr(III) was the exclusive form in solid products regardless of IHP existence. Results of ATR-FTIR and FESEM inferred that IHP was adsorbed on nZVI surface via inner-sphere complexation, thus averting encapsulation of [Fe, Cr](OH) coprecipitate and impeding solid particles agglomeration. Additionally, IHP expedited the production of surface-bound Fe(II), primarily attributable to the interaction between nZVI and oxygen. These surface-bound Fe(II) species played a pivotal role in Cr(VI) reduction. Electrochemical analysis unveiled that IHP lowered redox potential of Fe(III)/Fe(II), thereby facilitating reaction between Fe(II) and Cr(VI), whereas inhibited direct electron transfer from nZVI core to Cr(VI). Our findings proposed a novel potential ligand for alleviating nZVI passivation in Cr(VI) removal and deepened our understanding in the process of electron transfer.