Co-incorporation of lattice S and P into nano zero-valent iron induces multiple Kirkendall effects for enhanced trichloroethylene reduction efficiently

Abstract

Conventional zero-valent iron (ZVI) materials are limited by the constraints of reactivity-selectivity-stability trade-offs, so designing multi-heteroatom co-modified ZVI with synergistic effects is gradually gaining popularity. Herein, we developed a novel co-modified nZVI by simultaneously doping sulfur (S) and phosphorus (P) heteroatoms into nZVI using the one-step liquid-phase reduction method. In this case, the faster diffusion rate of core iron atoms compared to shell components triggeres multiple Kirkendall effects, causing the inward diffusion of vacancies with further coalescing into radial nanocracks. Regarding the reactivity and selectivity, sulfidation and phosphorylation co-modified nZVI exhibited the best performance, with a trichloroethylene (TCE) dechlorination rate ($k_{\mathrm{obs},\mathrm{TCE}}$) of 0.65 h⁻¹ and an electron efficiency (${\epsilon }_e$) of 14.5 %, which are 20.9 and 13.8 times higher than those of unmodified nZVI. A series of characterizations and electrochemical analyses indicated that S and P doping significantly altered the physicochemical properties of the core and shell layers, generating distinctive “lemon slice” nanocracks that could be used as electron transport channels, and ${\text{FeS}}_{\text{X}}$ significantly reduced the availability of hydrogen evolution reaction (HER) active surface sites and attenuates the passivation of nZVI. In addition, the co-modified S/P-nZVI exhibited excellent stability in different groundwater conditions, indicating its strong potential for application.