Nitrogen modification enhances conductivity and reactivity of sulfidated zero-valent iron: Mechanism and Cr(VI) removal

The incorporation of electronegative elemental nitrogen into zero-valent iron (ZVI)/sulfidated zero-valent iron (S-ZVI) has emerged as an outstanding and promising way to improve decontamination performance. However, the impact of nitrogen modification on the electrical structure of ZVI/S-ZVI remains unclear. Herein, nitrogen-modified sulfidated zero-valent iron (S-N-ZVI) was successfully obtained utilizing cheap and accessible ammo-nium chloride as the nitrogen source. Raman spectra, FTIR, and density functional theory (DFT) calculations demonstrated that NH3 acts as the dominant nitrogen species. According to the projected density of states and charge-density difference calculations, N is successfully bound to Fe, resulting in a redistribution of surface charge and an increase in electron density of S-N-ZVI, which is reflected in the improved conductivity of S-N-ZVI. Compared with S-ZVI, S-N-ZVI demonstrates better performance in terms of Cr(VI) removal kinetics (kobs improved by 2.075 folds), resistance to air aging, reusability and ability to preserve FeSX stability. This study highlights that the electronic structure significantly impacts the physicochemical properties of S-ZVI and reveals the mechanism of nitrogen modification on the electronic structure of S-ZVI.

Automated summary

Incorporating electronegative elemental nitrogen into zero-valent iron/sulfidated zero-valent iron enhances decontamination performance, but the influence of nitrogen modification on the electrical structure of ZVI/S-ZVI is unclear. This study successfully obtained nitrogen-modified sulfidated zero-valent iron and revealed that nitrogen species bind to iron, leading to redistributed surface charges and increased electron density, which improves the conductivity of S-N-ZVI.