Sulfidation Impacts on the Hydrophobicity of Stepped Iron Surfaces

Abstract

Nanoscale zero‐valent iron (nZVI) has demonstrated high potential for the remediation of contaminated groundwater. Its lifetime is directly related to the hydrophobicity of nZVI. A promising approach to enhance the lifetime of nZVI is through sulfidation. Herein, the density functional theory (DFT) is applied to understand the impact of sulfidation on the hydrophobicity of stepped Fe surfaces. Adsorption properties of sulfur (S) at different coverages on the flat Fe(110) and stepped Fe(210) and Fe(211) surfaces are investigated. Sulfur has the stronger adsorption at a low surface coverage due to limited S–S repulsion. At the highest coverage (⊖ = 1 ML) on Fe(210) and Fe(211), the atoms at the step edges catalyze the formation of iron sulfides. The DFT results show surface hydrophobicity is mainly determined by the S coverage. At the low S coverage, the surface may become more hydrophilic due to the enhanced adsorption strength of water on the surface. However, an increase in the S coverage can efficiently block water adsorption, which is further evidenced by ab initio molecular dynamics (AIMD) results. The findings show that controlling S coverages is essential to engineer the hydrophobicity of nZVI surfaces for practical water remediation applications.