Surface chemistry of monochloramine catalyzed by Fe(111)

Document Type

Article

Publication Date

3-2026

Department

Department of Chemistry; Department of Materials Science and Engineering

Abstract

Monochloramine (NH2Cl) is a secondary disinfectant used for water purification and interacts with iron materials in various environments. Iron surfaces undergo reduction-oxidation and corrosion, where zero-valent iron sites are produced at complex interfaces. The initial stages of the reaction of monochloramine (NH2Cl) have been studied on Fe(111), as a model for iron pipelines and mineral surfaces, at the gas/solid interface in ultra-high vacuum conditions. Using in situ infrared reflection absorption spectroscopy, NH2Cl was found to adsorb molecularly at -160 °C, by observation of amine vibrational signatures. Auger electron spectroscopy was used to detect the presence of chloride to amine in a 3:1 ratio. Upon annealing, the NH2Cl multilayer was found to desorb from Fe(111) at -120 °C, and the monolayer also undergoes molecular dissociation. At 34 °C, NH2Cl primarily binds through the chloride species, thus blocking sites for NH2 adsorption. Density functional theory computations and X-ray photoelectron spectroscopy confirmed two favorable chemisorbed orientations, both through binding of chloride. Further annealing allowed for chloride desorption before 400 °C, suggesting decomposition. The NH2Cl is found to undergo a dechlorination mechanism, similar to chlorohydrocarbon reactions on iron surfaces. These findings reveal the mechanism of the chloramine disinfectant on metallic iron interfaces and its role in pipelines and water systems.

Publication Title

Surface Science

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