Reactions of disinfectants at solution/iron interfaces: Modeling pipeline surface chemistry

Document Type

Article

Publication Date

3-1-2025

Department

Department of Chemistry; Department of Materials Science and Engineering

Abstract

Monochloramine (NH2Cl) is used as a secondary disinfectant to treat pathogens in the municipal water supply, but reacts with iron, undergoing decomposition and corrosion of pipeline surfaces. The interaction of NH2Cl was studied at the air/solution/Fe interface, to assess the surface oxidation, corrosion, and film formation as a model system for iron pipelines. The results were compared with oxidation in NaOCl(aq), NH4Cl(aq), and NaOH(aq), to explicitly define the NH2Cl reaction with iron. At the air/solution/Fe interface using in situ polarized modulated-infrared reflection absorption spectroscopy, atmospheric CO2 and O2 was found to adsorb into NH2Cl(aq), NaOCl(aq), and NH4Cl(aq) producing various inorganic films along with lepidocrocite, γ-FeOOH. In NH2Cl(aq) and NH4Cl(aq) amide films were grown on the iron surface, while in NaOCl(aq), the surface was strongly oxidized to grow a carbonate film. For the surface region submerged in NH2Cl(aq), localized, heterogenous corrosion was observed, where amides, carbonate, and iron oxides were produced, as measured by infrared spectroscopy, XPS, and XRD. For Fe in NH4Cl(aq), amides, carboxylate, and iron oxides were detected, with the least corrosion. In NaOCl(aq), the iron surface severely corroded to form carboxylate and iron oxides. Uncovering the surface reaction of disinfectants are vital towards understanding degradation of water pipelines.

Publication Title

Applied Surface Science

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