Redox-driven recrystallization of metal oxides is an environmental phenomenon that can influence biogeochemical cycles of both nutrients and contaminants. Lead(IV) oxides (PbO2) have been widely observed as a component of scales on the surface of lead pipes used for water supply. Two polymorphs of PbO2, scrutinyite (α-PbO2), and plattnerite (β-PbO2) may form from the reaction of Pb(II) species with free chlorine in drinking water. PbO2 has a much lower solubility than other lead-containing solids found in pipe scales and hence can be a sink for Pb in drinking water systems. However, PbO2 is only stable in the presence of free chlorine, and many chemical species can reduce it to release Pb(II) back to the water. Recrystallization may alter the inherent stability of PbO2 with respect to its reductive dissolution. Using 207Pb(II) as a stable isotope tracer, we observed the redox-driven recrystallization of PbO2 (both α and β forms). The rate of isotope exchange could be divided into two processes: 1) a fast component attributed to surface atom exchange followed by 2) a slow component attributed to bulk atom exchange. The overall isotope exchange rate of α-PbO2 was greater than that of β-PbO2. Heterogeneous and homogeneous recrystallization models were employed to interpret the experimental results, and the heterogeneous model provided the best fit for both α-PbO2 and β-PbO2 data. Solids harvested from the isotope exchange experiments were characterized by XRD and XPS, and no significant changes in crystallinity were observed. The experimental approach and detailed solid characterization allowed us to demonstrate the redox-driven recrystallization of PbO2.

Redox-driven recrystallization of lead(IV) oxide

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.