The interfacial chemistry of phosphate has fundamental significance for understanding phosphorus (P) sequestration and bioavailability in aquatic environments. Polyphosphate is an environmentally common P species that can be synthesized by almost all organisms in terrestrial and marine settings. The geochemical behaviors of polyphosphate at mineral–water interface play a critical role in mediating polyphosphate transformation and calcium phosphate formation. This study investigated iron oxide-catalyzed hydrolysis of polyphosphates and revealed its potential role on the precipitation of calcium phosphate minerals under marine environments. Iron oxides can greatly enhance the hydrolysis of polyphosphate in the presence of Ca2+, with the hydrolysis rate in the order of lepidocrocite &gt; hematite &gt; ferrihydrite &gt; goethite. The presence of Ca2+ significantly enhanced both the rate and extent of polyphosphate hydrolysis on all four iron oxides. 31P solution nuclear magnetic resonance (NMR) spectroscopy indicated that a terminal-only hydrolysis pathway was the dominant hydrolysis mechanism via one-by-one cleavage of terminal P−O−P bonds. P K-edge X-ray absorption near edge structure (XANES) spectroscopy revealed the formation of amorphous calcium phosphate (ACP) phase upon polyphosphate hydrolysis in the presence of Ca2+ at high pH conditions. Under artificial seawater condition, we also observed polyphosphate hydrolysis on iron oxides and subsequent ACP formation. However, the hydrolysis rate of polyphosphate and the percentage of formed ACP was relatively low, possibly due to the strong aggregation of iron oxides at highly ionic strength and subsequently reduced surface area. Our study provides new insights for understanding interfacial processes controlling polyphosphate transformation and can help advance our current understanding of marine P cycling.

Iron oxide-catalyzed hydrolysis of polyphosphates and its role on the precipitation of calcium phosphate minerals

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.