title: Visualizing Organophosphate Precipitation at the Calcite-Water Interface by in Situ Atomic-Force Microscopy.
abstract: Esters of phosphoric acid constitute a large fraction of the total organic phosphorus (OP) in the soil environment and, thus, play an important role in the global phosphorus cycle. These esters, such as glucose-6-phosphate (G6P), exhibit unusual reactivity toward various mineral particles in soils, especially those containing calcite. Many important processes of OP transformation, including adsorption, hydrolysis, and precipitation, occur primarily at mineral-fluid interfaces, which ultimately governs the fate of organophosphates in the environment. However, little is known about the kinetics of specific mineral-surface-induced adsorption and precipitation of organophosphates. Here, by using in situ atomic-force microscopy (AFM) to visualize the dissolution of calcite (1014) faces, we show that the presence of G6P results in morphology changes of etch pits from the typical rhombohedral to a fan-shaped form. This can be explained by a site-selective mechanism of G6P-calcite surface interactions that stabilize the energetically unfavorable (0001) or (0112) faces through step-specific adsorption of G6P. Continuous dissolution at calcite (1014)-water interfaces caused a boundary layer at the calcite-water interface to become supersaturated with respect to a G6P-Ca phase that then drives the nucleation and growth of a G6P-Ca precipitate. Furthermore, after the introduction of the enzyme alkaline phosphatase (AP), the precipitates were observed to contain a mixture of components associated with G6P-Ca, amorphous calcium phosphate (ACP)-hydroxyapatite (HAP) and dicalcium phosphate dihydrate (DCPD). These direct dynamic observations of the transformation of adsorption- and complexation-surface precipitation and enzyme-mediated pathways may improve the mechanistic understanding of the mineral-interface-induced organophosphate sequestration in the soil environment.
authors.affiliation: College of Resources and Environment, Huazhong Agricultural University , Wuhan 430070, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Wang
authors.affiliation: College of Resources and Environment, Huazhong Agricultural University , Wuhan 430070, China.
authors.forename: Lihong
authors.initials: L
authors.lastname: Qin
authors.affiliation: Institut für Mineralogie, University of Münster , 48149 Münster, Germany.|Nanochemistry Research Institute, Department of Chemistry, Curtin University , Perth, Western Australia 6845, Australia.
authors.forename: Christine V
authors.initials: CV
authors.lastname: Putnis
authors.affiliation: Department of Mineralogy and Petrology, University of Granada , Fuentenueva s/n, Granada 18071, Spain.
authors.forename: Encarnación
authors.initials: E
authors.lastname: Ruiz-Agudo
authors.affiliation: Department of Earth Sciences, Utrecht University , 3584 CD Utrecht, The Netherlands.
authors.forename: Helen E
authors.initials: HE
authors.lastname: King
authors.affiliation: Institut für Mineralogie, University of Münster , 48149 Münster, Germany.|The Institute for Geoscience Research (TIGeR), Curtin University , Perth, Western Australia 6102, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Putnis
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D011232:Chemical Precipitation; D018625:Microscopy, Atomic Force / Q000379:methods*; D010755:Organophosphates / Q000032:analysis / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D010755:Organophosphates; D012989:Soil Pollutants; D014867:Water; D002119:Calcium Carbonate