title: Phosphate alteration of chloride behavior at the boehmite-water interface: New insights from ion-probe flow adsorption microcalorimetry.
abstract: Surface complexation of phosphate to aluminum oxyhydroxides can alter surface reactivity depending on the time-scale and mode of attachment. The effects of phosphate adsorption on reactivity of boehmite (γ-AlOOH) particles were investigated using ion-probe flow adsorption microcalorimetry (ipFAMC). Consistent with previous studies on adsorption energetics, probing the surface of pristine γ-AlOOH with chloride ions yielded endothermically unimodal temperature signals with a measured molar heat of exchange (ΔH(exc)) of -3.1 kJ/mol. However, when the surface of γ-AlOOH was probed with chloride following phosphate complexation, significant changes in surface reactivity resulted. Irrespective of phosphate loading, the typical endothermic response of the chloride-surface hydroxyl interaction was replaced with a multi-modal energy signature consisting of exothermic and endothermic features. These features indicate that in the presence of phosphate, the overall nature of the interaction of chloride with specific surface hydroxyls located on different exposed planes and their subsequent reactivity was transformed to a more complex environment accompanied by two or more short-lived secondary reactions. It was also shown that phosphate-promoted surface alteration of γ-AlOOH was highly selective to probing with chloride since no changes in reactivity were observed when nitrate was employed as the primary ion probe under identical experimental conditions.
authors.affiliation: Department of Environmental Engineering Sciences, Engineering School of Sustainable Infrastructure & Environment, University of Florida, Gainesville, FL 32611, United States. Electronic address: gale@gsu.edu.
authors.forename: S Adrian
authors.initials: SA
authors.lastname: Gale
authors.affiliation: Department of Geography and Geology, University of Southern Mississippi, Hattiesburg, MS 39406, United States.
authors.forename: Omar R
authors.initials: OR
authors.lastname: Harvey
authors.affiliation: Department of Soil and Water Science, University of Florida, Gainesville, FL 32611, United States.
authors.forename: R Dean
authors.initials: RD
authors.lastname: Rhue
keywords: Boehmite; Flow-microcalorimetry; Ion-probe; Molar enthalpy; Phosphate adsorption; Surface reactivity