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Mechanism of Myo-inositol Hexakisphosphate Sorption on Amorphous Aluminum Hydroxide: Spectroscopic Evidence for Rapid Surface Precipitation
journal contribution
posted on 2014-06-17, 00:00 authored by Yupeng Yan, Wei Li, Jun Yang, Anmin Zheng, Fan Liu, Xionghan Feng, Donald L. SparksInositol hexakisphosphates are the
most abundant organic phosphates
(OPs) in most soils and sediments. Adsorption, desorption, and precipitation
reactions at environmental interfaces govern the reactivity, speciation,
mobility, and bioavailability of inositol hexakisphosphates in terrestrial
and aquatic environments. However, surface complexation and precipitation
reactions of inositol hexakisphosphates on soil minerals have not
been well understood. Here we investigate the surface complexation–precipitation
process and mechanism of myo-inositol hexakisphosphate (IHP, phytate)
on amorphous aluminum hydroxide (AAH) using macroscopic sorption experiments
and multiple spectroscopic tools. The AAH (16.01 μmol m–2) exhibits much higher sorption density than boehmite
(0.73 μmol m–2) and α-Al2O3 (1.13 μmol m–2). Kinetics of
IHP sorption and accompanying OH– release, as well
as zeta potential measurements, indicate that IHP is initially adsorbed
on AAH through inner-sphere complexation via ligand exchange, followed
by AAH dissolution and ternary complex formation; last, the ternary
complexes rapidly transform to surface precipitates and bulk phase
analogous to aluminum phytate (Al-IHP). The pH level, reaction time,
and initial IHP loading evidently affect the interaction of IHP on
AAH. In situ ATR-FTIR and solid-state NMR spectra further demonstrate
that IHP sorbs on AAH and transforms to surface precipitates analogous
to Al-IHP, consistent with the results of XRD analysis. This study
indicates that active metal oxides such as AAH strongly mediate the
speciation and behavior of IHP via rapid surface complexation–precipitation
reactions, thus controlling the mobility and bioavailability of inositol
phosphates in the environment.