Solid-State NMR Spectroscopic Study of Phosphate Sorption Mechanisms on Aluminum (Hydr)oxides

Sorption reactions occurring at mineral/water interfaces are of fundamental importance in controlling the sequestration and bioavailability of nutrients and pollutants in aqueous environments. To advance the understanding of sorption reactions, development of new methodology is required. In this study, we applied novel 31P solid-state nuclear magnetic resonance (NMR) spectroscopy to investigate the mechanism of phosphate sorption on aluminum hydroxides under different environmental conditions, including pH (4–10), concentration (0.1–10 mM), ionic strength (0.001–0.5 M), and reaction time (15 min–22 days). Under these conditions, the NMR results suggest formation of bidentate binuclear inner-sphere surface complexes was the dominant mechanism. However, it was found that surface wetting caused a small difference. A small amount (