While the mechanisms of the sorption of inorganic orthophosphate on environmental mineral surface have been well established, the understanding of surface complexation of organic phosphorus (e.g., phosphonates, polyphosphate, DNA, etc.) remains poorly understood. Owing to the complexity of the organic P molecules, there is a challenge to apply spectroscopic methods such as FTIR and EXAFS to determine the binding structure of surface adsorbed organic P. Here, we showed that the application of novel 31P/27Al double resonance method (i.e., Rotational Echo Adiabatic Passage Double Resonance，REAPDOR) can successfully address the structural issues. For example, 31P/27Al REAPDOR experiments revealed that glyphosate adsorbed on boehmite as a bidentate structure. With the addition of Zn2+, the bidentate binding structure transformed to a monodentate structure. We also studied a series of polyphosphates with different chain numbers. Using the same method, we can excellently determine which phosphate group on the chain was directly binded to the surface of boehmite. With this information, we reveal that the mineral surface could facilitate degradation of the long-chain polyphosphate. Overall, our results demonstrate that 31P solid state NMR is a powerful tool to advance the environmental geochemistry of organic phosphorus.

Surface complexation of organic phosphorus at boehmite surface revealed from 31P/27Al double resonance solid state NMR spectroscopy

ACS Fall 2021

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