Species identification of phosphate at the ZrO2/water interface: A combined ATR-FTIR and DFT study

In our work, in-situ attenuated-total-reflection Fourier transformation infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations were used to investigate the interface interactions between phos-phate and zirconium oxide surface. The results showed that phosphate mainly forms three inner-sphere com-plexes, (equivalent to ZrO)2PO2, (equivalent to ZrO)2(HO)PO and (equivalent to ZrO)(HO)2PO, on ZrO2 surface in a wide pH range. At pH 9 and above, no band shift was observed upon replacing light water by deuterium water as the medium, implying a non-protonated bidentate (NB) structure, (equivalent to ZrO)2PO2. At pH 4-7, surface phosphate species have similar structures due to similar spectra, while the band position differences in between the two media suggest that the surface phosphate is protonated. At pH 2, the spectra display remarkable differences in between the two media, suggesting a higher protonation degree of surface phosphate. On the comprehensive analysis, it is reasonable to confirm that the surface phosphate species are in modes of mono-protonated bidentate (MB) at pH 4-7 and bi-protonated monodentate (BM) at pH 2, designated as (equivalent to ZrO)2(HO)PO and (equivalent to ZrO)(HO)2PO, respectively. DFT calculations suggest the stability of these species follows the sequence: MB > NB > BM, and the bidentate structures are corner-sharing.

Automated summary

In this study, the interface interactions between phosphate and zirconium oxide surface were investigated using in-situ attenuated-total-reflection Fourier transformation infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations. The results showed that phosphate forms different complexes on the surface depending on the pH conditions, and the stability follows the order: mono-protonated bidentate (MB) > non-protonated bidentate (NB) > bi-protonated monodentate (BM).