A theoretical study on the selective adsorption of NH4+ and Cs+ on the phosphomolybdate ion

• [PMo12O40]3− is a cage-like structure formed by the three- and four-membered MoO rings.
• NH4+ and Cs+ are easily adsorbed at the bridge oxygen on the four-membered rings.
• Adsorption of Cs+ on [PMo12O40]3− is more energetically favorable than NH4+.

The adsorption mechanisms of NH4+ and Cs+ on phosphomolybdate ion were investigated in detail by density functional theory (DFT). The computational results indicate that [PMo12O40]3− is a cage-like structure formed by the three-membered rings and four-membered rings constructed by the MoO bonds. Both NH4+ and Cs+ could be easily adsorbed at the bridge oxygen site of the four-membered ring on the surface of the [PMo12O40]3− ion. The adsorption of Cs+ on [PMo12O40]3− is more energetically favorable than that of NH4+, which likely accounts for the better Cs+ adsorption capability of ammonium phosphomolybdate.

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