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A reverse-selective ion exchange membrane for the selective transport of phosphates via an outer-sphere complexation–diffusion pathway


Specific-ion selectivity is a highly desirable feature for the next generation of membranes. However, existing membranes rely on differences in charge, size and hydration energy, which limits their ability to target individual ion species. Here we demonstrate a nanocomposite ion-exchange membrane material that enables a reverse-selective transport mechanism that can selectively pass a single ion species. We demonstrate this transport mechanism with phosphate ions selectively transporting across negatively charged cation exchange membranes. Selective transport is enabled by the in situ growth of hydrous manganese oxide nanoparticles throughout a cation exchange membrane that provide a diffusion pathway via phosphate-specific, reversible outer-sphere interactions. On incorporating the hydrous manganese oxide nanoparticles, the membrane’s phosphate flux increased by a factor of 27 over an unmodified cation exchange membrane, and the selectivity of phosphorous over sulfate, nitrate and chloride reaches 47, 100 and 20, respectively. By pairing ion-specific outer-sphere interactions between the target ions and appropriate nanoparticles, these nanocomposite ion-exchange materials can, in principle, achieve selective transport for a range of ions.

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Fig. 1: Membrane characterization.
Fig. 2: Membrane performance and selectivity.
Fig. 3: Molecular dynamics simulations of phosphate transport.
Fig. 4: Comparing experimental values and model predictions.

Data availability

All data that support the plots within this paper are available via FigShare at Source data are provided with this paper.

Code availability

The source code for the model is available via GitHub at


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We thank the US Department of Agriculture (2017-67022-26135; D.J.) and the US Department of Energy (DOE) Chemical Sciences, Geosciences, and Biosciences Division under contract DE-AC02-05CH11231 (P.Z.).

Author information

Authors and Affiliations



D.J. designed and supervised the study. A.I. designed the study, developed the material, performed the experiments, developed the mathematical model and prepared the manuscript. P.Z. developed the molecular dynamics simulations for this work. C.M.K. and S.M. assisted with the characterization and analysis of the developed material. R.K. assisted in the development of the mathematical model and provided the source code for Donnan exclusion calculations. J.W. assisted in the development of the mathematical model. E.M.V.H., I.W. and Z.J.R. contributed to the editing of the manuscript and data analysis.

Corresponding author

Correspondence to David Jassby.

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The authors declare no competing interests.

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Nature Nanotechnology thanks Qilin Li, Sukalyan Sengupta and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–7, equations 1–26, Tables 1–3 and Sections 1 and 2.

Source data

Source Data Fig. 1

XPS and FTIR data for membrane characterization.

Source Data Fig. 2

Data files for concentration, pH and separation factor.

Source Data Fig. 4

Data files for flux and transport number.

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Iddya, A., Zarzycki, P., Kingsbury, R. et al. A reverse-selective ion exchange membrane for the selective transport of phosphates via an outer-sphere complexation–diffusion pathway. Nat. Nanotechnol. 17, 1222–1228 (2022).

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