# In situ potassium and hydrogen ion exchange into a cubic zirconium silicate microporous material

## TL;DR

This paper explores how a cubic zirconium silicate material selectively exchanges potassium ions, offering insights for applications in environmental and health management.

## Contribution

The study reveals a novel synchronous cation-cation repulsion mechanism in cubic zirconium silicate for potassium ion selectivity.

## Key findings

- Potassium ion selectivity in cubic zirconium silicate involves synchronous cation-cation repulsion.
- Partial protonation of the material enhances ion exchange by expanding the unit-cell and enlarging the 7-member-ring window.
- The process allows rapid and irreversible potassium ion exchange into the material's cage structures.

## Abstract

The selective separation of ions from aqueous systems, and even in the human body, is a crucial to overall environmental management and health. Nanoporous materials are widely known for their selective removal of cations from aqueous media, and therefore have been targeted for use as a pharmaceutical to treat hyperkalemia. This study investigated the detailed crystallographic molecular mechanisms that control the potassium ion selectivity in the nanoporous cubic zirconium silicate (CZS) related materials. Using time-resolved in situ Raman spectroscopy and time-resolved in situ X-ray diffraction, the selectivity mechanisms were determined to involve a synchronous cation-cation repulsion process that serves to open a favorable coordination bonding environment for potassium, not unlike the ion selectivity filter process found in potassium ion channels in proteins. Enhancement of ion exchange was observed when the CZS material was in a partial protonated state (≈3:1 Na:H), causing an expansion of the unit-cell volume, enlargement of the 7 member-ring window, and distortion of framework polyhedra, which allowed increased accessibility to the cage structures and resulted in rapid irreversible potassium ion exchange.