Transport selectivities in ion-exchange membranes: Heterogeneity effect and analytical method dependence

Ashwani Kumar, Sanhita Chaudhury

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Ion selectivity (Si) is an important parameter for designing ion-exchange membrane-based process and can possibly be estimated from diffusion properties. Here, we have explored this by comparing diffusion properties (responsible for Si) of multiple cations in heterogeneous Ralex membranes and homogenous Nafion membrane. Analysis also involves a direct comparison between commonly used electrochemical impedance spectroscopy (EIS) and extremely sensitive radiotracer-based method. Ion valence dominantly dictates conductivity in Ralex, unlike Nafion, where both ion hydration and ion valence play equally vital roles. Hence, mutual trend between conductivities/diffusion coefficients (so Si) in Ralex is noticeably different than that in Nafion. Polymer volume fraction analysis shows that electrostatic interaction potential of Ba2+/Eu3+ in Ralex was as high as (~40 mV) that of a significantly restricted diffusion in Nafion. The Si, calculated from EIS-based diffusion parameters, are notably lower than those determined from radiotracer diffusion ((Formula presented.)) and actual ion permeation experiments ((Formula presented.). The (Formula presented.) are always the ones closest to (Formula presented.). However, depending upon membrane heterogeneity and ion valence, (Formula presented.) may be lower/higher than (Formula presented.), and it is difficult to accurately predict actual experimental Si directly from conductivity/diffusion coefficients. Analytical method of diffusion parameters measurement is a key factor too.

Original languageEnglish
Pages (from-to)361-371
Number of pages11
JournalSeparation Science and Technology
Issue number2
StatePublished - 1 Jan 2023
Externally publishedYes


  • Ion selectivity
  • heterogeneous membrane
  • impedance spectroscopy
  • ion separation
  • radiotracer method

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Process Chemistry and Technology
  • Filtration and Separation


Dive into the research topics of 'Transport selectivities in ion-exchange membranes: Heterogeneity effect and analytical method dependence'. Together they form a unique fingerprint.

Cite this