Selective Fluoride Transport in Subnanometer TiO2Pores

Xuechen Zhou, Mohammad Heiranian, Meiqi Yang, Razi Epsztein, Kai Gong, Claire E. White, Shu Hu, Jae Hong Kim, Menachem Elimelech

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Synthesizing nanopores which mimic the functionality of ion-selective biological channels has been a challenging yet promising approach to advance technologies for precise ion-ion separations. Inspired by the facilitated fluoride (F-) permeation in the biological fluoride channel, we designed a highly fluoride-selective TiO2 film using the atomic layer deposition (ALD) technique. The subnanometer voids within the fabricated TiO2 film (4 Å < d < 12 Å, with two distinct peaks at 5.5 and 6.5 Å), created by the hindered diffusion of ALD precursors (d = 7 Å), resulted in more than eight times faster permeation of sodium fluoride compared to other sodium halides. We show that the specific Ti-F interactions compensate for the energy penalty of F- dehydration during the partitioning of F- ions into the pore and allow for an intrapore accumulation of F- ions. Concomitantly, the accumulation of F- ions on the pore walls also enhances the transport of sodium (Na+) cations due to electrostatic interactions. Molecular dynamics simulations probing the ion concentration and mobility within the TiO2 pore further support our proposed mechanisms for the selective F- transport and enhanced Na+ permeation in the TiO2 film. Overall, our work provides insights toward the design of ion-selective nanopores using the ALD technique.

Original languageEnglish (US)
Pages (from-to)16828-16838
Number of pages11
JournalACS Nano
Issue number10
StatePublished - Oct 26 2021
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Engineering
  • General Materials Science
  • General Physics and Astronomy


  • atomic layer deposition
  • cation-anion interplay
  • fluoride transport
  • hard-soft acid-base theory
  • ion-selective membranes
  • subnanometer confinement


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