Nanoconfinement Effects on the Transport of Redox Probes in Ionic Liquid-Loaded Mesoporous Silica Thin Films

Yuxin He, M. Arif Khan, Andrew D. Drake, Folami Ladipo, Stephen E. Rankin, Barbara L. Knutson

Research output: Contribution to journalArticlepeer-review


The transport of two redox probes, 1,1′-ferrocenedimethanol (FDM, hydrophilic) and 1,1′-dioctadecyl-4,4′-bipyridinium dibromide (DBD, hydrophobic), through ionic liquid-filled and/or functionalized silica nanoporous thin films is compared as a function of pore size (2.5 and 8 nm diameter pores). Electrochemical impedance spectroscopy (EIS) was used to measure the permeability of these aqueous probes through the bare silica films and silica films with pores containing a physically confined ionic liquid (IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6])), covalently tethered IL-like 3-methyl-1-[3-(trimethoxysilyl)propyl]-1H-imidazol-3-ium ([TMS-MIM]+), and [BMIM][PF6] confined in pores with tethered [TMS-MIM]. Functionalization of the nanoporous thin films with an IL-like group provides a barrier to the hydrophilic redox probe (a 40-fold decrease in permeability relative to bare 2.5 nm porous silica films), with only a 50% corresponding decrease in the permeability of the hydrophobic probe. The selectivity to hydrophobic solutes suggested by the barrier properties of IL-functionalized silica is less pronounced in the films with the larger 8 nm pores. Physically confining an IL in the pores of both bare and IL-functionalized pores results in similar transport as the corresponding non-IL filled pores. The ability to tune solute transport through nanoconfined ILs using pore size and surface functionalization is critical to the design of composite thin films for IL-based separation and energy storage applications.

Original languageEnglish
Pages (from-to)12107-12117
Number of pages11
JournalIndustrial and Engineering Chemistry Research
Issue number33
StatePublished - Aug 24 2022

Bibliographical note

Funding Information:
This work was financially supported by the United States National Science Foundation (NSF) under grant no. CBET-1604491 and Honeywell Corporation. Part of this work was performed in part at the Electron Microscopy Center which belongs to the National Science Foundation NNCI Kentucky Multiscale Manufacturing and Nano Integration Node, supported by ECCS-1542174. This research used resources of the Advanced Photon Source (APS) at Argonne National Laboratory, which is supported by the United States Department of Energy (DOE) Office of Science User Facility (Contract No. DE-AC02-06CH11357).

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

ASJC Scopus subject areas

  • Chemistry (all)
  • Chemical Engineering (all)
  • Industrial and Manufacturing Engineering


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