Proton conducting self-assembled metal-organic framework/polyelectrolyte hollow hybrid nanostructures

Unal Sen, Mustafa Erkartal, Chung Wei Kung, Vijay Ramani, Joseph T Hupp, Omar K. Farha

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Herein, a room temperature chemical process to synthesize functional, hollow nanostructures from zeolitic imidazolate framework-8 (ZIF-8) and poly(vinylphosphonic acid) (PVPA) is reported. Syntheses are initiated by physically blending the components - a process that is accompanied first by encapsulation of ZIF-8 crystallites by PVPA and then by fragmentation of the crystallites. The fragmentation process is driven by partial displacement of the methyl-imidazolate ligands of Zn(II) in ZIF-8 by phosphonate groups on PVPA. Differences in rates of diffusion for the components of the reactive mixture yield a Kirkendall-like effect that is expressed as a hollow-particle morphology. The obtained hollow nanostructures feature hybrid shells containing PVPA, ZIF-8, and their cross-reacted products. The hybrid structures display substantial proton conductivities that increase with increasing temperature, even under the anhydrous conditions prevailing at temperatures above the boiling point of water. For example, at T = 413 K the proton conductivity of ZIF-8@PVPA reaches 3.2 (±0.12) × 10-3 S cm-1, a value comparatively higher than that for PVPA (or ZIF-8) in isolation. The high value may reflect the availability in the hybrid structures of free (and partially free), amphoteric imidazole species, and their hydrogen-bonding interactions with phosphonate and/or phosphonic acid units. The persistence of ample conductivity at high temperature reflects the elimination of phosphonic acid group dehydration and dimerization - an effect that strikingly degrades the conductivity of pure PVPA under anhydrous conditions.

Original languageEnglish
Pages (from-to)23015-23021
Number of pages7
JournalACS Applied Materials and Interfaces
Volume8
Issue number35
DOIs
Publication statusPublished - Sep 7 2016

Fingerprint

Polyelectrolytes
Protons
Nanostructures
Metals
Acids
Organophosphonates
Proton conductivity
Crystallites
Temperature
Dimerization
Boiling point
poly(vinylphosphonic acid)
Dehydration
Encapsulation
Hydrogen bonds
Availability
Ligands
Water

Keywords

  • fuel cell
  • hollow nanostructures
  • proton conductivity
  • PVPA
  • ZIF-8

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Proton conducting self-assembled metal-organic framework/polyelectrolyte hollow hybrid nanostructures. / Sen, Unal; Erkartal, Mustafa; Kung, Chung Wei; Ramani, Vijay; Hupp, Joseph T; Farha, Omar K.

In: ACS Applied Materials and Interfaces, Vol. 8, No. 35, 07.09.2016, p. 23015-23021.

Research output: Contribution to journalArticle

Sen, Unal ; Erkartal, Mustafa ; Kung, Chung Wei ; Ramani, Vijay ; Hupp, Joseph T ; Farha, Omar K. / Proton conducting self-assembled metal-organic framework/polyelectrolyte hollow hybrid nanostructures. In: ACS Applied Materials and Interfaces. 2016 ; Vol. 8, No. 35. pp. 23015-23021.
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AB - Herein, a room temperature chemical process to synthesize functional, hollow nanostructures from zeolitic imidazolate framework-8 (ZIF-8) and poly(vinylphosphonic acid) (PVPA) is reported. Syntheses are initiated by physically blending the components - a process that is accompanied first by encapsulation of ZIF-8 crystallites by PVPA and then by fragmentation of the crystallites. The fragmentation process is driven by partial displacement of the methyl-imidazolate ligands of Zn(II) in ZIF-8 by phosphonate groups on PVPA. Differences in rates of diffusion for the components of the reactive mixture yield a Kirkendall-like effect that is expressed as a hollow-particle morphology. The obtained hollow nanostructures feature hybrid shells containing PVPA, ZIF-8, and their cross-reacted products. The hybrid structures display substantial proton conductivities that increase with increasing temperature, even under the anhydrous conditions prevailing at temperatures above the boiling point of water. For example, at T = 413 K the proton conductivity of ZIF-8@PVPA reaches 3.2 (±0.12) × 10-3 S cm-1, a value comparatively higher than that for PVPA (or ZIF-8) in isolation. The high value may reflect the availability in the hybrid structures of free (and partially free), amphoteric imidazole species, and their hydrogen-bonding interactions with phosphonate and/or phosphonic acid units. The persistence of ample conductivity at high temperature reflects the elimination of phosphonic acid group dehydration and dimerization - an effect that strikingly degrades the conductivity of pure PVPA under anhydrous conditions.

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