Effect of cross-linking on the performance of polymer inclusion membranes (PIMs) for the extraction, transport and separation of Zn(II)

Bosirul Hoque, M. Inês G.S. Almeida, Robert W. Cattrall, Thiruvancheril G. Gopakumar, Spas D. Kolev*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

37 Scopus citations

Abstract

This study demonstrated the advantages of cross-linking of polymer inclusion membranes (PIMs) in terms of improved stability, rate of extraction and extractive capacity. These advantages were illustrated with the new cross-linked PIM for the selective extraction of Zn(II), developed as part of this study and containing bis-(2-ethylhexyl)phosphoric acid (D2EHPA) as the carrier (extractant). Three different base-polymers were tested, namely poly(vinyl chloride) (PVC), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cellulose triacetate (CTA), using poly(ethylene glycol) dimethacrylate (PEG-DMA) as the cross-linking polymer and 2,2-dimethoxy-2-phenyl acetophenone (DMPA) as the initiator. Only PVDF-HFP- and CTA-based PIMs were found to be successful (i.e., homogenous, transparent and mechanically stable). CTA-based PIMs showed a higher extraction rate than the PVDF-HFP-based PIMs and non-cross-linked PIMs containing the same base-polymer, and thus CTA was chosen as the base-polymer for a more detailed study. The effect of the polymer ratio (CTA:PEG-DMA), concentration of D2EHPA, and concentration of plasticizer (i.e., 2-nitrophenyloctyl ether (NPOE)) on the membrane performance was studied. Best performance in terms of stability, rate of extraction and extractive capacity, which were superior to the corresponding non-cross-linked PIM, was achieved with the cross-linked PIM composed of 40 wt% D2EHPA, 10 wt% NPOE, polymers ratio of 6:4 (CTA:PEG-DMA), and 0.6 wt% DMPA. The PIM surface morphology, examined by atomic force microscopy (AFM), correlated well with the rate of Zn(II) extraction. It was also demonstrated that the cross-linked PIM could selectively extract Zn(II) from aqueous solutions at pH 3.0 in the presence of other common base metal ions such as Cd(II), Co(II), Cu(II), and Ni(II) in concentrations 5 times higher than that of Zn(II). Interference from Fe(III) was removed by precipitation with phosphate. The newly developed PIM transported practically all Zn(II) from a feed solution at pH 3 to a 1.0 M HCl receiving solution as a result of the simultaneous extraction and back-extraction of Zn(II) at the corresponding PIM/solution interfaces, and the facilitated transport of Zn(II) across the membrane.

Original languageEnglish
Article number117256
JournalJournal of Membrane Science
Volume589
DOIs
StatePublished - 1 Nov 2019
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2019 Elsevier B.V.

Keywords

  • Bis-(2-ethylhexyl)phosphoric acid (D2EHPA)
  • Cross-linking
  • Poly(ethylene glycol) dimethacrylate
  • Polymer inclusion membrane (PIM)
  • Zinc(II) extraction and transport

ASJC Scopus subject areas

  • Biochemistry
  • General Materials Science
  • Physical and Theoretical Chemistry
  • Filtration and Separation

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