Electron tomography reveals details of the internal microstructure of desalination membranes

Tyler E. Culp, Yue Xiao Shen, Michael Geitner, Mou Paul, Abhishek Roy, Michael J. Behr, Steve Rosenberg, Junsi Gu, Manish Kumar, Enrique D. Gomez

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

As water availability becomes a growing challenge in various regions throughout the world, desalination and wastewater reclamation through technologies such as reverse osmosis (RO) are becoming more important. Nevertheless, many open questions remain regarding the internal structure of thin-film composite RO membranes. In this work, fully aromatic polyamide films that serve as the active layer of state-of-the-art water filtration membranes were investigated using high-angle annular dark-field scanning transmission electron microscopy tomography. Reconstructions of the 3D morphology reveal intricate aspects of the complex microstructure not visible from 2D projections. We find that internal voids of the active layer of compressed commercial membranes account for less than 0.2% of the total polymer volume, contrary to previously reported values that are two orders of magnitude higher. Measurements of the local variation in polyamide density from electron tomography reveal that the polymer density is highest at the permeable surface for the two membranes tested and establish the significance of surface area on RO membrane transport properties. The same type of analyses could provide explanations for different flux variations with surface area for other types of membranes where the density is distributed differently. Thus, 3D reconstructions and quantitative analyses will be crucial to characterize the complex morphology of polymeric membranes used in next-generation water-purification membranes.

Original languageEnglish
Pages (from-to)8694-8699
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume115
Issue number35
DOIs
StatePublished - 2018

Keywords

  • Polyamide
  • Reverse osmosis
  • Tomography
  • Transmission electron microscopy
  • Voids

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