(272e) 3D Morphological Characterization of the Polyamide Active Layer of Reverse Osmosis Membranes Using TEM and Soft X-Ray Scattering

3D morphological characterization
of the polyamide active layer of reverse osmosis membranes using TEM and soft
X-ray scattering

Tyler Culp^a,
Yuexiao Shen^a, Mou
Paul^b, Abhishek Roy^b,
Steve Rosenberg^b, Michael Behr^c, Cheng Wang^d,
Manish Kumar^a, Enrique Gomez,^a,e

^a Department of Chemical
Engineering, The Pennsylvania State University, University Park, PA 16802

^b
DOW
Water and Process Solutions, Edina, MN 55439

^c
Analytical
Sciences, The DOW Chemical Company, Midland, MI 48667

^d
Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720

^eMaterials Research
Institute, The Pennsylvania State University, University Park, PA 16802

Abstract:

Polyamide-based thin-film composite (TFC) membranes
used for reverse osmosis (RO) and nanofiltration (NF) separation processes are
at the forefront of water desalination and purification technologies due to
their high salt rejection, high energy efficiency, and ease of operation. Nevertheless,
in spite of the benefits of RO and NF membranes, many open questions about the
internal nanostructure of the membrane active layer remain, such as the
dispersion and distribution of acid functional groups. We demonstrate that
resonant soft X-ray scattering (RSOXS), where the X-ray energy is tuned to
absorption edges of the constituent materials, is a powerful tool to examine
the microstructure of the polyamide layer. In conjunction with complementary
techniques such as transmission electron microscopy (TEM), where tomography is
used to obtain a 3D reconstruction of the polyamide active layer, the effect of
cross-linking can be quantified in 3D for a systematic series of membranes.
This relationship can then be applied to a series of commercially available RO
and NF membranes where the effect of polyamide cross-linking on their
respective structure and water transport properties can be evaluated. The
combination of RSOXS with traditional characterization tools provides a
strategy for linking the chemical structure to the morphology and water
transport properties of RO and NF membranes.