Highly Permeable Polymer Membranes Containing Directed Channels for Water Purification

Benjamin S. Hsiao, SUNY at Stony Brook, DMR 1019370

The concept of directed nano-sized channels regulating the flow of water, originally found in nature in the form of aquaporin membrane proteins, can be applied to the design of novel highly permeable membranes for water purification. Potential materials to fabricate these water channels include, e.g., carbon nanotubes, liquid crystals, and graphene oxide, all somewhat limited in terms of practical large-scale productions, as well as polymer matrices with embedded nanofibrous networks from polysaccharide nanofibers (cellulose and/or chitin). In the latter case, the directed water channels are formed by the continuously connected hollow cylindrical gaps between the cross-linked nanofibers and the polymer matrix (Figure 1). The gap thickness (and, thus, the size selectivity of the membrane) can be regulated by physical interactions or chemical bonding at the involved surfaces. Furthermore, adjusting the hydrophilicity as well as the charge density (and polarity) of the polysaccharide fiber surfaces by chemical functionalization (e.g., partial carboxylization), allows to fine-tune the membrane selectivity against specific species, e.g., heavy metal ions. The permeation flux in thin-film nanofibrous composite (TFNC) membranes with a three-tier structure (Figure 2) is typically 2-10 times higher than that of existing commercial membranes, at comparable rejection ratio.

Figure 1 Schematic representation of the nature of water channels in the nanocomposite barrier layer. A continuously cross-linked (see area marked by the red circle) skeleton of cellulose nanofibers (yellow) guides a continuously connected system of directed water channels (blue) formed by the connected hollow cylindrical gaps between the nanofibers and the polymer matrix (pink). Ma HY, Burger C, Hsiao BS, Chu B, ACS Macro Letters 1(6), 723–726, 2012.

Figure 2 (Left) Schematic hierarchical structure of a thin-film nanofiber composite membrane containing three layers of randomly deposited

fibers with different diameters. (Right) Cross-sectional SEM views of the barrier layer and nanofibrous scaffold in a typical TFNC membrane.

The PIs and the whole research team including research scientists, graduate students, undergraduate students, and high school students (summer) are working on the project.

The PIs are collaborating with Liquidity, Inc. (U.S.) for portable drinking water and Allied Aqua (AA) company (China) in order to scale up the membrane production to industrial scale. Initial AA applications of the produced water filter membranes will include the wastewater purification in oil fields in China and Africa.

The PIs and co-workers have published numerous articles in various journals, such as Bio-macromolecules, Journal of Materials Chemistry, ACS Macro Letters, etc., as well as book chapters, and presented this work at various international conferences.

Figure 3 Prof. Hsiao/Chu, scientists, graduate students, undergraduate students, and high school students.

Highly Permeable Polymer Membranes Containing Directed Channels for Water Purification

Benjamin S. Hsiao, SUNY at Stony Brook, DMR 1019370