(694f) Artificial Water Channels?Bioinspired and Energy-Efficient Filtration Materials

Authors: 
Shen, Y., University of California
Kumar, M., The Pennsylvania State University

Artificial
water channels
¨Dbioinspired
and energy-efficient filtration materials

Yue-xiao Shen and Manish
Kumar*

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

Water
purification is emerging as an important challenge in the 21st
century,1 globally, and even
in our own backyard with accidents of unsafe and scarce drinking water in
Milwaukee, Flint and California in recent years. Membrane-based technologies
that have been extensively used to produce fresh water from seawater and to
purify microbiologically and chemically contaminated water are energy
intensive. Nature provides excellent examples for energy-efficient desalination
and water filtration. Mangrove trees purify saline water through its root
systems with minimal energy input (Fig. A). In cell membranes, including those
in the mangrove roots (Fig. B), biological water channel proteins aquaporins
(AQPs) (Fig. C) conduct single channel water transport while excluding all
other molecules. This mechanism has inspired us to study on the design of
artificial structures that mimic AQPs and led to the exciting development of
biomimetic membranes for energy-efficient desalination using these structures.2

Here we report
that peptide-appended pillar[5]arene (PAP) artificial water channels (Fig. D)
combine the advantages of biological water channels Aquaporins (AQPs) and
carbon nanotubes (CNTs).3
These channels were functionally inserted into stable poly(butadiene)-b-poly(ethylene oxide) (PB-PEO)
amphiphilic block copolymers.4
We showed that the water conductance of PAP channels in BCPs was in the range
of AQPs¡¯ (~108-109 water molecules/s) (Fig. E). They
could also be vertically aligned in 2 dimensional block copolymers
membranes (Fig. F), with much higher packing density (~2´105/¦Ìm2)
than current synthetic CNTs-based membranes (0.1~2.5´103/¦Ìm2).
The channel based 2D materials were then assembled into a dense active layer on
track-etched polycarbonate membranes via layer-by-layer deposition. This
separating layer was further infiltrated with crosslinking reagents to enhance
its integrity (Fig. G). The resulting highly packed artificial channel based
composite membranes could be promising energy-efficient separation materials
for the future, and showed high water permeability while maintaining
selectivity.

Figure.
Bioinspired artificial water channels-based membranes are designed for
energy-efficient desalination. (A-B) Mangrove lives in the sea and rely on its
root system to purify sea water. (C) Biological water channel proteins
aquaporins (AQPs) in the cell membranes of the mangrove root system have high
water transport rate while rejecting any other solutes and ions. (D) Peptide-appended
pillar[5]arene (PAP) artificial water channels mimic
the structure of AQPs. (E) The water conductance of PAP channels are close to
that of AQPs and carbon nanotubes (CNTs). (F) PAP channels can form densely
packed polymer membranes. (G) Schematic representation of the alternate
multilayers artificial channel based 2D materials and polyethylenimine
deposited on track-etched membranes by layer-by-layer self-assembly.

References

1             Shannon,
M. A. et al. Science and technology
for water purification in the coming decades. Nature 452, 301-310,
(2008).

2             Shen,
Y.-x. et al. Biomimetic membranes: A
review. J. Membr. Sci. 454, 359-381, (2014).

3             Shen,
Y.-x. et al. Highly permeable
artificial water channels that can self-assemble into two-dimensional arrays. Proc. Natl. Acad. Sci. U.S.A. 112, 9810-9815, (2015).

4             Shen,
Y.-x. et al. Artificial water
channels self-assemble into nano-scale domains in block copolymers and retain
high permeability. Submitted to Adv.
Mater.