(314d) Expected Performance and Potential Design Strategies for Highly Selective Biomimetic Desalination Membranes

Expected Performance and Potential Design Strategies for Highly
Selective Biomimetic Desalination Membranes

Jay R. Werber,^1,2 Cassandra J. Porter,²
and Menachem Elimelech²

¹ Department of Chemistry, University of
Minnesota, Minneapolis, MN

² Department of Chemical and Environmental
Engineering, Yale University, New Haven, CT

Reverse
osmosis is a central technology in desalination and the potable reuse of
municipal wastewater. The need for increased selectivity, compared to
conventional thin-film composite (TFC) membranes, has led to interest in
biomimetic membranes. In these membranes, the selective layers mimic the
structure and performance of cell membranes by placing biological or artificial
water channels (e.g., aquaporin and carbon nanotube porins) within a bilayer of
lipids or amphiphilic block copolymers. Aquaporin in particular is nearly
perfectly selective, yet highly permeable to water. Despite much work on
designing water channels and fabricating biomimetic membranes, a fundamental
understanding of the expected performance of this class of membrane materials is
lacking. In this work, we characterize expected biomimetic membrane performance
using the resistance model, which considers individual components in a membrane
as analogs to resistors in a circuit. We first consider the selective layer,
which comprises channels and the surrounding bilayer. While channels have been
well-characterized, permeability data for block copolymer bilayers was scarce.
As such, permeabilities of water, neutral solutes, and ions were measured using
lipid and block copolymer vesicles. Using these permeabilities, we show that a
defect-free biomimetic selective layer could have water/salt selectivities ~100
billion times greater than current membranes, resulting in near-perfect salt
rejection. However, hydrophobic organic micropollutants relevant to wastewater
treatment would be highly permeable, leading to poor rejections. As a possible
solution, we next consider composite membrane structures, particularly the use
of TFC membranes as a support for biomimetic selective layers. We find that the
size-based permeability of TFC membranes would allow for high rejection of
micropollutants. Additionally, TFC membranes as support layers would minimize
the negative impact of defects in the biomimetic selective layer, allowing for
highly selective performance even with substantial defect areas (>1%). This
work provides fundamental insight into molecular transport through biomimetic membranes,
as well as a strategic path towards the fabrication of ultra-selective
desalination membranes.

References:

1.     Werber, J.R.; Deshmukh, A.; Elimelech, M. The
Critical Need for Increased Selectivity, Not Increased Water Permeability, for
Desalination Membranes. Environ. Sci.
Technol. Lett. 2016, 3, 112-120.
DOI: 10.1021/acs.estlett.6b00050

2.     Werber, J.R; Elimelech, M. Permeability and
Selectivity Limits of Biomimetic Desalination Membranes. Science Advances 2018, 4,
eaar8266. DOI: 10.1126/sciadv.aar8266

3.     Werber, J.R.; Porter, C.J.; Elimelech, M. A Path to
Ultra-Selectivity: Support Layer Properties to Maximize Performance of
Biomimetic Desalination Membranes. Environ.
Sci. Technol. 2018, 52,
10737-10747. DOI: 10.1021/acs.est.8b03426