Water Desalination

Water scarcity, resulting from the ever-increasing demand of freshwater has become one of the most prominent challenges of our time. Given the abundance of seawater and brackish groundwater, purifying saline water to produce freshwater could be a viable solution to this problem. Reverse osmosis (RO), which uses a semipermeable thin-film composite (TFC) membranes to remove salt ions from saline water under high pressure (a few MPa), has become the leading desalination technology. Despite the fact that TFC membranes and the associated processes have been extensively optimized, to date, the high energy consumption and high capital investment for RO desalination have limited its large-scale deployment. In general, the energy footprint and operating cost of desalinating water are largely dependent on the intrinsic permselectivity of RO membranes. Thus, there is a need to develop novel RO membranes with substantially enhanced water permeability and excellent ability to reject salt ions. This has stimulated vigorous efforts toward the discovery and design of novel membrane materials.

Recently, by employing state-of-the-art molecular simulation techniques, we demonstrated the great potential of several nanostructured materials such as aluminosilicate nanotubes (AlSiNTs)¹, nanoporous graphene (NPG)², reduced graphene oxide (rGO)³, covalent triazine frameworks (CTFs)⁴, two-dimensional hydrocarbon polymers (see the Figure 1 below)⁵, zeolites⁶, etc., as RO membranes in water desalination. A detailed understanding of permselectivity enhancement at an atomic level were also carried out to supply the transformative principles to rational design of better RO membranes for more energy-efficient and cost-effective desalination processes.

Figure 1. (a) Density maps of water inside 2D hydrocarbon polymer having elliptical pores of elongated major dimensions. (b) Comparison of 2D hydrocarbon polymer versus existing RO technologies and other classes of membranes (Graphyne, CTF or porous graphene (PG)) (Adopted from Lyu et al. (2018)⁵).

References

(1) Liou, K.-H.; Kang, D.-Y.; Lin, L.-C. Investigating the Potential of Single-Walled Aluminosilicate Nanotubes in Water Desalination. ChemPhysChem 2017, 18 (2), 179–183.

(2) Cohen-Tanugi, D.; Lin, L.-C.; Grossman, J. C. Multilayer Nanoporous Graphene Membranes for Water Desalination. Nano Lett. 2016, 16 (2), 1027–1033.

(3) Lin, L.-C.; Grossman, J. C. Atomistic Understandings of Reduced Graphene Oxide as an Ultrathin-Film Nanoporous Membrane for Separations. Nat. Commun. 2015, 6 (1), 8335.

(4) Lin, L. C.; Choi, J.; Grossman, J. C. Two-Dimensional Covalent Triazine Framework as an Ultrathin-Film Nanoporous Membrane for Desalination. Chem. Commun. 2015, 51 (80), 14921–14924.

(5) Lyu, Q.; Sun, S.; Li, C.; Hu, S.; Lin, L.-C. Rational Design of Two-Dimensional Hydrocarbon Polymer as Ultrathin-Film Nanoporous Membranes for Water Desalination. ACS Appl. Mater. Interfaces 2018, 10 (22), 18778–18786.

(6) Jamali, S. H.; Vlugt, T. J. H.; Lin, L.-C. Atomistic Understanding of Zeolite Nanosheets for Water Desalination. J. Phys. Chem. C 2017, 121 (21), 11273–11280.