Porous Graphene Membranes for Solute Separation …
147
them, and ion exchange membranes selectively allow anions or cations to pass
through. Electrodialysis, on the other hand, has some advantages and some limitations compared with conventional water desalination techniques (e.g. RO). For
example, it requires minimum water pretreatment. However, electrodialysis with
conventional membranes can only be operated for brackish/lower salt concentrated
water due to their higher thickness and lower permeability. Owing to the high water
permeability of the NPG membrane and its remarkable ion selectivity, it has a great
potential to overcome these limitations of conventional membranes [3, 23].
The selective ion transport through functionalized graphene nanopores was
detected in 2008 by Sint et al. [24], and they proposed that functionalized graphene
nanopores with certain size, charge, and chemical property possessed high selectivity
for different ions in aqueous solution. In 2010, Suk and Aluru [25] performed molecular dynamics (MD) simulations and showed that the NPG membrane possessed
a high water flux rate compared to the conventional RO membranes. The NPG
membrane was proposed as a promising candidate for water desalination by CohenTanugi and Grossman [1] in 2012 based on the MD simulation results, and later on,
they continued the work on graphene-based water desalination membranes in which
they reported that graphene exhibited a high salt rejection rate along with higher
water permeability compared to the conventional RO membranes [26]. Afterward in
2014, O’Hern et al. [2] conducted experiments in this novel study and measured the
transport rates of various ions across a single-layer NPG. In 2015, Surwade et al.
[27] presented the promising salt rejection rate of nearly 100% using single-layer
NPG with high water flux. In 2016, Rollings et al. [28] experimentally measured the
ion selectivity of graphene nanopore using electrodialysis technique and especially
the cation–anion selectivity at different voltage levels with different pore sizes. They
indicated that a comparatively large porous graphene membrane can exhibit phenomenal ion selectivity. Zhang et al. [29] also demonstrated that graphene can reject salt
ions effectively with energy conservation under low applied electric potential and
lower driving pressure.
In this chapter, we review the theoretical and experimental works regarding
NPG membranes for water purification using RO and electrodialysis techniques.
We summary the research achievements and discussions in these representative
works for the NPG membranes in the area of water purification. This chapter shows
that the NPG membrane has tremendous potential for water purification with a
good selective ionic transportability and high water flux. We anticipate that this
chapter will not only provide an exposure to the researchers in the research field of
solute separation but also navigate and lead toward the new applications of NPG
membranes in related areas like heavy metal removing [30], reverse electrodialysis
[31], gas separation [32].
2 Porous Graphene as Reverse Osmosis Membranes
(a) Experimental works
147
them, and ion exchange membranes selectively allow anions or cations to pass
through. Electrodialysis, on the other hand, has some advantages and some limitations compared with conventional water desalination techniques (e.g. RO). For
example, it requires minimum water pretreatment. However, electrodialysis with
conventional membranes can only be operated for brackish/lower salt concentrated
water due to their higher thickness and lower permeability. Owing to the high water
permeability of the NPG membrane and its remarkable ion selectivity, it has a great
potential to overcome these limitations of conventional membranes [3, 23].
The selective ion transport through functionalized graphene nanopores was
detected in 2008 by Sint et al. [24], and they proposed that functionalized graphene
nanopores with certain size, charge, and chemical property possessed high selectivity
for different ions in aqueous solution. In 2010, Suk and Aluru [25] performed molecular dynamics (MD) simulations and showed that the NPG membrane possessed
a high water flux rate compared to the conventional RO membranes. The NPG
membrane was proposed as a promising candidate for water desalination by CohenTanugi and Grossman [1] in 2012 based on the MD simulation results, and later on,
they continued the work on graphene-based water desalination membranes in which
they reported that graphene exhibited a high salt rejection rate along with higher
water permeability compared to the conventional RO membranes [26]. Afterward in
2014, O’Hern et al. [2] conducted experiments in this novel study and measured the
transport rates of various ions across a single-layer NPG. In 2015, Surwade et al.
[27] presented the promising salt rejection rate of nearly 100% using single-layer
NPG with high water flux. In 2016, Rollings et al. [28] experimentally measured the
ion selectivity of graphene nanopore using electrodialysis technique and especially
the cation–anion selectivity at different voltage levels with different pore sizes. They
indicated that a comparatively large porous graphene membrane can exhibit phenomenal ion selectivity. Zhang et al. [29] also demonstrated that graphene can reject salt
ions effectively with energy conservation under low applied electric potential and
lower driving pressure.
In this chapter, we review the theoretical and experimental works regarding
NPG membranes for water purification using RO and electrodialysis techniques.
We summary the research achievements and discussions in these representative
works for the NPG membranes in the area of water purification. This chapter shows
that the NPG membrane has tremendous potential for water purification with a
good selective ionic transportability and high water flux. We anticipate that this
chapter will not only provide an exposure to the researchers in the research field of
solute separation but also navigate and lead toward the new applications of NPG
membranes in related areas like heavy metal removing [30], reverse electrodialysis
[31], gas separation [32].
2 Porous Graphene as Reverse Osmosis Membranes
(a) Experimental works