154
C. Sun et al.
The theoretical model for predicting the transport rates of ions can be developed by
considering the diffusion effect and the convective effect. The basic formula should
be as follows:
Q i = D i
c i
L
A p + c i Q
(3)
where Q i is the molar flow rate of ions, c i is the concentration difference between
the two sides of NPG membranes, D i is the diffusion coefficient of ions, c i is the
ionic concentration of the bulk solutions, A p is the pore area. To our best knowledge,
currently such model was not yet established to predict the ion transport rates through
graphene nanopores.
3 Porous Graphene as Electrodialysis Membranes
(a) Experimental works
Few comprehensive experiments have been conducted so far in this promising field.
Rollings et al. [28] studied the ion selectivity of graphene nanopores in the electrodialysis process, focusing on the relationship between ion selectivity and pore
size. They created graphene nanopores by using the electrical pulse method. Their
study gave some surprising results that graphene nanopores showed K
+ /Cl
− selectivity ratios over 100 and monovalent/divalent cation selectivity up to 5, even when
the pores were as large as about 20 nm in diameter. They also showed that the
potential of graphene for ion selectivity was underestimated so far due to inappropriate mechanisms, because high throughput, highly selective graphene electrodialysis membranes had no necessity to precisely control the size of the pores (Fig. 5).
The promising ion selectivity of graphene for both monovalent and divalent cations
and anions even for large pores under high electric field intensity shows that the
porous graphene can be effectively used not only as electrodialysis membrane but
also for other selective ions transportation fields, especially in reverse electrodialysis. The low requirement on the precise control of pore size makes the membrane
synthesis would be more reliable, simple and cost-effective. Unfortunately, the experimental works on the water and ion transport through porous graphene membranes
under the electrical fields are very limited currently, and we hope that more and more
outstanding experimental measurements can be performed in the near future.
C. Sun et al.
The theoretical model for predicting the transport rates of ions can be developed by
considering the diffusion effect and the convective effect. The basic formula should
be as follows:
Q i = D i
c i
L
A p + c i Q
(3)
where Q i is the molar flow rate of ions, c i is the concentration difference between
the two sides of NPG membranes, D i is the diffusion coefficient of ions, c i is the
ionic concentration of the bulk solutions, A p is the pore area. To our best knowledge,
currently such model was not yet established to predict the ion transport rates through
graphene nanopores.
3 Porous Graphene as Electrodialysis Membranes
(a) Experimental works
Few comprehensive experiments have been conducted so far in this promising field.
Rollings et al. [28] studied the ion selectivity of graphene nanopores in the electrodialysis process, focusing on the relationship between ion selectivity and pore
size. They created graphene nanopores by using the electrical pulse method. Their
study gave some surprising results that graphene nanopores showed K
+ /Cl
− selectivity ratios over 100 and monovalent/divalent cation selectivity up to 5, even when
the pores were as large as about 20 nm in diameter. They also showed that the
potential of graphene for ion selectivity was underestimated so far due to inappropriate mechanisms, because high throughput, highly selective graphene electrodialysis membranes had no necessity to precisely control the size of the pores (Fig. 5).
The promising ion selectivity of graphene for both monovalent and divalent cations
and anions even for large pores under high electric field intensity shows that the
porous graphene can be effectively used not only as electrodialysis membrane but
also for other selective ions transportation fields, especially in reverse electrodialysis. The low requirement on the precise control of pore size makes the membrane
synthesis would be more reliable, simple and cost-effective. Unfortunately, the experimental works on the water and ion transport through porous graphene membranes
under the electrical fields are very limited currently, and we hope that more and more
outstanding experimental measurements can be performed in the near future.