Environmental Engineering Reference
In-Depth Information
34.1.3 Capacitive Deionization
Capacitive deionization (CDI) or electrosorption using porous electrodes is another con-
venient way to remove various ions from aqueous solution. Carbon-based materials such
as AC, carbon ibers, carbon aerogels, and CNTs have been employed as electrosorptive
electrodes because of their good conductivity, high surface area, and suitable pore size
distribution. Recent investigation points to the utility of graphene in this area. Li and
coworkers
80
made the irst attempt in this direction where they used chemically synthe-
sized graphene as electrosorptive electrodes for CDI. The experiments were conducted in
NaCl solutions at low voltage (~2 V), and the electrosorption performance was evaluated
(Figure 34.2a through c). A high electrosorption capacity of 1.85 mg/g was exhibited by
graphene via a physisorption-driven electrosorption. Removal of ferric ion by CDI process
Separator
Plate
(a)
(c)
55
Inlet
1.0 V
50
1.2 V
Outlet
45
1.4 V
Electrosorptive
capacity (µmol/g)
Graphene
electrode
Plate
40
1.6 V
24
20
16
12
8
4
(b)
CDI unit
35
1.8 V
30
Applied voltage (V)
2.0 V
Electrical power
1.0
1.2
1.4
1.6
1.8
2.0
25
0
Conductivity
meter
5
10
15
20
25
30
Pump
Time (min)
(d)
(e)
1.0
0.8
1
3
0.6
4
0.4
2
k
1
= 0.026 min
-1
k
2
= 0.050 min
-1
k
3
= 0.039 min
-1
k
4
= 0.041 min
-1
k
5
= 0.317 min
-1
15
0.2
5
0.0
500 nm
0
3
6
9
Time (min)
12
18
FIGURE 34.2
(a) Schematic of electrosorptive unit and (b) cell batch-mode experiment. The CDI unit consisted of graphite
plate, GNF ilm, and separator. (c) The electrosorption of Na
+
onto the GNF electrode at different bias potentials.
(Adapted from Li, H. et al
.
,
Environ. Sci. Technol
., 44, 8692, 2010. With permission.) (d) SEM image of heat-treated
G O/T i O
2
composites. (e) Photocatalytic degradation of 10 mg/L MO at pH 4.0 by (1) neat TiO
2
, (2) mixture of neat
TiO
2
and GO, (3) P25, (4) mixture of P25 with GO, and (5) heat-treated composite of GO/TiO
2
. (Adapted from
Liang, Y. et al
.,
Nano Res.
, 3, 701, 2010. With permission.)
