Environmental Engineering Reference
In-Depth Information
It is remarkable that the
R
ct
in the 2 wt% κ-carrageenan solid was almost the same as that
in the aqueous solution, athough the
R
ct
in the 2 wt% agarose solid was much larger than that
in the aqueous solution. In spite of the high hydrophilicity of the solid surface, there could be
some contact problem between the electrode and the agarose solid. As for the κ-carrageenan,
the sulfonate anionic groups would improve the contact between the electrode and the solid.
Figure 7. (a) Concentration dependence for the diffusion coefficient (
D
app
) of Fe(CN)
6
3-
in 2 wt%
agarose (squares), 2 wt% κ-carrageenan (triangles), and aqueous solution (diamonds) containing 0.5 M
KCl at the rest potential [3]. (b)
D
app
based on Cottrell's equation.
The dependence of the double layer capacitance (
C
dl
) on the Fe(CN)
3
6-
concentration is
shown in figure 8 b). In the aqueous solution,
C
dl
tends to increase with the Fe(CN)
6
3-
concentration, but for the solid system
C
dl
values are only weakly dependent on the Fe(CN)
6
3-
concentration. At 5 mM Fe(CN)
6
3-
concentration,
C
dl
values of the solids are similar to that in
the aqueous solution.
The polysaccharide concentration dependence of
D
app
in the agarose and κ-carrageenan
solids containing 10 mM Fe(CN)
6
3-
is shown in figure 9.
The
D
app
in an aqueous solution containing 10 mM Fe(CN)
6
3-
is also shown (on the y-
axis) in figure 9. The
D
app
values in theκ-carrageenan solid are even higher than that in the
aqueous solution. It can clearly be seen that the polysaccharide concentration does not greatly
affect the molecular diffusion in the solid. Figure 9 shows the plots of charge transfer
resistance (
R
ct
) versus polysaccharide concentration for the 10 mM Fe(CN)
6
3-
in the agarose
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