Chemistry Reference
In-Depth Information
1.55
0.50
1.45
1.35
1
1.25
0.45
1.15
1.05
0.40
1
2
0.95
2
0.85
0.35
3
0.75
3
0.65
4
0.30
0.55
0
100
200
300
0
100
200
300
Time (min)
(a)
(b)
Time (min)
11.4
(a) and (b) Changes in solution concentration of Ni(II) and
rongalite for an initial concentration ratio rongalite/Ni(II) of 1.5/0.5
as a function of time and at 313 K, containing (1) only Ni(II) and
rongalite; (2) 4.6 g L
-
1
freshly formed PAN fibre; (3) 20.0 g L
-1
freshly formed PAN fibre; (4) 29.6 g L
-
1
freshly formed PAN fibre
(
¥
) and equivalent amounts of PAN-fibre precursors. Data from
the modelling using Equations 11.1 and 11.2 are given in
bullets (•).
First, it can be seen that the content of Ni(II) in solution is much lower
when the PAN fibre or its precursors are present in solution. This is very
clear because, apart from the reduction of Ni(II) by rongalite in solution,
chelate formation also occurs between Ni(II) and PAN-active groups
(cyanide, carboxylic acid), resulting in a decrease of free Ni(II). In addition,
the drop in the concentration of rongalite is much more pronounced in the
presence of PAN fibre and its precursors. It is well known in the literature
that Ni(II) complexes formed with cyanide (e.g. Na
2
[Ni(CN)
4
]) are excel-
lent catalysts for the decomposition of rongalite. Therefore, formation of
complexes between Ni(II) and PAN fibre through cyanide results in the for-
mation of similar complexes, and they are responsible for the continuing
drop in the rongalite concentration.
Secondly, the drop in Ni(II) concentration is even more pronounced in
the presence of the PAN fibres compared with the fact that equivalent
amounts of PAN precursors are dissolved. By equivalent amounts, it is
meant that an equivalent amount of functional groups are dissolved in solu-
tion. This difference can be explained by two effects:
•
Using precursors, Ni(II) concentration drops because of reduction by
rongalite and complex formation with the functional groups of the PAN
precursors, followed by reduction.
•
Using fibres, the first effect also applies but, in addition, absorption of
Ni(II) in the fibre structure (not only on the surface) occurs. It should
also be noted that in the fibre, the functional groups are close to each
other, which means that complex formation can occur much faster com-
