44
3 Technetium Coordinated by Inorganic Ligands in Aqueous …
450
500
550
600
650
700
750
800
0.00
0.02
0.04
0.06
0.08
0.10
Absorbance / a.u.
wavelength / nm
0.30 V
0.28 V
0.26 V
0.24 V
0.22 V
0.20 V
Fig. 3.6 UV–Vis spectra recorded during chronoamperometric reduction of [Tc 2 O 2 ] 3+ in 4 M
H 2 SO 4 (reprinted with permission from Chotkowski and Czerwi´ nski (2014b) Copyright 2014
Elsevier)
assumed the generation of [Tc 2 O 2 ]
3+ at 0.3 V versus SHE. At potentials lower than
0.3 V, the intensity of the band at 500 nm decreased while above 600 nm an additional
increase in the absorbance was observed (Fig. 3.6). These authors concluded that such
evolution of the Vis spectrum is related to the generation of hydrated technetium(III)
oxyhydroxide, which exists in the solution as TcO(OH) aq . The overall reaction is
given by Eq. (3.29):
[Tc 2 O 2 ]
3+
+ 2H 2 O + e
−
2TcO(OH) aq + 2H
+
(3.29)
These authors proposed also the oxyhydroxide as the final reaction product on the
basis of literature data but this conclusion should be confirmed using respective crystallographic techniques. An increase in the absorption band above ca. 600 nm is probably due to scattering of the light on the aggregates of hydrated technetium(III) oxyhydroxide (Fig. 3.6). Calculated standard redox potential of the analyzed Tc(IV)/Tc(III)
couple is equal to 0.512 V versus SHE and is in a good agreement with the values
reported by other authors for the Tc(IV)/Tc(III) system (Rard 1983).
So far, no solid evidence has been provided regarding the existence of Tc
2+ in
aqueous solutions. Early literature reviews (see e.g., Magee and Cardwell 1974)
suggested the formation of these forms and they reported standard redox potential
of, e.g., Tc
2+
/Tc system as equal to E
⦵
= 0.4 V. However, more recent works do
not recommend assumptions about the formation of Tc
2+ species (Rard et al. 1999).
Due to the fact that the metallic technetium is important in nuclear fuel reprocessing,
its electrochemical properties are described in Chap. 5.
3 Technetium Coordinated by Inorganic Ligands in Aqueous …
450
500
550
600
650
700
750
800
0.00
0.02
0.04
0.06
0.08
0.10
Absorbance / a.u.
wavelength / nm
0.30 V
0.28 V
0.26 V
0.24 V
0.22 V
0.20 V
Fig. 3.6 UV–Vis spectra recorded during chronoamperometric reduction of [Tc 2 O 2 ] 3+ in 4 M
H 2 SO 4 (reprinted with permission from Chotkowski and Czerwi´ nski (2014b) Copyright 2014
Elsevier)
assumed the generation of [Tc 2 O 2 ]
3+ at 0.3 V versus SHE. At potentials lower than
0.3 V, the intensity of the band at 500 nm decreased while above 600 nm an additional
increase in the absorbance was observed (Fig. 3.6). These authors concluded that such
evolution of the Vis spectrum is related to the generation of hydrated technetium(III)
oxyhydroxide, which exists in the solution as TcO(OH) aq . The overall reaction is
given by Eq. (3.29):
[Tc 2 O 2 ]
3+
+ 2H 2 O + e
−
2TcO(OH) aq + 2H
+
(3.29)
These authors proposed also the oxyhydroxide as the final reaction product on the
basis of literature data but this conclusion should be confirmed using respective crystallographic techniques. An increase in the absorption band above ca. 600 nm is probably due to scattering of the light on the aggregates of hydrated technetium(III) oxyhydroxide (Fig. 3.6). Calculated standard redox potential of the analyzed Tc(IV)/Tc(III)
couple is equal to 0.512 V versus SHE and is in a good agreement with the values
reported by other authors for the Tc(IV)/Tc(III) system (Rard 1983).
So far, no solid evidence has been provided regarding the existence of Tc
2+ in
aqueous solutions. Early literature reviews (see e.g., Magee and Cardwell 1974)
suggested the formation of these forms and they reported standard redox potential
of, e.g., Tc
2+
/Tc system as equal to E
⦵
= 0.4 V. However, more recent works do
not recommend assumptions about the formation of Tc
2+ species (Rard et al. 1999).
Due to the fact that the metallic technetium is important in nuclear fuel reprocessing,
its electrochemical properties are described in Chap. 5.