Formation of iron(VI) in ozonalysis of iron(III) in alkaline solution

Article abstract of DOI:10.1016/j.ica.2006.11.019

Here we report the formation of iron in hexavalent state, Fe^VI O₄^{2 -} in ozonalysis of iron(III) in alkaline medium. The formation of tetrahedral Fe^VI O₄^{2 -} ion is confirmed by UV-Visible an

Full text of DOI:10.1016/j.ica.2006.11.019

Inorganica Chimica Acta 360 (2007) 2789–2791
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Note
Formation of iron(VI) in ozonalysis of iron(III) in alkaline solution
a
a
a
b,
*
Yurii D. Perfiliev , Elena M. Benko , Denis A. Pankratov , Virender K. Sharma
,
a
Sergey K. Dedushenko
a
Department of Chemistry, Moscow State University, 1 Lenin Hills, Moscow 119992, Russia
Florida Institute of Technology, Chemistry Department, 150 West University Boulevard, Melbourne, FL 32901, USA
b
Received 10 August 2006; received in revised form 10 November 2006; accepted 22 November 2006
Available online 29 November 2006
Abstract
Here we report the formation of iron in hexavalent state, FeVIO4 in ozonalysis of iron(III) in alkaline medium. The formation of
2ꢀ
tetrahedral FeVIO4 ion is confirmed by UV–Visible and Mo¨ssbauer spectroscopic techniques. The value of isomer shift, d, of the tetra-
2ꢀ
oxy anion is consistent with known d values for various salts of iron(VI) ion.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Iron(VI); Iron(III); Ozone; Mo¨ssbauer spectroscopy
1. Introduction
sis of green chemistry and alternates to use of chlorine are
being sought. In keeping with this goal, in this paper, we
attempted ozone as an oxidant to form iron(VI). Ozona-
tion is considered relatively environmentally-friendly pro-
cess and does not produce chlorinated by-products.
Ozone has strong oxidizing properties: the redox poten-
tials in acid, neutral, and alkaline solutions are as follows
[20]:
Iron is the most abundant transition element on Earth
and commonly exists in compounds of its +2 and +3 oxi-
dation states. Iron ions in these two oxidation states are
generally used in biological electron transfer processes [1].
Iron in higher oxidation states such as +4, +5, and +6
are involved in iron enzymes, organic synthesis, and Fen-
ton chemistry [2–4]. Examples include capability of Fe(IV)
and Fe(V) at enzymatic sites to abstract H and/or to break
C–C bond [2,5], participation of high-valent nonheme iron-
oxo species in biometric oxidations [6,7], and involvement
of aqua oxoiron(IV) in environmental and catalytic chem-
istry [8,9].
O3 þ 2Hþ þ 2eꢀ ¼ O2 þ H2O E0 ¼ þ2:075 V
O3 þ H2O þ 2eꢀ ¼ O2 þ 2OHꢀ E0 ¼ þ1:246 V
ð1Þ
ð2Þ
Ozone has the great advantage over other oxidants because
of its strong oxidizing property. Ozonation is commonly
used to prepare transition-metal complexes in which the
central atom has a high oxidation state [21]. For example,
iron(IV) in acidic solution can be formed by oxidation of
iron(II) with ozone Eq. (3) [22,23]. The iron(IV) species
in aqueous solution has a half life of about 10 s, thus al-
lowed to measure reaction kinetics of this species with inor-
ganic and organic compounds.
Under strong oxidizing environment, higher oxidation
states of iron have been obtained [10,11]. In recent years,
iron(VI) FeVIO4 has received much attention because of
2ꢀ
its potential use in high energy density rechargeable batter-
ies, in cleaner (‘‘greener’’) technology for organic synthesis,
and in wastewater treatment [3,12–18]. Iron(VI) is gener-
ally produced by oxidizing a basic solution of Fe(III) salt
by hypochlorite [19]. For the last few years, there is empha-
Feaq2þ þ O3 ! FeIVO2þ þ O2
ð3Þ
*
The reduction potentials of iron(VI)/iron(III) couples in
acid and alkaline solutions are presented by
Corresponding author. Tel.: +1 321 674 7310; fax: +1 321 674 8951.
E-mail address: vsharma@fit.edu (V.K. Sharma).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.11.019

2790
Y.D. Perfiliev et al. / Inorganica Chimica Acta 360 (2007) 2789–2791
FeO42ꢀ þ 8Hþ þ 3eꢀ ¼ Fe3þ þ 4H2O E0 ¼ þ2:20 V ð4Þ
1.2
FeO42ꢀ þ 4H2O þ 3eꢀ ¼ FeðOHÞ3 þ 5OHꢀ E0 ¼ þ0:72 V
ð5Þ
1.0
0.8
0.6
0.4
0.2
0.0
In alkaline solution, the redox potential of the ozone/oxy-
gen couple is higher than that of FeO42ꢀ=FeðOHÞ3 couple,
which suggests that ozone can oxidize iron(III) in alkaline
solution to give iron(VI). In the present work, formation of
Fe(VI) by ozonolysis of Fe(III) is demonstrated for the first
time.
Fe(VI)
Fe(III)
2. Experimental
Initially, Fe(NO3)3 was added to 10 M KOH solution,
heated and boiled for 2–3 h. After cooling to room temper-
ature, the Fe(OH)3 residues were separated by filtration. The
concentration of Fe(III) in solutions obtained was about
10ꢀ4 M. Ozonation was carried out in a bubble contactor
at room temperature. Oxygen-fed laboratory glass ozonizer
(Medozon/03, Russia) was used for ozone production. An
initial ozone concentration of 10ꢀ3 M, volume flow velocity
at 5–10 l/h of the gas mixture containing ozone and oxygen,
and the volume of the reaction mixture 5–20 ml were used.
Ozone concentration in the gas phase was recorded by ozone
spectrophotometer analyzer, Medozon 254/5. The contact
time between Fe(III) and ozone to observe the formation
of Fe(VI) was 30 min. There was approximately 70%
conversion of Fe(III) to Fe(VI), which gave an estimated
formation rate of Fe(VI) as 1.4 · 10ꢀ4 M/h.
The UV–Vis measurements were carried out on Cary 3E
Varian spectrometer. Mo¨ssbauer absorption spectra were
measured on a Perseus spectrometer working at constant
velocities. The control and the adjustment of the spectrom-
eter-vibrator rate were performed by a laser interferometer.
A standard c-source of 57Co in metallic chromium matrix
with the activity of 0.5 GBq (a product of Cyclotron,
Co., Ltd., Obninsk, Russia) was employed. Isomer shifts
in this paper are presented relative to a-Fe at 25 ꢁC.
300
400
500
600
700
Wavelength, nm
Fig. 1. Electron spectra of Fe(III) solution in 10 M KOH: before (1) and
after (2) completion of the ozonation (room temperature).
The spectrum in Fig. 1 appears compatible with a tetrahe-
dral geometry of other high-valent metal oxoanions such as
3ꢀ
CrO4 and MnO4ꢀ, which also absorb at long wave-
lengths. The band of iron(VI) at 510 nm corresponds to li-
gand-to-metal charge transfer [26].
Next, Mo¨ssbauer spectroscopic investigation of the
iron(VI) solution prepared by ozonation was carried out
in order to further confirm the oxidation state of iron. A
value of isomer shift, d, of Mo¨ssbauer spectrum is sensitive
to the oxidation state of iron [27]. The measurements of the
iron(VI) solution were unsuccessful due to low concentra-
2ꢀ
tion of FeO4 ions and strong absorption of low-energy
3. Results and discussion
The various forms of Fe(III) hydroxide/oxide are very
insoluble (except in aciꢀd solution), however, Fe(OH)3 is
converted into FeðOHÞ4 complex under strong alkali con-
dition [24]. Formation of complex can be obtained at pH
value as low as 10.7, but due to rapid formation of precip-
itates at this pH, it is advantageous to use pH valꢀues higher
than 12. In the experimental set up, the FeðOHÞ4 complex
was prepared in 10 M OHꢀ solution. The ozonation of the
solution resulted in a dark purple color; the spectrum of
which is shown in Fig. 1.
The absorption spectrum in Fig. 1 has a peak at 510 nm,
a characteristics of iron(VI) in alkaline solution [25]. The
formation of iron(VI) can be represented by:
2FeðOHÞ4ꢀ þ 3O3 þ 2OHꢀ ! 2FeO42ꢀ þ 3O2 þ 5H2O
Fig. 2. Mo¨ssbauer spectrum of Fe(VI) frozen solution in 5 M NaOH
(77 K).
ð6Þ

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2791
[5] J.E. Penner-Hahn, K.S. Eble, T.J. McMurty, M. Renner, A.L. Balch,
J.T. Groves, J.H. Dawson, K.O. Hodgson, J. Am. Chem. Soc. 108
(1986) 7819.
[6] X. Shan, L. Que Jr., J. Org. Biochem. 100 (2006) 421.
[7] A. Basan, M.R.A. Blomberg, P.E.M. Siegbahn, L. Que Jr., Ang.
Chem., Int. Ed. 44 (2005) 2939.
[8] L. Daguillaume, M. Leriche, K. Desboeufs, G. Maillhot, C. George,
N. Chaumerliac, Chem. Rev. 105 (2005) 3388.
[9] A. Ghosh, F.T.D. Oliveira, T. Yano, T. Nishioka, E.S. Beach, I.
Kinoshita, E. Munck, A.D. Ryabov, C.P. Horwitz, T.J. Collins, J.
Am. Chem. Soc. 127 (2005) 2505.
[10] R. Hoppe, K. Mader, Z. Anorg. Allg. Chem. 586 (1990) 115.
[11] M.T. Weller, A.L. Hector, Angew. Chem., Int. Ed. 39 (2000) 4162.
[12] S. Licht, B. Wang, S. Ghosh, Science 285 (1999) 1039.
[13] V.K. Sharma, Adv. Environ. Res. 6 (2002) 143.
[14] V.K. Sharma, Water Sci. Technol. 49 (2004) 69.
[15] V.K. Sharma, F. Kazama, H. Jiangyong, A.K. Ray, J. Water Health
3 (2005) 42.
Mo¨ssbauer radiation by the solvent. To solve this problem,
Fe(NO)3 enriched with 57Fe (95%) was used as iron(III)
source. Iron(VI) ions were prepared by ozonalysis of
iron(III) in 5 M NaOH. The resulted solution was frozen
in liquid nitrogen for Mo¨ssbauer measurements. Mo¨ss-
bauer spectrum of the frozen solution (77 K) is presented
in Fig. 2. The spectrum contains one single-line with the
isomer shift ꢀ0.80(1) mm sꢀ1 and full width at half-height
0.32(5) mm sꢀ1. The d in Fig. 2 is similar to values of d for
various salts of iron(VI) ion, which vary from ꢀ0.79 to
ꢀ0.85 mm sꢀ1 [28]. Thus, the iron(VI) species synthesized
in the present study is the same as has been prepared chem-
ically using hypochlorite ion and by other techniques
[15,29–31].
[16] V.K. Sharma, S.K. Mishra, N. Nesnas, Environ. Sci. Technol. (2006)
In press.
4. Conclusions
[17] J.Q. Jiang, S. Wang, A. Panagoulopoulos, Chemosphere 63 (2006)
212.
[18] J.Q. Jiang, A. Panagoulopoulos, M. Bauer, P. Pearce, J. Environ.
Manag. 79 (2006) 215.
[19] G.W. Thompson, L.T. Ockerman, J.M. Schreyer, J. Am. Chem. Soc.
73 (1951) 1279.
[20] A.J. Bard, R. Parsons, J. Jordon (Eds.), Standard Electrode Poten-
tials in Aqueous Solutions, Marcel Dekker Inc., New York, NY,
1985.
The high-valent iron(VI) was obtained in oxidation of
iron(III) by ozone in alkaline medium. This procedure
can be used as a simple and environmentally-friendly
method to produce FeO42ꢀ ion. The UV–Visible and Mo¨ss-
bauer spectra were found consistent with the hexavalent
iron state of the ion.
Acknowledgement
[21] W.P. Griffith, Coord. Chem. Rev. 219–221 (2001) 259.
[22] T. Logager, J. Holcman, K. Schested, T. Pedersen, Inorg. Chem. 31
(1992) 3523.
[23] O. Pestovsky, A. Bakac, J. Am. Chem. Soc. 126 (2004) 13757.
[24] B.H.J. Bielski, Method Enzymol. 186 (1990) 108.
[25] J.D. Rush, B.H. Bielski, J. Am. Chem. Soc. 108 (1986) 523.
[26] G.D. Michelis, L. Oleari, L.D. Sipio, A.E. Tondello, Coord. Chem.
Rev. 2 (1967) 53.
We thank Dr. Zoltan Homonnay for comments on the
paper. This work was supported by the Russian Founda-
tion for Basic Research, project no. 05-03-33079.
References
[27] Y.D. Perfiliev, Russ. J. Inorg. Chem. 47 (2002) 611.
[28] F. Menil, J. Phys. Chem. Solids 45 (1985) 763.
[29] R.H. Herber, D. Johnson, Inorg. Chem. 18 (1979) 2786.
[30] S. Licht, V. Naschitz, B. Liu, S. Ghosh, N. Halperin, L. Lelperin, D.
Rozen, J. Power Sources 99 (2001) 7.
[1] H. Beinert, R.H. Holm, E. Munck, Science 277 (1997) 653.
[2] J.T. Groves, J. Inorg. Biochem. 100 (2006) 434.
[3] L. Delude, P. Laszlo, J. Org. Chem. 61 (1996) 6350.
[4] S. Goldstein, D. Meyerstein, Acc. Chem. Res. 32 (1999) 547.
[31] K.E. Ayers, N.C. White, J. Electrochem. Soc. 152 (2005) A467.