ORIGINAL PAPER
Synthesis of novel oxidants by electrochemical technology
P. Can
˜
izares Æ C. Sa
´
ez Æ A. Sa
´
nchez-Carretero Æ
M. A. Rodrigo
Received: 19 September 2008 / Accepted: 8 January 2009 / Published online: 30 January 2009
Ó Springer Science+Business Media B.V. 2009
Abstract In this work it has been studied the electro-
chemical production of different oxidants with conductive-
diamond anodes. This technology was found to allow the
production of stable oxidants that can not be easily syn-
thesized using other electrodes or by other more usual
techniques. Thus, it has been found that monoperoxo-
phosphoric acid, and peroxodiphosphate, peroxodisulphate
and ferrate salts can be easily produced by this technology,
when the right operation conditions are used. In contrast,
the production of pure hypochlorite is not favoured,
because this technology leads to the formation of a mixture
of hypochlorite with other oxoanions of chlorine in a
higher oxidation state, particularly chlorates and perchlo-
rates, which seems to be the final product in these
electrolyses. The production of perbromates salts has also
been pointed, although in this case only preliminary results
are shown. In every case, it has been observed two marked
trends in the process efficiency as function of the current
density applied. This fact can be explained in terms of the
contribution of hydroxyl radicals in the oxidation mecha-
nisms that occur on diamond surfaces. Results obtained in
this work also allow explaining the influence of the elec-
trolyte salt on the efficiency of the electrochemical
oxidation of wastewaters.
Keywords Electrosynthesis Á Oxidants Á
Boron doped diamond
1 Introduction
During the recent years, many works have been focused on
the study of electrochemical oxidation with diamond
anodes as an alternative technology for the treatment of a
great variety of wastewaters. Compared with other elec-
trode materials, conductive-diamond has shown a higher
chemical and electrochemical stability, and also a higher
current efficiency in many oxidative processes. In addition,
the high overpotential for water electrolysis is the more
important property of conductive-diamond in the process-
ing of aqueous solutions. This electrochemical window is
large enough to produce hydroxyl radicals with high effi-
ciency, and this species seems to be directly involved in the
oxidation mechanisms that occur on diamond surfaces.
Thanks to these good properties, the use of conductive
diamond in the electrochemical treatment of wastewaters
has allowed achieving great results (in both efficiency and
yield) in comparison to other electrodes materials [1–10].
Likewise, as it has been reported better results are obtained
when supporting electrolytes (such as chloride, sulphate…)
are added to the reaction system to increase the conductivity
of the solution. In these cases, besides hydroxyl radicals
oxidation mechanism, the global oxidation process in con-
ductive-diamond anodes is known to be complemented by
mediated oxidation by other oxidants electrogenerated on
the surface from the electrolyte salts [11, 12]. This fact is
not observed when other electrodes are used. From this
observation, electrochemical oxidation with conductive-
diamond anodes can be considered as a very promising
technology in the electrosynthesis of powerful oxidants.
In this point, during the recent years, some studies have
been focused on the use of diamond electrodes for the
synthesis of oxidants that can be difficult to be generated by
more usual synthesis methods. Thus, several studied have
P. Can
˜
izares Á C. Sa
´
ez Á A. Sa
´
nchez-Carretero Á
M. A. Rodrigo (&)
Department of Chemical Engineering, Facultad de Ciencias
Quı
´
micas, Universidad de Castilla-La Mancha, Campus
Universitario s/n, 13071 Ciudad Real, Spain
e-mail: manuel.rodrigo@uclm.es
123
J Appl Electrochem (2009) 39:2143–2149
DOI 10.1007/s10800-009-9792-7