Chapter 9
Radical Reactions and Their Application
for Water Treatment
Pavel Hrabák and Stanisław Wacławek
Abstract Basic chemistry and water treatment of broad range of oxidants and
related radical species are covered in this chapter. A general introduction to oxidants
and radicals is followed by detailed sections on chlorine species, advanced oxidation
processes, persulfates, and non-consensual radical mechanisms. Further, detailed
information on oxidant applicability and activation, oxidant-specific recalcitrant
pollutants and commonly formed by-products is provided. To assess the suitability
of the specific oxidants for real water conditions, matrix components interferences
are discussed. Considerable attention is paid to chemistry of innovative oxidants
(persulfates) and to the controversial aspects of superoxide radical anion reactivity
with carbon tetrachloride.
Keywords AOP · Hydroxyl radical · Sulfate radical · Superoxide radical · Ozone ·
Reactive chlorine · Persulfates · Carbon tetrachloride
9.1 Introduction
Free radicals are, from the chemistry point of view definition, atoms or molecules
with one or more unpaired electrons in bonding orbitals whereby paramagnetic metal
ions are not normally regarded as radicals (IUPAC 1997). This electron arrangement
leads, apart from a few important exceptions (see below), to high reactivity of free
radicals. Oxidants generally possess the ability to attract the whole bonding electron
pair from their reaction counterparts. Free radicals, in contrast, often mediate
one-electron transfer reactions. Basic instrumentation for researching radical-driven
reactions is electron paramagnetic resonance (EPR) and stopped-flow spectroscopic
techniques (Hayyan et al. 2016; Qian and Buettner 1999).
Water-stable free radicals—molecular oxygen (O 2 ) and chlorine dioxide
(ClO 2 )—are examples of such important exceptions. Both O 2 and ClO 2 are well
P. Hrabák (*) · S. Wacławek
Institute for Nanomaterials, Advanced Technologies and Innovation, Technical University
of Liberec, Liberec, Czech Republic
e-mail: pavel.hrabak@tul.cz
© Springer Nature Switzerland AG 2020
J. Filip et al. (eds.), Advanced Nano-Bio Technologies for Water and Soil Treatment,
Applied Environmental Science and Engineering for a Sustainable Future,
https://doi.org/10.1007/978-3-030-29840-1_9
203
Radical Reactions and Their Application
for Water Treatment
Pavel Hrabák and Stanisław Wacławek
Abstract Basic chemistry and water treatment of broad range of oxidants and
related radical species are covered in this chapter. A general introduction to oxidants
and radicals is followed by detailed sections on chlorine species, advanced oxidation
processes, persulfates, and non-consensual radical mechanisms. Further, detailed
information on oxidant applicability and activation, oxidant-specific recalcitrant
pollutants and commonly formed by-products is provided. To assess the suitability
of the specific oxidants for real water conditions, matrix components interferences
are discussed. Considerable attention is paid to chemistry of innovative oxidants
(persulfates) and to the controversial aspects of superoxide radical anion reactivity
with carbon tetrachloride.
Keywords AOP · Hydroxyl radical · Sulfate radical · Superoxide radical · Ozone ·
Reactive chlorine · Persulfates · Carbon tetrachloride
9.1 Introduction
Free radicals are, from the chemistry point of view definition, atoms or molecules
with one or more unpaired electrons in bonding orbitals whereby paramagnetic metal
ions are not normally regarded as radicals (IUPAC 1997). This electron arrangement
leads, apart from a few important exceptions (see below), to high reactivity of free
radicals. Oxidants generally possess the ability to attract the whole bonding electron
pair from their reaction counterparts. Free radicals, in contrast, often mediate
one-electron transfer reactions. Basic instrumentation for researching radical-driven
reactions is electron paramagnetic resonance (EPR) and stopped-flow spectroscopic
techniques (Hayyan et al. 2016; Qian and Buettner 1999).
Water-stable free radicals—molecular oxygen (O 2 ) and chlorine dioxide
(ClO 2 )—are examples of such important exceptions. Both O 2 and ClO 2 are well
P. Hrabák (*) · S. Wacławek
Institute for Nanomaterials, Advanced Technologies and Innovation, Technical University
of Liberec, Liberec, Czech Republic
e-mail: pavel.hrabak@tul.cz
© Springer Nature Switzerland AG 2020
J. Filip et al. (eds.), Advanced Nano-Bio Technologies for Water and Soil Treatment,
Applied Environmental Science and Engineering for a Sustainable Future,
https://doi.org/10.1007/978-3-030-29840-1_9
203