proposed to participate in enzymatic reactions of living cell systems. Ferryl ion is
proven to be a part of non-heme iron metalloenzymes (Groves 2006; Krebs et al.
2007), which provide substrate hydroxylation. Some authors propose its equivalent
presence in H 2 O 2 systems with Fe
2+ activation (Lee and Sedlak 2009) and its
presence is also supposed in zero-valent iron corrosion systems, where H 2 O 2 is
generated as an intermediate species (Keenan and Sedlak 2008). Calculations of
Bossmann et al. (1998) have shown higher thermodynamic favourability for the
formation of FeO
2+ rather than of
• OH under the assumption that the Fe
2+ ion is
present as Fe(H 2 O) 5 (OH)
+ at circumneutral pH and H 2 O 2 must first be incorporated
into this complex to form Fe(OH)(H 2 O 2 )(H 2 O)4
+
. Let’s conclude with Barbusiński
(2009) it is possible that both
•
OH and FeO
2+ can coexist in Fenton chemistry and,
depending on the operating parameters, one of them predominates.
9.5 Persulfates Chemistry
Persulfates arouse enormous research interest. Over the course of the last 2 years
about ten review papers have been published on sulfate radical-based advanced
oxidation techniques (Boczkaj and Fernandes 2017; Brienza and Katsoyiannis 2017;
Ghanbari and Moradi 2017; Hu and Long 2016; Ike et al. 2018; Liu et al. 2018;
Matzek and Carter 2016; Oh et al. 2016; Wacławek et al. 2017; Wang and Wang
2018; Wang et al. 2016; Xiao et al. 2018; Ye et al. 2017; B.-T. Zhang et al. 2014).
There could be several different reasons why persulfates generate interest in
recent scientific publication that has also been reflected in the number of citations.
One of the reasons could be related to the simultaneous development of the heterogeneous catalysis field, which is directly interconnected with the persulfates one
(Oh et al. 2016). Another reason could be that some time ago a cheaper method was
developed for peroxydisulfate large scale production, which in combination with its
cheaper and safer transport due to the solid state (powder) consequently makes it one
of the most often used oxidants in ISCO (Ike et al. 2018; Wacławek et al. 2017).
Another explanation could be the fact that the sulfate radicals (generated in the PS
system) have different oxidation mechanism in comparison to the hydroxyl ones
(Boczkaj and Fernandes 2017) and possess a very high redox potential, which
consequently makes SO 4
À radical more suitable for degradation of several substances that are immune to standard AOP techniques, e.g., perfluorooctanoic acid
(PFOA) (Wacławek et al. 2017). Sulfate radical oxidation mechanism was broadly
described in a recent work of Ye et al. (2017) as shown in Fig. 9.1.
Persulfates are a group of two oxidants namely peroxydisulfate (PDS) and
peroxymonosulfate (PMS); the main difference between them is that in the PDS
molecule, the peroxide group bridges two sulfur atoms, whereas PMS is a type of an
S-inorganic hydroperoxide. Both of these oxidants are not very reactive when
non-activated, i.e., when they are not generating radical species. The main aim of
the catalytic activation is to weaken the O–O bond of the persulfates (which can
result in homolytic or heterolytic cleavage of the peroxide bond) (Wacławek et al.
9 Radical Reactions and Their Application for Water Treatment
209
proven to be a part of non-heme iron metalloenzymes (Groves 2006; Krebs et al.
2007), which provide substrate hydroxylation. Some authors propose its equivalent
presence in H 2 O 2 systems with Fe
2+ activation (Lee and Sedlak 2009) and its
presence is also supposed in zero-valent iron corrosion systems, where H 2 O 2 is
generated as an intermediate species (Keenan and Sedlak 2008). Calculations of
Bossmann et al. (1998) have shown higher thermodynamic favourability for the
formation of FeO
2+ rather than of
• OH under the assumption that the Fe
2+ ion is
present as Fe(H 2 O) 5 (OH)
+ at circumneutral pH and H 2 O 2 must first be incorporated
into this complex to form Fe(OH)(H 2 O 2 )(H 2 O)4
+
. Let’s conclude with Barbusiński
(2009) it is possible that both
•
OH and FeO
2+ can coexist in Fenton chemistry and,
depending on the operating parameters, one of them predominates.
9.5 Persulfates Chemistry
Persulfates arouse enormous research interest. Over the course of the last 2 years
about ten review papers have been published on sulfate radical-based advanced
oxidation techniques (Boczkaj and Fernandes 2017; Brienza and Katsoyiannis 2017;
Ghanbari and Moradi 2017; Hu and Long 2016; Ike et al. 2018; Liu et al. 2018;
Matzek and Carter 2016; Oh et al. 2016; Wacławek et al. 2017; Wang and Wang
2018; Wang et al. 2016; Xiao et al. 2018; Ye et al. 2017; B.-T. Zhang et al. 2014).
There could be several different reasons why persulfates generate interest in
recent scientific publication that has also been reflected in the number of citations.
One of the reasons could be related to the simultaneous development of the heterogeneous catalysis field, which is directly interconnected with the persulfates one
(Oh et al. 2016). Another reason could be that some time ago a cheaper method was
developed for peroxydisulfate large scale production, which in combination with its
cheaper and safer transport due to the solid state (powder) consequently makes it one
of the most often used oxidants in ISCO (Ike et al. 2018; Wacławek et al. 2017).
Another explanation could be the fact that the sulfate radicals (generated in the PS
system) have different oxidation mechanism in comparison to the hydroxyl ones
(Boczkaj and Fernandes 2017) and possess a very high redox potential, which
consequently makes SO 4
À radical more suitable for degradation of several substances that are immune to standard AOP techniques, e.g., perfluorooctanoic acid
(PFOA) (Wacławek et al. 2017). Sulfate radical oxidation mechanism was broadly
described in a recent work of Ye et al. (2017) as shown in Fig. 9.1.
Persulfates are a group of two oxidants namely peroxydisulfate (PDS) and
peroxymonosulfate (PMS); the main difference between them is that in the PDS
molecule, the peroxide group bridges two sulfur atoms, whereas PMS is a type of an
S-inorganic hydroperoxide. Both of these oxidants are not very reactive when
non-activated, i.e., when they are not generating radical species. The main aim of
the catalytic activation is to weaken the O–O bond of the persulfates (which can
result in homolytic or heterolytic cleavage of the peroxide bond) (Wacławek et al.
9 Radical Reactions and Their Application for Water Treatment
209