Acidic conditions around pH 3 also favor the conversion of the HO
• scavengers
carbonate and bicarbonate into carbonic acid, which has a low reactivity against HO
•
(Legrini et al. 1993). At circumneutral pH, it has been suggested that the oxidant
species are both HO
• and ferryl (Pouran et al. 2015). The participation of Fe(V)¼O
species in conjunction with visible absorbing iron species has been suggested
(Pignatello et al. 1999).
Although the method is efficient, H 2 O 2 has to be added continuously and acidic
conditions have to be maintained. The most frequent uses have been the treatment of
industrial water, soils, and leachates, nitroaromatics, polychlorinated phenols, herbicides (2,4-D and 2,4,5-T), and pesticides. The method is useful to treat highstrength organic wastewaters (Pouran et al. 2015).
The photoelectro-Fenton method (Boye et al. 2003) complements photo-Fenton
and EF reaction, but the photoelectrochemical process is more powerful than the EF
process (Brillas et al. 2003a).
As said for the dark Fenton processes, ZVI or nZVI can be used also as solid iron
materials in photo-Fenton reactions, and the first reports were published in 1998 for
pesticides, finding that there was no significant difference in the degradation rate
between the UV/Fe(0)/H 2 O 2 and the UV/Fe
2+ /H 2 O 2 systems (Doong and Chang
1998a, b). Later, reports on treatment of dyes (Kusic et al. 2006; Devi et al. 2009),
and total petroleum hydrocarbons from a diesel fuel (Dehghani et al. 2014) were
published. Fenton and photo-Fenton oxidation of petroleum aromatic hydrocarbons
using nZVI was recently reported (Fard et al. 2013).
The performance of nZVI in the heterogeneous Fenton process was compared
with EF and PEF processes for phenol degradation, finding that PEF was the most
efficient process (Babuponnusami and Muthukumar 2012).
7.3.7 Photoferrioxalate and Other Fe(III) Complexes
Oxalic acid forms complexes with Fe(III) that absorb strongly from 254 to 450 nm,
being active up to 510 nm (Hatchard et al. 1956; Pozdnyakov et al. 2008). The
absorption corresponds to a LMCT band, with ε max values around 10
3
–10
4
1/(M cm). Photolysis of trisoxalatoferrate(III) (ferrioxalate) constitutes the most
used chemical actinometer; the quantum yield of Fe
2+ formation is high
(ϕ ¼ 1.0–1.2) and almost independent of the wavelength (Hatchard et al. 1956).
If H 2 O 2 is added, the photochemical reduction of the Fe(III) complex will be
coupled to a Fenton reaction (Eq. 7.22) (Domènech et al. 2004; Litter 2005;
Safarzadeh-Amiri et al. 1997; Zuo and Hoigné 1992). Thus, the use of illuminated
mixtures of H 2 O 2 and ferrioxalate is very efficient for the photodegradation of
organic contaminants; the energy required to treat the same volume of the selected
wastewater is ca. 20% of the energy required by the common photo-Fenton system
(Safarzadeh-Amiri et al. 1997; Safarzadeh-Amiri et al. 1996a, b; Nogueira and
Jardim 1999).
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M. I. Litter
• scavengers
carbonate and bicarbonate into carbonic acid, which has a low reactivity against HO
•
(Legrini et al. 1993). At circumneutral pH, it has been suggested that the oxidant
species are both HO
• and ferryl (Pouran et al. 2015). The participation of Fe(V)¼O
species in conjunction with visible absorbing iron species has been suggested
(Pignatello et al. 1999).
Although the method is efficient, H 2 O 2 has to be added continuously and acidic
conditions have to be maintained. The most frequent uses have been the treatment of
industrial water, soils, and leachates, nitroaromatics, polychlorinated phenols, herbicides (2,4-D and 2,4,5-T), and pesticides. The method is useful to treat highstrength organic wastewaters (Pouran et al. 2015).
The photoelectro-Fenton method (Boye et al. 2003) complements photo-Fenton
and EF reaction, but the photoelectrochemical process is more powerful than the EF
process (Brillas et al. 2003a).
As said for the dark Fenton processes, ZVI or nZVI can be used also as solid iron
materials in photo-Fenton reactions, and the first reports were published in 1998 for
pesticides, finding that there was no significant difference in the degradation rate
between the UV/Fe(0)/H 2 O 2 and the UV/Fe
2+ /H 2 O 2 systems (Doong and Chang
1998a, b). Later, reports on treatment of dyes (Kusic et al. 2006; Devi et al. 2009),
and total petroleum hydrocarbons from a diesel fuel (Dehghani et al. 2014) were
published. Fenton and photo-Fenton oxidation of petroleum aromatic hydrocarbons
using nZVI was recently reported (Fard et al. 2013).
The performance of nZVI in the heterogeneous Fenton process was compared
with EF and PEF processes for phenol degradation, finding that PEF was the most
efficient process (Babuponnusami and Muthukumar 2012).
7.3.7 Photoferrioxalate and Other Fe(III) Complexes
Oxalic acid forms complexes with Fe(III) that absorb strongly from 254 to 450 nm,
being active up to 510 nm (Hatchard et al. 1956; Pozdnyakov et al. 2008). The
absorption corresponds to a LMCT band, with ε max values around 10
3
–10
4
1/(M cm). Photolysis of trisoxalatoferrate(III) (ferrioxalate) constitutes the most
used chemical actinometer; the quantum yield of Fe
2+ formation is high
(ϕ ¼ 1.0–1.2) and almost independent of the wavelength (Hatchard et al. 1956).
If H 2 O 2 is added, the photochemical reduction of the Fe(III) complex will be
coupled to a Fenton reaction (Eq. 7.22) (Domènech et al. 2004; Litter 2005;
Safarzadeh-Amiri et al. 1997; Zuo and Hoigné 1992). Thus, the use of illuminated
mixtures of H 2 O 2 and ferrioxalate is very efficient for the photodegradation of
organic contaminants; the energy required to treat the same volume of the selected
wastewater is ca. 20% of the energy required by the common photo-Fenton system
(Safarzadeh-Amiri et al. 1997; Safarzadeh-Amiri et al. 1996a, b; Nogueira and
Jardim 1999).
154
M. I. Litter