180 and 240 min, respectively, upon EF treatment of 50 mg/L of perfluorooctanoate
in 0.05 M Na 2 SO 4 with 1.0 mM Fe
2+ at pH 2.0 and E cath ¼ À0.40 V/SCE.
11.2.3 Non-Ferrous Metal-Modified Carbon Nanomaterials
For a given cathode material, the H 2 O 2 production can be maximized by optimizing
main experimental parameters like the electrolyte composition, pH, temperature, cell
configuration, and applied current or E cath (Yang et al. 2018a). Recently, the
modification of carbonaceous cathodes with nonferrous metals has been addressed
aiming at improving their electroactivity, i.e., trying to cause the ORR at less
negative potential in order to reach higher current values at lower overvoltage. In
this scenario, several authors have reported a large H 2 O 2 enhancement by using
Au-Pd (Pizzutilo et al. 2017) and Pt-Hg (Siahrostami et al. 2013) nanoparticles
immobilized onto glassy carbon (GC). However, only few papers have described the
use of bimetallic nanomaterials for the EF treatment of wastewater. For example,
Félix-Navarro et al. (2013) deposited bimetallic Pt-Pd nanoparticles on MWCNTs,
which were sprayed onto a reticulated vitreous carbon (RVC) GDE. This cathode
allowed the accumulation of 71 mM H 2 O 2 in 20 mL of 0.5 M H 2 SO 4 after 20 min at
E cath ¼ À0.50 V vs. Ag/AgCl. This was much greater than 2.2 mM obtained with a
similar cathode without nanoparticles, as a result of the great electroactive area of
Pt-Pd nanoparticles. Under these conditions, nitrobenzene was rapidly and
completely degraded by EF with 0.1 mM Fe
2+ .
Other authors have used metallic oxide nanoparticles, such as TaO 2 deposited
onto GDE (Carneiro et al. 2016), WO 2.72 mixed with Vulcan carbon to prepare
GDEs (Paz et al. 2018), and Ce x A 1-x O 2 (A ¼ Zr, Cu, or Ni) immobilized onto carbon
felt (Li et al. 2017), to enhance the electroactivity regarding the H 2 O 2 production.
The use of WO 2.72 @Vulcan GDE and Pt as the cathode and anode in a threeelectrode cell to degrade 350 mL of a 0.260 mM Orange II solution in 0.1 M
K 2 SO 4 with 0.50 mM Fe
2+ at pH 3.0 by EF yielded 100% decolorization after
120 min at E cath ¼ À0.70 V vs Ag/AgCl. This potential was selected because it led to
the maximum H 2 O 2 accumulation (i.e., 480 mg/L) in the absence of a catalyst (Paz
et al. 2018). The crucial role of
•
OH formed from Fenton’s reaction (Eq. 11.2) was
confirmed from the poorer color loss, ca. 20%, achieved under analogous conditions
but without Fe
2+ . In that so-called electrochemical oxidation with electrogenerated
H 2 O 2 (EO-H 2 O 2 ) process, heterogeneous Pt(
•
OH) is formed from water discharge
from the reaction in Eq. 11.3 (Brillas et al. 2009; Oturan and Aaron 2014; Sirés et al.
2014; Martínez-Huitle et al. 2015; Moreira et al. 2017). In EF, both
• OH and Pt(
•
OH)
contribute to the dye oxidation, with predominance of the former radical.
Pt þ H 2 O ! Pt
• OH
ð
ÞþH
þ
þ e
À
ð11:3Þ
266
I. Sirés and E. Brillas
in 0.05 M Na 2 SO 4 with 1.0 mM Fe
2+ at pH 2.0 and E cath ¼ À0.40 V/SCE.
11.2.3 Non-Ferrous Metal-Modified Carbon Nanomaterials
For a given cathode material, the H 2 O 2 production can be maximized by optimizing
main experimental parameters like the electrolyte composition, pH, temperature, cell
configuration, and applied current or E cath (Yang et al. 2018a). Recently, the
modification of carbonaceous cathodes with nonferrous metals has been addressed
aiming at improving their electroactivity, i.e., trying to cause the ORR at less
negative potential in order to reach higher current values at lower overvoltage. In
this scenario, several authors have reported a large H 2 O 2 enhancement by using
Au-Pd (Pizzutilo et al. 2017) and Pt-Hg (Siahrostami et al. 2013) nanoparticles
immobilized onto glassy carbon (GC). However, only few papers have described the
use of bimetallic nanomaterials for the EF treatment of wastewater. For example,
Félix-Navarro et al. (2013) deposited bimetallic Pt-Pd nanoparticles on MWCNTs,
which were sprayed onto a reticulated vitreous carbon (RVC) GDE. This cathode
allowed the accumulation of 71 mM H 2 O 2 in 20 mL of 0.5 M H 2 SO 4 after 20 min at
E cath ¼ À0.50 V vs. Ag/AgCl. This was much greater than 2.2 mM obtained with a
similar cathode without nanoparticles, as a result of the great electroactive area of
Pt-Pd nanoparticles. Under these conditions, nitrobenzene was rapidly and
completely degraded by EF with 0.1 mM Fe
2+ .
Other authors have used metallic oxide nanoparticles, such as TaO 2 deposited
onto GDE (Carneiro et al. 2016), WO 2.72 mixed with Vulcan carbon to prepare
GDEs (Paz et al. 2018), and Ce x A 1-x O 2 (A ¼ Zr, Cu, or Ni) immobilized onto carbon
felt (Li et al. 2017), to enhance the electroactivity regarding the H 2 O 2 production.
The use of WO 2.72 @Vulcan GDE and Pt as the cathode and anode in a threeelectrode cell to degrade 350 mL of a 0.260 mM Orange II solution in 0.1 M
K 2 SO 4 with 0.50 mM Fe
2+ at pH 3.0 by EF yielded 100% decolorization after
120 min at E cath ¼ À0.70 V vs Ag/AgCl. This potential was selected because it led to
the maximum H 2 O 2 accumulation (i.e., 480 mg/L) in the absence of a catalyst (Paz
et al. 2018). The crucial role of
•
OH formed from Fenton’s reaction (Eq. 11.2) was
confirmed from the poorer color loss, ca. 20%, achieved under analogous conditions
but without Fe
2+ . In that so-called electrochemical oxidation with electrogenerated
H 2 O 2 (EO-H 2 O 2 ) process, heterogeneous Pt(
•
OH) is formed from water discharge
from the reaction in Eq. 11.3 (Brillas et al. 2009; Oturan and Aaron 2014; Sirés et al.
2014; Martínez-Huitle et al. 2015; Moreira et al. 2017). In EF, both
• OH and Pt(
•
OH)
contribute to the dye oxidation, with predominance of the former radical.
Pt þ H 2 O ! Pt
• OH
ð
ÞþH
þ
þ e
À
ð11:3Þ
266
I. Sirés and E. Brillas