4 cm
2 CNTs sponge or graphite-based GDE as the cathode, at a cathodic potential
(E cath ) of À0.50 V/saturated calomel electrode (SCE). After 120 min of electrolysis,
the pollutant removal was 96% with 75% of total organic carbon (TOC) abatement
using the sponge. These values are much higher than the 48% and 35% obtained for
graphite-based GDE, respectively. A superior degradation performance upon the
incorporation of CNTs in the GDE has also been described during the EF treatment
of the dye Rhodamine B (Tian et al. 2016a). Excellent removal has also been
reported for Acid Red 14 with a MWCNTs-based GDE (Roth et al. 2016) and for
m-cresol (Chu et al. 2013), Basic Blue 41 (Pajootan et al. 2014), and Acid Red
14 and Acid Blue 92 (Babaei-Sati and Parsa 2017) with graphite-MWCNTs.
Graphene is composed of a 2D planar sheet with monoatomic thickness, made of
sp
2 carbon atoms densely organized into a honeycomb structure (see Fig. 11.1). As
in the case with CNTs, multilayers are also feasible. Graphene has been applied to
the EF process as a pristine nanomaterial (Mousset et al. 2016b; Chen et al. 2016a),
coated onto carbon felt (Le et al. 2015, 2017; Yang et al. 2017), carbon cloth
(Mousset et al. 2016a), carbon-cloth GDEs (Garcia-Rodriguez et al. 2018), or carbon
fiber (Mousset et al. 2017a), and mixed with graphite and PTFE (Zhang et al. 2018).
Table 11.1 collects the main results obtained for several target organic pollutants
using these cathodes. All the trials were carried out at bench scale using undivided
cells at the optimum pH for Fenton’s reaction (Eq. 11.2). Three-electrode cells with a
constant E cath between the cathode and the reference electrode (SCE) or
two-electrode cells with constant current (I) or current density ( j) were utilized.
In most cases, O 2 was bubbled into the solutions to ensure their saturation, aiming
at enhancing the largest H 2 O 2 production by the reaction in Eq. 11.1. In setups
equipped with carbon cloth GDE (Garcia-Rodriguez et al. 2018), O 2 was pumped
through the dry surface to produce H 2 O 2 at the wet surface, which is in contact with
the solution. Table 11.1 shows that very short electrolysis time was needed to
degrade the model pollutants, whereas much longer time (up to 480 min) was
necessary for achieving significant mineralization degrees because of the greater
recalcitrance of byproducts to the attack of
•
OH. In general, worse results were found
with raw cathodes without Gr. Figure 11.2 schematizes the preparation of a Gr/
carbon-cloth cathode, involving the electrochemical exfoliation of a graphite rod to
obtain graphene, which was mixed with Nafion
® (PTFE suspension) and then
ultrasonicated to obtain the graphene ink to coat the carbon cloth. Figure 11.2 also
highlights the greater H 2 O 2 electrogeneration with the Gr/carbon-cloth cathode
compared with the uncoated cloth. This led to the greatest degradation (92%) and
mineralization (57%) degrees for a 1.4 mM phenol solution using the coated cathode
(see Table 11.1), only reaching 72% and 41% in the absence of Gr. Therefore, the
larger H 2 O 2 production favored a greater accumulation of
•
OH, thus resulting in the
faster oxidation of organics.
11 The Use of Nanomaterials in Electro-Fenton and Photoelectro-Fenton Processes
261
2 CNTs sponge or graphite-based GDE as the cathode, at a cathodic potential
(E cath ) of À0.50 V/saturated calomel electrode (SCE). After 120 min of electrolysis,
the pollutant removal was 96% with 75% of total organic carbon (TOC) abatement
using the sponge. These values are much higher than the 48% and 35% obtained for
graphite-based GDE, respectively. A superior degradation performance upon the
incorporation of CNTs in the GDE has also been described during the EF treatment
of the dye Rhodamine B (Tian et al. 2016a). Excellent removal has also been
reported for Acid Red 14 with a MWCNTs-based GDE (Roth et al. 2016) and for
m-cresol (Chu et al. 2013), Basic Blue 41 (Pajootan et al. 2014), and Acid Red
14 and Acid Blue 92 (Babaei-Sati and Parsa 2017) with graphite-MWCNTs.
Graphene is composed of a 2D planar sheet with monoatomic thickness, made of
sp
2 carbon atoms densely organized into a honeycomb structure (see Fig. 11.1). As
in the case with CNTs, multilayers are also feasible. Graphene has been applied to
the EF process as a pristine nanomaterial (Mousset et al. 2016b; Chen et al. 2016a),
coated onto carbon felt (Le et al. 2015, 2017; Yang et al. 2017), carbon cloth
(Mousset et al. 2016a), carbon-cloth GDEs (Garcia-Rodriguez et al. 2018), or carbon
fiber (Mousset et al. 2017a), and mixed with graphite and PTFE (Zhang et al. 2018).
Table 11.1 collects the main results obtained for several target organic pollutants
using these cathodes. All the trials were carried out at bench scale using undivided
cells at the optimum pH for Fenton’s reaction (Eq. 11.2). Three-electrode cells with a
constant E cath between the cathode and the reference electrode (SCE) or
two-electrode cells with constant current (I) or current density ( j) were utilized.
In most cases, O 2 was bubbled into the solutions to ensure their saturation, aiming
at enhancing the largest H 2 O 2 production by the reaction in Eq. 11.1. In setups
equipped with carbon cloth GDE (Garcia-Rodriguez et al. 2018), O 2 was pumped
through the dry surface to produce H 2 O 2 at the wet surface, which is in contact with
the solution. Table 11.1 shows that very short electrolysis time was needed to
degrade the model pollutants, whereas much longer time (up to 480 min) was
necessary for achieving significant mineralization degrees because of the greater
recalcitrance of byproducts to the attack of
•
OH. In general, worse results were found
with raw cathodes without Gr. Figure 11.2 schematizes the preparation of a Gr/
carbon-cloth cathode, involving the electrochemical exfoliation of a graphite rod to
obtain graphene, which was mixed with Nafion
® (PTFE suspension) and then
ultrasonicated to obtain the graphene ink to coat the carbon cloth. Figure 11.2 also
highlights the greater H 2 O 2 electrogeneration with the Gr/carbon-cloth cathode
compared with the uncoated cloth. This led to the greatest degradation (92%) and
mineralization (57%) degrees for a 1.4 mM phenol solution using the coated cathode
(see Table 11.1), only reaching 72% and 41% in the absence of Gr. Therefore, the
larger H 2 O 2 production favored a greater accumulation of
•
OH, thus resulting in the
faster oxidation of organics.
11 The Use of Nanomaterials in Electro-Fenton and Photoelectro-Fenton Processes
261