PEF/photocatalysis method was shown by large TOC reduction (97%) achieved at
360 min. This can be attributed to the destruction of organics by: (i) heterogeneous
Pt(
•
OH) formed from the reaction in Eq. 11.3 and heterogeneous
•
OH from
photogenerated holes on ZnO by the reaction in Eq. 11.13, (ii) homogeneous
•
OH
formed from Fenton’s reaction (Eq. 11.2), from photolysis of Fe(OH)
2+ species via
the reaction in Eq. 11.4, and from UVC photolysis of electrogenerated H 2 O 2 , (iii)
photoinduced holes produced on ZnO, similarly to the reaction in Eq. 11.12, and
(iv) photodecomposition of intermediates under UVC radiation.
11.3.2 Electrocatalytic Anodes
Several authors have improved the EF method by synthesizing anodes with greater
electrocatalytic ability as compared to conventional ones, thereby enhancing the
production of heterogeneous
•
OH from water discharge, similarly to the reaction in
Eq. 11.3. Examples of some stable, nanostructured anodes for such a purpose are
β-PbO 2 (Sirés et al. 2010), porous Ni/BDD/Ta (Li et al. 2018), and ZnO-TiO 2 /GF
(El-Kacemi et al. 2017). The excellent performance of 3D β-PbO 2 deposits obtained
from carbon/polyvinyl-ester composite (Sirés et al. 2010) for the EF process has
been well proven for the treatment of 275 mL of an O 2 -saturated solution with
0.25 mM Methyl Orange in 0.05 M Na 2 SO 4 with 0.2 mM Fe
2+ at pH 3.0, using an
undivided glass cell with a carbon-felt cathode at I ¼ 60 mA. Total decolorization
was achieved after 60 min of electrolysis, a time shorter than 240 min needed for the
analogous EO with Ni cathode in the absence of Fe
2+ , at 300 mA. This corroborates
much greater oxidation power of
•
OH formed from Fenton’s reaction (Eq. 11.2) than
PbO 2 (
•
OH) in EF. Further work of these authors showed the applicability of PbO 2
deposits onto RVC to EO (Recio et al. 2011; Ramírez et al. 2016), being feasible to
incorporate TiNTs (Ramírez et al. 2016), which could be extended in the future to EF
and PEF. Similarly, for 60 mg/L Methylene Blue in 0.05 M Na 2 SO 4 at pH 3.0, the
use of a porous Ni/BDD/Ta anode allowed the overall loss of color after 80 min of
the EF treatment with 0.5 mM Fe
2+ at 120 mA. This was faster than the comparable
EO process, which required 240 min (Li et al. 2018). On the other hand, a nanostructured ZnO-TiO 2 /GF anode was coupled to a GF cathode to treat 250 mL of an
O 2 -saturated solution with 0.12 mM of the dye Amido Black 10, 0.06 M Na 2 SO 4 ,
and 0.1 mM Fe
2+ at pH 3.0 by EF at I ¼ 100 mA (El-Kacemi et al. 2017). Under
these conditions, the dye solution was completely decolorized in 60 min, whereas
91% mineralization was reached after 360 min of the treatment, showing good
effectiveness of this anode for dye destruction.
11 The Use of Nanomaterials in Electro-Fenton and Photoelectro-Fenton Processes
275
360 min. This can be attributed to the destruction of organics by: (i) heterogeneous
Pt(
•
OH) formed from the reaction in Eq. 11.3 and heterogeneous
•
OH from
photogenerated holes on ZnO by the reaction in Eq. 11.13, (ii) homogeneous
•
OH
formed from Fenton’s reaction (Eq. 11.2), from photolysis of Fe(OH)
2+ species via
the reaction in Eq. 11.4, and from UVC photolysis of electrogenerated H 2 O 2 , (iii)
photoinduced holes produced on ZnO, similarly to the reaction in Eq. 11.12, and
(iv) photodecomposition of intermediates under UVC radiation.
11.3.2 Electrocatalytic Anodes
Several authors have improved the EF method by synthesizing anodes with greater
electrocatalytic ability as compared to conventional ones, thereby enhancing the
production of heterogeneous
•
OH from water discharge, similarly to the reaction in
Eq. 11.3. Examples of some stable, nanostructured anodes for such a purpose are
β-PbO 2 (Sirés et al. 2010), porous Ni/BDD/Ta (Li et al. 2018), and ZnO-TiO 2 /GF
(El-Kacemi et al. 2017). The excellent performance of 3D β-PbO 2 deposits obtained
from carbon/polyvinyl-ester composite (Sirés et al. 2010) for the EF process has
been well proven for the treatment of 275 mL of an O 2 -saturated solution with
0.25 mM Methyl Orange in 0.05 M Na 2 SO 4 with 0.2 mM Fe
2+ at pH 3.0, using an
undivided glass cell with a carbon-felt cathode at I ¼ 60 mA. Total decolorization
was achieved after 60 min of electrolysis, a time shorter than 240 min needed for the
analogous EO with Ni cathode in the absence of Fe
2+ , at 300 mA. This corroborates
much greater oxidation power of
•
OH formed from Fenton’s reaction (Eq. 11.2) than
PbO 2 (
•
OH) in EF. Further work of these authors showed the applicability of PbO 2
deposits onto RVC to EO (Recio et al. 2011; Ramírez et al. 2016), being feasible to
incorporate TiNTs (Ramírez et al. 2016), which could be extended in the future to EF
and PEF. Similarly, for 60 mg/L Methylene Blue in 0.05 M Na 2 SO 4 at pH 3.0, the
use of a porous Ni/BDD/Ta anode allowed the overall loss of color after 80 min of
the EF treatment with 0.5 mM Fe
2+ at 120 mA. This was faster than the comparable
EO process, which required 240 min (Li et al. 2018). On the other hand, a nanostructured ZnO-TiO 2 /GF anode was coupled to a GF cathode to treat 250 mL of an
O 2 -saturated solution with 0.12 mM of the dye Amido Black 10, 0.06 M Na 2 SO 4 ,
and 0.1 mM Fe
2+ at pH 3.0 by EF at I ¼ 100 mA (El-Kacemi et al. 2017). Under
these conditions, the dye solution was completely decolorized in 60 min, whereas
91% mineralization was reached after 360 min of the treatment, showing good
effectiveness of this anode for dye destruction.
11 The Use of Nanomaterials in Electro-Fenton and Photoelectro-Fenton Processes
275