Subsequently, electrochemical techniques do not require the addition of
chemicals to take place, but they do require having a supporting electrolyte in
solution which is already present in most of the effluents to be treated [57, 59,
71]. The electrolyte is an important factor to keep in mind in the implementation of
electrochemical processes since its nature influences the type of chemical reactions
that can take place in solution [68]. Other parameters that make electrochemical
techniques feasible for the degradation of pharmaceuticals are the following: they
(a) can be operated at room temperature [62], (b) are versatile and easily controlled
[68], (c) use a low-cost equipment, and (d) can be scaled from the laboratory to the
industry since they operate at room conditions [65].
As we have mentioned before, the catalysis performance relies on its properties.
Thus, in electrooxidation, the anode material plays a key role on the oxidation
reactions that can take place on its surface [62, 72]. As an example, Coria et al.
showed that by using different electrodes, the efficiency of the degradation of
naproxen varied depending on the type of electrode material [69].
Nowadays, electrochemical advanced oxidation processes (EAOPs) have been
studied on a variety of electrode materials because of their chemical stability, low
cost, and high electrocatalytic activity. These materials include Ti/IrO 2 , boron-doped
diamond (BDD), Ti/SnO 2 , Ti/RuO 2 , Ti/RuO 2 –IrO 2 , Ti/RuO 2 –TiO 2 , Pt, Ti/SnO 2 –
Sb, PbO 2 , SnO 2 , Ti/Pt/PbO 2 , and Ti/SnO 2 -Sb 2 O 5 [60, 67]. These materials will
perform in a different way depending on the conditions mentioned, such as pH,
electrolyte, and substrates. Among them, BDD has shown a remarkable performance
under a variety of environments.
Doping diamond with boron makes it conductive but preserves some of its
characteristics such as being chemically inert and mechanically resistant. When
doped with boron, it becomes conductive because the introduction of boron allows
it to have intermediate states between the valence and the conduction gap, enhancing
the electron-transfer ability [73]. As a result, BDD has been studied for the degradation of pharmaceuticals present in wastewater because it is able to resist aggressive
conditions without corroding, it has a high durability, it is efficient and chemically
inert, and it has a high oxygen overpotential. This is important because it favors the
production of oxidizing species such as hydroxyl radicals, peroxodisulfates, hydrogen peroxide, and chlorine, without oxygen production, which permits a better
degradation efficiency [68, 74]. In fact, it has been found that BDD, as an anode,
allows the complete degradation of ketoprofen in a sodium sulfate medium
[72]. However, BDD has the limitation of being expensive and having a weak
adsorption capacity, limiting its application [75].
Therefore, with the aim of preparing cheaper but effective and stable electrode
materials, nanotechnology has been applied in the area of electrocatalysis to build
nanostructured-modified electrodes that show suitable electron transfer and own
remarkable properties such as high surface area, thermal and chemical stability,
tunable porosity, and biocompatibility. Some examples of nanomaterials
implemented in this field are carbon nanomaterials, nanostructured metal oxides,
and platinum nanoparticles which will be discussed here [76, 77].
290
M. Cerro-Lopez et al.
chemicals to take place, but they do require having a supporting electrolyte in
solution which is already present in most of the effluents to be treated [57, 59,
71]. The electrolyte is an important factor to keep in mind in the implementation of
electrochemical processes since its nature influences the type of chemical reactions
that can take place in solution [68]. Other parameters that make electrochemical
techniques feasible for the degradation of pharmaceuticals are the following: they
(a) can be operated at room temperature [62], (b) are versatile and easily controlled
[68], (c) use a low-cost equipment, and (d) can be scaled from the laboratory to the
industry since they operate at room conditions [65].
As we have mentioned before, the catalysis performance relies on its properties.
Thus, in electrooxidation, the anode material plays a key role on the oxidation
reactions that can take place on its surface [62, 72]. As an example, Coria et al.
showed that by using different electrodes, the efficiency of the degradation of
naproxen varied depending on the type of electrode material [69].
Nowadays, electrochemical advanced oxidation processes (EAOPs) have been
studied on a variety of electrode materials because of their chemical stability, low
cost, and high electrocatalytic activity. These materials include Ti/IrO 2 , boron-doped
diamond (BDD), Ti/SnO 2 , Ti/RuO 2 , Ti/RuO 2 –IrO 2 , Ti/RuO 2 –TiO 2 , Pt, Ti/SnO 2 –
Sb, PbO 2 , SnO 2 , Ti/Pt/PbO 2 , and Ti/SnO 2 -Sb 2 O 5 [60, 67]. These materials will
perform in a different way depending on the conditions mentioned, such as pH,
electrolyte, and substrates. Among them, BDD has shown a remarkable performance
under a variety of environments.
Doping diamond with boron makes it conductive but preserves some of its
characteristics such as being chemically inert and mechanically resistant. When
doped with boron, it becomes conductive because the introduction of boron allows
it to have intermediate states between the valence and the conduction gap, enhancing
the electron-transfer ability [73]. As a result, BDD has been studied for the degradation of pharmaceuticals present in wastewater because it is able to resist aggressive
conditions without corroding, it has a high durability, it is efficient and chemically
inert, and it has a high oxygen overpotential. This is important because it favors the
production of oxidizing species such as hydroxyl radicals, peroxodisulfates, hydrogen peroxide, and chlorine, without oxygen production, which permits a better
degradation efficiency [68, 74]. In fact, it has been found that BDD, as an anode,
allows the complete degradation of ketoprofen in a sodium sulfate medium
[72]. However, BDD has the limitation of being expensive and having a weak
adsorption capacity, limiting its application [75].
Therefore, with the aim of preparing cheaper but effective and stable electrode
materials, nanotechnology has been applied in the area of electrocatalysis to build
nanostructured-modified electrodes that show suitable electron transfer and own
remarkable properties such as high surface area, thermal and chemical stability,
tunable porosity, and biocompatibility. Some examples of nanomaterials
implemented in this field are carbon nanomaterials, nanostructured metal oxides,
and platinum nanoparticles which will be discussed here [76, 77].
290
M. Cerro-Lopez et al.