4.1 Carbon Nanotubes (CNTs) for NSAIDs Removal
Carbon nanotubes show a great potential for applications involving the oxidation of
compounds present in wastewaters due to their exceptional features which include a
good electrical conductivity, chemical stability, high surface area, and mechanical
strength. Consequently, they can be used to modify an electrode to increase its
electroactivity and stability [57, 65].
Moreover, it has been shown that CNTs have a strong adsorption capacity due to
reactive groups that are present at their surface, which enhance their capacity for the
removal of the target molecules. Parameters such as the size of the nanotubes or the
electrostatic interactions influence greatly their ability of adsorption [60, 78]. Montes
et al. reported that a current increase was achieved by a sequestration of naproxen
due to π-π interactions with the methoxy-naphthyl ring which is highly aromatic.
This observation also explains why this strong adsorption effect was not observed
with ibuprofen [79].
Furthermore, in the experiment performed by Díaz et al., an electrochemical
signal was only observed after the addition of CNTs for the degradation of naproxen,
which corroborates an electron transfer process. On top of that, it was established
that by increasing the volume of CNTs from 5 to 15 μL, the current increased as well,
due to more superficial area available for naproxen oxidation; but by increasing
volume up to 20 μL of CNTs, the current decreased, which means that having an
augmented thickness on the nanotubes film promotes its instability. The results
showed that the removal of naproxen in water was 82.5% and 77% for 500 and
250 rpm stirring, respectively [57].
In another interesting study, multiwalled carbon nanotubes (MWCNTs) were
dispersed in an electrolytic solution containing diclofenac. The purpose of this
experiment was to investigate the degradation of this drug under a variety of
conditions using three different electrode materials: Ti/RuO 2 , Ti/TiO 2 , and
Ti/RuO 2 -TiO 2 . The addition of MWCNTs had a positive effect on the percentage
removal of this pharmaceutical since a removal of about 75% was achieved with a
dosage of 70 mg/L MWCNTs. This result was explained based on an increase in the
hydroxyl radical production due the electrode-like behavior of the MWCNTs that
can, at an appropriate current density, produce additional OH radicals. These particle
electrodes reduce O 2 to H 2 O 2 and catalyze hydrogen peroxide decomposition to
hydroxyl radicals [60].
4.2 Titanium Dioxide (TiO 2 ) Nanostructures
TiO 2 nanomaterials are semiconductors that have been studied particularly as
photocatalysts in water remediation because ultraviolet light can induce the formation of an electron-hole pair capable of producing oxygen reactive species that can
oxidize organics in a high degree. Moreover, TiO 2 is cheap, chemically stable, and
nontoxic [80]. In the field of electrocatalysis, under an applied current or voltage,
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291
Carbon nanotubes show a great potential for applications involving the oxidation of
compounds present in wastewaters due to their exceptional features which include a
good electrical conductivity, chemical stability, high surface area, and mechanical
strength. Consequently, they can be used to modify an electrode to increase its
electroactivity and stability [57, 65].
Moreover, it has been shown that CNTs have a strong adsorption capacity due to
reactive groups that are present at their surface, which enhance their capacity for the
removal of the target molecules. Parameters such as the size of the nanotubes or the
electrostatic interactions influence greatly their ability of adsorption [60, 78]. Montes
et al. reported that a current increase was achieved by a sequestration of naproxen
due to π-π interactions with the methoxy-naphthyl ring which is highly aromatic.
This observation also explains why this strong adsorption effect was not observed
with ibuprofen [79].
Furthermore, in the experiment performed by Díaz et al., an electrochemical
signal was only observed after the addition of CNTs for the degradation of naproxen,
which corroborates an electron transfer process. On top of that, it was established
that by increasing the volume of CNTs from 5 to 15 μL, the current increased as well,
due to more superficial area available for naproxen oxidation; but by increasing
volume up to 20 μL of CNTs, the current decreased, which means that having an
augmented thickness on the nanotubes film promotes its instability. The results
showed that the removal of naproxen in water was 82.5% and 77% for 500 and
250 rpm stirring, respectively [57].
In another interesting study, multiwalled carbon nanotubes (MWCNTs) were
dispersed in an electrolytic solution containing diclofenac. The purpose of this
experiment was to investigate the degradation of this drug under a variety of
conditions using three different electrode materials: Ti/RuO 2 , Ti/TiO 2 , and
Ti/RuO 2 -TiO 2 . The addition of MWCNTs had a positive effect on the percentage
removal of this pharmaceutical since a removal of about 75% was achieved with a
dosage of 70 mg/L MWCNTs. This result was explained based on an increase in the
hydroxyl radical production due the electrode-like behavior of the MWCNTs that
can, at an appropriate current density, produce additional OH radicals. These particle
electrodes reduce O 2 to H 2 O 2 and catalyze hydrogen peroxide decomposition to
hydroxyl radicals [60].
4.2 Titanium Dioxide (TiO 2 ) Nanostructures
TiO 2 nanomaterials are semiconductors that have been studied particularly as
photocatalysts in water remediation because ultraviolet light can induce the formation of an electron-hole pair capable of producing oxygen reactive species that can
oxidize organics in a high degree. Moreover, TiO 2 is cheap, chemically stable, and
nontoxic [80]. In the field of electrocatalysis, under an applied current or voltage,
Nanotechnologies for Removal of Nonsteroidal Anti-inflammatory Drug from. . .
291