include (a) narrow solar light absorption spectrum limited to the UV spectrum (5%),
(b) low adsorption capacity for hydrophobic compounds, (c) high aggregation
tendency, and (d) difficult separation and recovery [24].
The TiO 2 nanomaterial Degussa P25 (P25 TiO 2 ) has proven to be a very efficient
photocatalyst for oxidation of several pollutants including pharmaceuticals.
Diclofenac, naproxen, and ibuprofen have shown a 100% removal within a 4 h
photocatalysis using a catalyst load from 0.1 g/L for diclofenac and naproxen to 1.0/
L g for ibuprofen when their initial concentration was 200 ppm [25], which is much
higher than the naturally occurring concentration of these NSAIDs. However, the
use of Degussa P25 TiO 2 has an important drawback: its fine particle size increases
its dispersion in aqueous media and its eventual agglomeration. Also, these
suspended particles can act as a screen that prevents irradiation from reaching
other catalyst particles in the reaction vessel. Therefore, it has been supported in
several substrates like glass and quartz materials with the aim to facilitate its
separation and recycling. Different types of films are found in literature for
photocatalysis on organic pollutants. It has been reported that photocatalysis with
a heterostructured film based on P25 TiO 2 and TEOS (tetraethyl orthosilicate)
supported on a glazed ceramic surface on salicylic acid, ibuprofen, naproxen, and
diclofenac achieved, under optimum conditions, degradation of 76%, 85%, 94%,
and 65%, respectively [26].
Nanotechnology on traditional photocatalysts promises to improve their properties not only in terms of the increase in active surface area but also in terms of their
photoconversion efficiency and stability. Photoconversion efficiency has been
improved by adding noble metal nanoparticles (Ag, Pt, Pd) to a metal oxide
semiconductor surface to reduce charge carriers recombination [27, 28] and, more
recently, by adding carbon nanomaterials such as graphene, reduced graphene oxide
(RGO), and carbon nanotubes. These hybrid nanocomposites have attracted attention of researchers because, in principle, these carbon materials can carry charges,
thus reducing electron-hole recombination [28]. However, Minella et al. have
pointed out that for reduced graphene oxide (RGO), there are results that show a
decrease in efficiency, which was attributed to the following: (a) the null electronhole transfer between TiO 2 and RGO and vice versa; (b) RGO can become a
recombination center by capturing both holes and electrons from TiO2; (c) it can
behave as a competitive light absorber; and (d) it can act as a nonreactive phase that
holds the substrate unchanged [29].
Graphene oxide has also been added to TiO 2 to make photocatalytic
nanocomposites. In these nanocomposites, it can act as an adsorbent, electron
acceptor, and photosensitizer. As a nanomaterial, GO has a large specific area that
increases the surface area on the nanocomposite. Its adsorption properties rely on the
possibility to form pi-pi conjugations between a benzenoid substrate and its aromatic
rings; besides, it can develop ionic interactions with the substrate through its oxygencontaining functional groups at the edges or on the surfaces of carbon-based
nanosheets [30].
Doping of TiO 2 with carbon [31, 32] nitrogen [33, 34], other nonmetals, and
metals and also co-doping are mechanisms to reduce this oxide band gap in order to
284
M. Cerro-Lopez et al.
(b) low adsorption capacity for hydrophobic compounds, (c) high aggregation
tendency, and (d) difficult separation and recovery [24].
The TiO 2 nanomaterial Degussa P25 (P25 TiO 2 ) has proven to be a very efficient
photocatalyst for oxidation of several pollutants including pharmaceuticals.
Diclofenac, naproxen, and ibuprofen have shown a 100% removal within a 4 h
photocatalysis using a catalyst load from 0.1 g/L for diclofenac and naproxen to 1.0/
L g for ibuprofen when their initial concentration was 200 ppm [25], which is much
higher than the naturally occurring concentration of these NSAIDs. However, the
use of Degussa P25 TiO 2 has an important drawback: its fine particle size increases
its dispersion in aqueous media and its eventual agglomeration. Also, these
suspended particles can act as a screen that prevents irradiation from reaching
other catalyst particles in the reaction vessel. Therefore, it has been supported in
several substrates like glass and quartz materials with the aim to facilitate its
separation and recycling. Different types of films are found in literature for
photocatalysis on organic pollutants. It has been reported that photocatalysis with
a heterostructured film based on P25 TiO 2 and TEOS (tetraethyl orthosilicate)
supported on a glazed ceramic surface on salicylic acid, ibuprofen, naproxen, and
diclofenac achieved, under optimum conditions, degradation of 76%, 85%, 94%,
and 65%, respectively [26].
Nanotechnology on traditional photocatalysts promises to improve their properties not only in terms of the increase in active surface area but also in terms of their
photoconversion efficiency and stability. Photoconversion efficiency has been
improved by adding noble metal nanoparticles (Ag, Pt, Pd) to a metal oxide
semiconductor surface to reduce charge carriers recombination [27, 28] and, more
recently, by adding carbon nanomaterials such as graphene, reduced graphene oxide
(RGO), and carbon nanotubes. These hybrid nanocomposites have attracted attention of researchers because, in principle, these carbon materials can carry charges,
thus reducing electron-hole recombination [28]. However, Minella et al. have
pointed out that for reduced graphene oxide (RGO), there are results that show a
decrease in efficiency, which was attributed to the following: (a) the null electronhole transfer between TiO 2 and RGO and vice versa; (b) RGO can become a
recombination center by capturing both holes and electrons from TiO2; (c) it can
behave as a competitive light absorber; and (d) it can act as a nonreactive phase that
holds the substrate unchanged [29].
Graphene oxide has also been added to TiO 2 to make photocatalytic
nanocomposites. In these nanocomposites, it can act as an adsorbent, electron
acceptor, and photosensitizer. As a nanomaterial, GO has a large specific area that
increases the surface area on the nanocomposite. Its adsorption properties rely on the
possibility to form pi-pi conjugations between a benzenoid substrate and its aromatic
rings; besides, it can develop ionic interactions with the substrate through its oxygencontaining functional groups at the edges or on the surfaces of carbon-based
nanosheets [30].
Doping of TiO 2 with carbon [31, 32] nitrogen [33, 34], other nonmetals, and
metals and also co-doping are mechanisms to reduce this oxide band gap in order to
284
M. Cerro-Lopez et al.