light. In this research, ibuprofen could be 100% eliminated from the model water
solution within 10 h of reaction, while paracetamol was removed in an 85% and
antipyrine in a 70% during the same reaction period [43].
In the search for better photocatalysts, graphitic carbon nitride g-C 3 N 4 , a metalfree organic polymeric semiconductor, is now being studied to remove organic
pollutants from water due to its nontoxicity, stability, low cost, and narrow band
gap (2.7eV) [44]. Polymeric graphite-like C 3 N 4 , prepared by the polycondensation
of melamine at 500
C for 4 h, has been used as a photocatalyst for the degradation of
pharmaceuticals including salicylic acid and ibuprofen. This material shows,
through SEM analysis, the formation of irregular particles and microlayers. Also,
adsorption-desorption isotherms indicate that it is mesoporous with a broad pore-size
distribution in the range of 5–100 nm with a mean size of 20 nm. This photocatalyst,
under UV-vis irradiation and after 4 h of reaction, achieved a low decomposition for
both NSAIDs, a 20% degradation for ibuprofen and a 30% for salicylic acid. This
low degradation suggests the formation of several intermediates identified in previous works; for ibuprofen some identified intermediates are 2-hydroxyl-propanoic
acid, 1,4-benzenecarboxylic acid, hydroxyl-acetic acid, and phenol. For salicylic
acid, some identified intermediates are 2,3-dihidroxybenzoic acid,
2,5-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid. These intermediates
suggest a mechanism where the first step involves the hydroxyl radicals attack to
the aromatic ring and, later on, the ring opening of their hydroxylated products to
form short-chain carboxylic acids. A second pathway that has also been suggested is
the direct cleavage of the aromatic ring which is highly stable; but, in any case, this
aromatic ring opening is the rate-determining step that leads to a low degradation
rate [45].
In a comparative study, exfoliated g-C 3 N 4 and P 25 TiO 2 were tested toward
paracetamol, ibuprofen, and diclofenac photocatalytic degradation. Almost complete
degradation of these pharmaceuticals was achieved with P25 TiO 2 under UV light,
and a less effective degradation (about 50–75%) was achieved with g-C 3 N 4 under
visible light. An interesting result of this study is the fact that intermediates from
both ibuprofen and paracetamol were completely removed; but for diclofenac,
intermediates were detected even after 12 h of irradiation. Some of these, identified
by GCMS, were carbazole-1-acetic acid, 2,6-dichloroaniline, and hydroxylated
derivatives [46].
Despite its suitable properties, g-C 3 N 4 photocatalytic performance still needs to
be improved by increasing its specific surface area, diminishing charge carrier
recombination, and broadening its visible-NIR light absorption spectrum.
Photocatalytic activity of g-C 3 N 4 is significantly enhanced when it is nanostructured
or combined, via doping or coupling, with metals, nonmetals, or other semiconductors. To this respect, Wang et al. synthesized a novel ternary photocatalyst based on
g-C 3 N 4 loaded with single atom-dispersed silver and carbon quantum dots and
studied its photocatalytic behavior toward naproxen. With this material, an 87.5%
naproxen and a 52.1% TOC removal were observed after 24 min of visible light
irradiation, and after 96 min of extended irradiation, a 65.2 % TOC removal was
attained. In this research, about a 10% inhibition on naproxen removal was observed
286
M. Cerro-Lopez et al.
solution within 10 h of reaction, while paracetamol was removed in an 85% and
antipyrine in a 70% during the same reaction period [43].
In the search for better photocatalysts, graphitic carbon nitride g-C 3 N 4 , a metalfree organic polymeric semiconductor, is now being studied to remove organic
pollutants from water due to its nontoxicity, stability, low cost, and narrow band
gap (2.7eV) [44]. Polymeric graphite-like C 3 N 4 , prepared by the polycondensation
of melamine at 500
C for 4 h, has been used as a photocatalyst for the degradation of
pharmaceuticals including salicylic acid and ibuprofen. This material shows,
through SEM analysis, the formation of irregular particles and microlayers. Also,
adsorption-desorption isotherms indicate that it is mesoporous with a broad pore-size
distribution in the range of 5–100 nm with a mean size of 20 nm. This photocatalyst,
under UV-vis irradiation and after 4 h of reaction, achieved a low decomposition for
both NSAIDs, a 20% degradation for ibuprofen and a 30% for salicylic acid. This
low degradation suggests the formation of several intermediates identified in previous works; for ibuprofen some identified intermediates are 2-hydroxyl-propanoic
acid, 1,4-benzenecarboxylic acid, hydroxyl-acetic acid, and phenol. For salicylic
acid, some identified intermediates are 2,3-dihidroxybenzoic acid,
2,5-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid. These intermediates
suggest a mechanism where the first step involves the hydroxyl radicals attack to
the aromatic ring and, later on, the ring opening of their hydroxylated products to
form short-chain carboxylic acids. A second pathway that has also been suggested is
the direct cleavage of the aromatic ring which is highly stable; but, in any case, this
aromatic ring opening is the rate-determining step that leads to a low degradation
rate [45].
In a comparative study, exfoliated g-C 3 N 4 and P 25 TiO 2 were tested toward
paracetamol, ibuprofen, and diclofenac photocatalytic degradation. Almost complete
degradation of these pharmaceuticals was achieved with P25 TiO 2 under UV light,
and a less effective degradation (about 50–75%) was achieved with g-C 3 N 4 under
visible light. An interesting result of this study is the fact that intermediates from
both ibuprofen and paracetamol were completely removed; but for diclofenac,
intermediates were detected even after 12 h of irradiation. Some of these, identified
by GCMS, were carbazole-1-acetic acid, 2,6-dichloroaniline, and hydroxylated
derivatives [46].
Despite its suitable properties, g-C 3 N 4 photocatalytic performance still needs to
be improved by increasing its specific surface area, diminishing charge carrier
recombination, and broadening its visible-NIR light absorption spectrum.
Photocatalytic activity of g-C 3 N 4 is significantly enhanced when it is nanostructured
or combined, via doping or coupling, with metals, nonmetals, or other semiconductors. To this respect, Wang et al. synthesized a novel ternary photocatalyst based on
g-C 3 N 4 loaded with single atom-dispersed silver and carbon quantum dots and
studied its photocatalytic behavior toward naproxen. With this material, an 87.5%
naproxen and a 52.1% TOC removal were observed after 24 min of visible light
irradiation, and after 96 min of extended irradiation, a 65.2 % TOC removal was
attained. In this research, about a 10% inhibition on naproxen removal was observed
286
M. Cerro-Lopez et al.