Photocatalytic degradation of acetaminophen over Ag, Au and Pt loaded TiO2 using solar light

Article abstract of DOI:10.1016/j.jphotochem.2019.01.032

The sustainability and feasibility of using solar irradiation instead of UV light in photocatalysis is a promising approach for water remediation. In this study, photocatalytic degradation (PCD) of a widely used analgesic and antipyretic drug, acetaminophen (AP), with noble metal loaded TiO₂ photocatalysts (Ag/TiO₂, Au/TiO₂ and Pt/TiO₂) was investigated in aqueous suspension using solar light. The deposition of noble metals (Ag, Au and Pt) onto the TiO₂ surface enhanced the PCD of AP under different operating conditions including pH, surfactants and drug excipients. However, lower degradation rate constants of AP were obtained under simulated and direct solar light as compared to UV light. The degradation mechanism of AP under UV as well as simulated solar light was found to follow similar, though not identical, reaction pathways leading to hydroxylated intermediates (e.g. 4-acetamidoresorcinol (4-AR), 4-acetamidocatechol (4-AC) and hydroquinone (HQ)) through competitive routes. The PCD of AP followed a pseudo first order kinetics according to Langmiur-Hinshelwood model. Noble metal (Ag, Au and Pt) loaded TiO₂ photocatalysts can be used effectively to degrade AP in water under both solar and UV light.

Full text of DOI:10.1016/j.jphotochem.2019.01.032

Accepted Manuscript
Title: Photocatalytic degradation of acetaminophen over Ag,
Au and Pt loaded TiO using solar light
2
Authors: Osama Nasr, Omima Mohamed, Al-Sayed
Al-Shirbini, Aboel-Magd Abdel-Wahab
PII:
S1010-6030(18)31458-8
DOI:
Reference:
https://doi.org/10.1016/j.jphotochem.2019.01.032
JPC 11691
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
9 October 2018
24 January 2019
29 January 2019
Please cite this article as: Nasr O, Mohamed O, Al-Shirbini A-Sayed, Abdel-Wahab A-
Magd, Photocatalytic degradation of acetaminophen over Ag, Au and Pt loaded TiO2
using solar light, Journal of Photochemistry and amp; Photobiology, A: Chemistry
(2019), https://doi.org/10.1016/j.jphotochem.2019.01.032
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Photocatalytic degradation of acetaminophen over
Ag, Au and Pt loaded TiO
2
using solar light
a
a
b
Osama Nasr , Omima Mohamed , Al-Sayed Al-Shirbini , and Aboel-Magd
a*
Abdel-Wahab
a
Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt
National Institute of Laser Enhanced Science (NILES), Cairo University, Giza 12613, Egypt
b

Corresponding author. Tel.: +2 01000104909; fax: +2 088 2080209
E-mail address: wahab_47@hotmail.com
Declarations of interest: none
Graphical abstract
HIGHLIGHTS

Noble metal (Ag, Au and Pt) loaded TiO
characterized.
2
photocatalysts were prepared and

Solar photocatalytic degradation of acetaminophen (AP) was investigated and
compared with UV light.


Noble metal/TiO enhances the photodegradation and mineralization of AP.
Degradation products were identified, and a plausible mechanism was
proposed.
2

Solar photocatalytic degradation of AP followed a pseudo first order kinetics.
Abstract
The sustainability and feasibility of using solar irradiation instead of UV light in
photocatalysis is a promising approach for water remediation. In this study,
1

photocatalytic degradation (PCD) of a widely used analgesic and antipyretic drug,
acetaminophen (AP), with noble metal loaded TiO photocatalysts (Ag/TiO , Au/TiO
and Pt/TiO ) was investigated in aqueous suspension using solar light. The deposition
of noble metals (Ag, Au and Pt) onto the TiO surface enhanced the PCD of AP under
2
2
2
2
2
different operating conditions including pH, surfactants and drug excipients. However,
lower degradation rate constants of AP were obtained under simulated and direct solar
light as compared to UV light. The degradation mechanism of AP under UV as well as
simulated solar light was found to follow similar, though not identical, reaction
pathways leading to hydroxylated intermediates (e.g. 4-acetamidoresorcinol (4-AR),
4
-acetamidocatechol (4-AC) and hydroquinone (HQ)) through competitive routes. The
PCD of AP followed a pseudo first order kinetics according to Langmiur-Hinshelwood
model. Noble metal (Ag, Au and Pt) loaded TiO photocatalysts can be used effectively
to degrade AP in water under both solar and UV light.
Keywords: Acetaminophen; Solar light; TiO ; Noble metal; Hydroxyl radical
2
2
1
. Introduction
Heterogeneous photocatalysis has received a great deal of attention due to its potential
in energy production and environmental remediation. In particular, TiO -based
2
photocatalytic materials can convert solar energy into chemical energy via redox
processes to yield useful materials such as hydrogen and hydrocarbons, and to
decompose pollutants in air and water [1]. Although TiO exhibits low toxicity, good
2
chemical stability and suitable band gap edges which can induce the desired redox
reactions, it only absorbs photons with light wavelengths in the UV or near-UV region
2

(
which accounts for less than 5% of the total solar light spectrum) because of its large
bandgap (3 ‒ 3.2 eV) [2, 3]. However, noble metal (e.g. Au, Ag, Pd and Pt) deposits on
the TiO surface can absorb visible light due to surface plasmon resonance (SPR),
2
extending the photocatalytic performance to visible region, thus enabling practical
applications using solar energy [4].
Pharmaceuticals and personal care products have emerged as significant classes of
organic contaminants which have been detected in wastewater, surface water, ground
water and even drinking water throughout the world [5, 6]. Their prevalence in aquatic
environments, even at low concentrations, have attracted great attention because of their
adverse health effects [7, 8].
Acetaminophen (paracetamol, N-acetyl-p-aminophenol or AP) is widely used
over-the-counter analgesic and antipyretic drug. It is one of the top 200 prescription
drug in the USA [9]. Although it is safer at therapeutic doses, AP may be fatal at higher
doses via oxidative transformation to N-acetyl-p-benzoquinone imine (NAPQI), which
is a toxic compound leading to hepatic necrosis [10]. It is also associated with a risk of
rare but serious skin reactions [11]. AP and its metabolites are excreted from the body
in 58 – 68% during therapeutic use and it has been detected in different aquatic
environments throughout the world at concentration levels from ng/L to μg/L [12-16].
The photocatalytic degradation, kinetic optimization and degradation pathways of
AP using UV/TiO have been extensively studied by many research groups [17-20].
2
However, few investigations related to the photocatalytic degradation of AP as well as
its degradation products under visible and/or solar light have been reported [21-23]. In
addition, the use of Au/TiO
2
and Pt/TiO for AP removal has not been substantially
2
examined [24, 25].
3

In this work, Ag/TiO
2
, Au/TiO
2
and Pt/TiO
2
were prepared, characterized and
employed to improve the activity of TiO
2
for the decomposition of AP under solar light.
Photocatalytic degradation of AP under direct solar radiation was examined to exploit
the high intensity of solar radiation in Egypt. In addition, UV light (ACE lamp) was
also used for comparison in order to investigate the effect of photon energy on the
photocatalytic degradation of AP. According to our knowledge from literature review
there are no comparative studies so far on the use of these light sources for AP
degradation. Effects of some operational parameters (e.g. catalyst dose, light intensity,
initial concentration of AP, pH, surfactant and drug excipients) were also investigated.
More interestingly, the photocatalytic degradation products were identified using GC
and GC/MS techniques in order to rationalize a plausible mechanism of the
photocatalytic degradation of AP.
2
. Experimental
.1. Materials
2
TiO
2
P25, AgNO3, HAuCl
4
.H
2
O and HPtCl
6
were purchased from Degussa,
Euromedex, Electron Microscopy Sciences and BDH, respectively. Acetaminophen
9
4
8%, resorcinol 98% and 1,2,4-benzenetriol 98% were purchased from Alfa Aesar.
-nitrocatechol
97%
was
obtained
with
from
1%
Sigma
Aldrich.
N,O-bis(trimethylsilyl)trifluoroacetamide
trimethylchlorosilane
(BSTFA+TMCS, 99:1) was purchased from Supelco, USA. All other chemicals used
in this study were of analytical or reagent grade.
2
.2. Instrumentation
X-ray diffraction (XRD) patterns were recorded on a PW2103 Philips diffractometer.
N
2
sorption isotherms were obtained using an automated gas sorption apparatus (Nova
4

3
200, Quantachrome). Transmission electron microscopy (TEM) images were acquired
using a FEI Tecnai G2 spirit microscope equipped with a Veleta camera operating at
20 kV. UV-Vis spectra were recorded on a PerkinElmer LAMBDA 750
Spectrophotometer. FTIR spectra were collected on a Thermo-Nicolet-6700 FTIR
1
1
13
spectrometer. H NMR and C NMR spectra were recorded on Varian EM390 (90
MHz) and Bruker (100 MHz) spectrometers, respectively. Gas chromatography
analyses were achieved using a Thermo Scientific Trace Ultra GC equipped with TG-
5
MS capillary column (30 m x 0.25 mm i.d., 0.25 μm film thickness) and coupled to a
FID detector. GC/MS analyses were performed using Agilent 7890B/5977A GC/MS
equipped with HP-5MS capillary column (30 m x 0.25 mm i.d., 0.25 μm film thickness).
Light sources
Solar simulator: The photocatalytic experiments were conducted in a Pyrex beaker
(covered from the top with quartz plate to minimize water evaporation) irradiated from
above, at a distance of 15 cm, by using a solar simulator (Oriel, New port) equipped
with a 1000 W xenon lamp and AM 1.5 G filter. The system was covered with
aluminum foil to minimize light loss.
Direct Sunlight: Photocatalytic experiments under direct sunlight were conducted out
in a Pyrex beaker covered from the top by quartz cover to minimize water evaporation.
The intensities of both natural and simulated sunlight were measured at the reaction site
using an auto digital Newport solar meter (model 91150V).
ACE lamp: A Vycor glass cell (29.5 × 2.5 cm), equipped with a reflux condenser, and
externally irradiated with a 450 W medium pressure mercury lamp (ACE glass Inc.,
USA, maximum emission at 296.7–578 nm (4.18-2.15 eV)) immersed in Pyrex well.
The distance between the sample cell and the lamp is 5 cm. The system was covered
with aluminum foil to decrease light loss, and the apparatus was set up in a metallic
5

cabinet [26]. The intensity of UV light at the reaction site was measured using Sper
Scientific UV-A/B light meter, model 1219B70.
2
.3. Preparation of Ag/TiO
In a typical procedure, to a 50 mL of AgNO
g of TiO was added and sonicated for 15 min. The mixture was stirred for 45 min
under N gas purging before irradiation with a 450 W ACE lamp for 1 h. The obtained
2
, Au/TiO
2
and Pt/TiO
2
photocatalysts
3
, HAuCl
4
or HPtCl in deionized water,
6
1
2
2
powder was collected by centrifugation, washed four times with deionized water and
finally dried at 80 °C for 8 h [27].
2
.4. Photocatalytic degradation of AP
.4.1. General procedure
2
To a 50 mL solution of AP in deionized water, the photocatalyst was added and the
mixture was sonicated for 15 minutes to get homogeneous suspension. The
magnetically stirred suspension was irradiated using the light source. Aliquots (5 mL)
were withdrawn from the suspension at different intervals and then filtered through 0.2
μm membrane filter (CHMLAB group, Spain) to remove essentially all the catalyst.
The degradation of AP was monitored by measuring its absorbance at 243 nm. The
chemical oxygen demand (COD) was measured by the closed reflux colorimetric
method (5220D) [28].
2
.4.2. Identification of photocatalytic degradation products
a) Sample preparation and derivatization
Aliquot (1 mL) was withdrawn from the reaction mixture, filtered through 0.2 μm
membrane filter to remove essentially all the catalyst, evaporated under vacuum at
4
0 °C to remove water and finally the residue was derivatized as described in previous
report [26].
6

b) GC and GC/MS Analyses
GC and GC/MS analyses of the aforementioned derivatized photolysates were carried
out using the same method described elsewhere [26]. The injector and MS detector were
maintained at 250 and 200 °C, respectively. The temperature programming was: 80 °C
for 1 min, 7 °C/min up to 150 °C, hold time for 5 min, 7 °C/min to 250 °C, hold time
for 5 min. The separated products were identified using authentic samples or/and Wiley
and NIST mass spectral libraries.
2
.4.3. Preparation of authentic samples
2
.4.3.1. 4-Acetamidocatechol (4-AC)
4
-AC was synthesized via one pot procedure where 4-nitrocatechol was reduced by
sodium hydrosulfite (Na
2
S
2
O
4
) followed by acetylation [29]
.
The obtained white solid
(410 mg, 76.2 % yield) was stored under vacuum to avoid darkening in air. mp 186 –
-1
-1
-1
1
88 °C; FTIR (KBr): 3327 cm (sharp, N-H), 3214-3184 cm (O-H), 1624 cm (C=O);
1H NMR (90 MHz, DMSO-d
): δ (ppm) 9.6 (s, 1H, NHCOCH
), 8.9 (s, 1H, OH), 8.45
6
3
(s, 1H, OH), 7.1 (d, 1H, aromatic), 6.65 (dd, 1H, aromatic), 6.5 (d, 1H, aromatic), 2 (s,
1
3
3
1
H, CH
3
). C NMR (100 MHz, DMSO-d ): δ (ppm) 167.8, 145.3, 141.6, 132, 115.7,
6
10.8, 108.4, 24.23.
2
.4.3.2. 4-nitroresorcinol (4-NR)
4
-NR was prepared as reported [30]. The obtained crude was purified by flash column
chromatography on silica gel (EtOAc/hexane = 1:4). The product, yellow solid (1.5 g,
2
1.5% yield), has mp 121–122 °C; IR (KBr): 3358-3290 cm-1 (O-H),
-1
-1
1
3
066 cm (aromatic C-H), 1532-1398 cm (NO
2
); H NMR (90 MHz, DMSO-d ):
6
δ 10.3 -10.8 (s, 2H, 2OH), 7.6 – 7.8 (d, 1H, aromatic), 6.15-6.25 (m, 2H, aromatic).
2
.4.3.3. 4-Acetamidoresorcinol (4-AR)
7

4
-nitroresorcinol was used to prepare 4-AR using the same procedure applied for 4- AC
[
29]. The obtained white solid (392 mg, 72.8% yield) was stored under vacuum to avoid
-1
-1
darkening in air. mp 188 – 191 °C; IR (KBr) 3368 cm (N-H), 3214-2569 cm (broad,
O-H), 1637 cm-1 (C=O); H NMR (90 MHz, DMSO-d
1
): δ (ppm) 9.6 (s, 1H,
6
NHCOCH ), 9.2 (s, 2H, 2OH), 7.2–7.3 (d, 1H, aromatic), 6.4 (d, 1H, aromatic), 6.2–
3
1
3
6
1
.3 (dd, 1H, aromatic), 2.1 (s, 3H, -CO-CH
3
). C NMR (100MHz, DMSO-d ): δ (ppm)
6
69.3, 155.7, 150.3, 124.6, 118.6, 106.5, 104, 23.6.
3
. Results and discussion
3
.1. Characterization of M/TiO
.1.1. XRD analysis
The powder XRD patterns of the bare and metal loaded TiO
2
photocatalysts
3
2
catalysts are shown in
Fig. 1. All catalysts show diffraction peaks corresponding to anatase (2θ = 25.58,
◦
3
5
8.08,48.08 and 54.58 ) (JCPDS, no. 21-1272) and rutile (2θ = 27.51, 36.51, 41.10,
◦
4.11 and 56.51 ) (JCPDS, no. 21-1276) phases of TiO
2
P25. No diffraction peaks of
Ag, Au or Pt were detected which might be attributed to the low loading amount
1 wt%) which is below the detection limit of the instrument, and the extremely small
size of the deposited metal nanoparticles [31]. The average crystal size of the TiO
(
2
nanoparticles was calculated using Debye–Scherrer's equation with the full width at
half-maximum (FWHM) of the (101), (004) and (200) peaks and found to be in the
range of 22 ‒ 25 nm for all the prepared catalysts.
8

d
c
b
a
2
0
30
40
50
60
70
80
2
θ (degree)
Fig. 1. XRD patterns of (a) TiO
d) 1%Pt/TiO photocatalysts.
2
P25, (b) 1%Ag/TiO
2
, (c) 1%Au/TiO and
2
(
2
3
.1.2. TEM and EDX analyses
As shown in Fig. 2, HRTEM observation reveals small Pt and Au nanoparticles
3 ‒ 5 nm) deposited on the surface of TiO particles (30 nm) with a high dispersion,
whereas Ag aggregates are observed in the case of Ag/TiO sample. Furthermore, EDX
analysis (Fig. 2) reveals the presence of Ag, Au, Pt, Ti and O peaks which confirms the
(
2
2
successful loading of Ag, Au and Pt nanoparticles onto the TiO surface.
2
9

8000
7000
6000
5000
4000
Ag/TiO
2
O
Ti
C
Ag/TiO2
Ag
3000
2
000
000
0
Cu
Cu
Ti
Cu
1
Ag
Energy (keV)
8000
7000
6000
5000
4000
3000
2000
1000
0
Au/TiO
2
Ti
O
C
Au/TiO2
Ti
Cu
Cu
Au
Cu
Au
Energy (keV)
7000
6000
5000
4000
3000
2000
1000
0
Pt/TiO
2
C
Ti
O
Pt/TiO2
Cu
Cu
Ti
Cu
Pt
Pt
Energy (keV)
Fig. 2. TEM images (left) and EDX analysis (right) of metal loaded TiO
2
photocatalysts.
1
0

3
.2. Photocatalytic degradation of acetaminophen
.2.1. Effect of TiO dose
Fig. 3 indicates that the rate of PCD of AP under simulated solar light increases as the
dose of TiO is increased from 0.2 g/L to 1 g/L due to the increased surface area and
hence greater number of active sites. However, further increase of TiO concentration
3
2
2
2
results in lower photocatalytic degradation which can be attributed to light scattering
caused by the turbidity of the solution [32].
0
0
0
.025
.02
.015
.01
0
0
.005
0
b
0
0.4
0.8
1.2
1.6
2
Catalyst dose (g/L)
Fig.3. Effect of TiO
pH = 6.3 (ambient), light intensity = 50.0 mW/cm ).
2
dose on the rate constant of the PCD of AP. ([AP] = 20 mg/L,
o
2
3
.2.2. Effect of the initial concentration of AP
Fig. 4 shows that the removal of AP decreases as the initial concentration of AP is
increased from 10 to 50 mg/L. The lower degradation efficiency at higher initial
concentration can be attributed to the fact that the higher AP concentrations could
absorb more photons, which reduces the available photons to activate the TiO
results in reduced degradation efficiency [33].
2
and this
1
1

1
.8
.6
.4
.2
0
10 mg/L
20 mg/L
40 mg/L
50 mg/L
0
0
0
0
0
30
60
90
120
150
180
Time (min)
Fig. 4. Effect of initial concentration of AP on the PCD of AP under simulated solar
2
light. ([TiO ] = 0.4 g/L, pH = 6.3 (ambient), light intensity = 50.0 mW/cm )
2
3
.2.3. Kinetics of the photocatalytic degradation of AP
The kinetics of AP degradation under simulated solar light was found to follow pseudo
first order kinetic (Fig. S4) and can be well described by Langmuir-Hinshelwood
(
L-H) model (Fig. 5) [34, 35]. The true degradation rate constant, k1, and L-H adsorption
rate constant, K, for AP during the PCD over TiO using simulated solar light were
found to be 0.385 mgL min and 0.0970 mg L, respectively.
2
-1
-1
-1
5
4
3
2
.5
5
.5
4
.5
3
.5
0
0.04
/C (mg L)
0.08
0.12
-
1
1
Fig. 5. Langmuir-Hinshelwood plot for photocatalytic degradation of AP under
simulated solar light.
1
2

3
.2.4. Effect of oxygen purging
The effect of air, oxygen and nitrogen bubbling on the degradation of AP under
simulated solar light is illustrated in Fig. 6, where the rate of AP degradation in oxygen
bubbling solution is 3.5 times higher than that in nitrogen bubbling solution. This
implies that oxygen plays a critical role in solar TiO photocatalysis, enhancing the
2
degradation efficiency even under lower concentration (20% oxygen in air, i.e. static
oxygen).
100
Static O₂
O₂ Bubbling
N₂ Bubbling
80
60
40
20
0
0
30
60
90
120
150
180
Time (min)
Fig. 6. Effect of gas purging on the photocatalytic degradation of AP under simulated
solar light. ([AP] = 20 mg/L, [TiO
2
] = 0.4 g/L, pH = 6.3 (ambient), light intensity =
o
2
5
0.0 mW/cm )
3
.2.5. Effect of simulated solar light intensity
Fig. 7 reveals that the degradation of AP increases as the light intensity is increased
2
from 25.0 to 100.0 mW/cm with degradation rate proportional to the square root of
light intensity. With increasing light intensity, the number of photogenerated charge
carriers and free radicals increases, which in turn promotes the photocatalytic process.
However, at high light intensity the rate of electron-hole formation becomes greater
than the photocatalytic rate, which favors the electron-hole recombination [34].
1
3

0
0
0
.025
0
.02
.015
0
.01
.005
0
4
5
6
7
8
9
10
11
12
I1/2 (mW /cm)
1/2
Fig. 7. Apparent degradation rate constant vs. different light intensity. ([AP] = 20
o
mg/L, [TiO ] = 0.4 g/L, pH = 6.3 (ambient))
2
3
.2.6. Effect of noble metal (Ag, Au and Pt) loading on the TiO
Fig. 8 shows that the PCD of AP over 1 wt% M/TiO photocatalysts is higher than that
of the bare TiO . The degradation rate constants were 0.0128, 0.0189, 0.0160 and
.0203 min for TiO , Ag/TiO , Au/TiO and Pt/TiO , respectively. The improved
photocatalytic activity of metal loaded TiO photocatalysts under simulated solar light
can be ascribed firstly to the improved visible light absorption of M/TiO triggered by
2
surface
2
2
-1
0
2
2
2
2
2
2
the surface plasmon resonance (SPR) of noble metal nanoparticles, and secondly to the
ability of noble metals deposits (Ag, Au and Pt) to scavenge the photogenerated
-
+
electrons from TiO
2
which boosts the e /h pair separation and promotes the interfacial
charge transfers [27, 36]. In addition, noble metal deposits can act as active sites for the
•
•−
•
formation of reactive species (e.g. OH, O
degradation efficiency [37, 38]. The highest photocatalytic activity of Pt/TiO
probably due to that Pt is a better trapping site for photoelectron than Ag and Au [39].
2
, OOH and H
2
O
2
) leading to higher
2
is
1
4

1
00
80
60
40
20
0
TiO₂
1%Ag/TiO₂
1
%Au/TiO₂
%Pt/TiO₂
1
0
30
60
90
120
150
180
Time (min)
Fig. 8. Photocatalytic degradation of AP under simulated solar light over bare TiO
2
and
metal loaded TiO photoctalysts. ([AP] = 20 mg/L, [catalyst] = 0.4 g/L, pH = 5.6 – 6.3
2
o
(
ambient), light intensity = 50.0 mW/cm2)
3
.2.7. Effect of initial pH
The influence of initial solution pH on the PCD of AP was examined in a pH range of
.5 ‒ 10. As shown in Fig. 9, the efficiency of AP degradation is strongly affected by
2
the initial pH of the solution. Bare TiO
2
P25 shows the highest photocatalytic activity
•
at weakly alkaline medium (pH 8) due to greater concentration of OH radical [17].
However, the reaction rate constant is significantly decreased when the solution
becomes more alkaline (pH 10), mainly due to the electrostatic repulsion between the
negatively charged TiO
2
surface (pHpzc= 6.3) and the anionic form of AP molecules
= 9.5), which result in poor adsorption of AP and decreased rate of AP degradation
17, 40]. For Ag/TiO , the highest AP removal is observed at pH 6.3, while Au/TiO
show the highest degradation efficiency for AP at pH 4.3 which can be
(
pK
a
[
2
2
and Pt/TiO
2
attributed to the enhanced formation of the superoxide anion (O
•−) and subsequent
2
•
formation of OH (Eqs. 1 - 4) [41].
1
5

However, TiO particles tend to agglomerate under strong acidic condition (e.g.
2
pH 2.5), therefore the surface area and photon absorption would be reduced, which
consequently decreases the rate of AP degradation [42]. Therefore, the pH range of
4
.2 – 8 is the optimal range for photocatalytic degradation of AP over the employed
photocatalysts under simulated solar light.
0
.04
.035
.03
.025
.02
.015
.01
pH=2.5
pH=6.3 (ambient)
pH=10
pH=4.2
pH=8
0
0
0
0
0
0
0
.005
0
TiO₂
1%Ag/TiO₂ 1%Au/TiO₂ 1%Pt/TiO₂
Fig. 9. Effect of initial pH on the simulated solar induced photocatalytic degradation
rate constant of AP. ([AP] = 20 mg/L, [catalyst] = 0.4 g/L, light intensity = 50.0
o
2
mW/cm )
3
.2.8. Effect of surfactants
Surfactants, from detergents and other products, are often present in wastewater and
enter the environment with pharmaceuticals through wastewater discharge. To
investigate the effect of surfactants on photocatalytic degradation of AP, two
surfactants of different categories were employed; CTAB and SDS as cationic and
anionic surfactants, respectively. Fig. 10 shows that, with all utilized photocatalysts,
1
6

the rate of photocatalytic degradation of AP is reduced in the presence of CTAB or SDS
surfactants at their critical micelles concentrations (CMC). This can be attributed to the
fact that the surfactants can compete with the AP for active sites on the photocatalyst,
and thus retard the degradation process. Inhibition of photocatalytic degradation of
phenol in the presence of cationic and anionic surfactants has been observed by several
research groups [43, 44]. More importantly, the metal loaded TiO
showed higher degradation of AP compared to bare TiO in the presence of surfactants
Fig. 10). These results further demonstrate the role of metal deposition in improving
2
photocatalysts
2
(
the photocatalytic efficiency of TiO
surfactants.
2
even in the presence of other competitors, i.e.
0.024
TiO₂
Ag/TiO₂
Pt/TiO₂
0.02
Au/TiO₂
0.016
0.012
0.008
0.004
0
No surfactant
CTAB
SDS
Fig. 10. Effect of CTAB and SDS surfactants on the photocatalytic degradation of AP
under simulated solar light. ([AP] = 20 mg/L, [catalyst] = 0.4 g/L, [CTAB] = 1mM,
o
2
[
SDS] = 6 mM, light intensity = 50.0 mW/cm )
3
.2.9. Photocatalytic degradation of Panadol drug under simulated solar light
The effect of Panadol drug (commercial AP prescription) excipients on the
photocatalytic degradation of AP over bare TiO P25 and 1% Pt/TiO photocatalysts
2
2
1
7

under simulated solar light is illustrated in Fig. 11. After 180 min simulated solar
irradiation, 83 % of Panadol was decomposed with 1%Pt/TiO compared to 99 % of
pure AP, while 69% of Panadol was decomposed with bare TiO compared to 94 % of
2
2
pure AP. The reduced degradation efficiency of Panadol drug can be attributed firstly
to the light scattering due to the turbidity of the solution caused by the insoluble
excipients (e.g. starch, talc, povidone, etc.) and secondly to the competition of the
excipients with the AP molecules for the active sites and reactive species on the
photocatalyst surface. The superiority of Pt/TiO
2
photocatalyst in Panadol degradation
proves the role of Pt deposits in enhancing the photocatalytic activity of TiO
2
.
100
80
60
40
20
0
Pure AP + TiO₂
Panadol + TiO₂
Pure AP + 1%Pt/TiO₂
Panadol + 1%Pt/TiO₂
0
30
60
90
120
150
180
Time (min)
Fig. 11. Effect of Panadol drug excipients on simulated solar light induced
photocatalytic degradation of AP over TiO
2
and Pt/TiO
2
. ([AP] = 20 mg/L, [catalyst]
o
2
=
0.4 g/L, pH = 5.6 – 6.3 (ambient), light intensity = 50.0 mW/cm )
3
.2.10. Effect of light source
Fig. 12 shows the photocatalytic degradation of AP, normalized to light intensity, under
different light sources, namely UV, simulated, and direct solar light. As clearly seen,
AP degradation over the 1% Ag/TiO
2
photocatalyst under UV light is much higher than
those with simulated and direct solar light. The normalized rate constants are 0.0034,
1
8

-1
2
0
.0003 and 0.0001 min /mW/cm with UV, simulated and direct solar light,
respectively.
0
0
0
0
0
0
0
0
0
.09
.08
.07
.06
.05
.04
.03
.02
.01
0
1%Ag/TiO₂ + UV light
1%Ag/TiO₂ + simulated solar light
1%Ag/TiO₂ + direct sunlight
0
30
60
90
120
150
180
210
Time (min)
Fig. 12. Effect of light source on the photocatalytic degradation of AP over 1%Ag/TiO
2
under direct sunlight. ([AP] = 20 mg/L, [catalyst] = 0.4 g/L, pH = 5.6 (ambient),
o
2
simulated solar light intensity = 50.0 mW/cm , direct sunlight intensity = 82.0 – 89.0
mW/cm , ACE lamp intensity = 37.4 mW/cm ).
2
2
3
.2.11. Determination of mineralization using COD analysis
In photocatalytic degradation processes, the accumulation of degradation products is of
great concern as they may pose health risks to the ecosystem [45]. Therefore, it is
important to identify the degradation products, as will be discussed later (vide infra),
and to determine the amount of dissolved organic carbon during the photocatalytic
degradation process. COD was measured to evaluate the AP mineralization, i.e.
complete oxidation to CO
photocatalysts show higher mineralization than bare TiO
solar light irradiation, the observed mineralization of AP over bare TiO
Au/TiO and Pt/TiO was 63.4, 73.7, 68.8 and 78.0%, respectively. On the other hand,
after 30 min UV irradiation, the observed mineralization of AP was found to be 81.0,
0.9, 85.7 and 89.4% with TiO , Ag/TiO , Au/TiO and Pt/TiO , respectively, which
2
and H
2
O. Fig. 13 demonstrates that the 1%M/TiO
. After 180 min of simulated
, Ag/TiO ,
2
2
2
2
2
2
9
2
2
2
2
1
9

are higher than those obtained in our previous work (66% after 60 min UV irradiation
over TiO /Fe ) and studies by other research groups [24,25,27]. For instance, Yavas
et al. reported 20 and 40% mineralization of AP with Au/TiO and Pt/TiO
respectively, upon 60 min UVC (254 nm) light irradiation [24,25]. The higher
mineralization efficiency of the 1%M/TiO photocatalysts is due to the enhanced
2
2
O
3
2
2
,
2
interfacial charge transfer process, favorable adsorption of degradation products onto
the metal nanoparticles surface and ability of the metal nanoparticles to drive catalytic
oxidation/reduction reactions (e.g. aerobic oxidation and catalytic hydrogenation) for
some degradation products [46-48].
a
b
Fig. 13. Photocatalytic mineralization of AP under (a) simulated solar light ([AP] = 20
o
2
mg/L, [catalyst] = 0.4 g/L, pH = 5.6 – 6.3 (ambient), light intensity = 50.0 mW/cm ,
COD
o
= 40.35 mg/L) (b) UV light ([AP]
o
= 50 mg/L, [catalyst] = 0.1 g/L, COD = 92.6
o
2
mg/L, light intensity = 37.4 mW/cm )
3
.2.12. Identification and mechanism of degradation products
Identification of the intermediate products generated during the degradation process is
of great concern as some intermediates may be persistent or toxic themselves [45]. In
addition, it is beneficial for the elucidation of reaction mechanism. GC and/or GC/MS
analyses were used to identify the photocatalytic degradation products. Due to the low
volatility and thermal instability of the degradation products (phenolic compounds and
acids), prior to analysis, the mixture was treated with BSTFA + TMCS and converted
2
0

into the more volatile trimethylsilyl derivatives so that can be analyzed by GC and/or
GC /MS techniques.
A total of twenty-one degradation products were recognized during the PCD of AP
over bare and metal loaded TiO
2
photocatalysts irradiated with simulated solar light
(Table S1, supporting information), while a total of nineteen products were identified
with ACE lamp (Table S2, supporting information). Suggested degradation pathways
leading to the formed products are sketched in Fig 16. The results provided in Tables
S1 & S2, indicate that the photocatalytic degradation process could be elucidated to be
•
dominated via the most powerful oxidizing OH radicals. This is obvious from the
predominance of the hydroxyl derivatives of AP (4-AC and 4-AR) as well as
hydroquinone in the early stages of photocatalytic decomposition of AP as illustrated
in Figs. 14 and 15. Hydroquinone formation could be explained through direct attack
•
of the non-selective OH radical on C-4 of AP followed by removal of acetamide
molecule (route a, Fig. 16). Similarly, the same mechanism can be proposed for the
formation of 1,2,4-benzenetriol from either 4-AC or 4-AR [28]. Alternatively,
+
•
h induced one electron oxidation of AP and/or hydrogen abstraction by the OH radical
•
(
route b, Fig 16) can be considered as competitive routes to the OH ring attack (route
a) leading to the formation of the compounds no. 5, 6 and 7 (Table S1) with simulated
solar irradiation. These compounds were not detected in the PCD of AP with UV light
in the present study, which can be ascribed to their rapid degradation by the higher
energy of UV light compared with simulated solar light. Also, these compounds were
not detected in our previous work [26] or in any reported related studies found in the
literature [17-20, 24, 25]. Moreover, compounds 5, 7 have not appeared in Table S1
and S2, respectively, in case of bare TiO
2
. It is worthwhile to note that Yavas et al.
could only detect hydroquinone and benzoquinone on their work concerning the PCD
2
1

of AP over Au/TiO
24, 25]. In addition, Moctezuma et al. [18] observed the formation of 4-aminophenol
via deacetylation of AP, which is inconsistent with our findings.
2
, Pd/TiO
2
, Au-Pd/TiO
2
and Pt/TiO
2
photocatalysts using UV light
[
•
Formation of carboxylic acids could be explained as reported via successive OH
oxidation of the hydroxyl aromatic derivatives followed by ring cleavage. For example,
hydroquinone undergoes oxidation to benzoquinone (not detected) which upon ring
cleavage and further oxidation produce the obtained maleic, fumaric, succinic, malic,
tartaric, malonic, glycolic and oxalic acids as reported [29]. Likewise, 4-AC and 4-AR
are logical precursors for 3-acetamido-4-hydroxyhex-2-enedioic acid, 3-acetamido-2,4-
dihydroxypent-2-enedioic acid and 2-acetamido-3-hydroxysuccinic acid which are
observed only during the PCD of AP with UV irradiation [29]. This can be attributed
to the high concentration of 4-AC and 4-AR (precursors for nitrogenous aliphatic
compounds) compared with that of HQ (main precursor for non-nitrogenous aliphatic
compounds) during the course of the reaction under UV light, which is opposite to what
is observed with simulated solar light (Figs. 14 and 15). Similarly, we could explain
the appearance of glycerol, dihydroxyacetone, adipic and glutaric acids only with
simulated solar irradiation. Virtually, the observed variation between the degradation
products in Tables S1 and S2 can be ascribed to the fact that the formation of these
compounds is dependent on energy and intensity of light, irradiation time as well as
type of photocatalyst. However, conclusive explanation for certain compounds
appeared on further degradation needs further extensive studies.
Oxamic acid, interestingly, could be produced through oxidation of acetamide by
•OH due to the electron attracting carbonyl group which makes the methyl hydrogen
•
atoms susceptible to OH oxidation forming oxamic acid. The latter is also a reasonable
precursor for the produced oxalic acid [19].
2
2

6
5
4
3
2
1
0
4
TiO2
HQ
4
4
-AC
-AR
HQ
Ag/TiO2
4
4
-AC
-AR
3
2
1
0
7
Au/TiO2
HQ
6
5
4
3
2
1
0
4-AC
4-AR
Pt/TiO2
HQ
5
4
3
2
1
0
4
4
-AC
-AR
0
30
60
90
120
150
180
Time (min)
Fig. 14. Evolution of primary degradation products formed during photocatlytic
degradation of AP under simulated solar light in the presence of (a) bare TiO , (b)
%Ag/ TiO , (c) 1%Au/ TiO and (d) 1%Pt/ TiO photocatlysts. ([AP] = 20 mg/L,
catalyst] = 0.4 g/L, pH = 5.6 – 6.3 (ambient), light intensity = 50.0 mW/cm )
2
1
[
2
2
2
o
2
2
3

9
8
7
6
5
4
3
2
1
0
TiO P25
2
HQ
4
-AC
4-AR
5
Ag/TiO2
HQ
4
3
2
1
4-AC
4
-AR
0
7
Au/TiO2
6
5
4
3
2
1
0
HQ
4-AC
4
-AR
5
Pt/TiO2
HQ
4
3
2
1
0
4-AC
4
-AR
0
5
10
15
20
25
30
35
40
Time (min)
Fig. 15. Evolution of primary degradation products formed during photocatlytic
degradation of AP using UV light in the presence of (a) bare TiO , (b) 1%Ag/ TiO , (c)
%Au/ TiO and (d) Pt/ TiO photocatlysts. ([AP] = 50 mg/L, [catalyst] = 0.1 g/L,
pH = 5.6 – 6.3 O
flow = 100 mL/min, light intensity = 37.4 mW/cm2)
2
2
1
2
2
o
2
2
4

Fig. 16. Proposed pathways for photocatalytic degradation of AP under both
simulated solar and UV light [26].
Conclusions
Three nanosized noble metal loaded TiO
Pt/TiO ) were fabricated, characterized and employed for photocatalytic degradation of
AP under solar light and compared with UV light. The metal loaded TiO photocatalysts
showed enhanced solar photocatalytic degradation of AP in a wide pH range of 4.2 –
.0 as well as in the presence of other interferences such as surfactants, and drug
excipients and binding materials. The highest photocatalytic activity observed with
Pt/TiO , which was ascribed to the fact that Pt is a better trapping site for photoelectron
2
photocatalysts (Ag/TiO
2
, Au/TiO and
2
2
2
8
2
than Ag and Au. A total of twenty-one degradation products (two are newly reported)
were identified during the degradation of AP with simulated solar light, whereas a total
of nineteen products were identified when illuminated with UV light. The main
degradation products were 4-acetamidocatechol, 4-acetamidoresorcinol and
hydroquinone. The mechanism of photodegradation of AP was proposed to be
2
5

•
dominated by OH radical attack onto the aromatic ring in case of UV as well as solar
+
•
light. Also, h induced oxidation of AP and/or hydrogen abstraction by the OH radical
pathway was proposed to account for formation of dimeric compounds in case of
simulated solar irradiation. The results demonstrated that the degradation products are
dependent upon light energy, irradiation time as well as the type of photocatalyst.
Photocatalysis with solar light could be implemented as a feasible and environmentally
benign method for effective degradation of AP using noble metal loaded TiO
photocatalysts.
2
References
[
[
1]
2]
K. Nakata, A. Fujishima, TiO
of Photochemistry and Photobiology C: Photochemistry Reviews 13 (2012)
69-189.
S.G. Kumar, L.G. Devi, Review on modified TiO
2
photocatalysis: design and applications, Journal
1
2
photocatalysis under
UV/visible light: selected results and related mechanisms on interfacial charge
carrier transfer dynamics, The Journal of Physical Chemistry A 115 (2011)
1
3211-13241.
L. Wang, J. Fan, Z. Cao, Y. Zheng, Z. Yao, G. Shao, J. Hu, Fabrication of
Predominantly Mn4+‐Doped TiO Nanoparticles under Equilibrium Conditions
[
[
3]
4]
2
and Their Application as Visible‐Light Photocatalyts, Chemistry–An Asian
Journal 9 (2014) 1904-1912.
L.G. Devi, R. Kavitha, A review on plasmonic metal–TiO composite for
2
generation, trapping, storing and dynamic vectorial transfer of photogenerated
electrons across the Schottky junction in a photocatalytic system, Applied
Surface Science 360 (2016) 601-622.
[
[
5]
6]
A.J. Ebele, M.A.-E. Abdallah, S. Harrad, Pharmaceuticals and personal care
products (PPCPs) in the freshwater aquatic environment, Emerging
Contaminants (2017).
F.A. Weber, A. Bergmann, S. Hickmann, I. Ebert, A. Hein, A. Küster,
Pharmaceuticals in the environment—Global occurrences and perspectives,
Environmental toxicology and chemistry 35 (2016) 823-835.
[
[
[
7]
8]
9]
K. Fent, A.A. Weston, D. Caminada, Ecotoxicology of human pharmaceuticals,
Aquatic toxicology 76 (2006) 122-159.
W.C. Li, Occurrence, sources, and fate of pharmaceuticals in aquatic
environment and soil, Environmental Pollution 187 (2014) 193-201.
S. Wu, L. Zhang, J. Chen, Paracetamol in the environment and its degradation
by microorganisms, Applied microbiology and biotechnology 96 (2012) 875-
884.
[
10] D. Nematollahi, H. Shayani-Jam, M. Alimoradi, S. Niroomand,
Electrochemical oxidation of acetaminophen in aqueous solutions: kinetic
2
6

evaluation of hydrolysis, hydroxylation and dimerization processes,
Electrochimica Acta 54 (2009) 7407-7415.
[
[
[
11] V.H.-T. Thi, B.-K. Lee, Effective photocatalytic degradation of paracetamol
using La-doped ZnO photocatalyst under visible light irradiation, Materials
Research Bulletin (2017).
12] N. Muir, J. Nichols, M. Stillings, J. Sykes, Comparative bioavailability of
aspirin and paracetamol following single dose administration of soluble and
plain tablets, Current Medical Research and Opinion 13 (1997) 491-500.
13] D.J. Fairbairn, M.E. Karpuzcu, W.A. Arnold, B.L. Barber, E.F. Kaufenberg,
W.C. Koskinen, P.J. Novak, P.J. Rice, D.L. Swackhamer, Sources and transport
of contaminants of emerging concern: A two-year study of occurrence and
spatiotemporal variation in a mixed land use watershed, Science of the Total
Environment 551 (2016) 605-613.
[
[
[
14] P.D. Scott, M. Bartkow, S.J. Blockwell, H.M. Coleman, S.J. Khan, R. Lim, J.A.
McDonald, H. Nice, D. Nugegoda, V. Pettigrove, A national survey of trace
organic contaminants in Australian rivers, Journal of Environmental Quality 43
(2014) 1702-1712.
15] M. Gómez, M.M. Bueno, S. Lacorte, A. Fernández-Alba, A. Agüera, Pilot
survey monitoring pharmaceuticals and related compounds in a sewage
treatment plant located on the Mediterranean coast, Chemosphere 66 (2007)
993-1002.
16] M.S. Fram, K. Belitz, Occurrence and concentrations of pharmaceutical
compounds in groundwater used for public drinking-water supply in California,
Science of the Total Environment 409 (2011) 3409-3417.
[
[
17] L. Yang, E.Y. Liya, M.B. Ray, Degradation of paracetamol in aqueous solutions
by TiO photocatalysis, Water research 42 (2008) 3480-3488.
2
18] E. Moctezuma, E. Leyva, C.A. Aguilar, R.A. Luna, C. Montalvo, Photocatalytic
degradation of paracetamol: Intermediates and total reaction mechanism,
Journal of Hazardous Materials 243 (2012) 130-138.
[
[
[
[
19] L. Yang, L.E. Yu, M.B. Ray, Photocatalytic oxidation of paracetamol: dominant
reactants, intermediates, and reaction mechanisms, Environmental Science &
Technology 43 (2008) 460-465.
20] C.J. Lin, W.-T. Yang, C.-Y. Chou, S.Y.H. Liou, Hollow mesoporous TiO
2
microspheres for enhanced photocatalytic degradation of acetaminophen in
water, Chemosphere 152 (2016) 490-495.
21] C.-J. Lin, W.-T. Yang, Ordered mesostructured Cu-doped TiO spheres as
2
active visible-light-driven photocatalysts for degradation of paracetamol,
Chemical Engineering Journal 237 (2014) 131-137.
22] C.J. Lin, Y.H. Liou, Y. Zhang, C.L. Chen, C.-L. Dong, S.-Y. Chen, G.D.
Stucky, Mesoporous Fe-doped TiO
2
sub-microspheres with enhanced
photocatalytic activity under visible light illumination, Applied Catalysis B:
Environmental 127 (2012) 175-181.
[
[
[
23] N. Jallouli, K. Elghniji, H. Trabelsi, M. Ksibi, Photocatalytic degradation of
paracetamol on TiO
2
nanoparticles and TiO /cellulosic fiber under UV and
2
sunlight irradiation, Arabian Journal of Chemistry 10 (2017) S3640-S3645.
24] A. Ziylan-Yavaş, N.H. Ince, Enhanced photo-degradation of paracetamol on n-
platinum-loaded TiO : The effect of ultrasound and OH/hole scavengers,
2
Chemosphere 162 (2016) 324-332.
25] A. Ziylan-Yavas, Y. Mizukoshi, Y. Maeda, N.H. Ince, Supporting of pristine
TiO with noble metals to enhance the oxidation and mineralization of
2
2
7

paracetamol by sonolysis and sonophotolysis, Applied Catalysis B:
Environmental 172 (2015) 7-17.
[
[
26] A.-M. Abdel-Wahab, A.-S. Al-Shirbini, O. Mohamed, O. Nasr, Photocatalytic
degradation of paracetamol over magnetic flower-like TiO
nanostructures, Journal of Photochemistry and Photobiology A: Chemistry 347
2017) 186-198.
27] A.A. Melvin, K. Illath, T. Das, T. Raja, S. Bhattacharyya, C.S. Gopinath, M–
Au/TiO (M= Ag, Pd, and Pt) nanophotocatalyst for overall solar water
2
/Fe
2
O
3
core-shell
(
2
splitting: role of interfaces, Nanoscale 7 (2015) 13477-13488.
28] APHA, Standard methods for the examination of waters and waste water, 21st
ed, , APHA, WWA and WEF, Washington DC, USA (2005).
[
[
29] D. Vogna, R. Marotta, A. Napolitano, M. d'Ischia, Advanced oxidation
chemistry of paracetamol. UV/H
pathways and N-aided inventory of nitrogenous breakdown products, The
Journal of organic chemistry 67 (2002) 6143-6151.
2
O -induced hydroxylation/degradation
2
1
5
[
[
[
30] R. An, P. Wei, D. Zhang, N. Su, A highly selective 7-hydroxy-3-methyl-
benzoxazinone based fluorescent probe for instant detection of thiophenols in
environmental samples, Tetrahedron Letters 57 (2016) 3039-3042.
31] S. Yurdakal, B.S. Tek, Ç. Değirmenci, G. Palmisano, Selective photocatalytic
oxidation of aromatic alcohols in solar-irradiated aqueous suspensions of Pt,
Au, Pd and Ag loaded TiO
32] X. Luo, J. Wang, C. Wang, S. Zhu, Z. Li, X. Tang, M. Wu, Degradation and
mineralization of benzohydroxamic acid by synthesized mesoporous La/TiO
International Journal of Environmental Research and Public Health 13 (2016)
97.
33] S.S. Muniandy, N.H.M. Kaus, Z.-T. Jiang, M. Altarawneh, H.L. Lee, Green
synthesis of mesoporous anatase TiO nanoparticles and their photocatalytic
2
catalysts, Catalysis Today 281 (2017) 53-59.
2
,
9
[
[
2
activities, RSC Advances 7 (2017) 48083-48094.
34] P. Chowdhury, J. Moreira, H. Gomaa, A.K. Ray, Visible-solar-light-driven
photocatalytic degradation of phenol with dye-sensitized TiO
kinetic study, Industrial & Engineering Chemistry Research 51 (2012) 4523-
532.
35] T.B. Nguyen, R.-a. Doong, Heterostructured ZnFe
2
: parametric and
4
[
[
2
O
4
/TiO nanocomposites
2
with a highly recyclable visible-light-response for bisphenol A degradation,
RSC Advances 7 (2017) 50006-50016.
36] L.G. Devi, R. Kavitha, A review on plasmonic metal–TiO composite for
2
generation, trapping, storing and dynamic vectorial transfer of photogenerated
electrons across the Schottky junction in a photocatalytic system, Applied
Surface Science 360 (2016) 601-622.
[
[
[
37] A. Zielińska-Jurek, Z. Wei, I. Wysocka, P. Szweda, E. Kowalska, The effect of
nanoparticles size on photocatalytic and antimicrobial properties of Ag-Pt/TiO
photocatalysts, Applied Surface Science 353 (2015) 317-325.
2
38] H. Yu, X. Wang, H. Sun, M. Huo, Photocatalytic degradation of malathion in
aqueous solution using an Au–Pd–TiO nanotube film, Journal of hazardous
2
materials 184 (2010) 753-758.
39] M.R. Khan, T.W. Chuan, A. Yousuf, M. Chowdhury, C.K. Cheng, Schottky
barrier and surface plasmonic resonance phenomena towards the photocatalytic
reaction: study of their mechanisms to enhance photocatalytic activity, Catalysis
Science & Technology 5 (2015) 2522-2531.
2
8

[
[
40] X. Zhang, F. Wu, X. Wu, P. Chen, N. Deng, Photodegradation of
acetaminophen in TiO suspended solution, Journal of Hazardous Materials 157
2008) 300-307.
41] H. Liao, T. Reitberger, Generation of free OHaq radicals by black light
illumination of Degussa (Evonik) P25 TiO aqueous suspensions, Catalysts 3
2013) 418-443.
42] M.A. Fox, M.T. Dulay, Heterogeneous photocatalysis, Chemical Reviews 93
1993) 341-357.
43] N. Kashif, F. Ouyang, Parameters effect on heterogeneous photocatalysed
2
(
2
(
[
[
(
degradation of phenol in aqueous dispersion of TiO
Sciences 21 (2009) 527-533.
2
, Journal of Environmental
[
[
[
[
[
44] D. Fabbri, A.B. Prevot, E. Pramauro, Effect of surfactant microstructures on
photocatalytic degradation of phenol and chlorophenols, Applied Catalysis B:
Environmental 62 (2006) 21-27.
45] W. Jardim, S. Moraes, M. Takiyama, Photocatalytic degradation of aromatic
chlorinated compounds using TiO
1 (1997) 1728-1732.
2
: toxicity of intermediates, Water Research
3
46] A.E. de Los Monteros, G. Lafaye, A. Cervantes, G. Del Angel, J. Barbier Jr, G.
Torres, Catalytic wet air oxidation of phenol over metal catalyst (Ru, Pt)
supported on TiO
47] Y. Shen, Y. Li, H. Liu, Base-free aerobic oxidation of glycerol on TiO
supported bimetallic Au–Pt catalysts, Journal of Energy Chemistry 24 (2015)
69-673.
48] Z. He, X. Wang, Highly selective catalytic hydrodeoxygenation of guaiacol to
cyclohexane over Pt/TiO and NiMo/Al catalysts, Frontiers of Chemical
Science and Engineering 8 (2014) 369-377.
2
–CeO
2
oxides, Catalysis Today 258 (2015) 564-569.
2
-
6
2
2
O
3
2
9