FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid degradation by advanced oxidation processes (AOPs)

Article abstract of DOI:10.1016/j.cattod.2014.03.050

In this study the degradation of an aqueous solution of clofibric acid was investigated during catalytic ozonation and Fenton-like process with FeOOH - derived catalysts. From the different calcination temperatures tested, it has been observed that the most active catalyst is the commercial FeOOH calcined at 200°C, when maghemite and hematite are the predominant phases obtained. The best result, at room temperature, for CFA mineralization was observed over 0.5 wt% Pd on FeOOH (calcined at 200°C) among all tested catalysts, achieving 68% and 81% mineralization degree, in 2 h and 6 h, respectively, in catalytic ozonation and 66% and 71% of mineralization degree within 2 h and 6 h, respectively for Fenton process. The efficiency of the Fenton-like process is enhanced at higher temperature (40-60°C), reaching a mineralization degree up to 82% in 6 h. Furthermore, Pd impregnation on FeOOH increased the catalyst stability.

Full text of DOI:10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
Catalysis Today xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
FeOOH and derived phases: Efficient heterogeneous catalysts for
clofibric acid degradation by advanced oxidation processes (AOPs)
Shailesh S. Sablea, Pallavi P. Ghutea, Pedro Álvarezb, Fernando J. Beltránb,
Francesc Medinaa, Sandra Contrerasa,∗
a Department d’Enginyeria Química, Universitat Rovira I Virgili, Av Països Catalans 26, 4300 Tarragona, Spain
b Departamento de Ingeniería Química y Química Física, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study the degradation of an aqueous solution of clofibric acid was investigated during catalytic
ozonation and Fenton-like process with FeOOH – derived catalysts. From the different calcination tem-
peratures tested, it has been observed that the most active catalyst is the commercial FeOOH calcined at
200 ◦C, when maghemite and hematite are the predominant phases obtained. The best result, at room
temperature, for CFA mineralization was observed over 0.5 wt% Pd on FeOOH (calcined at 200 ◦C) among
all tested catalysts, achieving 68% and 81% mineralization degree, in 2 h and 6 h, respectively, in catalytic
ozonation and 66% and 71% of mineralization degree within 2 h and 6 h, respectively for Fenton pro-
cess. The efficiency of the Fenton-like process is enhanced at higher temperature (40–60 ◦C), reaching a
mineralization degree up to 82% in 6 h. Furthermore, Pd impregnation on FeOOH increased the catalyst
stability.
Received 17 January 2014
Received in revised form 13 March 2014
Accepted 20 March 2014
Available online xxx
Keywords:
Fenton-like reaction
Catalytic ozonation
Clofibric acid
Maghemite
FeOOH
Palladium
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
plasmatic concentration of cholesterol and triglycerides [10,12].
This compound has an estimated environmental persistence of 21
Hundreds of tons of pharmaceuticals are annually released to
the environment unmodified or as metabolites. The presence of
pharmaceutically active compounds (PhACs) and their metabolites
in aquatic systems has become a concern due to their generally
persistent nature and ubiquity in the environments. However, at
present, the biodegradability and ecotoxicity of many of these com-
pounds remain unknown. Clofibric acid (CFA) is one of the most
widely and routinely reported drug metabolites found in open
water. CFA was detected in most aquatic systems where phar-
maceutical contaminants were monitored [1–6]. Clofibric acid has
shown high persistency when introduced in water; it is the pri-
mary metabolite of clofibrate, a drug used as a lipid regulator
which remains in the environment for a long time [7–10]. Due
to its polar character, clofibric acid does not significantly adsorb
in soil and can easily spread in surface and groundwater. Its bio-
logical effects are not completely understood, but it has been
associated with endocrine disruption through interference with
cholesterol synthesis [11]. CFA is the bioactive metabolite of clofi-
brate, widely used as blood lipid regulating drugs for decreasing the
days [13] and has been found in sewage treatment plant efflu-
ents, rivers, lakes, North Sea, ground water and drinking water
[10,14,15]. To avoid the potential adverse health effects of drugs
and their metabolites as water pollutants on both human and ani-
mals, research efforts are underway to develop efficient techniques
for achieving their total destruction. One way to reduce these con-
taminants is to decrease their presence by the “on-site” treatment
of pharmaceutical plant wastewaters. In recent years, advanced
oxidation processes (AOP) that make use of various combinations
of O3, H2O2, ultrasound, electron beam irradiation, and so on are
becoming more and more important technologies for wastewater
treatment.
AOPs involve the generation of reactive radicals, notably
hydroxyl radicals (HO•) that are highly oxidative and capable of
decomposing a wide range and variety of organic compounds
[16]. Ozonation and Fenton oxidation have both been widely used
in actual applications and many installations are commissioned
to treat waste flows in industrial plants. Catalytic ozonation has
emerged as a powerful technology for the treatment of pollutants
in water, even for refractory compounds [17–20]. The transition
metals Fe, Ni, Zn, Co and Cu have been widely studied in the form
of single or supported metal oxide. They were found to improve
TOC removal by promotion of hydroxyl radical formation through
∗
Corresponding author. Tel.: +34 977559680; fax: +34 977559621.
E-mail address: sandra.contreras@urv.cat (S. Contreras).
http://dx.doi.org/10.1016/j.cattod.2014.03.050
0920-5861/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
2
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
the ozone decomposition [21–23]. Heterogeneous catalytic ozona-
tion has received increasing attention since Chen et al. [24] studied
the removal of phenol and ethyl acetoacetate in a packed column
with ozone and a Fe2O3 catalyst, due to its higher effectiveness in
the degradation of organic pollutants. Some organic compounds
that are difficult to degrade by single ozonation can be oxidized by
catalytic ozonation at ambient temperature and pressure [25].
Concerning the Fenton reaction, the major problem of the homo-
geneous catalytic system is the pH control and the production
of toxic wastes that require further treatments [26]. Heteroge-
neous Fenton processes are very interesting because most of the
iron remains in the solid phase and can be reused [27,28]. Iron
oxides are found abundantly in nature and easily synthesized
in laboratory. There are some iron oxides that exist in nature,
e.g. hematite (␣-Fe2O3), maghemite (␥-Fe2O3), magnetite (Fe3O4),
goethite (␣-FeOOH), lepidocrocite (␥-FeOOH) and wustite (FeO).
Iron oxyhydroxide (FeOOH) materials have been used in heteroge-
neous catalytic ozonation of oxalic acid and phosphate as models
for organic and inorganic compounds, respectively [29]. Supported
and unsupported metals and metal oxides are the most commonly
tested catalysts for the ozonation of organic compounds in water
[30].
FeOOH as heterogeneous catalyst has also been used in Fenton-
like advanced oxidation processes due to its attractive properties
such as wide-operating pH range and controllable iron leach-
ing into solution. Goethite (␣-FeOOH), Cu-doped goethite and
supported nanosized ␣-FeOOH have been studied for the oxi-
dation of quinoline and dimethyl phthalate (DMP) by Fenton
and photoelectro-Fenton processes [26,31–33]. This study aims to
investigate the efficiency of FeOOH calcined at different tempera-
tures (to obtain different phases such as maghemite and hematite),
supported FeOOH on ␥-Al2O3 and ZrO2 and lepidocrocite catalysts,
for the degradation of aqueous solutions of clofibric acid at ambient
temperature and pressure by two types of heterogeneous advanced
oxidation processes: Fenton-like process and catalytic ozonation.
The addition of little amounts of Pd has also been studied.
2.2. Catalysts characterization
Metal content of the Lepidocrocite (␥-FeOOH) and commer-
cial FeOOH samples was measured by ICP-OES (SPECTRO-ARCOS
FHS16). The bulk and surface properties of the catalysts were stud-
ied by XRD, N2 physisorption method and X-ray photoelectron
spectroscopy. XRD measurements were made using a Bruker-AXS
D8-Discover diffractometer with parallel incident beam (Göbel
mirror) and vertical theta-theta goniometer, XYZ motorized stage
mounted on an Eulerian cradle, diffracted-beam Soller slits, a 0.02◦
receiving slit and a scintillation counter as a detector. The angular
2ꢀ diffraction range was between 5 and 70◦. The data were collected
with an angular step of 0.05◦ at 3 s per step and sample rotation.
Cuk radiation was obtained from a copper X-ray tube operated at
˚
40 kV and 40 mA (ꢁ = 1.541 A). N2 adsorption was performed using
a Micromeritics ASAP 2010 apparatus at 77 K. Before analysis, the
samples were degasified at 120 ◦C for 12 h. Total surface area was
calculated by the BET method. To investigate the surface oxidation
state of iron oxide in the samples, XPS analysis was carried out
using ESCA-3000 (VGScientific Ltd., England) with a base pressure
10−9 Pa. AlK␣ source (1486.6 eV), operated at 150 W was used as a
X-ray source. The binding energy values were charge-corrected to
the C1s signal (284.6 eV). Vibrating sample magnetometer (VSM),
model LakeShore 7307 was used for the magnetic measurements
of the samples. All the measurements were carried out at room
temperature.
Amount of leached Fe was measured by ICP-OES (SPECTRO-
ARCOS FHS16).
2.3. Experimental procedure
2.3.1. I. Fenton-like reaction
The degradation of clofibric acid (99%, Across Organics) was car-
ried out at ambient conditions (25 ◦C and atmospheric pressure) in
a glass reactor with a capacity of 250 mL. 100 mL of clofibric acid
solution (100 or 25 mg/L) and (0.25–5 g/L) of H2O2 with (1–3 g/L)
of catalyst was introduced. Oxidation experiments were conducted
for 2 and 6 h and samples were periodically withdrawn, quenched
by few drops of sodium thiosulfate solution and further analyzed
by HPLC (CFA concentration) and TOC analysis. CFA concentra-
tions were measured by high performance liquid chromatography
HPLC (Shimadzu LC-2010 equipped with a SPD-M10A Diode array
UV–vis detector) at 230 nm wavelength. A Varian OmniSpher C18
column and a solution containing an aqueous buffer (Milli-Q H2O
1 L, methanol 50 mL and H3PO4 4 mL) and acetonitrile (40:60) was
used as mobile phase. The reaction intermediates were identified
qualitatively by HPLC (1200 Series) coupled to a 6210 Time of Flight
(TOF) mass detector with electrospray ion source (ESI) (Agilent
Technologies, S.L.) using the same column as mentioned above. The
mobile phase was a mixture of solutions A and B with a flow rate of
0.4 mL/min. A was 0.1% formic acid and 5% Milli-Q water in acetoni-
trile and B was 0.1% formic acid in water (pH 3.5). The analyses were
performed under a linear gradient from 10% A to 100% A at 30 min.
remaining steady for further 5 min. Ion source and TOF param-
eters are as: drying gas temperature 350 ◦C, nebulizer gas flow
10 L/min, nebulizer gas pressure 50 psi, fragmentor voltage 150 V,
capillary voltage 4000 V, skimmer voltage 650 V, octapol voltage
250 V and acquisition range 50–1200 m/z. TOC was measured by
a Shimadzu 5000-A TOC analyzer. H2O2 was semi- quantitatively
measured by H2O2 indicator strips. All the reactions were per-
formed at darkness. Higher concentrations than those commonly
found in wastewaters were used to compare the efficiency of the
different catalysts tested and to favor the accuracy in the analytical
determinations.
2. Experimental
2.1. Catalyst preparation
Commercial FeOOH was purchased from Sigma–Aldrich and fur-
ther calcined at different temperatures (200–350 ◦C), for 2 h in
presence of static air.
Catalysts with 0.5 wt% Pd [Pd (NO3)2 by Johnson Matthey]
on FeOOH were prepared by impregnation method and further
calcined at 200 ◦C for 2 h in presence of static air. ␥-alumina syn-
thesized by sol–gel method and commercial ZrO2 (by Saint-Gobain)
were used to prepare supported catalysts. FeOOH supported on ␥-
alumina and ZrO2 catalysts were also prepared by impregnation
method and further calcined at 200 ◦C for 2 h in presence of static
air.
Lepidocrocite (␥-FeOOH) was synthesized at 25 ◦C following a
procedure from Schwertmann and Cornell [34]. 300 mL of distilled
water were introduced into a 500 mL glass beaker equipped with a
stirrer, a combined pH electrode and a buret containing 1 M NaOH
solution. Then, 12.0 g of FeCl2·4H2O (60 mM of Fe) were added and
the mixture was left in contact with oxygen (50 mL/min) under
stirring. NaOH (about 120 mL) was continuously added during the
synthesis in order to maintain the pH within the 6.7–6.9 range. After
about 3 h, the completion of the oxidation reaction was obtained,
as revealed by the orange color of the suspension. Filtration was
done and the solid was dried at ambient temperature and further
calcined at different temperatures (200– 350 ◦C) for 2 h in presence
of static air.
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
3
Table 1
Crystalline phases and BET surface area of the commercial FeOOH; FeOOH calcined at different temperatures, impregnated FeOOH and lepidocrocite catalysts.
Catalysts
BET surface area (m2/g)
Pore volume (cc/g)
XRD main phases
Commercial FeOOH
222.9
184.6
158.2
136.3
80.7
189.3
170.7
324.9
115.7
318.0
137.2
120.3
140.4
120.9
100.2
94.2
0.207
0.209
0.212
0.225
0.234
0.209
0.210
1.179
0.163
0.449
0.192
0.346
0.413
0.373
0.415
0.475
Goethite, hematite, maghemite
Maghemite, hematite
Hematite
Hematite
Hematite
Maghemite, hematite, palladium oxide
Maghemite, hematite, palladium oxide
␥ – Al2O3
FeOOH (calc. 200 ◦C)
FeOOH (calc. 250 ◦C)
FeOOH (calc. 300 ◦C)
FeOOH (calc. 350 ◦C)
0.5%Pd/FeOOH (-as)
0.5%Pd/FeOOH (calc. 200 ◦C)
␥-Al2O3
ZrO2
Zirconium oxide
25%FeOOH/␥ – Al2O3 (calc. 200 ◦C)
25%FeOOH/ZrO2 (calc. 200 ◦C)
Lepidocrocite
Maghemite, hematite
Zirconium oxide, baddeleyte
Lepidocrocite
Maghemite, hematite
Hematite, maghemite
Hematite, maghemite
Hematite, maghemite
Lepidocrocite (calc. 200 ◦C)
Lepidocrocite (calc. 250 ◦C)
Lepidocrocite (calc. 300 ◦C)
Lepidocrocite (calc. 350 ◦C)
Goethite (␣-FeOOH), lepidocrocite (␥-FeOOH), maghemite (␥-Fe2O3), hematite (␣ -Fe2O3), baddeleyite (ZrO2).
2.3.2. II. Ozonation tests
loading of FeOOH on alumina support increased its surface area and
pore volume. The 25%FeOOH/␥-Al2O3 sample calcined at 200 ◦C,
shows the highest surface area and pore volume, 318.0 m2/g and
0.449 cc/g, respectively. Among all these catalysts, lepidocrocite
calcined at 350 ◦C showed the lowest surface area (94.2 m2/g).
To further study the chemistry of the samples, XPS analysis was
carried out. The binging energies values obtained were calibrated
using C (1s) (285 eV) and/or O (1s) (530 eV) as the reference. The Fe
2p XPS of the FeOOH, calcined and Pd impregnated catalyst samples
are shown in Fig. 1S (see Supplementary Information), displaying
characteristic signals related to Fe 2p3/2 and Fe 2p1/2, O1s and Pd.
Of the two peaks Fe 2p3/2 peak is narrower and stronger than Fe
The ozonation reactions were performed in a 1.5 L glass reactor
containing a 500 mL aqueous solution of CFA (100 or 25 mg/L) at
ambient conditions (25 2 ◦C) and atmospheric pressure. To the
CFA solution, 250 mg catalyst was added and the ozone, main-
taining a constant production of 1.2 g/h of O3, was continuously
flowing through the reactor. Ozone was produced from pure O2
(40 L/h), by an ozone generator (ANSEROS COM-AD-02). The sam-
ples were taken at regular time intervals for CFA conversion and
mineralization degree by TOC analysis.
3. Results and discussion
2p1/2 and the area of Fe 2p3/2 peak is greater than that of Fe 2p1/2
.
Fig. 1SA and 1SAl depict the spectrum of commercial FeOOH
samples for Fe and oxygen revealing the absence of other ele-
ments, except Fe, O and C. The observed two strong peaks at 711.8
and 725.3 eV are attributed to binding energies of Fe 2p3/2 and
Fe 2p1/2, respectively. The peak at 530.5 eV is attributed to bind-
ing energies of O 1s. These values are in good agreement with the
reported FeOOH data. XPS spectra of calcined FeOOH are shown in
Fig. 1SB and 1SB1 in which two strong peaks at 711 and 724.5 eV
are attributed to binding energies of Fe 2p3/2 and Fe 2p1/2, respec-
tively. The peak at 530.2 eV is attributed to binding energies of O
1s which are correlated to Fe2O3. High resolution spectra of Fe 2p
and O 1s peaks show the presence of symmetric peaks, indicating
their single oxidation state (Fe3+ and O2−). Peak areas of Fe 2p and
O 1s, confirm the presence of Fe2O3 (mixture of maghemite and
hematite).
Fig. 1SC, 1SC1 and 1SC2 show spectra for Fe, O and Pd of Pd
impregnated FeOOH calcined catalysts. Binding energies observed
for Fe 2p and O1s are almost similar to the ones obtained for
calcined FeOOH sample, which correlates to Fe2O3. The peak at
340.5 eV is attributed to binding energy of PdO.
Hence, after calcinations and Pd impregnation, there is only a
slight difference in binding energies, therefore Fe oxidation state
remains the same (Fe+3).
3.1. Catalysts characterization
Table 1S (see Supplementary Information) shows Fe and Pd
metal content analysis (weight % ratios) of the samples. The
summary of surface properties and XRD patterns of commer-
cial FeOOH and synthesized lepidocrocite catalysts before and
after heat treatment at different temperatures is also presented
in Table 1 In case of lepidocrocite catalysts, heating at low tem-
perature (200 ◦C) increased slightly the surface area. However, the
surface area was reduced when lepidocrocite was treated at higher
temperatures (300–350 ◦C). In case of commercial FeOOH cata-
lysts, after calcination, the surface area was reduced drastically (see
Table 1). Commercial FeOOH showed the highest surface area up
to 222.9 m2/g. From XRD, goethite, maghemite and small amount
of hematite were the main crystalline phases observed. However,
the percentage of these phases was calculated using XRD TOPAS
software, even considering the poor crystallinity of the samples.
When FeOOH was calcined at 200 ◦C, maghemite (␥-Fe2O3, 67%)
and hematite (␣-Fe2O3, 33%) phases appeared with a decrease
in surface area. Surface area decreases with increasing calcina-
tion temperature from 200 to 350 ◦C, and pore volume increased
slightly. When FeOOH was calcined at different temperatures, for-
mation of different iron oxide phases occurred. However, when the
calcination temperature was in the range of 250–350 ◦C, the main
phase detected was hematite. For Pd impregnated on FeOOH cata-
lysts, maghemite, hematite and palladium oxide were detected as
predominant crystalline phases.
3.2. Degradation of clofibric acid
3.2.1. Catalytic ozonation
In synthesized lepidocrocite sample, pure lepidocrocite phase
was observed. When lepidocrocite catalyst was calcined at 200 ◦C,
maghemite (83%) formation was observed as the main phase with a
small amount of hematite (17%). After calcination between 250 and
350 ◦C, hematite was the main crystalline phase observed together
with maghemite. For supported catalysts the results show that the
The results of CFA degradation and Fe leaching after 2 h and 6 h
of catalytic ozonation using different FeOOH-based catalysts have
been summarized in Table 2. The reaction using single ozonation
resulted in a fast disappearance of CFA in less than 15 min (tak-
ing into account our detection limit, i.e., 0.1 mg/L). However the
TOC removal was not higher than 26% and 40% after 2 h and 6 h,
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
4
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
Table 2
Degree of mineralization and metal leaching results using single O3 and catalytic ozonation with FeOOH-based catalysts.
Catalysts
TOC removal (%)
2 h
Metal leaching (mg/L)
2 h
6 h
6 h
Single ozonation
26.1
41.2
53.8
58.5
43.0
42.1
57.4
68.0
48.2
40.0
41.6
47.2
43.0
46.8
50.2
35.0
40.0
59.3
75.1
71.7
70.7
66.0
79.6
81.5
59.5
58.6
52.7
57.8
52.7
54.3
58.4
45.46
Commercial FeOOH
2.5
2.9
5.25
4.5
1.43
1.2
1.0
1.2
4.2
2.3
2.1
1.5
2.1
2.3
4.5
3.5
5.4
6.02
3
1.5
1.2
1.9
6.8
3.5
4.6
4.1
3.6
2.9
FeOOH (calc. 200 ◦C)
FeOOH (calc. 250 ◦C)
FeOOH (calc. 300 ◦C)
FeOOH (calc. 350 ◦C)
0.5%Pd/FeOOH (-as)
0.5%Pd/FeOOH (calc. 200 ◦C)
25%FeOOH/␥ – Al2O3 (calc. 200 ◦C)
25%FeOOH/ZrO2 (calc. 200 ◦C)
Lepidocrocite
Lepidocrocite (calc. 200 ◦C)
Lepidocrocite (calc. 250 ◦C)
Lepidocrocite (calc. 300 ◦C)
Lepidocrocite (calc. 350 ◦C)
Fe = 3.5 mg/L
Reaction conditions: 500 mL, [CFA]0 = 100 mg/L, O3 production = 1.2 g/h, O2 flow rate = 40 L/h, catalyst = 0.5 g/L, Temp. = R.T, pH = free and time = 6 h.
respectively. Degradation of clofibric acid by ozonation in presence
of different FeOOH-derived catalysts was tested and similarly to
single ozonation, CFA conversion was completed in less than 15 min
in all cases. Commercial FeOOH and synthesized lepidocrocite show
59% and 58% TOC removal after 6 h of ozonation reaction. Compared
to single ozonation, among all calcined FeOOH catalysts, FeOOH cal-
cined at 200 ◦C (with maghemite and hematite as the main phases
from Table 1) shows higher TOC removal (55% in 2 h and 75% after
6 h of reaction). However, after 6 h of reaction, 3.5 mg/L leaching
of Fe was observed. It can be seen that the efficiency in mineral-
ization was greatly enhanced by the addition of FeOOH catalysts
when compared to single ozonation. The FeOOH calcined at 250 ◦C,
300 ◦C and 350 ◦C show 58, 43 and 41% of mineralization in 2 h,
respectively. Nevertheless, a high leaching of Fe was observed (5.2,
4.5 and 1.4 mg/L, (see Table 2) for FeOOH calcined at 250, 300 and
350 ◦C catalysts, respectively). The lepidocrocite calcined at 200 ◦C,
250 ◦C, 300 ◦C and 350 ◦C achieved TOC removals of 47%, 43%, 46%
and 50% after 2 h of ozonation process. Catalysts were tested for
adsorption, showing negligible (5–10%) adsorption of CFA.
The 25%FeOOH/␥-Al2O3 catalyst calcined at 200 ◦C, achieved
48% and 60% TOC removal after 2 h and 6 h reaction, respec-
tively, with low leaching of Fe (1.9 mg/L). The ozonation test
using 25%FeOOH/ZrO2 (calcined at 200 ◦C) show 40% and 59% TOC
removal after 2 h and 6 h reaction, respectively, but a high leaching
of Fe (4.2 and 6.8 mg/L) was observed. Therefore, supporting FeOOH
on ␥-Al2O3 present remarkable results of activity and stability, tak-
ing into account that in this case a low amount of leaching of Fe is
observed.
To further improve the catalyst stability, addition of Pd by
impregnation has been performed. After palladium impregnation,
the catalyst was calcined at 200 ◦C and tested in the catalytic
ozonation of CFA. Using as-synthesized and calcined 0.5%Pd/FeOOH
catalysts leads to further improvement in stability and activity,
achieving 80 and 82% of TOC removal after 6 h, respectively. Stabil-
ity was significantly improved, however some Fe leaching (1.5 mg/L
for as- and 1.2 mg/L for calcined) was observed after 6 h (see
Table 2).
Among all tested FeOOH-derived catalysts, 0.5%Pd/FeOOH (with
predominant phases such as maghemite, hematite and palladium,
see Table 1) is the one that leads to the highest degree of mineral-
ization with the lowest leaching of Fe.
have been found to substitute surface hydroxyl groups [35,36]. As
for the form of clofibric acid in solution, its pKa is 3.2 [37], therefore
it dissociates in aqueous solutions even under acidic conditions.
3.2.1.1. Homogeneous ozonation (leached Fe). The Fe leached during
the catalytic ozonation was measured in the final filtered solution
and the results are shown in Table 2. For FeOOH catalysts, after
Pd impregnation, the leaching of Fe decreased and TOC removal
increased.
In order to evidence the effect of dissolved Fe3+ on the per-
formance of CFA degradation by ozone, a homogeneous catalytic
ozonation experiment was performed using dissolved Fe3+ with a
concentration of 3.5 mg/L, which is higher than the final amount
of Fe leached after the reaction for the 0.5%Pd/FeOOH catalyst. The
results of these experiments are shown in Table 2, indicating a slight
improvement with respect to single ozonation. Complete degrada-
tion of CFA was also observed within 15 min, in the same way that
for heterogeneous catalysts. In homogeneous tests with 3.5 mg/L of
Fe, TOC removal increased by a 5% with respect to single ozonation.
This means that dissolved iron can slightly enhance the ozonation
process efficiency. However, the value of TOC removal was lower
than for the heterogeneous process.
3.2.2. Heterogeneous Fenton-like process
The results of CFA degradation, hydrogen peroxide decom-
position, TOC removal and metal leaching after 2 h and 6 h by
heterogeneous Fenton-like process using different FeOOH-derived
catalysts and at room temperature, have been summarized in
Table 3. Among all these tested catalysts, 100% CFA conversion
was obtained with FeOOH (calcined at 200 ◦C) and 0.5%Pd/FeOOH
(synthesized and calcined) in 6 h, but more remarkable results are
obtained at short reaction time (2 h), where already 95 and 97% CFA
conversion was achieved with FeOOH (calcined at 200 ◦C) without
and with Pd, respectively. After calcination at different tempera-
tures and Pd impregnated FeOOH catalysts, a clear promotion of
the efficiency of the system was observed when compared with
non-calcined FeOOH catalyst. FeOOH calcined at 200 ◦C (that shows
maghemite and hematite as the main phases, see Table 1) show
higher TOC removal (57% in 2 h and 61% after 6 h of Fenton reac-
tion with 3.5 and 3.8 mg/L of Fe leaching). It can be seen that the
efficiency in mineralization was enhanced by the impregnation of
Pd on FeOOH catalysts. The best activity and stability for CFA was
especially observed over calcined 0.5%Pd/FeOOH, achieving min-
eralization degrees up to 66% and 71% for 2 h and 6 h of Fenton
reaction, respectively (see Table 3).
Nevertheless, by starting these reactions, the pH dropped to <4
in 5–10 min, likely due to the formation of large amount of acidic
intermediates. Solutions have not been buffered to avoid the pres-
ence of ions that may interfere in the process. E.g., phosphate ions
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
5
Table 3
CFA degradation results in Fenton-like process with FeOOH-based catalysts.
Catalysts
%CFA conversion
%H2O2 decomposition
% TOC removal
2 h
Leached metal (mg/L)
2 h
6 h
2 h
6 h
80
6 h
2 h
6 h
FeOOH
84
95
90
98
80
78
73
81
55
49
63
59
95
100
100
100
90
40
90
85
95
75
70
65
79
55
60
80
40
35
57
59
66
48
37
27
49
46
41
50
13
39
61
65
71
60
44
32
55
51
45
56
24
3.0
3.5
2.8
2.6
1.9
3.9
1.2
1.2
0.3
0.2
0.2
4.9
3.8
3.1
2.9
3.15
6.5
1.4
1.7
1.6
0.3
0.6
FeOOH (calc. 200 ◦C)
100
100
100
90
0.5%Pd/FeOOH (-as)
0.5%Pd/FeOOH (calc. 200 ◦C)
25%FeOOH/␥ – Al2O3 (calc. 200 ◦C)
25%FeOOH/ZrO2 (calc. 200 ◦C)
Lepidocrocite
92
86
95
85
95
80
Lepidocrocite (calc. 200 ◦C)
Lepidocrocite (calc. 250 ◦C)
Lepidocrocite (calc. 300 ◦C)
Lepidocrocite (calc. 350 ◦C)
Fe = 3.5 mg/L
100
67
57
78
75
90
81
100
Reaction conditions: 100 mL, [CFA]0 = 100 mg/L, H2O2 = 0.5 g/L, catalyst = 2 g/L, Temp. = R.T, pH = free and time = 6 h.
The catalyst of 25%FeOOH/␥-Al2O3 (calcined at 200 ◦C) also
shows good activity in Fenton-like process, achieving 48% and 60%
TOC removal after 2 h and 6 h reaction, respectively, and a lower
leaching of Fe was observed (1.9 and 3.1 mg/L). The Fenton reac-
tion using 25%FeOOH/ZrO2 (calcined at 200 ◦C) shows 37% and 44%
TOC removal after 2 h and 6 h of reaction, respectively, but a high
leaching of Fe (3.9 and 6.5 mg/L) was produced.
For lepidocrocite catalysts, after calcination between 200 and
350 ◦C, the lepidocrocite phase disappears (results from XRD and
XPS). Maghemite and hematite were the main obtained phases. An
increase of the hematite phase, at expenses of the maghemite, was
observed when the calcination temperature increased (see Table 1).
All these catalysts showed high CFA conversion at room tempera-
ture. Total conversion of CFA with a mineralization degree of 55%
was obtained after 6 h of reaction for lepidocrocite catalyst calcined
at 200 ◦C. The CFA conversion for lepidocrocite and lepidocrocite
catalysts calcined at higher temperature was lower. However, the
TOC removal for all the catalysts was quite similar. Some leach-
ing of Fe was observed after the reaction test. Lepidocrocite and
lepidocrocite catalysts calcined at 200 ◦C and 250 ◦C showed the
highest amount of Fe leached (between 1.4 and 1.7 mg/L) after 6 h
of reaction. Higher calcination temperatures decreased the amount
of Fe leached (between 0.2 and 0.6 mg/L).
its stability, as shown in Fig. 2S (A). Like in the case of fresh cat-
alysts, a total disappearance of CFA occurred in less than 15 min.
It can be seen that the activity of these catalysts was maintained,
showing around 80% of TOC removal, when reused in three consec-
utive cycles for 6 h of ozonation reaction. These results corroborate
the improvement in the stability of these materials.
The CFA degradation was also tested in heterogeneous Fenton-
like process with 0.5%Pd/FeOOH (calc. 200 ◦C) and reused in three
consecutive runs, as shown in Fig. 2S (B). In Fenton-like reaction
also the activity of catalysts was maintained, showing mineraliza-
tion degree around 70%, when reused in three consecutive cycles
for 6 h of Fenton process.
3.4. Parametric study with calcined 0.5%Pd/FeOOH catalyst in
Fenton-like process
The performance of 0.5%Pd/FeOOH (calcined at 200 ◦C) has been
studied in Fenton-like reaction for clofibric acid degradation with
different parameters, such as the effect of pH, H2O2 concentration,
catalyst concentration and temperature.
3.4.1. Effect of H2O2 concentration
In order to study the effect of hydrogen peroxide concentra-
tion on the performance of CFA degradation by Fenton process,
experiments were performed using 2 g/L of calcined 0.5%Pd/FeOOH
catalyst with different hydrogen peroxide concentration in the
range of 0.25–5 g/L at room temperature. The results of these exper-
iments are shown in Fig. 1(A). As it can be seen, increasing the
hydrogen peroxide concentration in the range of 2 and 5 g/L did not
lead to any improvement of TOC results. Instead the %TOC removal
decreased around 10 and 15%. This means that higher concentra-
tion of hydrogen peroxide is not effective for Fenton process. The
results obtained using 1 g/L of hydrogen peroxide concentration
are almost similar to those obtained with 0.25 g/L of hydrogen per-
oxide. Using higher concentration (2–5 g/L) of hydrogen peroxide,
a fast decomposition of H2O2 was observed leading to a decrease
in TOC removal compared to reaction performed at lower hydro-
gen peroxide (0.25–0.5 g/L) concentration. These results are likely
due to the radical scavenger character of hydrogen peroxide. These
results indicate that 0.5 g/L of hydrogen peroxide is the optimal con-
centration in Fenton-like process for the CFA degradation achieving
100% CFA conversion and 71% TOC removal in 6 h.
To evidence the effect of dissolved Fe3+ on the performance
of CFA degradation by Fenton-like process, a homogeneous cat-
alytic experiment was performed using dissolved Fe3+ with a
concentration of 3.5 mg/L, working at room temperature. For the
homogeneous Fenton reaction and after 6 h of reaction, total CFA
conversion was observed but with a very low TOC removal (24%).
The obtained results indicate that these catalysts show higher activ-
ity in Fenton-like reactions compared to other iron oxide catalysts
[34]. It is important to note that FeOOH-derived materials, mainly
containing Pd, are promising catalysts for the degradation of clofib-
ric acid by Fenton-like process. A total CFA conversion with a TOC
removal of 66% was obtained at very mild reaction conditions (2 h
of reaction at room temperature).
3.3. Reuse and recycling of 0.5%Pd/FeOOH catalyst
Calcined 0.5%Pd/FeOOH catalyst has shown best activity and
stability in catalytic ozonation and in heterogeneous Fenton-like
process as well, achieving mineralization degrees of 68% and 82%, in
catalytic ozonation, and 66% and 71%, in heterogeneous Fenton-like
process, after 2 and 6 h, respectively.
3.4.2. Effect of temperature
In order to establish the reusability of catalyst for CFA removal,
CFA degradation was tested in the presence of 0.5%Pd/FeOOH cat-
alyst recovered after a run by filtering, washing and drying, and
reused in three consecutive runs of catalytic ozonation, to assess
Fig. 1B shows the influence of reaction temperature on conver-
sion and mineralization of CFA. In this series, experiments were
performed at room temperature, 40 ◦C and 60 ◦C using 2 g/L of
calcined 0.5%Pd/FeOOH catalyst and 0.5 g/L of hydrogen peroxide.
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
6
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
Fig. 1. Parametric study with 0.5%Pd/FeOOH catalyst calcined at 200 ◦C in Fenton-like process. (A) Effect of H2O2 concentration. (B) Effect of temperature. (C) Effect of catalyst
concentration and (D) Effect of pH (unless specified, free pH, T = 25 ◦C, concentration of H2O2 500 mg/L and catalyst concentration 2 g/L).
From Fig. 1B it can be seen that by increasing the temperature,
%TOC removal increased by 8–12% in 6 h of Fenton process when
compared to reaction performed at room temperature. When tem-
perature increases up to 60 ◦C, an 82% TOC removal is noticed in 6 h.
Thus, it can be concluded that a temperature increase enhances the
mineralization degree.
acidic pH. The reactions at initial pH 7 and 10 show a decrease in
TOC removal (58% and 48%, respectively) with respect to the reac-
tions at free pH 3.3 (71%). Also, from TOC profiles shown in Fig. 1D
it is seen that TOC removal rate is enhanced at lower pHs. Compar-
ing to the reactions at different pHs, it is clear that 0.5%Pd/FeOOH
(calcined at 200 ◦C) displays a better performance at initial acidic
pH (3–3.5).
From these results we can conclude that all catalysts show good
activity in heterogeneous Fenton-like reaction. FeOOH (calcined at
200 ◦C) and Pd impregnated catalysts show best performance in
both processes. For example, 98% CFA conversion and 66% min-
eralization degree were obtained with 0.5%Pd/FeOOH (calcined at
200 ◦C) in 2 h of Fenton-like reaction. With the use of this cat-
alyst, when the reaction was performed at higher temperature
(40–60 ◦C) a better performance was observed, achieving miner-
alization degree up to 75% in 2 h of Fenton-like process. After Pd
impregnation on FeOOH, an increase in the stability and activity of
the catalyst was observed with lower leaching of Fe.
3.4.3. Effect of catalyst concentration
In order to study the effect of catalyst loading on the perfor-
mance of CFA degradation by Fenton-like process, experiments
were performed using 0.5 g/L of hydrogen peroxide and different
catalyst concentration (1–3 g/L) at room temperature. TOC profiles
of these reactions are shown in Fig. 1C.
When catalyst concentration decreased (from 2 to 1 g/L), the
%TOC removal was also decreased, achieving a mineralization
degree of 50% in 6 h of Fenton-like reaction. But a further increase
of catalyst concentration (3 g/L) did not led to any further improve-
ment in TOC results. On the contrary, the %TOC removal decreased
near about 4–5% when compared to reaction performed using 2 g/L
of catalyst concentration, achieving 71% TOC removal in 6 h of Fen-
ton process.
3.5. Tests with lower CFA concentration
The calcined 0.5%Pd/FeOOH catalyst has shown the best activ-
ity and stability in both processes. The single ozonation, catalytic
ozonation and Fenton-like process with lower concentration of
CFA (25 mg/L) were also studied, using this catalyst at free pH. In
tests with single and catalytic ozonation, CFA concentrations below
our detection limit (0.1 mg/L) were detected within 15 min reac-
tion and a CFA concentration below the detection limit was also
observed after 4 h in heterogeneous Fenton-like reaction. In cat-
alytic ozonation, 72% and 84% TOC removal was achieved after 2
and 6 h of reaction, significantly higher than single ozonation. A
69% TOC removal was achieved in 2 h of Fenton-like reaction (See
3.4.4. Effect of pH
Fenton-like process was carried out at different initial pH
(pH = 3.3 (free), 7 and 10) to study the effect of pH on the per-
formance of CFA degradation using calcined Pd/FeOOH (2 g/L) and
hydrogen peroxide (0.5 g/L). Fig. 1D shows the results of TOC
removal. For this study, the pH of a 100 mg/L CFA solution was
adjusted at initial pH 7 and 10 with NaOH. At the start of oxidation,
the pH dropped to less than 4.5 in ca. 30 min, likely due to the forma-
tion of acidic intermediates. Final pH of solution was 3.6. Therefore
in case of pH 10 and pH 7 the rest of the reaction proceeded at
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
7
Scheme 1. Suggested reaction pathways for the catalytic ozonation of clofibric acid.
Fig. 2). Therefore, it can be seen that the efficiency in mineralization
was slightly enhanced at lower concentration of CFA.
obtained with TiO2 as catalyst at pH 3–5 range. Therefore, these
FeOOH derived materials are promising catalysts for the catalytic
ozonation of CFA, leading to 68 and 82% degree of mineralization
in 2 and 6 h, respectively.
Concerning heterogeneous Fenton-like process, with electro-
Fenton using Fe2+ and photoelectro-Fenton process using Fe2+ and
UVA light, more than 95% of TOC removal was obtained in 4–8 h
[39]. No reference for heterogeneous Fenton process for CFA degra-
dation has been found. Therefore, our results are very promising for
CFA mineralization, since a high % TOC removal (above 60% within
30–60 min.) has been obtained in a very short reaction time.
Concerning catalytic ozonation, and comparing with others
results reported in literature, to the best of our knowledge, and
apart from our previous study of CFA catalytic ozonation with cop-
per dawsonites [18], there is only one reference [38] dealing with
the catalytic ozonation of CFA, in which 25–30% mineralization was
3.6. Proposal of mechanism of oxidation of CFA by catalytic
ozonation and Fenton-like process
The CFA degradation using ozonation and Fenton-like process,
in the presence of 0.5%Pd/FeOOH (calcined at 200 ◦C) shows the
formation of various intermediates. The identification of oxidation
by-products was performed by HPLC-MS analysis of the samples
taken during the catalytic runs performed with 100 mg/L of clofibric
acid.
It should be said that all the intermediates were detected at neg-
ative ionization mode. The compounds denoted by numbers were
detected by MS.
As shown in Scheme 1, CFA degradation by catalytic ozona-
tion can proceed by three different routes (Scheme 1A–C) which
are C1 O bond breaking, C4 Cl bond breaking and aromatic ring
cleavage. CFA is oxidized to 4-chlorophenol (2) by the breaking
of the C(1) O bond, also forming 2-hydroxyisobutyric acid (1),
Fig. 2. TOC removal (%) during the CFA (25 mg/L) degradation by single ozona-
tion, catalytic ozonation and heterogeneous Fenton-like process using calcined
0.5%Pd/FeOOH catalyst (catalytic ozonation conditions: free pH, T = 25 ◦C, O3 pro-
duction = 1.2 g/h, O2 flow rate = 40 L/h, catalyst concentration = 0.5 g/L; Fenton-like
process conditions: free pH, T = 25 ◦C, concentration of H2O2 = 500 mg/L and catalyst
concentration = 2 g/L).
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
8
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
Scheme 2. Suggested reaction pathways for the heterogeneous Fenton-like process of clofibric acid.
which were identified at m/z 126.99 and m/z 103.03, respectively.
Further hydroxyl attack on C4 position of 4-chlorophenol yields
hydroquinone (4), whereas the oxidation on C2 position leads
to 4-chlorocatechol (3) detected at m/z 109.02 and m/z 142.99,
respectively. Through the second route, via attack on C4 Cl, leads
to the formation of 4-hydroxyphenoxy-isobutyric acid (5) found
at m/z 196.07, which further oxidized by ring-cleavage of CFA
results to (6) found at m/z 245.02. This compound undergoes ring
cleavage to reach oxalic acid (7) identified at m/z 88.98 and 2-
hydroxyisobutyric acid. Hydroxylation of aromatic ring may form
2-(4-chloro-2-hydroxyphenoxy)-2-methylpropionic acid, which
was not detected in catalytic ozonation. Subsequent oxidation
cleaves the aromatic ring and produces chloro carboxylic acids (8)
and (9). These compounds were identified at m/z 245.02 and 178.97,
respectively.
Almost similar intermediates identified in catalytic ozonation,
were identified in Fenton-like reaction, with addition of 2-
(4-chloro-2-hydroxyphenoxy)-2-methylpropionic acid and maleic
acid. And similar reaction pathways have been proposed, as
shown in Scheme 2(A–C), which are hydroxylation and further
aromatic ring cleavage, C1 O bond breaking and C4 Cl bond
breaking. Hydroxylation of aromatic ring forms 2-(4-chloro-2-
hydroxyphenoxy)-2-methylpropionic acid (1) which was detected
at m/z 229.02. Subsequent oxidation cleaves the aromatic ring
and produces 2-hydroxyisobutyric acid (3) and chloro-carboxylic
acids (2) and (4), which were identified at m/z 245.02 and 178.97,
respectively. CFA oxidizes to 4-chlorophenol (5) by the breaking
of the C1 O bond, also forming 2-hydroxyisobutyric acid. Further
hydroxyl attack on C4 position of 4-chlorophenol yields hydro-
quinone (6) and oxidation on C2 position leads to 4-chlorocatechol
(7). 4-hydroxyphenoxy-isobutyric acid (8) is formed by dechlori-
nation, which further oxidizes by ring cleavage resulting to (9).
This compound is also further oxidized to form maleic acid, which
was identified at m/z 115.00, and also to oxalic acid (11) and 2-
hydroxyisobutyric acid, thus completing the oxidative chain.
4. Conclusions
The results of this study indicate that FeOOH and its cal-
cined forms are suitable and highly effective catalysts for both
type of advanced oxidation treatments (catalytic ozonation and
Fenton–like process).
CFA can be effectively degraded by Fenton-like process and
catalytic ozonation with FeOOH and its derived phases after
calcination at various temperatures. Catalyst that shows better per-
formance in Fenton and catalytic ozonation is the one obtained
after calcination at 200 ◦C and predominant phases present are
maghemite and hematite (with higher percentage of maghemite).
In Fenton-like process maximum TOC removal is achieved within
the first period of reaction, 60–65% degree of mineralization after
60 min of reaction. As for catalytic ozonation, 68% mineralization
degree is reached after 2 h reaction.
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050

G Model
CATTOD-9000; No. of Pages9
ARTICLE IN PRESS
S.S. Sable et al. / Catalysis Today xxx (2014) xxx–xxx
9
Concerning stability of these materials, 0.66 and 0.29% of Fe
leaching was observed in catalytic ozonation and Fenton-like pro-
cesses, respectively, after 6 h of reaction. However, stability and
activity of these materials are increased after addition of a little
amount (0.5%) of Pd. Synthesized lepidocrocite catalysts also show
good performance in ozonation and Fenton-like reaction. Results
obtained supporting calcined (200 ◦C) commercial FeOOH on ␥-
Al2O3 are remarkable and deserve further study.
Among all tested catalysts, the highest activity and stabil-
ity for CFA ozonation and Fenton-like process was observed
over 0.5%Pd/FeOOH (calcined at 200 ◦C), achieving mineralization
degrees up to 68 and 82% for 2 and 6 h respectively, in ozonation,
and 63% and 66% for 1 and 2 h, respectively, in Fenton-like reaction.
A parametric study has also been performed with 0.5%Pd/FeOOH
(calcined at 200 ◦C) in Fenton-like reaction for clofibric acid
degradation using different variables, specifically, pH, H2O2 con-
centration, catalyst concentration and temperature. The reactions
performed at 40–60 ◦C, showed better results, achieving a miner-
alization degree up to 82% in 6 h with Fenton-like process. At acidic
pH (3–3.5) the reaction proceeded more efficiently as compared
to pH 7 and 10. Optimization of the reaction conditions like tem-
perature (60 ◦C), free pH, H2O2 (0.5 g/L) and proper loading of the
catalyst (2 g/L) would lead to the highest mineralization degree.
[2] M. Winkler, J.R. Lawrence, T.R. Neu, Water Res. 35 (2001) 3197–3205.
[3] V. Matamoros, J. Garcia, J.M. Bayona, Water Res. 42 (2008) 653–660.
[4] A. Dordio, A.J. palace Carvalho, D.M. Teixeira, C.B. Dias, A.P. Pinto, Bioresour.
Technol. 101 (2010) 886–892.
[5] T.A. Ternes, Water Res. 32 (1998) 3245–3260.
[6] A. Joss, S. Zabczynski, A. Gobel, B. Hoffmann, D. Loffler, C.S. McArdell, T.A. Ternes,
A. Thomsen, H. Siegrist, Water Res. 40 (2006) 1686–1696.
[7] F. Gagne, C. Blaise, C. Andre, Ecotoxicol. Environ. Saf. 64 (2006) 329–336.
[8] B. Halling-Sørensen, S. Nors Nielsen, P.F. Lanzky, F. Ingerslev, H.C. Holten
Lützhøft, S.E. Jørgensen, Chemosphere 36 (1998) 357–393.
[9] C. Tixier, H.P. Singer, S. Oellers, S.R. Muller, Environ. Sci. Technol. 37 (2003)
1061–1068.
[10] H.R. Buser, M.D. Muller, Environ. Sci. Technol. 32 (1998) 188–192.
[11] P. Pfluger, D.R. Dietrich, Pharmaceuticals in the Environment, Springer, Berlin,
2001, pp. 11–17.
[12] A. Tauxe-Wuersch, L.F.D. Alencastro, D. Grandjean, J. Tarradellas, Water Res. 39
(2005) 1761–1772.
[13] J.P. Emblidge, M.E. DeLorenzo, Environ. Res. 100 (2006) 216–226.
[14] Th. Heberer, H.J. Stan, Int. J. Environ. Anal. Chem. 67 (1997) 113–124.
[15] C. Tixier, H.P. Singer, S. Oellers, S.R. Muller, Environ. Sci. Technol. 37 (2003)
342–351.
[16] J.H. Ramirez, C.A. Costa, L.M. Maderia, G. Mata, M.A. Vicente, M.L. Rojas-
Cervantes, A.J. Lopez-Peinado, R.M. Martin-Aranda, Appl. Catal. B Environ. 71
(2007) 44–56.
[17] S. Contreras, M. Rodriguez, F. Al Momani, C. Sans, S. Esplugas, Water Res. 37
(2003) 3164–3171.
[18] M.S. Yalfani, S. Contreras, J. Llorca, F. Medina, Appl. Catal. B: Environ. 107 (2011)
9–17.
[19] S.T. Oyama, Catal. Rev. Sci. Eng. 42 (2000) 279–322.
[20] A. Goncalves, J.J.M. Orfao, M.F.R. Pereira, Appl. Catal. B Environ. 140–141 (2013)
82–91.
[21] C. Cooper, R. Burch, Water Res. 33 (1999) 3695–3700.
[22] J.Q. Haiyan Li, H. Liu, H. He, Catal. Today 90 (2004) 291–296.
[23] R. Allmann, H.H. Lohse, N. Jb. Min. 11 (1966) 161–180.
[24] J.W. Chen, C. Hui, G. Smith, 68th Annual Meeting of American Institute of Chem-
ical Engineers, 1975 (Los Angeles).
[25] Y. Guo, L. Yang, X. Cheng, X. Wang, J. Environ. Anal. Toxicol. 2 (2012) 1–7.
[26] J.A. Zazo, J.A. Casas, A.F. Mohedano, M.A. Gilarranz, J.J. Rodriguez, Environ. Sci.
Technol. 39 (2005) 9295–9302.
[27] S. Papia, D. Vujevia, N. Koprivanac, D. Ainko, J. Hazard. Mater. 164 (2009)
1137–1145.
[28] S. Parsons, Advanced Oxidation Processes for Water and Wastewater Treat-
ment, IWA Publishing, London, 2004 (XII+356pp).
[29] M. Sui, L. Sheng, K. Lu, F. Tian, Appl. Catal. B: Environ. 96 (2010) 94–100.
[30] L. Yang, C. Hu, Y. Nie, J. Qu, Appl. Catal. B: Environ. 97 (2010) 340–346.
[31] I.R. Guimaraes, L.C.A. Oliveria, P.F. Queiroz, T.C. Ramalho, M. Pereira, J.D. Fabris,
J.D. Ardisson, Appl. Catal. A: Gen. 347 (2008) 89–93.
[32] I.R. Guimaraes, A. Giroto, L.C.A. Oliveria, M.C. Guerreiro, J.D. Fabris, Appl. Catal.
B: Environ. 91 (2009) 581–586.
Acknowledgements
This work was funded by the Spanish Ministry of Science and
Innovation (MICINN), project CTM2008-02453 and the Spanish
Ministry of Economy and Competitiveness, project CTQ2012-
35789-C02-02. S.S. acknowledges Universitat Rovira i Virgili for the
Ph D grant. Irene Maijo (Scientific and Technical Service of URV) is
appreciated for the technical assistance in HPLC analysis. Authors
gratefully acknowledge Dr. K. R. Patil of the Centre of Materials
Characterization, National Chemical Laboratory, Pune (India) for
carrying out XPS characterization of catalysts and the related sci-
entific discussions. F. M. would like to thank ICREA Academia for
funding support.
[33] G. Zhang, S. Wang, F. Yang, J. Phys. Chem. C 116 (2012) 3623–3634.
[34] U. Schwertmann, R.M. Cornell, Iron Oxides in the Laboratory: Prepa-
ration and Characterization, VCH Publishers Inc., Weinheim, Germany,
1991.
[35] Y. Pi, M. Ernst, J.-C. Schrotter, Ozone: Sci. Eng. 25 (2003) 393–397.
[36] P.M. Álvarez, F.J. Beltrán, J.P. Pocostales, F.J. Masa, Appl. Catal. B: Environ. 72
(2007) 322–330.
[37] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173.
[38] R. Rosal, M.S. Gonzalo, A. Rodriguez, E. Garcia-Calvo, J. Hazard. Mater. 169
(2009) 411–418.
[39] I. Sires, F. Centellas, J.A. Garrido, R.M. Rodriguez, C. Arias, P.L. Cabot, E. Brillas,
Appl. Catal. B: Environ. 72 (2007) 373–381.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.cattod.
2014.03.050.
References
[1] R. Salgado, A. Oehmen, J.P. Noronha, M.A.M. Reis, J. Hazard. Mater. 241–242
(2012) 182–189.
Please cite this article in press as: S.S. Sable, et al., FeOOH and derived phases: Efficient heterogeneous catalysts for clofibric acid
degradation by advanced oxidation processes (AOPs), Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.050