International Journal of Geosciences, 2011, 2, 669-675
doi:10.4236/ijg.2011.24068 Published Online November 2011 (http://www.SciRP.org/journal/ijg)
Copyright © 2011 SciRes. IJG
Degradation of Gesaprim Herbicide by Heterogeneous
Photocatalysis Using Fe-Doped TiO2
Noemí Acevedo Quiroz1, Dulce Jocelyn Ramos Gutierrez1, Susana Silva Martínez2,
Cristina Lizama Bahena1
1Posgrado de la Facultad de Ciencias Químicas e Ingeniería y Centro de Investigación en Ingeniería y Ciencias
Aplicadas, Universid ad Autónoma del Estado de Morelos, Cuernavaca, Mexico
2Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos,
Received June 21, 2011; revised August 7, 2011; accepted September 26, 2011
Fe-doped TiO2 was prepared by the sol gel method and characterized by X-ray diffraction. All the Fe-doped
TiO2 were composed of an anatase crystal form. The activity of the Fe-doped TiO2 for the degradation of the
gesaprim commercial herbicide (which contains atrazine as active compound and formulating agents) was
studied by varying the iron content during UV (15 W), visible light and solar irradiations. The visible light
came from commercial saving energy lamps (13, 15 and 20 Watts). The gesaprim degradation rate depended
on the iron content in the photo catalyst. The Fe-doped TiO2 (0.5% by weight of TiO2) showed higher TOC
removal under visible light and was more active than the undoped TiO2 photo catalyst under the light irradia-
tion sources tested. Over 90% of chemical oxygen demand abatement was achieved with both UV and visi-
ble light but less time was required to decrease the chemical oxygen demand content by using the catalyst
doped with iron at 0.5% under visible light. It was observed that the degradation of gesaprim increased by
increasing the iron content in the catalyst under visible light.
Keywords: Atrazine, Iron Doped TiO2, Solar Irradiation, Visible Light Irradiation
Nowadays, the use of herbicides in agriculture activities to
control weedy plants and to increase food production has
become an important tool to the detriment of the en- vi-
ronment. The herbicides and their degradation products
(complex metabolites) may alter the natural habitats for
different plant and animal species depending on how they
are transported in the environment. Chlorinated tri- azines
are herbicides widely used for selective weed control, and
are amongst the most commonly used herbicides in the
world . The main compound of this family is the atrazine
(2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and it
is found in the environment contaminating soil and water
reserves . This herbicide belongs to the persistent or-
ganic pollutants because of its low biodegradability and
long half-life (60 and 100 days) in water.
Several processes have been developed to remove
atrazine from aqueous wastes, such as activated carbon
and its combination with ozone [3,4], adsorption onto
carbon nanotubes , adsorption onto zeolites , ad-
sorption on fractionated Al-pillared and Fe-Al-pillared
clays , photochemical degradation in the presence of
hydrogen peroxide and microwave , reverse osmosis
, ozone , hydrogen peroxide with ozone , elec-
tro-Fenton , Fenton and photo-Fenton , photoly-
sis by TiO2 semiconductor [14-18], atrazine by nanoscale
zero valent iron supported on organobentonite , and
hydrogen peroxide with TiO2, and Fe2O3 semiconductor
suspensions assisted by light [20-22], among others.
Amongst the treatment methods, the semiconductor
photocatalytic process for the photocatalytic oxidation
mediated by titanium dioxide appears to be an effective
strategy for degrading chlorinated triazine herbicides
because the semiconductor has shown a great potential as
a low-cost, and environmental friendly alternative for
wastewater treatment. Besides, this advanced oxidation
process has been widely demonstrated to remove persis-
tent organic compounds and microorganisms in water.
The photocatalytic oxidation of s-triazine herbicides and
670 N. A. QUIROZ ET AL.
the pathways of their degradation intermediates have
been reported by several studies [22,23]. It has been con-
cluded that the oxidation of the lateral chains and subse-
quent disappearance of the initial compound is very fast,
but the formation of the final product (cyanuric acid)
may require a long irradiation time . Also, it has
been reported that complete mineralization of atrazine
could not be attained because of the stability of the s-
triazine ring toward oxidation which only affects the
lateral chains with 5 of the 8 carbons removed as CO2.
Hustert et al. studied the photocatalytic treatment of
atrazine herbicide, and also other s-triazine herbicides
(simazine, and cyanzine) . These researchers re-
ported that the degradation of the s-triazines occurred in
various steps with cyanuric acid was formed as end
product of degradation. Hequet et al. studied the photo-
lytic degradation of atrazine and found that the UV
photolysis was efficient . They reported that the main
degradation pathway was deshalogenation and hydroxya-
trazine was generated as the main intermediate with
cyanuric acid as the final end product. These authors also
studied the photocatalytic degradation of atrazine, and
found that the major intermediates were desalkylated
compounds with cyanuric acid as the final degradation
product. McMurray and coworkers reported that the pri-
mary pathway for atrazine degradation on nanoparticu-
late TiO2 films involved the oxidation of the lateral side
chains of atrazine, producing dealkylated derivatives (2-
2-chlor o-4-ethyla mino-6 -(2-propanol)amino-1,3,5-triazin
e, desethylatrazine, deisopropylatrazine and desethylde-
sisopropyl atrazine) . They also reported that the
hydrolysis of the chlorine substituent in desethylatrazine,
desethyldesisopropyl atrazine and deisopropylatrazine
led to the production of 2-hydroxydesethyl atrazine with
the further displacement of the amino groups by hy-
droxyl groups resulting in cyanuric acid. These authors
proposed a secondary pathway which follows a hy-
droxylated pathway with immediate substitution of the
chlorine at position two with a hydroxyl group. They
neither observed complete mineralization of atrazine nor
photolysis of atrazine either with the UVA or UVB
source. Peñuela and Barceló studied the photo degrada-
tion of atrazine and desethylatrazine in water with TiO2/
H2O2 and FeCl3/H2O2 by using a xenon arc lamp and
sunlight irradiation . These authors reported that
atrazine degraded faster than desethylatrazine in the
presence of FeCl3 using both light sources with half-lives
varying from 5 to 11 min and from 19 to 26 min, respec-
tively. Měšt’ánková et al., reported that the degradation
rate of the herbicide monuron was enhanced when TiO2
was in contact with Fe(III) (from Fe(ClO4)3) because the
Fe(III) acted as scavenger of electrons photogenerated in
TiO2 particles which let down hole–electron recombina-
The doping with small amounts of metal impurities
aims at facing one relevant drawback of TiO2, which is
its poor absorption of visible light. Enhanced visible light
absorption has been reported in the presence of transition
metals [27,28], nitrogen and carbon as dopants . It
was reported that the UV-Vis absorption studies showed
significantly enhanced red-shift in UV-Vis absorption
spectra with an increased amount of iron [30,31]. The
photocatalytic activity of nano-sized Fe-doped TiO2,
examined by the mineralization of oxalic acid under
visible light irradiation, showed highest activity with 2%
of Fe-doped TiO2 . However, it was reported that the
photocatalytic efficiency of metal doped TiO2 strongly
depends on the conditions of preparation, on the mor-
phostructural properties (crystalline structure, specific
surface area) and on the type of the organic pollutant to
The aim of this work was to synthesize TiO2 and iron-
doped TiO2 with the sol-gel method and to study the ef-
ficiency of Fe-doped titania suspensions in the photo-
catalytic degradation of the gesaprim commercial herbi-
cide under UV light, visible light and solar light. Ge-
saprim, herbicide used for the control of broadleaf weeds
and some grassy weeds, contains atrazine as active com-
pound and formulating agents as additional components.
2. Material and Methods
Gesaprim herbicide (90 GDA) was directly purchased
from Syngenta Crop Protection Inc. (USA); the gesaprim
contained 90% of atrazine as active ingredient. Titanium
tetrabutoxide (Ti(OC4H9)4), anhydride ethanol, distilled
water, ferric chloride (FeCl3), HNO3 and H2SO4 were
analytical grade (Sigma-Aldrich). All chemicals were
used as received without further purification.
2.2. Synthesis of Fe-Modified TiO2 Photo
The Fe-doped TiO2 catalyst was prepared by the sol–gel
method as below: A mixture of H2O (1.25 ml), HCl (0.5
ml), C2H6O (5 ml) and FeCl3 (different iron amounts)
was prepared with stirring for 5 min. Separately,
Ti(OC4H9)4 solution at a concentration of 44.7 g/l ex-
pressed as TiO2 was added drop wise to 22.5 ml C2H6O
solution (99.9%) with stirring under nitrogen atmosphere,
this solution was kept under stirring during 20 min. Then,
the iron mixture was added drop by drop to the ethanol-
opyright © 2011 SciRes. IJG
N. A. QUIROZ ET AL.
titanium tetrabutoxide solution and kept under stirring
during 2 h until a gel was formed. The content of iron
was 0.0%, 0.1% and 0.5% by weight of TiO2. Afterwards,
the solvent was eliminated under vacuum. The resulting
powder was dried at 100˚C for 30 min followed by ther-
mal treatment at 400˚C with air during 2 h. The crystal
structure of the powders was studied by X-ray diffraction
on a diffractometer (Rigaku model DMAX 2200) with
Cu Ka radiation (
= 1.54439 Å) at 2
= 0˚ - 80˚, and the
morphology by the scanning microscope electron (LEO
2.3. Photocatalytic Degradation of Gesaprim
The photocatalytic degradation of gesaprim was carried
out employing white fluorescent light (visible light from
an energy saving compact lamp), UV and solar irradia-
tion. Gesaprim degradation, using TiO2 and Fe-doped
TiO2 suspension of the powders synthesized, was fol-
lowed by measuring the chemical oxygen demand (COD)
and Total organic carbon (TOC). The initial concentra-
tion of gesaprim which corresponds to its maxima solu-
bility in water at pH 3 is 40 ppm. Such concentration has
a COD and TOC content of 38 ppm and 20 ppm, respec-
tively. The photocatalytic activity of the photo catalyst
Fe-doped TiO2 was evaluated by measuring the decom-
position rate of gesaprim in a circulation type reactor.
The reactor was similar to a laboratory glassware con-
denser (made of glass Duran, 20 cm long and 4 cm
inner diameter). The UV or visible lamp was put inside
the inner glass tube of the condenser so that the irradia-
tion of the UV/Vis light was ~2 mm away from the
flowing gesaprim solution; while the gesaprim solution
was running in a similar way that a coolant does in a
laboratory glassware condenser using a centrifugal poly-
propylene circulating pump (Cole Parmer). Stock solu-
tions of gesaprim (0.106 g diluted in 2.5 L) were pre-
pared with distilled water at pH 3 adjusted with H2SO4
with gentle stirring during 2 d. The TiO2 (iron doped/
undoped) slurry solution, containing 40 ppm of initial
concentration of gesaprim at pH 3, in the reactor was
irradiated with a UV light (15 W, 352 nm, Cole Parmer)
or energy saving white fluorescent light (13, 15, and 20
W compact lamps, Phillips). The UV illumination inten-
sity at the surface of the sample was 0.068 W/cm2;
whereas it varied inside of 0.059 - 0.090 W/cm2 range
for the visible light. The gesaprim solution was in con-
tact with the photo catalyst for 20 min previous to switch
the lamp on. The COD of gesaprim in the reactor were
measured as a function of the photocatalytic degradation
time which started at the moment the lamp was on;
whereas TOC was analyzed when the experiment was
terminated. COD and TOC were analyzed using standard
methods and standard tubes (Hach) inside the concentra-
tion range of 0 - 40 ppm. Samples were filtered as col-
lected prior the analysis.
3. Results and Discussion
3.1. Characterization of Undoped TiO2 and Iron
Doped TiO2 Powders
Figure 1 shows the XRD patterns of the TiO2 and 0.5%
Fe doped TiO2 powder annealed at 400˚C. According to
the main reflection, the observed peaks can be attributed
to the anatase phase. Regarding to the Fe-doped TiO2,
the diffraction peaks for iron are completely missing
from the XRD pattern for the doped iron TiO2 powder.
This may be attributed to the low sensitivity of the XRD
method due to the low concentration of added iron .
It could also be attributed to the incorporation of iron
ions in the crystal structure of TiO2 , or by very fine
dispersion of iron in the titania resulting in X-ray amor-
phous behavior . Ambrus and coworkers doped the
titania with iron up to 10% of iron content (Fe(III)) and the
diffraction peaks for iron were completely missing from
the XRD pattern for the doped iron TiO2 powder .
3.2. Influence of Iron on the Photo Catalyst for
the Degradation of Gesaprim under Visible
The photocatalytic activity of the Fe-doped TiO2 was
observed for the decomposition of gesaprim which was
carried out employing white fluorescent light (visible
light) and solar irradiation. The COD decay profile for
the decomposition of gesaprim (Figure 2(a)) increased
by the presence of iron in the TiO2 photo catalyst (400
mg/L) under visible light irradiation (with 0.090 W/cm2
using 20 W lamp). The highest initial degradation rate of
Figure 1. XRD patterns of TiO2 and iron-doped TiO2
Copyright © 2011 SciRes. IJG
672 N. A. QUIROZ ET AL.
gesaprim was found to be at 0.5% of iron content (by
weight of TiO2) achieving 95% of COD removal after 60
min of visible light irradiation (with an energy consump-
tion of 288 kJ/L) which corresponds to a TOC removal
of ~50% at the same time. Increasing the degradation
time further, it was observed that TOC was decreased
90% of its original value (20 ppm) at 200 min of photo
While the undoped TiO2 photo catalyst showed ~21%
of COD removal at the same time under the same condi-
tions. The degradation of gesaprim under solar irradia-
tion (in a cloudless day from 10:00 to 14:00 h) is shown
in Figure 2(b). It can be seen from this figure that the
initial COD decay (decomposition rate) of gesaprim is
fast in the first 10 minutes and then the decomposition of
gesaprim slows down. COD abatements of 13%, 36%
and 65% were, respectively, achieved by undoped TiO2,
0.1% Fe-doped TiO2 and 0.5% Fe-doped TiO2 after 60
minutes under solar irradiation at pH 3 (with an energy
consumption of 267.9 kJ/L). TOC removal of ~23% was
achieved using 0.5% Fe-doped TiO2 under solar light at
60 min of reaction. These results show that the increased
activity of TiO2 doped with iron is because of the nature
of iron which can be an electron or hole scavenger and
results in the improvement of the separation of free car-
Figure 2. COD profile for the degradation of gesaprim
using TiO2 and iron-doped TiO2 (catalyst load: 400 ppm
and pH 3) under (a) visible light (20 W) and (b) solar
riers. Thus, the recombination rate of the electron–hole
pairs is lowered and the photocatalytic activity is en-
hanced. It has been reported that the photocatalytic activ-
ity of iron doped TiO2 strongly depends on the prepara-
tion method, iron precursor, and the amount and state of
iron (commonly a very low content of doped iron has a
positive effect on the enhancement of the photocatalytic
activity of Fe-doped TiO2).
It has also been reported that higher amount of Fe(III)-
doped TiO2 than an optimal iron content is detrimental
on the photocatalytic activity of the photo catalyst be-
cause the Fe(III) at high concentration in Fe-doped TiO2
can act as a recombination centres .
3.3. Influence of Light Irradiation on the Photo
Catalyst for the Degradation of Gesaprim
In order to study the effect of light source on the degra-
dation of gesaprim by 0.5% Fe-doped TiO2 catalyst, sev-
eral experiments were carried out and recorded as a func-
tion of the energy consumption to compare the degrada-
tion efficiency of gesaprim for each light source. It was
used different power lamps (Figure 3) and different
source of light irradiation (Figure 4) to record the COD
abatement profiles during the degradation of gesaprim.
Figure 3 reports that the initial rate of COD abatement
is fast and similar in the first 100 minutes of degradation
regardless of the power of the lamp used. Afterwards, the
COD was 95% abated when the lamp of the higher
power (20 W) was used in which it was required 300
kJ/L of energy consumption (after 60 min of photo ca-
talysis), attributable mainly to visible-light absorption by
the iron compound; whereas, only 85% of COD was
abated with the other two lamps even at higher energy
The profiles for COD abatement using different sources
Figure 3. COD removal profile for the degradation of ge-
saprim using 400 ppm of 0.5% Fe-doped TiO2 under dif-
ferent powers of the visible light.
opyright © 2011 SciRes. IJG
N. A. QUIROZ ET AL.
Figure 4. Photocatalytic degradation of gesaprim using 400
ppm of 0.5% Fe-doped TiO2 under different sources of light
of light irradiation (Figure 4) clearly show an improv-
ment in the degradation of gesaprim by the presence of
iron in the catalyst (0.5% Fe-doped TiO2) under visible
light from both the 20W Vis-lamp and the solar irradia-
tion (Figure 4(a)).
It is interesting to observe that the iron-doped TiO2
enhanced the initial rate of COD removal under the solar
irradiation with respect to that obtained with or without
undoped TiO2 under similar energy efficiency. Thus, the
iron in the catalyst increased the reactivity of the photo
catalyst under the visible-light of the solar irradiation.
COD removals of 23%, ~40% and 74% were achieved
by the sole effect of solar photolysis, solar photo cataly-
sis and solar Fe-doped photo catalysis, respectively. The
activation of the catalyst under solar irradiation is by
both visible and UV irradiation (with ~6% of UV light
contribution . This figure also shows that 95% of
COD removal was obtained by the Fe-doped TiO2 under
visible irradiation (20 W lamp) after 60 minutes of reac-
tion (with an energy consumption of 288 kJ/L). The high
COD removals achieved is because the iron deposition
on TiO2 surface improves the photocatalytic activity by
suppressing the electron-hole recombination .
In our previous study , it was shown that the
photodegradation of this commercial herbicide was en-
hanced by the use of ultrasound in the presence of TiO2
catalyst with COD removal of 84% at 150 minutes of
UV light irradiation. The combination of these two proc-
esses (sonophotocatalysis) gave very high decomposition
yields of the active compound (atrazine) reaching high
degree of mineralization (97%) . Thus, a comparison
of the results reported here with those obtained in our
previous study using the sonophotocatalytic process, it is
interesting to note that the employment of iron-doped
TiO2 catalyst (under visible light) gives similar results at
Figure 4(b) reports similar COD removal profiles un-
der the UV lamp irradiation (15W) with the achievement
of higher COD removals in comparison with those
reached under solar irradiation (with comparable energy
consumption in both systems). From these results, it
might be assumed that Fe-modification also improves
inherent photocatalytic activity of the TiO2 powders to
some extent because of an efficient charge separation of
the UV light generated electron-hole pairs.
The gesaprim degradation rate depended on the iron con-
tent in the photo catalyst. The Fe-doped TiO2 (0.5% by
weight of TiO2) showed higher TOC removal under visi-
ble light and was more active than the undoped TiO2
photo catalyst under the light irradiation sources tested.
Over 90% of chemical oxygen demand abatement was
achieved with both UV and visible light but less time
was required to decrease the chemical oxygen demand
content by using the catalyst doped with iron at 0.5%
under visible light (90% of TOC was removed after 200
min of photoreaction). It was observed that the degrada-
tion of gesaprim increased by increasing the iron content
in the catalyst under visible light. This can be explained
by the fact that the Fe(III) acted as scavenger of electrons
photogenerated in TiO2 particles which let down hole–
This advanced oxidation process offers an environ-
mental alternative for the treatment of water polluted
with this commercial herbicide.
This work was financially supported by the Programa de
Mejoramiento del Profesorado (PROMEP) of the Secre-
taría de Educación Pública (SEP). We thank CONACyT
for the Grant given to N.A.Q and D.J.R.G. to support
their postgraduate studies.
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