Open Journal of Physical Chemistry, 2011, 1, 28-36
doi:10.4236/ojpc.2011.12005 Published Online August 2011 (
Copyright © 2011 SciRes. OJPC
Photocatalytic Degradation of 4-Chlorophenol by
CuMoO4-Doped TiO2 Nanoparticles Synthesized by
Chemical Route
Tanmay K. Ghorai*
Department of Chemistry, West Bengal State University, Barasat, Kolkata, India
E-mail: *
Received April 23, 2011; revised May 29, 2011; accepted July 7, 2011
The photocatalytic degradation of 4-chlorophenol (4-CP) in aqueous solution was studied using CuMoO4-
doped TiO2 nanoparticles under Visible light radiation. The photocatalysts were synthesized by chemical
route from TiO2 with different concentration of CuMoO4 (CuxMoxTi1 xO6; where, x values ranged from 0.05
to 0.5). The prepared nanoparticles are characterized by XRD, BET surface area, TEM, UV-vis diffuse re-
flectance spectra, Raman spectroscopy, XPS and EDAX spectroscopy were used to investigate the nanopar-
ticles structure, size distribution, and qualitative elemental analysis of the composition. The CuxMoxTi1 xO6
(x = 0.05) showed high activity for degradation of 4-CP under visible light. The surface area of the catalyst
was found to be 101 m2/g. The photodegradation process was optimized by using CuxMoxTi1 xO6 (x = 0.05)
catalyst at a concentration level of 1 g/l. A maximum photocatalytic efficiency of 96.9% was reached at pH =
9 after irradiation for 3 hours. Parameters affecting the photocatalytic process such as catalyst loading, con-
centration of the catalyst and the dopant concentration, solution pH, and concentration of 4-CP have been
Keywords: Inorganic Compounds, Chemical Synthesis, Nanostructures, Optical Properties
1. Introduction
The photocatalytic degradation of different toxic com-
pounds such as organic or inorganic pollutants, elimi-
nated through photochemical reaction by using TiO2
photocatalysts, has been widely studied [1-8]. It is an
attractive technique for the complete destruction of un-
desirable contaminants in both liquid and gaseous phase
by using artificial light of solar illumination [9].
There are so many techniques used for the complete
annihilation of undesirable contaminants in both liquid
and gaseous phase by using artificial light and nano
photocatalyst TiO2 [10-12]. However, there are two se-
rious limitations, which were found in the conventional
TiO2 catalyst system that limits its practical applications.
First, setting velocity of aggregated TiO2 (average di-
ameter of 0.2 µm) is very slow, thus requiring a long
retention time in the clarifier. Second, as the quantity of
TiO2 is increased in order to increase the photocatalytic
rate, the high turbidity created by the high TiO2 concen-
tration can decrease the depth of UV penetration. This
effect can drastically lower the rate of photocatalytic
reaction on a unit TiO2 weight basis. Therefore the ap-
plications for metal ions have been used for doping TiO2
[13-16] to increase the photocatalytic property by influ-
encing generation and recombination of the charge carri-
ers under light. Barkat et al and Woo et al reported that
photodegradation of 2-chlorophenol by Co-doped TiO2
and 4-chlorophenol by Ni2+-doped TiO2 were photo-
active under UV light but they did not investigate the
degradation of 2/4-chlorophenol with P25 TiO2 [17-18].
The effects of copper (II) ions have been studied on the
photodegradation of the insecticide monocrophos [19],
photocatalytic degradation of sucrose [20], acetic acid
[21], phenol [22], and methyl orange [23]. But there is no
such example of copper molybdenum doped TiO2 photo-
catalysts. A successful application of CuMoO4-doped
TiO2 is the easy degradation of 4-chlorophenol in aque-
ous medium in presence of UV light. It is of interest to
know how the photocatalytic degradation induced by
TiO2 doped metal ions will affect the treatment of water.
The dopant ions or oxides can also modify the band gap
or act as change separators of the photoinduced electron-
hole pair thus enhancing the photocatalytic activity [24].
In this paper, we report the preparation of copper mo-
lybdenum doped TiO2 nano photocatalyst by chemical
solution decomposition methods. The photocatalytic ac-
tivities of the synthesized copper molybdenum doped
TiO2 nanocatalysts were compared with P 25 titania by
examining the photodegradation of 4-CP as a model pho-
tocatalytic reaction under visible light. The CuxMoxTi1 xO6
(x = 0.05) (CMT1) shows better photocatalytic activity
compared to P25 TiO2 and the other compositions of
copper molybdate doped titanium dioxide CuxMoxTi1 xO6
(x = 0.1) (CMT2), CuxMoxTi1 xO6 (x = 0.5) (CMT3)
photocatalyst for photodegradation of 4-CP.
2. Experimental Section
2.1. Synthesis of Nanosized Anatase
CuMoO4-Doped TiO2
The total synthesis was carried out in two steps by
chemical solution decomposition method (CSD). In the
first step the stock of Cu(NO3)2·6H2O (Aldrich, 99.99%),
(NH4)2MoO4 (Aldrich, 99.99%) and titanium tartarate
solutions were prepared. The titanium tartarate solution
was prepared by the following procedure. TiO2 powder
(Aldrich, 99.99%) is dissolved in 40% HF solution in a
500 ml teflon beaker kept on an water bath for ~24 h.
During warming on the water bath, the solution was
shaken occasionally. The clear fluoro complex of tita-
nium was then precipitated with 25% NH4OH solution.
The precipitate was filtered and thoroughly washed with
5% aqueous solution of NH4OH to make the precipitate
fluoride free. Then the hydroxide precipitate of titanium
is dissolved in tartaric acid (Aldrich, 99.99%) solution.
The strength of the Ti4+ in titanium tartarate solution was
estimated by gravimetric method.
In the second step, the equivalent amount of copper
nitrate, ammonium molybdate, and titanium tartarate solu-
tion were taken in a beaker as per chemical composition.
The complexing agent TEA (triethanolamine) (MERCK,
Mumbai, India) (where molecular ratio of metal ion:TEA
= 1:3) was added to the homogeneous solution of con-
stituents maintaining pH at 6 - 7 by nitric acid (65%) and
ammonia. The mixed solution was dried at 200˚C, re-
sulting in a black carbonaceous light porous mass which
was calcinated at three different temperatures namely
500˚C, 600˚C and 700˚C for 2 h at a heating rate of
5˚C/min for different chemical compositions of Cux-
MoxTi1 xO6 (x = 0.05, 0.1, 0.5) nano powders. Complete
synthesis procedure is presented below in the Flowchart
1 diagram.
2.2. Photocatalytic Activity
The photocatalytic activities of the newly prepared nano-
sized CuxMoxTi1 xO6 (x = 0.05, 0.1, 0.5) powders were
characterized using photodegradation of 4-chlorophenol
to carbon dioxide and water in aerated aqueous solution
as a model photoreaction. The photocatalytic reactions
were carried out by slow stirring the mixture using a
magnetic stirrer with simultaneous irradiation by visible
light source using a 300-W Xe lamp with a cut off filter
(λ > 420 nm). The reactions were performed by adding
nano powder of each photocatalyst (0.1 g) and the con-
centration of 4-CP is 50 ppm, into each set of a 100 ml of
different solution of 4-CP. However, the efficiency of
photodegradation of 4-CP is maximum at 10 ppm in the
presence of prepared catalyst. The system was thor-
oughly repeated by several cycles of evacuation.
A small volume (1ml) of reactant liquid was siphoned
out at regular interval of time for analysis. It was then
centrifuged at 1500 rpm for 15 min, filtered through a
0.2 µm-millipore filter to remove the suspended catalyst
particles and analyzed for the residual concentration of
4-CP by high performance liquid chromatograph (HPLC).
The efficiency of the decolorization process at pH = 9 is
measured by the following Equation (1), as a function of
Efficency = 100CC
Here C0 and C are the initial and remaining 4-CP con-
centrations in the solution, respectively.
2.3. Characterization
The crystallinity of the prepared nano powders was
checked by powder X-ray diffraction (XRD) with a Ri-
gaku Model Dmax 2000 diffractometer using CuKa ra-
diation (λ = 1.54056 Å) at 50 kV and 150 mA by scan-
ning at 2˚ 2θ min1. Scherer’s equation was applied using
the (101) peak to determine the pseudo-average particle
size of nanosized anatase CuMoO4 doped TiO2 to reveal
the effects of the preparation parameters on the crystal
growth: D = Kλ/(βcosθ), where K was taken as 0.9, and β
is the full width of the diffraction line at half of the
maximum intensity.
The energy dispersive X-ray spectroscopy (EDX) (JEOL
JMS-5800) was used to study the qualitative elemental
analysis and element localization on samples being ana-
lyzed. BET surface area measurements were carried out
using a (BECKMAN COULTER SA3100) on nitrogen
adsorption desorption isotherm at 77K.
The morphology and the size of TiO2 nanocrystallites
ere investigated by high resolution transmission elec- w
Copyright © 2011 SciRes. OJPC
Copyright © 2011 SciRes. OJPC
Flowchart 1. Synthesis of different composites of nanosized copper molybdenum doped titanium dioxide CuxMoxTi1-xO6 (x =
0.05, 0.1, 0.5) photocatalysts.
dioxide, CuxMoxTi1 xO6 [when x = 0.05 (CMT1), 0.1
(CMT2) & 0.5 (CMT3)], copper doped TiO2 [Cu-TiO2
(CT)] and CuMoO4 (CM) are shown in Figure 1 at
550˚C. It can be seen that the peaks at 2θ of 25.26˚,
38.16˚, 48.17˚, 54.03˚, 55.12˚, and 64.69˚ are assigned to
(101), (004), (200), (105), (211), and (204) respectively
(JCPDS data File No. 84 1285) lattice planes of TiO2,
which are attributed to the signals of anatase phase. No
additional peaks were found to be present, which could
be assigned to the CuMoO4 anorthic phase that indicated
that the resulting nano powder was alloy of copper mo-
lybdate with titanium dioxide. Rutile phase was not ob-
served for all specimens using different Ti precursors.
The XRD patterns of CuxMoxTi1 xO6 (x = 0.05) recorded
at room temperature after annealing the samples at vari-
ous temperatures, indicated no change of crystallogra-
phic characteristics shown in Figure 2. Furthermore, the
EDAX spectroscopy measurements (Figure 3) show a
molar ratio of CuMoO4: TiO2 equal to about 0.05:0.95.
tron microscopy (HRTEM) with a JEOL-2010F at 200
kV. The particle size distribution of TiO2 nanocrystallites
was determined by directly measuring the particle sizes
on the TEM images. The average particle size of each
sample was determined by using the size distribution
data based on a weighted-averages method.
The catalytic activity of the prepared nanoparticles
was measured in a batch photoreactor containing appro-
priate solutions of 4-CP with visible light irradiation of
300-W Xe lamp. High performance liquid chromatogra-
phy (HPLC) was used for analyzing the concentration of
4-CP in solution at different time intervals during the
photodegradation experiment.
Raman spectrum was obtained by using a Perkin
Elmer Spectrum GX Raman instrument. The UV-vis
diffuse reflectance spectra of the prepared powders were
obtained by a UV-vis spectrophotometer (UV-1601 Shi-
madzu) at room temperature
3. Results and Discussion
3.2. Transmission Electron Microscopy (TEM)
3.1. XRD Analysis
The XRD pattern of copper molybdenum doped titanium Bright field TEM (Model JEOL-2010F) micrograph of
Figure 1. XRD patterns of CuMoO4 (CM), copper doped
TiO2 (CT), copper molybdenum doped titanium dioxide
(CMT1, CMT2, CMT3), and TiO2 photocatalyst at 550˚C.
Figure 2. XRD of CuxMoxTi1 xO6 (x = 0.05) recorded at
room temperature after annealing the samples at various
CuxMoxTi1 xO6 (x = 0.05) (CMT1) nanoparticles is pre-
sented in Figure 4. The fine particles are spherical, of
narrow size distribution and have an average particle size
of about 10 ± 2 nm analyzed by soft ware Image Tool.
However, the average crystallite size of CMT determined
by the peak broadening method was found to be about 12 -
13 nm obtained from XRD analysis (shown in Table 1).
The corresponding selected area electron diffraction pat-
tern of the same sample (CMT1) showed distinct rings,
characteristic of a single crystalline nanoparticle as shown
in Figure 4 (inset).
Figure 3. EDAX of CuxMoxTi1 xO6 (x = 0.05).
Figure 4. Bright field TEM micrograph and selected area
electron diffraction (SAED) (inset) pattern of sample CMT1.
Table 1. Resultant properties of CMT1, CMT2, CMT3, P25
TiO2, CM and CT composites.
Sample PhotodegradationSBET Anatase
Crystal Bandgap
Efficiency (%) (m2/g) size (nm) Energy (eV)
CMT1 96.9 101 11.89 3.03
CMT2 87.8 92 12.52 3.09
CMT3 58.7 92 11.97 3.12
CM 38.2 50 24.21 3.15
CT 25.2 32 14.49 2.82
P25 TiO211.2 49 12.42 3.29
Photodegradation efficiency; BET surface area measured by dinitrogen
adsorption desorption isotherm at 550˚C; Anatase crystal size calculated
from Scherer equation.
3.3. Specific Surface Area (BET) Analysis
The BET of different compositions of CMT1, CMT2,
CMT3, P25 TiO2, CM and CT calcined at 550˚C tem-
peratures is listed in Table 1, which is measured by dini-
Copyright © 2011 SciRes. OJPC
trogen adsorption-desorption isotherm in BECKMAN
COULTER SA3100. It is noted that BET decreases as
dopant concentration of metal ions increases at a par-
ticular composition. The sample CMT1 having high spe-
cific surface area, which was about 101 ± 5 m2/g, pro-
vided good photocatalytic properties among all the pho-
tocatalysts against 4-CP. Hence the large surface area
enhanced photocatalytic activity through efficient ad-
sorption of the reactant on the catalyst surface.
3.4. Raman Spectroscopy
Raman analysis of CuMoO4-doped TiO2 alloy may allow
us to rationalize these results. The Raman spectra of
prepared nanoparticles calcined at 550˚C with varying
mol% of CuMoO4 in TiO2 is shown in Figure 5. The
analysis of Raman bands suggests that all active materi-
als having bands at 337 cm–1 for CuO2 [25] in-plane
bond-bending mode and 971 cm–1 for Mo [26] corre-
spond to Mo = O bond stretching modes. Except the
above two bands, all the mentioned bands matched with
characteristic bands of titania.
3.5. XPS Analysis
Figure 6 shows the results of XPS spectra of CuxMoxTi1xO6
(x = 0.05). CuMoO4 doped TiO2 where the concentration
of CuMoO4 is 0.05 mole, the Cu2O/CuO and MoO3 are
shown in Figure 6 to identify the copper and molybde-
num state on the surface of TiO2. The Cu (2p)- binding
energies of Cu2O/CuO were found to be 932.8 and 953.4
eV, respectively and corresponding Mo (2p)- binding
energy is 233.0 eV. According to the position and the
shape of the peaks, the copper on the surface of TiO2
may exist in multiple-oxidation states. Oxygen and Ti
show surface characteristic photoelectron peaks. Figure
Figure 5. Raman spectra of CMT1, CMT2, CMT3 and
Figure 6. XPS of CuxMoxTi1 xO6 (x = 0.05).
shows the binding energy of O (1s) at 533.4 eV and Ti
(2p) at 454.9 eV (2p3/2) and 461.3 eV (2p1/2) correspond-
ing to Oxygen and Ti metal.
3.6. UV-VIS Diffuse Reflectance Spectrum
The UV-vis diffuse reflectance spectrum and band gap
energy of all the compositions are shown in Figure 7 and
Table 1 respectively. From Figure 7 and Table 1 we
may conclude that the UV-vis diffuse reflectance spec-
trum of CuMoO4 doped TiO2 and pure TiO2, gave dis-
tinct band gap absorption edges at 409 nm, 401 nm, 397
nm and 387 nm for doped CMT1, CMT2, CMT3 and
pure TiO2 and corresponding band gap energies are 3.03,
3.09, 3.12 and 3.20 eV respectively. At lowest concen-
tration of CuMoO4, the absorption edge shift is maxi-
mum hence the corresponding calculated band gap en-
ergy is minimum. This is explained considering that
when the amount of dopants is small, the metals ions are
well incorporated into the lattice withstanding the
Figure 7. The UV-visible diffuse reflectance spectra of M-Ti
samples with the highest dopant-atom content.
Copyright © 2011 SciRes. OJPC
evolvement of local strains. On the other hand, when the
dopants are in excess, CuMoO4 cannot enter the TiO2
lattice but cover on the surface of TiO2 in MO3 form, and
leads to the formation of heterogeneity junction. So,
CuxMoxTi1 xO6 (x = 0.05) photocatalysts has lower band
gap energy (3.03 eV) highest within the temperature
range in which the experiments were carried out photo-
catalytic activity compared to other dopant concentra-
tions and P25 TiO2.
3.7. Photocatalytic Activity of the Prepared
The evaluation of the efficiency of photodegradation of
4-CP as a function of different experimental parameters
is demonstrated in Figures 8-11. To study the effect of
the catalyst on the 4-CP photodegradation rates, samples
are annealed at different calcinations temperatures. The
activities strongly depended on the calcination tempera-
ture of the catalysts. Figure 8 summarizes the results of
these experiments. The highest degradation of 4-CP was
achieved with samples that were annealed at 550˚C.
However, increase in the calcinations temperatures of the
catalysts decrease the photocatalytic activity due to in-
crease of particle size and decrease of the specific sur-
face area. The crystalline nature of the anatase structure
is primarily responsible for the photocatalytic activity of
the nanoparticles. Particles with anatase structure are
known to have a better photocatalytic activity [27]. More-
over, the small particle size of CMT1 (about ~10 nm)
provides a large surface area where the catalytic reac-
tions could occur and the photoreactivity is enhanced.
The effect of the dopant concentration on the photo-
Figure 8. Photocatalytic effect of the CMT1 crystal struc-
ture on the 4-CP photodegradation at different calcinations
catalytic activity of different compositions of copper mo-
lybdate doped titanium dioxide photocatalyst, on photo-
degradation of 4-CP has been presented in Figure 9.
From Figure 9, it could be noted that the dopant concen-
tration in TiO2 has a great impact upon its photocatalytic
activity to decolorize 4-CP solution at pH = 9. The
photodegradation efficiency of 4-CP decreased with in-
creasing CuMoO4 concentration, reaching a maximum
value of 96.9% with sample containing 0.05 mol% Cu-
MoO4 that was annealed at 550˚C. The photodegradation
efficiency of 4-CP using all the photocatalyst are pre-
sented in Table 1. The anatase CMT1 nanocrystallites
with regular crystal surfaces should have less surface
defects, giving highly efficient photocatalysis by sup-
pression of electron-hole pair recombination through
redox cycle between Cu(II) and Cu(I). Cu(II) ions work
as electrons scavengers which may react with the super-
oxide species and prevent the holes-electrons (h+/e) re-
combination and consequently increase the efficiency of
the photo-oxidation. The possible reaction is shown be-
Cu(II) + O2
(ads) = Cu(I) + O2(ads) (2)
Defect sites are identified as Ti3+ on the TiO2 surface
due to adsorption and photoactivation of oxygen thus,
increasing the photocatlaytic efficiency. Electron can be
also excited from defect energy levels Ti3+, to the TiO2
conduction band and photodegradation occurs.
Ti + OTi + O2
Figure 10 shows the effect of the CuMoO4-doped
TiO2 dosage on the 4-CP degradation. It can be seen that
in the absence of the catalyst about 12% of 4-CP was
removed at pH 9 after 3 h of irradiation of UV. This is
Figure 9. Photocatalytic effect of CMT1, CMT2, CMT3,
P25, CM and CT on the 4-CP photodegradation. Catalyst
dosage = 1 g/L, 4-CP = 50 ppm, pH = 9.
Copyright © 2011 SciRes. OJPC
mainly a photolysis process. The degradation of 4-CP is
increased by adding CuMoO4 doped TiO2 with CuMoO4
concentration of 0.05 mol%. The degradation reached a
maximum value of 96.9 with catalyst dosage of 1 g/L
and the optimize concentration of 4-CP is 50 ppm.
However, a further increase in the catalyst dosage sli-
ghtly decreased the degradation efficiency. The photo-
decomposition rates of pollutants are influenced by the
active site and the photo-absorption of the catalyst used.
Adequate loading of the catalyst increases the generation
rate of electron/hole pairs for enhancing the degradation
of pollutants. However, addition of a high dose of the
semiconductor decreases the light penetration by the
photocatalyst suspension [28] and reduces the degrada-
tion rate. A Langmuir-Hinshelwood type [29] of rela-
tionship can be used to describe the effect of 4-CP con-
centration on its degradation.
The pH of the solution has a strong effect on the
photodegradation process, as shown in Figure 11. Deg-
radation efficiency of 4-CP has not been found to be sig-
nificant at low pH values but increased rapidly with in-
crease of the pH, attaining a maximum value of 96.9%
for pH of 9. Further increase in pH of 4-CP decreases the
photodegradation efficiency, because the protons are
potential determining ions for TiO2, and the surface
charge development is affected by the pH [30].
Upon hydration, surface hydroxyl groups (TiOH) are
formed on TiO2. These surface hydroxyl groups can un-
dergo proton association or dissociation reactions, there-
by bringing about surface charge which is pH-dependent
and photodegradation occurs.
However, the dopant concentrations of the prepared
catalyst above an optimal value result in the formation of
Figure 10. Effect of the CuMoO4-doped TiO2 dosage on the
4-CP photodegradation. Co = 0.036 mol%, 2-CP = 50 ppm,
pH = 9.
Figure 11. Photocatalytic effect of the solution pH on the 4-
CP photodegradation. CMT1catalyst dosage = 1 g/L, 4-CP =
50 ppm.
recombination centers which traps the charges for a very
long time thereby reducing the photodegradation per-
4. Conclusions
In this study, nanophotocatalyst CuMoO4 (5 mole%)
doped TiO2 synthesized by CSD method is more photo-
active than all other compositions of copper molybdate
doped TiO2 and P25 TiO2 due to high surface area (101
m2/g), lower band-gap (3.03 eV) and photochemical
degradation on 4-CP through redox cycle between Cu(II)
and Cu(I). The typical composition of the prepared Cu-
MoO4 doped TiO2 was CuxMoxTi1 xO6 with the value
of x ranging from 0.05 to 0.5. The photocatalytic activity
strongly depends on CuMoO4 doping concentration. The
photodegradation process was optimized by using Cux
MoxTi1 xO6 (x = 0.05) catalyst at a concentration level
of 1g/L. A maximum photocatalytic efficiency of 96.9%
was reached at pH = 9 after irradiation for 3 hours. The
light absorption measurements confirmed that the pres-
ence of 5 mol% CuMoO4 doped TiO2 structure caused
significant absorption shift into the visible region com-
pared to the pure TiO2 powder.
5. Acknowledgements
The authors thank the Council of Scientific and Indus-
trial Research, India, for financial support and Prof.
Mukut Chakraborty for English correction of the manu-
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