Photocatalytic degradation of Eriochrome Black T dye using well-crystalline anatase TiO2 nanoparticles

Article abstract of DOI:10.1016/j.jallcom.2013.07.069

Well-crystalline anatase TiO₂ nanoparticles were prepared by facile solution process and characterized in terms of their morphological, structural, optical and photocatalytic properties. The detailed studies confirmed that the as-synthesized na

Full text of DOI:10.1016/j.jallcom.2013.07.069

Journal of Alloys and Compounds 581 (2013) 392–397
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Photocatalytic degradation of Eriochrome Black T dye
using well-crystalline anatase TiO nanoparticles
2
Sushil Kumar Kansal a, , Swati Sood , Ahmad Umar
⇑
b
c,d,
⇑
, S.K. Mehta b
a
Dr. S.S. Bhatnagar University Institute of Chemical Engineering & Technology, Panjab University, Chandigarh 160014, India
Department of Chemistry, Panjab University, Chandigarh 160014, India
Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, P.O. Box 1988, Najran 11001, Kingdom of Saudi Arabia
Department of Chemistry, College of Science and Arts, Najran University, P.O. Box 1988, Najran 11001, Kingdom of Saudi Arabia
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 May 2013
Received in revised form 5 July 2013
Accepted 10 July 2013
Available online 19 July 2013
Well-crystalline anatase TiO nanoparticles were prepared by facile solution process and characterized in
terms of their morphological, structural, optical and photocatalytic properties. The detailed studies con-
2
firmed that the as-synthesized nanoparticles are well-crystalline, grown in high density and exhibiting
good optical properties. For photocatalytic degradation, Eriochrome Black T (EBT) dye was used as a
model compound and about 82% of photo-degradation of EBT dye was achieved in 90 min under UV light
irradiation. The kinetic studies revealed that EBT photo-degradation follows pseudo-first order reaction
Keywords:
TiO nanoparticles
2
Eriochrome Black T
Photocatalytic degradation
ꢀ1
kinetics and rate constant was found to be 0.017 min . In addition to this, by comparing the photocat-
alytic performance with other commercially available catalysts (PC-50, PC-500, commercial ZnO), it was
observed that the as-synthesized TiO
2
nanoparticles exhibited superior photocatalytic performance.
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
etc. have emerged as popular techniques to destroy recalcitrant
compounds from wastewater. Heterogeneous semiconductor phot-
There has been a widespread disposal of harmful organic mole-
2
ocatalysts, especially using TiO has become much appealing be-
cules including dyes from textile, pharmaceuticals, leather tanning
and various other industries. Among those, azo dyes are the major
class of commercial dyes which are extensively used in textile
industries because of their versatility and cost-effectiveness but
these azo dyes pose a great threat to the environment [1–6]. How-
ever, an effective removal of these azo dyes from effluents is a
cumbersome job as they are highly stable to light, heat and oxidiz-
ing agents. Eriochrome Black T (EBT) is one of the important azo
dyes which is used in dyeing silk, wool, nylon, multifibres and in
cause of its inertness, non-toxicity and easy recovery by filtration
and centrifugation methods. Because of its wide band gap
(Ebg = 3.2 eV for anatase phase) and other versatile properties,
TiO
of various dyes and other organic pollutants [9–20].
In this paper, anatase phase TiO nanoparticles have been suc-
2
has been widely used for effective photocatalytic degradation
2
cessfully prepared by facile solution process and characterized by
various techniques. Furthermore, the prepared nanoparticles have
been used as photocatalyst for degradation of EBT.
2
+
laboratories as a complexometric titrant for estimation of Ca
,
2
+
2+
Mg and Zn . EBT is very hazardous dye and even its intermediate
product naphthaquinone is more carcinogenic. Therefore, it has al-
ways been a matter of serious concern around the globe for effec-
tive treatment of wastewater containing EBT and other types of
organic pollutants but, a little work has been reported in the liter-
ature on the effective decolorization of this dye [7,8]. Due to mas-
sive development in the oxidative degradation, various advanced
oxidation processes (AOPs) which include ozonolysis, sonocataly-
sis, photocatalysis, photo-Fenton, photo electro-Fenton processes
2
. Experimental details
2.1. Materials
All reagents used in our experiments were of analytical purity and were used as
received without further purification. Titanium tetraisopropoxide (TTiP) from Al-
drich, was used as precursor for preparing TiO nanoparticles. Eriochrome Black T
(C.I. 14645) was purchased from Merck, India. Titanium dioxide PC-50, Titanium
dioxide PC-500 was a gift from Millennium Inorganic Chemicals, France and ZnO
2
(
Merck, India) were used as received. Double distilled water was used for preparing
all aqueous solutions.
⇑
Corresponding authors at: Promising Centre for Sensors and Electronic Devices
PCSED), Najran University, P.O. Box 1988, Najran 11001, Kingdom of Saudi Arabia.
2
.2. Synthesis
(
Tel./fax: +91 172 2534920, +966 534574597.
The synthesis of anatase TiO
nanoparticles was done by simple solution meth-
2
E-mail addresses: sushilkk1@yahoo.co.in, sushilkk1@pu.ac.in (S.K. Kansal),
ahmadumar786@gmail.com (A. Umar).
od. In a typical reaction process, first Titanium tetraisopropoxide (TTiP) solution
was prepared in ethanol by mixing 20 mL TTiP in 60 mL ethanol. Then, an ethanolic
0
925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2013.07.069

S.K. Kansal et al. / Journal of Alloys and Compounds 581 (2013) 392–397
393
aqueous solution (obtained by mixing 20 mL deionised water with 40 mL ethanol)
was added dropwise to it which leading to formation of a white product. The colloi-
dal product was then allowed to stand for 24 h. The obtained material was dried
using Systronics-2202 spectrometer and the rate of degradation was observed in
terms of change in intensity at kmax of the dye. The degradation efficiency (%) has
been calculated as:
overnight at 80 °C and then ground in a mortar pestle to obtain fine TiO
Finally, the synthesized powder was calcined at 450 °C for 2 h to obtain desired
TiO nanoparticles which were characterized in detail in terms of their morpholog-
ical, structural, optical, thermal and photocatalytic properties.
2
powder.
Degradation efficiency ð%Þ ¼ ðC
0
ꢀ CÞ=C ꢁ 100
0
2
where C0 is the initial concentration of dye and C is the concentration of dye after
photo-irradiation
2.3. Characterizations of well-crystalline anatase TiO
2
nanoparticles
3
. Results and discussion
The prepared well-crystalline anatase TiO nanoparticles were characterized in
2
terms of their morphological, structural, optical, thermal and photocatalytic proper-
ties. The general and detailed morphological investigations of prepared nanoparti-
cles were done by field emission scanning electron microscopy (FESEM; JEOL-JSM-
3.1. FESEM, EDS, TEM and HRTEM observations
7
600F) and transmission electron microscopy (TEM) equipped with high-resolution
2
The general morphologies of prepared TiO powder was exam-
TEM (HR-TEM). To examine the crystallinity and crystal phases, the prepared nano-
particles were examined by the X-ray diffraction (XRD; PANanalytical Xpert Pro.)
pattern measured with Cu-K
The elemental and chemical compositions of synthesized nanoparticles were exam-
ined by energy dispersive spectroscopy (EDS) and Fourier transform infrared (FT-IR)
spectroscopy, respectively, in the range of 440–4000 cm . Thermogravimetric
analysis of the sample (TGA) was performed using TGA/DSC analyzer (Perkin–Elmer
STA 6000 simultaneous thermal analyzer) at a heating rate of 10 °C per minute up
to 1000 °C. Room-temperature photoluminescence (PL) spectroscopy was done to
examine the optical properties of synthesized nanoparticles. The PL measurement
was done in the range of 350–500 nm at an excitation wavelength of 290 nm.
ined by field emission scanning electron microscopy (FESEM)
which reveal that the synthesized products possess nanoparticles
shape and grown in high-density (Fig. 1(a)). Due to high-density
growth, most of the nanoparticles look agglomerated. The typical
sizes of the nanoparticles are ꢂ50 ± 10 nm (Fig. 1(a)). To examine
the elemental composition, the prepared nanoparticles were ana-
lyzed by energy dispersive spectroscopy (EDS) and shown in inset
a Radiation (k = 1.54178 Å) in the range of 10°–80°.
ꢀ
1
1
(a). The prepared nanoparticles were made by Ti and oxygen as
was confirmed by EDS measurement.
To closely examine the morphological and structural properties,
the prepared nanoparticles were examined by transmission elec-
tron microscopy (TEM) which confirms that the nanoparticles pos-
sess irregular shapes and grown in very high density and exhibit
full consistency with FESEM observations (Fig. 1(c)). The observed
high resolution TEM (HRTEM) image exhibit a very clear and well-
defined lattice fringes with the lattice spacing of ꢂ0.35 nm, which
is fully consistent with the distance of (101) crystalline plane of
2
.4. Photocatalytic experiments
2
The photocatalytic activity of prepared TiO nanoparticles was evaluated by the
UV light induced photo degradation of EBT dye in a specially designed double
walled reaction vessel [21]. For this, 0.025 g of the photocatalyst was added into
1
stirred for 30 min in dark in order to reach adsorption–desorption equilibrium be-
tween organic substrates and the photocatalyst. The aliquot was taken out with a
syringe after illumination at different time intervals and filtered through Millipore
00 mL of EBT (25 mg/L aqueous solution). Prior to illumination, the solution was
syringe filter of 0.45
l
m. The absorption spectra of the dye solutions were recorded
2
the anatase TiO (Fig. 1(d)).
2
Fig. 1. (a) and (b) FESEM images (c) TEM image and (d) HRTEM image of prepared TiO nanoparticles. Inset (a) typical EDS spectrum.

3
94
S.K. Kansal et al. / Journal of Alloys and Compounds 581 (2013) 392–397
3
.2. XRD observations
(211), (204), (116), (220) and (107) lattice planes and ascribed
to TiO crystals with the tetragonal anatase phase (JCPDS No. 21-
1272). Interestingly, it was observed that no peak related with
other crystalline forms of TiO i.e. rutile and brookite, were not de-
tected in the prepare sample which reveals the prepared nanopar-
ticles are possessing purely anatase phase. Moreover, no diffraction
reflection related with any impurities was observed, suggesting the
2
2
The crystallinity and crystal phases of prepared TiO nanoparti-
cles was examined by X-ray diffraction (XRD) and shown in Fig. 2.
Several well defined diffraction reflections are appeared in the ob-
tained pattern at 2h = 25.4°, 38.1°, 48°, 54.1°, 55.2°, 62.7°, 68.9°,
2
7
0.5° and 75.2° which are assigned as (101), (004), (200), (105),
2
high purity for the prepared TiO nanoparticles.
3.3. FTIR and PL spectrum
The chemical composition of prepared TiO
2
nanoparticles was
examined by Fourier transform infrared spectroscopy (FTIR) and
shown in Fig. 3(a). Various well-defined peaks were observed in
ꢀ1
the obtained FTIR spectrum. The peak at 3366 cm is attributed
to the characteristic absorption of surface OH bonds. The peak at
ꢀ
1
1
629 cm
bonds of the physisorbed water. The peaks at 722 and 488 cm
arise due to Ti–O stretching in TiO [22,24].
is assigned to the deformation vibration of H–O–H
ꢀ1
2
In order to investigate the structure and properties of the active
sites on the surface of metal oxides, PL technique has been widely
used. Though, the photo-induced electrons and holes mainly
recombine non-radiatively, the emission spectrum provides useful
2
Fig. 2. XRD pattern of prepared TiO nanoparticles.
2
Fig. 4. TGA/DSC of prepared TiO nanoparticles.
Fig. 3. (a) FTIR spectrum and (b) room-temperature PL spectrum of prepared TiO
2
Fig. 5. Typical UV–Vis. spectrum of the targeted EBT dye. Inset shows the chemical
nanoparticles.
structure of EBT dye.

S.K. Kansal et al. / Journal of Alloys and Compounds 581 (2013) 392–397
395
phenomena and voltage treatments [24,27]. In our work, the opti-
cal properties of prepared TiO nanoparticles was examined by
2
room-temperature photoluminescence (PL), measured in the range
of 350–550 nm at an excitation wavelength of 290 nm (Fig. 3(b)). A
well-defined peak was observed in the spectrum at 378 nm which
is significant and characteristic emission peak for inter-band
2
recombination for TiO . The peak at 500 nm can be attributed to
the indirect recombination via oxygen vacancies.
3.4. TGA and DSC curve
2
Further, in order to study the thermal behavior of TiO nanopar-
ticles, TGA and DSC analysis was also performed and shown in
Fig. 4. The weight loss up to 1000 °C of as prepared sample is about
6
.6%. The observed weight loss up to 100 °C is attributed to the loss
of adsorbed water on the surface of the powder, also confirmed by
endothermic desorption in DSC curve. The second range of weight
loss from 200–400 °C is attributed to the decomposition of volatil-
ization of organic solvents. Exothermic peaks localized at mainly
3
50 °C in the DSC curve reflect the processes of oxidation of the or-
ganic residuals. Similar kinds of thermal behavior of TiO nanopar-
2
ticles have been reported in literature. The studies conducted by
Wang et al. and Yodyingyon et al. showed that three weight loss
regions were observed in the TGA curve of the as-prepared TiO
Many authors have reported third weight loss region from 650–
00 °C corresponding to the polymorphic anatase–rutile transfor-
mation [28–30].
2
.
8
3.5. Evaluation of photocatalytic activity
Fig. 5 exhibits the typical UV–visible spectrum and inset of
Fig. 5 shows the chemical structure of the targeted EBT dye. Two
distinct bands, i.e. at 344 nm and 574.4 nm were observed in the
obtained UV–visible spectrum. To evaluate the photocatalytic
Fig. 6. (a) UV–Vis absorbance spectra of degradation of EBT dye under UV light over
prepared TiO nanoparticles, (b) % degradation of EBT with respect to irradiation
time in presence (black line) and absence (red line) of TiO photocatalyst. (For
interpretation of the references to colour in this figure legend, the reader is referred
to the web version of this article.)
2
2
2
activity of TiO nanoparticles, the photocatalytic degradation of
EBT dye was performed under UV irradiation. The photocatalytic
degradation was evaluated by measuring the absorbance at regular
time intervals. Interestingly, it was observed that the relative
absorption intensity continuously decreased as the UV illumina-
tion exposure time increased, significantly indicating that EBT
dye degraded effectively on the surface of TiO2 photocatalyst
(Fig. 6(a)). This is because, under illumination, highly oxidizing hy-
droxyl and oxy radicals are formed by the semiconducting metal
information. In literature, many workers have reported that the UV
emission around 360 nm corresponds to the inter-band (CB ? VB)
radiation recombination, which emits light with energy equal to or
slightly greater than the band gap [23–26]. Liu et al. have obtained
2
the inter-band recombination peak at 366 nm for TiO nanoparti-
cles and the peak at 550 nm was ascribed to indirect recombina-
tion via the oxygen vacancies and other peaks to the surface
electronic structure and indirect recombination arising from bulk
defects [23]. There can be some shift in these recombination peaks
depending upon synthesis methods, grain size, some surface
oxides like TiO , ZnO etc. via generation of electron–hole pairs
[31], which break the large organic materials into less harmful
small organic materials. The obtained degradation was 82% within
90 min. However, no significant degradation was observed in the
absence of the photocatalyst (Fig. 6(b)).
2
Fig. 7. Schematic illustration of photocatalysis reaction.

3
96
S.K. Kansal et al. / Journal of Alloys and Compounds 581 (2013) 392–397
0
Fig. 8. A Plot of ln C /C vs time.
3.6. Study of reaction mechanism and kinetics
When light with energy equal to or higher than band gap, reach
the surface of the photocatalyst, it causes molecular excitation. As
a result, electron and holes are generated in conduction and va-
lence band, respectively. After the generation of photogenerated
electron–hole pairs, the photocatalytic reactions will proceed
through a series of chemical events, eventually leading to forma-
tion of HOꢃ, which is the most plentiful radical species in TiO
2
aqueous suspension. The reaction of HOꢃ with organic pollutants
is the most important step that leads to the mineralization of or-
2
ganic pollutants. The schematic representation of the TiO photo-
catalytic mechanism is shown in Fig. 7. The reactions which take
place on the surface of photocatalyst can be shown through follow-
ing reaction sequence:
Fig. 9. (a) Extent of degradation of EBT dye using different photocatalysts and (b)
comparison of degradation efficiency for different photocatalysts.
TiO
2
! hþ þ eꢀ
3.7. Comparison with commercially available photocatalysts
OH þ hþ ! HOÅ
ꢀ
In order to compare the photocatalytic efficiency of prepared
TiO
such as, TiO
experiments have been done at a fixed EBT dye concentration
25 mg/L), and catalyst loading of 0.25 g/L for 90 min. Fig. 9(a) de-
picts the extent of degradation for EBT using different photocata-
lysts. The percentage degradation efficiency was also compared
(Fig. 9(b)) and it was found to be maximum for the synthesized
2
nanoparticles with commercially available photocatalysts
O
O
2
þ eꢀ ! O Å2 ꢀ
þ Hþ ! HOÅ
2
(PC-50), TiO (PC-500) and ZnO (Merck), several
2
(
Åꢀ
2
2
HO þ e ! HOꢀ
Å
ꢀ
2
2
TiO
sized TiO
2
nanoparticles. The better photocatalytic behavior of synthe-
can be attributed to their unique morphology, small par-
HO þ Hþ ! H
ꢀ
O
2
2
2
2
ticle size, high anatase content and excellent crystallinity.
H
2
O
2
þ eꢀ ! OHꢀ þ HOÅ
4. Conclusion
Å
2
In summary, anatase TiO nanoparticles were synthesized and
EBT þ HO ! CO
2
2
þ H O
characterized and utilized as an efficient photocatalyst for the
photo-catalytic degradation of EBT dye. The detailed characteriza-
tions revealed that the prepared nanoparticles were well-crystal-
line and possessing good optical properties. About 82% of photo-
degradation of EBT dye was achieved in 90 min under UV light irra-
In order to study the reaction kinetics of photocatalytic degra-
dation of EBT dye, the first order kinetic Langmuir Hinshelwood
model was followed which can be written as:
ln ðC
0
=CÞ ¼ kt
diation using TiO nanoparticles as photocatalyst. The high photo-
catalytic degradation of EBT dye was due to the small particle size,
2
where C
0
is the initial concentration and C is the concentration at
anatase contents and good crystallinity of the prepared nanoparti-
any time t. Fig. 8 exhibits the plot for ln (C /C) vs time which shows
0
2
cles. Importantly, it was observed that the TiO nanoparticles
the linear line with the irradiation time. This confirms that the
photo-degradation of EBT dye obeys pseudo-first order reaction
kinetics. The correlation constant for the fitted line was calculated
shows better photocatalytic degradation performance for EBT dye
as compared to other photocatalysts such as PC-50, PC-500 and
commercial ZnO which reveals that simply prepared TiO nanom-
2
aterials are effective photocatalysts for the photocatalytic degrada-
tion of harmful organic dyes like the EBT.
2
to be R = 0.969. From the first order reaction kinetics equation
ꢀ1
and slope of the graph, k was determined to be 0.017 min
.

S.K. Kansal et al. / Journal of Alloys and Compounds 581 (2013) 392–397
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c) S.K. Kansal, A.H. Ali, S. Kapoor, D.W. Bahnemann, Sci. Adv. Mater. 5 (2013)
The authors greatly acknowledge the financial support obtained
under the AICTE (RPS), Government of India through a project
grant 8023/RID/RPS-16/(POLICY-IV)(GOVT)/2011-12. A. Umar
would like to acknowledge the support of the Ministry of Higher
Education, Kingdom of Saudi Arabia through a grant (PCSED-001-
630–636.
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