Effect of different shapes of TiO2 nanoparticles on the catalytic photodegradation of salicylic acid under UV light

Article abstract of DOI:10.1166/jnn.2017.13851

Titania of different nanostructures was synthesized by microwave synthesis and the conventional method. The synthesized nanostructures of titanium dioxide were characterized by different optical and morphological techniques. The microwave assisted TiO₂ nanoparticles [TiO₂ (MW)] depicted higher photocatalytic activity along with degradation properties. Photocatalytic degradation is one of the major applications of TiO₂. Higher surface area of TiO₂ (MW) and TiO₂ (TP) was observed as 123 m²/g and 46 m²/g respectively while the specific surface area of TiO₂ P25 is 50 m²/g. TiO₂ (MW) shows crystallite size of 8.2 nm which holds good as compared with the size reported. The degradation profile of salicylic acid had shown that TiO₂ (MW) proved to be a promising catalyst as compared to conventionally synthesized and commercially available counterparts.

Full text of DOI:10.1166/jnn.2017.13851

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Nanoscience and Nanotechnology
Vol. 17, 5303–5309, 2017
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Effect of Different Shapes of TiO2
Nanoparticles on the Catalytic Photodegradation
of Salicylic Acid Under UV Light
Manpreet Kaur Aulakh, Nishi Arora, Ashish Kumar, Amjad Ali, and Bonamali Pal∗
School of Chemistry and Biochemistry, Thapar University, Patiala 147004, India
Titania of different nanostructures was synthesized by microwave synthesis and the conventional
method. The synthesized nanostructures of titanium dioxide were characterized by different optical
and morphological techniques. The microwave assisted TiO2 nanoparticles [TiO2 (MW)] depicted
higher photocatalytic activity along with degradation properties. Photocatalytic degradation is one
of the major applications of TiO2. Higher surface area of TiO2 (MW) and TiO2 (TP) was observed
as 123 m2/g and 46 m2/g respectively while the specific surface area of TiO2 P25 is 50 m2/g. TiO2
(MW) shows crystallite size of 8.2 nm which holds good as compared with the size reported. The
degradation profile of salicylic acid had shown that TiO2 (MW) proved to be a promising catalyst as
compared to conventionally synthesized and commercially available counterparts.
Keywords: Salicylic Acid, Photocatalytic Degradation, Microwave Synthesis, TiO2 Photocatalytic
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1. INTRODUCTION
and shape of the photocatalyst are tailored accordingly.
Photocatalytic property of TiO2 is highly influenced by its
crystal structure14 and mostly used forms are anatase and
rutile.15 As reported in the literature, many researchers had
proved that rutile is a least active form of TiO2ꢁ16
Photocatalysis is the type of catalytic reaction wherein
the reaction is initiated in the presence of photons of
light. Semiconductors have been vastly employed as cata-
lysts in heterogeneous photocatalysis and the semiconduc-
tor photocatalysis process occurs when a photon equal to
or greater than band gap energy is absorbed. These charge
carriers are responsible for photo-oxidation and photo-
reduction of organic moieties. There are many examples
of semiconductors as metal oxide, metal sulfides which are
used as photocatalysts such as ZnO,1ꢀ2 ZnS,3–5 TiO2ꢀ6–10
WO131ꢀ12 etc. Semiconductor photochemistry had greatly
enhanced the development of photocatalysis during 1970
and 1980.13
TiO2 being available in abundance has low toxicity,
low cost, good chemical, mechanical stability and high
photocatalytic activity so is used as an efficient photo-
catalyst. The importance of using this photocatalyst was
unfolded in the late 1960s. Many applications of TiO2 have
been reported in recent years. Its applications ranging in
ointments, pigments, oils, paints, sunscreens, mineralizing
organic acids, organic pollutants, dyes, herbicides, etc. The
efficiency of the TiO2 photocatalyst increases as the size
Many methods are listed in literature for the synthesis of
TiO2 nanoparticles; these include ultrasonic irradiation,17
hydrothermal,18–20
photoreductive
decomposition,21
precipitation,22 microwave synthesis etc. Out of numerous
techniques, microwave synthesis has great significance to
synthesize nano-powders. It is a green and eco-friendly
method and requires less amount of energy for carry-
ing out any reaction as compared to other methods.23
Microwave synthesis provides uniform heating for sol-
vents and reagents in the reaction mixture which results
into uniform production of nanoparticles.24ꢀ25 As com-
pared to hydrothermal synthesis, time is reduced by 2–3
orders in microwave synthesis. Moreover, it plays a crucial
role to control the size of nanoparticles.26 Hydrothermal
microwave synthesis is a recent technique to prepare
nanoparticles with low-temperature range and high rate of
reaction.27–29
Titanium dioxide has been employed in various pho-
tocatalytic activities, photodegradation being one of the
major applications. By enhancing the light intensity,
∗Author to whom correspondence should be addressed.
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doi:10.1166/jnn.2017.13851
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Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light Aulakh et al.
photocatalytic degradation rate also gets mounted30 while
reaction pathway is independent of nature of used light.31
Various wastewater textile dyes have been effectively
degraded using TiO2 and its metal loaded components.
Munusamy et al.,32 studied the effect of dopants and com-
pared its functionality with pure TiO2. It has been used
in mineralization of organic acids such as malic and mal-
onic acids. Aquatic as well as atmospheric pollutants can
be efficiently degraded by heterogeneous photocatalysis.33
Photocatalytic oxidation of CN− and SO32− with the help
of TiO2 was done under sunlight which proved to be a
great application of TiO2 initially34 and further followed by
the CO2 reduction.35 Further research explains the shape
and size effect of the various nanoparticles of TiO2 along
with the effect of catalyst loading and dopant effect on var-
ious photodegradation processes as well as esterification
and transesterification reactions. Different morphological
and characterization properties of TiO2 were explained and
further used the synthesized catalysts in the degradation of
formic acid.36
and transparent solution (A) was obtained. Simultaneously
another solution (B) constituting of 3.78 g of titanium
tetrachloride and 6 g dilute HCl (0.5 M) was kept under
stirring for 30 min to obtain a pale yellow colored solu-
tion. Finally, solution B was mixed with solution A and
resulted solution was stirred for 30 min. The pH of the
solution was maintained at 7 by adding dilute ammonium
hydroxide to the solution. The resulted solution was fur-
ther stirred for 1.5 h to obtain colorless precipitates which
were thoroughly washed with distilled water and kept in
microwave synthesizer for 30 min. Then the soꢀlid sample
was isolated by centrifugation, calcined at 300 C for 8 h
and cooled to obtain white colored TiO2 sample.
2.2.2. Synthesis of Template-Synthesized TiO2
Nanoparticles (TiO2 (TP))
The preparation method followed for synthesis of titanium
dioxide nanoparticles was as given by Damato et al.24
1 mL of titanium butoxide was added to 22.5 mL of ethy-
lene glycol and prepared mixture was kept under vigorous
stirring for 8 h at room temperature. The solution prepared
was quickly poured into another solution of 100 mL of
acetone, 1.25 mL of deionized water and 0.4 mL of acetic
acid. The mixture obtained was then kept under vigorous
stirring for 3 h at room temperature and then centrifuged at
10,000 rpm to obtain a white solid, which was successively
washed several times with ethanol and water. Nanoparti-
In this present work, titanium dioxide nanoparticles of
different morphologies are synthesized and characterized
by using various techniques such as X-ray diffraction
(XRD), UV-Vis spectrophotometer, FT-IR spectrophotome-
ter, transmission electron microscopy (TEM), gas chro-
matography, etc. As the photocatalytic activity of metal
loaded TiO2 is widely reported in the literature but bare
TiO with different morphologies is not used vastly in the
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2
Copyright: American Scientific Publishers
cles of titanium glycolate were stirred with 50 mL of water
area of degradation of organic compounds. Currently, pho-
ꢀ
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for 8 hours at 70 C to obtain a suspension. The precipi-
tatesꢀwere separated by centrifugation, dried and heated at
250 C for 2 h to obtain white colored TiO2 particles.
tocatalytic degradation activity of salicylic acid is studied.
2. EXPERIMENTAL DETAILS
2.1. Materials and Methods
2.3. Characterization Techniques
Titanium dioxide (TiO2 P25) was a gift sample from
Evonik Degussa, Germany. Titanium tetrachloride (TiCl4,
99.5%), Polyethylene glycol (PEG), Hydrochloric acid
(HCl) and Ammonium hydroxide (NH4OH) were bought
from Loba Chemie, India. Salicylic acid (C6H4 (OH) ·
COOH), acetic acid (CH3COOH) and Titanium butox-
ide [Ti(OBu)4] and ethylene glycol (C2H6O2, 99%) were
obtained from Spectrochem Pvt Ltd., India. Similarly, ace-
tone (CH3COCH3ꢂ, methanol (CH3OH, 99%) and Oleic
acid (C18H34O2ꢂ were purchased from SD Fine Chemical
Limited, India. All the synthesis was carried with deion-
ized water obtained from ultrafiltration system (Milli-Q,
Millipore) with a measured conductivity (35 mho cm−1
at 25 ꢀC).
The optical properties of prepared nanoparticles were ana-
lyzed by UV-Vis absorption spectrophotometer (Analytik
Jena Specord-205, scan range 190–800 nm) and Fourier
transform infrared technique (Agilent, Cary 600) and the
morphological characteristics were carried out by SEM-
EDX (JSM 7600F) and TEM (Hitachi 7500) analysis. Fur-
ther, the crystal structure determination was done by X-ray
diffraction. The specific surface area of the catalyst was
analyzed by BET surface area analyzer.
2.4. Photocatalytic Degradation of Salicylic Acid
The comparative study of the photocatalytic activity of
TiO2 nanoparticles was done as a function of their shape.
The photocatalytic activity of TiO2 (MW), TiO2 (TP) and
TiO2 (P25) for photodegradation of salicylic acid was
studied. A stock solution of 50 mL (0.2 mM) salicylic
acid (C7H6O3ꢂ was prepared for the photocatalytic activity
study. The photodegradation reaction was carried out in a
test tube containing 5 mL of stock solution and 20 mg
of catalyst. It is shown in Scheme 1. The photo mineral-
ization reaction was carried out by continuous magnetic
2.2. Synthesis of TiO2 Nanoparticles
2.2.1. Synthesis of Microwave-Assisted Sample of TiO2
(TiO2 (MW))
The microwave assisted titania nanoparticles were pre-
pared by following the literature reported method.23 2 g of
polyethylene glycol was added to 48 g of HCl (0.5 M) and
the solution was kept under vigorous stirring for 30 min
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Aulakh et al. Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light
Scheme 1. Schematic representation of photochemical reaction set up and photodegradation of salicylic acid.
stirring under UV light for different time intervals. Fur-
ther analysis of the reaction samples was done by UV-Vis
spectrophotometer and FT-IR spectroscopy.
spectrophotometer. As depicted from Figure 2, a broad
peak was observed in the 3000 to 3500 cm−1 region which
is a characteristic peak for the associated hydroxyl group
(–OH band) in all the three samples. Another sharp peak is
observed at around 1500 to 1600 cm−1 which correspond
to the Ti–O–Ti bond stretching and confirms the Titanium
dioxide nanoparticles.
3. RESULTS AND DISCUSSION
3.1. Optical Properties of TiO2 Nanoparticles of
Different Shapes
3.1.1. UV-Vis Analysis
The optical absorbance of the photocatalyst was analyzed
by UV-Vis spectrophotometer (290–1100 nm). The UV-
3.2. Surface Area Analysis
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The BET surface area (SBETꢂ analysis from Figure 3
Copyright: American Scientific Publishers
reveals a higher surface area for TiO2 (MW) (123 m2/g)
and surface area for TiO2 (TP) was observed as 46 m2/g
while specific surface area for TiO2 P25 is 50 m2/g.
Higher surface area results into higher photoactivity of
TiO2 (MW).
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visible shows a ꢃmax at 310 nm for TiO2 (MW) and at
342 nm for TiO2 (TP). The broader peak at absorption
maxima is due to the discrete energy levels in the elec-
tronic structure of the TiO2 nanoparticles. The band gap
for TiO2 (TP) and TiO2 (MW) was observed at 3.9 eV
and 3.6 eV, respectively while TiO2 (P25) shows band gap
of 3.2 eV. The absorbance of different nanoparticles is as
shown in Figure 1.
3.3. Morphological Characterizations
3.3.1. XRD Analysis
The XRD patterns for the different Titania nanoparticles
are described in Figure 4. TiO2 (TP) shows 2ꢄ ∼ 25ꢁ4ꢀ
peak which confirms anatase phase and it is further con-
firmed by comparing the anatase and rutile peaks with the
3.1.2. FT-IR Analysis
The IR spectra were collected with a resolution of
4 cm−1 and 32 scans by a Fourier transform infrared
P25
Ti-O-Ti
λ = 342.6 nm
-OH
TiO2(MW)
TiO2(MW)
λ = 310.5 nm
Ti-O-Ti
TiO2(TP)
-OH
λ = 387.5
TiO2(TP)
Ti-O-Ti
-OH
P25
4000
3500
3000
2500
2000
1500
1000
500
250
300
350
400
450
500
550
600
Wavelength (nm)
Wavenumber (cm–1
)
Figure 1. Absorbance spectra for various titania nanoparticles.
J. Nanosci. Nanotechnol. 17, 5303–5309, 2017
Figure 2. FT-IR spectra for various titania nanoparticles.
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Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light Aulakh et al.
confirms that TiO2 (P25) consists of a mixture of non-
spherical nanoparticles. Figure 6(a) clearly depicts the
TEM image of TiO2 (P25) which elucidates the size to be
50 nm for P25 nanoparticles. In Figure 6(b) TEM image
of nanorods is shown.
3.4. Photodegradation of Salicylic Acid
The UV-Vis spectrophotometry was used to analyze the
amount of unreacted sample (salicylic acid) left in the
reaction mixture. The Figure 7 gives the baseline corrected
UV graphs at different time intervals for the degradation
of salicylic acid. Degradation leads to decrease in concen-
tration of the acid solution.
To monitor the independent light leeching effect on sal-
icylic acid 5 ml of salicylic acid (0.02 mM) was irradiated
with UV radiation without any catalyst. The sample was
then studied for any change in the concentration by the
UV-Vis spectrophotometer at different time intervals (20,
40, 60 mins). No concentration change was observed in
the course of time.
Figure 3. Specific surface area of different TiO2 photo catalysts.
TiO2 (P25) and both TiO2 (MW) and TiO2 (TP) show
anatase peaks while the rutile peaks are absent. The crys-
tallite size as calculated by applying the Debye–Scherrer
equation is 10.1 nm for the TiO2 (TP) which is good agree-
ment with the data from literature.37 While TiO2 (MW)
shows crystallite size of 8.2 nm which holds good as com-
pared with the size reported.38
3.3.2. Energy Dispersive X-ray Spectrophotometer
(EDX)
Dark adsorption studies have been carried out to study
the adsorption–desorption equilibria on the surface of the
catalyst. In general, the heterogeneous catalysis follows
Freundlich and Langmuir adsorption isotherms.
The chemical composition of the selected area of the sam-
ple was determined by EDX. The EDX spectra of TiO2
(TP) and TiO2 (MW) confirm the presence of oxygen, car-
bon and titania elements. The EDX spectra of TiO2 (TP)
and TiO2 (MW) are shown in Figures 5(a and b) respec-
tively. The EDX analysis confirms the titanium to oxygen
atomic content to be almost half as suggested by its for-
mula unit.
3.4.1. Size and Shape Effect on Photodegradation
Figure 8 reveals the photodegradation of salicylic acid
(0.02 mM) under the influence of various shapes of TiO2
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Copyright: American Scientific Publishers
catalyst under UV irradiation for 2 hrs. The salicylic
acid shows ꢅ → ꢅ∗ a transition on irradiation of UV
light and the characteristic band appears at 295 nm due
to an aromatic ring. Fastest degradation occurs in the
case of TiO2 (MW) followed by TiO2 (TP) and then
P25 due to the elongated surface and more number of
active sites available for the adsorption process in the TiO2
(MW). The photoactivity of the various catalyst and their
concentration-time graph shows almost equal degradation
for the first 20 min i.e., 0.6 ꢆmols for TiO2 (MW) and
TiO2 (P25) and 0.8 ꢆmols for TiO2 (TP) but exponential
decrease is observed for TiO2 (MW) in the next 20 min
interval to 0.09 ꢆmols while it also showed substantial
decrease in concentration for TiO2 (TP) at 0.04 ꢆmols
while P25 showed concentration of 0.06 ꢆmols.
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3.3.3. Transmission Electron Microscopy (TEM)
The morphology of titania nanoparticles was also con-
firmed by transmission electron microscopy (TEM). It
20
30
40
50
60
70
80
Mw-TiO2
Tw-TiO2
3.5. Gas Chromatography (GC) Analysis
The amount of CO2 produced in the reaction process is
quantified by Gas chromatography. As can be seen from
the Figure 9, illustrates the CO2 evolution of different pho-
tocatalyst under prolong UV irradiation. It was observed
that complete photodegradation of salicylic acid occurs in
2 h with TiO2 (MW) showing maximum CO2 evolution
(1.5 ꢆmols) followed by TiO2 (TP) (0.6 ꢆmols) and then
TiO2 (P25) (0.5 ꢆmols). The band for salicylic acid disap-
pears in 80 minutes confirming the appearance of interme-
diates as shown in Figure 9 and the complete degradation
P25
20
30
40
50
60
70
80
2 Theta (degrees)
Figure 4. XRD patterns for various titania nanoparticles.
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Aulakh et al. Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light
(a)
(b)
Figure 5. (a) EDX spectrum of TiO2 (TP). (b) EDX spectrum of TiO2 (MW).
(b)
(a)
Figure 6. (a) TEM image for P25. (b) TEM image for TiO2 (MW).
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Figure 7. UV-Vis absorption spectra for dark adsorption of various TiO2 nanoparticles and their comparative analysis.
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Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light Aulakh et al.
Figure 8. UV-Vis spectra for photodegradation for various titania nanoparticles and their comparative analysis.
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Figure 9. GC graphs of time course evolution of CO2.
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Aulakh et al. Effect of Different Shapes of TiO2 Nanoparticles on the Catalytic Photodegradation of Salicylic Acid Under UV Light
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The microwave and conventional method used for the syn-
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Received: 9 March 2016. Accepted: 18 August 2016.
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