Calcination temperature effect on titanium oxide (TiO2) nanoparticles synthesis

Abstract

Present study investigates the calcination temperature influence by sol-gel based synthesis of
titanium dioxide (TiO2) nanoparticles using by titanium-tetraisoprooxide (TTIP), isopropanol as
primary source. For this purpose, calcinations of nanopowder was done at various temperature
range i.e. 300 ◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C. Several characterization techniques
such as X-ray diffraction (XRD), UV–Vis reflectance spectroscopy (DRS), Field Emission scanning
electron microscope (Fe-SEM), Energy dispersive spectroscopy (EDS), and Fourier transform
infra-red spectroscopy (FTIR) were used to examine the temperature effects on crystalline size,
crystalline phase, band gap and morphology of synthesized TiO2 nanoparticles. The XRD pattern
shows that TiO2 crystalline size was increased with increase in calcination temperature and
indicated that the size 7.68 nm at 400 ◦C with precursor TTIP and size enhances up to 37.54 at
temperature of 800 ◦C. Degree of crystallinity increases with increase in temperature and phase
formation occurred at 600 ◦C and showed transition from anatase rutile from anatase phase and
completely transform rutile phase at 800 ◦C. Fe-SEM micrographs pattern shows that sphere like
morphology of TiO2 nanoparticles and nanoparticles size increased with increase in calcination
temperature. The effective absorption line lies in the scale of 750 cm􀀀 1–550 cm􀀀 1detected by
FTIR which is associated with the characteristic vibration modes of TiO2. The band gap of TiO2
decreases with increase calcination temperature from 300 ◦C to 800 ◦C and at 400 ◦C band gap
(Eg) was 3.37 eV while 3.09 eV at 800 ◦C temperature. At temperature more than 700 ◦C the TiO2
spectra shifted in the visible region. The overall results demonstrated significantly improvement
in properties of TiO2 at lower temperature.

Full text

Optik - International Journal for Light and Electron Optics 241 (2021) 166934
Available online 27 April 2021
0030-4026/© 2021 Elsevier GmbH. All rights reserved.
Original research article
Calcination temperature effect on titanium oxide (TiO
2
)
nanoparticles synthesis
Manmohan Lal
a
, Praveen Sharma
a
,
*
, Chhotu Ram
b
a
Department of Environmental Science & Engineering, Guru Jambheshwar University of Science & Technology, Hisar, Haryana, India
b
Department of Chemical Engineering, College of Engineering and Technology, Adigrat University, Adigrat 7040, Ethiopia
ARTICLE INFO
Keywords:
TiO
2
nanoparticles
Sol-gel method
Characterization
Temperature
Particle size
ABSTRACT
Present study investigates the calcination temperature inuence by sol-gel based synthesis of
titanium dioxide (TiO
2
) nanoparticles using by titanium-tetraisoprooxide (TTIP), isopropanol as
primary source. For this purpose, calcinations of nanopowder was done at various temperature
range i.e. 300 ◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C. Several characterization techniques
such as X-ray diffraction (XRD), UV–Vis reectance spectroscopy (DRS), Field Emission scanning
electron microscope (Fe-SEM), Energy dispersive spectroscopy (EDS), and Fourier transform
infra-red spectroscopy (FTIR) were used to examine the temperature effects on crystalline size,
crystalline phase, band gap and morphology of synthesized TiO
2
nanoparticles. The XRD pattern
shows that TiO
2
crystalline size was increased with increase in calcination temperature and
indicated that the size 7.68 nm at 400 ◦C with precursor TTIP and size enhances up to 37.54 at
temperature of 800 ◦C. Degree of crystallinity increases with increase in temperature and phase
formation occurred at 600 ◦C and showed transition from anatase rutile from anatase phase and
completely transform rutile phase at 800 ◦C. Fe-SEM micrographs pattern shows that sphere like
morphology of TiO
2
nanoparticles and nanoparticles size increased with increase in calcination
temperature. The effective absorption line lies in the scale of 750 cm
−1
–550 cm
−1
detected by
FTIR which is associated with the characteristic vibration modes of TiO
2
. The band gap of TiO
2
decreases with increase calcination temperature from 300 ◦C to 800 ◦C and at 400 ◦C band gap
(E
g
) was 3.37 eV while 3.09 eV at 800 ◦C temperature. At temperature more than 700 ◦C the TiO
2
spectra shifted in the visible region. The overall results demonstrated signicantly improvement
in properties of TiO
2
at lower temperature.
1. Introduction
Water pollution has become a major problem in the developing societies and countries. Additionally, more pressure is increasing on
natural resources by increasing population, industrializations, and urbanizations [1]. Therefore, the generation of wastewater from
industries is increasing day by day activities due to modernization and utilizations of industrial based products. Thus, for effective
treatment and disposal of industrial wastewater, nanomaterial crystalline semiconductor can play a signicant role in the wastewater
treatment. Titanium dioxide (TiO
2
) nanomaterials a very good photocatalyst with high band gap and playing an important role in the
environmental purication, water purication, air purication, sensors, solar cell applications etc. [2]. Three different phase of
* Corresponding author.
E-mail addresses: manmohankamboj@gmail.com (M. Lal), ps.enbt@gmail.com (P. Sharma).
Contents lists available at ScienceDirect
Optik
journal homepage: www.elsevier.com/locate/ijleo
https://doi.org/10.1016/j.ijleo.2021.166934
Received 6 January 2021; Received in revised form 25 March 2021; Accepted 25 March 2021

Optik 241 (2021) 166934
2
crystalline TiO
2
are i.e. anatase, rutile and brookite where anatase phase is most stable form with a bandgap of 3.23 eV, rutile with 3.0
eV band gap and brookite 3.2 eV band gap [3]. For photocatalytic process remediation’s of pollutants, antase phase is widely rec-
ommended due to its high photocatalytic activity [4]. TiO
2
is a very good photocatalyst for degrading organic pollutants due to its high
photocatalytic property, little toxicity, low cost, thermal stability and good chemical property [5–8]. Photocatalysis technique is a
promising technique to decompose organic waste and wastewater utilizing solar energy another advantage with no secondary waste
generation [1,8]. Solar spectrum having the 3–5% ultraviolet (UV) radiations of the solar spectrum reaches the Earth, which greatly
lessen electron-e
-
/hole-h
+
pair generation and reduces the efciency of TiO
2
in the solar (visible) region [9,10].
Previous works cite the TiO
2
photocatalytic activity dependence upon the crystalline size and surface area of TiO
2
nanoparticles,
with further reduction in the crystalline size of TiO
2
nanoparticles increase in active surface area and high band gap [11–13]. Pho-
tocatalytic process a basically process in which a photon of light bombarded (from articial source or natural source of energy i.e. solar
energy) on its surface, photocatalyst TiO
2
semiconductor mixed with organic pollutant e
-
/h
+
pair generates after light absorption with
greater or equal bandgap energy of TiO
2
photocatalyst [14–16].
There are number of methods used to synthesize the TiO
2
nanoparticles i.e. sol-gel method [11,17–18], hydrothermal method
[11–12,19], solvothermal method [4,20], micelle and inverse micelle methods [4,21–22], liquid phase deposition [4,23], chemical
vapor deposition, direct oxidation method [4,24], reactive sputtering [4,25], electro deposition, physical vapor deposition, [4] mi-
crowave method, sonochemical method [11,26], in the laboratories. Sol-gel method synthesized TiO
2
nanoparticles widely adopted by
researcher due to its easy handling, environment friendly and cost effectiveness [27]. Various precursors and different type of solvent
has been used for the sol-gel synthesis of TiO
2
nanoparticles. The effects of calcination temperature, solvent amount, annealing
temperature, DI water, reux duration, temperature, organic pollutant concentrations, pH of solution (solution =catalyst amount +
organic pollutant conc.), and optimized condition like time, dose of photocatalyst, crystalline phase and size of particle, of nano-
particles play very important role in photocatalytic activity process. This variability affects the performance of the nanoparticles for
the deterioration of organic pollutants [11,28]. In this study, TiO
2
nanoparticles were prepared by sol-gel method at room temperature
from single precursor at different volume concentration at various temperatures. The effects of precursor volume and calcinations
temperature were investigated on crystalline size, crystalline phase, band gap and morphology of synthesized TiO
2
nanoparticles.
2. Material & method
The various chemicals such as ethanol (EtOH), titanium tetraisopropoxide (M=284.26, TTIP), isopropanol (IsoprOH) were pur-
chased from the sigma-aldrich. Analytical grade chemical has been used in this work and there is no need to purify them for use in
work.
2.1. Synthesis of TiO
2
catalyst
Sol-gel method was used for the synthesis of TiO
2
nanoparticles. Three various concentrations T4, T6, and T8 (4, 6, and 8) mL of
titanium-tetraisoprooxide (TTIP) was slowly added to 50 mL isopropanol (2-Propanol). Further, it was homogenous mixing on a
magnetic stirrer for 30-minute duration. The addition of 10 mL de-ionized water drops wise in the above solution, and precipitation
was formed under continuously stirring for 2 h for obtaining a homogeneous mixture. The obtained mixture was placed in ultra-
sonication reactor at 80 ◦C for 1 h and then mixture was aging at room temperature for 22 h, a gel is formed and several times washing
with double distilled water DDW and ethanol to remove the excess ions. White solid product was obtained by drying the gel at 70 ◦C for
2 h in an oven. The resulting product was calcined at 300–800 ◦C for 2 h and nally grinded in agate mortar. A ne white powder was
obtained at the end of the procedure and chemical reaction of TTIP with water to give TiO
2
nanoparticles [29] are given below:
Ti{OCH(CH
3
)
2
}
4
+2H
2
O→TiO
2
+4 (CH
3
)
2
CHOH (1)
2.2. Characterizations of TiO
2
catalyst
Calcinated TiO
2
nanoparticles prepared were characterized by diverse techniques such as FTIR, Fe-SEM/EDS, X-ray diffraction
(XRD), and UV-DRS diffuse reectance spectroscopy.TiO
2
nanoparticles crystalline size and phase were examined through XRD
technique by using (RIGAKU MINIFLEX II) diffractometer having tube load 450 W, copper (Cu) target with lter and cooling system
radiation (30 kV/15 mA). Surface morphological changes at different calcination temperature in TiO
2
nanoparticles were analyzed
through Field Emission Scanning Electron Microscopy (QUANTA, FEG-450). The functional group quality and occurrence was studied
of prepared sample TiO
2
nanoparticles by Fourier transform infrared spectroscope (FTIR) (Perkin Elmer Spectrum BX-II) in wave
number region between 4000 cm
−1
and 400 cm
−1
using potassium bromide (KBr) pellet methods. The UV-DRS absorbance spectra
were recorded by SHIMADZU-UV-2600.
M. Lal et al.

Optik 241 (2021) 166934
3
Fig. 2. Calcination temperatures variation (300
◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C.) inuence on TiO
2
(T4) in XRD pattern.
Fig. 1. Effect of calcinations temperature on crystalline size.
M. Lal et al.

Optik 241 (2021) 166934
4
3. Results and discussion
3.1. X-ray diffraction
Morphological, structural and chemical properties of prepared TiO
2
nanoparticles were characterized by XRD and crystalline phase
and size content of TiO
2
nanoparticles were measured. The observed peak (101) (2θ =25.17◦) of anatase and the peak (110) (2θ =
27.25◦) of rutile were used for the analysis. The Scherrer’s equation was used to determine the crystallite size (L in nm) [5].
L =kλ/βcosθ (2)
Where k is a constant and it is equivalent to 0.9.
λ- X-ray wavelength its value 0.154056 nm.
θ-half angle diffraction.
β-full width at maximum half intensity (FWHM).
Aatase phase to rutile phase content of sample calculated by this equation [Eq. (3)].
Rutile phase content% =100/1 +0.8(IA/IR) (3)
Where, IR and IA are integrated diffraction peak intensity of anatase (101) peak and rutile (110) peak, respectively.
XRD results (Figs. 2–4) show that the structural formation of TiO
2
nanoparticles was shifted anatase phase to rutile phase with
increasing calcinations temperatures (300 ◦C–800 ◦C) and mixed phase also obtained at the 600 ◦C temperature. XRD spectrum
showed that diffraction peaks of samples from (T6
300
◦
C
–T6
800
◦
C
) broader to narrow and intensity of peaks also increases with
increasing temperature due to this crystalline size increases with increase in calcinations temperature as shown in (Fig. 1). FWHM was
gradually decreases as shown in the Table 1, Sign of increases crystalline size of TiO
2
nanoparticles. The diffraction peaks identied at
2θ are 25.17◦, 37.83◦, 48.22◦, 54.66◦, 62.78◦, 69.22◦, 75.46◦, this pattern of XRD indicated strong anatase phase with tetragonal
structure is formed at lower calcinations temperatures and strongly agreement with JCPDS les No. 21-1272. At higher calcinations
temperature T6
600
◦
C
some extra peaks identied at 27.25◦, 38.59◦, 55.04◦in XRD pattern these peaks show that anatase phase mix
with small amount of rutile phase. This formation due to the oxygen vacancy found in the mixed anatase and rutile phase. The
crystalline size of TiO
2
nanoparticle was calculated by Scherrer formula (equation) with the help of highest intense peak (101), (110) of
anatase and rutile phase. FWHM and the calculated value of crystalline size is provided in the Table 1.
Fig. 3. Calcination temperatures variation (300
◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C) effects on TiO
2
(T6) in XRD pattern.
M. Lal et al.

Optik 241 (2021) 166934
5
Fig. 4. Calcination temperatures variation (300
◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C) effect on TiO
2
(T6) in XRD pattern.
Table 1
The effects of calcination temperature on the crystallite sizes of synthesized TiO
2
nanoparticle.
Sample
Name
Calcinations
Temp.
2θ
(Deg.)
β (FWHM)
(Deg.)
β (FWHM)
(Rad.)
Crystalline Size (L)
nm
Lattice constant ‘a′
nm
Lattice constant ‘c′
nm
T4 300 ◦C 25.17 0.96653 0.0168 8.45 0.5037 0.7124
T6 300 ◦C 25.17 0.92187 0.0160 8.88 0.4998 0.7068
T8 300 ◦C 25.17 0.99970 0.0174 8.16 0.4998 0.7068
T4 400 ◦C 25.15 1.04008 0.0181 7.85 0.5002 0.7073
T6 400 ◦C 25.17 1.06398 0.0185 7.68 0.4998 0.7068
T8 400 ◦C 25.17 1.04299 0.0182 7.80 0.4998 0.7068
T4 500 ◦C 25.17 0.59871 0.0104 13.66 0.4998 0.7068
T6 500 ◦C 25.16 0.63359 0.0110 12.91 0.5000 0.7071
T8 500 ◦C 25.14 0.61842 0.0107 13.27 0.5004 0.7076
T4 600 ◦C 25.16 0.33062 0.0057 24.92 0.5000 0.7071
T6 600 ◦C 25.15 0.33918 0.0059 24.07 0.5002 0.7073
T8 600 ◦C 25.16 0.33695 0.0058 24.49 0.5000 0.7071
T4 700 ◦C 27.30 0.23191 0.0040 35.66 0.4614 0.6526
T6 700 ◦C 27.30 0.22030 0.0038 37.54 0.4614 0.6526
T8 700 ◦C 27.29 0.21279 0.0037 38.55 0.4616 0.6528
T4 800 ◦C 27.31 0.21680 0.0037 38.55 0.4613 0.6523
T6 800 ◦C 27.29 0.22113 0.0038 37.54 0.4616 0.6528
T8 800 ◦C 27.30 0.21316 0.0037 38.55 0.4614 0.6526
T4, T6, T8-(4, 6, 8 mL) of titanium isopropoxide (TTIP).
M. Lal et al.

Optik 241 (2021) 166934
6
Rutile phase at 700 ◦C is very eminent and having high intensity, that meant crystallinity high. Additionally, this catalyst at 700 ◦C
phase component is 91.24% for rutile and for anatase 8.76%. As shown in anatase phase percent decrease with increasing calcination
temperatures. XRD spectra at 800 ◦C percent increase in rutile phase. As shown in XRD spectra anatase phase percent decrease with
increasing calcination temperatures while percent increase in rutile phase, so anatase phase at 800 ◦C completely transgure to rutile
phase. Crystallite size of rutile and anatase phase increases with increase in calcination temperatures. It was attributed due to the
agglomeration with increase in the crystallite size as increases calcination temperatures.
3.2. (FE-SEM) Field emission scanning electron microscopy
Laboratory prepared TiO
2
nanoparticles with variation in temperature were analyzed for morphological, shape and size study by
using Fe-SEM. SEM micrograph (Figs. 6 - 8) shows that at 300 ◦C calcinations temperature, TiO
2
nanoparticles observed to be small size
(~35 nm range) with roughly spherical and spongy shape. Further at 800 ◦C temperature the size of particles was observed to bigger
due to the agglomeration and nanoparticles exhibited non-uniform particles shape in (Figs. 6-8). It was observed that anatase phase
smaller particle size is smaller than the rutile and the similar results were observed from the XRD technique. This is also correlated that
the increase in calcination temperature leads to the increase in the size of TiO
2
nanoparticle as observed in XRD investigations.
3.2.1. Elemental analysis of TiO
2
(EDS)
Nanomaterial composition investigated using energy dispersive spectroscopy pattern indicates nanomaterial contains only element
of Ti and O without any other impurities. It was found to be Ti and O element as 59.94% and 40.06% weight (%) and 33.33% and
66.67% respectively, by atomic weight (%) as shown in (Fig. 5).
3.3. (FTIR) Fourier transform infrared spectroscopy
Spectra analyzed in range of 400 cm
−1
–4000 cm
−1
to scale quality and chemical conformation of TiO
2
nanoparticles. Figs. 9–11
represents FTIR spectra for samples T4, T6 and T8 at temperature range 300 ◦C–800 ◦C respectively. Range between 550 cm
−1
and
750 cm
−1
was used for observation of absorption band and associated TiO
2
lattice bond (O-Ti-O) bending vibrations that conrms
crystalline phase of TiO
2
.1615 cm
−1
–1625 cm
−1
range had sharp peak refer characteristic OH group bending vibrations [30,32–34].
Observed absorption peak having broad range of 3200 cm
−1
to 3800 cm
−1
is due to interaction with hydroxyl (OH) group of water
(H
2
O) molecule [31–33]. Due to calcination temperatures bond intensity decrease which inferred particle growth and water molecule
removal from sample.
3.4. DRS UV-Visible spectroscopy
TiO
2
(T6) nanoparticles energy band gap was measured by diffuse reectance spectra (DRS) that were prepared by sol-gel method.
To nd the band gap of synthesized TiO
2
nanoparticles at various temperatures were scanned at the range 200–800 nm. Synthesized
TiO
2
nanoparticles analyzed with DRS to estimate band gap energy is 3.31 eV, 3.37 eV, 3.30 eV, 3.29 eV, 3.11 eV, 3.09 eV, at
Fig. 5. EDX spectrum of TiO
2
(T6) at 400 ◦C.
M. Lal et al.

Optik 241 (2021) 166934
7
Fig. 6. SEM Images of TiO
2
(T4).
M. Lal et al.

Optik 241 (2021) 166934
8
Fig. 7. SEM Images of TiO
2
(T6).
M. Lal et al.

Optik 241 (2021) 166934
9
Fig. 8. SEM Images of TiO
2
(T8).
M. Lal et al.

Optik 241 (2021) 166934
10
Fig. 9. TiO
2
(T4) calcined FTIR spectra at various temperatures 300 ◦C, 400 ◦C, 500 ◦C, ᵒ 600 ◦C, 700 ◦C, 800 ◦C.
Fig. 10. TiO
2
(T6) calcined FTIR spectra at various temperatures 300 ◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C.
M. Lal et al.

Optik 241 (2021) 166934
11
temperature range 300 ◦C–600 ◦C, for TiO
2
–P25 which is higher than 3.2 eV as shown in (Fig. 12). Band gap decreases when calci-
nations temperature is increased 700 ◦C and 800 ◦C. As result of increase in crystallites size it can be accounted at higher temperature
agglomeration. At 400 ◦C calcination temperature band gap is 3.37 eV, it decreases to 3.09 eV at 800 ◦C, because bulk rutile phase
percent increase as shown in Table 2. The band gap was derived by drawing (
α
h
ν
)
1/2
versus (h
ν
). TAUC plot or TAUC equation is very
accessible tool to determine the energy band gap (E
g
) [Eq. (4)] [34].
(
α
h
ν
)
1/n
=A(h
ν
-E
g
) (4)
“Where
α
is the absorption coefcient, E
g
is the band gap value of nanoparticles, h
ν
is photon energy and A is the constant related to
the effective masses associated with the bonds, n determines the type of transition, n =1/2 is related to allowed direct transitions,
n=3/2 is related to forbidden direct transitions, n =2 is for allowed indirect transitions and n =3 is for forbidden indirect transi-
tions” [35].
4. Conclusion
XRD, Fe-SEM, DRS, and FTIR techniques were used to nd out the crystalline size, phase transition, crystallinity, morphology and
functional group behavior of TiO
2
nanoparticles synthesized by sol gel method. Results of the present study show the calcination
temperature effect on the properties (size, morphology and band gap) of TiO
2
nanoparticles. XRD results show that 400 ◦C is
appropriate calcinations temperature and volume 6 mL of TTIP to synthesized TiO
2
nanoparticles in terms of smaller crystalline size
(7.68 nm), suitable band gap (3.37 eV) and antase phase, while at 800 ◦C anatase phase completely transgure to rutile phase with
37.54 nm crystalline size. Fe-SEM micrograph shows that TiO
2
nanoparticles observed to be roughly spherical and spongy shape. At
high temperature agglomeration can result increase in size of crystallites. TiO
2
formation conrmed by FTIR, EDS spectra analysis. DRS
measurement give strong conrmation the band gap of nanoparticles decreases with increases temperature from (3.31–3.09 eV).
Fig. 11. TiO
2
(T8) calcined FTIR spectra at various temperatures 300 ◦C, 400 ◦C, 500 ◦C, 600 ◦C, 700 ◦C, 800 ◦C.
M. Lal et al.

Optik 241 (2021) 166934
12
(caption on next page)
M. Lal et al.

Optik 241 (2021) 166934
13
Declaration of Competing Interest
All the authors have no conict of interest.
Acknowledgments
Authors gratefully acknowledge the Guru Jambheshwar University of Science & Technology, Hisar (India) and University Grants
Commission (UGC), Govt. of India.
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