A. SAAVEDRA et al.: IMPROVEMENT OF TITANIUM DIOXIDE NANOPARTICLE SYNTHESIS WITH GREEN CHEMISTRY ...
755–759
IMPROVEMENT OF TITANIUM DIOXIDE NANOPARTICLE
SYNTHESIS WITH GREEN CHEMISTRY METHODS USING
LEMONGRASS (CYMBOPOGON CITRATUS) EXTRACT
IZBOLJ[ANA, OKOLJU PRIJAZNA KEMIJSKA SINTEZA
NANODELCEV TITANOVEGA OKSIDA Z UPORABO IZVLE^KA
LIMONSKE TRAVE
Angie Saavedra
1
, Sandra Correa
1
, Brucxen Nuñez
1
, Edgar Patiño
2
,
Adriana Herrera
3
1
Pontifica Bolivariana University, km7 road Piedecuesta, Floridablanca 681007, Colombia
2
ECOPETROL, km7 vía Piedecuesta, Colombia
3
University of Cartagena, Campus Piedra de Bolívar, 30 street #48-152, Cartagena, Colombia
Prejem rokopisa – received: 2019-08-21; sprejem za objavo – accepted for publication: 2020-07-15
doi:10.17222/mit.2019.200
In this research, titanium dioxide (TiO2) nanoparticles were synthesized through green chemistry using a plant extract, obtained
from lemongrass (Cymbopogon citratus) leaves. Two different methods for the leaf extraction were used, allowing the formation
of smaller nanoparticles as well as obtaining a greater amount of the product via synthesis. The first method was the synthesis
with ultrasound-assisted green chemistry, which used a precursor solution of titanium tetra-isopropoxide, obtaining
nanoparticles of 20.01 nm in size and a production of 0.05 g of TiO2 nanoparticles via synthesis; the second method was based
on the modification of the synthesis method using ultrasound-assisted green chemistry through the application of the pure pre-
cursor (titanium tetra-isopropoxide), obtaining nanoparticles with an average size of 18.67 nm and a production of 1.00 g of
TiO2 nanoparticles via synthesis. According to the results, the best synthesis method used the pure precursor, obtaining
nanoparticles of a smaller size and a production 20 times greater than the one obtained with the method using the precursor so-
lution. As a result, future studies will benefit by optimizing the production process, reducing the environmental impact by using
less reagents, maximizing the extraction of terpenes and flavonoids from lemongrass leaves and obtaining nanoparticles with
sizes similar to those available commercially.
Keywords: titanium dioxide, nanoparticles, lemongrass, improvement
Avtorji v ~lanku opisujejo raziskavo izdelave nanodelcev titanovega oksida, ki so jih sintetizirali s pomo~jo okolju prijaznega
kemijskega postopka pri katerem so uporabili izvle~ek iz listov limonske trave (Cymbopogon citratus). Pri tem so uporabili dve
razli~ni metodologiji ekstrakcije listov, ki omogo~ata tvorbo ve~je koli~ine manj{ih nanodelcev. Pri prvi metodi (metodologiji)
so uporabili z ultrazvokom podprto okolju prijazno sintezo, pri kateri so kot prekurzor (izhodno surovino) uporabili titanov
tetra-izopropoksid. S to metodo so dobili 0,05 gramov TiO2 nanodelcev velikosti 20,01v nm. Druga metoda temelji na modifi-
kaciji prve z uporabo ~istega prekurzorja. S to metodo so izdelali 1 gram nanodelcev TiO2 s povpre~no velikostjo 18,67 nm.
Rezultati so tako pokazali, da je ta metodologija s katero so uspeli izdelati 20-krat ve~jo koli~ino manj{ih delcev primernej{a kot
prva pri kateri so uporabili prekurzor v raztopini. Z nadaljnjimi {tudijami bodo poizku{ali {e optimizirati proces izdelave in
zmanj{ati vpliv na okolje z zmanj{anjem koli~ine reagentov, pove~anjem ekstrakcije terpenov in flavonoidov iz listov limonske
trave in tako dobiti nanodelce, ki so po velikosti podobni komercialno dosegljivim.
Klju~ne besede: titanov dioksid, nanodelci, limonska trava, izbolj{ava
1 INTRODUCTION
Nanotechnology (NT) has strengthened during the
last decades due to extraordinary properties that a
particle may exhibit at a nanometer level. Most of the
applications that have been made, have been chemically
synthesized using NPs, commercially obtained at a
certain size and having a high environmental impact due
to the process and the amount of reagents in the syn-
thesis.
1
A variety of physical and chemical procedures
have been developed to synthesize nanoparticles of
different compositions, sizes and shapes.
2
However, the
physicochemical techniques of the nanoparticle produc-
tion such as the photochemical reduction, laser ablation,
electrochemistry, aerosol technologies, ultrasound fields,
UV, lithography or high irradiation energy are highly
expensive and use highly toxic substances.
3
This paper presents an affordable, environmentally
friendly and straightforward synthesis alternative to
obtain TiO
2
nanoparticles using phytocomponents from
vegetables as the reducing agents
4
whose procedure does
not require neither strong and toxic chemical agents nor
organic solvents. Several investigators, among others,
5–8
have reported using natural resources such as inactivated
biomass and plants to produce silver or gold nanopart-
icles.
This paper seeks to present a green-chemistry synthe-
sis method, with which it is possible to obtain small
nanoparticles with high stability from plant extracts. In
Materiali in tehnologije / Materials and technology 54 (2020) 6, 755–759 755
UDK 67.017:621.791.725:669.715 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(6)755(2020)
*Corresponding author's e-mail:
sandra.correa@upb.edu.co (Sandra Correa)

this case, the synthesis of titanium oxide nanoparticles
from lemongrass (Cymbopogon citratus) leaf extracts
was performed at room temperature. In the present paper,
two nanoparticle-synthesis methods will be described;
with the first one, a stock solution of titanium tetra-
isopropoxide obtained with ultrasound-assisted green
chemistry was used; the second one was based on the ap-
plication of the pure precursor (titanium tetra-isopro-
poxide) with modifications to the previous method.
2 EXPERIMENTAL PART
2.1 Methods of TiO
2
nanoparticle synthesis
A comparison between the two methods of synthesis
was conducted to evaluate the production performance
according to the precursor used:
Synthesis of nanoparticles from the precursor
solution.
Synthesis of nanoparticles from the pure precursor.
2.2 Methodology for the nanoparticle synthesis from
the precursor solution
2.2.1 Extraction of terpenes and flavonoids from lemon-
grass leaves
To obtain the leaf extract, 100 g of leaves were dried
for six hours in a hot-air circulation oven at 60 °C and
mashed to get fine solids. The leaf extract was obtained,
using the Soxhlet method, from 50 g of biomass crushed
for6hin250mLofethanol (solvent) 10 % v/v. At the
end of the extraction, the extract was stored at 4 °C until
its final disposition.
2.2.2 Preparation of the TiO
2
precursor solution
The precursor solution (stock solution) of titanium
tetraisopropoxide was prepared by mixing 1.26 mL of
this reagent with 850 mL of distilled water. This mixture
was subjected to ultrasound-assisted agitation for
30 min. The result was a white solution witha5m M
concentration.
2.2.3 Synthesis of the nanoparticles from the precursor
solution
The synthesis of nanoparticles was carried out in
5 mL of titanium tetraisopropoxide. For this purpose,
20 mL of the lemongrass aqueous extract was added at a
rate of 1 mL/s. The reaction was carried out with mag-
netic stirring for 40 min. To complete this process, the
nanoparticles were subjected to three washes including
ethanol-water-ethanol 70 % v/v, using separation by
centrifugation at 6000 min
–1
for 15 min. Afterwards, the
nanoparticles were dried in a laboratory oven for2hat
80 °C. Finally, the product was calcinated in a muffle
furnace at 550 °C for 5 h.
2.3 Methodology for the nanoparticle synthesis from a
direct precursor
The extraction of terpenes and flavonoids from the
lemongrass leaves was done with the previously men-
tioned Soxhlet method. With this method, a difference
arose from the preparation of the TiO
2
solution.
2.3.1 Synthesis of the nanoparticles from the TiO
2
direct
precursor
The synthesis of nanoparticles was performed by
mixing 5 mL of pure titanium isopropoxide (to optimize
the time and number of nanoparticles) and 20 mL of
lemongrass aqueous extract. The reaction took place over
30 min of an ultrasound exposure. The obtained extract
was washed twice with ethanol and distilled water at
70 % v/v, while separation by centrifugation was
performed for 15 min at 6000 min
–1
. The nanoparticles
of titanium dioxide were subjected to a calcination at
5 5 0° Cf o r2ht opromote their crystalline anatase
phase.
9,10
2.4 Characterization of the titanium oxide nanopart-
icles
A scanning-electron-microscopy (SEM) analysis of
the titanium oxide nanoparticle solution was carried out
with a Quanta FEG 650 environmental scanning electron
microscope (ESEM) in the mode of high vacuum
operation, using a secondary electrons detector, Everhart
Thornley detector (ETD), and a backscatter electron
detector (BSED). Elemental analyses were made on this
instrument, which is coupled to an EDAX Apollo X
detector with a 126.1 eV (in MN K
 ) resolution to
perform EDS (energy dispersive spectroscopy) analyses,
providing qualitative and semi-quantitative information
about the chemical elements present in the synthesis of
TiO
2
nanoparticles. In addition, an XRD (X-ray
diffraction) analysis was performed on a BRUKER D8
ADVANCE powder diffractometer with DaVinci
geometry, and transmission electron microscopy (TEM)
was carried out at a maximum 1 million × magnification
with a resolution of 0.1 nm.
3 RESULTS AND DISCUSSION
The nanoparticles synthesized from lemongrass-leaf
extracts were analysed using of SEM, EDS, DRX, TEM
and the size distribution. Figure 1 shows the micro-
graphs of the nanoparticles synthesized with the TiO
2
green chemistry, obtained with SEM for the two methods
of synthesis: the precursor solution and direct precursor.
In Figures 1a and 1b, agglomerates of the titanium
dioxide nanoparticles obtained with the synthesis
methods are observed, with an average NP size of
20.01 nm for the precursor solution and average size of
18.67 nm for the pure precursor.
A. SAAVEDRA et al.: IMPROVEMENT OF TITANIUM DIOXIDE NANOPARTICLE SYNTHESIS WITH GREEN CHEMISTRY ...
756 Materiali in tehnologije / Materials and technology 54 (2020) 6, 755–759

The elemental composition obtained with EDS shows
that the TiO
2
nanoparticles synthesized with the pre-
cursor solution include titanium (47.81 %), oxygen
(49.25 %), carbon (1.95 %) and calcium (0.97 %). The
elemental composition of the TiO
2
nanoparticles synthe-
sized with the direct-precursor method was found to
include titanium (41.55 %), oxygen (42.81 %), carbon
(1.70 %) and calcium (0.86 %), demonstrating that the
compositions for both methods are very similar and
confirming that the composition includes some elements
from the leaf extract.
From the size distribution shown on Figure 2,itcan
be observed how the synthesis method using the pure
precursor exhibits smaller nanoparticles with an average
size of 18.67 nm and a composition of titanium and
oxygen. The comparison of the two methods shows that
a higher quantity of nanoparticles was produced with the
synthesis method that uses pure precursor, i.e., 1.00 g per
synthesis, while the method using the precursor solution
exhibits nanoparticles with an average size of 20.01 nm
and a quantity of 0.05 g per synthesis.
According to the results, both methods help us obtain
TiO
2
nanoparticles with similar physicochemical charac-
teristics. This result was achieved by controlling the
preparation processes of the two performed methods.
The performance of the production of nanoparticles
through synthesis (gram/synthesis) is better with the
method using the direct precursor since a production of
1 gram is achieved. When using the method with the pre-
cursor solution, the synthesis would have to be
performed twenty times to match the production of the
nanoparticles obtained with the first method. The
direct-precursor synthesis method facilitates a greater
production of TiO
2
nanoparticles, maintaining the re-
quired properties of the size and shape through the
control of the preparation process.
Also, it was found that, with respect to volume (mL),
the performance of producing nanoparticles from a
precursor was better with the method using a precursor
solution; this is possibly due to the amount of the plant
extract used in the synthesis, since that is the limiting
reagent in the synthesis of TiO
2
nanoparticles. This can
be maximized by increasing the amount of the plant
extract to achieve a performance similar to the con-
A. SAAVEDRA et al.: IMPROVEMENT OF TITANIUM DIOXIDE NANOPARTICLE SYNTHESIS WITH GREEN CHEMISTRY ...
Materiali in tehnologije / Materials and technology 54 (2020) 6, 755–759 757
Figure 1: Nanoparticles synthesized from the extracts of lemongrass leaves: a) with precursor solution; b) from direct precursor
Figure 3: TEM micrographs of TiO
2
nanoparticles synthesized with
green chemistry using pure precursor
Figure 2: Size distribution of TiO
2
nanoparticles synthesized from
lemongrass-leaf extracts: a) precursor solution, b) pure precursor

sumption of the precursor. Once the method with a better
performance was identified, characterization tests of the
TiO
2
nanoparticles obtained with the pure precursor were
performed. These analyses included TEM (transmission
electron microscopy) and XRD (X-ray diffraction) to
confirm the shape, size and formation of the desired
crystalline phase, in this case, anatase. Figure 3 shows
the micrograph obtained with TEM for the TiO
2
NPs
synthesized with green chemistry.
In Figure 3, nanoparticles with a hemispherical
shape are shown, having sizes between 11 and 16 nm
and an elemental composition of titanium, having a large
percentage of 65.93 % and 34.06 % of oxygen, carbon
and nitrogen in low proportions. Additionally, an X-ray
diffraction analysis was performed to confirm the desired
anatase crystalline phase, where the qualitative analysis
confirmed the presence of this phase in the titanium
dioxide nanoparticles, in addition to the halos obtained
with the electron diffraction of the TEM presented in
Figure 4, where the circular shape of the halos confirms
the presence of the anatase phase.
11,12
The nanoparticles of the size obtained with the above
methods can be used in different areas. In medicine, the
implementation of nanoparticles synthesized with plant
extracts is being investigated for the transport of medi-
cines and complementary treatments.
13,14
In addition,
NPs are implemented in crops, with the purpose of
improving the properties of the soil and the growth of
different plantations, having very positive results.
15,16
4 CONCLUSIONS
In the present work, green-chemistry methods were
evaluated to obtain TiO
2
nanoparticles with average sizes
of 20.01 nm and 18.67 nm. The nanoparticles were ob-
tained from lemongrass-leaf (Cymbopogon citratus)e x -
tracts and two methods of the precursor application were
used. Also, the nanoparticles were characterized with
SEM and EDX. With a direct implementation of the pre-
cursor, the preparation method allowed the highest
production of nanoparticles, representing an attractive
option for their production on a larger scale. The anatase
crystalline phase of these TiO
2
nanoparticles was con-
firmed with X-ray diffraction and TEM. The implemen-
tation of this method will allow a process with shorter
production times, lower costs and environmental im-
pacts, the use of renewable sources such as lemongrass
leaves, as well as a lower level of chemical-reagent con-
sumption. These nanoparticles with sizes between 18.61
nm and 20.01 nm can be applied in the same way as the
NPs synthesized with chemical methods because this
size allows the nanoparticles to cover a larger surface
area. They can be used as fungicides for crops and as-
phalt modifiers; they can also be used in the transport of
crude oil, food preservation, waste-water treatment and
in many other areas.
Acknowledgment
The authors thank Universidad Pontificia Boliva-
riana, Bucaramanga Headquarters and ECOPETROL –
Instituto Colombiano del Petróleo I.C.P. for the support
and financing of the research, carried out under the
convention "Marco de Cooperación de Ciencia y Tecno-
logía" No. 5226851 and "Acuerdo de Cooperación"
(Cooperation Agreement) No. 09. Moreover, authors are
grateful to Universidad de Cartagena for the technical
support with the green synthesis of TiO
2
nanoparticles.
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758 Materiali in tehnologije / Materials and technology 54 (2020) 6, 755–759
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