E. tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structure, photoluminescence and photo-catalytic activities

Journal of Science: Advanced Materials and Devices 3 (2018) 303e309

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Journal of Science: Advanced Materials and Devices
journal homepage: www.elsevier.com/locate/jsamd

Original Article

E. tirucalli plant latex mediated green combustion synthesis of ZnO
nanoparticles: Structure, photoluminescence and photo-catalytic
activities
K.H. Sudheer Kumar a, **, N. Dhananjaya b, *, L.S. Reddy Yadav a
a
b

Department of Chemistry, BMS Institute of Technology and Management, Bengaluru 560064, India
Department of Physics, BMS Institute of Technology and Management, Bengaluru 560064, India

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 16 February 2018
Received in revised form
20 June 2018
Accepted 13 July 2018
Available online 20 July 2018

ZnO nanoparticles were synthesized using esterases contained E. tirucalli plant latex as a fuel. The

structural, morphological and spectroscopic studies of the as-synthesized ZnO nanoparticles were
analyzed using powder X-ray Diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR),
UVeVisible absorption and photoluminescence (PL) spectroscopy. The structural parameters were
refined by the Rietveld refinement method using PXRD data and confirmed that the prepared compound
is pure hexagonal wurtzite structure with space group P63mc (No. 186). The average crystallite size was
estimated by Scherrer's and WeH plots and found to be in the range 17e23 and 20e26 nm respectively.
The band gap of ZnO nanoparticles was estimated using WoodeTauc relation and found to be in the
range of 3.10e3.25 eV. PL studies revealed that a broad yellow emission peak appeared at 570 nm upon
380 nm excitation peaks. Photocatalytic degradation of Methylene blue (MB) dye was studied under UV
irradiations. 5.5 ml of 5% esterases contained E. tirucalli plant latex used for the synthesis of ZnO shows
96% of degradation (5 Â 10À5 M MB at pH 12). The prepared ZnO nanoparticles find application in optical
and photo-catalytic degradations.
© 2018 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
Keywords:
E. tirucalli
Green synthesis
ZnO nanoparticles
FTIR
SEM
Photocatalytic degradation

1. Introduction
In recent years, the synthesis of oxide nanoparticles using green
products such as leaves, roots, latex, stem and bark has received
much attention by the researchers [1,2]. It is clean, non-toxic, ecofriendly, free from unwanted by-products and non-hazardous [3].
Recently, great efforts have been made to the synthesis of size and
shape controlled phosphor by different techniques [4,5]. Among
them, aqueous combustion synthesis technique has been used to
prepare cost-effective and cheap phosphors [6,7]. On the other

hand, the production of eco-friendly, low cost ZnO nanoparticles in
large scale by the existing routes remains difficult [8]. Therefore, it
was expected to be an important host material for several applications such as light emitting diodes (LEDs), X-ray imaging, scintillations, sensors, optical communication, fluorescence imaging [8e10].
Further, ZnO was non-toxic, compatible with skin and was highly

useful as UV-blocker in sun-screen and biomedical applications [11].
Various techniques have been employed to prepare ZnO nanoparticles such as solvothermal, hydrothermal, solegel, microwaveassisted hydrothermal, co-precipitation, MetaleOrganic Chemical
Vapour Deposition [12e17]. Most of these techniques need sophisticated equipment's, timeconsuming experimental procedure and
special precautions of experimental conditions [18]. Green combustion synthesis (GCS) is an alternative of a simple, versatile and
informal synthesis technique with time and energy saving prospect.
Green combustion methodology has been extended to other oxides,
such as LnCaAlO4, Sm2O3, ZnO, CuO, PdO, Co3O4, NiO with natural
plant extract [19e24].
In this study, ZnO nanoparticles were prepared by green combustion technique with esterases contained E. tirucalli plant latex as
a fuel. The structural, spectroscopic and photo-catalytic studies
were discussed in detail for environmental applications.
2. Experimental

* Corresponding author.
** Corresponding author.
E-mail addresses: (K.H. Sudheer Kumar),
(N. Dhananjaya).
Peer review under responsibility of Vietnam National University, Hanoi.

2.1. Synthesis of ZnO nanoparticles
In a typical synthesis of ZnO nanoparticles, 3 ml of 5% esterases
contained E. tirucalli plant latex was added in a borosil glass dish

/>2468-2179/© 2018 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
( />

304

K.H. Sudheer Kumar et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309

containing 2 g of Zn(NO3)3. 6H2O already dissolved in 10 ml of
double distilled water. This reaction mixture was mixed well using
magnetic stirrer for ~5e10 min and then placed in a preheated
muffle furnace maintained at 350 ± 10  C. The liquids of E. tirucalli
plant latex containing fats, unsaturated oils containing double
bonds, flavonoids and tannins are inclined to spontaneous ignition
of the mixture. The reaction mixture boils froths and thermally
dehydrates forming a foam. The entire process was completed in a
few minutes. A similar procedure was repeated by taking the
different volume of 5% esterases contained E. tirucalli plant latex
(4e8 ml) [4,25].

2.2. Characterization
The crystal structure of ZnO nanoparticles was determined using Shimadzu powder X-ray diffractometer using Cu Ka radiation.
The Fourier transform infrared (FTIR) spectra of the sample were
recorded using Perkin Elmer Spectrometer (Spectrum 1000) with
KBr pellets. The UVeVisible absorption spectra of the samples were
measured with SL 159 ELICO UVeVIS Spectrophotometer. Photoluminescence (PL) spectra were measured using Horiba Delta Flex
TCSPC system. Photocatalytic studies under UV light are carried out
in-house fabricated photochemical reactor.

2.3. Photocatalytic degradation of dye
Photocatalytic experiments were carried out using 250 W
high-pressure mercury lamps as the UV radiation source. An
aqueous suspension was prepared by dispersing 20 mg of ZnO

nanoparticles in 30 ml of 5 Â 10À5 M methylene blue dye solution. During the photocatalytic experiments, the slurry composed
of dye solution and catalyst was placed in the reactor and stirred
magnetically for agitation with simultaneous exposure to UV
light. A known volume (5 ml) of the exposed solution was
withdrawn at a specific interval of time (initially 20 min and then
30 min). Then, ZnO nanoparticles were removed from the solution by centrifugation to assess the extent of degradation. The
rate of degradation of dye was measured using spectrophotometer at 664 nm. The % degradation of dye can be determined
using the following formula.

% degradation ¼

Ci À Cf
 100
Ci

where Ci and Cf are the initial and final dye concentrations
respectively.

3. Results and discussions
3.1. Structural characterization (PXRD and Rietveld refinement)
Fig. 1(a) shows the PXRD patterns of ZnO nanoparticles prepared
by different volume of esterases contained E. tirucalli plant latex
(3e8 ml; 5% latex). It was evident from the Fig. 1 that, for all the
plant latex content, a broadening was observed, which indicates
that the particle sizes were in the nanoscale range. All the diffraction peaks were well indexed to pure hexagonal wurtzite ZnO
(JCPDS card no. 36-1451) having the lattice parameters a ¼ 3.2537
(Å), c ¼ 5.2063 (Å). No other impurity peaks are detected.
The average crystallite size for hexagonal ZnO nanoparticles for
a different volume of esterases contained E. tirucalli plant latex
were estimated by Scherer's (d) and Williamson and Hall (WeH)

plots (d0 ) using following relations [26,27]:

d¼

kl
b cos q

b cos q ¼ 3 ð4 sin qÞ þ

(1)
kl
d0

(2)

where l is the wavelength of the X-ray radiation (1.5418 Å), k is the
shape factor (0.9), q is scattering angle, b is (full width at half
maximum, FWHM in radian) measured for different XRD lines
corresponding to different planes and 3 is the strain.
The equation represents a straight line bcosq (Y-axis) versus 4
sinq (X-axis), the slope of the line gives the strain (3 ) and intercept
(kl/d0 ) of this line on the Y-axis gives average crystallite size (d0 )
(Fig. 1(b)). It was observed that d0 is slightly larger than d (Table 1),
because the strain component is assumed to be zero for calculating
d and observed broadening of the diffraction peak. In this case, the
finding is considered as a result of reducing crystallite size.
The structural parameters were refined by the Rietveld method
using powder PXRD data. The optimized parameters were scale
factor, background, global thermal factor, asymmetric factor, profile
half-width parameters (u, v, w), lattice parameters (a, c) and site

occupancy factors (Wyckoff) were used to obtain a structural
refinement with better quality and reliability. Fig. 2(a) shows the
Rietveld refinement performed on the green combustion synthesized ZnO nanoparticles. The refined parameters are displayed in
Table 2. The crystal structure of ZnO was modeled using Rietveld
refined structural parameters by Diamond program (Fig. 2(b)). In
this structure, Zn is connected to 4 oxygen atoms in a tetrahedral
configuration.

3.2. Spectroscopic studies (FTIR, UVeVisible and PL)
Fig. 3(aec) shows the FTIR spectra of 5% esterases contained
E. tirucalli plant latex and ZnO nanoparticles prepared with 3 and
5.5 ml, 5% esterases contained E. tirucalli plant latex respectively.
The absorption band near 3398 cmÀ1 was due to OeH mode and
1400e1649 cmÀ1 were attributed to C]O stretching mode. As the
volume of 5% latex increases the band at 1400e1649 cmÀ1 peak
decreases. The peak at ~ 2340 cmÀ1 arises due to absorption of
atmospheric CO2 on the metallic cations. The bands at 431 cmÀ1
correspond to the bonding between ZneO [28].
The UVeVisible absorption spectra of ZnO nanoparticles (3, 5.5
and 8 ml of 5% esterases contained E. tirucalli plant latex) were
shown in Fig. 4(aec) respectively. The abrupt change at ~380 nm is
due to lamp change over from UV to visible region in UV Visible
spectrophotometer. The direct energy band gap for the ZnO nanoparticles was estimated by Wood and Tauc relation [29]:

À
Á
ðahyÞ2 ¼ A hn À Eg

(3)

where a is the optical absorption coefficient, hn is the photon energy,
Eg is the direct bandgap and A is a constant. The plots of (ahn)1/2 vs
photon energy of ZnO nanoparticles were shown in Fig. 5. It was
found to be in the range 3.10e3.25 eV. These Eg values were smaller
than that of bulk ZnO (3.37 eV) [30].
The excitation spectrum of ZnO nanoparticles (5.5 ml; 5% latex)
recorded at room temperature (RT) and was shown in Fig. 6. The
near-band-edge (NBE) excitation peak at 380 nm was recorded at
an emission wavelength of 270 nm (inset of Fig. 6). The defect
emission in the visible region is attributed to ZnO surface detects, in
which oxygen deficiencies are the most suggested defects. Further,
the emission spectrum of pure ZnO showed a broad yellow emission at 570 nm along with sharp peaks at ~ 430 nm and ~ 460 nm,
which indicates the existence of a large number of surface defects.


K.H. Sudheer Kumar et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309

305

Fig. 1. (a) PXRD patterns and (b) WeH plots of ZnO nanoparticles for different volume of esterases contained E. tirucalli plant latex (3e8 ml; 5% latex).
Table 1
Various parameters of ZnO nanoparticles prepared with different volume of esterases contained E. tirucalli plant latex.
Plant
latex (ml)

Average crystallite size (nm)
Scherrer's
equation (d)

WeH plots (d )

3
4
5
5.5
6
7
8

17
18
19
20
21
22
23

20
21
22
23
24
25
26

0

Strain,
(10À3)

0.74
0.84
1.08
1.10
1.15
1.19
1.21

3

Band gap
(eV)

3.28
e
e
3.26
e
e
3.10

The broad ~ 570 nm peak may be due to the transition between
single charged oxygen vacancy and the photoexcited holes in the
valence band of the ZnO nanoparticles [31].
Fig. 7 shows the SEM image of ZnO nanoparticles (5.5 ml; 5%
latex). The image clearly shows the presence of almost spherically

shaped particles with agglomeration. The porous nature was
observed in SEM images. This is due to the liberation of a large
amount of gases during green combustion process.

3.3. Photo-catalytic activity
The photocatalytic activities of ZnO nanoparticles (5.5 ml; 5%
latex) were estimated by monitoring the degradation of Methylene
Blue (MB) as a model pollutant in a self-assembled apparatus with a
250 W high-pressure mercury lamps as the UV radiation source.
Typically, for the photocatalytic experiment, 20 mg of photocatalysts (ZnO nanoparticles) were suspended in 30 ml of MB
aqueous solution with a concentration of 5 Â 10À5 M in a beaker.
The suspension was magnetically stirred for 30 min to reach the
adsorption/desorption equilibration without light exposure.
Following this, the photocatalytic reaction was started by exposure
to UV light (20e120 min). After that, the 3 ml sample was centrifuged and collected for UVeVisible absorption measurement. The

Fig. 2. (a) Rietveld refinement and (b) wurtzite hexagonal crystal structure of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E. tirucalli plant latex.


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K.H. Sudheer Kumar et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309
Table 2
Rietveld refined structural parameters for ZnO nanoparticles
prepared with 5.5 ml of 5% plant latex.

(c)

Absorbance (a.u.)

Compound
Crystal system
Space group
Lattice parameter

a (Å)
b (Å)
Cell volume (Å)3
Zn1 (2)
x
y
z
O1 (À2)
x
y
z
R-factors
RP
RWP
Rexp

ZnO
Hexagonal
P63-mc (186)
3.2537(1)
5.2063(2)
47.73(4)
(2b)
0.3330
0.6667
0.0000
(2b)
0.3330
0.6667
0.3828(2)

RBragg
RF

(b)

(a)

8.08
8.85
8.14
1.18
4.17
3.85

c2

Lamp change over

200 300 400 500 600 700 800 900 1000 1100

Wavelength (nm)

431

1400

2340

3398

Transmittance (a.u.)

Fig. 4. UVeVisible spectra of ZnO nanoparticles prepared by (a) 3 ml (b) 5.5 ml and (c)
8 ml of 5% esterases contained E. tirucalli plant latex.

(c)

(b)

(a)

4000 3500 3000 2500 2000 1500 1000

500

-1

Wavenumber (cm )
Fig. 3. FTIR spectra of (a) 5% esterases contained E. tirucalli plant latex and ZnO
nanoparticles prepared by (b) 3 ml and (c) 5.5 ml of 5% esterases contained E. tirucalli
plant latex.

intensity of the main absorption peak (664 nm) of the MB dye was
referred to as a measure of the residual dye concentration [31].
Fig. 8(a) shows the degradation of MB in the presence of 20 mg
of ZnO (5.5 ml; 5% plant latex) nanoparticles with 20e120 min UV
irradiation. It was found that 120 min irradiation degrade 40% of
5 Â 10À5 M MB. Photocatalytic activity of ZnO was attributed to
both of the donor states caused by a large number of defect sites

such as oxygen vacancies and interstitial zinc atom and to the
acceptor states which arise from zinc vacancies and interstitial
oxygen atoms. Oxygen vacancies located at energy positions
2.35e2.50 eV were responsible for green luminescence upon illumination with UV light. Here, we assume that the interfacial electron transfer takes place predominantly between these donor
states (oxygen vacancies and interstitial Zn atom). Being a cationic
dye, MB acquires electron from excited donor states and
decomposes.
The kinetic behaviour of ZnO nanoparticles is shown in
Fig. 8(b). It is observed that the nanoparticles exhibit first-order

Fig. 5. Bandgap of ZnO nanoparticles prepared by (a) 3 ml (b) 5.5 ml and (c) 8 ml of 5%
esterases contained E. tirucalli plant latex.

kinetics in agreement with a general LangmuireHinshelwood
mechanism [32]:

R ¼ ÀdC=dt ¼ kKC=1 þ KC

(4)

where r is the degradation rate of reactant (mg/l min), C is the
concentration of reactant (mg/l), t the illumination time, K is the
absorption coefficient of reactant (l/mg) and k is the reaction rate


K.H. Sudheer Kumar et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309

Fig. 6. Excitation and emission spectra of ZnO nanoparticles prepared using 5.5 ml of
5% esterases contained E. tirucalli plant latex.

307

Fig. 9. Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E. tirucalli plant latex) with different pH
(5e12 pH).

constant (mg/l min). If C is very small then the above equation
could be simplified to:

lnðC0 =CÞ ¼ kKt ¼ kapp t

Fig. 7. (a) SEM Image of ZnO nanoparticles prepared using 5.5 ml of 5% esterases
contained E. tirucalli plant latex.

(5)

where C0 is the initial concentration of the MB aqueous solution
and C is the concentration of the MB aqueous solution for different
times of UV illuminations. From the plot of ln(C0/C) vs. the irradiation time (t) (Fig. 10), the reaction rate constant (k) value are
calculated and found to be 0.0038 minÀ1.
UV irradiation for different pH was recorded and shown in Fig. 9.
The 96% degradation of 5 Â 10À5 M MB (20 mg ZnO) was observed
for pH 12. This compound may be useful for catalytic applications.
Fig. 10 shows the mechanism of photocatalysis in ZnO nanoparticles under UV light. When a photon incident on ZnO nanoparticles, it will generate photoelectron (eÀcb) and photoinduced
holes (hþvb). The photoelectrons are trapped by adsorbed O2 as
electron acceptors and the photo-induced holes are accepted by the
negative species like OHÀ or organic pollutants, to oxidize organic
dyes such as MB. The oxygen vacancies are beneficial to the
degradation of the MB. It will restrain the combination of eÀcb and

Fig. 8. (a) Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E. tirucalli plant latex) with different UV

irradiation time and (b) First order kinetic reactions for ZnO nanoparticles.


308

K.H. Sudheer Kumar et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309

Fig. 10. Mechanism of photo catalysis in ZnO nanoparticles under UV light.

hþvb. The corresponding photocatalytic reaction process is as
follows:
ZnO þ hy / eÀcb þ hþvb
eÀcb þ O2 / OÀ2
hþvb þ OHÀ / OH
OÀ2 þ C16H18N3SCl / Oxidation products



OH þ C16H18N3SCl / Oxidation products



4. Conclusion
We have successfully synthesized ZnO nanoparticles via the
green synthesis technique using E. tirucalli plant latex as a fuel. Pure
hexagonal wurtzite structure was observed from PXRD studies. The
particle size was estimated from Scherer's and WeH plots and
found to be in the range 17e26 nm. The emission peaks at 570 nm
were observed under the excitations of 380 nm. The synthesized
nanoparticles were employed to study the catalytic activity of

Methylene blue dye degradation. UVeVisible spectra of Methylene
blue (5 Â 10À5 M) dye degradation as a function of different UV
irradiation time and pH were performed. ZnO nanoparticles prepared with 5.5 ml of 5% esterases contained E. tirucalli plant latex
show 96% dye degradation at pH ¼ 12. Further, the green combustion synthesized ZnO nanoparticles may be useful in display
and catalytic applications.

Acknowledgements
One of the authors N Dhananjaya greatly acknowledge the
Department of Science and Technology (DST), Government of India,
Science and Engineering Research Board (SERB) for their financial
support under Seed Money to Young Scientist for Research (Ref:
SERB/F/6219/2014-15, Grant: DST/SERB No: SR/FTP/PS-188/2013)).

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