tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structure, photoluminescence and photo-catalytic activities K.H.. Introduction In recent years, the synthe
Trang 1Original Article
E tirucalli plant latex mediated green combustion synthesis of ZnO
nanoparticles: Structure, photoluminescence and photo-catalytic
activities
K.H Sudheer Kumara,**, N Dhananjayab,*, L.S Reddy Yadava
a Department of Chemistry, BMS Institute of Technology and Management, Bengaluru 560064, India
b Department of Physics, BMS Institute of Technology and Management, Bengaluru 560064, India
a r t i c l e i n f o
Article history:
Received 16 February 2018
Received in revised form
20 June 2018
Accepted 13 July 2018
Available online 20 July 2018
Keywords:
E tirucalli
Green synthesis
ZnO nanoparticles
FTIR
SEM
Photocatalytic degradation
a b s t r a c t
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 105M MB at pH 12) The prepared ZnO nanoparticlesfind 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 (http://creativecommons.org/licenses/by/4.0/)
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,
eco-friendly, 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
applica-tions such as light emitting diodes (LEDs), X-ray imaging,
scintilla-tions, 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 nano-particles such as solvothermal, hydrothermal, solegel, microwave-assisted hydrothermal, co-precipitation, MetaleOrganic Chemical Vapour Deposition[12e17] Most of these techniques need sophis-ticated equipment's, timeconsuming experimental procedure and special precautions of experimental conditions [18] Green com-bustion 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 com-bustion 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 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
* Corresponding author.
** Corresponding author.
E-mail addresses: sudheerkh.158@gmail.com (K.H Sudheer Kumar),
ndhananjayas@bmsit.in (N Dhananjaya).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2018.07.005
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
Journal of Science: Advanced Materials and Devices 3 (2018) 303e309
Trang 2containing 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 ± 10C 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
us-ing Shimadzu powder X-ray diffractometer usus-ing Cu Karadiation
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
Photo-luminescence (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 105M methylene blue dye
solu-tion 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
solu-tion by centrifugasolu-tion to assess the extent of degradasolu-tion The
rate of degradation of dye was measured using
spectrophotom-eter at 664 nm The % degradation of dye can be dspectrophotom-etermined
using the following formula
% degradation¼Ci Cf
Ci 100
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 theFig 1that, for all the
plant latex content, a broadening was observed, which indicates
that the particle sizes were in the nanoscale range All the
diffrac-tion peaks were well indexed to pure hexagonal wurtzite ZnO
(JCPDS card no 36-1451) having the lattice parameters a¼ 3.2537
(Å), c¼ 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
bcosq¼ 3ð4 sinqÞ þkl
wherelis 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 linebcosq(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 d0is 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 synthe-sized 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 cm1was due to OeH mode and
1400e1649 cm1were attributed to C]O stretching mode As the volume of 5% latex increases the band at 1400e1649 cm1peak decreases The peak at ~ 2340 cm1 arises due to absorption of atmospheric CO2on the metallic cations The bands at 431 cm1 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 inFig 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 nano-particles was estimated by Wood and Tauc relation[29]:
ðahyÞ2¼ A hn Eg
(3)
whereais the optical absorption coefficient, hnis the photon energy,
Egis the direct bandgap and A is a constant The plots of (ahn)1/2vs photon energy of ZnO nanoparticles were shown inFig 5 It was found to be in the range 3.10e3.25 eV These Egvalues 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 inFig 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 emis-sion 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
304
Trang 3The 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 7shows 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 photo-catalysts (ZnO nanoparticles) were suspended in 30 ml of MB aqueous solution with a concentration of 5 105M 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 centri-fuged and collected for UVeVisible absorption measurement The
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
ester-ases contained E tirucalli plant latex.
Plant
latex (ml)
Average crystallite size (nm) Strain, 3
(103)
Band gap (eV) Scherrer's
equation (d)
WeH plots (d 0 )
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.
K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309 305
Trang 4intensity 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
5 105 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
illu-mination with UV light Here, we assume that the interfacial
elec-tron 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 exhibitfirst-order
kinetics in agreement with a general LangmuireHinshelwood mechanism[32]:
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
Table 2
Rietveld refined structural parameters for ZnO nanoparticles
prepared with 5.5 ml of 5% plant latex.
Lattice parameter
Cell volume (Å) 3 47.73(4)
R-factors
(c)
(b)
(a)
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.
200 300 400 500 600 700 800 900 1000 1100
Wavelength (nm)
(a)
(c)
(b)
u Lamp change over
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.
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.
K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309 306
Trang 5constant (mg/l min) If C is very small then the above equation could be simplified to:
where C0is 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 irradi-ation time (t) (Fig 10), the reaction rate constant (k) value are calculated and found to be 0.0038 min1
UV irradiation for different pH was recorded and shown inFig 9 The 96% degradation of 5 105M 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 particles under UV light When a photon incident on ZnO nano-particles, it will generate photoelectron (ecb) 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 OHor 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 ecband
Fig 6 Excitation and emission spectra of ZnO nanoparticles prepared using 5.5 ml of
5% esterases contained E tirucalli plant latex.
Fig 7 (a) SEM Image of ZnO nanoparticles prepared using 5.5 ml of 5% esterases
contained E tirucalli plant latex.
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
Fig 9 Degradation of MB in the presence of photocatalysts (ZnO nanoparticles pre-pared using 5.5 ml of 5% esterases contained E tirucalli plant latex) with different pH (5e12 pH).
K.H Sudheer Kumar et al / Journal of Science: Advanced Materials and Devices 3 (2018) 303e309 307
Trang 6hþvb The corresponding photocatalytic reaction process is as
follows:
ZnOþ hy/ ecbþ hþvb
ecbþ O2/O2
hþvbþ OH/OH
O2þ C16H18N3SCl/ Oxidation products
OHþ 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 105M) dye degradation as a function of different UV
irradiation time and pH were performed ZnO nanoparticles
pre-pared with 5.5 ml of 5% esterases contained E tirucalli plant latex
show 96% dye degradation at pH¼ 12 Further, the green
com-bustion 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 theirfinancial
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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