Green synthesis of AgeZnO nanoparticles: Structural analysis, hydrogen generation, formylation and biodiesel applications

Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

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

Original Article

Green synthesis of AgeZnO nanoparticles: Structural analysis,
hydrogen generation, formylation and biodiesel applications
L.S. Reddy Yadav a, b, S. Pratibha c, K. Manjunath d, M. Shivanna e, T. Ramakrishnappa b,
N. Dhananjaya c, G. Nagaraju a, *
a

Department of Chemistry, Siddaganga Institute of Technology, Tumakuru 572103, India
Department of Chemistry, BMS Institute of Technology, Bengaluru 560064, India
Department of Physics, BMS Institute of Technology, Bengaluru 560064, India
d
Centre for Nano and Material Sciences, Jain University, Bengaluru 562112, India
e
Chemistry and Physics of Materials Unit, JNCASR, Bengaluru 560064, India
b
c

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 26 January 2019

Received in revised form
27 February 2019
Accepted 5 March 2019
Available online 11 March 2019

The present work reveals the green combustion preparation of the Ag-doped ZnO nanoparticles (NPs)
using turmeric root extract as a fuel. The structure and morphology of Ag-doped ZnO NPs were investigated by several analytical techniques such as XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), FTIR (Fourier Transform Infrared), Raman, XPS (XRay Photoelectron Spectroscopy), and UV-Visible Spectroscopy (UVeVis). From XRD, the crystallite size
was found to be about 45 nm which agrees with the TEM results. SEM micrographs reveal the spherical
shaped agglomerated particles. XPS measurement anticipates that Ag is mainly in the metallic state and
ZnO is in the Wurtzite structure. UVeVisible spectroscopy shows the absorbance peak at 368 nm. Biodiesel synthesis from Terminalia belerica oil with AgeZnO as a nanocatalyst has been studied. AgeZnO
nanoparticles show hydrogen evolution up to 214 mmolgÀ1hÀ1. A convenient synthesis of Na-protected
formamides from protected amino acids was described using AgeZnO as a catalyst. This method provides
good yield of formamides with excellent purity after removal of the catalyst.
© 2019 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:
AgeZnO
TEM
XPS
Biodiesel
H2 generation
Formylation

1. Introduction
Due to the extensive range of applications in interdisciplinary
fields from biology/medicine to electronics, metal oxide nanoparticles have gained much attention in scientific community [1].
The catalytic and biological applications were addressed by the
low-cost metal oxides such as ZnO, CuO, MgO, TiO2 etc., instead of
noble metals like gold, silver, and platinum [2,3]. Among these, low
cost and easily accessible ZnO nanostructures are considered as

promising materials for numerous applications such as photocatalysis, emerging optical devices, sensor technology etc., because
of its excellent properties: large band gap, fast charge carrier
recombination, high quantum efficiency, optical transparency, high
surface area and electrochemical activity.

* Corresponding author.
E-mail address: (G. Nagaraju).
Peer review under responsibility of Vietnam National University, Hanoi.

ZnO nanostructures can be synthesized by various methods
namely, hydrothermal, solvothermal, ionothermal, co-precipitation
methods, etc. [4e6]. But these methods generally require hightemperature treatments, long preparation time, usage of expensive apparatus and harmful chemicals, etc. According to the literature survey, the green synthesis of AgeZnO nanoparticles has not
been widely reported. It includes the synthesis of nanoparticles
using plant parts. It is a cost-effective, safe, biocompatible method
that needs less processing time with low-cost equipment, and is
capable of high quality and purity of product [1,2]. Archana et al.
synthesized ZnO nanoparticles by green synthesis using Moringa
Oleifera natural extract and studied the enhanced photocatalytic
hydrogen generation and photostability [7]. Ali et al. synthesized
AgeZnO nanocomposite using Valeriana officinalis L. root extract
and investigated the application as a recyclable substance for the
decrease of organic dyes in an actual small period [8].
Since the first demonstration of photoelectrochemical H2 generation by Fujishima and Honda [9], rigorous research efforts have
been devoted towards the semiconductor photocatalytic

/>2468-2179/© 2019 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
( />

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L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

generation of H2 in recent years [10]. ZnO is a promising semiconductor having large exciton binding energy (60 meV) at room
temperature [11,12]. Also, oxygen vacancies in ZnO increase its
visible light photocatalytic activity [13,14]. The metal-metal oxide,
oxide-sulphide, oxide-nitride heterostructures [15] and noblemetal/oxide nanocrystals show excellent photocatalytic performance [16]. Cheng et al. observed the better photocatalytic properties due to enhanced charge transfer and separation process from
ZnOeTiO2 hybrid structures [17]. The major disadvantage of ZnO
photocatalyst is that the suffering from photo-corrosion and it has
been suppressed by doping, decorating with the optimum amount
of carbonaceous material or by modifying the synthetic protocol
[18].
Biodiesel, which is known as fatty acid methyl ester, is an
alternative fuel of diesel which is renewable, non-toxic, ecofriendly and recyclable. Presently, the homogeneous catalysts of
NaOH and KOH remain widely recycled for biodiesel production
[19]. These catalysts have many disadvantages, i.e. needs a large
amount of H2O, increased functioning and high cost [20]. Solid
mixed catalysts (SrO, CaO, MgO), mixed metal oxides (Ca/Zn, Ca/
Mg), and alkali-doped metal oxides are ecologically promising
materials for biodiesel production as it is easy to separate and
purify the ultimate yields [21]. Compared to these mixed catalysts,
the use of nanocatalyst gives higher catalytic activity, easy separation of products, recyclability and regenerates less pollution
[22,23,26]. Presently, non-edible oils such as Jatropha curcas,
Pongamia pinnata, and Cotton seeds are widely used for the production of biodiesel [24]. According to the literature survey, no
reports available on biodiesel synthesis from Terminalia belerica oil
with AgeZnO as a nanocatalyst. In the present study, Terminalia
belerica oil was used for the biodiesel production employing
AgeZnO nanocatalysts.
Formamide products such as imidazoles, fluoroquinones, and
nitrogen connected heterocycles etc., are valuable compounds for
general applications in medicine and organic chemistry [25e28].

They also serve as useful reagents in the asymmetric allylation,
Vilsmeier formylation reactions and hydrosilylation of carbonyl
compounds. Many useful formylation catalysts such as zinc metal,
CeO2, VB1, and HEU Zeolite with aq. HCOOH has been reported
[19,29,30]. However, many of these have drawbacks such as high
toxicity, harsh reaction conditions, and prolonged reaction time
demanding special care. Thus, we presented an alternative,
convenient method for the N-formylation of protected amino acids
in the presence of AgeZnO nanoparticles.
Curcuma longa (Turmeric) belonging to Zingiberaceae family
was used in Asia for thousands of years. It is a key part of Ayurveda,
Siddha medicine, Unani, and traditional Chinese medicine. Because
of its high antibiotic nature, it can be used in skin treatments. It is
widely used in Indian cuisine since the daily intake of turmeric will
enhance the immunity of the human body.
The present work reports the eco-friendly synthesis of Wurtzite
AgeZnO nanoparticles by Curcuma longa root extract using solution combustion method. The obtained nanoparticles were further
characterized using various techniques.

2.2. Synthesis of AgeZnO nanoparticles
Zinc nitrate [99% purity] and silver nitrate [98% purity] were
purchased from Sigma Aldrich and used without further purification. 60 ml of crude turmeric root powder solution is used as fuel.
Stoichiometric quantities of zinc nitrate, silver nitrate (1, 3, 5, 7 mol
%) were taken in a beaker and agitated well by a magnetic stirrer for
about 5e10 min. The mixture was placed in a pre-heated muffle
furnace maintained at 400 ± 10  C. The mixed combination boils
and thermally becomes dry to form a foamy product. The whole
procedure was ended in less than 5 min. The obtained product was
further calcined at 600  C for 2 h and then used for structural
analysis and further studies. A similar procedure is followed for the

synthesis of AgeZnO nanoparticles with different dopant concentrations of silver nitrate (1, 3, 5, 7 mol %).
2.3. Photochemical H2 generation
AgeZnO was utilized in photochemical water splitting and
generated hydrogen is measured by gas chromatography at room
temperature (25  C). The experimental procedure for photochemical H2 generation was similar to our previously reported work [33].
2.4. Biodiesel synthesis and formylation reaction
The Biodiesel Synthesis and Formylation reaction have been
carried out using Ag/ZnO NpS as nanocatalysts and the procedure
followed is similar to our previously published work and represented as in Scheme 1 [19]. The spectral data of the selected Naformamide derivatives protected amino acids has been given as
supplementary.
2.5. Characterization
The phase purity and crystallinity of the nanoparticles were
examined by Shimadzu X-Ray Diffractometer using Cu Ka radiation
(1.5406 Å) with nickel filter. The surface morphology of the nanoparticles was examined using a Hitachi 3000 scanning electron
microscope (SEM). Transmission electron microscopy measurements were carried out in a Jeol 200CX Transmission electron microscope. Absorbance was recorded by a Shimadzu UV-Visible
spectrophotometer. The Fourier transform infrared spectroscopy
studies have been performed on a Perkin Elmer Spectrometer
(Spectrum 1000) with KBr pellets The Raman spectrum is recorded
with a Peak Seeker Pro TM Raman system. The sample has been
excited with an inbuilt 785 nm wavelength laser. Photoluminescence (PL) spectra were examined by Agilent Cary Eclipse
Fluorescence spectrometer using Xe lamp with an excitation
wavelength of 397 nm. X-ray photoelectron spectroscopy (XPS)
analysis was carried out on an ESCALAB 250 (Thermo-VG Scientific), using Al Ka as the excitation source. The instrument was
standardized against the C1s spectral line at 284.600 eV. The H2
generation was performed by Perkin Elmer Clarus 580 GC

R1

2. Materials and methods
2.1. Collection of turmeric root

ZnO: Ag nanoparticles were prepared via a self-propagating
green combustion process using different concentrations of
turmeric root powder as a fuel. The turmeric root was collected
from the local market in Bangalore. The turmeric root was made
into well-grinded powder and used as a fuel.

OH

PgHN
O

i. NMM, EtOCOl
THF, aq. NaN3
ii. Toluene,

R1
PgHN

O
N
H

H

iii. HCOOH,
nano MgO
CH2Cl2

R1 = Amino acid side chains
Scheme 1. Synthesis of Na-formamide derivatives protected amino acids.

L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

7 mol%

$

$

*

$

5 mol%

*

$

$

$

*$

*

*

$

$

$

*

*

* *$

$

$

*

$$
Intensity (a.u.)

$Zn
*Ag

$

$

3 mol%

$

$

$

$

1 mol%

*

$

*

$

$

20

30

3. Results and discussion
Fig. 1 shows the XRD pattern of the AgeZnO nanoparticles with
crystal structure as the wurtzite phase of ZnO (JCPDS No. 75-576,
with unit cell parameters a ¼ 3.242 c ¼ 5.195, P63mc space group).
The extra peaks signify the cubic phase of the Ag (JCPDS No. 4-783,
with unit cell parameters a ¼ 4.0862, Fm-3m space group) and

attribute to the formation of the second phase clusters. It was
observed that there is a constant intensification in the intensity of
the Ag peaks with the increase in the fuel concentrations (1, 3, 5,
and 7 mol %). There is a change in the peak position at lower 2q
values with increasing fuel concentrations which implies the partial substitution of Agþ ions in ZnO lattice and the increase of lattice
parameters a and c, as estimated. The average crystallite size was
found to be about 45 nm which was estimated from the DebyeScherer equation given by, [31].

D¼

$$

40

50

$

60

$
70

80

2θ(deg.)
Fig. 1. XRD patterns of the AgeZnO nanoparticles with different fuel concentrations.

chromatograph equipped with a thermal conductivity detector
(TCD) with N2 as the carrier gas. Mass spectra of AgeZnO NPs were

recorded on a Micromass Q-ToF Micro Mass Spectrometer. 1H NMR
and 13C NMR spectra of AgeZnO NPs using Me4Si as an internal
standard and CDCl3 as a solvent by Bruker AMX 400 MHz
spectrometer.

427

kl
b cos q

where, b ¼ FWHM, q is Bragg angle, k ¼ 0.9 and l ¼ 1.54 Å (X-ray
wavelength).
The microstructure and morphology of the AgeZnO nanoparticles are obtained in detail from SEM observations. Fig. 2 shows
the SEM images of AgeZnO nanoparticles of different sized
spherical structures with agglomeration.
Fig. 3 shows the TEM and SAED images of the AgeZnO nanoparticles. TEM image presents the size of the AgeZnO nanoparticles
in the range 20e30 nm and the results are comparable with the
XRD. Selected Area Electron Diffraction (SAED) pattern indicates
the polycrystalline nature of nanoparticles.
Fig. 4 shows the FT-IR spectrum for different fuel concentrations
of AgeZnO nanoparticles between the range of 400e4000 cmÀ1.
The obtained sharp peak at 440 cmÀ1 is attributed to the ZneO
stretching vibration mode. The presence of hydroxyl ions (OH) in

Fig. 2. SEM images of AgeZnO nanoparticles; (a) 1 (b) 3 (c) 5 and (d) 7 mol % of fuel concentrations.


428

L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

Fig. 3. (a, b) TEM images and (c) SAED pattern of AgeZnO nanoparticles.

AgeZnO nanoparticles is revealed by the peaks in the range of
3020e3650 cmÀ1. The peaks at 1580 cmÀ1 and 1410 cmÀ1 represent
the symmetric and asymmetric bending modes of C]O bonds
whereas the peak located at 2860 cmÀ1 and 2950 cmÀ1 were
related to symmetric and asymmetric CeH stretching bonds,
respectively. The absorption band at 1020 cmÀ1 could be attributed
to bending vibrational modes [34].

5 mol %

368 nm

7 mol %

Absorbance (a.u.)

-1

421 Cm

1383 Cm

1 mol %

1652 Cm

-1

-1

-1

3 mol %
3431 Cm

Transmittance (a.u.)

7 mol %

The optical absorption spectra of the AgeZnO nanoparticles
were analyzed by UV-visible spectrophotometer in the range of
200e800 nm as shown in Fig. 5. The strong UV absorption edge at
368 nm of AgeZnO nanoparticles indicates the existence of the
wurtzite crystal structure. Absorption edge is independent from the
concentration of fuel used while preparing AgeZnO nanoparticles,
which indicates that only doping causes variations in band structure due to the intercalation of the metal ion in the band gap [28].
XPS spectra of Ag 3d, Zn 2p, and O 1s are shown in Fig. 6. Fig. 6(a)
shows two peaks at 1024 eV for Zn 2p3/2 corresponds to the hydroxyl groups attached to the Zn ions on the surface of nanoparticles. Another peak at 1044.2 eV corresponds to Zn atoms

5 mol %

3 mol %

1 mol %

O-H
3500

3000

C=O
2500

2000

Zn-O
1500

1000

500

-1

Wavenumber (cm )
Fig. 4. FT-IR spectra of the as-synthesized AgeZnO nanoparticles with different fuel
concentrations.

225

300

375

450

525

600

Wavelength (nm)
Fig. 5. UV-Visible spectra of AgeZnO nanoparticles with different fuel concentrations.


L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

(a)

(b)

Zn 2p3/2

1010

1020

1030

1040

1050

1060

526

Binding energy (eV)

(c)

O 1s

Intensity (a.u.)

Intensity (a.u.)

Zn 2p1/2

429

528

530

532

534

536

538

Binding energy (eV)

Ag 3d5/2

Intensity (a.u.)

Ag 3d3/2

364

366

368

370

372

374

376

378

380

Binding energy (eV)
Fig. 6. X-ray photoelectron spectroscopy of the AgeZnO nanoparticles.

bonded to oxygen atoms to form ZnO instead of ZneCeO alloys.
XPS spectrum of O 1s Fig. 6(b) shows a strong peak at 530.2 eV
which is the characteristic of lattice oxygen in ZnO: Ag. Fig. 6 (c), i.e.,
Ag 3d5/2 and Ag 3d3/2 binding energies appeared at 369 eV and
375 eV respectively. This is in good agreement with metallic silver
values [32].

Fig. 7 shows the room temperature PL spectra of Ag-doped ZnO
nanoparticles excited by a wavelength of 325 nm. All the samples
have related emission peaks centered at 358, 405, 430, 440 and
534 nm. As the dopant concentration increased, the emission peaks
disappeared. The peak at 358 nm dominates. Generally, there are
two emission bands in the PL spectra of ZnO nanoparticles. One is
due to near band edge emission through the collision between a

358nm

Ag-ZnO

1mol %
3mol %
5mol %
7mol %

430nm 440nm

534nm
-1

H2 ( μmolgh )

PL Intensity (a.u.)

405nm

pair of an exciton in the UV region. The other is due to the
recombination of the electron-hole pair caused by the intrinsic and

surface point defects in the visible region. The near band edge
emission peak is at 358 nm in as-synthesized pure ZnO and the
peak originated due to the defect states is after 405 nm. The
emission at 430 nm was associated with an electron transition from
a shallow donor level of neutral zinc interstitial to the top level of
the valence band. The emission at 440 nm is ascribed to surface
defects of ZnO. The green emission at 534 nm may be allocated to
oxygen vacancies. The asymmetric spectra are due to the native
defect states of ZnO. The size, structural morphology, surface
porosity and addition of dopants for ZnO donate in the defect

350

400

450

500

550

600

Wavelength (nm)
Fig. 7. PL spectra of the AgeZnO nanoparticles with different fuel concentrations.

0

20

40

60

80

100

120

Time (min)
Fig. 8. Photocatalytic hydrogen evolution of the AgeZnO nanoparticles.


430

L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431

Table 1
Fuel properties of Terminalia belerica biodiesel.
Properties

Units

Density
Acid value
Flash point
Viscosity at 40  C
Copper strip corrosion, 50  C, 3 h

Kg/m3
Mg KOH/g
C
mm2/sec
e

Testing procedure ASTM

Terminalia belerica biodiesel

Biodiesel standard ASTM 6751

D93
D664
D4052
D445
D130

880
0.32
64
4.5
1a

870e900
0.8 max
>130
1.9-6.0
no. 3 max

Table 2
List of formamides derivatives of aromatic amines and amino acid esters using AgeZnO nanoparticles.
Entry

1a

1b

Formamide

1c

1d

NHCHO

NHCHO

NHCHO

1e

NHCHO

HO

NHCHO

HOOC

O2N

Cl
Yield (%)

90

76

95

90

88

Entry

2a

2b

2c

2d

2e

Formamide

O

H

N
H

COOMe

O

90

H

N

O

O
HN
H

COOMe

H
Yield (%)

O

S

80

N
H

COOMe

H

N
H

COOMe

86

states, which affects the luminescence. Thus, the defects due to
native oxygen vacancies were accountable for the visible emissions
in ZnO samples. But still, there is some dispute in allocating the
defect emissions in ZnO [34].
Fig. 8 shows the photocatalytic H2 evolution (Water splitting
reaction) activity measured for AgeZnO nanoparticles calcined at
400  C for 3 h. The rate of hydrogen evolution for the water-ethanol
system in the presence of AgeZnO nanoparticles was determined
by gas chromatography. The quantity of gas liberated is plotted as
the function of UV exposure time. We have experimentally
observed that 214 mmolgÀ1hÀ1 of H2 produced for 2.5 h of UV
exposure time.
The generation of H2 gas was also stopped indicating that the
gas evolution was brought by the UV irradiation when the UV light

was turned off. From the graph, it is clear that AgeZnO nanoparticles act as a very good photocatalyst for hydrogen generation
from water splitting reaction [33].
Biodiesel applications using AgeZnO was carried out. After the
trans-esterification procedure, the yield of biodiesels originates by
employing the AgeZnO nanocatalyst was found to be about 83%.
The AgeZnO catalyst shows better catalytic activity which could be
a possible catalyst for the synthesis of biodiesel [19]. In this direction, to assess the quality of biodiesel, fuel properties kinematic
viscosity, flash point, density, acid value, and copper strip corrosion
were evaluated and compared with ASTM standards as shown in
Table 1.
Formylation reactions were performed using AgeZnO nanocatalysts at room temperature. Improved effects were found associated with the reported protocols, once the reaction was catalyzed
by 0.5 mmol of nanocatalyst AgeZnO at room temperature for
protected amino acids. Also, we tried the reaction in the presence of
a huge amount of catalyst (>0.5 mmol) which was considerably
decreased the percentage yield of products. The list of formamides
derivatives of aromatic amines and amino acid esters using
AgeZnO nanoparticles is tabulated in Table 2. Spectral data of the
selected compounds are given as supplementary.

SH
80

O
OH

88

4. Conclusion
In this work, we have synthesized the AgeZnO NPs with
different mol% concentration of Ag dopant using novel fuel by green

combustion method based on Curcuma longa root extract. It is an
environmentally friendly, facile as well as a cost-effective method
for the synthesis of nanoparticles. XRD shows the hexagonal
wurtzite structure. AgeZnO NPs demonstrates as a promising
material for photocatalytic hydrogen evolution. Furthermore, it is a
good catalyst for the synthesis of biodiesel from the Terminalia
belerica oil. About 83% yield has been achieved by the implementation of AgeZnO as a nanocatalyst for the synthesis of biodiesel. Hence, AgZnO NPs shows prominence towards the biodiesel
applications. It also catalyzes the N-formylation reactions, which
involves the clean procedure under milder reaction conditions with
an excellent yield of the desired products. These Formamides are of
most significance in synthetic organic chemistry as they are preliminary materials for a variety of products such as isocyanides,
monomethylated amines, and formamidines.
Acknowledgments
The author G. Nagaraju thanks to DST-Nano Mission, (SR/NM/
NS-1226/2013) Govt. of India, for funding. LSR Yadav acknowledges
BMSIT, Bangalore for constant support and encouragement.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
/>References
[1] L. Wu, Y. Wu, X. Pan, F. Kong, Synthesis of ZnO nanorod and the annealing
effect on its photoluminescence property, Opt. Mater. 28 (2006) 418.
[2] J. Xie, Q. Wu, One-pot synthesis of ZnO/Ag nanospheres with enhanced
photocatalytic activity, Mater. Lett. 64 (2010) 389.


L.S.R. Yadav et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 425e431
[3] H. Raveesha, S. Nayana, D. Vasudha, J. Shabaaz Begum, S. Pratibha,
N. Dhananjaya, The electrochemical behavior, antifungal and cytotoxic activities of phytofabricated MgO nanoparticles using Withania Somnifera leaf
extract, J. Sci. Adv. Mater. Dev. 4 (2019) 57e65.
[4] Z. Abdel Hamid, A. Abdel Aal, A. Shaaban, H.B. Hassan, Electrodeposition of

CoMoP thin film as diffusion barrier layer for ULSI applications, Surf. Coat.
Technol. 203 (2009) 3692.
[5] V. An Du, T. Jurca, G.R. Whittell, I. Manners, Aluminum borate nanowires from
the pyrolysis of polyaminoborane precursors, Dalton Trans. 45 (2016) 1055.
[6] H. Moussa, E. Girot, K. Mozet, H. Alem, ZnO rods/reduced graphene oxide
composites prepared via a solvothermal reaction for efficient sunlight-driven
photocatalysis, Appl. Catal. B Environ. 185 (2016) 11.
[7] B. Archana, K. Manjunath, G. Nagaraju, K.B. Chandra Sekhar, K. Nagaraju,
Enhanced photocatalytic hydrogen generation and photostability of ZnO nanoparticles obtained via green synthesis, Int. J. Hydrogen Energy 42 (2017) 5125.
[8] L.S. Reddy Yadav, K. Lingaraju, K. Manjunath, G.K. Raghu, K.H. Sudheer Kumar,
G. Nagaraju, Synergistic effect of MgO nanoparticles for electrochemical
sensing, photocatalytic-dye degradation and antibacterial activity, Mater. Res.
Express 4 (2017) 25.
[9] K. Fujishima, Honda, Electrochemical photolysis of water at a semiconductor
electrode, Nature 238 (1972) 37.
[10] M.R. Bindhu, M. Umadevi, M.K. Micheal, M.V. Arasu, Structural, morphological
and optical properties of MgO nanoparticles for antibacterial applications,
Mater. Lett. 166 (2016) 19.
[11] T. Mokkelbost, I. Kaus, T. Grande, M.A. Einarsrud, Combustion synthesis and
characterization of nanocrystalline CeO2-based powders, Chem. Mater. 16
(2004) 5489.
[12] Y. Zhai, Q. Zhang, F. Liu, G. Gao, Synthesis of nanostructure rutile TiO2 in a
carboxyl-containing ionic liquid, Mater. Lett. 62 (2008) 4563.
[13] K. Vanheusden, W.L. Warren, C.H. Seager, D.R. Tallant, J.A. Voigt, B.E. Gnade,
Mechanisms behind green photoluminescence in ZnO phosphor powders,
J. Appl. Phys. 79 (1996) 7983.
[14] L. Yabin, L. Zhifeng, L. Zhichao, H. Jianhua, ZnO/CuInS2 core/shell heterojunction nanoarray for photoelectrochemical water splitting, Int. J. Hydrogen
Energy 37 (2012) 15029.
[15] L.S. Reddy Yadav, B. Archana, K. Lingaraju, C. Kavitha, D. Suresh, Electrochemical sensing, photocatalytic and biological activities of ZnO nanoparticles: synthesis via green chemistry route, Int. J. Nanosci. 15 (2016) 165.
[16] L.S. Reddy Yadav, Danith Kumar, C. Kavitha, H. Rajanaika, B. Daruka Prasad,

H. Nagabhushana, G. Nagaraju, Antibacterial and photocatalytic activities of
ZnO nanoparticles: synthesized using water melon juice as fuel, Int. J. Nanosci.
15 (2015) 155.
[17] C. Cheng, A. Amini, C. Zhu, Z. Xu, H. Song, N. Wang, Enhanced photocatalytic
performance of TiO2-ZnO hybrid nanostructures, Sci. Rep. 4 (2014) 4181.
[18] S. Muthulingam, K.B. Bae, R. Khan, Improved daylight-induced photocatalytic
performance and suppressed photocorrosion of N-doped ZnO decorated with
carbon quantum dots, RSC Adv. 5 (2015) 46247.
[19] L.S. Reddy Yadav, M. Raghavendra, Udayabhanu, K. Manjunath, G. Nagaraju,
Photocatalytic, biodiesel, electrochemical sensing properties and formylation

[20]

[21]

[22]

[23]

[24]

[25]
[26]
[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

431

reactions of ZnO nanoparticles synthesized via eco-friendly green synthesis
method, J. Mater. Sci. Mater. Electron. 29 (2018) 8747.
G. Kafuku, M. Kee Lam, J. Kansedo, K. Teong Lee, M. Mbarawa, Heterogeneous
catalyzed biodiesel production from Moringa oleifera oil, Fuel Process. Technol. 91 (2010) 1525.
A.M. Dehcordi, M. Ghasemi, Transesterification of waste cooking oil to biodiesel using Ca and Zr mixed oxides as heterogeneous base catalysts, Fuel
Process. Technol. 97 (2012) 45.
L.S. Reddy Yadav, K. Manjunath, C. Kavitha, G. Nagaraju, An investigation of
hydrogen generation and antibacterial activity of TiO2nanoparticles synthesized by the ionic liquid aided ionothermal method, J. Sci. Adv. Mater. Dev. 3
(2018) 181.
S. Hu, L. Wen, Y. Wang Y, X. Zhen, Gaseliquid countercurrent integration
process for continuous biodiesel production using a microporous solid base
KF/CaO as catalyst, Bioresour. Technol. 123 (2012) 413.
K.V. Yatish, H.S. Lalithamba, R. Suresh, S.B. Arun, P. Vinay Kumar, Optimization
of scum oil biodiesel production by using response surface methodology,
Process Saf. Environ. 102 (2016) 667.
M.H. Sarvari, H. Sharghi, ZnO as a new catalyst for N-formylation of amines
under solvent-free conditions, J. Org. Chem. 71 (2006) 6652.
M. Rahman, D. Kundu, A. Hajra, A. Majee, Formylation without catalyst and
solvent at 80 C, Tetrahedron Lett. 51 (2010) 2896.

S. Kobayashi, K. Nishio, Facile and highly stereoselective synthesis of homoallylic alcohols using organosilicon intermediates, J. Org. Chem. 59 (1994)
6620.
L.S.R. Yadav, M. Raghavendra, K.H.S. Kumar, G. Nagaraju, ZnO Biosynthesised,
Dy3þ nanoparticles: biodiesel properties and reusable catalyst for N-formylation of aromatic amines with formic acid L.S. Eur. Phys. J. Plus Biosynth.
133 (2018) 153.
S. Guo, B. Qian, Y. Xie, C. Xia, H. Huang, Copper-catalyzed oxidative amination
of benzoxazoles via CÀH and CÀN bond activation: a new strategy for using
tertiary amines as nitrogen group sources, Org. Lett. 13 (2011) 522.
M. Lei, L. Ma, L. Hu, A convenient one-pot synthesis of formamide derivatives
using thiamine hydrochloride as a novel catalyst, Tetrahedron Lett. 51 (2010)
4186.
A.K. Ramasami, H. Raja Naika, H. Nagabhushana, T. Ramakrishnappa,
G.R. Balakrishna, G. Nagaraju, Tapioca starch: an efficient fuel in gelcombustion synthesis of photocatalytically and anti-microbially active ZnO
nanoparticles, Mat. Character. 99 (2015) 266.
Grisel Corro, Esmeralda Vidal, Surinam Cebada, Umapada Pal,
Fortino Banuelos, Diana Vargas, Emmanuel Guilleminot, Electronic state of
silver in Ag/SiO2 and Ag/ZnO catalysts and its effect on diesel particulate
matter oxidation:An XPS study, Appl. Catal. B Environ. 216 (2017) 1e10.
K. Manjunath, L.S. Reddy Yadav, G. Nagaraju, J. Dupont, T. Ramakrishnappa,
Progressive addition of GO to TiO2nanowires for remarkable changes in
photochemical hydrogen production, Ionics (Kiel) 23 (2017) 2887e2894.
K.H. Sudheer Kumar, N. Dhananjaya, L.S.R. Yadav, E. tirucalli plant latex mediated
green combustion synthesis of ZnO nanoparticles: structure, photoluminescence
and photo-catalytic activities, J. Sci. Adv. Mater. Dev. 3 (2018) 303e309.