One-pot green synthesis of zinc oxide nano rice and its application as sonocatalyst for degradation of organic dye and synthesis of 2-benzimidazole derivatives

Article abstract of DOI:10.1016/j.jpcs.2017.01.007

In this paper, we report novel and green approach for one-pot biosynthesis of zinc oxide (ZnO) nanoparticles (NPs). Highly stable and hexagonal phase ZnO nanoparticles were synthesized using seeds extract from the tender pods of Parkia roxburghii and characterized by XRD, FT-IR, EDX, TEM, and N₂ adsorption-desorption (BET) studies. The present method of synthesis of ZnO NPs is very efficient and cost effective. The powder XRD pattern furnished evidence for the formation of hexagonal close packing structure of ZnO NPs having average crystallite size 25.6 nm. The TEM image reveals rice shapes ZnO NPs are with an average diameter of 40–60 nm. The as-synthesized ZnO NPs has proved to be an excellent sonocatalysts for degradation of organic dye and synthesis of 2-benzimidazole derivatives.

Full text of DOI:10.1016/j.jpcs.2017.01.007

Author’s Accepted Manuscript
One-pot green synthesis of zinc oxide nano rice and
its application as sonocatalyst for degradation of
organic dye and synthesis of 2-benzimidazole
derivatives
Bappi Paul, Sethumathavan Vadivel, Siddhartha
Sankar Dhar, Shyama Debbarma, M. Kumaravel
www.elsevier.com/locate/jpcs
PII:
S0022-3697(16)30299-2
http://dx.doi.org/10.1016/j.jpcs.2017.01.007
PCS7959
DOI:
Reference:
To appear in: Journal of Physical and Chemistry of Solids
Received date: 11 July 2016
Revised date: 25 November 2016
Accepted date: 11 January 2017
Cite this article as: Bappi Paul, Sethumathavan Vadivel, Siddhartha Sankar Dhar,
Shyama Debbarma and M. Kumaravel, One-pot green synthesis of zinc oxide
nano rice and its application as sonocatalyst for degradation of organic dye and
synthesis of 2-benzimidazole derivatives, Journal of Physical and Chemistry o
Solids, http://dx.doi.org/10.1016/j.jpcs.2017.01.007
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One-pot green synthesis of zinc oxide nano rice and its application as sonocatalyst for
degradation of organic dye and synthesis of 2-benzimidazole derivatives
1
*
2
1
3
Bappi Paul , Sethumathavan Vadivel , Siddhartha Sankar Dhar *, Shyama Debbarma , M.
2
Kumaravel
1
Department of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam,
India
2
Department of Chemistry, PSG College of Technology, Coimbatore- 641004, Tamilnadu- India
3
Department of Civil Engineering, National Institute of Technology Silchar, Silchar-788010,
Assam, India
*
Corresponding author. Tel: +91-03842-242915; Fax: +91-03842-224797
Email: bappipaulnits@gmail.com (B. Paul); ssd_iitg@hotmail.com (S.S. Dhar).
Abstract
In this paper, we report novel and green approach for one-pot biosynthesis of zinc oxide (ZnO)
nanoparticles (NPs). Highly stable and hexagonal phase ZnO nanoparticles were synthesized
using seeds extract from the tender pods of Parkia roxburghii and characterized by XRD, FT-IR,
EDX, TEM, and N adsorption-desorption (BET) studies. The present method of synthesis of
2
ZnO NPs is very efficient and cost effective. The powder XRD pattern furnished evidence for the
formation of hexagonal close packing structure of ZnO NPs having average crystallite size 25.6
nm. The TEM image reveals rice shapes ZnO NPs are with an average diameter of 40-60 nm.
The as-synthesized ZnO NPs has proved to be an excellent sonocatalysts for degradation of
organic dye and synthesis of 2-benzimidazole derivatives.
Keywords: Biosynthesis; Nanorice; Sonocatalyst; Polluting dyes; 2-benzimidazoles

Introduction
Synthesis of semiconductor nanoparticles has been one of the most widely studied subjects for
the researchers in material science due to their novel optical, photoelectrochemical, electronic
and chemical properties which are different from that of bulk [1, 2]. ZnO NPs has attained the
remarkable attention, for its semiconducting properties, unique antifungal, antibacterial, wound
healing and UV filtering properties, humidity sensing, photochemical and high catalytic activity
[
3-5]. Furthermore, ZnO NPs finds wide range of applications in pigments, gas sensors, rubber
additive, optical devices and varistors [6, 7]. The characteristics and application of ZnO nano
powder depend on its size, shape and methods of preparation. There are several methods
available for the preparation of nanosized ZnO, such as chemical microemulsion [8], wet
chemical [9], hydrothermal [10], sol–gel method [11], electrochemical depositions [12],
microwave assisted combustion [13], co-precipitation [14], chemical [15], and sonochemical
[
16] etc. All of these methods have their own advantages and drawbacks. For example in
chemical methods, the synthesis can be carried out in large scale but use of toxic chemicals pose
major environmental and biological problems. To avoid the use of toxic chemical and harsh
reaction conditions for the preparation of nanoparticles, biosynthesis has proved to be a useful
tool. Recently, green synthesis of nanoparticles has gained much attention due to its inexpensive,
simplicity and eco-friendly procedure. Biosynthesis of metal or metal oxide NPs using plant
extract, bacteria and fungi for is considered to be immense importance owing to modern
legislation on clean environment. Therefore, the synthesis of nanoparticles using natural sources
is an excellent strategy that could reduce the environmental impact. Such methods are also useful
for large-scale synthesis of nanoparticles with well-defined size and shape of nanoparticles [17-
2
0]. Parkiaroxburghii, which is traditionally used as food source among local communities in

northeast Indian states, has proved to be an excellent extract for the biosynthesis of gold and
silver nanoparticles [21, 22]. Inspired by the efficiency of leaf extract of Parkiaroxburghii
towards biosynthesis of gold and silver NPs, we contemplated to use seeds from the tender pods
of Parkiaroxburghii for the synthesis of ZnO NPs. A comprehensive literature survey reveals that
there is no report on the biosynthesis of ZnO NPs using the seed of Parkiaroxburghii.
It is important to mention that demand for good quality textile materials across the globe is rising
consistently. Due to this a great deal of attention has been devoted in recent years for their
removal from the environment particularly from wastewater [23-25]. Therefore tackling this
problem is major concern for people in industry. Among the various known methods,
photocatalytic techniques have been extensively considered as energy-saving and a “green”
means to degrade the soluble dyes from wastewater. In degrading the organic pollutant
ultrasound irradiation has been proved to be an useful tool in enhancing reaction rates,
accelerating dissolution, renewing the surface of solid catalysts or reactants etc [26, 27]. Thus
combination of nanocatalysts with ultrasound irradiation in degradation reactions will certainly
open up a new avenue for highly efficient environmentally friendly synthetic protocols [26-29].
Synthesis of 2-benzimidazole and its derivatives are important because such compounds find
application in pharmaceuticals industries as anticancer, antifungals, antiulcer, antihypertensive,
antiviral and antihistaminics agent [30, 31]. For example, 2-benzimidazole derivatives act as
important scaffold in the synthesis of drugs such as stemizole, lansoprazole, telmisartan, and
albendazole drugs [32-34]. Thus 2-benzimidazoles and other related heterocycles are considered
to be of utmost significance in pharmaceutical industries. A survey of recent literature reveals a
number of works on their synthesis. Most of such procedures involve condensation of o-
phenylenediamine and aldehydes over various oxidants or catalysts such as VO(acac) [35],
2

In(OTf) [36], FeCl [37], I [38], NH OAc [39] and Dowex 50W [40], etc. These methods have
3
3
2
4
registered remarkable improvement over the previously reported procedures. However they still
process some limitations from green chemistry perspective. It may be emphasized here that use
of nanocatalyst might be a viable choice to replace the conventional catalyst in the synthesis of
2
-benzimidazoles. In this connection one such catalyst that has attracted attention of researchers
in recent past is zinc oxide nanoparticles. ZnO NPs have been proved to be remarkably efficient
to catalyze synthesis of 2-benzimidazoles and the related compounds. For example D. O. Jang et
al. have reported ZnO NPs catalyzed synthesis of benzimidazole, benzoxazole, and
benzothiazole derivative using ball milling technique [41]. S Banerjee et al. have reported ZnO
NPs as green and efficient catalyst for biologically active benzothiazole and benzoxazole
derivatives [42].
Attention of the readers may be drawn to the fact that ultrasound irradiation in chemical
reactions is proved to be an useful tool in accelerating dissolution, enhancing reaction rates,
renewing the surface of solid catalysts or reactants etc. Thus combination of nanocatalysts with
ultrasound irradiation in chemical reactions will certainly open up a new avenue for highly
efficient environmentally friendly synthetic protocols. Keeping in mind the environmental
legislations on the practice of processes for development of industrially important products
including pharmaceuticals, one has to look to develop synthetic methods that are suitable for
industry.
As a sequel to our current endeavour [10, 21, 25, 43, 44] on the synthesis and application of
nanocatalysts, we report herein a green approach for the synthesis of ZnO NPs and their
application as catalyst for ultrasound assisted degradation of organic dye and synthesis of 2-
benzimidazole derivatives.

2
2
. Experimental
.1 Materials and physical measurements
Zinc chloride (ZnCl ), o-phenylenediamine (OPD), and all the aldehyde was purchased from
2
Merck India Ltd. Sonication was performed in Qsonica Q700 sonicator with a frequency 20 kHz
and at a nominal power of 250 W. FT-IR spectrum was recorded on KBr matrix with Bruker
3
000 Hyperion Microscope with Vertex 80 FT-IR system. XRD measurements were carried out
on a Bruker AXS D8-Advance powder X-ray diffractometer with Cu-Kα radiation (λ=1.5418Å)
with a scan speed of 2°/min. Transmission electron microscopy images were obtained on a
JEOL, JEM2100 equipment. TEM grids were prepared using a few drops of the ethanol
dispersed sample.
2
.2. Synthesis of ZnO NPs
The seeds from the tender pods of Parkiaroxburghii were brought to laboratory cleaned
thoroughly by distilled water and then shade dried for a week. The dried seeds were crushed into
fine powder in a glass mortar. 10 g of powder was mixed with 50 mL of water for two hours at
O
1
00 C using soxhlet apparatus. The resulting extract was filtered using a pure cotton cloth
followed by Whatmann No. 1 filter paper. As collected filtrated was directly used as the
hydrolyzing agent in the synthesis of NPs. 0.1 M stock solution of zinc nitrate hexahydrate were
mixed with 25 ml of extract under vigorous stirring for 2 hours. After the completion of the
reaction, the dirty precipitate those formed was allowed to settle for 24 h, centrifuged, washed
with deionized water and ethanol several times and dried in a hot air oven. The as-obtained
precursor powder was then calcined in a muffle furnace for 4 h at 400°C to obtain powders of
ZnO NPs.
2
.3 Catalytic performance test

Zno nanorice catalyst was investigated ultrasound assisted degradation of methylene blue (MB)
and rhodamine B (RhB) dyes. In a typical catalytic reaction, 2 ml of freshly prepared sodium
-1
borohydride (SB) solution (0.2 M) was added to 50 ml (10 mg L ) aqueous solution of dye at
o
room temperature (25 ± 1 C) followed by addition of 1 mg of catalyst. The resultant mixture was
irradiated with ultrasound. At a regular interval of time, 4 ml of the suspension was withdrawn
and centrifuged immediately. The measurement of absorbance of the supernatant was carried out
using UV-visible spectrophotometer. A blank reaction without the catalysts was also performed
and its UV-visible measurement was conducted.
2
.3. Synthesis of 2-benzimidazoles derivatives using ZnO NPs as catalyst
In a typical procedure, aldehyde (10 mmol) and o-phenylenediamine (10 mmol) was dissolved in
1
0 ml ethanol. To this 0.5 mol% of ZnO (4.1 mg) nanocatalyst was added to the solution. The
O
mixture was sonicated at a room temperature (25 C) with ultrasound irradiation for 10 min.
After completion of the reaction as indicated by the TLC, the reaction mixture was poured in ice
cold water. The solid was filtered and the product was washed with water twice, dried and then
purified by recrystallization from ethanol.
3
3
. Results and Discussion
.1. Catalyst characterization
<Fig.1.>
The FT-IR spectrum of the ZnO NPs (Fig.1(a)) shows a strong absorption peaks at 3415 and
-1
1
6614 cm could be assigned to O–H stretch and N–H bend functional groups respectively. The
−1
bands observed at 2927, 756 and 644 cm can be assigned as –C–H stretch (alkanes), C–H
−
1
(
aromatics) and –C=C–H (alkynes). The absorption peaks around 1525 and 1445 cm can be
attributed the C=C bending and C–C stretching of aromatic rings, whereas peaks around 1235,

−
1
and 1031 cm assigned to the C–N stretching mode in aliphatic amines [45]. An intense peak at
-1
5
49 cm which corresponds to hexagonal phase Zn-O stretching vibration [18].
The phases exhibited by the synthesized ZnO NPs were identification by powder XRD patterns.
The XRD patterns of the synthesized ZnO nanoparticles is presented in (Fig.1(b)). The
diffraction peaks are found to be consistent with those of the reported data ZnO (JCPDS File no.
8
9-0511), which further indexed to a hexagonal ZnO NPs. No peaks of impurities were observed
indicating a high purity of the NPs. The sharp, strong and narrow peaks shows the good
crystallinity of the synthesized NPs. Debye-Scherrer equation [43,44] was used to evaluate the
average crystallite sizes of the synthesized ZnO, d=kλ/βCosθ, where‘d’ represents average
crystallite size of the particles, ‘k’ is a constant whose value is 0.9, ‘λ’ is the wavelength of Cu-
Kα radiation. The FWHM (full width at half intensity) of highest intensity peak is indicated by
‘β’ while ‘θ’ is the Bragg diffraction angle. The average crystallite sizes of as-synthesized ZnO
NPs was found to be 25.6 nm.
<Fig.2.>
The morphology, size and shape of the as-synthesized nanoparticle were analysed by using HR-
TEM. The TEM image of as-synthesized ZnO NPs (Fig.2(a,b,c)) showed rice shape particles of
diameter 40-60 nm. ZnO NPs are well known for many years having variety of sizes and shapes,
however, rice shaped ZnO NPs are rarely found. From the HRTEM image (Fig.2 (d,e)) it has
been observed that the lattice fringes is separated by 0.252 nm, which corresponds to the (101)
plane of ZnO NPs. The electron diffraction (ED) pattern (Fig.2 (f)) indicated single crystalline
in nature of the particles. The EDX patterns (Fig.3(a)) also showed presence of Zn and O in the
synthesized materials.
<Fig.3.>

To determine the specific surface area of synthesized ZnO NPs N adsorption-desorption
2
measurements were conducted. ZnO NPs synthesized by present biosynthesis routes exhibits
2
3
high specific surface area and pore volume of 13.25 (m /g) and 0.073 (cm /g), respectively
(
Fig.3(b)). This follows the characteristics of a type IV isotherm with a type H hysteresis loop
3
associated with aggregates of plate-like particles forming slit-like pores [46]. The Barrett Joyner
Halenda (BJH) pore size distribution indicated that most of the pores range from 4 to 10 nm (Fig.
3
3
(b) inset).
.2. The catalytic efficiency towards ultrasound assisted degradation of organic dye
<Fig.4.>
The catalytic efficiency of ZnO NPs was investigated under ultrasound irradiation for the
degradation of organic dyes MB and RhB in aqueous solution in presence of SB. The UV-visible
spectra (Fig.4(a)) of an aqueous solution of MB showed the absorption peak (λmax) at 662 nm
which corresponds to n-π* transition [23] and a shoulder peak at 612 nm [23]. The decrease of
absorbance at λmax = 662 nm with time was monitored spectrophotometrically. The intense blue
color of the MB solution faded and became colorless during the degradation process. While in
the other hand, the RhB dye showed strong absorption at 554 nm (Fig.4(b)) and the absorption
maxima steadily decreased as the exposure time increased [47]. The intense pink color of the
initial solution vanished gradually and became colorless during the process. The reduction of dye
is a thermodynamically favorable process and the color change indicates the degradation of
organic dye under ultrasound irradiation. It was observed that complete decolorization of both
the dyes occurred within 8 min. A slightly decrease in the absorbance of dye was observed under
US irradiation without the catalyst indicating very slow reaction rate, whereas that with catalyst
decreases abruptly, suggesting the faster reaction rate. ZnO NPs act as an electron relay and

-
-
initiate shifting of electron from BH ion (donor B H /BH ) to (acceptor LMB/MB, LRhB
4
2
4
4
-
/
RhB) and thus causing reduction of dye. BH ion simultaneously adsorbed on the surface of
4
-
NPs and thus electron transfer occurs from BH ion to dye through NPs [48]. The degradation of
4
MB and RhB dye fitted well with the pseudo first order equation. The equation may be
considered as ln(A /A)=kt, where ‘A ’ and ‘A’ corresponds to the absorbance of solution at
o
o
different illumination time, ‘k’ is the rate constant of the reaction and ‘t’ is the reaction time
(
min). The value of ‘k’ was obtained from the slope of the graph between ln(A /A) and time. The
o
‘k’ values in case of degradation of MB and RhB with ZnO NPs (Fig.4(c,d)) were found to be
-
1
-1
0
0
.232 min and 0.198 min . The standard error of the slope for MB and RhB was found to be
2
.003 and 0.007. Whereas R for MB and RhB. was found to be 0.995 and 0.982 respectively.
The sonocatalytic activities of ZnO nanoparticles in degradation of MB and RhB dyes were
calculated using the formula [(A -A)/A ]×100, where ‘A ’ is the initial absorbance and ‘A’ is the
o
o
o
absorbance of the dyes at time ‘t’ and were found to be 99.1 and 98.6% respectively. A
comparison table between our work and some of the previously reported literature for
degradation of MB and RhB dyes, showing the efficiency of sonocatalyst with some of the
literature reported ZnO photocatalyst is shown in table 1.
<Table 1.>
3
.3 Catalytic activity of nano ZnO in ultrasound assisted synthesis of 2-benzimidazoles
After successful synthesis and full characterization of ZnO nanocatalyst, we examined its
catalytic activity for synthesis of a few selected 2-benzimidazoles under ultrasound irradiation.
Our initial aim in this study was to obtain optimum reaction conditions for efficient condensation
o-phenylenediamine with aldehyde to get highest yield of the product. To this end, benzaldehyde
was chosen as model aldehydes for reaction with OPD. The other reaction parameters such

catalyst amount, solvent etc. are described in table 2. The effect of ZnO NPs was investigated
with varying amount of catalyst from 0.1 to 0.5 mol% keeping other parameters constant. It was
observed that the increase of the amount of catalyst up to 0.5 mol % results in sharp increase in
the yield while further increase in the amount of the catalyst did not show any significant rise in
yield. The effect of solvent on the reaction was also investigated by conducting the reaction in
acetonitrile, water, ethanol and t-butanol. The best results was obtained with ethanol. The blank
reaction without the catalyst was also carried out to judge the impact of catalyst on the reaction.
The yield of the product was only about 40% after about two hours of reaction. The role of
ultrasound on the reaction time was evaluated by doing the reaction under room temperature
magnetic stirring without ultrasonication. The yield of the product after 10 min of reaction was
almost negligible. Even after prolonging the reaction up to 2 hours, there was no significant rise
in the yield.
<Table 2.>
All these studies suggest that roles of ultrasound as well as that of the catalyst are very important
in getting the optimized reaction conditions.
Scaling up of this reaction up to 10 times exhibit equally good results and thus methodology
proves to be suitable for industrial purpose. A variety of 2-benzimidazole derivatives are
synthesized using the present methodology (Table 3). The probable mechanism for the synthesis
of 2-benzimidazoles is shown in scheme 1.
<
Table 3.>
Scheme 1
.4 Recovery and reclyability of the catalyst
3
<Fig.5.>

Another intriguing facet of this protocol is the easy recyclability of the catalyst. The recyclability
was tasted for the synthesis of 2-benzimidazoles under ultrasound irradiation. While doing the
recrystallization of the product from ethanol, the undissolved solid catalyst was recovered by
filtration. The catalyst was further washed with methanol and vacuum dried to ensure purity of
recovered catalyst. The recovered catalyst was further used to check the catalytic efficiency. It
was observed that, there is no significant decline in the catalytic activity of the recovered catalyst
after 5 consecutive runs (Fig.5(b)) in terms of yield and selectivity. While the average
crystallite size of the catalyst after five catalytic cycles increased to 28.12 nm (fig.5(a)).
4
. Conclusion
In summary, a novel green approach for one-pot biosynthesis of zinc oxide nano rice has been
demonstrated. ZnO NPs has been achieved using seeds extract from the tender pods of Parkia
roxburghii, a traditional vegetable grow abundantly in different areas of north-east India. As
synthesized ZnO NPs were found to be highly efficient sonocatalysts for degradation of MB and
RhB. The particles also proved to be highly effective in the ultrasound assisted synthesis of 2-
benzimidazole derivatives. The 2-benzimidazole derivatives were obtained with high yield and
selectivity in short reaction times. Moreover, this catalytic protocol is simple and efficient with
advantages of easy recovery and recyclability of the catalyst. Thus, this new protocol may serve
as viable alternative to numerous existing procedures.
Acknowledgement
The authors thank SAIF, IIT Madras, SAIF, IIT Bombay and SAIF, North Eastern Hill
University for analysis. The Director NIT Silchar is acknowledged for financial support.
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Figure and table captions
Fig.1. (a) FT-IR Spectrum of ZnO NPs. (b) Powder XRD patterns of ZnO nanocatalysts.
Fig.2. (a, b, c) TEM images (d, e) HRTEM image and (f) ED pattern of ZnO nanocatalyst.
Fig.3. (a) EDX pattern of ZnO NPs. (b) N adsorption-desorption isotherms of ZnO nanocatalyst.
2
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o
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tests of ZnO nanocatalyst for the reaction of o-phenylenediamine and benzaldehyde.
Table 1. Comparison of the literature reported catalyst with the present catalyst.
Table 2. Optimization conditions for the reaction of o-phenylenediamine and benzaldehyde
under ultrasound irradiation.
Table 3. Synthesis of various benzimidazole derivatives under ultrasound irradiation at room
temperature.
Scheme 1. The proposed mechanism for the synthesis of benzimidazole.
<Fig.1.>

<Fig.2.>
<Fig.3.>

<Fig.4.>
<Fig.5.>

Table 1.
S.No
Material
ZnO
Preparation
method
Application
Photocatalyst
Photocatalyst
Efficiency
and dye
degradation
92 % MB
Reference
[49]
1
2
Precipitation
followed by
calcination
Precipitation
followed by
calcination
Sol-Gel
ZnO
97% MB
[50]
3
4
ZnO-clay
Photocatalyst
Photocatalyst
98% MB
96% MB
[51]
[52]
Fe O /ZnO
Hydrothermal
method
2
3
5
ZnO
doped SnO2
ZnO
Hydrothermal
method
Refluxing method Photocatalyst
Refluxing method Photocatalyst
Photocatalyst
75% MB
[53]
6
7
8
95% RhB
99% RhB
90 % RhB
[54]
[55]
[56]
Fe O /ZnO
3
4
polymer-coated Refluxing method
AgZnO
Photocatalys
sonocatalyst
sonocatalyst
9
ZnO
nano rice
ZnO
nano rice
Biosynthesis
99 % MB
99 % RhB
Present
work
Present
work
1
0
Biosynthesis
Table 2.
CHO
H
N
NPs (0.5 mol %)
U.S, RT, 10 min
NH2
NH2
+
N
Entry Catalyst Catalyst Solvent Time Yield
(%)
Mol%
1
2
3
4
ZnO
ZnO
ZnO
ZnO
0.5
0.5
0.3
0.5
CH CN 60
84
76
82
97
3
H O
60
60
10
2
EtOH
EtOH

5
6
7
ZnO
ZnO
Neat
0.7
0.5
-
EtOH
t-BuOH 60
EtOH 120
60
95
60
42
Table 3.
H
N
NH2
NH2
NPs (0.5 mol %)
U.S, RT, 10 min
R
+
R-CHO
N
H
N
H
N
H
N
OH
N
N
N
3a, 93 %
3b, 97 %
3c, 95 %
H
N
H
N
H
N
Me
N
N
N
HO
OH
3f, 93 %
3e, 96 %
3
d, 91 %
H
N
H
N
H
N
Cl
NO2
OMe
N
N
N
3g, 92 %
3h, 92 %
3i, 94 %

RCHO
+
XH
X
N
NH2
R
XH
N
H
R
X
R
= ZnO
CB
VB
H
e-
N
H
XH
_
+
e-
X
H
R
N
H
N
H
R
_
X
H
R
N
H
<Scheme 1>
Graphical abstract

Highlights
ZnO NPs were biosynthesized using seeds extract of Parkia roxburghii.
The TEM image showed rice shaped particles having diameters 40-60 nm.
ZnO NPs is an excellent sonocatalyst for degradation of organic polluting dyes.
ZnO NPs effectively catalyze ultrasound assisted synthesis of 2-benzimidazoles