International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 01, January 2019, pp. 1547-1554, Article ID: IJMET_10_01_157
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=01
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
ZINC OXIDE NANOPARTICLES FOR WATER
REMEDIATION IN AGRICULTURE
D. Gnanasangeetha*
Department of Chemistry, PSNA College of Engineering and Technology, Dindigul, Tamilnadu
V. Prathipa
Department of Chemistry, PSNA College of Engineering and Technology, Dindigul,
Tamilnadu, India.
*corresponding author
ABSTRACT
Zinc oxide nanoparticle embedded in activated silica (ZnO-NPs-AS-Ai) as adsorbent
with nano cube shape were synthesized from leaf extract of Acalypha indica via green
method. Adsorbent were characterized using SEM, XRD EDAX and FT-IR. Exploration
shows that the adsorbent is nano cube shape with an average size of 80 nm with elemental
composition of zinc, oxygen and silica with Secondary amine at 2357 cm-1 and Olefinic
compound at 1600-1450 cm-1. The percentage of As (III) removal was very significant at
0.03ppm with arsenic removal of 79.47 to 96.19% with 2g adsorbent dosage at a pH of 6
with a contact time of 60 min and at an agitation speed of 300rpm. Results showed that
the adsorption process by ZnO-NPs-AS-Ai is monolayer chemisorptions. This research
uses existing principles of green chemistry to combat agricultural land contaminated with
arsenic (III) by bioremediation of water to prevent biological magnification.
Key Words: Activated Silica, Adsorbate, Adsorbent, Isotherm and Kinetics, Zinc oxide
Nanoparticles
Cite this Article: D. Gnanasangeetha and V. Prathipa, Zinc Oxide Nanoparticles for Water
Remediation in Agriculture, International Journal of Mechanical Engineering and
Technology, 10(01), 2019, pp.1547–1554
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&Type=01
1. INTRODUCTION
Green synthesis of nanoparticle for water remediation using plants is in the exploitation by
researchers. Nanotechnology applications are highly suitable for biological molecules, because
of their exclusive properties. Although chemical method of synthesis requires short period of time
for synthesis of large quantity of nanoparticles, this method requires capping agents for size
stabilization of the nanoparticles. Chemicals used for nanoparticles synthesis and stabilization
are toxic and lead to non-ecofriendly by products [1]. Green nanotechnology has goals to produce
nanomaterials and products without harming the environment or human health and produce nano
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D. Gnanasangeetha and V. Prathipa
products that provide solutions to environmental problems. To pursue a healthy life and space it
is imperative to develop a green synthetic approach to obtain nano materials targeted on different
applications. Many such experiments have already been started such as the synthesis of various
metal nanoparticles [2] using plants like Oryza sativa, Helianthus annus, Saccharum officinarum,
Sorghum bicolour, Zea mays, Basella alba, Aloe vera [3], Capsicum annuum, Magnolia kobus,
Medicago sativa (Alfalfa) [4], Cinamomum camphora, Geranium sp, Camellia sinensis (green
tea), Azadirachta indica (neem) [5], Oscimum sanctum (tulsi), Corriandrum sativum (Corriander)
[6], Emblica officinalis (amla) [7], Sesbania drummondii (leguminous shrub) various leaf broth,
natural rubber, starch and lemongrass leaves extract. This method is novel, sustainable and cost
effective to combat agricultural land contaminated with arsenic (III) by bioremediation of water
to prevent biological magnification. This research uses existing principles of green chemistry and
green engineering to make nanomaterials and nano-products without toxic ingredient to warfare
the environmental issues like runoff and accumulation of agricultural land with pesticides,
fertilizers and heavy metal contaminants.
2. MATERIALS AND METHODS
2.1. Characterization
Leaf extract of Acalypha (0.25, 0.5ml, 1ml to three sets)
50ml of distilled water
Vigorous stirring – leave it for 30min
1gm of Zinc acetate dihydrate (Zn (CH3 COO)2.2H2O)
10gm activated silica (AS)
2.0m NaOH
Stirr – 2hrs
White aq soln at pH12
Washed with distilled water followed by ethanol
Δ 60°C
ZnO-NPs-AS-Ai
Figure 1. Schematic Representation of Green Adsorbent Synthesis (ZnO-NPs-AS-Ai)
Synthesis of the adsorbent (ZnO-NPs-AS-Ai) is schematically presented in Fig. 1. The
external morphology of ZnO-NPs-AS-Ai were characterized by scanning electron microscope
(SEM) (JEOL JSM 6390). The X-Ray powder diffraction pattern of ZnO-NPs-AS-Ai were
recorded on X-ray diffractometer (XRD, SHIMADZU, 6000) using Cu (Kα) radiation (λ=1.5416
A˚) operating at 40 kv and 30 mA with 2θ ranging from 10 to 90˚. The average particle size of
ZnO-NPs-AS-Ai was determined from XRD patterns using Scherrer’s equation were summarized
in Table 1. A Fourier transform infrared (FT-IR) spectrum was recorded on Jasco FT-IR5300
model spectro photometer in KBr pellets in the range of 4000-400cm-1. The surface characteristic
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Zinc Oxide Nanoparticles for Water Remediation in Agriculture
and particle size distribution of ZnO-NPs-AS were investigated using Particle Size analyser
(Malvern Model Micro-P, range 0.05-550 micron).
Table 1: Grain Size of Zinc Oxide Nanoparticles using Acalypha indica
Strong
Peaks (2θ)
(θ)
Planes
Hkl
31.7705
34.4265
36.2650
15.8852
17.2132
18.1325
100
002
101
Spacing
(dhkl ±
0.0006)
0.2771
0.3002
0.3163
FWHM
β
(radians)
Crystalline
size (nm)
Morphology
(shape)
0.3342
0.3314
0.3163
5.82x10-3
5.78x10-3
5.75x10-3
86
79
76
Nano cubes
3. RESULTS AND DISCUSSION
Batch experiments were conducted to study the effect of concentration, adsorbent dosage, pH,
contact time and agitation speed on ZnO-NPs-AS-Ai for percentage removal of As(III) ions.
3.1. Effect of Concentration
Figure 2. Effect of Concentration for ZnO-NPs-AS-Ai
The effect of initial concentration of As(III) were studied with a fixed dose of adsorbent 1g,
contact time 50min, agitation speed 200 rpm and pH 5 by varying the initial concentration. The
experimental results show that the amount of adsorbate adsorbed exponentially increases while
the percentage removal decreases from 79.47% with the increase in initial concentration of
adsorbate from 0.005ppm. Fig. 2 shows gradual decrease in adsorption with increase in
concentration from 0.005ppm to 0.03ppm with removal of As(III) from 79.47% to 61.61% and
then constant. The optimum concentration of As(III) is found to be 0.03ppm with 61.61%
removal and beyond 0.03ppm concentration, the percentage removal decreases to 23.85% at
0.08ppm. This indicates that there exists a reduction in immediate solute adsorption due to the
lack of available active sites on the adsorbent surface compared to the relatively large number of
active sites required for the high concentration of adsorbate8.
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D. Gnanasangeetha and V. Prathipa
3.2. Effect of Adsorbent Dosage
Figure 3. Effect of Adsorbent Dosage for ZnO-NPs-AS- Ai
Effect of adsorbent dosage on the adsorption of As (III) is studied by changing the adsorbent
(ZnO-NPs-AS-Ai) dosage from 0.5g to 4g and the initial concentration of As (III) was fixed as
0.03ppm. Fig. 3 shows an increase in adsorption from 79.47% for 0.5gto 96.19 for 3g due to
greater availability of the surface area. Any further addition of the adsorbent (ZnO-NPs-AS-Ai)
beyond 3g did not cause any significant change in the adsorption and begins to decrease to
77.02% and 70.6% for 3.5g and 4g. This is due to over lapping of adsorption sites as a result of
overcrowding of adsorbent particle. The maximum As (III) removal of 96.19% was obtained in
for adsorbent dose of 3g.
3.3. Effect of pH
Figure 4. Effect of pH for ZnO-NPs-AS- Ai
It is clear from Fig. 4 that increasing the pH of the solution from 1 to 7 increases the
percentage removal of As (III) form 70.6% to 96.19%. This is due to the decline in the
competition between H+ ions and As (III) ions for surface sites. Basic pH was also attempted but
it could not be investigated due to precipitation. At pH 8 removal of As (III) decreases to 78.2%
and optimum pH was selected as 6.
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Zinc Oxide Nanoparticles for Water Remediation in Agriculture
3.4. Effect of Contact Time
Figure 5. Effect of Contact Time for ZnO-NPs-AS- Ai
The purpose of studying the effect of time on adsorption is to establish the equilibrium
reaction time between adsorbent and As (III) ions. The adsorption experiment was carried out
using contact time ranging from 10 min to 100 min and the results are depicted in the Fig. 5. It
was observed that metal adsorption occurred rapidly for 10 min with 65.62% As (III) removal.
The adsorption efficiency of As (III) increased gradually with increasing contact time up to 70
min with 96.19% removal and reached a plateau afterwards and there was no change in adsorption
and the equilibration time is 70 min. The data showed that time is a significant factor contributing
largely to the adsorption under different sets of condition, as time is required for As (III) ions to
diffuse in to the ZnO-NPs-AS-Ai .
3.5. Effect of Agitation Speed
Figure.6. Effect of Agitation Speed for ZnO-NPs-AS- Ai
The effect of agitation speed on the adsorption rate was investigated by changing the speed
in the range of 50 to 400 rpm. The rate of As (III) removal was very significant from 50 rpm to
300 rpm of about 65.62%, 70.6%, 83.69%, 91.38%, 94.98% and 96.19%. Increase in agitation
makes the particle to collide with each other with the greater speed resulting in detachment of
loosely bound ions also they did not get appropriate time to interact with each other. As shown
in Fig. 6 by increasing the speed beyond 350 rpm there was no further increase in adsorption
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D. Gnanasangeetha and V. Prathipa
instead adsorption decreases to 83.69% at 400 rpm. This is because all the binding sites have
been utilized and no binding sites were available for further adsorption. An increasing agitation
rate reduces the film boundary layer surrounding the ZnO-NPs-AS-Ai.
Maximum percentage removal for varing concentration (ppm), dosage (g), pH, contact time
(min) and agitation speed (rpm) with equilibrium parameters are summarised for adsorbent (ZnONPs-AS-Ai) in Table 2.
Table 2: Experimental Statistics for Adsorption of As(III) using ZnO-NPs-As-Ai
Variables
Range
Maximum Percentage
Removal (%)
Initial arsenic concentration (N)
Adsorbent dosage (g)
Initial pH
Contact time (min)
Agitation speed (rpm)
0.005-0.1
0.5-4.5
1-8
10-120
50-400
79.47
96.19
96.19
96.19
96.19
Equilibrium
Parameters
0.03 (N)
2 (g)
6
60 (min)
300 (rpm)
3.6. Equilibrium Study
The plot of Freundlich, Langmuir, Tempkin and BET isotherm values of the constants are shown
in Table 3. The linear regression coefficient of Freundlich, Tempkin and BET equation (R2 =
0.962, 0.960 & 0.979) value is comparatively low suggesting that this model is not so suitable for
the description of adsorption process when compared with Langmuir isotherm. The Langmuir
graph is linear with a reasonably high linear regression coefficient (R2 = 0.989) suggesting that
the adsorption process obeys Langmuir model. Also the RL value is 0.980 showing that the
Langmuir adsorption is favorable .Therefore the adsorption of As (III) on ZnO-NPs-AS-Ai is said
to be monolayer type.
Table 3: Adsorption Isotherm Parameters for ZnO-NPs-AS-Ai
S. No.
1.
Equilibrium
Isotherm
Equilibrium Parameters
Adsorbent
ZnO-NPs-AS -Ai
n
11.494
KF (L/g)
13.83
Freundlich
R
2.
Langmuir
3.
Tempkin
2
0.962
KL (L/mg)
0.665
RL
R2
A
B
0.980
0.989
0.16
0.008
R2
0.960
R2
4.
BET
0.979
2
Surface Area (m /g)
Pore size (nm)
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164.2008 m²/g
44.688 Å
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Zinc Oxide Nanoparticles for Water Remediation in Agriculture
3.7. Kinetic Study
Comparison of the kinetic models using the linear regression coefficient (R2) values in the Table
4 shows that pseudo-second order model best describes the adsorption process (R2=0.603) and
confirmed chemisorptions.
Table 4: Adsorption Kinetics for Adsorbent ZnO-NPs-AS-Ai
S.No.
1.
2.
Adsorption Kinetics
Pseudo first order equation
Pseudo second order equation
Adsorbent ZnO-NPs-AS -Ai
0.452
0.603
3.8. Phytochemical Analysis
Phytoconstituent Responsible for Crystallinity, Size, Morphology and Elemental Composition of
ZnO-NPs-AS-Ai were summarized in Table 5.
Table 5: Phytoconstituent Responsible for Crystallinity, Size, Morphology and Elemental Composition
of ZnO-NPs-AS-Ai
Plant
Species and
Plant parts
Botanical
and
Common
Name
Stabilizing
Phytoconstituents
Crystal
size and
Morphology
Acalypha
indica and
Kuppaimalli
Inter molecular
hydrogen bonding
3400-3300 cm-1,
Aromatic CH2 894
cm-1, Aromatic ring
stretch1002 cm-1,
Aromatic azide1334
cm-1, Secondary
amine 2357 cm-1,
Olefinic compound
1600-1450 cm-1, ZnO
NPs 500-400 cm-1.
80 nm
and
Nano
cubes
leaves
Elemental
Composition
Isotherm
and
Adsorption
Kinetics
and
Adsorption
Maximum
removal of
As(III)
Zinc and
Oxygen
Langmuir
isotherm
and
Monolayer
homogeneous
adsorption
Pseudo
second
order
and
Chemisorption
96.19%
4. CONCLUSION
Exploit of aqueous leaf extracts of Acalypha indica in the synthesis of zinc oxide nano particle
embedded in activated silica is novel leading to fairly green chemistry, which provide progression
over chemical method as it is cost effective and environment friendly and easily scaled up for
large scale synthesis. The aqueous leaf extracts acts as a complexing template which prevents the
particles from aggregating due to its physicochemical properties. The experimental results show
the significant removal of arsenic ions upto 96.19%. The key phytochemical responsible for the
synthesis of ZnO-NPs-AS-Ai are secondary amines and olefins. In continuation of the efforts an
undemanding monolayer chemical adsorption for the removal of As(III) ions fabricated helps to
improve the detoriation of agricultural land contaminated with arsenic (III). Bioremediation of
arsenic contaminated agricultural land could be achieved fairly by using ZnO-NPs-AS-Ai to
prevent biological accumulation.
ACKNOWLEDGEMENT
The authors are thankful to Karunya University, Coimbatore and PSNA College of Engineering
and Technology, Dindigul for provision of laboratory facilities which intensified the triumph of
this study.
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