Saraca Indica as Reducing agent for Synthesis of Modified Copper Oxide Nanoparticles at Low Temperatures Using

Green Synthesis Method

S. Shiva Samhitha1,a), B. Ajay Kumar1, G. Raghavendra1 and P. Hima Bindu1,b)

1)Department of Physics, Nizam College (OU), Hyderabad, Telangana – 500001a)Corresponding author: samhithashiva@gmail.com

b)bindu_phys@yahoo.com

Abstract:Copper Oxide (CuO) being one of the transition metal oxide has an unfathomable number of applications such as photoconductive functionalities, industrial and medical applications. The current study aims at the synthesis of CuO nanoparticles with the use of SaracaIndica (Ashoka) leaf extract, which acts as a reducing agent. The experimental conditions were optimized for nano-range synthesis of CuO particles. The obtained CuO nanoparticles have been characterized using various analytical techniques such as SEM, FTIR, XRD. Scanning Electron Microscope images revealed that the nanoparticles are in petal like shaped structures, having an average crystallite size of~ 14 nm. The XRD graph confirmed that the obtained CuO nanoparticles have monoclinic structure and has a preferred Morphology Index. The FTIR plot further confirmed the presence of Cu-O bonding with a slight modifications with functional groups. CuO nanoparticles of different properties and dimensions can be prepared with the help of different leaf concentrations and Copper salts. This work provides a simple, environmental friendly, tailor made and a cost effective way of synthesizing CuO nanoparticles using Green method.

INTRODUCTION

Production of desirable products in an eco-friendly manner without causing much harm to the environment by the emission of harmful by-products is only possible with the help of methods such as Green synthesis. The fabrication of such products also helps us in maintaining a balance in the environment. The main parameter in synthesis of nanoparticles is dependent on the control of particle size, morphology and crystallinity. Thus chemical [1,2], physical [3] and biological methodologies [4] have been adopted to synthesize CuO nanoparticles .

The transition metal oxide nanoparticles such as CuO, FeO, Zno, ZrO2 are biologically and chemically stable and have superior absorption capacity [5]. Among these nanoparticles, CuO tends to be an important P-type semiconductor having a very narrow bandgap of 1.2eV, thus possessing photovoltaic and photocatalytic properties[6]. The wide range of applications of CuO such as High Tc super conductors [7], sensors [8,9],catalytic [10],optical [11], electrical [12], degradation of dyes [13] had led to special interest, apart from such industrial applications it also has its uses in agricultural and medical fields such as antimicrobial, antibiotic and antifungal agent when integrated in coatings, plastics textiles [14],cosmetics and microelectronics [15].

Different synthesis methods have been used by several researchers to prepare CuO nanoparticles namely,solgel [16], sonochemical [17],alkoxide based route [18], electrochemical methods [19],precipitation pyrolysis [20], microware irradiators [21], solid state reaction methods [22],thermal decomposition precursor [23].Research is directional towards the field where we can directly depend on such natural methods which are not only environment friendly but also abundant in nature and are cost effective, whereas chemical synthesis of nanoparticles methods leads to absorption of toxic chemicals on the surface thus altering the medical applications [24]. Recently green synthesis of CuO nanoparticles have been accomplished using the extracts of Gum kaya [25], Gloriosa superba L [24], fruits such as Papaya [26], tea and coffee powder [27], where plant extracts were identified as the stabilizing agents[28].

The extract used in this work is Saraca Indica, a rainforest tree mainly and commonly found in the central areas of Deccan Plateau and in western coastal zone of the Indian subcontinent. Saraca Indica is reported to contain glycoside, flavanoids, tannins and saponins which can be used in various fields as spasmogenic,oxytocic, uterotonic, anti-bacterial, anti-implantation, anti-tumour, anti-progestational, antiestrogenic activity against menorrhagia and anti-cancer [29].

MATERIALS AND METHODS

Chemicals

For synthesizing CuO nanoparticles, Copper Nitrate (Cu(NO3)2) pellets, liquid Potassium Hydroxide (KOH) and Ethanol (C2H5OH)(for washing) were used.

Preparation of Leaf Extract from Sarca Indica (Asoca)

Fresh leaves of Saraca Indica, commonly known as Ashokawere washed in distilled water for five times to remove dust. Moisture was removed properly from the leaves using blotting paper and thereafter the leaves were microwave dried for 4-5 minutes. It was taken care to see that the leaves remained green in colour during the process of drying. Then 15grams of smashed leaves (microwave dried) was added to 300ml distilled water and heated at 60-700C for 30 minutes until the colour of the aqueous solution changes from transparent to greenish. Then the leaf extract was collected by filtration at room temperature for further use.

Synthesis of CuO NPs

CuO nanoparticles were prepared by adding 10 grams of Copper Nitrate (Cu(NO3)2) pellets to 100 ml of the Asoka leaf extract. This solution was mixed well with the help of magnetic stirrer for 30 minutes. Pottasium Hydroxide (KOH) solution was added dropwise to the prepared Cu(NO3)2 solution until precipitate was formed. This precipitate was filtered, washed with distilled water and ethanol several times to remove the ionic impurities and collected in a crucible. Crucible was kept in muffle furnace at 250O C for 2 hours. A greenish fine powder was obtained.

Characterization of CuO NPs

For confirmation of formation of CuO NPs , X-Ray Diffraction was performed on the powder CuO Nps using X-Ray diffractometer.

CuONps were examined under Scanning Electron Microscope to obtain information about the surface topography and composition

In addition, to investigate and characterize CuO NPs, Fourier Transform Infrared Spectroscopy(FTIR) was performed using FTIR spectrophotometer.

RESULTS AND DISCUSSION

XRD Studies

XRD Particle Size Calculation

The XRD pattern of the prepared sample of Copper Oxide is shown in Fig. 1. The XRD studies reveal that the sample is formed in nano sized and the obtained crystal structure is monoclinic.

20 30 40 50 60 70

0

1000

2000

3000

4000

5000

Inte

nsity

(a.u

)

2q

(110

)

(11-

1)

(111

)

(20-

2)

(020

)

(202

) (113

)

(022

),(31

1)(2

20)

FIGURE 1 XRD pattern of Copper Oxide Nano particles

In the spectrum, peaks observed at 32.69, 35.72, 38.95, 49, 53.63, 58.46, 61.75, 66.34, 68.18 corresponding to (110), (1 1 -1), (111), (20-2), (020), (202),(113), (311), (220) planes of Copper Oxide, thus confirming successful biosynthesis of Copper Oxide nanoparticles and are in agreement with reference data. [30]

The size of the obtained CuONPs was calculated using the Scherrers Equation

D = 0.9λ/β cosθ (1)

where λ represents wavelength of X rays, β represents half width at full maximum and θ is the diffraction angle.The average grain size of the particles is found to be 13.75 nm.

XRD-Lattice Parameters

Further, the lattice parameters were extracted from XRD graph. Table 1 shows us the calculated lattice constants of the monoclinic structure of Copper Oxide .

TABLE1 Lattice constants

Lattice constant Calculated Value (Å)A 4.681B 3.418C 5.122

The unit cell volume of Monoclinic Copper Oxide can be calculated by the formula

V= (a b c sin β) (2) Where β representshalf width at full maximum.

The calculated Unit cell volume for the obtained synthesized CuO nanoparticles is observed to be 51.12Å3.

XRD-Dislocation Density

The dislocation density is defined as the length of dislocationlines per unit volume of the crystal. A dislocation is defined as a crystallographic defect, orirregularity, that exists within a crystal structure. The presence ofdislocations strongly influences the properties of materials. A larger dislocation density implies a larger hardness.

Dislocation density can be calculated by δ=1/D2 (3)Where δ is dislocation densityand D is particle size (in nm).

The number of unit cells can be calculated by

n = π x (4/3) x (D/2)3 x (1/V) (4)

Where D is the crystallite size and V is the calculated unit cell volume. It is observed from Fig. 2and 3 that the dislocation density is indirectly proportional to particle size and number of unit cell. Dislocation density increases while both particle size and number of unit cell decreases.

8 10 12 14 16 18 20 220.002

0.004

0.006

0.008

0.01

0.012

0.014

Dis

loca

tion

Den

sity

Particle Size

δ=1/D2

FIGURE2. Particle size vs Dislocation Density .

0 10 20 30 40 500.002

0.004

0.006

0.008

0.01

0.012

0.014

Dis

loca

tion

dens

ity

Number of Unit cells

FIGURE3. Number of Unit cells vs Dislocation Density

6 8 10 12 14 16 18

10

20

30

40

50

Num

ber o

f Uni

t cel

ls

Particle Size

FIGURE 4 Particle size vs Number of Unit cells

XRD-Morphology Index

A XRD morphology index (MI) is calculated fromFWHM of XRD data using the relation

M . I=FWHM h

FWHMh+FWHM p (5)

Where M.I. is morphology index, FWHMh is highestFWHM value obtained from peaks and FWHMp isvalue of particular peak’s FWHM for which M.I. is to becalculated. The M.I. values are represented in table 2

XRD- Lorentz factor and Lorentz Polarization factor

With XRD data, Lorentz factor and Lorentz-polarization factor can be calculated by for equations (6) and (7), which controls the experimental quantities of X-rayintensity with respect to diffraction angle

Lorentz Factor = cos (θ)sin2(2 θ)

= 1

4 sin 2 (θ ) cos (θ) (6)

Lorentz Polarization factor = 1+cos2(2 θ)sin2 (θ )cos (θ)

(7)

The Micro strain can also be calculated by

ε = β

4 tanθ (8)

whereβ representshalf width at full maximum(in radians)

TABLE2 Size, Morphology index, Lorentz factor and Lorentz polarization factor of CuO Nanoparticles

2 θ (Degrees)

Crystalline size(nm)

Height (cts) Micro Strain [%]

Morphology index

Lorentz factor

Lorentz Polarization

factor32.69 14.365 289.65 0.008574 0.6520 3.29 22.4735.72 16.835 3491.69 0.006713 0.6853 2.79 18.5338.95 12.193 2995.47 0.008528 0.6097 2.39 15.3249.00 14.314 742.64 0.005840 0.6390 1.60 9.1453.63 14.441 170.94 0.005321 0.6366 1.38 7.4458.46 14.847 297.66 0.004781 0.6378 1.20 6.1261.75 15.901 494.71 0.004248 0.6497 1.11 5.4266.34 8.791 502.65 0.007207 0.5000 1.00 4.6368.18 12.026 477.81 0.005143 0.5751 0.96 4.37

Clark [31] exploredLorentz factor combined with the polarization factor in the calculationsintensity and also the variation of the Lorentz's factor withthe Bragg angle. The effect of Lorentz factor is to reducethe intensity of the reflections at intermediate angles compared tothose in the forward or backward directions. The values of Lorentz andLorentz polarization decreases with the increase in Bragg's angleand is in good agreement with the lowering of intensities.

Scanning Electron Microscope

(a) (b)FIGURE 6 (a) & (b).SEMimages of CuO nanoparticles in different magnifications

In addition, scanning electron microscopy (SEM) was usedto determine the shape, average size, and particle size distribution of the CuO nanoparticles. As shown inFig. 6 (a) & (b), the synthesized particles have petal like structure and are free from agglomeration. It showed that the synthesized copper oxidenanoparticles were approximately homogeneous in nature.However, most of the Chemical synthesis methods listed in Table 3,used higher energy, hazardous materials to obtain CuO NPs. In addition, the listed biologicalmethods synthesized the larger sized CuO NPswhen compared to the CuO NPs we synthesized.

TABLE 3Synthesis of copper oxide nanoparticles with different shapes through different methodsMethod Particle Size Shape ReferencesBiological Synthesis -Daphnia Magna 100-250 nm Oval [32]Biological Synthesis -CaloporisProcera 40 nm Cylindrical [33]Biological Synthesis -Seedless date 78 nm Spherical [34]Chemical Precipitation 75 – 150 nm Vesicular [35]Thermolysis 80-200 nm Wire Shaped [36]Sol gel 17 nm Seed Speroid [16]Sol gel 80 nm Agglomerated [37]

FTIR Analysis

Wavenumber [cm^-1]2500240023002200210020001900180017001600150014001300120011001000900800700600500400

Tra

nsm

itta

nce [

%]

100959085807570656055504540353025201510

430.1

05

508

.385

678

.259

812.6

02

880.4

48

104

7.4

2

1315.9

6

1422.8

5

1676

.91

2344.7

27

40.8

9

344

9.2

8

3537.6

9

3651.4

3

3753.3

5

3807.4

9

38

55.5

2

3905.8

6

3963.6

5

ftir CuO

FIGURE 8 FTIR Spectrum of synthesized CuO nanoparticle

FTIR spectrum, shown in Figure 7, of the synthesized CuO nanoparticles revealed the presence of eight main peaks at 1676.9, 1422.85, 1315.96, 1047.42, 880.448, 812.602, 678.259, 508.385 cm -1 thus representing C =O stretching vibrations (Conjugated Ketone), C – H bending, C – N stretching, CO –O – CO stretching, C – H bending, C = C bending, C- I stretching are shown in Table 3.Saraca Indica constitutes a number of complex active ingredients such as carbohydrates, tannins, gallic acid and egallic acid which reduced nanoparticles by decomposition of molecules. The plant extract thus acts as a stabilizing agent by forming a coating on the surface.The characteristic band observed at 430.1 cm -1 can be assigned to the Au mode of CuO [38]. No other IR active mode was observed in the range of 605 to 660 cm -1, which totally rules out the existence of another phase, i.e., Cu2O [39].

Table 3 FTIR spectrum of synthesized CuO NPs showing absorption peaks of functional groupNo Absorption Peak Position

(Wavenumber)(cm-1)Bond Functional Group Compound Class

1 508.385 Strong C-I Stretching Halo Compound2 678.259 Strong C =C Bending Alkene3 812.602 Medium C =C Bending Alkene4 880.448 Strong C – H Bending 1,2,4 Tri substitute5 1047.42 Strong CO-O-CO Stretching Anhydride

6 1315.96 Strong C –N Stretching Aromatic Amine7 1422.85 Medium C – H Bending Alkane8 1676.91 Strong C = O Stretching Conjugated Ketone

CONCLUSION

In this paper we have reported the synthesis of CuO nano powder by environmental Green method with Saraca Indica leaf extract aqueous solution. XRD data revealed a monoclinic structure from which crystalline size is calculated as ~ 14 nm and Lorentz factor and Lorentz polarization factor has been estimated.SEM picture showed that particles were in petal like structured morphology and are arranged almost homogenously. The FTIR characteristic data confirmed the presence of CuO Au mode. Due to the presence of phenolic compounds in the leaf extract, the CuO NPs surface were more stable. Thus Green synthesis of CuOnanoparticles using the extract of Saraca Indica leaf extracts can be useful and a preferable alternative to harmful chemical methods.

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