Synthesis of Metallic Nanoparticles by Physical, Chemical and Biological

Methods and Their Characterization

Aisha Shamim1, Zaheer Ahmad1, Tariq Mahmood2, Faisal Nawaz1, Faiza Asghar1, Shazia

Naheed1, Muhammad Ajmal1

Authors: 1. Department of Chemistry, University of Wah, Wah Cantt 47040, Pakistan,

2. Nano Sciences and Technology Department, National Centre for Physics, QAU, Islamabad

45320, Pakistan

Corresponding Author: Ms. Aisha Shamim, Department of Chemistry, University

Of Wah, Wah Cantt, Pakistan

e. mail: aishashamim22@gmail.com

Cell: +92-317-5051024

Abstract

Nanoparticles are the particles ≥100 nm. They have diverse applications. Physical method is

top down method. It is time consuming. Chemical method is simple, but expensive and

requires expensive chemicals with high purity. Biological method is very simple, cheap and

environment friendly requiring no expensive chemicals, temperature and is time saving. The

plant or fungal extract can be used in this method. These are available anywhere. In present

work we synthesized Zinc, Nickel and Chromium oxide nanoparticles by sol-gel method and

biological method. We used fungal extract in which enzymes converted metal salts in to

nanoparticles. These particles were characterized by XRD (X-ray Diffraction), EDX (Energy

Dispersive X-Ray Spectroscopy), UV-Vis (Ultraviolet Visible) and SEM (Scanning Electron

Microscopy). Their size was calculated. It was in nm range. The size of nanoparticles of ZnO,

NiO and Cr2O3 was 47, 38 and 45 nm respectively. The use of these nanoparticles is versatile.

ZnO NPs are used in cosmetics and in bioenergy production, as a catalyst and as antibacterial

material. NiO nanoparticles have potential applications in electronics, magnetism, energy

technologies and in nanomedicines. The Cr2O3 nanoparticles are used in wear resistant

materials, pigments and solar energy collectors.

Key Words: Nanoparticles, Sol-Gel method, Biological method, Chromium oxide nanoparticles,

Scanning Electron Microscopy.

1-Introduction

Nanotechnology is the engineering of individual atoms and molecules with dimensions of less

than 100 nm [1]. Idea of nanotechnology was given by Richard Feynman and this term was

used in scientific fields in 1974 [2] .Nanoparticles have outstanding physicochemical

properties. Nanoparticles have various applications in catalysis, electronic devices, dyes and

pigments [3,4].When size of the particles becomes less than 70 nm, Van der Waals force is

developed. Gecko can climb the walls and walk on ceilings because of minute hairs on their

limbs. Gold NPs change their ability to reflect light when their size is less than 20 nm. Al NPs

are extremely reactive when their size is less than 20 nm. The fascinating aspect of nano is

change in properties of particles when they are very small [5]. General procedures for metal

nanoparticles synthesis are electrochemical method, thermal decomposition, electromagnetic

irradiation, sol-gel method, chemical reduction, ultraviolet irradiation, aerosol technologies,

lithography, laser ablation, photochemical reduction techniques, attrition and pyrolysis.

Chemical methods have drawbacks of contamination by toxic solvents and production of

hazardous byproducts. Biological methods using microorganisms are clean, nonhazardous,

eco-friendly and energy efficient. These reduce metal ions at faster rate and are carried out

at ambient conditions. Microorganisms can survive in difficult conditions such as high

concentration of metals by adopting survival mechanisms such as efflux system, extracellular

combination and precipitation and chemical detoxification. According to Beveridge efflux

system, alternation of solubility and toxicity by reduction, biosorption, bioaccumulation and

lack of specific metal transportation system are the mechanisms responsible for biosynthesis

[6,7].

Zinc oxide (ZnO) is considered magic material because of its unique properties and vast range

of applications [8]. Precipitation method was used for ZnO NPs synthesis using Zn (NO3)2.6H2O

as a precursor and Potassium carbonate as a precipitator [9]. The ZnO NPs can be prepared by

Biological methods using leaf extract of Coriandrum sativum, Acaphyla indica, milky latex of

Calotropis procera and Arya sativa [10]. Trifolium pretense flower extract and fruit extract

of Rosa canina is also used for the synthesis of ZnO NPs [11]. Zinc oxide NPs are used in

biomedicine like biomedical imaging, drug delivery, gene delivery, and bio sensing

[12].Various techniques have been developed to synthesize Cr2O3 nanoparticles. Chromium

oxide nanoparticles can be synthesized by aqueous precipitation method using ammonia as a

precipitating agent and Cr2(SO4)3 as a precursor. Gibot and L.Vidal prepared Cr2O3 NPs by the

thermal decomposition of Cr(NO3)3.9H20 at 550°C [13]. Kohli et al prepared Cr2O3 NPs by a

precipitation method.V.S.Jaswal et al used precipitation method for synthesis of Cr2O3 NPs by

reacting Cr2(SO4)3 and aqueous ammonia [14]. The Cr2O3 nanoparticles are also synthesized

biologically by the reduction of potassium dichromate solution with Mukia Maderaspatana

plant extract [15]. Chromium oxide nanoparticles have vast domain of applications in optical

and electronic devices, as catalysts, colorants, hydrogen storage coatings and wear resistance

materials [16]. Nickel oxide NPs have fascinating properties like anodic electrochromism,

excellent durability, electrochemical stability and large spin optical density. Variety of

methods are used for the production of Nickel Nanoparticles. Nickel nanoparticles were

synthesized by chemical reduction method using nickel chloride hex hydrate as a precursor

and polyvinylpyrolidone (PVP) as a capping agent. Nickel nanoparticles are also synthesized by

solution reduction process using acetonitrile as a solvent, benzildiethylenetriamine as a

reducing agent and nickel nitrate hex hydrate as a precursor [17]. The dead biomass of fungus

Hypocrea lixii was used as an ecofriendly method for nickel NPs synthesis through biosorption

[18]. Nickel Oxide NPs have extensive applications such as catalysis, battery cathodes, gas

sensors, electro chromic films, dye sensitized photocathode and magnetic materials [19].

1.1-Experimental

In present study we synthesized ZnO, Cr2O3 and NiO NPs by using Chemical and biological

methods. This study was carried out at Nanoscience & Technology Department, National

Centre for Physics, QAU Islamabad and Department of Chemistry, University of Wah, Wah

Cantt. These nanoparticles were synthesized by sol-gel technique and were characterized by

using X-ray diffraction, UV-Visible spectroscopy, Scanning Electron Microscopy and Electron

Dispersive X-ray Spectroscopy. During this work all chemicals were purchased from local

market of Sigma-Aldrich. These were AR-Grade and there was no need of further purification.

The Chemicals used were Zinc chloride (ZnCl2), chromic sulfate (Cr2(SO4)3), nickel nitrate

Ni(NO3)2 and sodium hydroxide .We used deionized water throughout the experiment.

1.1.1. Chemical Synthesis

In this method aqueous solutions of salts were prepared by dissolving 3-4 g of nickel,

chromium and zinc salts in 100 ml of deionized water. We stirred the solutions to dissolve the

salts completely. We titrated salt solutions by adding 0.5M NaOH drop wise from burette with

vigorous stirring. Frequently we checked the pH. The precipitates were formed when pH was

11.The colour of precipitates of zinc was pale white while that of nickel and chromium was

blue green and green respectively. These precipitates were washed 4-5 times with de-ionized

water and then were dried at 95°C to remove moisture. Dried precipitates were calcined at

550°C for three hours in a muffle furnace. The calcined material was grinded by mortar and

pistil and samples were prepared. These samples were characterized by analytical techniques

like XRD, SEM, UV-Vis and EDX.

2

1.1.2. Biological Synthesis

In this method first of all salt solution was prepared by dissolving 3-4 g of salt in deionized

water and mixed with 2 g crushed powder of Aspargillus niger and stirred for 30 minutes.

Then the resultant material was placed in dark for 3 days. After 3 days we filtered the

solution. The filtrate was characterized by UV-Visible for finding size and concentration of

nanoparticles. The filtrate was then dried and calcined in furnace at 550°C for 3 hours .Now

the material was grinded and analyzed by XRD, SEM and EDX.

We analyzed nanoparticles by using XRD model D8 ADVANCE BRUKER X-Source Copper/

(anode). UV-Vis was performed on UV-Vis Spectrometer Perkin Elmer, Lambda 25.Both

instruments were placed at Nanoscience & Technology Department, QAU Islamabad. The

Scherrer formula was used for finding size. All the samples were characterized by XRD and

their results were noted in nanometer. The synthesized NPs were also characterized by SEM

performed on SEM, TESCAN, VEGA3 placed at Advanced Energy &Material lab NUST. The SEM

study was carried out to find size and morphology of nanoparticles. The EDX was done on

EDX Oxford placed at Fracture Mechanics and Fatigue Lab, Mechanical Engineering

Department, UET Taxila. The EDX was used to find elemental composition and purity of

samples.

1.1.3. Results and Discussions

We characterized samples by XRD. The XRD was used to find size of particles and crystallinity.

The scherrer formula was used to find crystalline size of NPs. The XRD analysis of biologically

synthesized nanoparticles is described below.

10 20 30 40 50 60 70

0

200

400

600

800

1000

B

A

B

Figure 1- The XRD spectrum of ZnO NPs

The above XRD pattern of ZnO nanoparticles indicates that the peaks are sharp and are

located at 2Ө values of 31°,34°,36°,38°,47°,56°,62° and 69°.Sharp peaks show good

crystalline growth and the position of peaks at respective 2Ө values indicate the formation of

pure ZnO nanoparticles These results were matched with (Arora et al ., 2014),(Farahmandjou

and Jurablu, 2014) and (Zargar and Arora, 2017).

2𝜃(𝑖𝑛 𝑑𝑒𝑔𝑟𝑒𝑒𝑠)

Inte

nsi

ty(a

.u.)

S.NO PEAKS POSITIO OF of PEAKS

PARTICLE SIZE

1 1 31 47nm

2 2 34

3 3 36

4 4 38

5 5 47

6 6 56

7 7 62

8 8 69

Table 1 XRD data of ZnO NPs

Average particle size found for ZnO NPs according to positions of XRD peaks was 47 nm.

Figure 2 - The XRD spectrum of NiO NPs

The diffraction peaks for NiO nanoparticles were at 19°,28°,29°,32°,34°,37°,43°,49°,54°

and 63° which were matched with ( Vasudeo and Pramod, 2016) and ( Sudhasree et al.,

2014).Peaks were sharp and prominent representing formation of NiO NPs.The peaks line

width described nanoparticle nature of sample.

S.NO PEAKS POSITION OF OF PEAKS

PARTICE SIZE

1 1 19 38nm

2 2 28

3 3 29

4 4 32

Inte

nsi

ty(a

.u.)

2𝜃(𝑖𝑛 𝑑𝑒𝑔𝑟𝑒𝑒𝑠)

10 20 30 40 50 60 70

50

100

150

200

250

300

350

B

A

B

1

10 20 30 40 50 60 70

0

50

100

150

200

250

300

350

400

B

A

B

5 5 34

6 6 37

7 7 43

8 8 49

9 9 54

10 10 63

Table -2 The XRD data of NiO NPs

Average particle size for NiO NPs was found to be 38 nm according to the XRD data plotted in

table 2.

.

Figure 3 - The XRD spectrum of Cr2O3 NPs

The peaks for chromium oxide NPs were formed at 2Ѳ values of 24°,33°,36°,41°,50°,54°,63°

and 65°.These results were matched with (Kalantari and Olayai,2015).The peaks were sharp

and clearly distinguishable. All the peak positions and intensity of peaks indicate crystalline

Cr2O3 NPs.

S.NO PEAKS POSITIN OF PEAKS

PARTICLE SIZE

1 1 24 45nm

2 2 33

3 3 36

4 4 41

5 5 50

Inte

nsi

ty(a

.u.)

2𝜃(𝑖𝑛 𝑑𝑒𝑔𝑟𝑒𝑒𝑠)

6 6 54

7 7 63

8 8 65

Table 3 The XRD data for Cr2O3 NPs

The XRD data for Cr2O3 nanoparticles shows that the average particle size was 45 nm.

Chemically synthesized nanoparticles of nickel, chromium and zinc show diffraction peaks at

19°,31°,37°,42°,54 - 24°,28°,33°,36°,41°,46°,54° -31°,34°,36°,47°,56° respectively

Figure 4 -The EDX of ZnO NPs

The EDX study showed the elements Zn and O. The Zn content was 85.9% while O content was

8.6%.The EDX results indicated that ZnO NPs were pure with only traces of impurities.

Figure 5 -The EDX OF NiO NPs

Elemental analysis of NiO NPs demonstrated that synthesized NiO NPs consisted of 53.8% Ni

content and 46.2% O content without any trace of other materials.

Figure 6 –The EDX of Cr2O3 NPs

The EDX analysis confirmed the presence of of Cr2O3 NPs.It showed 61% Cr2O3, 38.8% O and 0.2

% S .

Figure 7 – The SEM micrographs of Cr2O3 NPs

SEM is used to study surface morphology of NPs by scanning the surface with high energy

electrons.SEM study shows that Cr2O3 NPs are beautiful white hexagonal crystals. All the

crystals are uniform sized with average crystalline size of 73 nm. There were very fine

particles detected but because of their instability we could not find their exact size.

Figure 8- The SEM Micrographs of NiO NPs

SEM study of NiO NPs showed spherical black uniform sized nanoparticles with average size of

47 nm which is very near to its XRD size of 45 nm. There was agglomeration noted at different

locations.

Figure 9- The SEM Micrographs of ZnO NPs

The SEM micrographs of ZnO NPs clearly show beautiful white evenly sized crystals with

hexagonal morphology. The average size of crystals was 72 nm. Intense agglomeration in case

of ZnO NPs is due to large surface energy of NPs.

200 300 400 500 600 700 800

0

1

2

3

4

5

6

B

A

B

Figure 10- The UV-Visible Spectrum of ZnO NPs

The UV-Visible analysis was recorded in the range of 200-800 nm. The UV-Visible analysis

indicates that ZnO NPs show maximum absorbance at 350 nm due to SPR, which occurs due to

resonance of collective conduction electrons with incident electromagnetic radiations. The

value was matched with the literature where values of maximum absorbance were between

340-380 nm.

Figure 11- The UV-Visible Spectrum of NiO NPs

NiO NPs show wide absorbance in the range of 220-350 nm. Wide absorbance represents wide

size distribution of nanoparticles.

Wavelength(nm)

Ab

sorb

ance

Wavelength(nm)

Ab

sorb

ance

200 300 400 500 600 700 800

0

1

2

3

4

5

6

7

B

A

B

200 300 400 500 600 700 800

0

1

2

3

4

5

6

B

A

B

Figure 12-UV-Visible Spectrum of Cr2O3 NPs

Chromium oxide NPs showed exciton absorbance around 430 nm which was matched with the

literature .The second peak at around 580 nm is may be due to the presence of impurities or

transition state.

2. Conclusion

The present study shows that Nickel oxide, Zinc oxide and Chromium oxide NPs were

successfully synthesized by chemical and biological methods. The XRD study shows that the

size of zinc, nickel and chromium NPs synthesized by biological method was 47, 38 and 45 nm

respectively. The size of Biologically Synthesized nickel oxide, chromium oxide and zinc oxide

NPs was 36.6, 37.4 and 40.8 nm respectively. The SEM study shows that ZnO and Cr2O3 NPs are

hexagonal while NiO NPs have spherical morphology. The EDX shows that synthesized

nanoparticles are pure and there is only trace of impurities present in the samples. Chromium

oxide NPs have applications in the stropping knives, glasses, inks, paints and precursor to the

magnetic pigment. Nickel oxide NPs are used as catalysts, battery cathodes and gas sensors.

The ZnO is used in ceramics, glass, cement, ointments, paints and lubricants, adhesives,

plastics, pigments, batteries and fire retarders.

3- Acknowledgement

We acknowledge the provision of services of NS & TD, NCP, QAU Islamabad.

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