ISSN 2279 0381

Influence of NaOH on structural, morphological and bandgap analysis of CdS Nanoparticles

Sakthivishnu R*.,Nithya R., Alagappan M., Meenakshi Sundaram N.

Department of Biomedical Engineering, PSG College of Technology, Coimbatore-641004, India.

*sakthirangaswamy@gmail.com

http://www.indiasciencetech.com/index.php/nanotechnology

Keywords: Cadmium Sulfide, NaOH, Molar concentration, Particle size, Bandgap.

Abstract.Cadmium sulfide (CdS) nanoparticles

plays a pivotal role in photovoltaics, sensors and

detectors. The present work is on preparation of

monodisperse CdS nanoparticles by using

cadmium iodide and sodium sulfide as a

precursor, where sodium hydroxide (NaOH) acts

as a capping agent in methanol solvent. Synthesis

of CdS nanoparticles was carried out with

different molar concentrations of NaOH. The

particle sizes were calculated from Brus equation

by using UV-Visible absorption spectrum. The

functional groups of the samples and morphology

were studied by FTIR and HRTEM respectively.

Introduction

Nanometer sized semiconductor CdS

nanoparticles belonging to II-VI group have lot of

research progress in various fields. Depending on

the physical and chemical properties with respect

to size has possible applications in the areas of

optoelectronics including solar cells, LED, photo

diodes, quantum confined materials, photonics,

sensors and detectors. CdS is commonly studied

semiconductor with a bulk phase bandgap of

2.43eV [1]. It has been synthesized by variety of

methods including solvothermal reaction,

Chemical bath deposition, thermal evaporation,

microwave irradiation etc [2]. In the present work

we have synthesized CdS nanoparticles by

precipitation method by varing the concentration

of sodium hydroxide.

Experimental method

Powder preparation. The CdS nanoparticles

was synthesized from Cadmium Iodide (99%),

Sodium Sulfide (Extra pure) as precursors

material purchased from Loba Chemie Ltd.

Different concentration of 0.05M, 0.1M and 1M,

Sodium Hydroxide (NaOH) capping agent was

used for synthesizing CdS nanoparticles at

different nanometer ranges. Initially, 2.5ml of

methanol was added to above different

concentration NaOH solutions and ultrasonicated

for 1hr. Sodium sulphide (Na2S) of 1M solution

was then added slowly to the sonicated sample

under constant stirring at room temperature [3].

Finally Cadmium Iodide (CdI2) of 1M was added

in drops to the above solution. Preliminary

conformation of CdS nanoparticles was due to the

formation of precipitate in yellow to orange colors.

The precipitate is filtered and dried at 80C for

30mins to remove methanol and moisture from

the sample. Dried powder is then grinded using

mortar and pestle for characterizing it in UV-Vis,

FTIR and HRTEM.

Characterization

UV-Visible spectrometry (Agilent technologies)

study was used to examine the material band gap

and absorption spectra of CdS nanoparticles.

Morphology of the nanoparticles were studied in

HRTEM (JEOL, JEM2100). Vibrational analysis

of nanoparticles was studied using FTIR

spectrometer (Agilent technologies).

Results and discussion

UV Visible absorption spectra of CdS.

Optical property of semiconductor nanoparticlesis

efficiently determined by UV-Visible

Spectrophotometer. In the figure 1 and 2 a UV

spectrum which has well defined spectrum is

absorbed between 220230nm. According to Brus

equation when the wavelength of the particle get

reduced more of quantum confinement occurs in

the CdS nanoparticles. Sharp absorption at

226.4nm confirms the quantum confinement of

direct band gap material (CdS) particle at

nanometer range.

Band gap of the nanoparticles is calculated

using the Eq.1 and size of the particle can be

calculated using the Brus equation as give in

Eq.2.

Journal of NanoScience and NanoTechnology | Vol 1 | Issue 1 | Autumn Edition| ISSN 2279 0381

/* chE = ..1 [4]

h = Planks constant (6.626*10-34 Joules sec)

C = Speed of light ( 3.0*108 meter/sec)

= cut off wavelength (252.3*10-9 meters)

200 225 250 275 300 325 350

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5 227.09

Ab

s

Wavelength (nm)

CdS 0.5M NaOH

CdS 0.1M NaOH

CdS 1M NaOH

CdS 0M NaOH

Figure 1. UV-Visible Spectrum of CdS

nanoparticles synthesized with 0M, 1M,

0.1M, 0.05M NaOH.

200 225 250 275 300 325 350

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

226.41

226.41

Ab

s

Wavelenght (nm)

CdS 1M NaOH

CdS 0M NaOH

Figure 2. UV-Visible Spectrum of CdS

nanoparticles synthesized with 0M and

1M NaOH.

Calculated bandgap of CdS nanoparticleswhich

has the cutoff wavelength at 252.3nm as shown in

the figure.3 was 4.9 eV.

1

2 2 2 4*

2 * * 2 2 * *

0 0

1 1 1.8 0.124 1 1

2 4 (4 )

bulk

g g

e h e h

h e eE E

r m m r h m m

= + + + .eV

2 [5]

= band gap energy of the nanoparticles, which

will be determined from the UV-Visible

absorbance spectrvum

= band gap energy of the bulk CdS at room

temperature, which has the value

of 3.88*10-19 J.

Figure 3. Cutoff wavelength for bandgap

calculation.

= Plancks Constant, 6.625*10-34 J.s.

r = particle radius (m)

= mass of a free electron, 9.11x10-31 Kg

= 0.19 (effective mass of a conduction band

electron in CdS)

= 0.80 (effective mass of a valence band

hole in CdS)

e = elementary charge, 1.602*10-19 C.

0 = 8.854*10-12 C2N*-1m-2. (permittivity of free

space) = 5.7 (relative permittivity of CdS).

Using the above eq.2 the particle size was

calculated as 2.1 nm. Theoritical calculation was

correlated with the result of HRTEM, as show in

figure 5 the particle size calculated is in the range

of 3 to 6 nm.

Fourier Transform Infrared Spectroscopy

(FTIR).

The elemental chemical analysis of the

synthesized CdS powders is analyzed by FTIR

spectrophotometer. The measurements have been

done in the range of 500 cm-1 to 4000 cm-1. The

vibrational assignment of CdS nanoparticles has

been provided in Table 1 for the result shown in

the figure 4. Analyzing the FTIR spectra of CdS

nanoparticles, prepared with NaOH agent and

without NaOH agent were almost similar there is

negligible shifting in absorption peaks of all

spectra.

The absorption bands at 3608 cm-1 is assigned

to O-H stretching vibration of water molecules,

due to presence of moisture in the sample. CdS

nanoparticles showed two stretching bands,

asymmetric and symmetric, around 2910 cm-1 and

2899 cm-1 are associated with C-H stretching. C-C

stretching bending vibrations of water molecules

appeared at 1597 cm-1. Stretching vibrations of

sulphate group are found in the range of 1370 cm-1

1386 cm-1.

Journal of NanoScience and NanoTechnology | Vol 1 | Issue 1 | Autumn Edition| ISSN 2279 0381

4000 3500 3000 2500 2000 1500 1000 500

10

20

30

40

50

60

291

0291

7

1597

1620

13

70

1385

1109

1093

651

665

3608

36

05

% T

ran

sm

itta

nce

Wave number (cm-1)

CdS 1M Capping

CdS 0M Capping

Figure 4. FTIR of CdS Nanoparticles.

Traces of SO4- ion as impurity is seen as there

are small absorptions appears in the range of

1089 cm-1 - 1150 cm-1. There are medium to strong

absorption bands at 665 cm-1 and 665 cm-1,

possibly due to Cd-S stretching. Hence the

existences of above mentioned bands identify the

presence of CdS and also the impurities that the

samples consisted of water molecules or hydroxide

ions.

Table 1: Vibrational assignment of CdS

nanoparticles [1]

S.No Wave number

(cm-1)

Assignment

1. 3600-3610 O-H stretching

2. 2853.4-2922 C-H stretching

3.

1580-1625 C-C stretching,

bending vibration of

H2O

4. 1375-1460 S=O

5. 1089-1150 SO4- as traces

6. 611-723 Cd-S stretching

High Resolution Transmission Electron

Microscope (HRTEM).

A JEM2100 microscope operating at 120 kV

was employed to study the morphologies of the

prepared samples. The sample for TEM was

prepared by dispersing a small amount of the

sample in ethanol and sonication for 30 minutes.

A few drops of the resultant suspension were

dropped on to a copper grid. The results from

EDAX coupled TEM shows that the obtained

samples have spherical nanoparticles in the range

of 2 to 7 nm as in figure 5. Figure 6 shows

Selected Area Diffraction (SAD) pattern that the

prepared nanoparticles are polycrystalline and the

Energy Dispersive X-ray Analysis (EDAX)

confirms the presence of cadmium and sulfide

particles from the figure 7.

Figure 5: TEM of CdS (0M capping) Nanoparticle.

Figure 6: Selected area diffraction of CdS

Nanoparticle

Figure 7: EDAX of CdS Nanoparticle

Conclusion

A simple and optimistic method were developed

to synthesis 2-7 nm size CdS nanoparticles. The

bandgap of CdS nanoparticle were calculated to be

4.9 eV which is more intesting and has wide

application in the field of semiconductor

Journal of NanoScience and NanoTechnology | Vol 1 | Issue 1 | Autumn Edition| ISSN 2279 0381

22 |www.indiasciencetech.com

technology. The particle size were calculated by

Brus Quantum confinement relation and

compared with HRTEM. The size of synthesised

CdS nanoparticles is directly proprotional to the

NaOH concentration. Theoritically calculated

value is been correlated to the result obtained

from the HRTEM.

References

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Salamat Ali, Fabrication and Characterization of

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Characterization of chemically synthesized CdS

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[3] Dumbrava, Badea C, Prodana G, Ciupina V,

Synthesis and characterization of cadmium sulfide

obtained at room temperature, Chalcogenide

Letters, vol. 7, no. 2, (2010), 111 118.

[4] Bansal P, Jaggi N, Rohilla S K, Green Synthesis

of CdS nanoparticles and effect of capping agent

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[5] Manickathai K, Kasi Viswanathan S, Alagar M,

Synthesis and characterization of CdO and CdS

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