Salavati Niasari, M.

Electronic Sumy State University Institutional Repository

Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              107  SYNTHESIS OF CADMIUM SULFIDE  NANOSTRUCTURES BY NOVEL PRECURSOR M. Salavati Niasari 1,2*   1 Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. Box. 87317–51167, I. R. Iran 2 Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 87317–51167, I. R. Iran  ABSTRACT A thioglycolic acid (TGA)-assisted hydrothermal process has been developed to synthesize cadmium sulfide nanostructures via the reaction between a new precursor cadmium (II) phthalate and TGA. X-ray diffraction (XRD), transmission electron mi-croscopy (TEM), photoluminescence spectroscopy (PL) and Fourier transform infrared (FT-IR) were employed to characterize the obtained product. The effect of the reactant concentration,  mole  ratio  of  TGA  to  the  Cd2+, temperature and reaction time on the morphology, size of particles and phase of nanocrystalline CdS products were investi-gated.  Key words: Chemical synthesis, CdS, Nanostructured materials, Inorganic mate-rials.  INTRODUCTION Cadmium sulfide (CdS), with a wide band gap of 2.42 eV (in bulk), is among one of the most important nano-structured semiconductors that have been widely studied due to their potential applicability in the possible applica-tion in optoelectronic devices, photocatalysis and potential applications in solar cells [1]. In 2004, Yang et al. developed a mild hydrothermal route to synthe-size metal sulfides using thioglycolic acids (TGA) as nontoxic template [2], which shows that TGA acts as the oriented growth reactant during above pro-cess. Recently, our group reported synthesis of metal sulfide nanoparticles via hydrothermal process in the presence of TGA [3–5]. In our research novel inor-ganic complex precursor, [bis(salicylaldehydato)zinc(II)], was applied for syn-thesis of ZnS nanoclusters in the presence of TGA via hydrothermal method for the first time. We found out that precursors also play an important role in con-trolling size of particles and morphology. Meanwhile a major interest is in the development of organometallic or inorganic precursors. Our strategy has been to use a thioglycolic acid as capping agent for hydrothermal synthesis of CdS nanoparticles. It still remains a great challenge in the way of developing facile                                                * e-mail: salavati@kashanu.ac.ir, tel: (+98)03615912383 fax: (+98)03615552935 108                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              and environmentally benign methods for creating CdS nanoparticles through a simple method. In this paper, we report a novel thioglycolic acid (TGA)-assisted hydrothermal method to fabricate well-crystallized CdS nanoparticles. We have presented a hydrothermal method, which is milder, simpler, more practical, and more environmental than any other methods. The trick in hydrothermal synthesis of CdS nanostructures presented here is the use of thio-glycolic acid (TGA) as sulfur source and stability agent, which was previously used as the stability agent to prevent the chalcogenide nanocrystals from aggre-gating [6]. In this method cadmium (II) phthalate was used as a new precursor. We discussed three critical factors for hydrothermal formation of the CdS na-noparticles, namely, Cd2+/TGA mole ratio, hydrothermal temperature, and reaction time. It is reasonable to believe that the TGA-assisted hydrothermal process offers great opportunities for preparation of tin chalcogenide nanostruc-tures. To the best of our knowledge, this is the first report on the synthesis of CdS nanoparticles via hydrothermal method from cadmium phthalate in the presence of TGA as sulfur source. METHODS OF SAMPLE MANUFACTURING AND ANALYSIS In a typical synthesis 10 ml of thioglycolic acid (TGA) were added into 0.6 g [Cd(Pht)(H2O)]n under stirring and heating. The precursor complexes [Cd(Pht)(H2O)]n was prepared according to the literature [7]. After 40 min the solution was stirred vigorously.   Fig. 1 – The proposed evolution process for preparation of CdS nanostructures. Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              109  The final solution was put into a Teflon-lined stainless steel autoclave un-der stirring. Then, the autoclave was maintained under a static condition at 100–160 ºC for 12–36 h and then gradually cooled down to room temperature. The mixture turned yellow due to the formation of CdS precipitates. The prod-uct was centrifuged, washed with alcohol and distilled water for several times, and dried in the air at 60 ºC for 8 h (Fig. 1). RESULTS AND DISCUSSION The XRD pattern of the synthesized product for 24 h at 100 ÛC shows that the majority of the products were poorly crystallized and diffraction pattern matched with no JCPDS card No. When the reaction temperature increases from 100 ÛC to 120 ÛC, the crystallinity of the products will improves. The X-ray powder diffraction pattern of the CdS nanoparticles showing the reflections from (100), (002) and (101) planes, which indicates the formation of a pure hexagonal phase with space group of P63mc, which is close to the values in the literature (JSPDS No.41–1049 with cell constant a = 4.1409 Å, b = 114.1409 Å, c = 6.7198 Å).  Synthesis was carried out in different experimental conditions to get the optimum condition for the formation of CdS nanostructures. In solvother-mal/hydrothermal process the decomposition of the precursors at a particular solvent depends on the temperature and pressure inside the reaction vessel. Here,  pressure  was  related  to  the  filing  fraction  of  the  solvent  and  was  kept  constant for all the experiments. Initially synthesis was performed in water with different concentrations of thioglycolic acid (TGA) using the same cadmium source. Then synthesis temperature was adjusted to achieve the favorable con-dition for the synthesis of CdS hollow spheres and subsequently the experi-ments were carried out with different reaction time of the TGA solutions. The effects of the Cd2+ to TGA mole ratio in the starting solution on the morphology and shape of CdS powders are shown in Fig. 2. In a series of ex-periments, the temperature was kept at 120 °C and the reaction time was 24 h. Fig. 2 shows the powder SEM and TEM images of the resultant products ob-tained with TGA: Cd2+ (1:1 to 3:1) at 120 ÛC for 24 h. With the raising mole ratio, TGA: Cd2+, from 1:1 to 3:1, morphologies of the as-synthesized CdS products change. When synthesis was performed with the mole ratio of TGA/ Cd2+ was 1:1, quasi naospheres were formed (Fig. 2a). The typical TEM image of the CdS nanoparticles prepared with TGA: Cd2+, from 1:1 at 120 ºC for 24 h is indicated in Fig. 2b. CdS nanoparticles with 40–50 nm diameters are shown in Fig. 2b. Upon increasing the TGA: Cd2+ mole ratio to 2, hollow sphere was produced (Fig. 2c). This data indicates that how reactant concentration could change the morphology of the product. Increasing the molar ratio to 3:1 hollow spheres, including some of nanoparticles were observed (not shown here).  110                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I               Fig. 2 – SEM and TEM images of the as-synthesized product at 120 °C for 24 h at dif-ferent concentration of TGA: (a, b) 0.04 M and (c, d) 0.08 M.  To further probe the effect of growth conditions has been hanged the syn-thesis temperature with constant TGA/Cd2+ mole ratio, i.e. 2:1. The SEM image in Fig. 3a shows that CdS powders obtained with TGA (0.08 M) for 24 h at 100 ºC consist of irregular nanoparticles, whereas the product obtained at 120 ºC for 24 h possesses CdS hollow-sphere based nanoparticles as shown in Fig. 4c.     Fig. 3 – SEM images of as-synthesized CdS with TGA (0.08 M) for 24 h at: (a) 100 °C, (b) 140 °C and (c) 160 °C  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              111  As shown in Fig. 3b one can see that by increasing the reaction tempera-ture to 140 ºC, CdS hollow sphere was observed. It is noticeable that these hollow spheres were stable at 140 ºC. Upon raising the temperature to 160 ºC, all of the CdS hollow-sphere based nanoparticles collapsed and irregular nano-particles were obtained (Fig. 3c). This occurs at higher reaction temperatures, TGA decomposed faster and thus the nanocrystallites grew at a relatively high-er rate to larger sizes. The photoluminescence spectrum of the CdS samples obtained at 120 ºC at different TGA concentration: (a) 0.04 M and (b) 0.08 M, show an emission maximum at 594 nm and 580 nm (Ȝexc = 392 nm). It presents some blue-shift compared to bulk CdS at 650nm, which are consistent with the result of above UV–vis absorption spectrum. Previous reports suggest that the emission arises from the recombination of an electron trapped in a sulfur vacancy with a hole in the valence band of CdS [8]. As the crystallite size decreases, intensity of emis-sion peak increases and the peak shifts to higher frequencies that indicates the quantum confinement effect. CONCLUSIONS CdS nanostructures have been successfully synthesized through a thiogly-colic acid-assisted hydrothermal processing using a new precursor [Cd(pht)(H2O)]n; as the source of Cd2+and thioglycolic acid (TGA) as sulfiding reagent. The possible growth mechanism of formation of the CdS nanosructures was discussed and the effects of TGA concentration, reaction time and reaction temperature on morphology and phase were proposed. We believe that this synthesis process can be extended to become a general method for the prepara-tion of other novel structure function materials.  Acknowledgements Authors  are  grateful  to  the  council  of  university  of  Kashan for  their  un-ending effort to provide financial support to undertake this work. REFERENCES [1] X.He, L.Gao, Mater. Lett. 2009, 63, P. 995–997. [2] H.Zhang, D.Yang, S.Li, et al. Nanotechnology 2004, 15, P. 1122–1125. [3] M.Salavati-Niasari, D.Ghanbari, F.Davar, J. Alloys Compd. 2009, 488, P. 442–447. [4] M. Salavati-Niasari, M.R. Loghman-Estarki, F. Davar, J. Alloys Compd. 2009, 475, P. 782–788. [5] M. Salavati-Niasari, F. Davar, M.R. Loghman-Estarki, J. Alloys Compd. 2010, 494, P. 199–204. [6] M. Gao, S. Kirstein, H. Mohwald, J. Phys. Chem. B 1998, 102, P. 8360–8363. [7] M. Salavati-Niasari, F. Mohandes, F. Davar, K. Saberyan, Appl. Surface Sci. 2009, 256, P. 1476–1480. [8] P.S. Nair, T. Radhakrishnan, N. Revaprasadu, G.A. Kolawole, P. O’Brien, Polyhe-dron 2003, 22, P. 3129–3135.   

Synthesis of cadmium sulfide nanostructures by novel precursor

SocioEconomic Challenges Journal (Sumy State University)

Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              107 
 
SYNTHESIS OF CADMIUM SULFIDE  
NANOSTRUCTURES BY NOVEL PRECURSOR 
M. Salavati Niasari 1,2*  
 
1 Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. 
Box. 87317–51167, I. R. Iran 
2 Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 
87317–51167, I. R. Iran 
 
ABSTRACT 
A thioglycolic acid (TGA)-assisted hydrothermal process has been developed to 
synthesize cadmium sulfide nanostructures via the reaction between a new precursor 
cadmium (II) phthalate and TGA. X-ray diffraction (XRD), transmission electron mi-
croscopy (TEM), photoluminescence spectroscopy (PL) and Fourier transform infrared 
(FT-IR) were employed to characterize the obtained product. The effect of the reactant 
concentration,  mole  ratio  of  TGA  to  the  Cd2+, temperature and reaction time on the 
morphology, size of particles and phase of nanocrystalline CdS products were investi-
gated. 
 
Key words: Chemical synthesis, CdS, Nanostructured materials, Inorganic mate-
rials. 
 
INTRODUCTION 
Cadmium sulfide (CdS), with a wide band gap of 2.42 eV (in bulk), is 
among one of the most important nano-structured semiconductors that have 
been widely studied due to their potential applicability in the possible applica-
tion in optoelectronic devices, photocatalysis and potential applications in solar 
cells [1]. In 2004, Yang et al. developed a mild hydrothermal route to synthe-
size metal sulfides using thioglycolic acids (TGA) as nontoxic template [2], 
which shows that TGA acts as the oriented growth reactant during above pro-
cess. Recently, our group reported synthesis of metal sulfide nanoparticles via 
hydrothermal process in the presence of TGA [3–5]. In our research novel inor-
ganic complex precursor, [bis(salicylaldehydato)zinc(II)], was applied for syn-
thesis of ZnS nanoclusters in the presence of TGA via hydrothermal method for 
the first time. We found out that precursors also play an important role in con-
trolling size of particles and morphology. Meanwhile a major interest is in the 
development of organometallic or inorganic precursors. Our strategy has been 
to use a thioglycolic acid as capping agent for hydrothermal synthesis of CdS 
nanoparticles. It still remains a great challenge in the way of developing facile 
                                               
* e-mail: salavati@kashanu.ac.ir, tel: (+98)03615912383 fax: (+98)03615552935 
108                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I             
 
and environmentally benign methods for creating CdS nanoparticles through a 
simple method. In this paper, we report a novel thioglycolic acid (TGA)-
assisted hydrothermal method to fabricate well-crystallized CdS nanoparticles. 
We have presented a hydrothermal method, which is milder, simpler, 
more practical, and more environmental than any other methods. The trick in 
hydrothermal synthesis of CdS nanostructures presented here is the use of thio-
glycolic acid (TGA) as sulfur source and stability agent, which was previously 
used as the stability agent to prevent the chalcogenide nanocrystals from aggre-
gating [6]. In this method cadmium (II) phthalate was used as a new precursor. 
We discussed three critical factors for hydrothermal formation of the CdS na-
noparticles, namely, Cd2+/TGA mole ratio, hydrothermal temperature, and 
reaction time. It is reasonable to believe that the TGA-assisted hydrothermal 
process offers great opportunities for preparation of tin chalcogenide nanostruc-
tures. To the best of our knowledge, this is the first report on the synthesis of 
CdS nanoparticles via hydrothermal method from cadmium phthalate in the 
presence of TGA as sulfur source. 
METHODS OF SAMPLE MANUFACTURING AND ANALYSIS 
In a typical synthesis 10 ml of thioglycolic acid (TGA) were added into 
0.6 g [Cd(Pht)(H2O)]n under stirring and heating. The precursor complexes 
[Cd(Pht)(H2O)]n was prepared according to the literature [7]. After 40 min the 
solution was stirred vigorously.  
 
Fig. 1 – The proposed evolution process for preparation of CdS nanostructures. 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              109 
 
The final solution was put into a Teflon-lined stainless steel autoclave un-
der stirring. Then, the autoclave was maintained under a static condition at 
100–160 ºC for 12–36 h and then gradually cooled down to room temperature. 
The mixture turned yellow due to the formation of CdS precipitates. The prod-
uct was centrifuged, washed with alcohol and distilled water for several times, 
and dried in the air at 60 ºC for 8 h (Fig. 1). 
RESULTS AND DISCUSSION 
The XRD pattern of the synthesized product for 24 h at 100 ?C shows that 
the majority of the products were poorly crystallized and diffraction pattern 
matched with no JCPDS card No. When the reaction temperature increases 
from 100 ?C to 120 ?C, the crystallinity of the products will improves. The X-
ray powder diffraction pattern of the CdS nanoparticles showing the reflections 
from (100), (002) and (101) planes, which indicates the formation of a pure 
hexagonal phase with space group of P63mc, which is close to the values in the 
literature (JSPDS No.41–1049 with cell constant a = 4.1409 Å, b = 114.1409 
Å, c = 6.7198 Å).  
Synthesis was carried out in different experimental conditions to get the 
optimum condition for the formation of CdS nanostructures. In solvother-
mal/hydrothermal process the decomposition of the precursors at a particular 
solvent depends on the temperature and pressure inside the reaction vessel. 
Here,  pressure  was  related  to  the  filing  fraction  of  the  solvent  and  was  kept  
constant for all the experiments. Initially synthesis was performed in water with 
different concentrations of thioglycolic acid (TGA) using the same cadmium 
source. Then synthesis temperature was adjusted to achieve the favorable con-
dition for the synthesis of CdS hollow spheres and subsequently the experi-
ments were carried out with different reaction time of the TGA solutions. 
The effects of the Cd2+ to TGA mole ratio in the starting solution on the 
morphology and shape of CdS powders are shown in Fig. 2. In a series of ex-
periments, the temperature was kept at 120 °C and the reaction time was 24 h. 
Fig. 2 shows the powder SEM and TEM images of the resultant products ob-
tained with TGA: Cd2+ (1:1 to 3:1) at 120 ?C for 24 h. With the raising mole 
ratio, TGA: Cd2+, from 1:1 to 3:1, morphologies of the as-synthesized CdS 
products change. When synthesis was performed with the mole ratio of TGA/ 
Cd2+ was 1:1, quasi naospheres were formed (Fig. 2a). The typical TEM image 
of the CdS nanoparticles prepared with TGA: Cd2+, from 1:1 at 120 ºC for 24 h 
is indicated in Fig. 2b. CdS nanoparticles with 40–50 nm diameters are shown 
in Fig. 2b. Upon increasing the TGA: Cd2+ mole ratio to 2, hollow sphere was 
produced (Fig. 2c). This data indicates that how reactant concentration could 
change the morphology of the product. Increasing the molar ratio to 3:1 hollow 
spheres, including some of nanoparticles were observed (not shown here).  
110                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I             
 
 
Fig. 2 – SEM and TEM images of the as-synthesized product at 120 °C for 24 h at dif-
ferent concentration of TGA: (a, b) 0.04 M and (c, d) 0.08 M. 
 
To further probe the effect of growth conditions has been hanged the syn-
thesis temperature with constant TGA/Cd2+ mole ratio, i.e. 2:1. The SEM image 
in Fig. 3a shows that CdS powders obtained with TGA (0.08 M) for 24 h at 100 
ºC consist of irregular nanoparticles, whereas the product obtained at 120 ºC for 
24 h possesses CdS hollow-sphere based nanoparticles as shown in Fig. 4c.  
  
 
Fig. 3 – SEM images of as-synthesized 
CdS with TGA (0.08 M) for 24 h at: (a) 
100 °C, (b) 140 °C and (c) 160 °C 
 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              111 
 
As shown in Fig. 3b one can see that by increasing the reaction tempera-
ture to 140 ºC, CdS hollow sphere was observed. It is noticeable that these 
hollow spheres were stable at 140 ºC. Upon raising the temperature to 160 ºC, 
all of the CdS hollow-sphere based nanoparticles collapsed and irregular nano-
particles were obtained (Fig. 3c). This occurs at higher reaction temperatures, 
TGA decomposed faster and thus the nanocrystallites grew at a relatively high-
er rate to larger sizes. 
The photoluminescence spectrum of the CdS samples obtained at 120 ºC 
at different TGA concentration: (a) 0.04 M and (b) 0.08 M, show an emission 
maximum at 594 nm and 580 nm (?exc = 392 nm). It presents some blue-shift 
compared to bulk CdS at 650nm, which are consistent with the result of above 
UV–vis absorption spectrum. Previous reports suggest that the emission arises 
from the recombination of an electron trapped in a sulfur vacancy with a hole in 
the valence band of CdS [8]. As the crystallite size decreases, intensity of emis-
sion peak increases and the peak shifts to higher frequencies that indicates the 
quantum confinement effect. 
CONCLUSIONS 
CdS nanostructures have been successfully synthesized through a thiogly-
colic acid-assisted hydrothermal processing using a new precursor 
[Cd(pht)(H2O)]n; as the source of Cd2+and thioglycolic acid (TGA) as sulfiding 
reagent. The possible growth mechanism of formation of the CdS nanosructures 
was discussed and the effects of TGA concentration, reaction time and reaction 
temperature on morphology and phase were proposed. We believe that this 
synthesis process can be extended to become a general method for the prepara-
tion of other novel structure function materials. 
 
Acknowledgements 
Authors  are  grateful  to  the  council  of  university  of  Kashan for  their  un-
ending effort to provide financial support to undertake this work. 
REFERENCES 
[1] X.He, L.Gao, Mater. Lett. 2009, 63, P. 995–997. 
[2] H.Zhang, D.Yang, S.Li, et al. Nanotechnology 2004, 15, P. 1122–1125. 
[3] M.Salavati-Niasari, D.Ghanbari, F.Davar, J. Alloys Compd. 2009, 488, P. 442–447. 
[4] M. Salavati-Niasari, M.R. Loghman-Estarki, F. Davar, J. Alloys Compd. 2009, 475, 
P. 782–788. 
[5] M. Salavati-Niasari, F. Davar, M.R. Loghman-Estarki, J. Alloys Compd. 2010, 494, 
P. 199–204. 
[6] M. Gao, S. Kirstein, H. Mohwald, J. Phys. Chem. B 1998, 102, P. 8360–8363. 
[7] M. Salavati-Niasari, F. Mohandes, F. Davar, K. Saberyan, Appl. Surface Sci. 2009, 
256, P. 1476–1480. 
[8] P.S. Nair, T. Radhakrishnan, N. Revaprasadu, G.A. Kolawole, P. O’Brien, Polyhe-
dron 2003, 22, P. 3129–3135. 
  


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Synthesis of cadmium sulfide nanostructures by novel precursor

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SocioEconomic Challenges Journal (Sumy State University)