International Journal of the Physical Sciences Vol. 6(6), pp. 1496-1500, 18 March, 2011 Available online at http://www.academicjournals.org/IJPS DOI: 10.5897/IJPS10.260 ISSN 1992 - 1950 ©2011 Academic Journals
Full Length Research Paper
Synthesis of various nano and micro ZnSe morphologies by using hydrothermal method F. Mollaamin*, S. Gharibe, and M. Monajjemi Department of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran. Accepted 25 February, 2011
In this contribution, hydrothermal method was used to synthesize ZnSe nanostructures. Effect of different sources of Zn, Se and cetyl tri-methyl-ammonium bromide (CTAB) (cationic) surfactant on the morphology of ZnSe was studied. The prepared nanostructures were characterized using powder X-ray diffraction (XRD) and emission scanning electron microscopy (SEM). The XRD patterns showed that the ZnSe samples have a zinc blende structure. The SEM images demonstrated clearly that the ZnSe nanoparticles prepared with ZnCl2 and Zn (acetate)2.2H2O as Zn sources are in spherical and micro rod forms, respectively. Also, the results indicated that the nanoparticles prepared using CTAB surfactant with different types of sources of Zn and Se are spherical. The results demonstrated that the source of Se has no effect on the morphology of ZnSe. The size of nano particles ranging from 10 to 15 nm was estimated by Scherrer’s equation. Key words: Nanoparticles, nanosphere, hydrothermal, CTAB. INTRODUCTION In recent years, synthesis of nanostructured materials has attracted great interests. Also, these materials have been widely studied for their unique physical and chemical properties. The preparation of nanomaterials with controlled sizes, morphologies and size distribution is always potentially important in the synthesis of materials suitable for optoelectronic and luminescent applications (Yang et al., 2009; El-Zawawi and El-shabani, 2004; Jana et al., 2008; Monajjemi et al., 2008, 2009). As one of the most important II to VI group semiconductors, ZnSe with a room temperature bulk bandgap of 2.7eV, is a good candidate for short wavelength lasers and other photoelectronic devices such as blue-green diode lasers and turnable mid-IR laser sources Yang et al., 2009; Jana et al., 2008; Jiao et al., 2007; Cheng and Chen, 2009; Jiang et al., 2005). Dimensionality, size and size distribution are known to play important roles in determining the physical and
*Corresponding author. E-mail:
[email protected].
chemical properties of nanostructured materials (Monajjemi et al., 2010; Lei et al., 2008). Controlling the size distribution is difficult and this results in a broad and profoundly red shifted photoluminescence emission. Hence, there is a need for developing approaches to obtain monodispersed ZnSe nanoparticles (Deshpande et al., 2008). Various methods such as molecular beam epitaxy, metalorganic chemical vapor deposition and organometallic vapor phase epitaxy have been used to synthesize ZnSe nanoparticles (Yang et al., 2009; El-Zawawi and Elshabani, 2004; Cheng and Chen, 2009; Monajjemi et al., 2008). Recently, solvothermal method is used for the synthesizing of different nanostructures, such as nanotubes, nanorods, nanowires and nanodonuts at low temperatures (Monajjemi et al., 2010; Monajjemi et al., 2009; Tang et al., 2003). The advantage of the solvothermal process is that it can be performed at low temperatures and pressures (Monajjemi et al., 2008). However, organic solvents are usually harmful to the environment; therefore, non-toxic solvents should be used to obtain the products in a large scale. Different
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Table 1. Different steps of ZnSe samples synthesis.
1
Step 1 dissolving in 40 ml de-ionized water 5 mmol ZnCl2
Step 2 adding under sonication for 30 min 5 mmol Na2SeO3.5H2O
2
5 mmol Zn(Ac)2.2H2O
5 mmol Na2SeO3.5H2O
3 4
5 mmol ZnCl2 5 mmol Zn(Ac)2.2H2O
5 6
5 mmol ZnCl2 + 5mmol CTAB 5 mmol Zn(Ac)2.2H2O + 5 mmolCTAB
Samples
Average particle size (nm)
Lattice constant (Å)
15
5.66
-
5.66
5 mmol SeO2 5 mmol SeO2
13 -
5.65 5.66
5 mmol Na2SeO3.5H2O 5 mmol Na2SeO3.5H2O
10 13
5.64 5.65
hydrothermal processes have also been developed for the preparation of ZnSe nanostructures (Monajjemi et al., 2008). In this work, the hydrothermal synthesis of ZnSe microrods and nanospheres by changing the sources of the started materials and cetyl trimethyl-ammonium bromide (CTAB) (cationic) surfactant at 160°C is reported. The aim was to assess the effect of the source of the started materials and CTAB on the morphology of ZnSe nanostructures.
Step 3
adding 5 ml N2H4.H2O (80%) under sonication for 2 h
temperature, the resulting yellowish product was separated by centrifugation, washed with absolute ethanol and deionized water several times, and then was dried under vacuum at 60°C for 10 h. Characterization The crystal phase and particle size of the synthesized products after purification were characterized by X-ray diffraction (XRD) method using FK60-04 with Cu Kα radiation (λ= 1.540560 Å), and with instrumental setting of 35 kV and 20 mA. The morphology of the nanostructures was observed by emission scanning electron microscopy (SEM, Philips-XLφ30).
MATERIALS AND METHODS
reflections of 111, 220 and 311 were used for the determination of the size of the nanoparticles using Debye-Scherrer’s formula and the lattice constants. The average size of the nanoparticles and lattice constants are given in Table 1. It can be seen from this table that the average particle size shows a variation from 10 to 15 nm. This means that the starting material plays a major role in particle sizing. These results indicate that the lattice parameter of the nanoparticles are smaller than those of the bulk crystalline ZnSe (Table 1). It is shown that in most of the reported nanoparticles, the lattice constants often decrease with decreasing particle size (Monajjemi et al., 2008; Zhang et al., 2002; Gon et al., 2007).
All reagents were analytical grade and were purchased from Merck Company. Reagents were used without further purifications.
RESULTS AND DISCUSSION XRD analysis
Characterization of morphology
Preparation of ZnSe samples
The XRD patterns of prepared ZnSe nanostructuers are shown in Figure 1. All peaks can be well indexed to cubic zinc blend (JCPDS, No.050522, a = 5.667 Å). No other crystalline phase was found in the XRD patterns. The three strongest
The morphology of the products was observed by SEM. The SEM images of the synthesized products using ZnCl2 as source of Zn are shown in Figure 2 (a to c). These images clearly indicate that the products are spherical. It can also be
Different steps of the processes of synthesis of ZnSe samples are given in Table 1. After completion of step 3, the sample was transferred into an autoclave, sealed and kept at 160°C for 8 h. After the system was cooled to room
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Figure 1. XRD pattern of ZnSe nanostructuers; (a) sample 5, (b) sample 3, (c) sample 1, (d) sample 6, (e) sample 4, and (f) sample 2.
seen that there is a well sized distribution in all products. The grain size distribution of ZnSe prepared with Zn/Se = 1 is narrow and agrees well with the unimodal normal distribution (Zhang et al., 2002). This narrowness may also be due to the effect of sonication before transferring into autoclave. The SEM observations show that the sample prepared with CTAB surfactant (Figure 2c) is almost monodispers. This is due to coating of inorganic core by the surfactant, which prevents the nanoparticles to aggregate. It has been proven that the prevention of aggregation of nanoparticles in the presence of the surfactant is more effective when the surfactant has a long and branched chain structure (Monajjemi et al., 2010; Choy et al., 2009). The SEM images of the synthesized products
using Zn(Ac)2.2H2O as source of Zn are shown in Figure 2(d to f). Figure 2(d to e) clearly show that the prepared products without surfactant are microrod with some spherical nanoparticles. The pure microrod ZnSe may be synthesized by increasing the reaction temperature and time. The results indicate that the prepared ZnSe samples using Zn (Ac)2.2H2O as source of Zn are microrod. Also, these results demonstrate that the source of Se has no effect on the ZnSe morphology. Figure 2(f) shows that the prepared ZnSe with CTAB surfactant is spherical. Also, the results exhibit that the presence of surfactant prevents ZnSe to be formed in microrod structure. The energy dispersive X-ray (EDAX) analyses of the prepared samples confirm that the Zn and Se elemental ratio is 1:1 for all ZnSe samples. Mollaamin et al. 1499
Figure 2. SEM images of ZnSe nanostructuers; (a) sample 1, (b) sample 3, (c) sample 5, (d) sample 2, (e) sample 4, and (f) sample 6.
Conclusion ZnSe nanostructures have been synthesized using hydrothermal method. The results show that the ZnSe nanoparticles prepared with ZnCl2 and Zn(Ac)2.2H2O as Zn source are in spherical and microrod forms, respectively. The results demonstrate that the source of Se has no effect on the morphology of ZnSe. Also, it is concluded that the presence of the surfactant prevents ZnSe to the formed in microrod structure. REFERENCES
Cheng CL, Chen YF (2009) . low temperature synthesis of ZnSe nanowires by self-catalytic liquid-solid growth. Chem. phys., 115 :158-160. Choy WCH, Xiong S, Sun Y (2009). A facile synthesis of zinc blende ZnSe Nanocrystals. J. Phys. D: Appl. Phys., 42 :125410(6pp). Deshpande AC, Singh SB, Abyaneh MK, Pasricha R, Kulkarin SK (2008). Low temperature synthesis of ZnSe nanoparticles. Mate. Lett., 62 :3803-3805. El-Zawawi IK, El-shabani AM (2004). Characterization of nanostructural ZnSe prepared by inert gas condensation method. J. Solids., 27: 223-
1500
Int. J. Phys. Sci.
232. Gon H, Huang H, Wang M, Liu K (2007). Characterization and growth mechanism of ZnSe microspheres prepared by hydrothermal synthesis. Ceram. Inl., 33:1381-1384. Jana S, Baek IC, Lim MA, Seok SI (2008). ZnSe colloidal nanoparticles synthesized by solvothermal method in the presence of ZrCl4. J. Colloid Interface Sci., 322:437- 477. Jiang C, Zhang W, Zou G, Yu W, Qian Y (2005). Synthesis and characterization of ZnSe hollow nanospheres via a hydrothermal route.Nanotechnol., 16 :551-554. Jiao Y, Yu D, Wang Z, Tang K, Sun X (2007). Synthesis, nonlinear optical properties and photoluminescence of ZnSe quantum dots in stable solutions. Mate. Lett., 61:1541-1543. Lei Z, Wei X, Bi S, He R (2008). Synthesis of ZnSe nanodonuts via a surfactant-assisted process. Mater. Lett., 62 :3694-3696. Monajjemi M, Baei MT, Mollaamin F (2008). Quantum mechanic study of hydrogen chemisorptions on nanocluster vanadium surface. Russian J. Inorganic Chem., 53:1430-1437. Monajjemi M, Mahdavian L, Mollaamin F (2008). Characterization of nanocrystalline cylicon germanium film and nanotube in adsoption gas by monte carlo and langevin dynamic simulation. Bull .Chem. Soc. Ethiop., 22: 1-10.
Monajjemi M, Mahdavian L, Mollaamin F, Khaleghian M (2009). Interaction of Na, Mg, Al, Si with Carbon Nanotube (CNT): NMR and IR Study.Russian J. Inorganic Chem., 54: 1465–1473. Monajjemi M, Khaleghian M, Tadayonpour M, Mollaamin F (2010). The Effect of Different Solvents and Temperatures on Stability of SingleWalled Carbon Nanotube: A Qm/Md Study. Int. J. Nanosci., 9:517529. Tang KB, Qian YT, Zeng JH, Yang XG (2003). Solvothermal route to semiconductor nanowires. Adv. Mater., 15: 448-450. Yang J, Wang G, Liu H, Park J, Chen X (2009) .Controlled synthesis and characterization of ZnSe nanostructures via a solvothermal approach in a mixed solution. Mater. Chem. Phys., 115: 204-208. Zhang F, Chan SW, Spanier HE, Apak E, Jin Q, Robinson RD , Herman IP (2002). Cerium oxide nanoparticles: Size-selective formation and structure analysis. Appl. Phys. Lett., 80:127-129.
