- Email: [email protected]
Influence of solvents on the morphological properties of AgBr nano-structures prepared using ultrasound irradiation
Ultrasonics Sonochemistry 19 (2012) 540–545
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultsonch
Influence of solvents on the morphological properties of AgBr nano-structures prepared using ultrasound irradiation Amir Reza Abbasi, Ali Morsali ⇑ Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Islamic Republic of Iran
a r t i c l e
i n f o
Article history: Received 21 December 2010 Received in revised form 9 August 2011 Accepted 9 August 2011 Available online 25 August 2011 Keywords: Silver bromide Spongy Nano-structures Ultrasound Nanoparticle
a b s t r a c t Nano-structures of AgBr have been prepared by reaction between AgNO3 and KBr under ultrasound irradiation. Particle sizes and morphology of nanoparticle are depending on temperature, power of sonicating, reaction time and concentration. The effects of these parameters in growth and morphology of the nano-structures have been studied. Results suggest that an increasing of temperature, sonication power and concentration led to a decreasing of particle size. The samples were characterized with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In the recent years the preparation and application of nanometer size materials have been had a major interest since they exhibit special properties in the industry [1]. Inorganic materials have broad application in materials chemistry and it is well documented that the properties of inorganic nano-materials depend strongly on their size and morphologies. Thus, the design and controlled synthesis of nano-structures with different size and morphology is very important from the viewpoint of both basic science and technology [2–5]. Silver bromide is an important material used in medicine, antibacterial [6], electronic, magnetic, optical, catalytic properties [7] for a variety of metals and semiconductors. Many technologies have been explored to fabricate silver halides nanostructures. These technical approaches can be grouped in several ways. One way is to group the techniques according to the form of products: electrospinning method [8], template synthesized [9], microemulsion method [10,11], reverse micelles [2], laserbased synthesis [7], host–guest nanocomposite material [12], ultrasonic spray pyrolysis [13]. The manufacturing of high valueadded products such as smart medical and protective textiles has increased rapidly in the last several years. Sonochemistry is the research area in which molecules undergo a chemical reaction due to the application of powerful ultrasound radiation [14,15]. The efficiency of heterogeneous reactions involving solids dispersed in liquids will depend upon the available ⇑ Corresponding author. Tel.: +98 21 82884416; fax: +98 21 88009730. E-mail address: [email protected] (A. Morsali). 1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2011.08.002
reactive surface area and mass transfer. The ultrasonicallyenhanced mass transport is thought to be due to two transient processes: (1) Bubble collapse at or near the solid–liquid interface with microjetting directed towards the surface, (2) Bubble motion near or within the diffusion layer of the surface. From an inorganic chemistry point of view, most of the effects of interest regarding ultrasonication are related to cavitation. Cavitation causes solute thermolysis along with the formation along with the formation of highly reactive radicals and reagents [16]. In addition, if a solid is present in solution, the sample size of the particles is diminished by solid disruption, thereby increasing the total solid surface in contact with the solvent [17]. The effects of ultrasound radiation on chemical reactions were reported in the recent works [18]. In this paper, we have developed a simple sonochemical to prepare nano-structures of AgBr. The concentration of initial precursors, sonicating time, the temperature of reaction were the parameters which were changed for reaching the optimized condition. For the characterization of the products, scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) were used. 2. Experimental 2.1. Materials All reagents and solvents were used as supplied by Merck chemical company and used without further purification. Powder X-ray diffraction (XRD) was carried out on a Philips diffractometer of X’pert Company with mono chromatized Co Ka radiation. The samples were characterized with a scanning electron microscope
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(SEM) (Philips XL 30 and S-4160) with gold coating. Ultrasonic generator was carried out on a SONICA-2200 EP, input: 50–60 Hz/ 305 W and TECNO-GAZ, S.P.A., Tecna 6, input: 50–60 Hz/138 W. 2.2. Sample preparation In this paper, nano-structures of AgBr were prepared by reaction between AgNO3 and KBr precursors with the molar ratio of 1:1 under ultrasound irradiation. AgNO3 and KBr separately dissolved in ethanol and water. The KBr solution was added drop-wise to the AgNO3 solution under ultrasound irradiation. The sonochemical reactions were carried in sonochemical bath as shown in Fig. 1. The blank reaction (sample III-5) was performed without ultrasound irradiation. The nano-structures of AgBr were prepared in different solvents among which methanol, ethanol, n-propanol, 2-propanol, tert-butanol, n-butanol, ethanolamine, 2-amino-1butanol and ethylene glycol (samples I–IX). Synthesis of silver bromide powders was performed using a sonicator bath operated under continuous mode. In this method 0.05 M KBr solution of methanol and water (1:1 v/v) was added drop-wise to a 0.05 M AgNO3 solution of methanol and water (1:1 v/v) in a 100-mL sonication flask. In this method sonication was carried out for 35 min continuously. During sonication, the temperature of the bath was maintained around 30 °C. The powder formed was washed thoroughly (two times) with distilled water and ethanol by centrifugation with 6000 rpm. At the end of the sonication process, the resulting powder was dried at 50 °C. This protocol was repeated for the other samples (II–IX). The influences of various solvents on the size and size distribution of AgBr are summarized in Table 1. 3. Results and discussion It was found that the solvents have noticeable influences on the size of the products. For example, for the synthesis of AgBr in the above solvents, the particle size increases in the following order: methanol < n-butanol < ethanol < n-propanol < ethanolamine < tert-butanol < 2-amino-1-butanol < ethylene glycol < 2propanol. Also, results show that the solvents have a noticeable influence on the morphology of the products. Fig. 2 shows scanning electron microscope (SEM) of AgBr nano-structures prepared with I–IX as solvents, respectively, under otherwise similar synthesis conditions. AgBr particles with spongy nanoparticles were obtained using I–V as solvents, whereas nano and micro AgBr
Table 1 The influences of various solvents on the size of AgBr nanoparticle. Samples
Reagents
Average diameter (nm)
Morphology
I II III IV V VI VII VIII IX
Methanol Ethanol n-Propanol 2-Propanol tert-Butanol n-Butanol Ethanolamine 2-Amino-1-butanol Ethylene glycol
58 90 100 695 300 73 151 420 551
Spongy Spongy Particle Spongy Spongy Particle Particle Particle Particle
particles were formed when IV–IX were used as solvents. It can be seen that the particle size decreases with increasing chain length for primary and secondary alcohols [19]. Such an influence may be explained by the fact that stronger reduction reagent would generate an abrupt surge of the concentration of growth species, resulting in a very high supersaturation. Consequently, a large number of initial nuclei would form [20,21]. For a given concentration of metal precursors, the formation of a larger number of nuclei would result in a smaller size of the grown nanoparticles. 3.1. Temperature effect Particle sizes and morphology of nanoparticle are depending on temperature [22]. An increasing of temperature results in an increasing of solubility. As a result, nuclei of large size may become unstable and dissolve back into the solution. Thus, an increasing of temperature led to a decreasing of particle size. Table 2, Figs. 2 and 3 show the average diameter and scanning electron micrographs (SEM) of the prepared samples (samples III-1, III-2 and III-3). Silver bromide nanoparticles with spongy shape were obtained at 60 °C, whereas spherical shape silver bromide particles were formed for low temperature reactions. 3.2. Sonication power In order to investigate the role of power ultrasound irradiation on the nature of products, reactions were performed under different power ultrasound irradiation. Ultrasonic generator was carried out on a SONICA-2200 EP and TECNO-GAZ, S.P.A., Tecna 6. Reaction of sample III-4 was performed by TECNO-GAZ S.P.A. Tecna 6 (input power and frequency of 138 W and 60 Hz) and the other reactions were prepared in an ultrasonic bath with an input power and frequency of 305 W and 60 Hz respectively (SONICA-2200 EP). Results show a decrease in the particles size as increasing power ultrasound irradiation [22,23]. Comparison between the samples with similar conditions and different power ultrasound irradiation shows that high power ultrasound irradiation decreased agglomeration, and thus particles size of sample III-2, 106 nm (Fig. 2) is smaller than particles size of sample III-4, 165 nm (Fig. 4). 3.3. Ultrasound effects
Fig. 1. Schematics of the experimental setup used for the sonochemical reactions: (a) double jacketed vessel, (b) ultrasound bath, (c) water circulation, (d) electrical mixer, (e) thermometer.
For the sake of investigating the role of sonicating, sample III-5 (as blank reaction) was performed without ultrasound irradiation. Results show that the average particle size for sample III-5 is around 197 nm (Fig. 5). The average particle size for ultrasound method in similar conditions (sample III-2) is around 106 nm. The sonochemical irradiation of a liquid causes two primary effects, namely, cavitations (bubble formation, growth, collapse) and heating. When the microscopic cavitations bubbles collapse near the surface of the solid substrate, they generate powerful shock waves and microjets that cause effective stirring/mixing of
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Fig. 2. The SEM photographs of the AgBr obtained at the various solvents (methanol: I, ethanol: II, n-propanol: III, 2-propanol: IV, tert-butanol: V, n-butanol: VI, VII, ethanolamine, 2-amino-1-butanol: VIII and ethylene glycol: IX).
the adjusted layer of liquid. The after-effects of the cavitations are several hundred times greater in heterogeneous systems than in
homogeneous systems [24]. In our case, the ultrasonic waves promote the fast migration of the newly-formed nanoparticles to the
A.R. Abbasi, A. Morsali / Ultrasonics Sonochemistry 19 (2012) 540–545
543
Table 2 The influences of temperature, reaction time and sonication power on the size of AgBr nanoparticle.
a b c
Samples
T (°C)a
t (min)b
Sonication (input power) (W)
SEMc
III-1 III-2 (=III) III-3 III-4 III-5 III-6 III-7 III-8
5 30 60 30 30 30 5 60
35 35 35 35 35 35 70 70
305 305 305 138 0 305 305 305
148 100 63 165 197 256 188 398
Reaction temperature. Reaction time. Average diameter (nm).
Fig. 4. SEM photographs of sample III-4 (138 W).
Fig. 5. SEM images of sample III-5 without ultrasound irradiation.
Fig. 3. SEM photographs of samples III-1 and III-3 at 5 and 60 °C.
fabric’s surface. There is reliable evidence that applying ultrasound not only induces nucleation, but also increases reproducibility. Another effect of ultrasound on nucleation is shortening the induction time between the establishment of supersaturation and the onset of nucleation and crystallization. The cavitation events allow the excitation energy barriers associated with nucleation to be surmounted, in which case it should be possible to correlate the number of cavitation and nucleation events in a quantitative way [25]. It has been suggested that nucleation caused by scratching the walls of a vessel containing a supersaturated solution with a glass rod spatula could be the result of cavitation [26,27]. Results show
Fig. 6. SEM photographs of sample III-6.
that in present of ultrasound radiation, particle sizes are in a very low range. This finding has already been observed in other studies on ultrasound-assisted synthesis of nano-particles [28].
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Fig. 8. XRD pattern of sample III-2.
at half maximum of an observed peak, respectively [30], the average size of the crystals of sample III-2 was 92 nm. The four major peaks found at 36.11°, 51.98°, 64.90° and 76.55° on the 2 theta scale correspond respectively to the (2 0 0), (2 2 0), (2 2 2) and (4 0 0) crystal planes [30].
4. Conclusion
Fig. 7. SEM photographs of samples for 35 and 70 min.
In summary, nano-structures of AgBr have been prepared by reaction between AgNO3 and KBr under ultrasound irradiation. Influences of temperature, power of sonicating, reaction time and concentration on the morphological properties of AgBr were studied. These parameters have noticeable influences on the morphology of the silver bromide nanoparticles. To verify the crystalline nature of the product, the XRD patterns of the resulting product were investigated. From XRD, it is clearly confirmed that the AgBr particles were successfully prepared by the ultrasound irradiation method. These systems depicted a decrease in the particles size accompanying an increase in the temperature, reaction time and sonication power. As a result, an increase in concentration led to decrease of particle size.
3.4. Concentration and reaction time effects
Acknowledgements
Comparison between the samples III-2 (III) (0.05 M of raw reagents) and III-6 (0.025 M of raw reagents) shows that a decreasing of concentration leads to an increasing of particle size. A decreasing of concentration results in a decreasing of nucleation. As a result, nuclei with small sizes may become unstable and dissolve back into the solution; dissolved species will then deposit onto the surfaces of large particles. This finding has already been observed in other studies on ultrasound-assisted synthesis of nanoparticles (Table 2 and Fig. 6) [29]. In order to investigate the role of reaction time on the nature of products, reactions were performed under 35 and 70 min. These systems depicted an increasing the reaction time to 70 min increase the particle size (Table 2 and Fig. 7) [30].
Support of this investigation by Tarbiat Modares University and Iran Water Resources Management Co. (Code No.: WRE1-87066) are gratefully acknowledged.
3.5. XRD spectroscopy The XRD patterns (Fig. 8) of the product demonstrate that the silver bromide is crystalline in nature, and the diffraction peaks match those of the cubic silver bromide phase in the Joint Committee for Power Diffraction Studies (JCPDS) database (06-0438) [31]. Estimated from the Sherrer formula, D = 0.891k/bcosh, where D is the average crystallite size, k is the X-ray wavelength (0.17889 nm), and h and b are the diffraction angle and full-width
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A.R. Abbasi, A. Morsali / Ultrasonics Sonochemistry 19 (2012) 540–545 [10] M.M. Husein, E. Rodil, J.H. Vera, A novel method for the preparation of silver chloride nanoparticles starting from their solid powder using microemulsions, J. Colloid Interface Sci. 288 (2005) 457–467. [11] M. Husein, E. Rodil, J.H. Vera, Formation of silver bromide precipitate of nanoparticles in a single microemulsion utilizing the surfactant counterion, J. Colloid Interface Sci. 273 (2004) 426–434. [12] L. Zhao, Y. Wang, Z. Chen, Y. Zou, Preparation, characterization, and optical properties of host–guest nanocomposite material SBA-15/AgI, J. Phys. B 403 (2008) 1775–1780. [13] I.L. Validzic, V. Jokanovic, D.P. Uskokovi, J.M. Nedeljkovi, Influence of solvent on the structural and morphological properties of AgI particles prepared using ultrasonic spray pyrolysis, Mater. Chem. Phys. 107 (2008) 28–32. [14] K.S. Suslick, Science, Sonochemistry 247 (1990) 1439–1445. [15] K.H. Kim, K.B. Kim, Ultrasound assisted synthesis of nano-sized lithium cobalt oxide, Ultrason. Sonochem. 15 (2008) 1019–1025. [16] G. Wibetoe, D.T. Takuwa, W. Lund, G. Sawula, Coulter particle analysis used for studying the effect of sample treatment in slurry sampling electrothermal atomic absorption spectrometry, Fresenius J. Anal. Chem. 363 (1999) 46–54. [17] J.L. Capelo-Martínez, P. Ximénez-Embún, Y. Madrid, C. Cámara, Advanced oxidation processes for sample treatment in atomic spectrometry, Trends Anal. Chem. 23 (2004) 331–340. [18] M.A. Alavi, A. Morsali, Syntheses and characterization of Sr(OH)2 and SrCO3 nanostructures by ultrasonic method, Ultrason. Sonochem. 17 (2010) 132– 138. [19] T.G. Clarke, N.A. Hampson, J.B. Lee, J.R. Morley, B. Scanlon, Oxidations involving silver. 11. The oxidation of alcohols and aldehydes with silver (1I) picolinate, Can. J. Chem. 47 (1969) 1649–1654. [20] M.T. Reetz, M. Maase, Redox-controlled size-selective fabrication of Redoxcontrolled size-selective fabrication of nanostructured transition metal colloids, Adv. Mater. 11 (1999) 773–777.
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Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultsonch
Influence of solvents on the morphological properties of AgBr nano-structures prepared using ultrasound irradiation Amir Reza Abbasi, Ali Morsali ⇑ Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Islamic Republic of Iran
a r t i c l e
i n f o
Article history: Received 21 December 2010 Received in revised form 9 August 2011 Accepted 9 August 2011 Available online 25 August 2011 Keywords: Silver bromide Spongy Nano-structures Ultrasound Nanoparticle
a b s t r a c t Nano-structures of AgBr have been prepared by reaction between AgNO3 and KBr under ultrasound irradiation. Particle sizes and morphology of nanoparticle are depending on temperature, power of sonicating, reaction time and concentration. The effects of these parameters in growth and morphology of the nano-structures have been studied. Results suggest that an increasing of temperature, sonication power and concentration led to a decreasing of particle size. The samples were characterized with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In the recent years the preparation and application of nanometer size materials have been had a major interest since they exhibit special properties in the industry [1]. Inorganic materials have broad application in materials chemistry and it is well documented that the properties of inorganic nano-materials depend strongly on their size and morphologies. Thus, the design and controlled synthesis of nano-structures with different size and morphology is very important from the viewpoint of both basic science and technology [2–5]. Silver bromide is an important material used in medicine, antibacterial [6], electronic, magnetic, optical, catalytic properties [7] for a variety of metals and semiconductors. Many technologies have been explored to fabricate silver halides nanostructures. These technical approaches can be grouped in several ways. One way is to group the techniques according to the form of products: electrospinning method [8], template synthesized [9], microemulsion method [10,11], reverse micelles [2], laserbased synthesis [7], host–guest nanocomposite material [12], ultrasonic spray pyrolysis [13]. The manufacturing of high valueadded products such as smart medical and protective textiles has increased rapidly in the last several years. Sonochemistry is the research area in which molecules undergo a chemical reaction due to the application of powerful ultrasound radiation [14,15]. The efficiency of heterogeneous reactions involving solids dispersed in liquids will depend upon the available ⇑ Corresponding author. Tel.: +98 21 82884416; fax: +98 21 88009730. E-mail address: [email protected] (A. Morsali). 1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2011.08.002
reactive surface area and mass transfer. The ultrasonicallyenhanced mass transport is thought to be due to two transient processes: (1) Bubble collapse at or near the solid–liquid interface with microjetting directed towards the surface, (2) Bubble motion near or within the diffusion layer of the surface. From an inorganic chemistry point of view, most of the effects of interest regarding ultrasonication are related to cavitation. Cavitation causes solute thermolysis along with the formation along with the formation of highly reactive radicals and reagents [16]. In addition, if a solid is present in solution, the sample size of the particles is diminished by solid disruption, thereby increasing the total solid surface in contact with the solvent [17]. The effects of ultrasound radiation on chemical reactions were reported in the recent works [18]. In this paper, we have developed a simple sonochemical to prepare nano-structures of AgBr. The concentration of initial precursors, sonicating time, the temperature of reaction were the parameters which were changed for reaching the optimized condition. For the characterization of the products, scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) were used. 2. Experimental 2.1. Materials All reagents and solvents were used as supplied by Merck chemical company and used without further purification. Powder X-ray diffraction (XRD) was carried out on a Philips diffractometer of X’pert Company with mono chromatized Co Ka radiation. The samples were characterized with a scanning electron microscope
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(SEM) (Philips XL 30 and S-4160) with gold coating. Ultrasonic generator was carried out on a SONICA-2200 EP, input: 50–60 Hz/ 305 W and TECNO-GAZ, S.P.A., Tecna 6, input: 50–60 Hz/138 W. 2.2. Sample preparation In this paper, nano-structures of AgBr were prepared by reaction between AgNO3 and KBr precursors with the molar ratio of 1:1 under ultrasound irradiation. AgNO3 and KBr separately dissolved in ethanol and water. The KBr solution was added drop-wise to the AgNO3 solution under ultrasound irradiation. The sonochemical reactions were carried in sonochemical bath as shown in Fig. 1. The blank reaction (sample III-5) was performed without ultrasound irradiation. The nano-structures of AgBr were prepared in different solvents among which methanol, ethanol, n-propanol, 2-propanol, tert-butanol, n-butanol, ethanolamine, 2-amino-1butanol and ethylene glycol (samples I–IX). Synthesis of silver bromide powders was performed using a sonicator bath operated under continuous mode. In this method 0.05 M KBr solution of methanol and water (1:1 v/v) was added drop-wise to a 0.05 M AgNO3 solution of methanol and water (1:1 v/v) in a 100-mL sonication flask. In this method sonication was carried out for 35 min continuously. During sonication, the temperature of the bath was maintained around 30 °C. The powder formed was washed thoroughly (two times) with distilled water and ethanol by centrifugation with 6000 rpm. At the end of the sonication process, the resulting powder was dried at 50 °C. This protocol was repeated for the other samples (II–IX). The influences of various solvents on the size and size distribution of AgBr are summarized in Table 1. 3. Results and discussion It was found that the solvents have noticeable influences on the size of the products. For example, for the synthesis of AgBr in the above solvents, the particle size increases in the following order: methanol < n-butanol < ethanol < n-propanol < ethanolamine < tert-butanol < 2-amino-1-butanol < ethylene glycol < 2propanol. Also, results show that the solvents have a noticeable influence on the morphology of the products. Fig. 2 shows scanning electron microscope (SEM) of AgBr nano-structures prepared with I–IX as solvents, respectively, under otherwise similar synthesis conditions. AgBr particles with spongy nanoparticles were obtained using I–V as solvents, whereas nano and micro AgBr
Table 1 The influences of various solvents on the size of AgBr nanoparticle. Samples
Reagents
Average diameter (nm)
Morphology
I II III IV V VI VII VIII IX
Methanol Ethanol n-Propanol 2-Propanol tert-Butanol n-Butanol Ethanolamine 2-Amino-1-butanol Ethylene glycol
58 90 100 695 300 73 151 420 551
Spongy Spongy Particle Spongy Spongy Particle Particle Particle Particle
particles were formed when IV–IX were used as solvents. It can be seen that the particle size decreases with increasing chain length for primary and secondary alcohols [19]. Such an influence may be explained by the fact that stronger reduction reagent would generate an abrupt surge of the concentration of growth species, resulting in a very high supersaturation. Consequently, a large number of initial nuclei would form [20,21]. For a given concentration of metal precursors, the formation of a larger number of nuclei would result in a smaller size of the grown nanoparticles. 3.1. Temperature effect Particle sizes and morphology of nanoparticle are depending on temperature [22]. An increasing of temperature results in an increasing of solubility. As a result, nuclei of large size may become unstable and dissolve back into the solution. Thus, an increasing of temperature led to a decreasing of particle size. Table 2, Figs. 2 and 3 show the average diameter and scanning electron micrographs (SEM) of the prepared samples (samples III-1, III-2 and III-3). Silver bromide nanoparticles with spongy shape were obtained at 60 °C, whereas spherical shape silver bromide particles were formed for low temperature reactions. 3.2. Sonication power In order to investigate the role of power ultrasound irradiation on the nature of products, reactions were performed under different power ultrasound irradiation. Ultrasonic generator was carried out on a SONICA-2200 EP and TECNO-GAZ, S.P.A., Tecna 6. Reaction of sample III-4 was performed by TECNO-GAZ S.P.A. Tecna 6 (input power and frequency of 138 W and 60 Hz) and the other reactions were prepared in an ultrasonic bath with an input power and frequency of 305 W and 60 Hz respectively (SONICA-2200 EP). Results show a decrease in the particles size as increasing power ultrasound irradiation [22,23]. Comparison between the samples with similar conditions and different power ultrasound irradiation shows that high power ultrasound irradiation decreased agglomeration, and thus particles size of sample III-2, 106 nm (Fig. 2) is smaller than particles size of sample III-4, 165 nm (Fig. 4). 3.3. Ultrasound effects
Fig. 1. Schematics of the experimental setup used for the sonochemical reactions: (a) double jacketed vessel, (b) ultrasound bath, (c) water circulation, (d) electrical mixer, (e) thermometer.
For the sake of investigating the role of sonicating, sample III-5 (as blank reaction) was performed without ultrasound irradiation. Results show that the average particle size for sample III-5 is around 197 nm (Fig. 5). The average particle size for ultrasound method in similar conditions (sample III-2) is around 106 nm. The sonochemical irradiation of a liquid causes two primary effects, namely, cavitations (bubble formation, growth, collapse) and heating. When the microscopic cavitations bubbles collapse near the surface of the solid substrate, they generate powerful shock waves and microjets that cause effective stirring/mixing of
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Fig. 2. The SEM photographs of the AgBr obtained at the various solvents (methanol: I, ethanol: II, n-propanol: III, 2-propanol: IV, tert-butanol: V, n-butanol: VI, VII, ethanolamine, 2-amino-1-butanol: VIII and ethylene glycol: IX).
the adjusted layer of liquid. The after-effects of the cavitations are several hundred times greater in heterogeneous systems than in
homogeneous systems [24]. In our case, the ultrasonic waves promote the fast migration of the newly-formed nanoparticles to the
A.R. Abbasi, A. Morsali / Ultrasonics Sonochemistry 19 (2012) 540–545
543
Table 2 The influences of temperature, reaction time and sonication power on the size of AgBr nanoparticle.
a b c
Samples
T (°C)a
t (min)b
Sonication (input power) (W)
SEMc
III-1 III-2 (=III) III-3 III-4 III-5 III-6 III-7 III-8
5 30 60 30 30 30 5 60
35 35 35 35 35 35 70 70
305 305 305 138 0 305 305 305
148 100 63 165 197 256 188 398
Reaction temperature. Reaction time. Average diameter (nm).
Fig. 4. SEM photographs of sample III-4 (138 W).
Fig. 5. SEM images of sample III-5 without ultrasound irradiation.
Fig. 3. SEM photographs of samples III-1 and III-3 at 5 and 60 °C.
fabric’s surface. There is reliable evidence that applying ultrasound not only induces nucleation, but also increases reproducibility. Another effect of ultrasound on nucleation is shortening the induction time between the establishment of supersaturation and the onset of nucleation and crystallization. The cavitation events allow the excitation energy barriers associated with nucleation to be surmounted, in which case it should be possible to correlate the number of cavitation and nucleation events in a quantitative way [25]. It has been suggested that nucleation caused by scratching the walls of a vessel containing a supersaturated solution with a glass rod spatula could be the result of cavitation [26,27]. Results show
Fig. 6. SEM photographs of sample III-6.
that in present of ultrasound radiation, particle sizes are in a very low range. This finding has already been observed in other studies on ultrasound-assisted synthesis of nano-particles [28].
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Fig. 8. XRD pattern of sample III-2.
at half maximum of an observed peak, respectively [30], the average size of the crystals of sample III-2 was 92 nm. The four major peaks found at 36.11°, 51.98°, 64.90° and 76.55° on the 2 theta scale correspond respectively to the (2 0 0), (2 2 0), (2 2 2) and (4 0 0) crystal planes [30].
4. Conclusion
Fig. 7. SEM photographs of samples for 35 and 70 min.
In summary, nano-structures of AgBr have been prepared by reaction between AgNO3 and KBr under ultrasound irradiation. Influences of temperature, power of sonicating, reaction time and concentration on the morphological properties of AgBr were studied. These parameters have noticeable influences on the morphology of the silver bromide nanoparticles. To verify the crystalline nature of the product, the XRD patterns of the resulting product were investigated. From XRD, it is clearly confirmed that the AgBr particles were successfully prepared by the ultrasound irradiation method. These systems depicted a decrease in the particles size accompanying an increase in the temperature, reaction time and sonication power. As a result, an increase in concentration led to decrease of particle size.
3.4. Concentration and reaction time effects
Acknowledgements
Comparison between the samples III-2 (III) (0.05 M of raw reagents) and III-6 (0.025 M of raw reagents) shows that a decreasing of concentration leads to an increasing of particle size. A decreasing of concentration results in a decreasing of nucleation. As a result, nuclei with small sizes may become unstable and dissolve back into the solution; dissolved species will then deposit onto the surfaces of large particles. This finding has already been observed in other studies on ultrasound-assisted synthesis of nanoparticles (Table 2 and Fig. 6) [29]. In order to investigate the role of reaction time on the nature of products, reactions were performed under 35 and 70 min. These systems depicted an increasing the reaction time to 70 min increase the particle size (Table 2 and Fig. 7) [30].
Support of this investigation by Tarbiat Modares University and Iran Water Resources Management Co. (Code No.: WRE1-87066) are gratefully acknowledged.
3.5. XRD spectroscopy The XRD patterns (Fig. 8) of the product demonstrate that the silver bromide is crystalline in nature, and the diffraction peaks match those of the cubic silver bromide phase in the Joint Committee for Power Diffraction Studies (JCPDS) database (06-0438) [31]. Estimated from the Sherrer formula, D = 0.891k/bcosh, where D is the average crystallite size, k is the X-ray wavelength (0.17889 nm), and h and b are the diffraction angle and full-width
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