- Email: [email protected]
Using microwave heating for synthesis of SrCO3 nanostructures with different morphologies
Accepted Manuscript Title: Using Microwave Heating for Synthesis of SrCO3 Nanostructures with Different Morphologies Author: Hasan Jahangiri Mehdi Ranjbar Mohammad Ali Taher Hanif kazerooni PII: DOI: Reference:
S1226-086X(14)00274-3 http://dx.doi.org/doi:10.1016/j.jiec.2014.05.025 JIEC 2052
To appear in: Received date: Revised date: Accepted date:
14-4-2014 7-5-2014 14-5-2014
Please cite this article as: H. Jahangiri, M. Ranjbar, M.A. Taher, H. kazerooni, Using Microwave Heating for Synthesis of SrCO3 Nanostructures with Different Morphologies, Journal of Industrial and Engineering Chemistry (2014), http://dx.doi.org/10.1016/j.jiec.2014.05.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Using Microwave Heating for Synthesis of SrCO3 Nanostructures with Different Morphologies
a
ip t
Hasan Jahangiri a, Mehdi Ranjbar b,*, Mohammad Ali Taher c, Hanif kazerooni d Faculty of Chemistry, Department Of Analytical Chemistry, University of Kashan, Kashan,
cr
P.O. Box 87317-51167, Iran
Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman, Iran
c
Department of Chemistry, Shahid Bahonar University of Kerman, P.O. Box 76175-133
d
Faculty of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic),
an
us
b
M
Tehran, Iran
d
*Corresponding author: Tel.: +98 9366592379
Ac ce p
te
Email: [email protected]
Abstract
Strontium carbonate (SrCO3) nanostructures were synthesized successfully via simple microwave approach by Sr(NO3)2, carbonate powder and sodium hydroxide (NaOH) as reagents. The effects of microwave time and power were investigated on product size and morphology. The products were characterized with X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ultraviolet–Visible (UV-Vis) and room temperature photoluminescence spectroscopy (PL). KEY WORDS: Strontium carbonate; Microwave; Nanostructures.
Page 1 of 18
1. Introduction In the past few decades, the nanostructures materials have shown increasing research interest due
ip t
to their unique physical and chemical properties. These properties are greatly affected by the morphology, size, shape and crystallography of nanomaterials [1, 2]. Strontium carbonate
cr
(SrCO3) and barium carbonate (BaCO3) are very important materials for a number of industries.
us
SrCO3 is used as a constituent of ferrite magnets for small direct current motors, an additive in the production of glass for color television tubes, modern electric industries, and for the
an
production of iridescent and special glasses, pigments, driers, paints, pyrotechnics, strontium metals and other strontium compounds [3, 4]. A variety of processes for the preparation of
M
SrCO3 have been reported [5, 6]. So far, SrCO3 particles with different morphologies have been produced, such as nanowires [7], flowerlike nanostructures [3] and hexahedral ellipsoids [8].
d
Furthermore, strontium carbonate has only one crystal-phase, so it has been widely studied as a
te
model system for bio-crystallization [6]. Various processes for the preparation of SrCO3
Ac ce p
including, hydrothermal method [3], self-assembled monolayers [5], ball milling of celestite [9], microemulsion, mediated solvothermal method [10], sonochemical method [11] homogeneous precipitation by enzyme-catalyzed reaction [12], biological synthesis [13] and solvothermal methods [14] have been reported. Recently, microwave method has attracted wide interest in material science which helps to increase the nucleation rate, reduce the synthesis time and provide the small particles with narrow size distribution and high purity. Hence, it is quite promising and easy to use for industrial applications [15, 16]. In this experimental work, SrCO3 nanostructures were synthesized via a smile microwave approach. Different parameters such as microwave time and power were investigated on the product size and morphology. Optical
Page 2 of 18
properties of the product were studied. Different analysis such as XRD, SEM, TEM and PL were used to characterization of the synthesized products.
ip t
2. Experimental 2.1. Materials and physical measurements
cr
All the chemical's reagents used in experiments such as Sr(NO3)2, carbonate powder and NaOH were of analytical grade and used as received without further purification. For characterization of the products
us
XRD patterns were recorded by a Rigaku D-max C III, X-ray diffractometer using Ni filtered Cu Ka
an
radiation. SEM images were obtained by scanning electron microscope (SEM) (Philips XL- 30ESM). Transmission electron microscope (TEM) images were obtained on a Philips EM208S transmission
M
electron microscope with an accelerating voltage of 100 kV. Room temperature PL was studied on an F4500 fluorescence spectrophotometer. The electronic spectra of the products were taken on a Shimadzu
d
Ultraviolet–Visible (UV–Vis) scanning spectrometer (Model 2101PC).
te
2.2. Synthesis of SrCO3 nanostructures
Ac ce p
In a typical experimental procedure equal mole of Sr(NO3)2 and carbonate powder were dissolved in water separately and then two solutions were mixed together. Then certain amount of NaOH was dissolved in final solution to adjust pH of the solution. After that the solution was transferred to beaker and exposed to microwave irradiation for different times and powers. After that obtained powders were centrifuged and washed several times with water and absolute ethanol for removing probably by-products. Finally, the products were dried at 80 oC for 10 h. Experimental conditions of SrCO3 formation were shown in table 1. 3. Result and discussion Fig. 1 shows XRD pattern of sample No. 5. As shown in this figure, the main diffraction peaks were observed at 25.2°, 26°, 37°, 44.5°, 48°, 50.5° in the XRD pattern of the SrCO3 which
Page 3 of 18
confirm the formation of SrCO3 with orthorhombic structure (JCPDS No. 71-2393). Also lattice constants of the product were a= 5.0900 A⁰, b= 8.3580 A⁰ and c=5.9970 A⁰. Fig. 2 (a-c) shows SEM images of S1-S3, respectively. As shown in this figure, microwave
ip t
power has important role in determination of product size and morphology. When the reaction was done at 600 W, aggregated particles were obtained that can be attributed to low produce
cr
energy of the microwave in this power (Fig. 2a). In fact, at 600 W, microwave can’t prepare
us
require energy for synthesis of separated tiny particles. By increasing microwave power to 750 W, required energy is prepared and very tiny particles are created (Fig. 2b). By further
an
increase in microwave power to 900 W, higher energy is prepared and due to high energetic of nanoparticles surface, they aggregated together and lump-like structures are synthesized (Fig.
M
2c).
d
SEM images of samples prepared at 6 min in different powers are shown in Fig. 3. It can be seen
te
that at 600W microwave power (Fig. 3a), aggregated particles are obtained that by increasing microwave power to 750 W, these particles are separated and very tiny particles are achieved
Ac ce p
(Fig. 3b). When microwave power is adjusted to 900 W the particles prepared at 750 W aggregated together in one dimension and rod-like structures are synthesized (Fig. 3c). So microwave power in this time has also significant effect on product size and morphology and by choosing the best microwave time, it is capable to synthesizing very tiny particles. Fig. 4(a-c) shows SEM images of S6–S9 respectively. The effect of microwave power on product size and morphology in this time is similar to previous times. At initial power of microwave for preparation of the product, lump-like and bulk structure with some tiny particles are synthesized that indicates 600W power at this time cant prepare required energy for creation of separated nanoparticles (Fig. 4a). By increasing microwave power to 750 W, aggregated
Page 4 of 18
particles are appeared that is shown in this time the power of 750 W, prepared more energy than other times and subsequently lump-like structures formed from very small particles are achieved (Fig. 4b). Further increase in microwave power is led to aggregation particles in one direction
ip t
and tiny rod-like structures are obtained (Fig. 4c).
The effect of microwave time on product size and morphology is similar to microwave power
cr
effect. Fig. 2a, 3a and 4a show the effect of microwave time on product size and morphology at
us
600W microwave power. It can be seen that at 4 min microwave irradiation (Fig. 2a), aggregated particles are obtained that by increasing time to 6 min (Fig. 3a), the particles become separated
an
and nanoparticles are synthesized. In fact in 6 min, microwave can prepare required energy for synthesizing of small and separated particles. When microwave time was selected to 8 min, more
M
energy of microwave was prepared that was led to aggregation of particles and hence bulk and
d
lump-like structures were obtained (Fig. 4a). It can be concluded that in this power, 6 min
te
irradiation is optimum microwave time for creation very small particles. The effect of microwave time at 750 W power is shown in Fig. 2b, 3b and 4b. The observation in
Ac ce p
this power is similar to 600 W microwave power. As shown in Fig. 2b, using microwave irradiation at 750 W for 4 min prepares tiny particles that some of them are aggregated together. By increasing microwave time to 6 min (Fig. 3b), separated and tiny particles are achieved that can be attributed to more produce energy of the microwave at 6 min irradiation. Further increase of microwave time to 8 min (Fig. 4b) was led to synthesizing of lump structure with aggregated tiny particles. These results show that at 750 W microwave power, the optimum time for creation of separated nanoparticles is 6 min and other times crate lower and higher energy that is not appropriate for nanoparticles synthesizing.
Page 5 of 18
The influence of microwave time ion product size and morphology at 900 W power was investigated. Produced microwave energy at 900 W is higher than other powers and so in the lowest time (4min) at this power aggregated particles are obtained that some of them has rod-like
ip t
structures (Fig. 2c). By increasing time to 6 min, the growth of rod structures is increased and large rod structures are created (Fig. 3c). Finally by further increase microwave time to 8 min,
cr
the rod structures aggregated together and spheres with aggregated rod-like structures are
us
obtained (Fig. 4c). Schem. 1 shows the influence of microwave power and time on product size and morphology.
an
For more investigation on the particle size and calculation of product size in more precisely, transmission electron microscopy (TEM) was used. Fig. 5 shows TEM image of sample No. 5. It
M
can be seen that product is composed from very tiny particles with about 40-50 nm diameter that
d
confirm SEM images observation.
te
Fig. 6 (a-c) shows PL spectroscopy of S2, S5 and S8 respectively. It was found that different microwave times at 750 W irradiation create the products with different optical properties and
Ac ce p
band gaps. Sample No. 5 shows the maximum band gap that confirms decreasing the particles size led to increasing optical band gap. In fact, samples prepared at 4 min and 8 min are composed from aggregated particles and show lower band gap respect with sample No. 5. It can be concluded that particle size and morphology has important role in optical properties of the samples.
Fig. 7 shows UV-Vis spectrum and plot of (αhν)2 versus (hν) of the samples No. 2, 5 and 8. The energy band gaps of these nanostructures were obtained with the help of absorption spectra. To measure the energy band gap, we have to draw (αhν)2 versus (hν) where α is the absorption coefficient and hν is the photon energy. The absorption coefficient α is proportional to:
Page 6 of 18
α(hν) = B(hν - Eg)n Where B is a constant and n is an index indicating the type of the transition. It is known that the value of n for direct band gap semiconductor is 1/2, and for indirect band gap semiconductor is
ip t
2. From extrapolation (αhν)2 versus (hν) plot to (αhν)2=0 the band gap of nanostructures can be
cr
calculated. As shown in this figure the band gap of S2, S5 and S8 were 3.1 eV, 3.6 eV and 2.85 eV, respectively. It can be observed that obtained band gaps from UV-Vis spectra are similar to
us
PL results.
an
4. Conclusion
It can be concluded that microwave time and morphology have significant effect on product size
M
and morphology and by choosing the best microwave time and power we can obtain very tiny particles. Each microwave power has optimum time and each microwave time has optimum
d
microwave power that can produce sufficient and appropriate microwave energy for creation of
Ac ce p
properties of the samples.
te
separation and tiny nanostructures. Also it was found that synthesis conditions affect on optical
Acknowledgment
Authors are grateful to council of University of Shahid Bahonar of Kerman and University of Kashan for supporting this work.
Page 7 of 18
References [1] A. Wu, J. Xu, B. Lu, X. Wu, X. Li, G. Qian, Materials Research Bulletin, 41 (2006) 861-866.
2007.
cr
[3] S. Li, H. Zhang, J. Xu, D. Yang, Materials Letters, 59 (2005) 420-422.
ip t
[2] V.I. Klimov, in Spectral and dynamical properties of multiexcitons in semiconductor nanocrystals,
[4] J. Du, Z. Liu, Z. Li, B. Han, Y. Huang, J. Zhang, Microporous and Mesoporous Materials, 83 (2005)
us
145-149.
[5] J. Küther, M. Bartz, R. Seshadri, G.B.M. Vaughan, W. Tremel, Journal of Materials Chemistry, 11
an
(2001) 503-506.
[6] D. Rautaray, S.R. Sainkar, M. Sastry, Langmuir, 19 (2003) 888-892.
M
[7] Q. Huang, L. Gao, Y. Cai, F. Aldinger, Chemistry Letters, 33 (2004) 290-291. [8] L. Shi, F. Du, Materials Letters, 61 (2007) 3262-3264.
d
[9] A. Obut, P. Baláž, I. Girgin, Minerals Engineering, 19 (2006) 1185-1190.
te
[10] M. Cao, X. Wu, X. He, C. Hu, Langmuir, 21 (2005) 6093-6096.
Ac ce p
[11] T. Thongtem, N. Tipcompor, A. Phuruangrat, S. Thongtem, Materials Letters, 64 (2010) 510-512. [12] I. Sondi, E. Matijević, Chemistry of Materials, 15 (2003) 1322-1326. [13] D. Rautaray, A. Sanyal, S.D. Adyanthaya, A. Ahmad, M. Sastry, Langmuir, 20 (2004) 6827-6833. [14] L. Shi, F. Du, Materials Research Bulletin, 42 (2007) 1550-1555. [15] I. Bilecka, M. Niederberger, Nanoscale, 2 (2010) 1358-1374. [16] G.A. Tompsett, W.C. Conner, K.S. Yngvesson, ChemPhysChem, 7 (2006) 296-319.
Page 8 of 18
Figure caption Fig. 1. XRD pattern of sample No. 5.
ip t
Fig. 2 (a-c). SEM images of S1 – S3, respectively.
cr
Fig. 3 (a-c). SEM images of S4 – S6, respectively.
Fig. 5. TEM image of S5.
an
Fig. 6 (a-c). PL spectar of S2, S5 and S8, respectively.
us
Fig. 4 (a-c). SEM images of S7 – S9, respectively.
Fig. 7. (a, c, e) UV-Vis spectra of S2, S5 and S8. (b, d, f) (αhν)2 versus (hν) of S2, S5 and S8,
M
respectively.
te
morphology.
d
Schem. 1. Schematic of the influence of microwave power and time on product size and
Ac ce p
Table 1. Samples preparation conditions.
Page 9 of 18
Microwave Power (W)
4 4 4 6 6 6 8 8 8
600 750 900 600 750 900 600 750 900
1. Samples preparation conditions.
us
cr
ip t
Microwave Time (min)
te
d
M
an
Sample No 1 2 3 4 5 6 7 8 9
Ac ce p
Table
Page 10 of 18
ip t cr us an M d
XRD
pattern
te
1.
of
sample
No.
5.
Ac ce p
Fig.
Page 11 of 18
ip t cr us an M d te Ac ce p
Fig.
2
(a-c).
SEM
images
of
S1
–
S3,
respectively.
Page 12 of 18
ip t cr us an M d te Ac ce p
Fig. 3 (a-c). SEM images of S4 – S6, respectively.
Page 13 of 18
ip t cr us an M d te Ac ce p
Fig. 4 (a-c). SEM images of S7 – S9, respectively.
Page 14 of 18
ip t cr us an M d te
Ac ce p
Fig. 5. TEM image of S5.
Page 15 of 18
ip t cr us an M d
Ac ce p
te
Fig. 6 (a-c). PL spectar of S2, S5 and S8, respectively.
Page 16 of 18
ip t cr us an M d te Ac ce p Fig. 7. (a, c, e) UV-Vis spectra of S2, S5 and S8. (b, d, f) (αhν)2 versus (hν) of S2, S5 and S8, respectively.
Page 17 of 18
ip t cr us an
Ac ce p
te
d
M
Schem. 1. Schematic of the influence of microwave power and time on product size and morphology.
Page 18 of 18
S1226-086X(14)00274-3 http://dx.doi.org/doi:10.1016/j.jiec.2014.05.025 JIEC 2052
To appear in: Received date: Revised date: Accepted date:
14-4-2014 7-5-2014 14-5-2014
Please cite this article as: H. Jahangiri, M. Ranjbar, M.A. Taher, H. kazerooni, Using Microwave Heating for Synthesis of SrCO3 Nanostructures with Different Morphologies, Journal of Industrial and Engineering Chemistry (2014), http://dx.doi.org/10.1016/j.jiec.2014.05.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Using Microwave Heating for Synthesis of SrCO3 Nanostructures with Different Morphologies
a
ip t
Hasan Jahangiri a, Mehdi Ranjbar b,*, Mohammad Ali Taher c, Hanif kazerooni d Faculty of Chemistry, Department Of Analytical Chemistry, University of Kashan, Kashan,
cr
P.O. Box 87317-51167, Iran
Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman, Iran
c
Department of Chemistry, Shahid Bahonar University of Kerman, P.O. Box 76175-133
d
Faculty of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic),
an
us
b
M
Tehran, Iran
d
*Corresponding author: Tel.: +98 9366592379
Ac ce p
te
Email: [email protected]
Abstract
Strontium carbonate (SrCO3) nanostructures were synthesized successfully via simple microwave approach by Sr(NO3)2, carbonate powder and sodium hydroxide (NaOH) as reagents. The effects of microwave time and power were investigated on product size and morphology. The products were characterized with X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ultraviolet–Visible (UV-Vis) and room temperature photoluminescence spectroscopy (PL). KEY WORDS: Strontium carbonate; Microwave; Nanostructures.
Page 1 of 18
1. Introduction In the past few decades, the nanostructures materials have shown increasing research interest due
ip t
to their unique physical and chemical properties. These properties are greatly affected by the morphology, size, shape and crystallography of nanomaterials [1, 2]. Strontium carbonate
cr
(SrCO3) and barium carbonate (BaCO3) are very important materials for a number of industries.
us
SrCO3 is used as a constituent of ferrite magnets for small direct current motors, an additive in the production of glass for color television tubes, modern electric industries, and for the
an
production of iridescent and special glasses, pigments, driers, paints, pyrotechnics, strontium metals and other strontium compounds [3, 4]. A variety of processes for the preparation of
M
SrCO3 have been reported [5, 6]. So far, SrCO3 particles with different morphologies have been produced, such as nanowires [7], flowerlike nanostructures [3] and hexahedral ellipsoids [8].
d
Furthermore, strontium carbonate has only one crystal-phase, so it has been widely studied as a
te
model system for bio-crystallization [6]. Various processes for the preparation of SrCO3
Ac ce p
including, hydrothermal method [3], self-assembled monolayers [5], ball milling of celestite [9], microemulsion, mediated solvothermal method [10], sonochemical method [11] homogeneous precipitation by enzyme-catalyzed reaction [12], biological synthesis [13] and solvothermal methods [14] have been reported. Recently, microwave method has attracted wide interest in material science which helps to increase the nucleation rate, reduce the synthesis time and provide the small particles with narrow size distribution and high purity. Hence, it is quite promising and easy to use for industrial applications [15, 16]. In this experimental work, SrCO3 nanostructures were synthesized via a smile microwave approach. Different parameters such as microwave time and power were investigated on the product size and morphology. Optical
Page 2 of 18
properties of the product were studied. Different analysis such as XRD, SEM, TEM and PL were used to characterization of the synthesized products.
ip t
2. Experimental 2.1. Materials and physical measurements
cr
All the chemical's reagents used in experiments such as Sr(NO3)2, carbonate powder and NaOH were of analytical grade and used as received without further purification. For characterization of the products
us
XRD patterns were recorded by a Rigaku D-max C III, X-ray diffractometer using Ni filtered Cu Ka
an
radiation. SEM images were obtained by scanning electron microscope (SEM) (Philips XL- 30ESM). Transmission electron microscope (TEM) images were obtained on a Philips EM208S transmission
M
electron microscope with an accelerating voltage of 100 kV. Room temperature PL was studied on an F4500 fluorescence spectrophotometer. The electronic spectra of the products were taken on a Shimadzu
d
Ultraviolet–Visible (UV–Vis) scanning spectrometer (Model 2101PC).
te
2.2. Synthesis of SrCO3 nanostructures
Ac ce p
In a typical experimental procedure equal mole of Sr(NO3)2 and carbonate powder were dissolved in water separately and then two solutions were mixed together. Then certain amount of NaOH was dissolved in final solution to adjust pH of the solution. After that the solution was transferred to beaker and exposed to microwave irradiation for different times and powers. After that obtained powders were centrifuged and washed several times with water and absolute ethanol for removing probably by-products. Finally, the products were dried at 80 oC for 10 h. Experimental conditions of SrCO3 formation were shown in table 1. 3. Result and discussion Fig. 1 shows XRD pattern of sample No. 5. As shown in this figure, the main diffraction peaks were observed at 25.2°, 26°, 37°, 44.5°, 48°, 50.5° in the XRD pattern of the SrCO3 which
Page 3 of 18
confirm the formation of SrCO3 with orthorhombic structure (JCPDS No. 71-2393). Also lattice constants of the product were a= 5.0900 A⁰, b= 8.3580 A⁰ and c=5.9970 A⁰. Fig. 2 (a-c) shows SEM images of S1-S3, respectively. As shown in this figure, microwave
ip t
power has important role in determination of product size and morphology. When the reaction was done at 600 W, aggregated particles were obtained that can be attributed to low produce
cr
energy of the microwave in this power (Fig. 2a). In fact, at 600 W, microwave can’t prepare
us
require energy for synthesis of separated tiny particles. By increasing microwave power to 750 W, required energy is prepared and very tiny particles are created (Fig. 2b). By further
an
increase in microwave power to 900 W, higher energy is prepared and due to high energetic of nanoparticles surface, they aggregated together and lump-like structures are synthesized (Fig.
M
2c).
d
SEM images of samples prepared at 6 min in different powers are shown in Fig. 3. It can be seen
te
that at 600W microwave power (Fig. 3a), aggregated particles are obtained that by increasing microwave power to 750 W, these particles are separated and very tiny particles are achieved
Ac ce p
(Fig. 3b). When microwave power is adjusted to 900 W the particles prepared at 750 W aggregated together in one dimension and rod-like structures are synthesized (Fig. 3c). So microwave power in this time has also significant effect on product size and morphology and by choosing the best microwave time, it is capable to synthesizing very tiny particles. Fig. 4(a-c) shows SEM images of S6–S9 respectively. The effect of microwave power on product size and morphology in this time is similar to previous times. At initial power of microwave for preparation of the product, lump-like and bulk structure with some tiny particles are synthesized that indicates 600W power at this time cant prepare required energy for creation of separated nanoparticles (Fig. 4a). By increasing microwave power to 750 W, aggregated
Page 4 of 18
particles are appeared that is shown in this time the power of 750 W, prepared more energy than other times and subsequently lump-like structures formed from very small particles are achieved (Fig. 4b). Further increase in microwave power is led to aggregation particles in one direction
ip t
and tiny rod-like structures are obtained (Fig. 4c).
The effect of microwave time on product size and morphology is similar to microwave power
cr
effect. Fig. 2a, 3a and 4a show the effect of microwave time on product size and morphology at
us
600W microwave power. It can be seen that at 4 min microwave irradiation (Fig. 2a), aggregated particles are obtained that by increasing time to 6 min (Fig. 3a), the particles become separated
an
and nanoparticles are synthesized. In fact in 6 min, microwave can prepare required energy for synthesizing of small and separated particles. When microwave time was selected to 8 min, more
M
energy of microwave was prepared that was led to aggregation of particles and hence bulk and
d
lump-like structures were obtained (Fig. 4a). It can be concluded that in this power, 6 min
te
irradiation is optimum microwave time for creation very small particles. The effect of microwave time at 750 W power is shown in Fig. 2b, 3b and 4b. The observation in
Ac ce p
this power is similar to 600 W microwave power. As shown in Fig. 2b, using microwave irradiation at 750 W for 4 min prepares tiny particles that some of them are aggregated together. By increasing microwave time to 6 min (Fig. 3b), separated and tiny particles are achieved that can be attributed to more produce energy of the microwave at 6 min irradiation. Further increase of microwave time to 8 min (Fig. 4b) was led to synthesizing of lump structure with aggregated tiny particles. These results show that at 750 W microwave power, the optimum time for creation of separated nanoparticles is 6 min and other times crate lower and higher energy that is not appropriate for nanoparticles synthesizing.
Page 5 of 18
The influence of microwave time ion product size and morphology at 900 W power was investigated. Produced microwave energy at 900 W is higher than other powers and so in the lowest time (4min) at this power aggregated particles are obtained that some of them has rod-like
ip t
structures (Fig. 2c). By increasing time to 6 min, the growth of rod structures is increased and large rod structures are created (Fig. 3c). Finally by further increase microwave time to 8 min,
cr
the rod structures aggregated together and spheres with aggregated rod-like structures are
us
obtained (Fig. 4c). Schem. 1 shows the influence of microwave power and time on product size and morphology.
an
For more investigation on the particle size and calculation of product size in more precisely, transmission electron microscopy (TEM) was used. Fig. 5 shows TEM image of sample No. 5. It
M
can be seen that product is composed from very tiny particles with about 40-50 nm diameter that
d
confirm SEM images observation.
te
Fig. 6 (a-c) shows PL spectroscopy of S2, S5 and S8 respectively. It was found that different microwave times at 750 W irradiation create the products with different optical properties and
Ac ce p
band gaps. Sample No. 5 shows the maximum band gap that confirms decreasing the particles size led to increasing optical band gap. In fact, samples prepared at 4 min and 8 min are composed from aggregated particles and show lower band gap respect with sample No. 5. It can be concluded that particle size and morphology has important role in optical properties of the samples.
Fig. 7 shows UV-Vis spectrum and plot of (αhν)2 versus (hν) of the samples No. 2, 5 and 8. The energy band gaps of these nanostructures were obtained with the help of absorption spectra. To measure the energy band gap, we have to draw (αhν)2 versus (hν) where α is the absorption coefficient and hν is the photon energy. The absorption coefficient α is proportional to:
Page 6 of 18
α(hν) = B(hν - Eg)n Where B is a constant and n is an index indicating the type of the transition. It is known that the value of n for direct band gap semiconductor is 1/2, and for indirect band gap semiconductor is
ip t
2. From extrapolation (αhν)2 versus (hν) plot to (αhν)2=0 the band gap of nanostructures can be
cr
calculated. As shown in this figure the band gap of S2, S5 and S8 were 3.1 eV, 3.6 eV and 2.85 eV, respectively. It can be observed that obtained band gaps from UV-Vis spectra are similar to
us
PL results.
an
4. Conclusion
It can be concluded that microwave time and morphology have significant effect on product size
M
and morphology and by choosing the best microwave time and power we can obtain very tiny particles. Each microwave power has optimum time and each microwave time has optimum
d
microwave power that can produce sufficient and appropriate microwave energy for creation of
Ac ce p
properties of the samples.
te
separation and tiny nanostructures. Also it was found that synthesis conditions affect on optical
Acknowledgment
Authors are grateful to council of University of Shahid Bahonar of Kerman and University of Kashan for supporting this work.
Page 7 of 18
References [1] A. Wu, J. Xu, B. Lu, X. Wu, X. Li, G. Qian, Materials Research Bulletin, 41 (2006) 861-866.
2007.
cr
[3] S. Li, H. Zhang, J. Xu, D. Yang, Materials Letters, 59 (2005) 420-422.
ip t
[2] V.I. Klimov, in Spectral and dynamical properties of multiexcitons in semiconductor nanocrystals,
[4] J. Du, Z. Liu, Z. Li, B. Han, Y. Huang, J. Zhang, Microporous and Mesoporous Materials, 83 (2005)
us
145-149.
[5] J. Küther, M. Bartz, R. Seshadri, G.B.M. Vaughan, W. Tremel, Journal of Materials Chemistry, 11
an
(2001) 503-506.
[6] D. Rautaray, S.R. Sainkar, M. Sastry, Langmuir, 19 (2003) 888-892.
M
[7] Q. Huang, L. Gao, Y. Cai, F. Aldinger, Chemistry Letters, 33 (2004) 290-291. [8] L. Shi, F. Du, Materials Letters, 61 (2007) 3262-3264.
d
[9] A. Obut, P. Baláž, I. Girgin, Minerals Engineering, 19 (2006) 1185-1190.
te
[10] M. Cao, X. Wu, X. He, C. Hu, Langmuir, 21 (2005) 6093-6096.
Ac ce p
[11] T. Thongtem, N. Tipcompor, A. Phuruangrat, S. Thongtem, Materials Letters, 64 (2010) 510-512. [12] I. Sondi, E. Matijević, Chemistry of Materials, 15 (2003) 1322-1326. [13] D. Rautaray, A. Sanyal, S.D. Adyanthaya, A. Ahmad, M. Sastry, Langmuir, 20 (2004) 6827-6833. [14] L. Shi, F. Du, Materials Research Bulletin, 42 (2007) 1550-1555. [15] I. Bilecka, M. Niederberger, Nanoscale, 2 (2010) 1358-1374. [16] G.A. Tompsett, W.C. Conner, K.S. Yngvesson, ChemPhysChem, 7 (2006) 296-319.
Page 8 of 18
Figure caption Fig. 1. XRD pattern of sample No. 5.
ip t
Fig. 2 (a-c). SEM images of S1 – S3, respectively.
cr
Fig. 3 (a-c). SEM images of S4 – S6, respectively.
Fig. 5. TEM image of S5.
an
Fig. 6 (a-c). PL spectar of S2, S5 and S8, respectively.
us
Fig. 4 (a-c). SEM images of S7 – S9, respectively.
Fig. 7. (a, c, e) UV-Vis spectra of S2, S5 and S8. (b, d, f) (αhν)2 versus (hν) of S2, S5 and S8,
M
respectively.
te
morphology.
d
Schem. 1. Schematic of the influence of microwave power and time on product size and
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Table 1. Samples preparation conditions.
Page 9 of 18
Microwave Power (W)
4 4 4 6 6 6 8 8 8
600 750 900 600 750 900 600 750 900
1. Samples preparation conditions.
us
cr
ip t
Microwave Time (min)
te
d
M
an
Sample No 1 2 3 4 5 6 7 8 9
Ac ce p
Table
Page 10 of 18
ip t cr us an M d
XRD
pattern
te
1.
of
sample
No.
5.
Ac ce p
Fig.
Page 11 of 18
ip t cr us an M d te Ac ce p
Fig.
2
(a-c).
SEM
images
of
S1
–
S3,
respectively.
Page 12 of 18
ip t cr us an M d te Ac ce p
Fig. 3 (a-c). SEM images of S4 – S6, respectively.
Page 13 of 18
ip t cr us an M d te Ac ce p
Fig. 4 (a-c). SEM images of S7 – S9, respectively.
Page 14 of 18
ip t cr us an M d te
Ac ce p
Fig. 5. TEM image of S5.
Page 15 of 18
ip t cr us an M d
Ac ce p
te
Fig. 6 (a-c). PL spectar of S2, S5 and S8, respectively.
Page 16 of 18
ip t cr us an M d te Ac ce p Fig. 7. (a, c, e) UV-Vis spectra of S2, S5 and S8. (b, d, f) (αhν)2 versus (hν) of S2, S5 and S8, respectively.
Page 17 of 18
ip t cr us an
Ac ce p
te
d
M
Schem. 1. Schematic of the influence of microwave power and time on product size and morphology.
Page 18 of 18