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Preparation of Cu2O nanostructures by changing reducing agent and their optical properties
Materials Letters 153 (2015) 1–4
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation of Cu2O nanostructures by changing reducing agent and their optical properties Maryam Sabbaghan n, Javad Beheshtian, Rasoul Niazmand Liarjdame Chemistry Department, Faculty of Sciences, Shahid Rajaee Teacher training University, PO Box 16785-163, Tehran, Iran
art ic l e i nf o
a b s t r a c t
Article history: Received 2 December 2014 Accepted 30 March 2015 Available online 6 April 2015
Different morphologies of Cu2O nanostructures were successfully synthesized through a reflux method in water by changing carbohydrates as reducing agents. The effects of reducing carbohydrates with different types of concentrations, and basic conditions on the morphology and size of nanostructures were investigated. The structural and optical properties of these Cu2O particles were studied by using XRD, SEM and UV–visible. The characteristic results revealed that using different carbohydrates in a specific concentration in water is not only reducing agent but also a directing agent to control Cu2O nanostructure morphologies. A possible mechanism was proposed to explain the formation of Cu2O nanostructures with different morphologies. The band gaps are estimated to be 1.89–2.08 eV according to the results of the optical measurements of the Cu2O nanostructures. & 2015 Elsevier B.V. All rights reserved.
Keywords: Cu2O Green synthesis Octahedral Nanosize Microstructure Nanoparticles
1. Introduction In recent years, controlling the structure of inorganic nanomaterial to search for new properties has become one of the major objectives of nanoscale science and technology, because such kind of material possesses structure-dependent characteristics and novel electronic, optical, magnetic, chemical and mechanical properties that cannot be obtained in their bulk counterparts [1,2]. Oxides of transition metals which have different oxidation states and coordination numbers are especially welcomed due to their unique electronic optical, thermal, photonic and catalytic properties in different morphologies [3]. As an important p-type semiconductor with a band gap 2.2 eV, cuprous oxide (Cu2O) has been widely used in applications such as catalysis, magnetic storage media, solar energy conversion, electrodes for lithium-ion batteries and gas sensors [4–6]. Synthesis of shape controlled Cu2O nano- and micro-crystals has already been performed [7–8]. To date, various morphologies of Cu2O structures such as hollow octahedral [9], flowerlike [10], hollow nanoparticles [11], cubic spherical shape [12] and hollow spheres [13] have been prepared under different conditions. The multi-pod, star-like, spheres and cubic Cu2O crystals were synthesized by reducing using Cu(II) salts with glucose [14–20]. These morphologies are produced using templates. Nevertheless, these strategies sometimes limit the size to within a few hundred nanometers. However, to the best of our knowledge, there is no report about
n
Corresponding author. Tel.: þ 98 21 22970003; fax: þ 98 21 22970033. E-mail addresses: [email protected], [email protected] (M. Sabbaghan). http://dx.doi.org/10.1016/j.matlet.2015.03.147 0167-577X/& 2015 Elsevier B.V. All rights reserved.
changing the carbohydrates as reducing agent to produce different morphologies and sizes of Cu2O nanostructures. Herein we disclose a general, high yielding, green synthetic of Cu2O nanostructures using different carbohydrates in definite concentration of precursor and base without using template with the reflux method. The structures as well as optical properties of the various morphologies of Cu2O were studied. 2. Experimental Copper acetate dihydrate was purchased from Aldrich. Sodium hydroxide was used without further purification. Copper acetate was employed as a copper source. In a typical experiment, 0.4 g of Cu(AcO)2 2H2O (2 mmol) was dissolved in distilled water under vigorous stirring, followed by addition of a reducing agent with specific concentration to the mixture (Table 1). In order to change to basic conditions (pH ¼14), 0.6 g of NaOH (6 mmol) was dissolved in the solution (S5–S6). The solution transferred to a round bottomed flask and was refluxed at 70 1C for 2 h. The precipitate was collected by filtration and washed with distilled water and ethanol (96%) several times. Finally, the Cu2O samples were dried in the air at room temperature. The detailed synthesis conditions are summarized in Table 1. 2.1. Characterization The morphology of nanostructure Cu2O was determined by using scanning electron microscopy (SEM) of a Holland Philips XL30 microscope. The X-ray diffraction (XRD) analysis was carried out at room temperature using a Holland Philips Xpert X-ray
2
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
Table 1 Preparation of Cu2O nanostructures in the reflux method in water with information on morphology, crystallite particle size and band gap energy. Sample Cu(OAc)2 H2O (mmol)
Reductant (mmol)
S1
1
Glucose (1) 10
7
S2
1
Glucose (1) 30
7
S3 S4 S5
2 1 1
Glucose (2) 30 Glucose (4) 30 Glucose (1) 30
7 7 14
S6
1
Glucose (2) 30
14
S7
1
S8 S9
1 2
Galactose (1) Ribose (1) Ribose (2)
Solvent (ml)
pH Morphology Size Band (nm) gap (eV)
30
7
Truncated octahedral NanorodNanoparticle Octahedral Nanoparticle Nanosheetlike NanorodNanoparticle Nanoparticle
46
1.44
34
1.90
31 35 41
1.89 1.97 2.0
47
2.08
32
1.96
30 30
7 7
Nanoparticle 18 Nanoparticle 22
1.92 1.96
powder diffractometer with Cu Kα radiation (λ ¼ 0.15406 nm), over the 2θ collection range of 20–801. Average crystallite sizes of products were calculated using Scherrer's formula: D¼ 0.9λ/β cosθ [21], where D is the diameter of the nanoparticles, λ (Cu Kα) ¼1.5406 Å and β is the full-width at half-maximum of the diffraction lines. The band gaps of our samples were determined by a UV–visible spectrometer on an instrument PG T80/T80 þ with drift and solid cell. The spectra were recorded at room temperature in the wavelength range of 200–800 nm and with the accuracy of 0.5 nm.
3. Results and discussion The cuprous oxide nanostructures were synthesized with the assistance of reducing carbohydrates by the reflux method in water. Fig. 1 shows the XRD patterns of as-prepared samples. The entire diffraction peaks match with cubic crystal type of Cu2O (JCPDS 05-0667). No reflections of impurity can be found in the pattern, which proves that pure cuprous oxide has been successfully prepared. The morphologies of the products were analyzed by SEM images shown in Fig. 2. Truncated octahedral morphology with size of in the scale of micrometers was synthesized in 10 ml of water (S1). For the preparation of nanostructure of Cu2O the solvent was increased up to 30 ml. The mixture of nanorods and nanoparticles was synthesized (S2). Homogeneous samples with uniform octahedral morphology (S3) were formed by increasing the reactants and glucose up to twice in 30 ml water in comparing of S2. By changing the ratio of Glucose/Cu (OAc)2.H2O to 4:1, nanoparticle morphology (S4) was obtained in this condition. To determine the effect of basic conditions, the experiments were carried out in pH¼14. When the proportion of Cu(OAc)2.H2O to glucose was 1:1 nanosheet like morphology was formed (S4). It seems that agglomeration of nanosheets sticking together is formed. By changing the ratio of Cu(OAc)2 H2O to glucose to 1:2, the mixture of nanorod and nanopartile was obtained. To determine the effect of other reducing carbohydrate in the formation of Cu2O nanostructures, experiments were carried out with ribose and Galactose, while keeping other reaction parameters unchanged. The SEM images of S7, S8 and S9 prepared show homogeneous samples with uniform nanoparticle morphologies in the same condition with S2 and S3. It is noticed that the morphology is the same with S4, but the size of particles is different. These morphologies were formed by the thermodynamically controlled reaction. Reactants concentration and reaction time are enough to have the thermodynamically controlled reaction in the reflux method.
Fig. 1. SEM images of Cu2O nanostructures.
Oxidation of anomeric carbon of glucose and other carbohydrates by cupric acetate produced a red cuprous oxide precipitate. In the hemiacetal form, C-1 of carbohydrates cannot be oxidized by Cu2 þ . However, the open-chain form is in equilibrium with the ring form, eventually the oxidation reaction goes to completion [22]. It seems that reducing carbohydrates are not only a reducing agent but also in hemiacetal form with forming the coordination with Cu2 þ is a directing agent to control Cu2O nanostructure morphologies (see supplementary data, Fig. SD1). There is more explanation about the effect of glucose and precursor on morphologies of Cu2O in supplementary data (Fig. SD2) [18–19]. It might be various carbohydrates form different complexes. The coordination would transfer to Cu2O after reflux at 70 1C for 2 h [23]. Also Cu2 þ reacted with OH̄ to form [Cu(OH)4]2- product upon the addition of NaOH (S5, S6). This complex coordination with carbohydrate by hydrogen bond causes to different morphologies in comparison neutral conditions. It can be concluded from the above results
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
S1
3
S2
2 µm
200 nm
S3
S4
200 nm
100 nm
S6
S5
200 nm
200 nm
S8
S7
S9
Fig. 2. XRD patterns of Cu2O nanostructures.
where K is a constant, α is the absorption coefficient, Ephoton is the discrete photoenergy and Eg is the band gap energy. The energy intercept of a plot of (αEphoton)2 vs. Ephoton yields Eg for a direct transition. Supplementary data show the corresponding band gap calculations of the as synthesized samples (Fig. SD3). The value of band gap energies is presented in Table 1. The band gap of nano Cu2O with various morphologies ranges from 1.89 to 2.08 which are redshift with respect to the band gap for bulk Cu2O (2.2 eV) [25]. The results show that the size, shape greatly affect band gap energy of the Cu2O samples.
4. Conclusion
Fig. 3. UV–visible absorption spectrum of the samples.
that different reducing agents in different concentrations and sodium hydroxide play important role in the morphology control and size of the Cu2O nanostructures. The UV–vis spectroscopy was performed on samples to observe changing in optical properties. Fig. 3 shows the absorption spectra of Cu2O nanostructures. The band gap energies can be estimated on according to following equation [24]: αEphoton ¼ K Ephoton Eg 1=2
Octahedral, nanorod and nanoparticle Cu2O samples could be obtained by adjusting the concentrations of glucose. By changing the reducing carbohydrate, nanoparticles structures of the products with size as small as 18–32 nm were obtained. Nanosheet like morphology was obtained with the addition of sodium hydroxide. The advantage of the present procedure is that the reaction is performed under green conditions by simple mixing of the starting materials at ambient pressure.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.03.147.
4
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Hupp JT, Poeppelmeier KR. Science 2005;309:2008–9. Chen J, Xu LN, Li WY, Gou XL. Adv Mater 2005;17:582–5. Toberer ES, Seshadri R. Adv Mater 2005;17:2244–6. Zhang H, Ren X, Cui ZL. J Cryst Growth 2007;304:206–10. White B, Yin M, Hall A, Le D, Stolbov S, Rahman T, et al. Nano Lett 2006;6:2095–8. Zhang JT, Liu JF, Peng Q, Wang X, Li YD. Chem Mater 2006;18(4):867–71. Duan X, Zhang Y, Gao R, Jian Z, Zhao Y, Liu W, et al. Mater Lett 2012;68:146–8. Cai A, Wang Y, Du L, Ma Z. Mater Lett 2012;70:149–51. Feng L, Zhang C, Gao G, Cui D. Nanoscale Res Lett 2012;7:276–86. Yang Z, LiPing G, Xin S, JianJi W. Sci China Chem 2012;55:1580–6. Hung LI, Tsung CK, Huang W, Yang P. Adv Mater 2010;22:1910–4. Li H, Liu R, Zhao R, Zheng Y, Chen W, Xu Z. Cryst Growth Des 2006;6:2795–8. Gao JN, Li QS, Zhao HB, Li LS, Liu CL, Gongand QH, et al. Chem Mater 2008;20:6263–9.
[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]
Wang D, Mo M, Yu D, Xu L, Li F, Qian Y. Cryst Growth Des 2003;3:717–20. Zhang Y, Deng B, Zhang TR, Gao DM, Xu AW. J Phys Chem C 2010;114:5073–9. Kang W, Liu F, Su Y, Wang D, Shen Q. CrystEngComm 2011;13:4174–80. Hua Q, Chen K, Chang S, Ma Y, Huang WJ. Phys Chem C 2011;115:20618–27. Sui Y, Fu W, Yang H, Zeng Y, Zhang Y, Zhao Q, et al. Cryst Growth Des 2010;10:99–108. Cho YS, Huh YD. Bull. Korean Chem Soc 2014;35:309–12. Basu M, Sinha AK, Pradhan M, Sarkar S, Pal A, Mondal CJ. Phys Chem C 2012;116:25741–7. Sabbaghan M, Anaraki Firooz A, Jan Ahmadi V. Mol Liq 2012;175:135–40. Stick RV, Williams S. Carbohydrates: the essential molecules of life. 2nd ed. Elsevier Science; 2008. Guan L, Pang H, Wang J, Lu Q, Yinac J, Gao F. Chem Commun 2010;46:7022–4. Sabbaghan M, Mirzaei Behbahani B. Mater Lett 2014;117:28–30. Li H, Liu R, Liu Y, Huang H, Yu H, Ming H, et al. J.Mater Chem 2012;22:17470–5.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation of Cu2O nanostructures by changing reducing agent and their optical properties Maryam Sabbaghan n, Javad Beheshtian, Rasoul Niazmand Liarjdame Chemistry Department, Faculty of Sciences, Shahid Rajaee Teacher training University, PO Box 16785-163, Tehran, Iran
art ic l e i nf o
a b s t r a c t
Article history: Received 2 December 2014 Accepted 30 March 2015 Available online 6 April 2015
Different morphologies of Cu2O nanostructures were successfully synthesized through a reflux method in water by changing carbohydrates as reducing agents. The effects of reducing carbohydrates with different types of concentrations, and basic conditions on the morphology and size of nanostructures were investigated. The structural and optical properties of these Cu2O particles were studied by using XRD, SEM and UV–visible. The characteristic results revealed that using different carbohydrates in a specific concentration in water is not only reducing agent but also a directing agent to control Cu2O nanostructure morphologies. A possible mechanism was proposed to explain the formation of Cu2O nanostructures with different morphologies. The band gaps are estimated to be 1.89–2.08 eV according to the results of the optical measurements of the Cu2O nanostructures. & 2015 Elsevier B.V. All rights reserved.
Keywords: Cu2O Green synthesis Octahedral Nanosize Microstructure Nanoparticles
1. Introduction In recent years, controlling the structure of inorganic nanomaterial to search for new properties has become one of the major objectives of nanoscale science and technology, because such kind of material possesses structure-dependent characteristics and novel electronic, optical, magnetic, chemical and mechanical properties that cannot be obtained in their bulk counterparts [1,2]. Oxides of transition metals which have different oxidation states and coordination numbers are especially welcomed due to their unique electronic optical, thermal, photonic and catalytic properties in different morphologies [3]. As an important p-type semiconductor with a band gap 2.2 eV, cuprous oxide (Cu2O) has been widely used in applications such as catalysis, magnetic storage media, solar energy conversion, electrodes for lithium-ion batteries and gas sensors [4–6]. Synthesis of shape controlled Cu2O nano- and micro-crystals has already been performed [7–8]. To date, various morphologies of Cu2O structures such as hollow octahedral [9], flowerlike [10], hollow nanoparticles [11], cubic spherical shape [12] and hollow spheres [13] have been prepared under different conditions. The multi-pod, star-like, spheres and cubic Cu2O crystals were synthesized by reducing using Cu(II) salts with glucose [14–20]. These morphologies are produced using templates. Nevertheless, these strategies sometimes limit the size to within a few hundred nanometers. However, to the best of our knowledge, there is no report about
n
Corresponding author. Tel.: þ 98 21 22970003; fax: þ 98 21 22970033. E-mail addresses: [email protected], [email protected] (M. Sabbaghan). http://dx.doi.org/10.1016/j.matlet.2015.03.147 0167-577X/& 2015 Elsevier B.V. All rights reserved.
changing the carbohydrates as reducing agent to produce different morphologies and sizes of Cu2O nanostructures. Herein we disclose a general, high yielding, green synthetic of Cu2O nanostructures using different carbohydrates in definite concentration of precursor and base without using template with the reflux method. The structures as well as optical properties of the various morphologies of Cu2O were studied. 2. Experimental Copper acetate dihydrate was purchased from Aldrich. Sodium hydroxide was used without further purification. Copper acetate was employed as a copper source. In a typical experiment, 0.4 g of Cu(AcO)2 2H2O (2 mmol) was dissolved in distilled water under vigorous stirring, followed by addition of a reducing agent with specific concentration to the mixture (Table 1). In order to change to basic conditions (pH ¼14), 0.6 g of NaOH (6 mmol) was dissolved in the solution (S5–S6). The solution transferred to a round bottomed flask and was refluxed at 70 1C for 2 h. The precipitate was collected by filtration and washed with distilled water and ethanol (96%) several times. Finally, the Cu2O samples were dried in the air at room temperature. The detailed synthesis conditions are summarized in Table 1. 2.1. Characterization The morphology of nanostructure Cu2O was determined by using scanning electron microscopy (SEM) of a Holland Philips XL30 microscope. The X-ray diffraction (XRD) analysis was carried out at room temperature using a Holland Philips Xpert X-ray
2
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
Table 1 Preparation of Cu2O nanostructures in the reflux method in water with information on morphology, crystallite particle size and band gap energy. Sample Cu(OAc)2 H2O (mmol)
Reductant (mmol)
S1
1
Glucose (1) 10
7
S2
1
Glucose (1) 30
7
S3 S4 S5
2 1 1
Glucose (2) 30 Glucose (4) 30 Glucose (1) 30
7 7 14
S6
1
Glucose (2) 30
14
S7
1
S8 S9
1 2
Galactose (1) Ribose (1) Ribose (2)
Solvent (ml)
pH Morphology Size Band (nm) gap (eV)
30
7
Truncated octahedral NanorodNanoparticle Octahedral Nanoparticle Nanosheetlike NanorodNanoparticle Nanoparticle
46
1.44
34
1.90
31 35 41
1.89 1.97 2.0
47
2.08
32
1.96
30 30
7 7
Nanoparticle 18 Nanoparticle 22
1.92 1.96
powder diffractometer with Cu Kα radiation (λ ¼ 0.15406 nm), over the 2θ collection range of 20–801. Average crystallite sizes of products were calculated using Scherrer's formula: D¼ 0.9λ/β cosθ [21], where D is the diameter of the nanoparticles, λ (Cu Kα) ¼1.5406 Å and β is the full-width at half-maximum of the diffraction lines. The band gaps of our samples were determined by a UV–visible spectrometer on an instrument PG T80/T80 þ with drift and solid cell. The spectra were recorded at room temperature in the wavelength range of 200–800 nm and with the accuracy of 0.5 nm.
3. Results and discussion The cuprous oxide nanostructures were synthesized with the assistance of reducing carbohydrates by the reflux method in water. Fig. 1 shows the XRD patterns of as-prepared samples. The entire diffraction peaks match with cubic crystal type of Cu2O (JCPDS 05-0667). No reflections of impurity can be found in the pattern, which proves that pure cuprous oxide has been successfully prepared. The morphologies of the products were analyzed by SEM images shown in Fig. 2. Truncated octahedral morphology with size of in the scale of micrometers was synthesized in 10 ml of water (S1). For the preparation of nanostructure of Cu2O the solvent was increased up to 30 ml. The mixture of nanorods and nanoparticles was synthesized (S2). Homogeneous samples with uniform octahedral morphology (S3) were formed by increasing the reactants and glucose up to twice in 30 ml water in comparing of S2. By changing the ratio of Glucose/Cu (OAc)2.H2O to 4:1, nanoparticle morphology (S4) was obtained in this condition. To determine the effect of basic conditions, the experiments were carried out in pH¼14. When the proportion of Cu(OAc)2.H2O to glucose was 1:1 nanosheet like morphology was formed (S4). It seems that agglomeration of nanosheets sticking together is formed. By changing the ratio of Cu(OAc)2 H2O to glucose to 1:2, the mixture of nanorod and nanopartile was obtained. To determine the effect of other reducing carbohydrate in the formation of Cu2O nanostructures, experiments were carried out with ribose and Galactose, while keeping other reaction parameters unchanged. The SEM images of S7, S8 and S9 prepared show homogeneous samples with uniform nanoparticle morphologies in the same condition with S2 and S3. It is noticed that the morphology is the same with S4, but the size of particles is different. These morphologies were formed by the thermodynamically controlled reaction. Reactants concentration and reaction time are enough to have the thermodynamically controlled reaction in the reflux method.
Fig. 1. SEM images of Cu2O nanostructures.
Oxidation of anomeric carbon of glucose and other carbohydrates by cupric acetate produced a red cuprous oxide precipitate. In the hemiacetal form, C-1 of carbohydrates cannot be oxidized by Cu2 þ . However, the open-chain form is in equilibrium with the ring form, eventually the oxidation reaction goes to completion [22]. It seems that reducing carbohydrates are not only a reducing agent but also in hemiacetal form with forming the coordination with Cu2 þ is a directing agent to control Cu2O nanostructure morphologies (see supplementary data, Fig. SD1). There is more explanation about the effect of glucose and precursor on morphologies of Cu2O in supplementary data (Fig. SD2) [18–19]. It might be various carbohydrates form different complexes. The coordination would transfer to Cu2O after reflux at 70 1C for 2 h [23]. Also Cu2 þ reacted with OH̄ to form [Cu(OH)4]2- product upon the addition of NaOH (S5, S6). This complex coordination with carbohydrate by hydrogen bond causes to different morphologies in comparison neutral conditions. It can be concluded from the above results
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
S1
3
S2
2 µm
200 nm
S3
S4
200 nm
100 nm
S6
S5
200 nm
200 nm
S8
S7
S9
Fig. 2. XRD patterns of Cu2O nanostructures.
where K is a constant, α is the absorption coefficient, Ephoton is the discrete photoenergy and Eg is the band gap energy. The energy intercept of a plot of (αEphoton)2 vs. Ephoton yields Eg for a direct transition. Supplementary data show the corresponding band gap calculations of the as synthesized samples (Fig. SD3). The value of band gap energies is presented in Table 1. The band gap of nano Cu2O with various morphologies ranges from 1.89 to 2.08 which are redshift with respect to the band gap for bulk Cu2O (2.2 eV) [25]. The results show that the size, shape greatly affect band gap energy of the Cu2O samples.
4. Conclusion
Fig. 3. UV–visible absorption spectrum of the samples.
that different reducing agents in different concentrations and sodium hydroxide play important role in the morphology control and size of the Cu2O nanostructures. The UV–vis spectroscopy was performed on samples to observe changing in optical properties. Fig. 3 shows the absorption spectra of Cu2O nanostructures. The band gap energies can be estimated on according to following equation [24]: αEphoton ¼ K Ephoton Eg 1=2
Octahedral, nanorod and nanoparticle Cu2O samples could be obtained by adjusting the concentrations of glucose. By changing the reducing carbohydrate, nanoparticles structures of the products with size as small as 18–32 nm were obtained. Nanosheet like morphology was obtained with the addition of sodium hydroxide. The advantage of the present procedure is that the reaction is performed under green conditions by simple mixing of the starting materials at ambient pressure.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.03.147.
4
M. Sabbaghan et al. / Materials Letters 153 (2015) 1–4
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Hupp JT, Poeppelmeier KR. Science 2005;309:2008–9. Chen J, Xu LN, Li WY, Gou XL. Adv Mater 2005;17:582–5. Toberer ES, Seshadri R. Adv Mater 2005;17:2244–6. Zhang H, Ren X, Cui ZL. J Cryst Growth 2007;304:206–10. White B, Yin M, Hall A, Le D, Stolbov S, Rahman T, et al. Nano Lett 2006;6:2095–8. Zhang JT, Liu JF, Peng Q, Wang X, Li YD. Chem Mater 2006;18(4):867–71. Duan X, Zhang Y, Gao R, Jian Z, Zhao Y, Liu W, et al. Mater Lett 2012;68:146–8. Cai A, Wang Y, Du L, Ma Z. Mater Lett 2012;70:149–51. Feng L, Zhang C, Gao G, Cui D. Nanoscale Res Lett 2012;7:276–86. Yang Z, LiPing G, Xin S, JianJi W. Sci China Chem 2012;55:1580–6. Hung LI, Tsung CK, Huang W, Yang P. Adv Mater 2010;22:1910–4. Li H, Liu R, Zhao R, Zheng Y, Chen W, Xu Z. Cryst Growth Des 2006;6:2795–8. Gao JN, Li QS, Zhao HB, Li LS, Liu CL, Gongand QH, et al. Chem Mater 2008;20:6263–9.
[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]
Wang D, Mo M, Yu D, Xu L, Li F, Qian Y. Cryst Growth Des 2003;3:717–20. Zhang Y, Deng B, Zhang TR, Gao DM, Xu AW. J Phys Chem C 2010;114:5073–9. Kang W, Liu F, Su Y, Wang D, Shen Q. CrystEngComm 2011;13:4174–80. Hua Q, Chen K, Chang S, Ma Y, Huang WJ. Phys Chem C 2011;115:20618–27. Sui Y, Fu W, Yang H, Zeng Y, Zhang Y, Zhao Q, et al. Cryst Growth Des 2010;10:99–108. Cho YS, Huh YD. Bull. Korean Chem Soc 2014;35:309–12. Basu M, Sinha AK, Pradhan M, Sarkar S, Pal A, Mondal CJ. Phys Chem C 2012;116:25741–7. Sabbaghan M, Anaraki Firooz A, Jan Ahmadi V. Mol Liq 2012;175:135–40. Stick RV, Williams S. Carbohydrates: the essential molecules of life. 2nd ed. Elsevier Science; 2008. Guan L, Pang H, Wang J, Lu Q, Yinac J, Gao F. Chem Commun 2010;46:7022–4. Sabbaghan M, Mirzaei Behbahani B. Mater Lett 2014;117:28–30. Li H, Liu R, Liu Y, Huang H, Yu H, Ming H, et al. J.Mater Chem 2012;22:17470–5.