- Email: [email protected]
Synthesis and characterization of spherical hollow composed of Cu2S nanoparticles
Applied Surface Science 255 (2008) 1750–1753
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Synthesis and characterization of spherical hollow composed of Cu2S nanoparticles Ming Yang a,*, Xiao Yang b, Lufeng Huai a, Wei Liu a a b
Department of Chemistry and Environmental Engineering, Wuhan Polytechnic University, ChangQing Garden, Hankou, Wuhan 430023, PR China School of Material Science and Chemical Engineering, Hainan University, Haikou 570228, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 February 2008 Received in revised form 9 June 2008 Accepted 9 June 2008 Available online 17 June 2008
Hollow spheres of Cu2S nanoparticles with an average diameter of 200–400 nm have been prepared by thermal decomposition of CuSCN spheres at 450 8C and reaction with aqueous ammonia. The products were characterized by powder X-ray diffraction, transmission electron microscopy and UV–vis absorption spectroscopy. The band gap is estimated to be 2.96 eV according to the results of optical measurements of the hollow spheres of Cu2S nanoparticles. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Hollow spheres Copper(I) sulfide Semiconducting materials
1. Introduction Hollow spheres of nanometer to micrometer dimensions are pursued with great interest because of possible technical applications in catalysis, solar cells, drug delivery systems, separation techniques, photonics as well as piezoelectric and other dielectric devices [1,2]. Cu2S has been known for a long time as a type of indirect bandgap semiconductor [3]. It has been extensively investigated and widely used as components of solar cells [4,5]. Cu2S nanoparticles have been prepared by several different methods, such as liquid phase reaction [6], electrosynthesis [7], solventless synthesis [8], in situ preparation [9] and solvothermal route [10]. In this paper, we report a method to synthesize hollow spheres of Cu2S by thermal decomposition of CuSCN spheres at 450 8C and reaction with aqueous ammonia. Hollow spheres of Cu2S nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy.
gelatin were purchased from Shanghai Chemical Reagent Factory (China). Doubly distilled water was used throughout. 2.2. Synthesis of CuSCN spheres as precursor CuO powder was prepared by adding 50 mL of 1.0 mol L1 NaOH solution to the same volume of 0.5 mol L1 CuSO4 solution, aging the precipitated Cu(OH)2 gel at 90 8C for 24 h in a laboratory oven, thoroughly washing with doubly distilled water and freeze drying. The 0.5 mol L1 CuO suspension solution was prepared using double distilled water and CuO powder in which 6% gelatin was contained. 30 mL of 0.5 mol L1 (NH2OH)2H2SO4 solution and 30 mL of 1.0 mol L1 KSCN solution were slowly added to 50 mL of the 0.5 mol L1 CuO suspension stabilized solution with stirring for 4 h under agitation at 30 8C. pH was adjusted to 4–6 with H2SO4 in the course of the reaction. The CuSCN as intermediate product was separated by centrifugation. 2.3. Preparation of hollow spheres of Cu2S nanoparticles
2. Experimental procedure 2.1. Chemicals All the reagents used in the experiment were of the analytical purity. CuSO4, NaOH, (NH2OH)2H2SO4, KSCN, H2SO4, NH3H2O and
* Corresponding author. Fax: +86 27 83937409. E-mail address: [email protected] (M. Yang). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.06.027
The precipitates were thermal decomposed at 450 8C for 10 min, then reacted with 50 mL of 6 mol L1 NH3H2O solution for 5 h. The Cu2S nanocrystals obtained were washed thoroughly with doubly distilled water and vacuum dried at room temperature overnight. Powder XRD patterns were recorded on a Shimadzu XD-3A Xray diffractometer (Cu Ka radiation, l = 0.15418 nm). TEM was performed using a JEOL-JEM 200CX instrument. The samples used for TEM observations were prepared by dispersing some products
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753
1751
in ethanol followed by sonication for 10 min and then placing a drop of the dispersion onto a copper grid coated with a layer of amorphous carbon. A shimadzu UV-3100 photospectrometer was used to record the UV–vis absorption spectra of the as-prepared Cu2S. 3. Results and discussion 3.1. XRD pattern analysis An XRD pattern of the Cu2S particles is given in Fig. 1. The peaks of the XRD spectrum are clearly distinguishable. All of them can be perfectly assigned to cubic Cu2S, not only in the peak position, but also in their relative intensity. The peak positions are in good agreement with those for Cu2S powder obtained from the International Center of Diffraction Data (ICDD, formerly JCPDS, 65-2980). Fig. 1. XRD pattern of hollow spheres of Cu2S nanoparticles.
3.2. TEM measurements The morphologies of the intermediate products and asprepared Cu2S particles were studied by TEM. The CuSCN as
Fig. 2. TEM micrographs of (a) the CuSCN particles as intermediate product under standard procedure, (b) the hollow spheres of Cu2S nanoparticles, and (c) the CuO crystals.
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753
1752
Fig. 4. The controllable synthesis route for hollow spheres of Cu2S nanoparticles.
3.4. Proposed reaction path Based on the investigation of the formation of Cu2S hollow spheres, the possible mechanism has been summarized: CuSO4 þ 2NaOH ! CuO þ H2 O þ Na2 SO4 4CuO þ ðNH2 OHÞ2 H2 SO4 þ H2 SO4 þ 4KSCN ! 4CuSCN þ N2 O þ 5H2 O þ 2K2 SO4 6CuSCN þ 11O2 ! 2Cu2 S þ 2CuO þ 4SO2 þ 6CO2 þ 3N2 CuO þ 4NH3 H2 O ! CuðNH3 Þ4 2þ þ 2OH þ 3H2 O
Fig. 3. (a) The UV–vis absorption spectrum of the Cu2S hollow spheres dispersed in ethanol solution, and (b) plots of (aEphot)2 vs. Ephot for direct transitions.
intermediate products exhibited spheres as shown in Fig. 2a. Fig. 2b was shown the spherical structure of Cu2S particles with average dimensions of about 200–400 nm. The TEM image exhibits a clear porous structure on the spherical surface and the hollow inside can also be observed. 3.3. Optical properties We have carried out the UV–vis absorption spectrum of the product in order to resolve the excitonic or interband transitions of Cu2S particles. The UV–vis absorption spectrum of the asprepared Cu2S particles dispersed in ethanol solution as shows in Fig. 3a. The Cu2S particles were well dispersed in ethanol to form a transparent solution by sonication for 10 min. An estimate of the optical band gap is obtained using the following equation for a semiconductor:
aðyÞ ¼ A
m=2 hy Eg ; 2
where A is a constant, a is the absorption coefficient and m equals 1 for a direct transition. The energy intercept of a plot of (aEphot)2 vs. Ephot yields Eg for a direct transition (Fig. 3b) [11]. The band gap of the hollow spheres of Cu2S is calculated from the UV–vis absorption spectrum to be 2.96 eV, which is larger than the reported value for the bulk Cu2S (Eg = 1.8 eV) [12].
In this experiment, the CuO crystals (TEM micrograph is show in Fig. 2c) were prepared by the reaction between CuSO4 and NaOH. Hydroxylamine hydrosulfate was used as a reducing agent. The gelatin has been used a protective medium for synthesizing CuSCN nanospheres. The spherical CuSCN particles can be prepared by the reaction of CuO, (NH2OH)2H2SO4 and KSCN in the presence of gelatin. We employed CuSCN spheres as the precursory solid. The CuSCN spheres were thermal decomposed at 450 8C. Then, the unwanted component CuO can be fully removed using NH3H2O solutions. The preparation of hollow spheres of pure Cu2S is achieved. The controllable synthesis route for hollow spheres of Cu2S nanoparticles as shown in Fig. 4. 4. Conclusion Hollow spheres of Cu2S nanoparticle have been successfully prepared by a simple technique. The possible mechanism was summarized. The band gap is estimated to be 2.96 eV according to the result of optical measurements of the Cu2S. It is expected that the method can be extended to prepare hollow spheres of other semiconducting materials. Acknowledgements This work was supported by the National Nature Science Foundation of China (No. 60171004), and the Nature Science Foundation of Hubei Province (2004ABA095). References [1] [2] [3] [4] [5]
S.H. Park, Y. Xia, Adv. Mater. 10 (1998) 1045. F. Caruso, Chem. Eur. J. 6 (2000) 413. S. Wang, L. Guo, X. Wen, S. Yang, J. Zhao, J. Liu, Z. Wu, Mater. Chem. Phys. 75 (2002) 32. A.P. Alivisatons, Science 271 (1996) 933. M. Dachraoui, J. Vedel, Sol. Cells 22 (1987) 187.
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753 [6] C.H. An, X.Y. Chen, S.T. Wang, Chin. J. Inorg. Chem. 23 (2007) 319. [7] D.R. Rodrigo, B. Daniela, S. Ricardo, G. Humberto, C. Ricardo, J. Phys. Chem. B 106 (2002) 12684. [8] J.M.B. Sigman, A. Ghezelbash, T. Hanrath, A.E. Saunders, F. Lee, B.A. Korgel, J. Am. Chem. Soc. 125 (2003) 16050.
1753
[9] G.M. Liu, T. Schulmeyer, A. Thissen, A. Klein, W. Jaegermann, Appl. Phys. Lett. 82 (2003) 2269. [10] S. Gorai, D. Ganguli, S. Chaudhuri, Mater. Lett. 59 (2005) 826. [11] S. Tsunekawa, T. Fukuda, A. Kasuya, J. Appl. Phys. 87 (2000) 1319. [12] I. Grozdanov, J. Solid State Chem. 114 (1995) 469.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Synthesis and characterization of spherical hollow composed of Cu2S nanoparticles Ming Yang a,*, Xiao Yang b, Lufeng Huai a, Wei Liu a a b
Department of Chemistry and Environmental Engineering, Wuhan Polytechnic University, ChangQing Garden, Hankou, Wuhan 430023, PR China School of Material Science and Chemical Engineering, Hainan University, Haikou 570228, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 February 2008 Received in revised form 9 June 2008 Accepted 9 June 2008 Available online 17 June 2008
Hollow spheres of Cu2S nanoparticles with an average diameter of 200–400 nm have been prepared by thermal decomposition of CuSCN spheres at 450 8C and reaction with aqueous ammonia. The products were characterized by powder X-ray diffraction, transmission electron microscopy and UV–vis absorption spectroscopy. The band gap is estimated to be 2.96 eV according to the results of optical measurements of the hollow spheres of Cu2S nanoparticles. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Hollow spheres Copper(I) sulfide Semiconducting materials
1. Introduction Hollow spheres of nanometer to micrometer dimensions are pursued with great interest because of possible technical applications in catalysis, solar cells, drug delivery systems, separation techniques, photonics as well as piezoelectric and other dielectric devices [1,2]. Cu2S has been known for a long time as a type of indirect bandgap semiconductor [3]. It has been extensively investigated and widely used as components of solar cells [4,5]. Cu2S nanoparticles have been prepared by several different methods, such as liquid phase reaction [6], electrosynthesis [7], solventless synthesis [8], in situ preparation [9] and solvothermal route [10]. In this paper, we report a method to synthesize hollow spheres of Cu2S by thermal decomposition of CuSCN spheres at 450 8C and reaction with aqueous ammonia. Hollow spheres of Cu2S nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy.
gelatin were purchased from Shanghai Chemical Reagent Factory (China). Doubly distilled water was used throughout. 2.2. Synthesis of CuSCN spheres as precursor CuO powder was prepared by adding 50 mL of 1.0 mol L1 NaOH solution to the same volume of 0.5 mol L1 CuSO4 solution, aging the precipitated Cu(OH)2 gel at 90 8C for 24 h in a laboratory oven, thoroughly washing with doubly distilled water and freeze drying. The 0.5 mol L1 CuO suspension solution was prepared using double distilled water and CuO powder in which 6% gelatin was contained. 30 mL of 0.5 mol L1 (NH2OH)2H2SO4 solution and 30 mL of 1.0 mol L1 KSCN solution were slowly added to 50 mL of the 0.5 mol L1 CuO suspension stabilized solution with stirring for 4 h under agitation at 30 8C. pH was adjusted to 4–6 with H2SO4 in the course of the reaction. The CuSCN as intermediate product was separated by centrifugation. 2.3. Preparation of hollow spheres of Cu2S nanoparticles
2. Experimental procedure 2.1. Chemicals All the reagents used in the experiment were of the analytical purity. CuSO4, NaOH, (NH2OH)2H2SO4, KSCN, H2SO4, NH3H2O and
* Corresponding author. Fax: +86 27 83937409. E-mail address: [email protected] (M. Yang). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.06.027
The precipitates were thermal decomposed at 450 8C for 10 min, then reacted with 50 mL of 6 mol L1 NH3H2O solution for 5 h. The Cu2S nanocrystals obtained were washed thoroughly with doubly distilled water and vacuum dried at room temperature overnight. Powder XRD patterns were recorded on a Shimadzu XD-3A Xray diffractometer (Cu Ka radiation, l = 0.15418 nm). TEM was performed using a JEOL-JEM 200CX instrument. The samples used for TEM observations were prepared by dispersing some products
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753
1751
in ethanol followed by sonication for 10 min and then placing a drop of the dispersion onto a copper grid coated with a layer of amorphous carbon. A shimadzu UV-3100 photospectrometer was used to record the UV–vis absorption spectra of the as-prepared Cu2S. 3. Results and discussion 3.1. XRD pattern analysis An XRD pattern of the Cu2S particles is given in Fig. 1. The peaks of the XRD spectrum are clearly distinguishable. All of them can be perfectly assigned to cubic Cu2S, not only in the peak position, but also in their relative intensity. The peak positions are in good agreement with those for Cu2S powder obtained from the International Center of Diffraction Data (ICDD, formerly JCPDS, 65-2980). Fig. 1. XRD pattern of hollow spheres of Cu2S nanoparticles.
3.2. TEM measurements The morphologies of the intermediate products and asprepared Cu2S particles were studied by TEM. The CuSCN as
Fig. 2. TEM micrographs of (a) the CuSCN particles as intermediate product under standard procedure, (b) the hollow spheres of Cu2S nanoparticles, and (c) the CuO crystals.
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753
1752
Fig. 4. The controllable synthesis route for hollow spheres of Cu2S nanoparticles.
3.4. Proposed reaction path Based on the investigation of the formation of Cu2S hollow spheres, the possible mechanism has been summarized: CuSO4 þ 2NaOH ! CuO þ H2 O þ Na2 SO4 4CuO þ ðNH2 OHÞ2 H2 SO4 þ H2 SO4 þ 4KSCN ! 4CuSCN þ N2 O þ 5H2 O þ 2K2 SO4 6CuSCN þ 11O2 ! 2Cu2 S þ 2CuO þ 4SO2 þ 6CO2 þ 3N2 CuO þ 4NH3 H2 O ! CuðNH3 Þ4 2þ þ 2OH þ 3H2 O
Fig. 3. (a) The UV–vis absorption spectrum of the Cu2S hollow spheres dispersed in ethanol solution, and (b) plots of (aEphot)2 vs. Ephot for direct transitions.
intermediate products exhibited spheres as shown in Fig. 2a. Fig. 2b was shown the spherical structure of Cu2S particles with average dimensions of about 200–400 nm. The TEM image exhibits a clear porous structure on the spherical surface and the hollow inside can also be observed. 3.3. Optical properties We have carried out the UV–vis absorption spectrum of the product in order to resolve the excitonic or interband transitions of Cu2S particles. The UV–vis absorption spectrum of the asprepared Cu2S particles dispersed in ethanol solution as shows in Fig. 3a. The Cu2S particles were well dispersed in ethanol to form a transparent solution by sonication for 10 min. An estimate of the optical band gap is obtained using the following equation for a semiconductor:
aðyÞ ¼ A
m=2 hy Eg ; 2
where A is a constant, a is the absorption coefficient and m equals 1 for a direct transition. The energy intercept of a plot of (aEphot)2 vs. Ephot yields Eg for a direct transition (Fig. 3b) [11]. The band gap of the hollow spheres of Cu2S is calculated from the UV–vis absorption spectrum to be 2.96 eV, which is larger than the reported value for the bulk Cu2S (Eg = 1.8 eV) [12].
In this experiment, the CuO crystals (TEM micrograph is show in Fig. 2c) were prepared by the reaction between CuSO4 and NaOH. Hydroxylamine hydrosulfate was used as a reducing agent. The gelatin has been used a protective medium for synthesizing CuSCN nanospheres. The spherical CuSCN particles can be prepared by the reaction of CuO, (NH2OH)2H2SO4 and KSCN in the presence of gelatin. We employed CuSCN spheres as the precursory solid. The CuSCN spheres were thermal decomposed at 450 8C. Then, the unwanted component CuO can be fully removed using NH3H2O solutions. The preparation of hollow spheres of pure Cu2S is achieved. The controllable synthesis route for hollow spheres of Cu2S nanoparticles as shown in Fig. 4. 4. Conclusion Hollow spheres of Cu2S nanoparticle have been successfully prepared by a simple technique. The possible mechanism was summarized. The band gap is estimated to be 2.96 eV according to the result of optical measurements of the Cu2S. It is expected that the method can be extended to prepare hollow spheres of other semiconducting materials. Acknowledgements This work was supported by the National Nature Science Foundation of China (No. 60171004), and the Nature Science Foundation of Hubei Province (2004ABA095). References [1] [2] [3] [4] [5]
S.H. Park, Y. Xia, Adv. Mater. 10 (1998) 1045. F. Caruso, Chem. Eur. J. 6 (2000) 413. S. Wang, L. Guo, X. Wen, S. Yang, J. Zhao, J. Liu, Z. Wu, Mater. Chem. Phys. 75 (2002) 32. A.P. Alivisatons, Science 271 (1996) 933. M. Dachraoui, J. Vedel, Sol. Cells 22 (1987) 187.
M. Yang et al. / Applied Surface Science 255 (2008) 1750–1753 [6] C.H. An, X.Y. Chen, S.T. Wang, Chin. J. Inorg. Chem. 23 (2007) 319. [7] D.R. Rodrigo, B. Daniela, S. Ricardo, G. Humberto, C. Ricardo, J. Phys. Chem. B 106 (2002) 12684. [8] J.M.B. Sigman, A. Ghezelbash, T. Hanrath, A.E. Saunders, F. Lee, B.A. Korgel, J. Am. Chem. Soc. 125 (2003) 16050.
1753
[9] G.M. Liu, T. Schulmeyer, A. Thissen, A. Klein, W. Jaegermann, Appl. Phys. Lett. 82 (2003) 2269. [10] S. Gorai, D. Ganguli, S. Chaudhuri, Mater. Lett. 59 (2005) 826. [11] S. Tsunekawa, T. Fukuda, A. Kasuya, J. Appl. Phys. 87 (2000) 1319. [12] I. Grozdanov, J. Solid State Chem. 114 (1995) 469.