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A hydrothermal reaction to synthesize CuFeS2 nanorods
www.elsevier.nl/locate/inoche Inorganic Chemistry Communications 2 (1999) 569–571
A hydrothermal reaction to synthesize CuFeS2 nanorods Junqing Hu a,b, Qingyi Lu a,b, Bin Deng b, Kaibin Tang a,b,*, Yitai Qian a,b,U, Yuzhi Li a, Guien Zhou a, Xianming Liu a a
Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, PR China b Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, PR China Received 27 September 1999
Abstract A hydrothermal reaction route has been developed to prepare chalcopyrite phase CuFeS2 nanorods at 200–2508C. X-ray powder diffraction and transmission electron microscopy results reveal that the CuFeS2 synthesized displays nanorods with diameters of 20–40 nm and lengths ¨ of up to several micrometers. Elemental analysis gives the atomic ratio of Cu:Fe:S of 1:1.04:2.11. The 57Fe Mossbauer spectrum exhibits a six-peak hyperfine magnetic spectrum and a like-splitted line non-magnetic peak. The factors influencing the formation of the CuFeS2 nanorods were discussed. q1999 Elsevier Science S.A. All rights reserved. Keywords: Hydrothermal reaction; Synthesis; CuFeS2; Nanorods
Recently, considerable progress has been made in the synthesis of metal chalcogenide semiconductor nanocrystallines due to their important physical and chemical properties and their great potential applications [1–6]. Current attention of this field has focussed on the development of new methods for preparing one-dimensional nanocrystallines, such as nanotubes and nanorods [7,8]. They are expected to have remarkable properties as building blocks for many novel functional materials. Our research group has succeeded in applying a solvothermal synthetic technique for the preparation of binary metal chalcogenide nanorods [9–11]. The hydrothermal reaction route is one of the most promising solvothermal synthetic methods, which allows the size of the particles and their distribution as well as their morphology to be controlled [12,13]. In this paper, we report a hydrothermal reaction route for the synthesis of CuFeS2 nanorods. CuFeS2, I-III-VI2 compound, is known among the ternary semiconductors as an antiferromagnetic semiconductor with chalcopyrite structure [14,15]. It has novel optical, electrical and magnetic properties such as a very small optical absorp´ tempertion edge (0.5–0.6 eV) [16], and a very high Neel ature (5508C) [17]. CuFeS2 powders are obtained from a direct combination of the elements or a sinter-reaction of CuS and FeS [18,19] requiring a high temperature (600–8008C) and long reaction time (2–3 days). To our knowledge, the * Corresponding authors. Fax: q86 551 363 1760; e-mail: kbtang@ ustc.edu.cn
synthesis of CuFeS2 nanorods by a hydrothermal synthetic route has not been reported previously. CuCl, FeCl3P6H2O and (NH4)2S aqueous solution were selected as the reactants. The synthesis was carried out in an autoclave and can be represented by Eq. (1) CuClqFeCl 3q2(NH 4)2 S™CuFeS 2q4NH 4 Cl
(1)
In a typical procedure, appropriate amounts of CuCl, FeCl3P6H2O and (NH4)2S aqueous solution were put into a stainless steel autoclave of 50 ml capacity. The autoclave was then filled with distilled water up to 90% of the total volume. The autoclave was maintained at 200–2508C for 10 h and allowed to cool to room temperature. The precipitate was separated by filtration and was then washed several times with distilled water to remove NH4Cl and the other impurities. A dark yellow powder was obtained after being dried in a vacuum at 708C for 3 h. The sample was characterized by X-ray powder diffraction (XRD), on a Japan Rigaku Dmax-gA X-ray diffractometer with graphite-monchromatized Cu Ka radiation (ls ˚ 1.54178 A). Transmission electron microscopy (TEM) images were recorded on a Hitachi H-800 transmission electron microscope, using an accelerating voltage of 200 kV. Elemental analysis results were obtained from a Perkin-Elmer 1100B atomic absorption spectrophotometer (AAS), and a combustion neutralization titration. The magnetic behavior ¨ of iron in chalcopyrite CuFeS2 was studied by Mossbauer ¨ spectroscopy, using an Oxford MS-500 Mossbauer spectrom-
1387-7003/99/$ - see front matter q1999 Elsevier Science S.A. All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 9 9 ) 0 0 1 5 4 - 9
Friday Nov 19 01:15 PM
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292
570
J. Hu et al. / Inorganic Chemistry Communications 2 (1999) 569–571
Fig. 1. XRD pattern of the CuFeS2 nanorod sample prepared by a hydrothermal reaction route.
eter with Fe57 source in Pd on a constant velocity drive at room temperature. Chalcopyrite-type CuFeS2 is derived from the zinc blende structure in which two zinc ions are replaced orderly by one copper ion and one iron ion [16]. The lattice constants of ˚ and the cthis tetragonal cell are as5.2914, cs10.422 A, axis is nearly doubled. The unit cell contains two molecules (2CuFeS2) [20]. The XRD pattern of the CuFeS2 sample is shown in Fig. 1. All reflections can be indexed to the chalcopyrite phase CuFeS2. After refinement, the lattice constants as5.2867, ˚ and a c/a ratio of 1.97 are close to the values cs10.4126 A, reported in the literature [20] (JCPDS, 37-471). No impurity phases such as Cu2S and FeS were detected from this pattern. The broadened nature of these diffraction peaks indicates that the grain sizes of the sample are on nanometre scale. The elemental analysis gives a formula of CuFe1.04S2.11, which indicates the stoichiometrical relations between Cu, Fe and S. The TEM images of the CuFeS2 sample are given in Fig. 2. It can be seen that the synthesized CuFeS2 crystallites display a rodlike morphology with diameters of 20–40 nm and lengths of up to several micrometers. ¨ The room temperature Mossbauer spectrum of the CuFeS2 nanorods is illustrated in Fig. 3 and resembles spectra previously reported [21]. The spectrum consists of a six-peak hyperfine magnetic spectrum (isomer shift, 0.2925 mm/s; quadrupole splitting, y0.0361 mm/s; internal magnetic field, 342.73 kilogauss), and has been interpreted as due to the presence of high-spin Feq3 on the tetrahedral lattice sites of the chalcopyrite structure. However, the spectrum also
Friday Nov 19 01:15 PM
exhibits a like-splitted line non-magnetic peak (isomer shift, 0.4035 mm/s; quadrupole splitting, 0.6313 mm/s) close to the center. This indicates that the iron is in a non-magnetically ordered state, which may be due to the amorphous phase in the product. The influence of reaction temperature and time on the formation of CuFeS2 was studied. It was found that a suitable reaction temperature for the formation of CuFeS2 nanorods was 200–2508C. At temperatures up to 1808C CuFeS2 formed with a disk-like morphology and the size of the as-prepared CuFeS2 nanorods obviously increased at temperatures higher than 2808C. However, the pressure of water in the autoclave increases from 9.89 atm at 1808C to 63.29 atm at 2808C [22], so a change in the CuFeS2 morphology could also be attrib-
Fig. 2. TEM images ((a) and (b)) of the CuFeS2 nanorod sample.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292
J. Hu et al. / Inorganic Chemistry Communications 2 (1999) 569–571
571
¨ Fig. 3. Mossbauer spectrum of the CuFeS2 nanorods at room temperature.
uted to the influence of pressure on the synthetic reaction. The corresponding pressure range for the CuFeS2 nanorod is from 15.34 atm at 2008C to 39.23 atm at 2508C [22]. To obtain a CuFeS2 nanorod with a higher crystallinity, a reaction time of longer than 8 h at a suitable temperature was needed. The effect of different sulfur sources on the morphology of CuFeS2 was also investigated. Elemental S, Na2S and thiourea (NH2CSNH2) were used to replace (NH4)2S, keeping the other reaction conditions identical. From the TEM images (images not shown), the CuFeS2 crystallites also display a rodlike morphology when NH2CSNH2 was used whereas the CuFeS2 powders synthesized using S consist mainly of hexagon disk-like particles. When using Na2S as the sulfur source, the reaction did not produce CuFeS2; the products were mostly Cu2S and FeS. In conclusion, a hydrothermal reaction route has been developed to prepare chalcopyrite phase CuFeS2 nanorods at 200–2508C. The as-prepared CuFeS2 nanorods had diameters of 20–40 nm and lengths of up to several micrometers. The magnetic behavior of iron in chalcopyrite CuFeS2 was studied ¨ by Mossbauer spectroscopy at room temperature. The influence of various factors on the formation of the CuFeS2 nanorods was discussed. The present route can be readily extended to synthesize other analogous I-III-VI2 nanorods such as AgMS2 and CuMS2 (MsGa, In).
Friday Nov 19 01:15 PM
Acknowledgements This work was supported by the National Natural Science Foundation of China under Grant No. 59771017. References [1] L. Spanhel, M. Haase, H. Weller, A. Henglein, J. Am. Chem. Soc. 109 (1987) 5649. [2] M.G. Bawendi, et al., Phys. Rev. Lett. 65 (1990) 1623. [3] L.E. Brus, Appl. Phys. A 53 (1991) 465. [4] H. Weller, Angew. Chem., Int. Ed. Engl. 32 (1993) 41. [5] C.B. Murray, et al., Science 270 (1995) 1335. [6] P.V. Braum, et al., Nature 380 (1996) 325. [7] Y.D. Li, et al., Chem. Mater. 10 (1998) 2301. [8] W.Z. Wang, et al., Adv. Mater. 10 (1998) 1479. [9] S.H. Yu, et al., Chem. Mater. 10 (1998) 2309. [10] W.Z. Wang, et al., J. Am. Chem. Soc. 121 (1999) 4062. [11] W.Z. Wang, et al., Inorg. Chem. Commun. 2 (1999) 83. [12] M. Rozman, M. Drofenik, J. Am. Chem. Soc. 78 (1995) 2449. [13] J. Moom, et al., J. Mater. Res. 12 (1997) 189. [14] C.H.L. Goodman, R.W. Douglas, Physica 20 (1954) 1107. [15] T. Hamajima, et al., Phys. Rev. B 24 (1981) 3349. [16] T. Teranishi, K. Sato, K. Kondo, J. Phys. Soc. Jpn. 36 (1974) 1618. [17] G. Donney, et al., Phys. Rev. 112 (1958) 1917. [18] J.A. Tossell, et al., J. Chem. Phys. 77 (1982) 77. [19] J.E. Dutrizac, R.J.C. MacDonald, Mater. Res. Bull. 8 (1973) 961. [20] L. Pauling, L.O. Brockway, Z. Krist. 82 (1932) 188. [21] J.D. Vaughan, A.J. Tossell, Science 26 (1973) 375. [22] R.C. Weast, Handbook of Chemistry and Physics, CRC, Boca Raton, FL, 1984.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292
A hydrothermal reaction to synthesize CuFeS2 nanorods Junqing Hu a,b, Qingyi Lu a,b, Bin Deng b, Kaibin Tang a,b,*, Yitai Qian a,b,U, Yuzhi Li a, Guien Zhou a, Xianming Liu a a
Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, PR China b Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, PR China Received 27 September 1999
Abstract A hydrothermal reaction route has been developed to prepare chalcopyrite phase CuFeS2 nanorods at 200–2508C. X-ray powder diffraction and transmission electron microscopy results reveal that the CuFeS2 synthesized displays nanorods with diameters of 20–40 nm and lengths ¨ of up to several micrometers. Elemental analysis gives the atomic ratio of Cu:Fe:S of 1:1.04:2.11. The 57Fe Mossbauer spectrum exhibits a six-peak hyperfine magnetic spectrum and a like-splitted line non-magnetic peak. The factors influencing the formation of the CuFeS2 nanorods were discussed. q1999 Elsevier Science S.A. All rights reserved. Keywords: Hydrothermal reaction; Synthesis; CuFeS2; Nanorods
Recently, considerable progress has been made in the synthesis of metal chalcogenide semiconductor nanocrystallines due to their important physical and chemical properties and their great potential applications [1–6]. Current attention of this field has focussed on the development of new methods for preparing one-dimensional nanocrystallines, such as nanotubes and nanorods [7,8]. They are expected to have remarkable properties as building blocks for many novel functional materials. Our research group has succeeded in applying a solvothermal synthetic technique for the preparation of binary metal chalcogenide nanorods [9–11]. The hydrothermal reaction route is one of the most promising solvothermal synthetic methods, which allows the size of the particles and their distribution as well as their morphology to be controlled [12,13]. In this paper, we report a hydrothermal reaction route for the synthesis of CuFeS2 nanorods. CuFeS2, I-III-VI2 compound, is known among the ternary semiconductors as an antiferromagnetic semiconductor with chalcopyrite structure [14,15]. It has novel optical, electrical and magnetic properties such as a very small optical absorp´ tempertion edge (0.5–0.6 eV) [16], and a very high Neel ature (5508C) [17]. CuFeS2 powders are obtained from a direct combination of the elements or a sinter-reaction of CuS and FeS [18,19] requiring a high temperature (600–8008C) and long reaction time (2–3 days). To our knowledge, the * Corresponding authors. Fax: q86 551 363 1760; e-mail: kbtang@ ustc.edu.cn
synthesis of CuFeS2 nanorods by a hydrothermal synthetic route has not been reported previously. CuCl, FeCl3P6H2O and (NH4)2S aqueous solution were selected as the reactants. The synthesis was carried out in an autoclave and can be represented by Eq. (1) CuClqFeCl 3q2(NH 4)2 S™CuFeS 2q4NH 4 Cl
(1)
In a typical procedure, appropriate amounts of CuCl, FeCl3P6H2O and (NH4)2S aqueous solution were put into a stainless steel autoclave of 50 ml capacity. The autoclave was then filled with distilled water up to 90% of the total volume. The autoclave was maintained at 200–2508C for 10 h and allowed to cool to room temperature. The precipitate was separated by filtration and was then washed several times with distilled water to remove NH4Cl and the other impurities. A dark yellow powder was obtained after being dried in a vacuum at 708C for 3 h. The sample was characterized by X-ray powder diffraction (XRD), on a Japan Rigaku Dmax-gA X-ray diffractometer with graphite-monchromatized Cu Ka radiation (ls ˚ 1.54178 A). Transmission electron microscopy (TEM) images were recorded on a Hitachi H-800 transmission electron microscope, using an accelerating voltage of 200 kV. Elemental analysis results were obtained from a Perkin-Elmer 1100B atomic absorption spectrophotometer (AAS), and a combustion neutralization titration. The magnetic behavior ¨ of iron in chalcopyrite CuFeS2 was studied by Mossbauer ¨ spectroscopy, using an Oxford MS-500 Mossbauer spectrom-
1387-7003/99/$ - see front matter q1999 Elsevier Science S.A. All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 9 9 ) 0 0 1 5 4 - 9
Friday Nov 19 01:15 PM
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292
570
J. Hu et al. / Inorganic Chemistry Communications 2 (1999) 569–571
Fig. 1. XRD pattern of the CuFeS2 nanorod sample prepared by a hydrothermal reaction route.
eter with Fe57 source in Pd on a constant velocity drive at room temperature. Chalcopyrite-type CuFeS2 is derived from the zinc blende structure in which two zinc ions are replaced orderly by one copper ion and one iron ion [16]. The lattice constants of ˚ and the cthis tetragonal cell are as5.2914, cs10.422 A, axis is nearly doubled. The unit cell contains two molecules (2CuFeS2) [20]. The XRD pattern of the CuFeS2 sample is shown in Fig. 1. All reflections can be indexed to the chalcopyrite phase CuFeS2. After refinement, the lattice constants as5.2867, ˚ and a c/a ratio of 1.97 are close to the values cs10.4126 A, reported in the literature [20] (JCPDS, 37-471). No impurity phases such as Cu2S and FeS were detected from this pattern. The broadened nature of these diffraction peaks indicates that the grain sizes of the sample are on nanometre scale. The elemental analysis gives a formula of CuFe1.04S2.11, which indicates the stoichiometrical relations between Cu, Fe and S. The TEM images of the CuFeS2 sample are given in Fig. 2. It can be seen that the synthesized CuFeS2 crystallites display a rodlike morphology with diameters of 20–40 nm and lengths of up to several micrometers. ¨ The room temperature Mossbauer spectrum of the CuFeS2 nanorods is illustrated in Fig. 3 and resembles spectra previously reported [21]. The spectrum consists of a six-peak hyperfine magnetic spectrum (isomer shift, 0.2925 mm/s; quadrupole splitting, y0.0361 mm/s; internal magnetic field, 342.73 kilogauss), and has been interpreted as due to the presence of high-spin Feq3 on the tetrahedral lattice sites of the chalcopyrite structure. However, the spectrum also
Friday Nov 19 01:15 PM
exhibits a like-splitted line non-magnetic peak (isomer shift, 0.4035 mm/s; quadrupole splitting, 0.6313 mm/s) close to the center. This indicates that the iron is in a non-magnetically ordered state, which may be due to the amorphous phase in the product. The influence of reaction temperature and time on the formation of CuFeS2 was studied. It was found that a suitable reaction temperature for the formation of CuFeS2 nanorods was 200–2508C. At temperatures up to 1808C CuFeS2 formed with a disk-like morphology and the size of the as-prepared CuFeS2 nanorods obviously increased at temperatures higher than 2808C. However, the pressure of water in the autoclave increases from 9.89 atm at 1808C to 63.29 atm at 2808C [22], so a change in the CuFeS2 morphology could also be attrib-
Fig. 2. TEM images ((a) and (b)) of the CuFeS2 nanorod sample.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292
J. Hu et al. / Inorganic Chemistry Communications 2 (1999) 569–571
571
¨ Fig. 3. Mossbauer spectrum of the CuFeS2 nanorods at room temperature.
uted to the influence of pressure on the synthetic reaction. The corresponding pressure range for the CuFeS2 nanorod is from 15.34 atm at 2008C to 39.23 atm at 2508C [22]. To obtain a CuFeS2 nanorod with a higher crystallinity, a reaction time of longer than 8 h at a suitable temperature was needed. The effect of different sulfur sources on the morphology of CuFeS2 was also investigated. Elemental S, Na2S and thiourea (NH2CSNH2) were used to replace (NH4)2S, keeping the other reaction conditions identical. From the TEM images (images not shown), the CuFeS2 crystallites also display a rodlike morphology when NH2CSNH2 was used whereas the CuFeS2 powders synthesized using S consist mainly of hexagon disk-like particles. When using Na2S as the sulfur source, the reaction did not produce CuFeS2; the products were mostly Cu2S and FeS. In conclusion, a hydrothermal reaction route has been developed to prepare chalcopyrite phase CuFeS2 nanorods at 200–2508C. The as-prepared CuFeS2 nanorods had diameters of 20–40 nm and lengths of up to several micrometers. The magnetic behavior of iron in chalcopyrite CuFeS2 was studied ¨ by Mossbauer spectroscopy at room temperature. The influence of various factors on the formation of the CuFeS2 nanorods was discussed. The present route can be readily extended to synthesize other analogous I-III-VI2 nanorods such as AgMS2 and CuMS2 (MsGa, In).
Friday Nov 19 01:15 PM
Acknowledgements This work was supported by the National Natural Science Foundation of China under Grant No. 59771017. References [1] L. Spanhel, M. Haase, H. Weller, A. Henglein, J. Am. Chem. Soc. 109 (1987) 5649. [2] M.G. Bawendi, et al., Phys. Rev. Lett. 65 (1990) 1623. [3] L.E. Brus, Appl. Phys. A 53 (1991) 465. [4] H. Weller, Angew. Chem., Int. Ed. Engl. 32 (1993) 41. [5] C.B. Murray, et al., Science 270 (1995) 1335. [6] P.V. Braum, et al., Nature 380 (1996) 325. [7] Y.D. Li, et al., Chem. Mater. 10 (1998) 2301. [8] W.Z. Wang, et al., Adv. Mater. 10 (1998) 1479. [9] S.H. Yu, et al., Chem. Mater. 10 (1998) 2309. [10] W.Z. Wang, et al., J. Am. Chem. Soc. 121 (1999) 4062. [11] W.Z. Wang, et al., Inorg. Chem. Commun. 2 (1999) 83. [12] M. Rozman, M. Drofenik, J. Am. Chem. Soc. 78 (1995) 2449. [13] J. Moom, et al., J. Mater. Res. 12 (1997) 189. [14] C.H.L. Goodman, R.W. Douglas, Physica 20 (1954) 1107. [15] T. Hamajima, et al., Phys. Rev. B 24 (1981) 3349. [16] T. Teranishi, K. Sato, K. Kondo, J. Phys. Soc. Jpn. 36 (1974) 1618. [17] G. Donney, et al., Phys. Rev. 112 (1958) 1917. [18] J.A. Tossell, et al., J. Chem. Phys. 77 (1982) 77. [19] J.E. Dutrizac, R.J.C. MacDonald, Mater. Res. Bull. 8 (1973) 961. [20] L. Pauling, L.O. Brockway, Z. Krist. 82 (1932) 188. [21] J.D. Vaughan, A.J. Tossell, Science 26 (1973) 375. [22] R.C. Weast, Handbook of Chemistry and Physics, CRC, Boca Raton, FL, 1984.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 292