Ultrasonics Sonochemistry 16 (2009) 800–804
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Sonochemical growth of antimony sulfoiodide in multiwalled carbon nanotube M. Nowak a,*, M. Jesionek a, P. Szperlich a, J. Szala b, T. Rzychon´ b, D. Stróz_ c a b c
´ skiego 8, 40-019 Katowice, Poland Solid State Physics Section, Institute of Physics, Silesian University of Technology, ul. Krasin ´ skiego 8, 40-019 Katowice, Poland Department of Materials Science, Silesian University of Technology, ul. Krasin Institute of Material Science, University of Silesia, ul. Bankowa 12, 40-007 Katowice, Poland
a r t i c l e
i n f o
Article history: Received 26 January 2009 Received in revised form 24 February 2009 Accepted 5 March 2009 Available online 20 March 2009 PACS: 61.48.De 71.20.Nr 81.07.Bc 82.70.Gg
a b s t r a c t This paper presents for the ﬁrst time the nanocrystalline, semiconducting ferroelectrics antimony sulfoiodide (SbSI) grown in multiwalled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, S and I in the presence of methanol under ultrasonic irradiation (35 kHz, 2.6 W/cm2) at 323 K for 3 h. The CNTs ﬁlled with SbSI were characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, and optical diffuse reﬂection spectroscopy. These investigations exhibit that the SbSI ﬁlling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect forbidden energy band gap EgIf = 1.871(1) eV. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: Carbon nanotubes Antimony sulfoiodide Sonochemistry Encapsulation Semiconductors
1. Introduction Since their discovery by  various potential applications have been proposed for carbon nanotubes (CNTs): sensors, ﬁeld emission displays, nanometer-sized semiconductor devices and hydrogen storage media. There is a huge literature stream related to nanotube research. On a fundamental level, there are still challenges to mass-produce controlled nanostructures at reasonable cost and new features. One strategy is to use the CNTs themselves, controlling useful properties via their radii and morphologies. An alternative approach leading to new features of CNTs, i.e., directional action on their versatile electronic characteristics, is based on ﬁlling them with condensed substances from a wide range of materials. CNTs are sp2 graphene carbon cylinders capable of hosting a variety of species, including 1D crystals of metals, metal salts and oxides; semiconductors; superconductors; helical iodine chains; and chains of fullerene or endofullerene molecules (see e.g., literature cited in [2–4]). Among crystals grown within CNTs there are halogenides: BaI2 , KI , LaI2 , LaI3 , CoI2 , LaCl3 , UCl4 , (KCl)x(UCl4)1x , and AgCl1xIx . Such objects are distinguished in their properties from both hollow nano* Corresponding author. Tel.: +48 32 6034167; fax: +48 32 6034370. E-mail address: [email protected]
(M. Nowak). 1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2009.03.007
tubes and the encapsulated substances, which permits one to purpose-tailor ‘‘nanowires” and ‘‘nanocables” with unique physical and chemical properties [2,7]. These studies have been prompted by a desire to synthesize a new hybrid material on the nanometric scale: the antimony sulfoiodide (SbSI) within CNTs. Recently  a novel sonochemical method for direct preparation of semiconducting and ferroelectric SbSI nanowires has been established. The determined  value of the indirect forbidden energy band gap of SbSI gel EgIf = 1.829(27) eV is well compared to the bulk value of band gap of SbSI reported in the literature (see Refs. in ). The maximum of dielectric constant e = 1.6 104 of SbSI nanowires was observed at Curie temperature Tc = 292(1) K  that well corresponds with the phase transition in bulk SbSI crystals. It should be underlined that the bulk SbSI has an unusually large number of very interesting properties. Among them there are the photoferroelectricity, pyroelectric, pyrooptic, piezoelectric, electromechanical, electrooptic, photorefractive and nonlinear optical effects. Therefore SbSI is taken into consideration as a valuable material for many applications (see the literature cited in ). The current status of research in sorption properties of CNTs was reviewed in . There are known a few methods for ﬁlling CNTs with different substances : catalytic synthesis of nanotubes using the metals as catalysts, capillary drawing-in of molten
M. Nowak et al. / Ultrasonics Sonochemistry 16 (2009) 800–804
materials or materials dissolved in solvents having a low surface tension, saturation with metal vapor as well as electrochemical methods based on passing the electrical current through an electrolyte containing dissolved metal atoms. In this paper we used another method for inserting materials into the inner cavity of a nanotube. Our method is based on sonochemistry. It is well known [13–16] that ultrasound can induce new reactivities leading to the formation of unexpected chemical species, what makes sonochemistry unique is the remarkable phenomenon of cavitation [16,17]. Comparing sonochemical method of preparing materials with the traditional ones, it can be seen that ultrasound irradiation can be used at room temperature and ambient pressure to promote heterogeneous reactions that normally occur only under extreme conditions of hundreds of atmospheres and degrees (see e.g., [13,18]). 2. Experiment The SbSI was prepared in CNTs ultrasonically from the constituents (the elements Sb, S and I). Methanol served as the solvent for this reaction. All the reagents used in our experiments were of analytical purity and were used without further puriﬁcation. Antimony (99.95%) and multiwalled CNTs (90+%) were purchased from Sigma–Aldrich. Sublimated sulfur (pure p.a.), iodine (pure p.a.) and absolute methanol (pure p.a.) were purchased from POCH SA (Gliwice, Poland). In a typical procedure, the elemental mixture with stoichiometric ratio of e.g., 0.380 g Sb, 0.099 g S and 0.394 g I, was immersed with 0.282 g of CNTs in 40 ml absolute methanol, which was contained in a 54 ml Pyrex glass cylinder of 20 mm inside diameter. The cylinder was partly submerged in water in an ultrasonic reactor (InterSonic IS-UZP-2, frequency 35 kHz, with 75 W electrical power and 2.6 W/cm2 power density guaranteed by the manufacturer). The used experimental set up and the applied procedure were the same as the described in . The sonochemical process was continued 3 h at 323 K temperature of the water in the ultrasonic reactor. When the soniﬁcation process was ﬁnished a dark sol was obtained. It was centrifuged using the MPW-223e centrifuge, MPW Med. Instruments (Poland), to extract the products. Then the liquid above the sediment was replaced with pure methanol to wash the precipitates. The centrifugation and washing were performed 5 times. At the end methanol was evaporated from the sample during the drying in air at room temperature, so a brown-purple substance was obtained. Characterization of the multiwalled CNTs ﬁlled with SbSI was accomplished using different techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and optical diffuse reﬂection spectroscopy (DRS). Description of the used equipments and the applied procedures were given in .
Fig. 1. The powder XRD pattern of dried multiwalled CNTs ﬁlled with SbSI ultrasonically in methanol.
Table 1 Positions of the unidentiﬁed X-ray diffraction peaks in the powder XRD pattern of dried multiwalled CNTs ﬁlled with SbSI ultrasonically in methanol. 2h (°)
16.51 18.66 29.00
0.536 0.475 0.308
P63mc with the cell constants a = 0.2470 nm and c = 0.6790 nm . The third group of a few additional X-ray diffraction lines is presented in Table 1. They are discussed in the next section. The typical SEM micrograph of dried CNTs ﬁlled with SbSI prepared ultrasonically in methanol is shown in Fig. 2. The EDAX analysis of this material was also done, and only characteristic peaks for carbon, antimony, sulfur and iodide were observed (Fig. 3). The measured atomic concentrations of Sb, S, I and C are presented in Table 2 and discussed in the next section. The TEM (Figs. 4 and 5) and HRTEM (Fig. 6) of an individual CNTs sonochemically ﬁlled with SbSI reveals that the product consists of coaxial nanocables. The lateral dimension of the nanocables (see the representative SEM and TEM images in Figs. 2, 4 and 5) is
3. Results The powder XRD pattern of the CNTs ﬁlled with SbSI is shown in Fig. 1. The well-deﬁned, sharp diffraction lines suggest the wellcrystallized substance. It was found that the diffraction lines can be divided into three groups. In the ﬁrst group, containing most of the lines, the peaks can be indexed to be a pure orthorhombic phase for SbSI with the cell constants a = 0.858 nm, b = 1.017 nm, and c = 0.414 nm. The identiﬁcation was done using the PCSIWIN computer program and the data from JCPDS-International Centre for Diffraction Data 2000. The intensities and positions of the peaks are in good agreement with literature values for SbSI . The second group of diffraction lines can be indexed to be a carbon phase
Fig. 2. The typical SEM micrographs of dried multiwalled CNTs ﬁlled with SbSI ultrasonically in methanol.
M. Nowak et al. / Ultrasonics Sonochemistry 16 (2009) 800–804
Fig. 3. The EDAX spectra of dried multiwalled CNTs ﬁlled with SbSI ultrasonically in methanol.
Table 2 Atomic concentration of components of the dried multiwalled CNTs ﬁlled with SbSI ultrasonically in methanol determined by EDAX. Element
Sb S I C
Fig. 5. Typical TEM image of the end of relatively thick individual multiwalled CNT ﬁlled with SbSI ultrasonically in methanol.
Results of EDAX investigations Concentration of all detected elements (at. %)
Concentration of components without C (at. %)
5.1(3) 1.7(3) 3.8(3) 89.4(13.4)
46(2) 21(3) 33(2)
Fig. 6. Typical HRTEM image of an individual multiwalled CNT ﬁlled with SbSI ultrasonically in methanol. The fringe spacings of 0.319(2) nm (1) and 0.209(2) nm (2) correspond to the interplanar distances between the (2 2 0) planes of SbSI crystal and (1 0 1) planes of carbon nanotube, respectively.
Fig. 4. Typical TEM image of a relatively thin individual multiwalled CNT ﬁlled with SbSI ultrasonically in methanol.
in the range from 30 to 200 nm, and their lengths reach up to several micrometers. The HRTEM image of an individual CNT sonochemically ﬁlled with SbSI (Fig. 6) exhibits good crystallinity of the SbSI and its clear (2 2 0) lattice fringes parallel to the nanocable axis. It indicates the growth of SbSI inside the CNT in [0 0 1] direction. The interplanar spacing is about 0.319(2) nm, which coincide with the interplanar spacing 0.32494 nm of (2 2 0) planes of the
orthorhombic structure of conventional SbSI . Fig. 6 shows also the lattice fringes of the CNT walls. The fringe spacings of 0.209(2) nm match with the 0.21390 nm interplanar distances between the (1 0 0) planes of carbon nanotubes . All these results correspond well with the XRD patterns (Fig. 1) of the CNTs sonochemically ﬁlled with SbSI. The SAED pattern (Fig. 7) recorded on the end of multiwalled CNT ﬁlled with SbSI (presented in Fig. 5) indicates the interplanar spacings appropriate for CNTs as well as SbSI crystals (see Table 3). In Fig. 8 the diffuse reﬂectance spectrum of CNTs ﬁlled with SbSI is compared with the spectrum registered for hollow CNTs in methanol. In the ﬁrst case one can see the characteristic for semiconducting materials edge of fundamental absorption around
M. Nowak et al. / Ultrasonics Sonochemistry 16 (2009) 800–804
Fig. 8. Comparison of the diffuse reﬂectance spectra of the multiwalled CNTs ﬁlled with SbSI (j) ultrasonically in methanol and of the empty multiwalled CNTs (h) in methanol.
Fig. 7. SAED pattern of multiwalled CNT ﬁlled with SbSI ultrasonically in methanol (shown in Fig. 5). The diffraction patterns correspond to the interplanar distances presented in Table 3.
Table 3 Comparison of interplanar spacings determined by SAED (Fig. 7) of multiwalled CNT ﬁlled with SbSI ultrasonically in methanol with literature data for CNTs and SbSI bulk crystals. Sign
Results of the SAED dhkl (nm)
4 5 2 6 3
0.3732 0.3470 0.2189 0.2089 0.1446
8 Circle 9 Circle
Reﬂex Reﬂex Reﬂex
10 Circle 11 Circle 12 Circle
0.1036 0.07874 0.07038
Literature data For C [20–22]
For SbSI [19,25]
(h k l)
(h k l)
– – – 0.33950 0.21390 0.20402 – – – – 0.12350 0.11606 0.11464 0.11316 0.10425 0.07954 0.07720
– – – (0 0 2) (1 0 0) (1 0 1) – – – – (1 1 0) (1 1 2) (1 0 5) (0 0 6) (2 0 2) (1 2 2) (2 0 6)
0.43402 0.42450 0.38465 0.35036 0.21663 0.20800 0.14244 0.14244 0.12031 0.11960 – – – – – – –
(1 2 0) (2 0 0) (0 1 1) (1 1 1) (3 3 0) (0 0 2) (4 2 2) (5 3 1) (1 4 3) (1 8 1) – – – – – – –
615 nm. However, the diffuse reﬂectance decreases also with increasing wavelengths (Fig. 8), probable due to the large amount of free carriers absorbing light. Fig. 9 presents the spectrum of Kubelka–Munk function (FKM) derived from the diffuse reﬂectance data presented in Fig. 8. This spectrum was least square ﬁtted with theoretical dependences appropriate for different mechanisms of absorption. The best ﬁtting was obtained for the sum of indirect forbidden absorption without excitons and phonon statistics (a1), free carrier absorption (a2) and constant absorption term (a3) (see the literature in [11,23]):
a ¼ a1 þ a2 þ a3 where
Fig. 9. Fitting of the spectrum of the Kubelka–Munk function calculated for diffuse reﬂectance (presented in Fig. 8) of the multiwalled CNTs ﬁlled with SbSI. Solid curve represents the least square ﬁtted theoretical dependence for the sum of indirect forbidden absorption without excitons and phonon statistics, free carrier absorption and constant absorption term (description in the text; values of the ﬁtted parameters are given in Table 4).
a1 ¼ 0 for hm 6 EgIf a1 ¼ A60 ðhm EgIf Þ3 for hm > EgIf a2 ¼ A125 k2 a3 ¼ A0
ð2Þ ð3Þ ð4Þ
where EgIf represents the indirect forbidden energy gap, EU is the Urbach energy, A0, A60, A125 are constant parameters, hm is the photon energy. The determined values of these parameters are given in Table 3. In the same table they are compared with parameters of SbSI nanowires prepared sonochemically in methanol  and ethanol . 4. Discussion It is known that the mode of insertion dictates the nature and morphology of the obtained ﬁlling of CNTs . When the ﬁlling is induced via solution-deposition, small discrete encapsulates are obtained, whereas when it is obtained via capillarity, continuously ﬁlled CNTs are observed. Probably the last happens when CNTs are ﬁlled sonochemically by SbSI. As in the case of ultrasonically produced alone SbSI , the transient high-temperature and high-pressure ﬁeld produced during ultrasound irradiation provide a favorable environment for the 1D growth of the SbSI
M. Nowak et al. / Ultrasonics Sonochemistry 16 (2009) 800–804
Table 4 Comparison of the values of indirect forbidden energy gap EgIf and the other parameters of multiwalled CNTs ﬁlled with SbSI with parameters of SbSI gels produced sonochemically in methanol  and ethanol (after ) that were determined from the ﬁtting of the spectrum of Kubelka–Munk function evaluated from the measured diffuse reﬂectance. Fitted parameters
CNTs ﬁlled with SbSI sonochemically prepared in methanol
SbSI nanowires sonochemically prepared in methanol 
SbSI nanowires sonochemically prepared in ethanol 
EgIf (eV) A60 (1/(eV3m)) A125 (1012 m2) A0 (1/m) EU (eV) AU (1/m)
1.871(1) 95.6(7) 8.24(1) 2.702(3) – –
1.854(3) 157(1) – 0.0213(1) 0.1470(20) 84.4(3) 109
1.829(27) 54.83(14) – 0.0321(13) 0.1031(16) 0.3570(19) 109
nanocrystals from elements inside multiwalled CNTs in methanol, though the bulk solution surrounding the collapsing bubbles is at ambient temperature and atmospheric pressure. Despite the tubes ﬁlling, the observed nanowire type morphology of the product (Fig. 6) is possibly due to the inherent chain type structure and growth habit of the SbSI [11,25]. Discussion of the crystal habit, the anisotropy of growth kinetics, and the critical role of unusual chain-type structure of SbSI played in the formation of the nanowires was presented in . The application of sonochemistry to prepare CNTs ﬁlled with SbSI is also justiﬁed by the fact that ultrasonication is often used in an attempt to cut the outer caps of CNTs . The additional X-ray diffraction lines (Table 1) observed in the case of SbSI ﬁlling the CNTs may be explained as follows. The XRD investigations  of SbSI sonochemically produced in methanol show the coexistence of phases with Pna21 and Pnam crystal symmetry that are characteristic for ferroelectric and paraelectric domains, respectively. Hence, such data obtained at 298 K represent a structure of just below or very near the transition temperature of SbSI. Another explanation for the additional X-ray diffraction lines can be given taking into account existence of unknown phase in the investigated material. This problem will be discussed in the future. The nanocrystalline SbSI ﬁlling the CNTs is a semiconductor with little larger energy gap than the free SbSI nanowires (Table 3). This shift can be interpreted in terms of the quantum size effect . To prove this we will synthesize the SbSI in CNTs of smaller diameters. The observed free carrier absorption of light in the case of CNTs ﬁlled with SbSI is evoked by the CNTs material because it is absent in the case of alone SbSI nanowires . Instead of it the Urbach absorption was reported in the latter case . May be latter mechanism of absorption exists also in CNTs ﬁlled with SbSI but it is hidden by the free carrier absorption. It is known (see e.g., ) that a metal atom intercalated inside the internal cavity of a CNT displays a tendency towards the transfer of some part of the valence electrons to the outer surface of the nanotube, where unoccupied electronic states exist. As a result of such a transfer there arises an additional mechanism of electrical conduction, related to the travel of an electron about those states. 5. Conclusions In summary, this is to our knowledge the ﬁrst example of ﬁlling CNTs with semiconducting and ferroelectric SbSI. The resulting SbSI/CNT composite is a highly anisotropic 1D structure whose electronic and optical properties are considerably modiﬁed with respect to the encapsulating nanotube. The presented very simple, sonochemical synthesis of nanophase SbSI in CNTs at low temperature is a convenient, fast, mild, efﬁcient and environmentally friendly route for producing novel type of hybrid nanomaterials. It should be extended to the preparation of some other AVBVICVII semiconductors within CNTs.
The composition, morphology, dimensions, microstructures, and optical properties of the new form of substance were characterized. Microstructural analysis reveals that the SbSI in CNTs crystallizes in an orthorhombic structure and predominantly grows along the [0 0 1] direction. The XRD and HRTEM patterns show that the SbSI nanowires are well crystallized. Since the sonochemical process was carried out at ambient temperature and pressure, it may be predicted that upscaling of this method will lead to large quantities of nanosized SbSI nanowires with uniform morphology. Further studies on the properties of the sonochemically prepared SbSI are underway. Its growth can be directed to provide a ‘‘bottom-up” approach for the manufacture of future nanoscale devices. Acknowledgement This paper was partially supported by the MNiSzW (Poland) under Contract No. NN507157733. References  S. Iijima, Nature 354 (1991) 56–58.  A.V. Eletskii, Physics-Uspekhi 47 (2004) 1119–1154.  J. Sloan, M. Terrones, S. Nufer, S. Friedrichs, S.R. Bailey, H.-G. Woo, M. Rühle, J.L. Hutchison, M.L.H. Green, J. Am. Chem. Soc. 124 (2002) 2116–2117.  J. Sloan, S.J. Grosvenor, S. Friedrichs, A.I. Kirkland, J.L. Hutchison, M.L.H. Green, Angew. Chem. Int. Ed. 41 (2002) 1156–1159.  J. Sloan, M.C. Novotny, S.R. Bailey, G. Brown, C. Xu, V.C. Williams, S. Friedrichs, E. Flahaut, R.L. Callendar, A.P. York, K.S. Coleman, M.L.H. Green, R.E. DuninBorkowski, X.L. Hutchison, Chem. Phys. Lett. 329 (2000) 61–65.  S. Friedrichs, A.I. Kirkland, R.R. Meyer, J. Sloan, M.L.H. Green, Electron Microsc. Anal. (2004) 455–458.  S. Friedrichs, U. Falke, M.L.H. Green, Chem. Phys. Chem. 6 (2005) 300–305.  E. Philp, J. Sloan, A.I. Kirkland, R.R. Meyer, S. Friedrichs, J.L. Hutchison, M.L.H. Green, Nature (Materials) 2 (2003) 788–791.  M. Wilson, S. Friedrichs, Acta Cyst. A62 (2006) 287–295.  J. Sloan, J. Cook, A. Chu, M. Zwiefka-Sibley, M.L.H. Green, J.L. Hutchison, J. Solid, State Chem. 140 (1998) 83–90. _ Ultrason.  M. Nowak, P. Szperlich, Ł. Bober, J. Szala, G. Moskal, D. Stróz, Sonochem. 15 (2008) 709–716. _  P. Szperlich, M. Nowak, Ł. Bober, J. Szala, D. Stróz, Ultrason. Sonochem. 16 (2009) 398–401.  K.S. Suslick, G.J. Price, Annu. Rev. Mater. Sci. 29 (1999) 295–326.  T.J. Mason, Ultrason. Sonochem. 10 (2003) 175–179.  A. Gedanken, Ultrason. Sonochem. 11 (2004) 47–55.  G. Cravotto, P. Cintas, Chem. Soc. Rev. 35 (2006) 180–196.  K.S. Suslick, Y. Didenko, M.M. Fang, T. Hyeon, K.J. Kolbeck, W.B. McNamara, M.M. Mdleleni, M. Wong, Phil. Trans. Roy. Soc. A 357 (1999) 335–353.  B. Li, Y. Xie, J. Huang, Y. Qian, Ultrason. Sonochem. 6 (1999) 217–220.  Antimony Sulﬁde Iodide, JCPDS-International Centre for Diffraction Data 2000, PCPDFWIN vol. 2.1, Card File No. 74-0149.  Carbon, JCPDS-International Centre for Diffraction Data 2000, PCPDFWIN vol. 2.1, Card File No. 75-1621.  H. Lipson, A.R. Stokes, Nature 149 (1942) 328.  P. Trucano, R. Chen, Nature 258 (1975) 136–137.  J.I. Pankove, Optical Processes in Semiconductors, Prentice-Hall Inc., New Jersey, 1971.  A. Starczewska, R. Wrzalik, M. Nowak, P. Szperlich, M. Jesionek, G. Moskal, T. _ P. Mas´lanka, Ultrason. Sonochem. doi:10.1016/ Rzychon´, J. Szala, D. Stróz, j.ultsonch.2008.12.010.  E. Dönges, Z. Anorg, Allg. Chem. 263 (1950) 112–132.  Ye. Hui, Xu. Yuhuan, J.D. Mackenzie, Proc. SPIE 3943 (2000) 95–101.