Materials Letters 106 (2013) 33–36

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Materials Letters

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Hydrothermal synthesis, characterization and hydrogen storageof SnS nanorods

M. Zubair Iqbal a, Fengping Wang a,n, M. Yasir Rafique a, Shujjat Ali a, M. Hassan Farooq b,Mujtaba Ellahi b

a Department of Physics, School of Applied Science, University of Science and Technology Beijing, Beijing 100083, PR Chinab School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China

a r t i c l e i n f o

Article history:Received 28 March 2013Accepted 23 April 2013Available online 30 April 2013

Keywords:Nanocrystalline materialsSnSHydrothermal methodHydrogen storage

7X/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.matlet.2013.04.051

esponding author. Tel.: +86 10 62332587; faxail address: fpwang@ustb.edu.cn (F. Wang).

a b s t r a c t

Stannous sulfide (SnS) with high absorption coefficient and dual nature semiconductivity is a promisingcandidate for solar cell fabrication. In the present research, the single crystalline SnS nanorods weresynthesized using the hydrothermal growth technique. The as-prepared nanoparticles were character-ized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), Raman spectroscopy, field emissionscanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolutiontransmission electron microscopy (HRTEM) with selected area electron diffraction (SAED). Structuralcharacterizations result have illustrated that length of the as-grown tin (II) sulfide nanorod is 1−2 μm,width is about 80 nm and thickness is few nanometers. Selected area electron diffraction (SAED) andX-ray diffraction (XRD) patterns have revealed that the as-synthesized SnS nanorods exist in single-crystalline nature. Two Raman modes 190.5 cm−1 and 219.6 cm−1 were observed by Raman spectroscopy,which are consistent with nanoorthorhombic SnS herzenbergite phase. The first ever study on hydrogenabsorption characteristics of SnS nanorods performed at 373 K shows a good absorption capacity of0.73 wt%.

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1. Introduction

Recently, binary semiconductors especially, chalcogenides thatbelong to IV–VI groups of periodic table such as SnS, SnS2, Sn2S3,Sn3S4, and Sn4S5, have been receiving an immense importance owingto their interesting potential applications. One of these, a p-typestannous sulfide (SnS) semiconductor with orthorhombic structurehas attracted a considerable attention due to its usage in photovoltaic(PV), optoelectronics, data storage and photodetectors. SnS (herzen-bergite) has indirect 1–1.2 eV and direct optical band gap of 1.2–1.5 eV,a high conversion efficiency of ∼25% and a high absorption coefficientα4104 cm−1. Particularly, high absorption coefficient, dual nature(p-type and n-type), nontoxicity, low-cost, double layered (Sn–S)crystal structure and environmental safeness havemade it a promisingcandidate for solar cell applications [1,2]. In recent decades, research-ers have been focusing to investigate novel minuscule structures dueto their development in nanoscience and technology. However, it isstill a challenge to synthesize novel three-dimensional (3D), 2D andspecially 1D architectures with a controlled morphology under facileconditions because 1D nanostructures such as wires, tubes, belts androds present an excellent performance in the fabrication of nano-

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scale devices. To date, few types of stannous sulfide (SnS) micro-nanostructures such as particles [3], nano-flowers [4], dendrite-likenanoparticles [5], flake [6], belts-like nanocrystals and wires [7] havebeen synthesized using different techniques. Moreover, various phy-sical and chemical schemes have been employed to synthesize ofstannous sulfide thin films such as molecular beam epitaxy (MBE) [8],thermal evaporation [9], pulsed electrochemical deposition [10] andphysical vapor transport methods. Additionally, only some efforts havebeen developed to prepare SnS nanopowder using polyol route,solvothermal, aqueous solution and hydrothermal approaches.

In this paper, we report the facile synthesis and structuralcharacterization of SnS nanorods by using the low temperaturehydrothermal growth technique. Furthermore, the effect of hydro-thermal temperature on the growth mechanism, phonon modesby Raman spectroscopy and their hydrogen absorption character-istics will be discussed.

2. Experimental

Sample preparation: SnS nanorods were synthesized using thelow temperature hydrothermal method. In the present work, thepreliminary materials were SnCl2 �2H2O, N2H4 �H2O and CS(NH2)2.All chemicals were of analytical grade (Beijing Chemicals Co., Ltd.)

M. Zubair Iqbal et al. / Materials Letters 106 (2013) 33–3634

and were used without further refinement. In a typical synthesis,2 g of SnCl2 �2H2O were dissolved ultrasonically in 40 ml ofN2H4 �H2O to obtained homogeneous solution. Subsequently, 1 gof CS(NH2)2 was added into the obtain a solution and mixedvigorously stirred at 80 1C temperature for 30 min. The finalparticipation transferred into 40 ml Teflon-lined stainless auto-clave. The autoclave was put into the electric oven at a tempera-ture of 180 1C for 23 h then cooled down naturally. The greenpowder was collected and washed for several times with distilledwater and ethanol to eliminate the impurities before drying at90 1C overnight.

2.1. Characterization

Characterization: The identification of crystal structure wasperformed by a Rigaku D/MAX-RB X-ray diffractometer (XRD)using Cu Kα radiation (λ¼1.54056 Å). The elemental compositionand structural characterization of the as-synthesized powder wereanalyzed by energy dispersive analysis (EDS) (INCA X-MAX 50,England), field emission scanning electron microscopy (Zeiss Ultra55, Germany), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED, JEM-2010). Confocal Raman micro-spectroscopy (Horiba Jobin Yvon HR 800 Raman spectrometer France,with a 532 nm wavelength as excitation source) was used toanalyze phonon modes of as-synthesized SnS nanorods. Hydrogenadsorption characteristics were conducted by Sieverts-type gas reac-tion controller.

3. Results and discussion

Fig. 1 illustrates the typical XRD pattern of the as-preparedstannous sulfide SnS. All the diffraction peaks are well indexed toorthorhombic SnS herzenbergite with lattice parameters a¼0.4329nm, b¼1.1192 nm, c¼0.3984 nm and α¼β¼γ¼901 (JCPDF Cards39–0354). No other contamination peaks such as SnS2, Sn2S3, Sn3S4,etc. are observed. The strong and sharp diffraction peaks indicate thatthe product is well crystallized. The lattice parameters of the as-synthesized SnS have been calculated using the crystal planes of (111),(120) and (110). The resulting values are a¼4.327 Å, b¼11.180 Å andc¼3.9717 Å, which are consistent with the standard values (JCPDF

Fig. 1. (a) X-ray diffraction pattern (XRD) of as-prepared SnS nanorods structureand (b) EDS spectrum of SnS nanorods.

Cards 39–0354). The minor difference compared to the bulk propertiesoccurs due to the grown structures conditions. The crystallite size ofthe SnS structure has been calculated from XRD line broadeningaccording to the Debye–Scherrer formula. The average crystallite sizeof the synthesized material is estimated to be approximately 25 nm.The composition of elements is measured through EDS analysis byselecting a single nanorod as shown in Fig. 1(b). The EDS spectrum hascontained only Sn and S elements, which is in good agreement withthe XRD result. The impurities such as other binary sulfides and oxideswere not detected within apparatus detection limit. These resultsconfirm the configuration of pure SnS.

The structure of the as-synthesized material was initiallydetermined with FE-SEM. The low magnification FE-SEM image(Fig. 2a) exhibits that the SnS precursor has one dimensional rod-like architectures which become agglomerated and are randomlydistributed over a carbon tape. Fig. 2b manifests the high magni-fication image of these acquired SnS nanorods, which reveals thatthe lengths of these rods are several micrometers and the width isabout 80 nm. Further in depth structural characterizations of theas-synthesized one dimensional stannous sulfide were performedby TEM and HRTEM. Fig. 2(c) is the TEM image of a single nanorod.The typical length of the as-grown nanorod is about 1 μm, width is80 nm and thickness is few nanometers. The lattice fringes in theHRTEM image [Fig. 2(d)] provide strong evidence about the singlecrystalline nature of the SnS nanostructure. The spacing betweenadjacent lattice planes are 0.32 nm and 0.28 nm corresponding to(021) and (111) respectively. Furthermore, selected area electrondiffraction (SAED) pattern from an individual nanorod confirmsthat the as-synthesized herzenbergite SnS nanorods are single-crystalline in nature and has a preferential growth along the [111]direction (inset of (d)). Generally, 1D nanomaterials have a significantinfluence on the solar cell applications because of their effective wayto trap photons due to special geometrical pattern in the excitongeneration step and their physical dimensions which are the source ofincrease in the energy conversion efficiency.

To investigate the growth mechanism of the nanorods, anexperimental series have been performed at different tempera-tures. The formation mechanism of SnS nanorods structures in thetemperature range of 100–180 1C is illustrated in Fig. 3. Theparticipating agent CS(NH2)2 contributed a significant role in theformation of SnS nanorods. During the nonexistence of the sulfursource (thiourea), the SEM result of as-prepared homogeneousmixture of SnCl2 �2H2O and N2H4 �H2O is shown in Fig. 3a. Theresult shows only agglomerated nanoparticles formed and thatthere is not any significant evidence for the growth of nanorods atstarting stage without thiourea. These agglomerated nanoparticlesare transformed into rod like architecture after the addition ofthiourea by using the hydrothermal process.

The formation of primary structure at low hydrothermaltemperature (100 1C) is manifested in Fig. 3b. The obvious struc-tural transformation splitting view for the buddle of the nanorodscan be seen at 140 1C. The splitting of rods is due to the prolongedhydrothermal reaction temperature. Finally, structural fragmenta-tion is high as to completely form SnS nanorods and the surface ofnanorods gradually becomes smooth at high temperature 180 1Cas shown in Fig. 3d. The structural results illustrated that thioureahas strong influence not only to provide the sulfur source but alsoto enhance the growth of nanorods. Subsequently after the growthof nanorods, hydrothermal reaction temperature provides them inparticular shape.

Furthermore, structural and vibrational modes of the preparedtin monosulfide nanoparticles were measured by Raman spectro-scopy. Raman spectroscopy is one of the advanced techniques toexamine the compositions and chemical states. Fig. 4(a) indicatesthe Raman spectrum of the as-prepared SnS nanorods shapedarchitectures. The dominant Raman peaks at 190.5 and 214.6 cm−1

Fig. 2. (a, b) FESEM images of nanorods, (c) TEM image of a single SnS nanorod, (d) HRTEM image of the SnS product and (e) the corresponding SAED pattern taken from thesingle nanorod-like SnS.

Fig. 3. Growth mechanism for the formation of SnS nanorod like structure at various temperatures.

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Fig. 4. (a) Raman spectra, and (b) hydrogen absorption curve measured at 373 K for SnS nanorods.

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are corresponding to the Ag vibrational mode of SnS. The resultsare in good agreement with reported literature [11,12].

Recently, researchers have investigated various materials toexplore the safe, condensed, reliable, and cost-effective energystorage methods. Hydrogen plays a promising role to become afuture fuel because of its environmental cleanness, natural exis-tence and high gravimetric energy capacity. The utilization ofhydrogen fuel has a significant influence on the vehicle's cost, size,performance and fuel economy. However, it's still a challenge forscientists to synthesize novel nanostructures which are suitablefor hydrogen storage. Fig. 4(b) shows the hydrogen absorptioncurve of SnS nanorods measured at 373 K with 5 MPa pressure inone cycle. These measuring conditions made the materials practi-cally applicable for the fabrication of energy storage devices.

The absorption graph demonstrated that hydrogen storageincreases suddenly in the initial hour and then increases slowlywith time. The maximum value attained for hydrogen absorptionin orthorhombic SnS nanorods is approximately 0.73 wt%. Thehydrogen storage capability of the as-synthesized SnS nanostruc-tures may be associated with precursor which is involved tosynthesize SnS such as hydrazine hydrate or surface defects ofnanocrystalline material and this capacity can be increased bycreating more defects in nanostructured material [13]. This firstever report on SnS nanorods is larger than the reported ones ofother compounds like 0.20 wt% for bulk BN powder and ball-milled nitrides such as 0.472 wt% (Mg3N2), 0.397 wt% (AlN),0.480 wt% (TiN), 0.476 wt% (ZrN) [14–16]. These results illustratethat the SnS nanorods will be a promising candidate not only forsolar cell but also for energy storage applications.

4. Conclusions

In summary, this paper is the first ever report made tosynthesize the single crystalline SnS nanorods using hydrazinehydrate. The FESEM results had exhibited that the length ofprepared SnS nanorods was in the range of several micrometers,the width was about 80 nm and the average crystallite size was

estimated to be approximately 25 nm. The structural results hadshowed that thiourea and hydrothermal reaction temperaturehave a strong influence on synthesis, growth and shape of SnSnanorods. Raman spectroscopy analyses indicated that the as-prepared nanorods mainly exhibit SnS phase. The novel study onhydrogen storage capability of synthesized SnS nanomaterialexamined at 373 K indicated an absorption capacity of 0.73 wt%.Such materials with controlled morphologies may exhibit a specialperformance in solar cell and energy storage applications.

Acknowledgments

This research work has been performed with the financialsupports of University of Science and technology Beijing (funda-mental development fund and chancellor scholarship program),National Key Scientific Instruments and Equipment DevelopmentSpecial Fund (2011YQ14014506 and 2011YQ14014507) and theOriented Award Foundation for Science and Technological Innova-tion, Inner Mongolia Autonomous Region, China (2012).

References

[1] Jiang T, Ozin GA. J Mater Chem 1998;8:1099–108.[2] Cheng S, Chen Y, He Y, Chen G. Mater Lett 2007;61:1408–12.[3] Sohilaa S, Rajalakshmi M, Ghoshc C, Arorab AK, Muthamizhchelvana C. J Alloys

Compd 2011;509:5843–7.[4] Zhu H, Yang D, Zhang H. Mater Lett 2006;60:2686–9.[5] Fleury V. Nature 1997;390:145–8.[6] Panda SK, Gorai S, Chaudhuri S. Mater Sci Eng B 2006;129:265–9.[7] Liu Y, Hou D, Wang G. Chem Phys Lett 2003;379:67–73.[8] Biswas S, Kar S, Chaudhuri S. Appl Surf Sci 2007;253:9259–66.[9] Cheng S, Conibeer G. Thin Solid Films 2011;520:837–41.[10] Gunasekaran M, Ichimura M. Solar Energy Mater Solar Cells 2007;91:774–7.[11] Gou XL, Chen J, Shen PW. Mater Chem Phys 2005;93:557–66.[12] Cheng S, Conibeer G. Thin Solid Films 2011;520:837–41.[13] Sakintuna B, Darkrim FL, Hirscher M. Int J Hydrogen Energy 2007;32:1121–40.[14] Khan WS, Cao CB, Ali Z, Butt FK, Niaz NA, Baig A. Mater Lett 2011;65:2127–9.[15] Ma RZ, Bando Y, Zhu HW, Sato T, Xu CL, Wu DH. J Am Chem Soc 2002;124:7672–3.[16] Kojima Y, Kawai Y, Ohba N. J Power Sources 2006;159:81–7.