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Preparation of ternary metal chalcogenide (M1-xFexS, M = Cd and Zn) nanocrystallites using single source precursors
Journal of Organometallic Chemistry 696 (2011) 3328e3336
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Preparation of ternary metal chalcogenide (M1-xFexS, M ¼ Cd and Zn) nanocrystallites using single source precursors Sujit D. Disale, Shivram S. Garje* Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai 400 098, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 July 2010 Received in revised form 23 June 2011 Accepted 5 July 2011
M1xFexS (M ¼ Cd, Zn) nanocrystallites were prepared by pyrolysis and solvothermal decomposition methods using [M(Aftscz)2] and [M(AftsczH)2Cl2] (M ¼ Cd, Zn and AftsczH ¼ monoacetylferrocene thiosemicarbazone) as single source precursors. The M1xFexS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis and UVeVisible spectroscopy. XRD patterns show that the Cd1xFexS and Zn1xFexS nanocrystallites prepared by pyrolysis and solvothermal decomposition routes have hexagonal phase. TEM images show presence of spherical and spherical plate-like morphology of M1xFexS nanoparticles. M1xFexS nanoparticles obtained by solvothermal decomposition in ethylene glycol are found to be capped with ethylene glycol as evident from IR spectra. Ó 2011 Elsevier B.V. All rights reserved.
Keywords: Single-source precursors M1xFexS Nanocrystallites Diluted magnetic semiconductor
1. Introduction Dilute magnetic semiconductors (DMSs) [1] have attracted much attention due to their capacity to store wealth of scientific information and potential technological applications. DMSs are IIeVI, IVeVI or IIIeV compounds in which fraction of nonmagnetic cations has been substituted by magnetic transition metal or rare-earth metal ions, e.g., Fe2þ in CdS to form Cd1xFexS. In these materials, the large sp-d exchange interaction between magnetic ions and electrons in valence band [2e4] can lead to a number of unusual electronic, optical and magneto-optical properties including the ability to magnetically tune the band gap. These properties make DMSs promising candidates for fabricating magneto optical devices such as magnetic field sensors, isolators and magneto optical switches [5]. Because DMSs have interesting magnetic properties and can be easily integrated into microelectronic devices, they are considered to be one of the most promising candidate materials for spintronics [6e8] which involve manipulation of spin degrees of freedom rather than electric charge in a solid state system [9]. Fe doped CdS based DMSs are useful as magneto optical devices (magnetic field sensors, isolators and magneto optical switches), field-emission displays, photocatalyst, photoelectronics, photocatalytic hydrogen evolution, solar cells and gas sensors [10,11]. Thin films of (Fe, Zn)S and single crystals of (Fe, Zn)S composite molecular species are being investigated for their magnetic * Corresponding author. Tel.: þ91 22 2654 3368; fax: þ91 22 2652 85 47. E-mail addresses: [email protected], [email protected] (S.S. Garje). 0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2011.07.001
susceptibility in dilute magnetic semiconductors, absorption coefficients and band gap energy, which are attractive for solar energy conversion [12e15]. The calculations on Zn1xXxS nanostructures have reported that these materials can be ferromagnetic when X ¼ Cr, Fe and Ni [16]. The luminescent properties of the various metal doped ZnS nanoparticles, nanowires and nanobelts were extensively investigated [17,18]. ZnS based DMS also show electrical [19], magnetic [18] and optical properties [20]. Though many methods of synthesis have been tried [10,11,20e22] there is no report on synthesis of M1xFexS (M ¼ Cd, Zn) using single source precursors (SSPs). The use of SSPs in which the metal-chalcogen bond is available has proven to be a very efficient route for the preparation of nanoparticles. The SSPs also known as single molecule precursors contain desired elements in a single molecule. They are preferred over multiple sources because of intrinsic advantages such as improved air/moisture stability, no or limited pre-reactions, low toxicity, control over stoichiometries, volatility control using suitable ligands, etc. Recently we have reported the synthesis of chalcopyrite (CuFeS2) nanorods and nanoparticles and CuxFe1xS thin films using [CuL2] and [Cu(LH)2Cl2] (LH ¼ monoacetylferrocene thiosemicarbazone) as single source precursors [23,24]. To the best of our knowledge, the SSPs have not been used for the preparation of M1xFexS (M ¼ Cd and Zn) nanocrystallites till date. Herein, we report preparation of M1xFexS using [M(Aftscz)2] and [M(AftsczH)2Cl2] (M ¼ Cd, Zn and AftsczH ¼ monoacetylferrocene thiosemicarbazone) as single-source precursors by pyrolysis and solvothermal decomposition routes.
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Fig. 1. Probable structures of [M(Aftscz)2] (I) and [M(AftsczH)2Cl2] (II) [M ¼ Cd and Zn].
2. Experimental All the solvents, metal salts and other reagents used were of AR grade and used without further purifications. Monoacetylferrocene thiosemicarbazone was prepared by the reported method [25]. The complexes were prepared as follows: 2.1. Synthesis of precursors 2.1.1. Preparation of [Cd(Aftscz)2] A hot solution of cadmium acetate (0.374 g, 1.40 mmol) in 20 mL absolute ethanol was added drop wise with stirring to the monoacetylferrocene thiosemicarbazone (0.885 g, 2.80 mmol) dissolved in 30 mL absolute ethanol. Then 10 ml 0.1 N NaOH was added and the reaction mixture was stirred for 24 h to get an orange coloured product. The product was filtered, washed several times with water and cold ethanol and dried in air (Yield: 0.86 g, 86.1%, M.P. 164e165 C). (Elemental analyses found (%): C, 43.50; H, 4.20; N, 12.01; S, 8.75; Fe, 15.95; Cd, 16.00. Calc. for C26H28N6S2Fe2Cd: C, 43.86; H, 3.96; N, 11.78; S, 8.99; Fe, 15.66; Cd, 15.76%.). I.R.: 3443 cm1, 3308 cm1 (yNH2 sym and asym), 1607 cm1 (yC¼N shifted after complexation), 761 cm1 (yCeS).
Fig. 2. XRD patterns of hexagonal Cd1xFexS (JCPDS: 41e1049) obtained from pyrolysis of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in furnace at 485 C (* implies FeS).
Fig. 3. XRD patterns of hexagonal Cd1xFexS (JCPDS: 41e1049) obtained from solvothermal decomposition of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in ethylene glycol after 15 min and 12 h reflux time.
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N.M.R (d in ppm) 1H: 1.69 (s, 3H; CH3); 4.16e4.40 (m, cyclopentadienyl rings); 6.26 and 6.77 (s, s, each corresponding to one H; eNH2) (Disappear after D2O exchange); 13C: 16.00 (eCH3), 67.25e85.63 (cyclopentadienyl ring carbons), 151.10 (H3CeC¼N), 170.06 (H2NeCeSe). 2.1.2. Preparation of [Cd(AftsczH)2Cl2] 0.350 g (1.91 mmol) of cadmium chloride dissolved in 35 mL absolute ethanol was added to a warm solution of monoacetylferrocene thiosemicarbazone (1.149 g, 3.82 mmol) dissolved in 40 mL absolute ethanol. The resulting mixture was stirred continuously, after 10e12 h clear orange solution became turbid with separation of some orange precipitate. Stirring was continued for 24 h till all the product was separated out completely. The orange product formed was removed by filtration, washed with water, cold ethanol and n-hexane and dried in air (Yield: 1.33 g, 88.4%, M.P. 203e205 C (decompose)). (Elemental analyses found (%): C, 40.02; H, 4.16; N, 11.01; S, 7.95; Fe, 14.51; Cd, 14.53; Cl, 9.40. Calc. for C26H30N6S2Fe2CdCl2: C, 39.79; H, 3.84; N, 10.69; S, 8.16; Fe, 14.21; Cd, 14.30; Cl, 9.02). I.R.: 3455 cm1, 3335 cm1 (yNH2 sym and asym), 3191 cm1 (yNH), 1589 cm1 (yC¼N shifted after complexation), 820 cm1 (yC¼S). N.M.R (d in ppm) 1H: 2.18 (s, 3H; CH3); 4.14e4.79 (m, cyclopentadienyl rings); 7.69 and 8.12 (s, s, each corresponding to one H; eNH2), 9.97 (s, 1H; NH) (Disappear after D2O exchange); 13C: 15.62 (eCH3), 67.78e83.20 (cyclopentadienyl ring carbons), 151.77 (H3CeC¼N), 177.67 (H2NeC¼S). 2.1.3. Preparation of [Zn(Aftscz)2] 0.395 g (1.80 mmol) of Zn(CH3COO)2.2H2O dissolved in 35 mL absolute ethanol was added drop wise with continuous stirring to a warm solution of monoacetylferrocene thiosemicarbazone (1.085 g, 3.60 mmol). The resulting mixture was stirred continuously, after 20 min clear orange solution became turbid with separation of some orange precipitate. Stirring was continued for 10 h till all orange solid separated out completely. It was filtered,
washed with water and cold ethanol and dried in air (Yield: 0.74 g, 62.0%, M.P. 225e229 C (decompose)). (Elemental analyses found (%): C, 47.20; H, 3.97; N, 12.70; S, 9.25; Fe, 16.55; Zn, 10.12. Calc. for C26H28N6S2Fe2Zn: C, 46.95; H, 4.24; N, 12.61; S, 9.62; Fe, 16.76; Zn, 9.81). I.R.: 3413 cm1, 3362 cm1 (yNH2 sym and asym), 1595 cm1 (yC¼N shifted after complexation), 768 cm1 (yCeS). N.M.R (d in ppm) 1H: 1.80 (s, 3H; CH3); 4.16e4.40 (m, cyclopentadienyl rings); 6.21 and 6.75 (s, s, each corresponding to one H; eNH2) (Disappear after D2O exchange); 13C: 18.88 (eCH3), 69.30e85.48 (cyclopentadienyl ring carbons), 164.24 (H3CeC¼N), 172.23 (H2NeCeSe). 2.1.4. Preparation of [Zn(AftsczH)2Cl2] A hot solution of zinc chloride (0.184 g, 1.35 mmol) in 20 mL absolute ethanol was added drop wise with stirring to the monoacetylferrocene thiosemicarbazone (0.815 g, 2.70 mmol) dissolved in 30 mL absolute ethanol. The resulting mixture was stirred continuously for 48 h. The volume of solution was reduced to half under vacuum and n-hexane was added to get the product. It was filtered, washed with water and cold ethanol and dried in air (Yield: 0.70 g, 70.1%, M.P. 196e199 C (decompose)). (Elemental analyses found (%): C, 41.96; H, 3.90; N, 11.80; S, 9.02; Fe, 15.40; Zn, 8.98; Cl, 9.90. Calc. for C26H30N6S2Fe2ZnCl2: C, 42.32; H, 4.08; N, 11.37; S, 8.68; Fe, 15.11; Zn, 8.84; Cl, 9.59). I.R.: 3406 cm1, 3345 cm1 (yNH2 sym and asym), 3195 cm1 (yNH), 1587 cm1 (yC¼N shifted after complexation), 818 cm1 (yC¼S). N.M.R (d in ppm) 1H: 2.17 (s, 3H; CH3); 4.15e4.78 (m, cyclopentadienyl rings); 7.66 and 8.09 (s, s, each corresponding to one H; eNH2), 9.95 (s, 1H; NH) (Disappear after D2O exchange); 13C: 15.50 (eCH3), 67.72e83.50 (cyclopentadienyl ring carbons), 151.15 (H3CeC¼N), 178.29 (H2NeC¼S). 2.2. Preparation of M1xFexS (M ¼ Cd, Zn) nanocrystallites The pyrolysis and solvothermal decompositions of above complexes were carried out to get nanocrystallites.
Fig. 4. TEM images of Cd1xFexS nanocrystallites obtained from pyrolysis of (a), (b) [Cd(Aftscz)2] and (c), (d) [Cd(AftsczH)2Cl2] in furnace at 485 C.
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Fig. 5. TEM images of Cd1xFexS nanocrystallites obtained from solvothermal decomposition of (a), (b) [Cd(Aftscz)2] and (c), (d) [Cd(AftsczH)2Cl2] after 12 h reflux time.
2.2.1. Preparation of M1xFexS nanocrystallites using pyrolysis in furnace In a typical experiment, 0.150 g of precursor was taken in quartz boat which was then inserted to the center of a horizontal wall furnace. The furnace was then heated to the desired temperature under the flowing nitrogen atmosphere for 2 h at a heating rate of 10 C/min. The inert (N2) atmosphere was maintained through out the experiment. The furnace was then cooled to room temperature. After cooling to room temperature the residue from the quartz boat was withdrawn. 2.2.2. Preparation of M1xFexS nanocrystallites using solvothermal decomposition in ethylene glycol 0.250 g of precursor dissolved in 30 cm3 ethylene glycol in 100 cm3 round bottom flask was refluxed at 198 C under nitrogen atmosphere with continuous stirring for the desired time. The initial orange colour turned to grayish-black after some time. Then the reaction mixture was cooled to room temperature. Methanol was added whereupon a black powder was obtained. It was separated by centrifugation. The particles thus obtained were washed repeatedly with methanol and dried under vacuum for 1 h. The materials obtained were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray analysis (EDAX), IR and UVeVisible spectroscopy.
absorption spectra were recorded on a UV-2401 PC Shimadzu UVeVis spectrophotometer. The X-ray Powder Diffraction studies were carried out using Cu Ka radiation on X’pert PRO PANalytical X-ray diffractometer (Philips). Transmission Electron Microscopy images and EDAX analysis were carried out on a Philips, CM 200 microscope with operating voltages between 20 and 200 kV. 3. Results and discussion The single source precursor complexes were prepared by reacting MX2 (M ¼ Cd, Zn and X ¼ Cl, CH3COO) with monoacetylferrocene thiosemicarbazone ligand in 1:2 stoichiometries in absolute ethanol. A simple addition reaction gave [M(AftsczH)2Cl2] complexes (Eq. (1)). When metal acetate was used, [M(Aftscz)2]
2.3. Instrumentation The infrared spectra were recorded as KBr pellets using KBr press on a Perkin Elmer Spectrum One FTIR spectrometer in the range from 4000 to 400 cm1. 1H and 13C{1H} NMR were recorded in 5 mm NMR tube in DMSO-d6 on a Bruker Avance II 300 MHz NMR spectrometer. The 1H and 13C{1H} chemical shifts are relative to internal standard TMS. Elemental analyses (C, H, N, S) of all the compounds were carried out using Thermo Finnigan, Italy Model FLASH EA 1112 Series elemental analyzer. The
Fig. 6. UVevisible spectra of Cd1xFexS nanoparticles obtained from pyrolysis of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in furnace at 485 C.
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Fig. 7. UVevisible spectra of Cd1xFexS nanoparticles obtained from solvothermal decomposition of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] after 12 h reflux time.
complexes were formed by elimination of acetic acid (Eq. (2)). However, addition of dilute NaOH was necessary in order to separate out [Cd(Aftscz)2] complex.
Abs:Ethanol R:T:Stirring MCI2 þ 2AftsczH/ MðAftsczHÞ2 Cl2
(1)
Abs:Ethanol R:T:Stirring MðCH3 COOÞ2 :2H2 O þ 2AftsczH / MðAftsczÞ2 2CH3 COOH 2H2 O (2) where M ¼ Cd and Zn, AftsczH ¼ Monoacetylferrocene thiosemicarbazone. The resulting complexes were characterized by elemental analysis, IR and NMR (1H and 13C{1H}) spectroscopy. The elemental analyses of [Cd(Aftscz)2], [Cd(AftsczH)2Cl2], [Zn(Aftscz)2] and
[Zn(AftsczH)2Cl2] complexes were found to match with 1:2 metal to ligand stoichiometries. In the IR spectra of [Cd(AftsczH)2Cl2] and [Zn(AftsczH)2Cl2] complexes, eNH2 symmetric and asymmetric stretching modes are observed between 3406 cm1e3335 cm1 indicating the noninvolvement of eNH2 in bonding. A band due to eNH is observed at 3191 cm1 and 3195 cm1 respectively suggesting that deprotonation of eNH group has not taken place. The bands at 1589 cm1, 1587 cm1 and 820 cm1, 818 cm1 are attributed to nC¼N and nC¼S respectively. In case of [Cd(Aftscz)2] and [Zn(Aftscz)2] complexes, bands observed at 3413 cm1 and 3308 cm1 are assigned to eNH2 symmetric and asymmetric stretching modes respectively. The other bands present at 1607 cm1, 1595 cm1 and 761 cm1, 768 cm1 are due to nC¼N and nC-S respectively. A band due to eNH stretching which is observed at 3140 cm1 in the ligand is absent in the spectra of both the complexes. These observations are consistent with monoacetylferrocene thiosemicarbazone ligand coordination through sulfur and azomethine nitrogen atoms [23,24]. In the 1H NMR of [Cd(AftsczH)2Cl2] and [Zn(AftsczH)2Cl2], the signals at 9.97 ppm and 9.95 ppm respectively are due to eNH protons. In case of [Cd(Aftscz)2] and [Zn(Aftscz)2] the signals due to eNH protons are absent in the 1H NMR indicating deprotonation of eNH group. The other signals in both the complexes are in accordance with the monoacetylferrocene thiosemicarbazone ligand. In the 13C{1H} NMR spectra of [Cd(AftsczH)2Cl2], [Cd(Aftscz)2], [Zn(AftsczH)2Cl2] and [Zn(Aftscz)2], the signals due to two cyclopentadienyl ring carbons are observed between 67.25 and 85.63 ppm. Whereas, signals due to eCH3, eC¼N and H2N_C]S are observed at w15, w151 and w177 ppm respectively. These observations are consistent with the ligand coordination through sulphur and azomethine nitrogen. On the basis of above observations the probable structures of [M(Aftscz)2] (I) and [M(AftsczH)2Cl2] (II) are given in the Fig. 1. The [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes were used as single source precursors for the preparation of nanocrystalline Cd1xFexS using pyrolysis and solvothermal decomposition routes. Fig. 2 and Fig. 3 show the X-ray diffraction patterns of the material obtained after pyrolysis in a furnace at 485 C and solvothermal decomposition in ethylene glycol at 15 min and 12 h
Fig. 8. IR spectra of (a) pure ethylene glycol (as a neat liquid) and Cd1xFexS nanoparticles obtained from solvothermal decomposition of (b) [Cd(Aftscz)2] and (c) [Cd(AftsczH)2Cl2] after 12 h reflux time.
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reflux time of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2]. It is very interesting that the diffraction patterns match with the hexagonal phase of CdS (JCPDS; 41e1049). So there is possibility that the iron is doped in the structure of cadmium sulfide with the formula Cd1xFexS. Kim and co-workers have reported the Cd1xFexS phase with varying ratio of Cd and Fe [10]. It is clearly seen from the XRD pattern that due to the doping of Fe in CdS, the peak positions (2q) for the planes (100), (002), (101), (102), (110), (103) and (112) are shifted to slightly higher position (for pyrolysis w0.70, 2q degrees and for solvothermal w 0.35, 2q degrees). This phenomenon is generally observed in most of the doping cases [24,26e29]. The peaks in the diffraction patterns of nanocrystalline samples are broadened by the finite size effects. The broadening in the XRD pattern suggests the nanocrystalline nature of the as prepared material. The particle size calculated using Scherrer formula of the materials obtained after pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in a furnace at 485 C are 10.6 nm and 10.3 nm respectively, whereas for the materials obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol, the calculated sizes are 12.6 nm and 18.0 nm (for 15 min reflux time) respectively. The particle size of the materials obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol for 12 h reflux time are 10.0 nm and 15.9 nm respectively. Presence of some minor impurity peaks
in the XRD patterns which can be attributed to cubic FeS (JCPDS: 80-1033) can be seen. No other impurity phase is observed in the materials obtained by solvothermal decomposition. The elemental composition of the material was found out using EDAX. The EDAX analysis of Cd1xFexS nanocrystallites obtained from [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes using pyrolysis at 485 C matches with Cd0.41Fe0.60S0.99 and Cd0.41Fe0.61S0.98 formulae respectively. The EDAX analysis of Cd1xFexS nanocrystallites obtained from the solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes matches with Cd0.71Fe0.29S and Cd0.62Fe0.34S1.04 formulae respectively. Fig. 4 and Fig. 5 show the TEM images of Cd1xFexS nanoparticles obtained from pyrolysis and solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] respectively. TEM images of Cd1xFexS nanoparticles obtained from pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] show the uniformly dispersed nearly spherical shape morphology with the grain size of about 10e14 nm and 26e29 nm respectively (Fig. 4). TEM images of Cd1xFexS nanoparticles obtained from solvothermal decomposition of [Cd(Aftscz)2] show nearly spherical-nanoplates like morphology
Fig. 9. XRD patterns of wurtzite Zn1xFexS (JCPDS: 36-1450) obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 500 C and 540 C (* implies FeS).
Fig. 10. XRD patterns of wurtzite Zn1xFexS (JCPDS: 36-1450) obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in ethylene glycol after 1 h and 6 h reflux time.
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Fig. 11. TEM images of Zn1xFexS nanocrystallites obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 540 C.
with 100e125 nm size (Fig. 5a and b). TEM images of Cd1xFexS nanoparticles obtained from solvothermal decomposition of [Cd(AftsczH)2Cl2] show uniformly dispersed spherical plate-like morphology with diameter of the plates of about 85e94 nm (Fig. 5c and d). UVevisible absorption spectra of Cd1xFexS nanocrystallites dispersed in ethanol are shown in Fig. 6 and Fig. 7. In the absorption spectra, absorption bands at 362 nm and 376 nm are observed for Cd1xFexS obtained from pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] respectively. UVeVisible spectra of Cd1xFexS nanoplates obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol after 12 h reflux time show the broad band at 362 nm with the shoulder band at 477 nm and the broad band at 366 nm with the shoulder band at 496 nm respectively. The absorption bands are blue shifted as compared to bulk CdS which indicates the formation of smaller particles and doping of Fe in the structure of CdS [21]. The IR spectra of Cd1xFexS nanocrystallites obtained by solvothermal route exhibit capping by ethylene glycol (Fig. 8). The IR spectra of Cd1xFexS nanocrystallites obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol after 12 h reflux time matches with the IR spectrum of ethylene glycol. All IR bands in the spectrum of Cd1xFexS nanocrystallites match with the bands in the spectrum of ethylene glycol. This proves that ethylene glycol capping is present on Cd1xFexS nanocrystallites (Fig. 8). The Zn (II) monoacetylferrocene thiosemicarbazone complexes, [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] were further used as single source precursors for the synthesis of nanocrystalline Zn1xFexS using pyrolysis and solvothermal decomposition routes. Fig. 9 and Fig. 10 shows the X-ray diffraction patterns of residue obtained after pyrolysis in a furnace at 500 C and 540 C and solvothermal decomposition in ethylene glycol at 1 h and 6 h reflux time of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively.
In case of pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] it is observed that no or small peaks are present in the XRD pattern of the material obtained at 500 C (Fig. 9a and b). However, in the XRD patterns of the materials obtained at higher decomposition temperature i.e. 540 C, well resolved broad diffraction peaks are present which could be perfectly indexed to wurtzite ZnS (JCPDS; 36-1450) (Fig. 9). The EDAX analysis of Zn1xFexS nanocrystallites matches with Zn0.40Fe0.55S1.05 and Zn0.45Fe0.51S1.04 formulae for the materials obtained by pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. This suggests that the doping of Fe does not change the crystal structure of ZnS [22,30]. Few impurity peaks present in the XRD patterns may be due to cubic FeS (JCPDS: 80-1033). Thus higher decomposition temperature is required to get crystalline Zn1xFexS material. Fig. 10 shows the X-ray diffraction patterns of the residue obtained after solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 1 h and 6 h reflux time. It is observed that no peak is present in the diffractogram of the material obtained after 1 h reflux time. When the reflux time was increased to 6 h, wurtzite ZnS (JCPDS; 36-1450) was obtained as evident from the XRD patterns. The EDAX analysis of Zn1xFexS nanocrystallites obtained from the solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] at 6 h reflux time matches with Zn0.69Fe0.26S1.05 and Zn0.60Fe0.38S1.02 formulae respectively. This suggests doping of Fe in ZnS. The doping of Fe does not change the crystal structure of ZnS [22,30] with formula Zn1xFexS. No other impurity phases were observed in the XRD pattern. These observations suggest that the choice of reaction time is an important factor to get Zn1xFexS phase from precursors. In the XRD patterns, it is observed that the peak positions (2q) for the planes (100), (002), (101), (102), (110), (103) and (112) are shifted to slightly upper positions (for pyrolysis w0.60, 2q degrees and for solvothermal w 0.25, 2q degrees) because of doping of Fe in
Fig. 12. TEM images of Zn1xFexS nanocrystallites obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] after 6 h reflux time.
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Fig. 13. IR spectra of (a) pure ethylene glycol (as a neat liquid) and Zn1xFexS nanoparticles obtained from solvothermal decomposition of (b) [Zn(Aftscz)2] and (c) [Zn(AftsczH)2Cl2] after 6 h reflux time.
ZnS structure. The peak broadening in the XRD pattern clearly indicates the nanocrystalline nature of the Zn1xFexS. The particle sizes calculated using Scherrer formula of the materials obtained after pyrolysis of [Zn(Aftscz)2] at 500 C and [Zn(AftsczH)2Cl2] at 540 C in a furnace are 28.9 nm and 5.3 nm respectively, whereas for the materials obtained from solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol for 6 h, the calculated sizes are 15.0 nm and 16.9 nm (for 6 h reflux time) respectively. TEM images show presence of spherical shape nanoparticles with average grain size of 20e25 nm and 22e24 nm of Zn1xFexS obtained from pyrolysis decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively (Fig. 11). Fig. 12 shows the TEM micrographs of Zn1xFexS nanocrystallites prepared using solvothermal route from [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 6 h reflux time. Uniformly dispersed nanoflakes like morphology is observed in the TEM micrographs. The grain size of as prepared Zn1xFexS nanoflakes
obtained by solvothermal route from [Zn(Aftscz)2] is found to be about 150e155 nm. In case of Zn1xFexS nanocrystallites prepared using the solvothermal route from [Zn(AftsczH)2Cl2] nearly spherical shape particles were observed in the TEM micrographs with grain size of 13e16 nm. In most of the cases, the particle sizes calculated using Scherrer formula match with those seen in the respective TEM images. In few cases, the particles sizes seen in the TEM image are bigger than those calculated using Scherrer formula. This is due to difficulty in measuring the particle sizes exactly in the TEM images as there is overlapping of the nanoplates (Fig. 5) and nanoflakes (Fig. 12a). The IR spectrum of Zn1xFexS nanoparticles obtained from solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 6 h reflux time matches with the IR spectrum of pure ethylene glycol; suggesting the capping of ethylene glycol over Zn1xFexS nanoparticles (Fig. 13).
Fig. 14. UVevisible spectra of Zn1xFexS nanoparticles obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 540 C.
Fig. 15. UVevisible spectra of Zn1xFexS nanoparticles obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] after 6 h reflux time.
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Fig. 14 and Fig. 15 show the UV absorption spectra of Zn1xFexS nanocrystallites dispersed in ethanol obtained from the pyrolysis and solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. The absorption band for Zn1xFexS is observed at 310 nm and 315 nm for the materials obtained by pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. Whereas in case of solvothermal decomposition the absorption bands are observed at 345 nm and 370 nm for [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. These absorption bands are blue shifted as compared to bulk ZnS which indicates formation of smaller particles and doping of Fe in the structure of ZnS [20,29,30]. 4. Conclusions Mixed metal thiosemicarbazones were successfully used as single source precursors for the preparation of M1xFexS nanocrystallites by pyrolysis and solvothermal decomposition routes. Thus, Cd (II) and Zn (II) monoacetylferrocene thiosemicarbazone complexes gave hexagonal Fe doped CdS (Cd1xFexS)and wurtzite Fe doped ZnS (Zn1xFexS) nanocrystallites respectively. It is evident from the present investigation that the experimental conditions such as decomposition temperature, reflux time, etc. affect the properties like crystallinity, morphology etc. of the M1xFexS. This single-source precursor approach can be extended for the preparation of other ternary metal chalcogenide materials. Acknowledgment Authors are thankful to UGC for financial support, TIFR (Mumbai) for XRD and SAIF, IIT Bombay for TEM characterization facility. References [1] J.K. Furdyna, J. Appl. Phys. 64 (1988) R29eR64. [2] A. Twardowski, T. Dietl, M. Demianiuk, Solid State Commun. 48 (1983) 845e848.
[3] A. Twardowski, M.V. Ortenberg, M. Demianiuk, R. Pauthenet, Solid State Commun. 51 (1984) 849e852. [4] J.K. Furdyna, N. Samarth, J. Appl. Phys. 61 (1987) 3526e3531. [5] Y.H. Hwang, Y.H. Um, J.K. Furdyna, Semicond. Sci. Technol. 19 (2004) 565e570. [6] H. Ohno, Science 281 (1998) 951e956. [7] I. Malajovich, J.J. Berry, N. Samarth, D.D. Awshalom, Nature 411 (2001) 770e772. [8] S.A. Wolf, D.D. Awschalom, R.A. Buhrman, J.M. Daughton, S. Molnar, M.L. Roukes, A.Y. Chtchelkanova, D.M. Treger, Science 294 (2001) 1488e1495. [9] I. Zutic, J. Fabian, S.D. Sarma, Rev. Mod. Phys. 76 (2004) 323e410. [10] C. Cho, S. Park, H. Kim, Bull. Korean Chem. Soc. 21 (2000) 805e808. [11] H.H. Afify, I.K. EL Zawawi, I.K. Battisha, J. Mater. Sci. Mater. Electronics 10 (1999) 497e502. [12] A.B. Kashyout, A.S. Arico, N. Giordano, V. Antonucci, Mater. Chem. Phys. 41 (1995) 55e60. [13] S.H. Deulkar, C.H. Bhosale, M. Sharon, J. Phys. Chem. Solids 65 (2004) 1879e1885. [14] B.B. Stojic, Z. Soskic, M. Stojic, D. Milivojevic, J. Magn. Magn. Mater. 195 (1999) 76e80. [15] A. Twardowski, H.J.M. Swagten, W.J.M. de Jonge, Phys. Rev. B. 44 (1991) 2220e2226. [16] R.A. Stern, T.M. Schuler, J.M. MacLaren, D.L. Ederer, V. Perez-Dieste, F.J. Himpsel, J. Appl. Phys. 95 (2004) 7468e7470. [17] J.Z. Liu, P.X. Yan, G.H. Yue, J.B. Chang, D.M. Qu, R.F. Zhuo, J. Phys. D: Appl. Phys. 39 (2006) 2352e2356. [18] S. Bhattacharya, D. Chakravorty, Chem. Phys. Lett. 444 (2007) 319e323. [19] S.V. Sharma, R.J. Singh, Bull. Mat. Sci. 14 (1991) 71e75. [20] S. Sambasivam, B.K. Reddy, A. Divya, N.M. Rao, C.K. Jayasankar, B. Sreedhar, Phys. Lett. A 373 (2009) 1465e1468. [21] K. Liu, J.Y. Zhang, X. Wu, B. Li, Y. Lu, X. Fan, D. Shen, Physica B. 389 (2007) 248e251. [22] T. Kang, J. Sung, W. Shim, H. Moon, J. Cho, Y. Jo, W. Lee, B. Kim, J. Phys. Chem. C 113 (2009) 5352e5357. [23] S.D. Disale, S.S. Garje, Appl. Organometal. Chem. 23 (2009) 492e497. [24] S.D. Disale, S.S. Garje, Appl. Organometal. Chem. 24 (2010) 734e740. [25] Y. Omote, R. Kobayashi, N. Sugiyama, Bull. Chem. Soc. Jpn. 46 (1973) 2896e2897. [26] K.W. Liu, J.Y. Zhang, D.Z. Shen, B.H. Li, X.J. Wu, B.S. Li, Y.M. Lu, X.W. Fan, Thin Solid Films 515 (2007) 8017e8021. [27] Y.C. Zhang, W.W. Chen, X.Y. Hu, Cryst. Growth Des 7 (2007) 580e586. [28] L. Junwu, Z. Zhixiang, Z. Kaihui, W. Yucheng, J. Wuhan Univ. Technol. . Mater. Sci. Ed. 21 (2006) 57e60. [29] P.H. Borse, N. Deshmukh, R.F. Shinde, S.K. Date, S.K. Kulkarni, J. Mater. Sci. 34 (1999) 6087e6093. [30] S. Sambasivam, D.P. Joseph, D.R. Reddy, B.K. Reddy, C.K. Jayasankar, Mater. Sci. Eng. B. 150 (2008) 125e129.
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Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Preparation of ternary metal chalcogenide (M1-xFexS, M ¼ Cd and Zn) nanocrystallites using single source precursors Sujit D. Disale, Shivram S. Garje* Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai 400 098, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 July 2010 Received in revised form 23 June 2011 Accepted 5 July 2011
M1xFexS (M ¼ Cd, Zn) nanocrystallites were prepared by pyrolysis and solvothermal decomposition methods using [M(Aftscz)2] and [M(AftsczH)2Cl2] (M ¼ Cd, Zn and AftsczH ¼ monoacetylferrocene thiosemicarbazone) as single source precursors. The M1xFexS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis and UVeVisible spectroscopy. XRD patterns show that the Cd1xFexS and Zn1xFexS nanocrystallites prepared by pyrolysis and solvothermal decomposition routes have hexagonal phase. TEM images show presence of spherical and spherical plate-like morphology of M1xFexS nanoparticles. M1xFexS nanoparticles obtained by solvothermal decomposition in ethylene glycol are found to be capped with ethylene glycol as evident from IR spectra. Ó 2011 Elsevier B.V. All rights reserved.
Keywords: Single-source precursors M1xFexS Nanocrystallites Diluted magnetic semiconductor
1. Introduction Dilute magnetic semiconductors (DMSs) [1] have attracted much attention due to their capacity to store wealth of scientific information and potential technological applications. DMSs are IIeVI, IVeVI or IIIeV compounds in which fraction of nonmagnetic cations has been substituted by magnetic transition metal or rare-earth metal ions, e.g., Fe2þ in CdS to form Cd1xFexS. In these materials, the large sp-d exchange interaction between magnetic ions and electrons in valence band [2e4] can lead to a number of unusual electronic, optical and magneto-optical properties including the ability to magnetically tune the band gap. These properties make DMSs promising candidates for fabricating magneto optical devices such as magnetic field sensors, isolators and magneto optical switches [5]. Because DMSs have interesting magnetic properties and can be easily integrated into microelectronic devices, they are considered to be one of the most promising candidate materials for spintronics [6e8] which involve manipulation of spin degrees of freedom rather than electric charge in a solid state system [9]. Fe doped CdS based DMSs are useful as magneto optical devices (magnetic field sensors, isolators and magneto optical switches), field-emission displays, photocatalyst, photoelectronics, photocatalytic hydrogen evolution, solar cells and gas sensors [10,11]. Thin films of (Fe, Zn)S and single crystals of (Fe, Zn)S composite molecular species are being investigated for their magnetic * Corresponding author. Tel.: þ91 22 2654 3368; fax: þ91 22 2652 85 47. E-mail addresses: [email protected], [email protected] (S.S. Garje). 0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2011.07.001
susceptibility in dilute magnetic semiconductors, absorption coefficients and band gap energy, which are attractive for solar energy conversion [12e15]. The calculations on Zn1xXxS nanostructures have reported that these materials can be ferromagnetic when X ¼ Cr, Fe and Ni [16]. The luminescent properties of the various metal doped ZnS nanoparticles, nanowires and nanobelts were extensively investigated [17,18]. ZnS based DMS also show electrical [19], magnetic [18] and optical properties [20]. Though many methods of synthesis have been tried [10,11,20e22] there is no report on synthesis of M1xFexS (M ¼ Cd, Zn) using single source precursors (SSPs). The use of SSPs in which the metal-chalcogen bond is available has proven to be a very efficient route for the preparation of nanoparticles. The SSPs also known as single molecule precursors contain desired elements in a single molecule. They are preferred over multiple sources because of intrinsic advantages such as improved air/moisture stability, no or limited pre-reactions, low toxicity, control over stoichiometries, volatility control using suitable ligands, etc. Recently we have reported the synthesis of chalcopyrite (CuFeS2) nanorods and nanoparticles and CuxFe1xS thin films using [CuL2] and [Cu(LH)2Cl2] (LH ¼ monoacetylferrocene thiosemicarbazone) as single source precursors [23,24]. To the best of our knowledge, the SSPs have not been used for the preparation of M1xFexS (M ¼ Cd and Zn) nanocrystallites till date. Herein, we report preparation of M1xFexS using [M(Aftscz)2] and [M(AftsczH)2Cl2] (M ¼ Cd, Zn and AftsczH ¼ monoacetylferrocene thiosemicarbazone) as single-source precursors by pyrolysis and solvothermal decomposition routes.
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Fig. 1. Probable structures of [M(Aftscz)2] (I) and [M(AftsczH)2Cl2] (II) [M ¼ Cd and Zn].
2. Experimental All the solvents, metal salts and other reagents used were of AR grade and used without further purifications. Monoacetylferrocene thiosemicarbazone was prepared by the reported method [25]. The complexes were prepared as follows: 2.1. Synthesis of precursors 2.1.1. Preparation of [Cd(Aftscz)2] A hot solution of cadmium acetate (0.374 g, 1.40 mmol) in 20 mL absolute ethanol was added drop wise with stirring to the monoacetylferrocene thiosemicarbazone (0.885 g, 2.80 mmol) dissolved in 30 mL absolute ethanol. Then 10 ml 0.1 N NaOH was added and the reaction mixture was stirred for 24 h to get an orange coloured product. The product was filtered, washed several times with water and cold ethanol and dried in air (Yield: 0.86 g, 86.1%, M.P. 164e165 C). (Elemental analyses found (%): C, 43.50; H, 4.20; N, 12.01; S, 8.75; Fe, 15.95; Cd, 16.00. Calc. for C26H28N6S2Fe2Cd: C, 43.86; H, 3.96; N, 11.78; S, 8.99; Fe, 15.66; Cd, 15.76%.). I.R.: 3443 cm1, 3308 cm1 (yNH2 sym and asym), 1607 cm1 (yC¼N shifted after complexation), 761 cm1 (yCeS).
Fig. 2. XRD patterns of hexagonal Cd1xFexS (JCPDS: 41e1049) obtained from pyrolysis of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in furnace at 485 C (* implies FeS).
Fig. 3. XRD patterns of hexagonal Cd1xFexS (JCPDS: 41e1049) obtained from solvothermal decomposition of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in ethylene glycol after 15 min and 12 h reflux time.
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N.M.R (d in ppm) 1H: 1.69 (s, 3H; CH3); 4.16e4.40 (m, cyclopentadienyl rings); 6.26 and 6.77 (s, s, each corresponding to one H; eNH2) (Disappear after D2O exchange); 13C: 16.00 (eCH3), 67.25e85.63 (cyclopentadienyl ring carbons), 151.10 (H3CeC¼N), 170.06 (H2NeCeSe). 2.1.2. Preparation of [Cd(AftsczH)2Cl2] 0.350 g (1.91 mmol) of cadmium chloride dissolved in 35 mL absolute ethanol was added to a warm solution of monoacetylferrocene thiosemicarbazone (1.149 g, 3.82 mmol) dissolved in 40 mL absolute ethanol. The resulting mixture was stirred continuously, after 10e12 h clear orange solution became turbid with separation of some orange precipitate. Stirring was continued for 24 h till all the product was separated out completely. The orange product formed was removed by filtration, washed with water, cold ethanol and n-hexane and dried in air (Yield: 1.33 g, 88.4%, M.P. 203e205 C (decompose)). (Elemental analyses found (%): C, 40.02; H, 4.16; N, 11.01; S, 7.95; Fe, 14.51; Cd, 14.53; Cl, 9.40. Calc. for C26H30N6S2Fe2CdCl2: C, 39.79; H, 3.84; N, 10.69; S, 8.16; Fe, 14.21; Cd, 14.30; Cl, 9.02). I.R.: 3455 cm1, 3335 cm1 (yNH2 sym and asym), 3191 cm1 (yNH), 1589 cm1 (yC¼N shifted after complexation), 820 cm1 (yC¼S). N.M.R (d in ppm) 1H: 2.18 (s, 3H; CH3); 4.14e4.79 (m, cyclopentadienyl rings); 7.69 and 8.12 (s, s, each corresponding to one H; eNH2), 9.97 (s, 1H; NH) (Disappear after D2O exchange); 13C: 15.62 (eCH3), 67.78e83.20 (cyclopentadienyl ring carbons), 151.77 (H3CeC¼N), 177.67 (H2NeC¼S). 2.1.3. Preparation of [Zn(Aftscz)2] 0.395 g (1.80 mmol) of Zn(CH3COO)2.2H2O dissolved in 35 mL absolute ethanol was added drop wise with continuous stirring to a warm solution of monoacetylferrocene thiosemicarbazone (1.085 g, 3.60 mmol). The resulting mixture was stirred continuously, after 20 min clear orange solution became turbid with separation of some orange precipitate. Stirring was continued for 10 h till all orange solid separated out completely. It was filtered,
washed with water and cold ethanol and dried in air (Yield: 0.74 g, 62.0%, M.P. 225e229 C (decompose)). (Elemental analyses found (%): C, 47.20; H, 3.97; N, 12.70; S, 9.25; Fe, 16.55; Zn, 10.12. Calc. for C26H28N6S2Fe2Zn: C, 46.95; H, 4.24; N, 12.61; S, 9.62; Fe, 16.76; Zn, 9.81). I.R.: 3413 cm1, 3362 cm1 (yNH2 sym and asym), 1595 cm1 (yC¼N shifted after complexation), 768 cm1 (yCeS). N.M.R (d in ppm) 1H: 1.80 (s, 3H; CH3); 4.16e4.40 (m, cyclopentadienyl rings); 6.21 and 6.75 (s, s, each corresponding to one H; eNH2) (Disappear after D2O exchange); 13C: 18.88 (eCH3), 69.30e85.48 (cyclopentadienyl ring carbons), 164.24 (H3CeC¼N), 172.23 (H2NeCeSe). 2.1.4. Preparation of [Zn(AftsczH)2Cl2] A hot solution of zinc chloride (0.184 g, 1.35 mmol) in 20 mL absolute ethanol was added drop wise with stirring to the monoacetylferrocene thiosemicarbazone (0.815 g, 2.70 mmol) dissolved in 30 mL absolute ethanol. The resulting mixture was stirred continuously for 48 h. The volume of solution was reduced to half under vacuum and n-hexane was added to get the product. It was filtered, washed with water and cold ethanol and dried in air (Yield: 0.70 g, 70.1%, M.P. 196e199 C (decompose)). (Elemental analyses found (%): C, 41.96; H, 3.90; N, 11.80; S, 9.02; Fe, 15.40; Zn, 8.98; Cl, 9.90. Calc. for C26H30N6S2Fe2ZnCl2: C, 42.32; H, 4.08; N, 11.37; S, 8.68; Fe, 15.11; Zn, 8.84; Cl, 9.59). I.R.: 3406 cm1, 3345 cm1 (yNH2 sym and asym), 3195 cm1 (yNH), 1587 cm1 (yC¼N shifted after complexation), 818 cm1 (yC¼S). N.M.R (d in ppm) 1H: 2.17 (s, 3H; CH3); 4.15e4.78 (m, cyclopentadienyl rings); 7.66 and 8.09 (s, s, each corresponding to one H; eNH2), 9.95 (s, 1H; NH) (Disappear after D2O exchange); 13C: 15.50 (eCH3), 67.72e83.50 (cyclopentadienyl ring carbons), 151.15 (H3CeC¼N), 178.29 (H2NeC¼S). 2.2. Preparation of M1xFexS (M ¼ Cd, Zn) nanocrystallites The pyrolysis and solvothermal decompositions of above complexes were carried out to get nanocrystallites.
Fig. 4. TEM images of Cd1xFexS nanocrystallites obtained from pyrolysis of (a), (b) [Cd(Aftscz)2] and (c), (d) [Cd(AftsczH)2Cl2] in furnace at 485 C.
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Fig. 5. TEM images of Cd1xFexS nanocrystallites obtained from solvothermal decomposition of (a), (b) [Cd(Aftscz)2] and (c), (d) [Cd(AftsczH)2Cl2] after 12 h reflux time.
2.2.1. Preparation of M1xFexS nanocrystallites using pyrolysis in furnace In a typical experiment, 0.150 g of precursor was taken in quartz boat which was then inserted to the center of a horizontal wall furnace. The furnace was then heated to the desired temperature under the flowing nitrogen atmosphere for 2 h at a heating rate of 10 C/min. The inert (N2) atmosphere was maintained through out the experiment. The furnace was then cooled to room temperature. After cooling to room temperature the residue from the quartz boat was withdrawn. 2.2.2. Preparation of M1xFexS nanocrystallites using solvothermal decomposition in ethylene glycol 0.250 g of precursor dissolved in 30 cm3 ethylene glycol in 100 cm3 round bottom flask was refluxed at 198 C under nitrogen atmosphere with continuous stirring for the desired time. The initial orange colour turned to grayish-black after some time. Then the reaction mixture was cooled to room temperature. Methanol was added whereupon a black powder was obtained. It was separated by centrifugation. The particles thus obtained were washed repeatedly with methanol and dried under vacuum for 1 h. The materials obtained were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray analysis (EDAX), IR and UVeVisible spectroscopy.
absorption spectra were recorded on a UV-2401 PC Shimadzu UVeVis spectrophotometer. The X-ray Powder Diffraction studies were carried out using Cu Ka radiation on X’pert PRO PANalytical X-ray diffractometer (Philips). Transmission Electron Microscopy images and EDAX analysis were carried out on a Philips, CM 200 microscope with operating voltages between 20 and 200 kV. 3. Results and discussion The single source precursor complexes were prepared by reacting MX2 (M ¼ Cd, Zn and X ¼ Cl, CH3COO) with monoacetylferrocene thiosemicarbazone ligand in 1:2 stoichiometries in absolute ethanol. A simple addition reaction gave [M(AftsczH)2Cl2] complexes (Eq. (1)). When metal acetate was used, [M(Aftscz)2]
2.3. Instrumentation The infrared spectra were recorded as KBr pellets using KBr press on a Perkin Elmer Spectrum One FTIR spectrometer in the range from 4000 to 400 cm1. 1H and 13C{1H} NMR were recorded in 5 mm NMR tube in DMSO-d6 on a Bruker Avance II 300 MHz NMR spectrometer. The 1H and 13C{1H} chemical shifts are relative to internal standard TMS. Elemental analyses (C, H, N, S) of all the compounds were carried out using Thermo Finnigan, Italy Model FLASH EA 1112 Series elemental analyzer. The
Fig. 6. UVevisible spectra of Cd1xFexS nanoparticles obtained from pyrolysis of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] in furnace at 485 C.
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Fig. 7. UVevisible spectra of Cd1xFexS nanoparticles obtained from solvothermal decomposition of (a) [Cd(Aftscz)2] and (b) [Cd(AftsczH)2Cl2] after 12 h reflux time.
complexes were formed by elimination of acetic acid (Eq. (2)). However, addition of dilute NaOH was necessary in order to separate out [Cd(Aftscz)2] complex.
Abs:Ethanol R:T:Stirring MCI2 þ 2AftsczH/ MðAftsczHÞ2 Cl2
(1)
Abs:Ethanol R:T:Stirring MðCH3 COOÞ2 :2H2 O þ 2AftsczH / MðAftsczÞ2 2CH3 COOH 2H2 O (2) where M ¼ Cd and Zn, AftsczH ¼ Monoacetylferrocene thiosemicarbazone. The resulting complexes were characterized by elemental analysis, IR and NMR (1H and 13C{1H}) spectroscopy. The elemental analyses of [Cd(Aftscz)2], [Cd(AftsczH)2Cl2], [Zn(Aftscz)2] and
[Zn(AftsczH)2Cl2] complexes were found to match with 1:2 metal to ligand stoichiometries. In the IR spectra of [Cd(AftsczH)2Cl2] and [Zn(AftsczH)2Cl2] complexes, eNH2 symmetric and asymmetric stretching modes are observed between 3406 cm1e3335 cm1 indicating the noninvolvement of eNH2 in bonding. A band due to eNH is observed at 3191 cm1 and 3195 cm1 respectively suggesting that deprotonation of eNH group has not taken place. The bands at 1589 cm1, 1587 cm1 and 820 cm1, 818 cm1 are attributed to nC¼N and nC¼S respectively. In case of [Cd(Aftscz)2] and [Zn(Aftscz)2] complexes, bands observed at 3413 cm1 and 3308 cm1 are assigned to eNH2 symmetric and asymmetric stretching modes respectively. The other bands present at 1607 cm1, 1595 cm1 and 761 cm1, 768 cm1 are due to nC¼N and nC-S respectively. A band due to eNH stretching which is observed at 3140 cm1 in the ligand is absent in the spectra of both the complexes. These observations are consistent with monoacetylferrocene thiosemicarbazone ligand coordination through sulfur and azomethine nitrogen atoms [23,24]. In the 1H NMR of [Cd(AftsczH)2Cl2] and [Zn(AftsczH)2Cl2], the signals at 9.97 ppm and 9.95 ppm respectively are due to eNH protons. In case of [Cd(Aftscz)2] and [Zn(Aftscz)2] the signals due to eNH protons are absent in the 1H NMR indicating deprotonation of eNH group. The other signals in both the complexes are in accordance with the monoacetylferrocene thiosemicarbazone ligand. In the 13C{1H} NMR spectra of [Cd(AftsczH)2Cl2], [Cd(Aftscz)2], [Zn(AftsczH)2Cl2] and [Zn(Aftscz)2], the signals due to two cyclopentadienyl ring carbons are observed between 67.25 and 85.63 ppm. Whereas, signals due to eCH3, eC¼N and H2N_C]S are observed at w15, w151 and w177 ppm respectively. These observations are consistent with the ligand coordination through sulphur and azomethine nitrogen. On the basis of above observations the probable structures of [M(Aftscz)2] (I) and [M(AftsczH)2Cl2] (II) are given in the Fig. 1. The [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes were used as single source precursors for the preparation of nanocrystalline Cd1xFexS using pyrolysis and solvothermal decomposition routes. Fig. 2 and Fig. 3 show the X-ray diffraction patterns of the material obtained after pyrolysis in a furnace at 485 C and solvothermal decomposition in ethylene glycol at 15 min and 12 h
Fig. 8. IR spectra of (a) pure ethylene glycol (as a neat liquid) and Cd1xFexS nanoparticles obtained from solvothermal decomposition of (b) [Cd(Aftscz)2] and (c) [Cd(AftsczH)2Cl2] after 12 h reflux time.
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reflux time of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2]. It is very interesting that the diffraction patterns match with the hexagonal phase of CdS (JCPDS; 41e1049). So there is possibility that the iron is doped in the structure of cadmium sulfide with the formula Cd1xFexS. Kim and co-workers have reported the Cd1xFexS phase with varying ratio of Cd and Fe [10]. It is clearly seen from the XRD pattern that due to the doping of Fe in CdS, the peak positions (2q) for the planes (100), (002), (101), (102), (110), (103) and (112) are shifted to slightly higher position (for pyrolysis w0.70, 2q degrees and for solvothermal w 0.35, 2q degrees). This phenomenon is generally observed in most of the doping cases [24,26e29]. The peaks in the diffraction patterns of nanocrystalline samples are broadened by the finite size effects. The broadening in the XRD pattern suggests the nanocrystalline nature of the as prepared material. The particle size calculated using Scherrer formula of the materials obtained after pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in a furnace at 485 C are 10.6 nm and 10.3 nm respectively, whereas for the materials obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol, the calculated sizes are 12.6 nm and 18.0 nm (for 15 min reflux time) respectively. The particle size of the materials obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol for 12 h reflux time are 10.0 nm and 15.9 nm respectively. Presence of some minor impurity peaks
in the XRD patterns which can be attributed to cubic FeS (JCPDS: 80-1033) can be seen. No other impurity phase is observed in the materials obtained by solvothermal decomposition. The elemental composition of the material was found out using EDAX. The EDAX analysis of Cd1xFexS nanocrystallites obtained from [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes using pyrolysis at 485 C matches with Cd0.41Fe0.60S0.99 and Cd0.41Fe0.61S0.98 formulae respectively. The EDAX analysis of Cd1xFexS nanocrystallites obtained from the solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] complexes matches with Cd0.71Fe0.29S and Cd0.62Fe0.34S1.04 formulae respectively. Fig. 4 and Fig. 5 show the TEM images of Cd1xFexS nanoparticles obtained from pyrolysis and solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] respectively. TEM images of Cd1xFexS nanoparticles obtained from pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] show the uniformly dispersed nearly spherical shape morphology with the grain size of about 10e14 nm and 26e29 nm respectively (Fig. 4). TEM images of Cd1xFexS nanoparticles obtained from solvothermal decomposition of [Cd(Aftscz)2] show nearly spherical-nanoplates like morphology
Fig. 9. XRD patterns of wurtzite Zn1xFexS (JCPDS: 36-1450) obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 500 C and 540 C (* implies FeS).
Fig. 10. XRD patterns of wurtzite Zn1xFexS (JCPDS: 36-1450) obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in ethylene glycol after 1 h and 6 h reflux time.
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Fig. 11. TEM images of Zn1xFexS nanocrystallites obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 540 C.
with 100e125 nm size (Fig. 5a and b). TEM images of Cd1xFexS nanoparticles obtained from solvothermal decomposition of [Cd(AftsczH)2Cl2] show uniformly dispersed spherical plate-like morphology with diameter of the plates of about 85e94 nm (Fig. 5c and d). UVevisible absorption spectra of Cd1xFexS nanocrystallites dispersed in ethanol are shown in Fig. 6 and Fig. 7. In the absorption spectra, absorption bands at 362 nm and 376 nm are observed for Cd1xFexS obtained from pyrolysis of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] respectively. UVeVisible spectra of Cd1xFexS nanoplates obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol after 12 h reflux time show the broad band at 362 nm with the shoulder band at 477 nm and the broad band at 366 nm with the shoulder band at 496 nm respectively. The absorption bands are blue shifted as compared to bulk CdS which indicates the formation of smaller particles and doping of Fe in the structure of CdS [21]. The IR spectra of Cd1xFexS nanocrystallites obtained by solvothermal route exhibit capping by ethylene glycol (Fig. 8). The IR spectra of Cd1xFexS nanocrystallites obtained from solvothermal decomposition of [Cd(Aftscz)2] and [Cd(AftsczH)2Cl2] in ethylene glycol after 12 h reflux time matches with the IR spectrum of ethylene glycol. All IR bands in the spectrum of Cd1xFexS nanocrystallites match with the bands in the spectrum of ethylene glycol. This proves that ethylene glycol capping is present on Cd1xFexS nanocrystallites (Fig. 8). The Zn (II) monoacetylferrocene thiosemicarbazone complexes, [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] were further used as single source precursors for the synthesis of nanocrystalline Zn1xFexS using pyrolysis and solvothermal decomposition routes. Fig. 9 and Fig. 10 shows the X-ray diffraction patterns of residue obtained after pyrolysis in a furnace at 500 C and 540 C and solvothermal decomposition in ethylene glycol at 1 h and 6 h reflux time of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively.
In case of pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] it is observed that no or small peaks are present in the XRD pattern of the material obtained at 500 C (Fig. 9a and b). However, in the XRD patterns of the materials obtained at higher decomposition temperature i.e. 540 C, well resolved broad diffraction peaks are present which could be perfectly indexed to wurtzite ZnS (JCPDS; 36-1450) (Fig. 9). The EDAX analysis of Zn1xFexS nanocrystallites matches with Zn0.40Fe0.55S1.05 and Zn0.45Fe0.51S1.04 formulae for the materials obtained by pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. This suggests that the doping of Fe does not change the crystal structure of ZnS [22,30]. Few impurity peaks present in the XRD patterns may be due to cubic FeS (JCPDS: 80-1033). Thus higher decomposition temperature is required to get crystalline Zn1xFexS material. Fig. 10 shows the X-ray diffraction patterns of the residue obtained after solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 1 h and 6 h reflux time. It is observed that no peak is present in the diffractogram of the material obtained after 1 h reflux time. When the reflux time was increased to 6 h, wurtzite ZnS (JCPDS; 36-1450) was obtained as evident from the XRD patterns. The EDAX analysis of Zn1xFexS nanocrystallites obtained from the solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] at 6 h reflux time matches with Zn0.69Fe0.26S1.05 and Zn0.60Fe0.38S1.02 formulae respectively. This suggests doping of Fe in ZnS. The doping of Fe does not change the crystal structure of ZnS [22,30] with formula Zn1xFexS. No other impurity phases were observed in the XRD pattern. These observations suggest that the choice of reaction time is an important factor to get Zn1xFexS phase from precursors. In the XRD patterns, it is observed that the peak positions (2q) for the planes (100), (002), (101), (102), (110), (103) and (112) are shifted to slightly upper positions (for pyrolysis w0.60, 2q degrees and for solvothermal w 0.25, 2q degrees) because of doping of Fe in
Fig. 12. TEM images of Zn1xFexS nanocrystallites obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] after 6 h reflux time.
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Fig. 13. IR spectra of (a) pure ethylene glycol (as a neat liquid) and Zn1xFexS nanoparticles obtained from solvothermal decomposition of (b) [Zn(Aftscz)2] and (c) [Zn(AftsczH)2Cl2] after 6 h reflux time.
ZnS structure. The peak broadening in the XRD pattern clearly indicates the nanocrystalline nature of the Zn1xFexS. The particle sizes calculated using Scherrer formula of the materials obtained after pyrolysis of [Zn(Aftscz)2] at 500 C and [Zn(AftsczH)2Cl2] at 540 C in a furnace are 28.9 nm and 5.3 nm respectively, whereas for the materials obtained from solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol for 6 h, the calculated sizes are 15.0 nm and 16.9 nm (for 6 h reflux time) respectively. TEM images show presence of spherical shape nanoparticles with average grain size of 20e25 nm and 22e24 nm of Zn1xFexS obtained from pyrolysis decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively (Fig. 11). Fig. 12 shows the TEM micrographs of Zn1xFexS nanocrystallites prepared using solvothermal route from [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 6 h reflux time. Uniformly dispersed nanoflakes like morphology is observed in the TEM micrographs. The grain size of as prepared Zn1xFexS nanoflakes
obtained by solvothermal route from [Zn(Aftscz)2] is found to be about 150e155 nm. In case of Zn1xFexS nanocrystallites prepared using the solvothermal route from [Zn(AftsczH)2Cl2] nearly spherical shape particles were observed in the TEM micrographs with grain size of 13e16 nm. In most of the cases, the particle sizes calculated using Scherrer formula match with those seen in the respective TEM images. In few cases, the particles sizes seen in the TEM image are bigger than those calculated using Scherrer formula. This is due to difficulty in measuring the particle sizes exactly in the TEM images as there is overlapping of the nanoplates (Fig. 5) and nanoflakes (Fig. 12a). The IR spectrum of Zn1xFexS nanoparticles obtained from solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] in ethylene glycol after 6 h reflux time matches with the IR spectrum of pure ethylene glycol; suggesting the capping of ethylene glycol over Zn1xFexS nanoparticles (Fig. 13).
Fig. 14. UVevisible spectra of Zn1xFexS nanoparticles obtained from pyrolysis of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] in furnace at 540 C.
Fig. 15. UVevisible spectra of Zn1xFexS nanoparticles obtained from solvothermal decomposition of (a) [Zn(Aftscz)2] and (b) [Zn(AftsczH)2Cl2] after 6 h reflux time.
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Fig. 14 and Fig. 15 show the UV absorption spectra of Zn1xFexS nanocrystallites dispersed in ethanol obtained from the pyrolysis and solvothermal decomposition of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. The absorption band for Zn1xFexS is observed at 310 nm and 315 nm for the materials obtained by pyrolysis of [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. Whereas in case of solvothermal decomposition the absorption bands are observed at 345 nm and 370 nm for [Zn(Aftscz)2] and [Zn(AftsczH)2Cl2] respectively. These absorption bands are blue shifted as compared to bulk ZnS which indicates formation of smaller particles and doping of Fe in the structure of ZnS [20,29,30]. 4. Conclusions Mixed metal thiosemicarbazones were successfully used as single source precursors for the preparation of M1xFexS nanocrystallites by pyrolysis and solvothermal decomposition routes. Thus, Cd (II) and Zn (II) monoacetylferrocene thiosemicarbazone complexes gave hexagonal Fe doped CdS (Cd1xFexS)and wurtzite Fe doped ZnS (Zn1xFexS) nanocrystallites respectively. It is evident from the present investigation that the experimental conditions such as decomposition temperature, reflux time, etc. affect the properties like crystallinity, morphology etc. of the M1xFexS. This single-source precursor approach can be extended for the preparation of other ternary metal chalcogenide materials. Acknowledgment Authors are thankful to UGC for financial support, TIFR (Mumbai) for XRD and SAIF, IIT Bombay for TEM characterization facility. References [1] J.K. Furdyna, J. Appl. Phys. 64 (1988) R29eR64. [2] A. Twardowski, T. Dietl, M. Demianiuk, Solid State Commun. 48 (1983) 845e848.
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