SnO2/TiO2 nano particles are novel wide band gap semiconductors with modified applications of SnO2 and TiO2 in some fields including gas sensing, photo catalytic, solar cells and so on. The Co-doped SnO2/TiO2 nano particles were obtained via sol-gel method with different amounts of doping material as 2.5 %, 6 % and 10 mol %. The crystallite sizes of resulting material were from 3.8 nm for 0.1 wt % Co-doped SnO2/TiO2 to 19.1 nm for un-doped. Morphology and nanostructure of the crystalline SnO2/TiO2 nano particles were characterized by means of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). It has been shown that fine semiconductor nano structures were formed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/933

Beigi, H.

Devi, G.S.

Hamoon, H.Z.R.

Nanaji, A.

Rao, J.V.R.

Reddy, K.R.

Electronic Sumy State University Institutional Repository

   J. Nano- Electron. Phys. 3 (2011) No1, P.59-66  2011 SumDU (Sumy State University)   59 PACS numbers: 81.20.Fw, 81.07.Bc, 07.07.Df.  SYNTHESIS AND CHARACTERIZATION OF Co-DOPED SnO2/TiO2 SEMICONDUCTOR NANO CRYSTALLITES VIA SOL-GEL METHOD  H.Z.R. Hamoon1, G.S. Devi1, H. Beigi2, J.V.R. Rao2, K.R. Reddy1, A. Nanaji1  1 Inorganic and Physical Chemistry division,   Indian Institute of Chemical Technology,  Tarnaka, Hyderabad, AP, India  E-mail: hedayatzadehamoon@yahoo.com 2 Center for Nano Science & Technology,   Institute of Science and Technology, JNTUH,  Kukatpally, Hyderabad, 500085, AP, India  SnO2/TiO2 nano particles are novel wide band gap semiconductors with modified applications of SnO2 and TiO2 in some fields including gas sensing, photo catalytic, solar cells and so on. The Co-doped SnO2/TiO2 nano particles were obtained via sol-gel method with different amounts of doping material as 2.5 %, 6 % and 10 mol %. The crystallite sizes of resulting material were from 3.8 nm for 0.1 wt % Co-doped SnO2/TiO2 to 19.1 nm for un-doped. Morphology and nanostructure of the crystalline SnO2/TiO2 nano particles were characterized by means of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). It has been shown that fine semiconductor nano structures were formed.  Keywords: SnO2/TiO2, Co-DOPED, SEMICONDUCTOR, XRD, NANOPARTICLE.  (Received 04 February 2011, in final form 20 March 2011)  1. INTRODUCTION  SnO2 is an opto electrical n-type semiconductor that has many interesting properties. These properties have made it a reliable material for gas sensing and catalysis applications [1, 2]. Even gas sensors based on SnO2 materials are commercially available today [3]. SnO2-based nano powders and devices are obtained by means of a variety of synthesis techniques including the co precipitation [4], ion sputtering [5], microwave heating method [6], surfactants mediate [7,8], sol-gel methods [9] and so on.  On  the  other  hand  TiO2 is  also  an  n-type  semiconductor  that  has  been  subject of many research studies in the last decade. It has been extensively employed in many applications mainly to photo catalytic decontamination treatments. [11-12].  One of the effective methods for obtaining desired material with modified properties is mixing two different semiconductors with appropriate conduction and valence band edges [13]. With coupling two metal oxide nanoparticles, better structures with more advantages for sensor applications can be achieved [14-15].  The  energy  levels  of  the  valence  and  conduction  bands  are  3.7  eV  and  (ECB   0 V versus NHE at pH 7) for SnO2 and 2.7 eV (ECB    0.5 V versus    60 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL.  NHE at pH 7) for TiO2 [16, 17]. The band gap energy level of SnO2 is higher than that of TiO2; the conduction band of SnO2 is at a lower level than that TiO2‘s. The higher reduction power of electrons and the higher oxidation power of holes correspond to the higher position of conduction band and the lower position of valence band, respectively. Therefore, mixing two semiconductors with different energy levels for their corresponding conduction and valence bands can provide an approach to achieve better applications by increasing the efficiency of charge separation, charge carrier lifetime, ,interfacial charge transfer rate and extending the energy range of photo excitation [16]. Mixed oxides can be formed in three ways along follow lines: (1) Chemical compound. (2) Solid solution (3) Mix of (1) and (2) types.  The SnO2-TiO2 mixture belongs to second category [18]. The SnO2-TiO2 coupled semiconductor commonly is synthesized by mixing the colloidal solutions of SnO2 and  TiO2 [19, 20].In recent years the properties of Co-doped SnO2 nanoparticles  and  Co-doped  TiO2 nano particles have been exhaustively investigated. [21, 22, 23]  In  the  case  of  Co-doped  TiO2 the main focus has been on the inherent ferromagnetism  property  of  resulting  nano  structure  at  or  above  room  temperature. Co: TiO2 nano particles are one of the most prominent diluted magnetic semiconductors (DMS) In the field of spintronics, especially for magneto-opto-electronic applications [24-25] DMSs have significant potential for future applications in the solar cells, biomedical and environmental fields. Co-doping SnO2 also  has  been  widely  studied  [21].  One  of  the  new  emerging applications of SnO2 nano particles doped with Co is in varistor base materials.  SnO2 with native oxygen vacancies compensated by electrons:    0 2( )0O 2 0.5Ox ge V cc      Using tin oxide ceramics is limited as dense ceramic since it is hard to make it denser because of evaporation and condensation, which enhance the grain growth, mostly dominate mass transport [26, 27]. Several sintering aids have been used to improve the densification of SnO2 ceramics [23, 28]. Recent reports suggest Co is used as sintering aids [23, 29].   Hence the investigation of nano particles of mix of SnO2-TiO2 doped via Co would have many advantages and it selected as a novel semiconductor for the  current  subject  of  this  study.  In  this  paper,  a  fine  mixture  nano-structural SnO2-TiO2 with different dosages of doped-Co is synthesized via sol-gel method while SnCl4 as a common precursor for producing SnO2 nano crystallite structure has been used. The mixture ratio of 3:1 has been kept constant  for  all  samples  and  the  Co  doped  amount  varied  from  0  %  to  10  mol  %.  Geometry,  particle  size,  morphology  of  nano  crystallite  structures are estimated by measurements.  2. EXPERIMENTAL WORK  Stannic chloride (SnCl4, spectrochem Pvt. Ltd, Mumbai), titanium chloride (TiCl4,  spectrochem Pvt.  Ltd,  Mumbai),  Poly Ethylene Glycol  (6000LR, s-d fine-chem Limited, Mumbai), Ammonia solution 25% (Extra pure, s-d fine-    SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 61  chem Limited,  Mumbai)  were purchased as  precursors.  0.3 mol  (SnCl4) and 0.1 mol TiCl4 were separately diluted using distilled water under simultaneous stirring condition for 45 min. 13 grams of PEG was dissolved in  300  ml  distilled  water  and  was  stirred  for  30  min  until  transparent  solution was obtained. Diluted SnCl4 and TiCl4 were added drop by drop to the above solution simultaneously. Solution continued to remain under vigorous stirring for more than an hour. Appropriate amounts of CoCl2 for (0.25 mol %) Co-doping after dissolving in distilled water was added to mixture and was stirred for 30 min. 25 % aqueous ammonia solution was employed for adjusting PH value of the resulting solution to around 3. Then stirring condition was continued vigorously for one hour. The resulting sol was filtered and washed with distilled water and acetone twice, respectively, and dried overnight at 80 qC. Resulting solid was ground followed by calcination at 550 qC for 2 hours. This procedure was repeated three times with varying the amounts of CoCl2 addition for obtaining four different nano powders with 0%, 2.5%, 6%, 10 mol % Co-doped finally.   3. RESULTS  3.1 TGA  Main  Co-doped  SnO2/TiO2 (6 mol % doped) thermo gravimetric analysis (TGA)  was  accomplished  in  a  flow  of  air  with  a  temperature  ramp  of   50 qC/min and D-alumina was used as the reference. Fig. 1 shows the weight loss (TG) and the differential thermo-analysis (DTA) curves corresponding to Co-doped SnO2/TiO2 without any thermal annealing. The TG curve exhibits one endothermic weight loss at temperatures lower than 130 qC with 16.6 % weight loss that is associated with the loss of the residual water and trapped solvent in the particles. From 130 qC to 275 qC and 275 qC to 310 qC there are two small exothermic peaks corresponding to 6.6 % and 9.3 % relative weight losses respectively. About 360 qC  a  vigorous  exothermic  peak  was  observed accompanied by 9.3 % loss weight. Last exothermic peak at 500 qC corresponds to 6.6 weight loss. These exothermic peaks are likely due to decomposition of resulting nano crystallite structures, as confirmed by XRD analysis shown in Fig. 2. No more peak and no further weight loss observed in the TGA/DTA curves.   3.2 XRD  Structural properties of all 0 %, 2.5 %, 6 %, 10 mol % Co-doped SnO2/TiO2 samples were studied using X-ray diffraction (XRD: XRG 3000, Inel, France). The XRD results obtained were compared to the Joint Committee on Powder Diffraction Standards (JCPDS) X-ray data file. The crystallite size of the samples was calculated using the Scherrer formula:   T   0.9O/(EcosT)   Where T is the particle size in nanometers, O is  the  wavelength  of  Co  radiation (O   1.78897), ȕ is the FWHM of the strongest peak and ș is the peak position. By using the equation the crystal size of all different nanoparticles were calculated for each calcined temperature and are depicted     62 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL.    Fig. 1  TGA and DTA curves of Co-doped SnO2/TiO2  in  Table  1.  Presence of  SnO2 and rutile TiO2 were confirmed by PDF# 77-0451 (5 peaks are match) and PDF#76-0326 (2 peaks 111 and 211) respectively.  Also  CoO  (hexagonal)  peak  was  observed  (PDF#89-2803  and  peak 110). Decreasing the crystallite size is proportional with amount of Co-doped to SnO2/TiO2.  Table 1  Crystallite and particle size of Co-doped SnO2/TiO2 nanostructures  Sample Crystallite size (nm) Particle size (nm) Un-doped SnO2/TiO2 19.1 27 2.5 mol % Co-doped SnO2/TiO2 15.5 21 6 mol % Co-doped SnO2/TiO2 4.3 17 10 mol % Co-doped SnO2/TiO2 3.8 16  3.3 Raman  The Raman spectra of all samples were depicted in Fig. 3 and were compared with literature data [30, 31, 32]. For characterization the wave length 633 cm– 1 was used for adjusting Raman apparatus (Labram Horibb yvon). Commercial CoO Raman spectra are shown in Fig. 3e, two peaks at 648, 485 cm– 1. The SnO2 peak about 630 cm– 1 corresponding to A1g mode, and two bands at 773 and 472 cm– 1 corresponding to B2g and Eg modes, respectively; this being in accordance with literature data. TiO2 rutile  has  peaks with following values: 235, 447 [30] or 235, 447, 612 [31].  Peaks  of  TiO2 rutile  and  SnO2 and  CoO  were  confirmed  and  that  is  in  agreement with other characterization data.      SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 63   Fig. 2 – XRD pattern of Co-doped SnO2/TiO2 (a) un-doped (b) 2.5 mol % doped (c) 6 mol % doped (d) 10 mol % doped  3.4 FTIR   The FTIR analysis was carried out in order to determine the functional group of materials existed in Co-doped to SnO2/TiO2 samples. The analysis was recorded using FTIR spectrometer (bruker) in a range between 4000 and 400 cm– 1.   Fig. 4 shows the FTIR spectra of Co-doped to SnO2/TiO2.  The  bands  at  3543 - 3393 cm– 1 correspond to the O-H mode of vibration [33]. The broad O-H  peaks  become  narrower  with  an  increase  Co-doped  amount,  3380  and  3050 cm– 1, which may be due to the adsorbed water and NH. The N-H band observed around ca. 3050 cm– 1 may  be  due  to  the  use  of  ammonia  to  promote SnCl4 and  TiCl4 hydrolysis,  which  leads  to  the  formation  of  ammonia. The strong asymmetric stretching mode of vibration of C   O was observed between 1668 cm– 1. The symmetric stretching occurs between 1400 and 1334cm– 1 because of the presence of C-O. The C-O-C peak is present about 1070 cm– 1.  According  to  Du  et  al.  [34],  the  C-O-C  peak  usually  appears  at  1256  cm– 1. The absorption peaks at 1359, 1343, 1280, 1240, 1149 and 1077 cm– 1 result from the bending vibration of the O-H bond and stretching vibration of the C-O bond of the -CH2-OH group. In fact the XRD and EDX analysis proved that the synthesized powders in this work are Co-doped to SnO2/TiO2 with the good stoichiometric composition.     64 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL.     Fig. 3  Raman spectra of Co-doped SnO2/TiO2 un-doped (a), 2.5 mol % doped (b,) 6 mol % doped (c), 10 mol % doped (d), and commercial CoO (e)  Fig. 4  FT-IR spectra of Co-doped SnO2/TiO2 un-doped (a), 2.5 mol % doped (b), 6 mol % doped (c), and 10 mol % doped (d)   The particle size caused a large shift in the IR peak. The SnO2 peak that appears 660 cm– 1 shows that formation of tin oxide was completed. The FTIR results support the RAMAN, XRD, FESEM results.   3.5 FESEM  The  surface  morphology,  particles  size  and  composition  of  Co-doped  to  SnO2/TiO2 nanoparticles were investigated by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX).  FESEM  and  EDX  images  of  Co-doped  to  SnO2/TiO2 powder nanoparticles  are  shown  in  Fig.  5.  Nano  particles  with  relatively  high  agglomeration are shown in Fig. 5 a and b. This agglomeration is a result of the acidic sols during the synthesis process. The particle sizes were estimate for all samples using images Table 1.      SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 65      Fig. 5  FESEM and EDX images of Co-doped to SnO2/TiO2 un-doped (a) 2.5 mol % doped (b) 10 mol % doped (c)  4. CONCLUSION  A modified sol-gel process was designed to prepare Co-doped to SnO2/TiO2. The  products  were  characterized  by  means  of  X-ray  diffraction,  Raman  spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). Crystallite and particle size of the nano structures were decreased from 19.1 to 3.8 nm and 27 to 16 respectively by the addition of Co to the precursor solution. Fine Co-doped to SnO2/TiO2 nano particles were obtained and applications were discussed.  ACKNOWLEDGEMENT Hamoon  H.Z.R.  thanks  Director  IICT  for  permitting  him  to  carry  out  his  thesis  work  at  IICT.  A.  Nanaji  and  Ravindranath  Reddy  thank  CSIR  and  UGC for research fellowship. a a a b b b c c c    66 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL.  REFERENCES  1. M. Batzill, U. Diebold, Prog. Surf. Sci. 79, 47 (2005). 2. M. Tiemann, Chem. Eur. J. 13, 8376 (2007). 3. Microsens Inc. (http://www.microsens.ch). 4. A. Mosquera, J.E. Rodríguez-Páez, J.A. Varela, P.R. Bueno, J. Eur. Ceram. Soc. 27, 3893 (2007). 5. M. Ruske, G. Brauer, J. Pistner, U. Pfafflin, J. Szczyrbowski, Thin Solid Films 351, 146 (1999). 6. J.-J. Zhu, J.-M. Zhu, X.-H. Liao, J.-L. Fang, M.-G. Zhou, H.-Y. Chen, Mater. Lett. 53, 12 (2002). 7. J. Pal, P. Chauhan, Mater. Charact. 60, 1512 (2009). 8. C. Liang, Y. Shimizu, T. Sasaki, N. Koshizaki, J. Phys. Chem. B 107, 9220 (2003). 9. A. Kurz, K. Brakecha, J. Puetz, M.A. Aegerter, Thin Solid Films. 502, 212 (2006). 10. N. Negishi, T. Iyoda, K. Hashimoto, A. Fujishima, Chem. Lett. 9, 841 (1995). 11. I. Sopyan, M. Watanabe, S. Murasawa, Chem. Lett. 1, 69 (1996). 12. A.L. Linsebigler, G.Q. Lu, J.T. Yates, Jr. Chem. Rev. 95, 735 (1995). 13. J. Shang, W. Yao,  Appl. Catal. A-Gen 257, 25 (2004). 14. K. Zakrzewska, Thin Solid Films 391, 229 (2001). 15. P. Nelli, L.E. Depero, M. Ferroni, S. Groppelli, V. Guidi, F. Ronconi, L. Sangaletti, G. Sberveglieri, Sens. Actuat. B Chem. 31, 89 (1996). 16. O. Carp, C.L. Huisman, A. Reller, Prog. Solid State Chem. 32, 33 (2004). 17. K. Vinodgopal, P.V. Kamat, Environ. Sci. Technol. 29, 841 (1995). 18. N.V. Duy, N.V. Hieu, Physica E 41, 258 (2008). 19. P.V. Kamat, Chem. Rev. 93, 267 (1993). 20. I. Bedja, S. Hotchandani, P.V. Kamat, B. Bunsen-Ges, Phys. Chem. Chem. Phys. 101, 1651 (1997). 21. R. Parra, L.A. Ramajo, Mater. Res. Bull. 43, 3202 (2008). 22. K.A. Griffin, A.B. Pakhomov, Phys. Rev. Lett. 94, 157204 (2005). 23. R. Metz, D. Koumeir, J. Morel, J. Panisot, M. Houabes, M. Hassanzadeh, J. Eur. Ceram. Soc. 28, 829 (2008). 24. H. Ohno, Science 281, 951 (1998). 25. S.J. Pearton, W.H. Heo, M. Ivill, D.P. Norton, T. Steiner, Semicond. Sci. Technol. 19, 59 (2004). 26. C. Li, J. Wang, W. Su, H. Chen, W. Zhong, P. Zhang, Ceram. Int. 27, 655 (2001). 27. T. Kimura, S. Inada, T. Yamaguchi, J. Mater. Sci. 24, 220 (1989). 28. J.A Varela, O.J. Whittemore, E Longo, Ceram. Int. 16, 177 (1990). 29. S.A. Pianaro, P.R. Bueno, E. Longo, J.A. Varela, J. Mater. Sci. Lett. 14, 692 (1995). 30. V.N. Kuznetsov, N. Serpone, J Phys. Chem. B. 110, 25203 (2006). 31. T. Hirata, K. Ishioka, M. Kitajima, H. Doi, Phys. Rev. B. 53, 8442 (1996). 32. Y. Liu, M. Liu, Adv. Funct. Mater. 15, 57 (2005). 33. D.M. Fernandes, R. Silva, A.A.W. Hechenleitner, E. Radovanovic, M.A.C. Melo, E.A.G. Pineda, Mater. Chem. Phys. 115, 110 (2009). 34. H. Du, F. Yuan, S. Huang, J. Li, Y. Zhu, Chem. Lett. 33, 770 (2004). 

Synthesis And Characterization Of Co-Doped SnO2/TiO2 Semiconductor Nano Crystallites Via Sol-Gel Method

SocioEconomic Challenges Journal (Sumy State University)

 
 
 
J. Nano- Electron. Phys. 
3 (2011) No1, P.59-66 
 2011 SumDU 
(Sumy State University) 
 
 
59 
PACS numbers: 81.20.Fw, 81.07.Bc, 07.07.Df. 
 
SYNTHESIS AND CHARACTERIZATION OF Co-DOPED SnO2/TiO2 
SEMICONDUCTOR NANO CRYSTALLITES VIA SOL-GEL METHOD 
 
H.Z.R. Hamoon1, G.S. Devi1, H. Beigi2, J.V.R. Rao2, K.R. Reddy1, A. Nanaji1 
 
1 Inorganic and Physical Chemistry division,  
 Indian Institute of Chemical Technology, 
 Tarnaka, Hyderabad, AP, India 
 E-mail: hedayatzadehamoon@yahoo.com 
2 Center for Nano Science & Technology,  
 Institute of Science and Technology, JNTUH, 
 Kukatpally, Hyderabad, 500085, AP, India 
 
SnO2/TiO2 nano particles are novel wide band gap semiconductors with modified 
applications of SnO2 and TiO2 in some fields including gas sensing, photo catalytic, 
solar cells and so on. The Co-doped SnO2/TiO2 nano particles were obtained via sol-gel 
method with different amounts of doping material as 2.5 %, 6 % and 10 mol %. The 
crystallite sizes of resulting material were from 3.8 nm for 0.1 wt % Co-doped 
SnO2/TiO2 to 19.1 nm for un-doped. Morphology and nanostructure of the crystalline 
SnO2/TiO2 nano particles were characterized by means of X-ray diffraction, Raman 
spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric 
analysis (TGA), field emission scanning electron microscopy (FESEM) and energy 
dispersive X-ray spectroscopy (EDX). It has been shown that fine semiconductor nano 
structures were formed. 
 
Keywords: SnO2/TiO2, Co-DOPED, SEMICONDUCTOR, XRD, NANOPARTICLE. 
 
(Received 04 February 2011, in final form 20 March 2011) 
 
1. INTRODUCTION 
 
SnO2 is an opto electrical n-type semiconductor that has many interesting 
properties. These properties have made it a reliable material for gas sensing 
and catalysis applications [1, 2]. Even gas sensors based on SnO2 materials 
are commercially available today [3]. SnO2-based nano powders and devices 
are obtained by means of a variety of synthesis techniques including the co 
precipitation [4], ion sputtering [5], microwave heating method [6], 
surfactants mediate [7,8], sol-gel methods [9] and so on. 
 On  the  other  hand  TiO2 is  also  an  n-type  semiconductor  that  has  been  
subject of many research studies in the last decade. It has been extensively 
employed in many applications mainly to photo catalytic decontamination 
treatments. [11-12]. 
 One of the effective methods for obtaining desired material with modified 
properties is mixing two different semiconductors with appropriate 
conduction and valence band edges [13]. With coupling two metal oxide 
nanoparticles, better structures with more advantages for sensor 
applications can be achieved [14-15]. 
 The  energy  levels  of  the  valence  and  conduction  bands  are  3.7  eV  and  
(ECB   0 V versus NHE at pH 7) for SnO2 and 2.7 eV (ECB    0.5 V versus 
 
 
 
60 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL. 
 
NHE at pH 7) for TiO2 [16, 17]. The band gap energy level of SnO2 is higher 
than that of TiO2; the conduction band of SnO2 is at a lower level than that 
TiO2‘s. The higher reduction power of electrons and the higher oxidation 
power of holes correspond to the higher position of conduction band and the 
lower position of valence band, respectively. Therefore, mixing two 
semiconductors with different energy levels for their corresponding 
conduction and valence bands can provide an approach to achieve better 
applications by increasing the efficiency of charge separation, charge carrier 
lifetime, ,interfacial charge transfer rate and extending the energy range of 
photo excitation [16]. 
Mixed oxides can be formed in three ways along follow lines: 
(1) Chemical compound. 
(2) Solid solution 
(3) Mix of (1) and (2) types. 
 The SnO2-TiO2 mixture belongs to second category [18]. The SnO2-TiO2 
coupled semiconductor commonly is synthesized by mixing the colloidal 
solutions of SnO2 and  TiO2 [19, 20].In recent years the properties of Co-
doped SnO2 nanoparticles  and  Co-doped  TiO2 nano particles have been 
exhaustively investigated. [21, 22, 23] 
 In  the  case  of  Co-doped  TiO2 the main focus has been on the inherent 
ferromagnetism  property  of  resulting  nano  structure  at  or  above  room  
temperature. Co: TiO2 nano particles are one of the most prominent diluted 
magnetic semiconductors (DMS) In the field of spintronics, especially for 
magneto-opto-electronic applications [24-25] DMSs have significant potential 
for future applications in the solar cells, biomedical and environmental 
fields. Co-doping SnO2 also  has  been  widely  studied  [21].  One  of  the  new  
emerging applications of SnO2 nano particles doped with Co is in varistor 
base materials. 
 SnO2 with native oxygen vacancies compensated by electrons:  
 
 0 2( )0
O 2 0.5Ox ge V cc     
 
Using tin oxide ceramics is limited as dense ceramic since it is hard to make 
it denser because of evaporation and condensation, which enhance the grain 
growth, mostly dominate mass transport [26, 27]. Several sintering aids 
have been used to improve the densification of SnO2 ceramics [23, 28]. 
Recent reports suggest Co is used as sintering aids [23, 29].  
 Hence the investigation of nano particles of mix of SnO2-TiO2 doped via 
Co would have many advantages and it selected as a novel semiconductor for 
the  current  subject  of  this  study.  In  this  paper,  a  fine  mixture  nano-
structural SnO2-TiO2 with different dosages of doped-Co is synthesized via 
sol-gel method while SnCl4 as a common precursor for producing SnO2 nano 
crystallite structure has been used. The mixture ratio of 3:1 has been kept 
constant  for  all  samples  and  the  Co  doped  amount  varied  from  0  %  to  
10  mol  %.  Geometry,  particle  size,  morphology  of  nano  crystallite  
structures are estimated by measurements. 
 
2. EXPERIMENTAL WORK 
 
Stannic chloride (SnCl4, spectrochem Pvt. Ltd, Mumbai), titanium chloride 
(TiCl4,  spectrochem Pvt.  Ltd,  Mumbai),  Poly Ethylene Glycol  (6000LR, s-d 
fine-chem Limited, Mumbai), Ammonia solution 25% (Extra pure, s-d fine-
 
 
 
 SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 61 
 
chem Limited,  Mumbai)  were purchased as  precursors.  0.3 mol  (SnCl4) and 
0.1 mol TiCl4 were separately diluted using distilled water under 
simultaneous stirring condition for 45 min. 13 grams of PEG was dissolved 
in  300  ml  distilled  water  and  was  stirred  for  30  min  until  transparent  
solution was obtained. Diluted SnCl4 and TiCl4 were added drop by drop to 
the above solution simultaneously. Solution continued to remain under 
vigorous stirring for more than an hour. Appropriate amounts of CoCl2 for 
(0.25 mol %) Co-doping after dissolving in distilled water was added to 
mixture and was stirred for 30 min. 25 % aqueous ammonia solution was 
employed for adjusting PH value of the resulting solution to around 3. Then 
stirring condition was continued vigorously for one hour. The resulting sol 
was filtered and washed with distilled water and acetone twice, respectively, 
and dried overnight at 80 qC. Resulting solid was ground followed by 
calcination at 550 qC for 2 hours. This procedure was repeated three times 
with varying the amounts of CoCl2 addition for obtaining four different 
nano powders with 0%, 2.5%, 6%, 10 mol % Co-doped finally.  
 
3. RESULTS 
 
3.1 TGA 
 
Main  Co-doped  SnO2/TiO2 (6 mol % doped) thermo gravimetric analysis 
(TGA)  was  accomplished  in  a  flow  of  air  with  a  temperature  ramp  of   
50 qC/min and D-alumina was used as the reference. Fig. 1 shows the weight 
loss (TG) and the differential thermo-analysis (DTA) curves corresponding to 
Co-doped SnO2/TiO2 without any thermal annealing. The TG curve exhibits 
one endothermic weight loss at temperatures lower than 130 qC with 16.6 % 
weight loss that is associated with the loss of the residual water and trapped 
solvent in the particles. From 130 qC to 275 qC and 275 qC to 310 qC there 
are two small exothermic peaks corresponding to 6.6 % and 9.3 % relative 
weight losses respectively. About 360 qC  a  vigorous  exothermic  peak  was  
observed accompanied by 9.3 % loss weight. Last exothermic peak at 500 qC 
corresponds to 6.6 weight loss. These exothermic peaks are likely due to 
decomposition of resulting nano crystallite structures, as confirmed by XRD 
analysis shown in Fig. 2. No more peak and no further weight loss observed 
in the TGA/DTA curves.  
 
3.2 XRD 
 
Structural properties of all 0 %, 2.5 %, 6 %, 10 mol % Co-doped SnO2/TiO2 
samples were studied using X-ray diffraction (XRD: XRG 3000, Inel, France). 
The XRD results obtained were compared to the Joint Committee on Powder 
Diffraction Standards (JCPDS) X-ray data file. The crystallite size of the 
samples was calculated using the Scherrer formula: 
 
 T   0.9O/(EcosT)  
 
Where T is the particle size in nanometers, O is  the  wavelength  of  Co  
radiation (O   1.78897), ȕ is the FWHM of the strongest peak and ș is the 
peak position. By using the equation the crystal size of all different 
nanoparticles were calculated for each calcined temperature and are depicted  
 
 
 
62 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL. 
 
 
 
Fig. 1  TGA and DTA curves of Co-doped SnO2/TiO2 
 
in  Table  1.  Presence of  SnO2 and rutile TiO2 were confirmed by PDF# 77-
0451 (5 peaks are match) and PDF#76-0326 (2 peaks 111 and 211) 
respectively.  Also  CoO  (hexagonal)  peak  was  observed  (PDF#89-2803  and  
peak 110). Decreasing the crystallite size is proportional with amount of Co-
doped to SnO2/TiO2. 
 
Table 1  Crystallite and particle size of Co-doped SnO2/TiO2 nanostructures 
 
Sample Crystallite size 
(nm) 
Particle size (nm) 
Un-doped SnO2/TiO2 19.1 27 
2.5 mol % Co-doped SnO2/TiO2 15.5 21 
6 mol % Co-doped SnO2/TiO2 4.3 17 
10 mol % Co-doped SnO2/TiO2 3.8 16 
 
3.3 Raman 
 
The Raman spectra of all samples were depicted in Fig. 3 and were compared 
with literature data [30, 31, 32]. For characterization the wave length 633 
cm– 1 was used for adjusting Raman apparatus (Labram Horibb yvon). 
Commercial CoO Raman spectra are shown in Fig. 3e, two peaks at 648, 485 
cm– 1. The SnO2 peak about 630 cm– 1 corresponding to A1g mode, and two 
bands at 773 and 472 cm– 1 corresponding to B2g and Eg modes, 
respectively; this being in accordance with literature data. TiO2 rutile  has  
peaks with following values: 235, 447 [30] or 235, 447, 612 [31]. 
 Peaks  of  TiO2 rutile  and  SnO2 and  CoO  were  confirmed  and  that  is  in  
agreement with other characterization data. 
 
 
 
 
 SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 63 
 
 
Fig. 2 – XRD pattern of Co-doped SnO2/TiO2 (a) un-doped (b) 2.5 mol % doped (c) 
6 mol % doped (d) 10 mol % doped 
 
3.4 FTIR  
 
The FTIR analysis was carried out in order to determine the functional group of 
materials existed in Co-doped to SnO2/TiO2 samples. The analysis was recorded 
using FTIR spectrometer (bruker) in a range between 4000 and 400 cm– 1.  
 Fig. 4 shows the FTIR spectra of Co-doped to SnO2/TiO2.  The  bands  at  
3543 - 3393 cm– 1 correspond to the O-H mode of vibration [33]. The broad 
O-H  peaks  become  narrower  with  an  increase  Co-doped  amount,  3380  and  
3050 cm– 1, which may be due to the adsorbed water and NH. The N-H band 
observed around ca. 3050 cm– 1 may  be  due  to  the  use  of  ammonia  to  
promote SnCl4 and  TiCl4 hydrolysis,  which  leads  to  the  formation  of  
ammonia. The strong asymmetric stretching mode of vibration of C   O was 
observed between 1668 cm– 1. The symmetric stretching occurs between 
1400 and 1334cm– 1 because of the presence of C-O. The C-O-C peak is 
present about 1070 cm– 1.  According  to  Du  et  al.  [34],  the  C-O-C  peak  
usually  appears  at  1256  cm– 1. The absorption peaks at 1359, 1343, 1280, 
1240, 1149 and 1077 cm– 1 result from the bending vibration of the O-H 
bond and stretching vibration of the C-O bond of the -CH2-OH group. In fact 
the XRD and EDX analysis proved that the synthesized powders in this 
work are Co-doped to SnO2/TiO2 with the good stoichiometric composition.  
 
 
 
64 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL. 
 
  
 
Fig. 3  Raman spectra of Co-doped 
SnO2/TiO2 un-doped (a), 2.5 mol % doped 
(b,) 6 mol % doped (c), 10 mol % doped 
(d), and commercial CoO (e) 
 
Fig. 4  FT-IR spectra of Co-doped 
SnO2/TiO2 un-doped (a), 2.5 mol % 
doped (b), 6 mol % doped (c), and 
10 mol % doped (d) 
 
 The particle size caused a large shift in the IR peak. The SnO2 peak that 
appears 660 cm– 1 shows that formation of tin oxide was completed. The 
FTIR results support the RAMAN, XRD, FESEM results.  
 
3.5 FESEM 
 
The  surface  morphology,  particles  size  and  composition  of  Co-doped  to  
SnO2/TiO2 nanoparticles were investigated by field emission scanning 
electron microscopy (FESEM) and energy dispersive X-ray spectroscopy 
(EDX).  FESEM  and  EDX  images  of  Co-doped  to  SnO2/TiO2 powder 
nanoparticles  are  shown  in  Fig.  5.  Nano  particles  with  relatively  high  
agglomeration are shown in Fig. 5 a and b. This agglomeration is a result 
of the acidic sols during the synthesis process. The particle sizes were 
estimate for all samples using images Table 1. 
 
 
 
 
 SYNTHESIS AND CHARACTERIZATION OF Co-DOPED… 65 
 
 
 
 
 
Fig. 5  FESEM and EDX images of Co-doped to SnO2/TiO2 un-doped (a) 2.5 mol % 
doped (b) 10 mol % doped (c) 
 
4. CONCLUSION 
 
A modified sol-gel process was designed to prepare Co-doped to SnO2/TiO2. 
The  products  were  characterized  by  means  of  X-ray  diffraction,  Raman  
spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermal 
gravimetric analysis (TGA), field emission scanning electron microscopy 
(FESEM) and energy dispersive X-ray spectroscopy (EDX). Crystallite and 
particle size of the nano structures were decreased from 19.1 to 3.8 nm and 
27 to 16 respectively by the addition of Co to the precursor solution. Fine 
Co-doped to SnO2/TiO2 nano particles were obtained and applications were 
discussed. 
 
ACKNOWLEDGEMENT 
Hamoon  H.Z.R.  thanks  Director  IICT  for  permitting  him  to  carry  out  his  
thesis  work  at  IICT.  A.  Nanaji  and  Ravindranath  Reddy  thank  CSIR  and  
UGC for research fellowship. 
a a 
a 
b b 
b 
c c 
c 
 
 
 
66 H.Z.R. HAMOON, G.S. DEVI, H. BEIGI, ET AL. 
 
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Synthesis And Characterization Of Co-Doped SnO2/TiO2 Semiconductor Nano Crystallites Via Sol-Gel Method

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