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TiO2 nanocomposite rods synthesized by microwave-assisted method for humidity sensor application
Superlattices and Microstructures 76 (2014) 46–54
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
ZnO/TiO2 nanocomposite rods synthesized by microwave-assisted method for humidity sensor application CH. Ashok, K. Venkateswara Rao ⇑ Centre for Nano Science and Technology, Institute of Science and Technology, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad 500085, Andhra Pradesh, India
a r t i c l e
i n f o
Article history: Received 25 July 2014 Accepted 23 September 2014 Available online 7 October 2014 Keywords: Microwave-assisted method ZnO/TiO2 nanorods XRD SEM TEM TG/DTA
a b s t r a c t The nanocomposite rods shows well known properties compared with nano structured materials for various applications like lightemitting diodes, electron field emitters, solar cells, optoelectronics, sensors, transparent conductors and fabrication of nano devices. Present paper investigates the properties of ZnO/TiO2 nanocomposite rods. The bi component of ZnO/TiO2 nanocomposite rods was synthesized by microwave-assisted method which is very simple, rapid and uniform in heating. The frequency of microwaves 2.45 GHz was used and temperature maintained 180 °C. Zinc acetate and titanium isopropoxide precursors were used in the preparation. The obtained ZnO/TiO2 nanocomposite rods were annealed at 500 °C and 600 °C. ZnO/TiO2 nanocomposite rods have been characterized by X-ray Diffraction (XRD) for average crystallite size and phase of the composite material, Particle Size Analyser (PSA) for average particle size, Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) for morphology study, Energy Dispersive X-ray Spectrometry (EDX) for elemental analysis, and Thermal Gravimetric and Differential Thermal Analysis (TG–DTA) for thermal property. Ó 2014 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. E-mail address: [email protected] (K. Venkateswara Rao). http://dx.doi.org/10.1016/j.spmi.2014.09.029 0749-6036/Ó 2014 Elsevier Ltd. All rights reserved.
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1. Introduction The different semiconductor nanostructures like zero-dimensional, one-dimensional, twodimensional and three-dimensional are showing variety of applications due to the dimensionality. One-dimensional nanostructures are showing interesting properties because of their low dimensionality and high surface to volume ratio [1]. Semiconductor nanostructured materials have been used in catalysis, short wave length light-emitting diodes, electron field emitters, solar cells, optoelectronics, transparent conductors, sensors and fabrication of nano devices. Frequently used semiconductor materials are CdS, SnO2, TiO2, ZnO and CuO. ZnO and TiO2 nano structured materials are very promising materials compared with other semiconductor materials. ZnO and TiO2 nanostructured semiconductor materials have been used in many above mentioned applications due to its interesting properties [2,3]. ZnO/TiO2 1-dimensional nanostructured materials such as nanotubes, nanowires and nanorods were shown extraordinary properties in the various exclusive applications like sensors, electronics, mechanics, environmental and nano device fabrication [4,5]. ZnO/TiO2 nanostructured rods were very active materials due to its unique properties. These rods were multifunctional semiconductor materials with a direct wide-band gap and large excitation binding energy [6,7]. Most of the papers Nanostructured semiconductor ZnO and TiO2 nanocomposite rods were synthesized using various techniques like sol–gel, solution combustion, chemical precipitation and thermal decomposition [8,9]. But in the present paper deals with the simple and easiest technique using microwave-assisted synthesis technique. The obtained ZnO/TiO2 nanocomposite rods were showed that excellent structural and thermal properties [10,11]. 2. Experimental details The ZnO/TiO2 nanocomposite rods were prepared by microwave-assisted method. Zinc acetate, titanium isopropoxide and NaOH were used as precursor materials. 0.1 M Zinc Acetate and 0.01 M NaOH taken into a beaker and stirred at 45 °C for 15 min. This solution was kept into a Microwave oven for 5 min, this oven maintaining 180 °C constant temperature and 2.45 GHz frequency. This solution was cooled up to room temperature. Then centrifuge the solution at 4000 rpm for 15 min, the obtained nanomaterials washed with water and ethanol several times. The ZnO nanostructured rods were formed. Titanium isopropoxide (1 ml) and 0.01 M NaOH solution mixed with each other using vigorous stirring at 45 °C for 15 min. The above solution is kept into a microwave oven for 5 min; it maintained same specifications as mentioned above. Then centrifuge the solution, washed with water and ethanol several times. The TiO2 nanostructured rods were formed. Add these ZnO and TiO2 nanocomposite rods by mechanical milling. Finally the ZnO/TiO2 nanocomposite rods were obtained. These nanocomposite rods were annealed at 500 °C and 600 °C. 3. Characterization techniques The obtained ZnO/TiO2 nanocomposite rods have been characterized by Bruker D8 X-ray Diffractometer for average crystallite size and crystal structure. The position (2h) range from 25° to 70° and the wavelength of the Cu Ka radiation is 0.154 nm. Horiba SZ-100 Particle Size Analyser for average particle size. PHILIPS Scanning Electron Microscope for morphology as well as elemental analysis by EDX. The thermal properties were measured by S-II EXSTAR-6000, TG/DTA-6300 thermal analyser, and JEM-100 CXII Transmission Electron Microscope for morphology studies [12]. 4. Results and discussion 4.1. X-ray diffraction The XRD pattern of ZnO/TiO2 nanocomposite rods was shown in Fig. 1. The ZnO/TiO2 nanocomposite rods were annealed at 500 °C and 600 °C.
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Fig. 1. XRD pattern of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
In the XRD pattern, Anatase TiO2 peak was observed at 25° in 500 °C but not in case of 600 °C. Generally, ZnTiO3 cannot be synthesized under the normal conditions, because the phase of the ZnTiO3 readily transform to Zn2Ti3O8. This form is known as the metastable form of ZnTiO3. In the above figure ZnO (Hexagonal), TiO2 (Anatase), ZnTiO3 (Hexagonal) and Zn2Ti3O8 (Cubic) phases were observed. These peaks were good agreement with various standard diffraction spectrum JCPDS card numbers of ZnO, TiO2, ZnTiO3 and Zn2Ti3O8 as 36–1451, 21–1272, 87–1781 and 85–0547 respectively. Each peak having different positions corresponding crystalline planes (h k l). According to the Debye–Scheerer’s formula
D¼
K k b Cos h
ð1Þ
The average crystallite sizes observed to be 33 nm and 24 nm for annealing temperatures of 500 °C and 600 °C respectively. This result shows that when the annealing temperature increases the average crystallite size was decreases due to the evaporation of unreacted materials. The micro strain and crystallite size of the sample are measured from the Williamson–Hall equation. The equation is as follows
bCos h ¼
Kk þ 2eSin h t
ð2Þ
where b is the full width half maximum (FWHM) of the XRD corresponding peaks, K is Debye–Scherer’s constant, t is crystallite size, k is wave length of the X-ray, e is lattice strain and h is the Bragg angle. In this process 2Sin h is plotted against bCos h, using a linear extrapolation to this plot, the intercept gives the crystallite size and slope gives the micro strain (e). The average crystallite size and micro strain value obtained as 34 nm and 0.0253 103 and 27 nm and 0.0461 103 for annealing temperatures at 500 °C and 600 °C respectively [13–15]. 4.2. Particle size analyser The average particle size was measured by particle size analyser using the principle of Dynamic Light Scattering as shown in Fig. 2. The as prepared ZnO/TiO2 nanocomposite rods were dispersed in ethanol solution and this solution was characterised with the help of YD-laser light (wavelength
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Fig. 2. Particle distribution of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
of YD-laser 532 nm) in particle size analyser. The mean value of the distributed histogram was taken as average particle size of the particular material. The obtained average particle sizes were 36 nm and 31 nm for annealing temperatures at 500 °C and 600 °C respectively. 4.3. Scanning Electron Microscope SEM images of ZnO/TiO2 nanocomposite rods at different annealing temperatures 500 °C and 600 °C were shown in Figs. 3 and 4 respectively. The grain size, shape and surface properties like morphology were observed by the SEM with different magnifications. The obtained nanocomposite rods shows respectable morphology at 600 °C annealing temperature compared with 500 °C annealing ones. Here, observed that smooth nanocomposite rods are formed at 600 °C whereas at 500oC the nanocomposite rods were agglomerated and looks like flakes. The diameters of the ZnO/TiO2 nanocomposite rods were nearly 250 nm and 150 nm for 500 °C and 600 °C annealing temperatures. The length of the nanocomposite rods about 2000 nm and 1000 nm for
Fig. 3. SEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 500 °C.
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Fig. 4. SEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 600 °C.
500 °C and 600 °C annealing temperatures. The shape of the nanocomposite rods was spherical and regular manner [16]. 4.4. Transmission Electron Microscope TEM images of ZnO/TiO2 nanocomposite rods are shown in Figs. 5 and 6 at different temperatures. The images exhibit rods like structures. At 500 °C temperature the rods are slightly bended and forms uneven distribution, whereas in 600 °C temperature the rods are straight and smooth. These morphologies coincide with the SEM images morphology [17,18]. 4.5. Energy dispersive X-ray spectrometer The elemental compositions of ZnO/TiO2 nanocomposite rods at different annealing temperatures shows in Fig. 7. The EDX pattern shows that at 500 °C annealing temperature the carbon element was appeared along with zinc, titanium and oxygen whereas in 600 °C it was disappeared, reason for this carbon material evaporated at 600 °C. The elemental weight percentages were shown in Table 1. From Table.1 the elemental compositions were nearly same at 500 °C annealing temperature whereas at 600 °C the compositions were changed, because at this temperature phase shift was occurred [19].
Fig. 5. TEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 500 °C.
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Fig. 6. TEM image of ZnO/TiO2 nanocomposite rod at annealing temperature 600 °C.
Fig. 7. EDX pattern of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
4.6. Thermo gravimetric/differential thermal analyser The thermal properties of ZnO/TiO2 nanocomposite rods have been studied with the help of TG/DTA. Figs. 8 and 9 shows those ZnO/TiO2 nanocomposite rods which were annealed at 500 °C and 600 °C temperatures respectively. In the presence of air atmosphere the synthesized ZnO/TiO2 nanocomposite rods were heated at the rate of 10 °C per minute. In 500 °C annealing temperature the TG curve showed small fluctuations below 100 °C these fluctuations due to evaporation of water
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Table 1 Elemental composition of ZnO/TiO2 nanocomposite rods at different annealing temperatures. Elements
Zinc Titanium Oxygen Carbon Total
Weight percentages of ZnO/TiO2 nanocomposite rods at 500 °C annealing
Weight percentages of ZnO/TiO2 nanocomposite rods at 600 °C annealing
34.29 30.93 31.76 3.02
37.73 23.69 38.58 –
100.00
100.00
Fig. 8. TG/DTA curves of ZnO/TiO2 nanocomposite rods at 500 °C annealing temperature.
Fig. 9. TG/DTA curves of ZnO/TiO2 nanocomposite rods at 600 °C annealing temperature.
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molecules in the sample, the corresponding DTA curve was observed a broad exothermic peak in between 300 °C and 350 °C due to oxidation of the material. After this temperature the material decomposed and formed ZnO and TiO2 phases. In 600 °C annealing temperature uniform weight loss was observed from TG curve. Broad exothermic and endothermic peaks were observed in the DSC curve. In the range of 300 °C and 350 °C exothermic peak appeared due to the oxidation and endothermic peak appeared in between 500 °C and 550 °C due to the decomposition of material. After this temperature this material was again decomposed and phase transitions occurred. The ZnO/TiO2 phases changed as ZnTiO3 and Zn2Ti3O8 above mentioned in the XRD. The weight loss percentages of the ZnO/TiO2 nanocomposite rods were 6.3% and 1.2% for 500 °C and 600 °C annealing temperatures respectively. The weight loss was caused by the un-reacted organic materials evaporation and combustion [20]. 5. Conclusions ZnO/TiO2 nanocomposite rods have been successfully synthesized by Microwave-assisted method and these nanocomposite rods were annealed at 500 °C and 600 °C temperatures. The XRD-pattern of ZnO/TiO2 nanocomposite rods shows that the different phases were observed such as ZnO (Hexagonal), TiO2 (Anatase), ZnTiO3 (Hexagonal) and Zn2Ti3O8 (Cubic). The average crystallite sizes were measured by Debye–Scherer’s formula 33 nm and 24 nm for different annealing temperatures 500 °C and 600oC respectively whereas Williamson–Hall equation the average crystallite sizes were 34 nm and 27 nm. The strain values of the ZnO/TiO2 nanocomposite rods were increases along with annealing temperature increases. The average particle sizes were decreased with increasing of annealing temperatures. SEM images shows that smooth nano rods were formed at 600 °C and agglomerated flakes like structures formed at 500 °C. ZnO/TiO2 nanocomposite rods diameter and lengths were decreased with increasing of annealing temperature. The shape of the nanocomposite rods was spherical and regular manner. TEM results were coinciding with SEM results and diameter of the rods was 80– 120 nm range. EDX results conclude that the obtained nanocomposite rods were ZnO/TiO2 nanocomposite rods only. TG/DTA graphs explain the ZnO/TiO2 nanocomposite rods were changed its phase as ZnTiO3 and Zn2Ti3O8 and the weight loss was very less at high annealing temperature. From all the above results conclude that the ZnO/TiO2 nanocomposite rods at annealing 600 °C are having excellent properties. So it has been used in humidity sensor application. Acknowledgements It is a great pleasure to express my thanks to ‘University Grants Commission’ for providing Fellowship and Special thanks to Ms. CH. Shilpa Chakra, Head of the Department, CNST, IST, JNTU Hyderabad. References [1] Qi Qi, Tong Zhang, Qingjiang Yu, Rui Wang, Yi Zeng, Li Liu, Haibin Yang, Properties of humidity sensing ZnO nanorods-base sensor fabricated by screen-printing, Sens. Actuat. 133 (2008) 638–643. [2] Yizhuo He, Pradip Basnet, Simona E. Hunyadi Murph, Yiping Zhao, Ag nanoparticle embedded TiO2 composite nanorod arrays fabricated by oblique angle deposition: toward plasmonic photocatalysis, Appl. Mater. Interfaces 5 (2013) 11818– 11827. [3] Kimleang Khun, Zafar Hussain Ibupoto, Mohamad S. AlSalhi, Muhammad Atif, Anees A. Ansari, Magnus Willander, Fabrication of well-aligned ZnO nanorods using a composite seed layer of ZnO nanoparticles and chitosan polymer, Materials 6 (2013) 4361–4374. [4] Faheem Ahmed, Shalendra Kumar, Nishat Arshi, M.S. Anwar, Ram Prakash, Growth and characterization of ZnO nanorods by microwave-assisted route: green chemistry approach, Adv. Mater. Lett. 2 (2011) 183–187. [5] S. Benkara, S. Zerkout, Preparation and characterization of ZnO nanorods grown into aligned TiO2 nanotube array, J. Mater. Environ. Sci. 1 (2010) 173–188. [6] Jinhong Yu, Wei Wu, Dan Dai, Yingze Song, Chaoyang Li, Nan Jiang, Crystal structure transformation and dielectric properties of polymer composites incorporating zinc oxide nanorods, Macromol. Res. 22 (2014) 19–25. [7] Xiaoyan Cai, Yun Cai, Yongjun Liu, Shaojuan Deng, Yan Wang, Yude Wang, Igor Djerdj, Photocatalytic degradation properties of Ni(OH)2 nanosheets/ZnO nanorods composites for azo dyes under visible-light irradiation, Ceram. Int. 40 (2014) 57–65. [8] Bing Zhao, Ruizhe Liu, Xinhui Cai, Zheng Jiao, Minghong Wu, Xuetao Ling, Bo Lu, Yong Jiang, Nanorod-like Fe2O3/graphene composite as a high-performance anode material for lithium ion batteries, J. Appl. Electrochem. 44 (2014) 53–60.
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[9] Xuefeng Song, Lian Gao, Facile synthesis of polycrystalline NiO nanorods assisted by microwave heating, J. Am. Ceram. Soc. 91 (2008) 3465–3468. [10] Xingtian Yin, Wenxiu Que, Duan Fei, Fengyu Shen, Qiushi Guo, Ag nanoparticle/ZnO nanorods nanocomposites derived by a seed-mediated method and their photocatalytic properties, J. Alloys Compd. 524 (2012) 13–21. [11] Richard N. Gedye, Frank E. Smith, Kenneth Charles Westaway, The rapid synthesis of organic compounds in microwave ovens, Can. J. Chem. 66 (1988) 17–26. [12] Vadivel Murugan, T. Muraliganth, A. Manthiram, Rapid microwave-solvothermal synthesis of phospho-olivine nanorods and their coating with a mixed conducting polymer for lithium ion batteries, Electrochem. Commun. 10 (2008) 903–906. [13] Tatjana Dedova, Olga Volobujeva, Jelena Klauson, Arvo Mere, Malle Krunks, ZnO nanorods via spray deposition of solutions containing zinc chloride and thiocarbamide, Nanoscale Res. Lett. 2 (2007) 391–396. [14] B.C. Yadav, Amit K. Srivastava, P.K. Khanna, Synthesis of TiO2–Nb2O5 and TiO2–CuO nano Co-oxides and their application as solid state humidity sensors, Int. J. Green Nanotechnol. 3 (2011) 160–169. [15] M. Venkaiah, R. Singh, Effect of thickness on structural, optical and mechanical properties of Mn doped ZnO nanocrystalline thin films RF sputtered in nitrogen gas environment, Superlattices Microstruct. 72 (2014) 164–171. [16] Gajendra Kumar Pradhan, Deepak Kumar Padhi, K.M. Parida, Fabrication of a-Fe2O3 nanorod/RGO composite: a novel hybrid photocatalyst for phenol degradation, Appl. Mater. Interfaces 5 (2013) 9101–9110. [17] M.A. Ahmed, S.I. El-Dek, A. Abd Elazim, Fascinating properties of multifunctional nanocomposites manganite/magnetite, Superlattices Microstruct. 74 (2014) 34–51. [18] Chun Lan, Kunquan Hong, Wenzhong Wang, Guanghou Wang, Synthesis of ZnS nanorods by annealing precursor ZnS nanoparticles in NaCl flux, Solid State Commun. 125 (2003) 455–458. [19] Elshad Abdullayev, Keita Sakakibara, Ken Okamoto, Wenbo Wei, Katsuhiko Ariga, Yuri Lvov, Natural tubule clay template synthesis of silver nanorods for antibacterial composite coating, Appl. Mater. Interfaces 3 (2011) 4040–4046. [20] Chang Sung. Lim, Synthesis and characterization of TiO2–ZnO nanocomposite by a two-step chemical method, J. Ceram. Proc. Res. 11 (2010) 631–635.
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
ZnO/TiO2 nanocomposite rods synthesized by microwave-assisted method for humidity sensor application CH. Ashok, K. Venkateswara Rao ⇑ Centre for Nano Science and Technology, Institute of Science and Technology, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad 500085, Andhra Pradesh, India
a r t i c l e
i n f o
Article history: Received 25 July 2014 Accepted 23 September 2014 Available online 7 October 2014 Keywords: Microwave-assisted method ZnO/TiO2 nanorods XRD SEM TEM TG/DTA
a b s t r a c t The nanocomposite rods shows well known properties compared with nano structured materials for various applications like lightemitting diodes, electron field emitters, solar cells, optoelectronics, sensors, transparent conductors and fabrication of nano devices. Present paper investigates the properties of ZnO/TiO2 nanocomposite rods. The bi component of ZnO/TiO2 nanocomposite rods was synthesized by microwave-assisted method which is very simple, rapid and uniform in heating. The frequency of microwaves 2.45 GHz was used and temperature maintained 180 °C. Zinc acetate and titanium isopropoxide precursors were used in the preparation. The obtained ZnO/TiO2 nanocomposite rods were annealed at 500 °C and 600 °C. ZnO/TiO2 nanocomposite rods have been characterized by X-ray Diffraction (XRD) for average crystallite size and phase of the composite material, Particle Size Analyser (PSA) for average particle size, Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) for morphology study, Energy Dispersive X-ray Spectrometry (EDX) for elemental analysis, and Thermal Gravimetric and Differential Thermal Analysis (TG–DTA) for thermal property. Ó 2014 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. E-mail address: [email protected] (K. Venkateswara Rao). http://dx.doi.org/10.1016/j.spmi.2014.09.029 0749-6036/Ó 2014 Elsevier Ltd. All rights reserved.
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1. Introduction The different semiconductor nanostructures like zero-dimensional, one-dimensional, twodimensional and three-dimensional are showing variety of applications due to the dimensionality. One-dimensional nanostructures are showing interesting properties because of their low dimensionality and high surface to volume ratio [1]. Semiconductor nanostructured materials have been used in catalysis, short wave length light-emitting diodes, electron field emitters, solar cells, optoelectronics, transparent conductors, sensors and fabrication of nano devices. Frequently used semiconductor materials are CdS, SnO2, TiO2, ZnO and CuO. ZnO and TiO2 nano structured materials are very promising materials compared with other semiconductor materials. ZnO and TiO2 nanostructured semiconductor materials have been used in many above mentioned applications due to its interesting properties [2,3]. ZnO/TiO2 1-dimensional nanostructured materials such as nanotubes, nanowires and nanorods were shown extraordinary properties in the various exclusive applications like sensors, electronics, mechanics, environmental and nano device fabrication [4,5]. ZnO/TiO2 nanostructured rods were very active materials due to its unique properties. These rods were multifunctional semiconductor materials with a direct wide-band gap and large excitation binding energy [6,7]. Most of the papers Nanostructured semiconductor ZnO and TiO2 nanocomposite rods were synthesized using various techniques like sol–gel, solution combustion, chemical precipitation and thermal decomposition [8,9]. But in the present paper deals with the simple and easiest technique using microwave-assisted synthesis technique. The obtained ZnO/TiO2 nanocomposite rods were showed that excellent structural and thermal properties [10,11]. 2. Experimental details The ZnO/TiO2 nanocomposite rods were prepared by microwave-assisted method. Zinc acetate, titanium isopropoxide and NaOH were used as precursor materials. 0.1 M Zinc Acetate and 0.01 M NaOH taken into a beaker and stirred at 45 °C for 15 min. This solution was kept into a Microwave oven for 5 min, this oven maintaining 180 °C constant temperature and 2.45 GHz frequency. This solution was cooled up to room temperature. Then centrifuge the solution at 4000 rpm for 15 min, the obtained nanomaterials washed with water and ethanol several times. The ZnO nanostructured rods were formed. Titanium isopropoxide (1 ml) and 0.01 M NaOH solution mixed with each other using vigorous stirring at 45 °C for 15 min. The above solution is kept into a microwave oven for 5 min; it maintained same specifications as mentioned above. Then centrifuge the solution, washed with water and ethanol several times. The TiO2 nanostructured rods were formed. Add these ZnO and TiO2 nanocomposite rods by mechanical milling. Finally the ZnO/TiO2 nanocomposite rods were obtained. These nanocomposite rods were annealed at 500 °C and 600 °C. 3. Characterization techniques The obtained ZnO/TiO2 nanocomposite rods have been characterized by Bruker D8 X-ray Diffractometer for average crystallite size and crystal structure. The position (2h) range from 25° to 70° and the wavelength of the Cu Ka radiation is 0.154 nm. Horiba SZ-100 Particle Size Analyser for average particle size. PHILIPS Scanning Electron Microscope for morphology as well as elemental analysis by EDX. The thermal properties were measured by S-II EXSTAR-6000, TG/DTA-6300 thermal analyser, and JEM-100 CXII Transmission Electron Microscope for morphology studies [12]. 4. Results and discussion 4.1. X-ray diffraction The XRD pattern of ZnO/TiO2 nanocomposite rods was shown in Fig. 1. The ZnO/TiO2 nanocomposite rods were annealed at 500 °C and 600 °C.
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Fig. 1. XRD pattern of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
In the XRD pattern, Anatase TiO2 peak was observed at 25° in 500 °C but not in case of 600 °C. Generally, ZnTiO3 cannot be synthesized under the normal conditions, because the phase of the ZnTiO3 readily transform to Zn2Ti3O8. This form is known as the metastable form of ZnTiO3. In the above figure ZnO (Hexagonal), TiO2 (Anatase), ZnTiO3 (Hexagonal) and Zn2Ti3O8 (Cubic) phases were observed. These peaks were good agreement with various standard diffraction spectrum JCPDS card numbers of ZnO, TiO2, ZnTiO3 and Zn2Ti3O8 as 36–1451, 21–1272, 87–1781 and 85–0547 respectively. Each peak having different positions corresponding crystalline planes (h k l). According to the Debye–Scheerer’s formula
D¼
K k b Cos h
ð1Þ
The average crystallite sizes observed to be 33 nm and 24 nm for annealing temperatures of 500 °C and 600 °C respectively. This result shows that when the annealing temperature increases the average crystallite size was decreases due to the evaporation of unreacted materials. The micro strain and crystallite size of the sample are measured from the Williamson–Hall equation. The equation is as follows
bCos h ¼
Kk þ 2eSin h t
ð2Þ
where b is the full width half maximum (FWHM) of the XRD corresponding peaks, K is Debye–Scherer’s constant, t is crystallite size, k is wave length of the X-ray, e is lattice strain and h is the Bragg angle. In this process 2Sin h is plotted against bCos h, using a linear extrapolation to this plot, the intercept gives the crystallite size and slope gives the micro strain (e). The average crystallite size and micro strain value obtained as 34 nm and 0.0253 103 and 27 nm and 0.0461 103 for annealing temperatures at 500 °C and 600 °C respectively [13–15]. 4.2. Particle size analyser The average particle size was measured by particle size analyser using the principle of Dynamic Light Scattering as shown in Fig. 2. The as prepared ZnO/TiO2 nanocomposite rods were dispersed in ethanol solution and this solution was characterised with the help of YD-laser light (wavelength
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Fig. 2. Particle distribution of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
of YD-laser 532 nm) in particle size analyser. The mean value of the distributed histogram was taken as average particle size of the particular material. The obtained average particle sizes were 36 nm and 31 nm for annealing temperatures at 500 °C and 600 °C respectively. 4.3. Scanning Electron Microscope SEM images of ZnO/TiO2 nanocomposite rods at different annealing temperatures 500 °C and 600 °C were shown in Figs. 3 and 4 respectively. The grain size, shape and surface properties like morphology were observed by the SEM with different magnifications. The obtained nanocomposite rods shows respectable morphology at 600 °C annealing temperature compared with 500 °C annealing ones. Here, observed that smooth nanocomposite rods are formed at 600 °C whereas at 500oC the nanocomposite rods were agglomerated and looks like flakes. The diameters of the ZnO/TiO2 nanocomposite rods were nearly 250 nm and 150 nm for 500 °C and 600 °C annealing temperatures. The length of the nanocomposite rods about 2000 nm and 1000 nm for
Fig. 3. SEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 500 °C.
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Fig. 4. SEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 600 °C.
500 °C and 600 °C annealing temperatures. The shape of the nanocomposite rods was spherical and regular manner [16]. 4.4. Transmission Electron Microscope TEM images of ZnO/TiO2 nanocomposite rods are shown in Figs. 5 and 6 at different temperatures. The images exhibit rods like structures. At 500 °C temperature the rods are slightly bended and forms uneven distribution, whereas in 600 °C temperature the rods are straight and smooth. These morphologies coincide with the SEM images morphology [17,18]. 4.5. Energy dispersive X-ray spectrometer The elemental compositions of ZnO/TiO2 nanocomposite rods at different annealing temperatures shows in Fig. 7. The EDX pattern shows that at 500 °C annealing temperature the carbon element was appeared along with zinc, titanium and oxygen whereas in 600 °C it was disappeared, reason for this carbon material evaporated at 600 °C. The elemental weight percentages were shown in Table 1. From Table.1 the elemental compositions were nearly same at 500 °C annealing temperature whereas at 600 °C the compositions were changed, because at this temperature phase shift was occurred [19].
Fig. 5. TEM image of ZnO/TiO2 nanocomposite rods at annealing temperature 500 °C.
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Fig. 6. TEM image of ZnO/TiO2 nanocomposite rod at annealing temperature 600 °C.
Fig. 7. EDX pattern of ZnO/TiO2 nanocomposite rods at different annealing temperatures.
4.6. Thermo gravimetric/differential thermal analyser The thermal properties of ZnO/TiO2 nanocomposite rods have been studied with the help of TG/DTA. Figs. 8 and 9 shows those ZnO/TiO2 nanocomposite rods which were annealed at 500 °C and 600 °C temperatures respectively. In the presence of air atmosphere the synthesized ZnO/TiO2 nanocomposite rods were heated at the rate of 10 °C per minute. In 500 °C annealing temperature the TG curve showed small fluctuations below 100 °C these fluctuations due to evaporation of water
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Table 1 Elemental composition of ZnO/TiO2 nanocomposite rods at different annealing temperatures. Elements
Zinc Titanium Oxygen Carbon Total
Weight percentages of ZnO/TiO2 nanocomposite rods at 500 °C annealing
Weight percentages of ZnO/TiO2 nanocomposite rods at 600 °C annealing
34.29 30.93 31.76 3.02
37.73 23.69 38.58 –
100.00
100.00
Fig. 8. TG/DTA curves of ZnO/TiO2 nanocomposite rods at 500 °C annealing temperature.
Fig. 9. TG/DTA curves of ZnO/TiO2 nanocomposite rods at 600 °C annealing temperature.
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molecules in the sample, the corresponding DTA curve was observed a broad exothermic peak in between 300 °C and 350 °C due to oxidation of the material. After this temperature the material decomposed and formed ZnO and TiO2 phases. In 600 °C annealing temperature uniform weight loss was observed from TG curve. Broad exothermic and endothermic peaks were observed in the DSC curve. In the range of 300 °C and 350 °C exothermic peak appeared due to the oxidation and endothermic peak appeared in between 500 °C and 550 °C due to the decomposition of material. After this temperature this material was again decomposed and phase transitions occurred. The ZnO/TiO2 phases changed as ZnTiO3 and Zn2Ti3O8 above mentioned in the XRD. The weight loss percentages of the ZnO/TiO2 nanocomposite rods were 6.3% and 1.2% for 500 °C and 600 °C annealing temperatures respectively. The weight loss was caused by the un-reacted organic materials evaporation and combustion [20]. 5. Conclusions ZnO/TiO2 nanocomposite rods have been successfully synthesized by Microwave-assisted method and these nanocomposite rods were annealed at 500 °C and 600 °C temperatures. The XRD-pattern of ZnO/TiO2 nanocomposite rods shows that the different phases were observed such as ZnO (Hexagonal), TiO2 (Anatase), ZnTiO3 (Hexagonal) and Zn2Ti3O8 (Cubic). The average crystallite sizes were measured by Debye–Scherer’s formula 33 nm and 24 nm for different annealing temperatures 500 °C and 600oC respectively whereas Williamson–Hall equation the average crystallite sizes were 34 nm and 27 nm. The strain values of the ZnO/TiO2 nanocomposite rods were increases along with annealing temperature increases. The average particle sizes were decreased with increasing of annealing temperatures. SEM images shows that smooth nano rods were formed at 600 °C and agglomerated flakes like structures formed at 500 °C. ZnO/TiO2 nanocomposite rods diameter and lengths were decreased with increasing of annealing temperature. The shape of the nanocomposite rods was spherical and regular manner. TEM results were coinciding with SEM results and diameter of the rods was 80– 120 nm range. EDX results conclude that the obtained nanocomposite rods were ZnO/TiO2 nanocomposite rods only. TG/DTA graphs explain the ZnO/TiO2 nanocomposite rods were changed its phase as ZnTiO3 and Zn2Ti3O8 and the weight loss was very less at high annealing temperature. From all the above results conclude that the ZnO/TiO2 nanocomposite rods at annealing 600 °C are having excellent properties. So it has been used in humidity sensor application. Acknowledgements It is a great pleasure to express my thanks to ‘University Grants Commission’ for providing Fellowship and Special thanks to Ms. CH. Shilpa Chakra, Head of the Department, CNST, IST, JNTU Hyderabad. References [1] Qi Qi, Tong Zhang, Qingjiang Yu, Rui Wang, Yi Zeng, Li Liu, Haibin Yang, Properties of humidity sensing ZnO nanorods-base sensor fabricated by screen-printing, Sens. Actuat. 133 (2008) 638–643. [2] Yizhuo He, Pradip Basnet, Simona E. Hunyadi Murph, Yiping Zhao, Ag nanoparticle embedded TiO2 composite nanorod arrays fabricated by oblique angle deposition: toward plasmonic photocatalysis, Appl. Mater. Interfaces 5 (2013) 11818– 11827. [3] Kimleang Khun, Zafar Hussain Ibupoto, Mohamad S. AlSalhi, Muhammad Atif, Anees A. Ansari, Magnus Willander, Fabrication of well-aligned ZnO nanorods using a composite seed layer of ZnO nanoparticles and chitosan polymer, Materials 6 (2013) 4361–4374. [4] Faheem Ahmed, Shalendra Kumar, Nishat Arshi, M.S. Anwar, Ram Prakash, Growth and characterization of ZnO nanorods by microwave-assisted route: green chemistry approach, Adv. Mater. Lett. 2 (2011) 183–187. [5] S. Benkara, S. Zerkout, Preparation and characterization of ZnO nanorods grown into aligned TiO2 nanotube array, J. Mater. Environ. Sci. 1 (2010) 173–188. [6] Jinhong Yu, Wei Wu, Dan Dai, Yingze Song, Chaoyang Li, Nan Jiang, Crystal structure transformation and dielectric properties of polymer composites incorporating zinc oxide nanorods, Macromol. Res. 22 (2014) 19–25. [7] Xiaoyan Cai, Yun Cai, Yongjun Liu, Shaojuan Deng, Yan Wang, Yude Wang, Igor Djerdj, Photocatalytic degradation properties of Ni(OH)2 nanosheets/ZnO nanorods composites for azo dyes under visible-light irradiation, Ceram. Int. 40 (2014) 57–65. [8] Bing Zhao, Ruizhe Liu, Xinhui Cai, Zheng Jiao, Minghong Wu, Xuetao Ling, Bo Lu, Yong Jiang, Nanorod-like Fe2O3/graphene composite as a high-performance anode material for lithium ion batteries, J. Appl. Electrochem. 44 (2014) 53–60.
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