Analysis on the effect of ZnO on Carbon nanotube by spray pyrolysis method
© The Author(s). 2016
Received: 12 March 2016
Accepted: 18 May 2016
Published: 2 June 2016
ZnO/CNT nanocomposites were prepared using Zinc acetate source materials and with the assistance of copper plate, glycine and sugar solution. The combined behavior between these two materials may give rise to the production of advanced materials with a wide range of applications in electronics and optoelectronics.
The ZnO-CNT nanostructures are successfully prepared by simple perfume spray pyrolysis method on copper substrate. The possible growth mechanism of ZnO-CNT nanocrystals formation by this method has been tried to explore the sensor and optical properties has been demonstrated.
The as-synthesized ZnO-CNT nanostructures were characterized using the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) pattern measured with Cu Kα radiation. Studies of the morphologies of the ZnO-coated CNTs revealed no significant change in the internal structures single walled graphite sheets and the diameters of the CNTs, but the ZnO appeared to form a layer of thinfilm single crystalline particles attaching to the surface of the nanotubes. The photoluminescence (PL) measurements excited by the 380 nm were done at room temperature. CNTs are easy to be entangled and agglomerate due to their long length and low diffusive mobility in base fluids.
The lower mobility was found to occur for the ZnO/CNT composite where a linear sensitivity behavior was measured and it reaches high at the temperature of 200 °C. The samples luminescence is dominated by well-structured ultraviolet band emission and almost no deep level emission was observed, revealing a high optical quality of the produced structures.
KeywordsZnO-CNT Photoluminescence studies Morphological studies and sensor studies
The carbon nanotubes (CNTs) have also strained much attention since their unique fundamental physical structures, eminent mechanical and electronic properties which leading to potential high-technology applications (Odaci et al. 2008; Wei et al. 2008; Iyakutti et al. 2009). The ZnO is one of the most important functional metal oxides for their versatile practical applications, ranging from photodetector (Jun et al. 2009), transparent electrode (Oh et al. 2005), spintronic devices (Gupta et al. 2008), surface acoustic wave devices (Krishnamoorthy and Iliadis 2008), and thin film gas sensors(Tang et al. 2006), attributed to their outstanding properties such as wide direct optical band gap, large exciton binding energy, excellent chemical and thermal stability, and excellent piezoelectric properties(Gupta et al. 2009). When the ZnO metal oxide is combined with CNT, it is marvelous that, the novel extraordinary properties of ZnO-CNT composite is appear.
In recent years, nano structured materials such as ZnO-CNT nano composites have also been incorporated into electrochemical sensors for biological and pharmaceutical analyses (Suchea et al. 2006). While they have many properties similar to other types of materials, they offer unique advantages including enhanced electron transfer, large edge plane/basal plane ratios and rapid kinetics of the electrode processes (Banks et al. 2006). Nanocomposites of a variety of shapes, sizes and compositions are changing modern bioanalytical measurement (Moradi et al. 2013).
Ching-Feng Li, Chia-Yen Hsu, Yuan-Yao Li et al. reported that, an 80 nm-thick ZnO film was prepared via the sol–gel method at 500 °C using zinc acetate, 2-methoxyethanol, and mono ethanolamine as precursors. Characterization of the film showed that it was composed of 20–30 nm sintered ZnO nanoparticles with good crystallinity. The NH3 sensing properties of gas-sensing devices with a 5 μm gap that utilized the prepared ZnO film were examined. The highest sensor response (57.5 %) was achieved with 600 ppm NH3 in air at 150 °C. The response and recovery times were 160 s and 660 s, respectively. This study also examined the effects of NH3 and oxygen concentration as well as the temperature on the sensor response performance. The findings show that oxygen plays an important role in the conductivity of ZnO thin films, and thus affects the sensor response toward NH3 (Lia et al. 2014).
Herran, I. Fernandez, E. Ochoteco, G. Cabanero, H. Grande et al. reported that, the role of water vapour in ZnO nanostructures for humidity sensing at room temperature is presented and discussed. Experimental and theoretical results demonstrate that ZnO nanoparticles and nanorods, show different physico-chemical behaviour under different relative humidity atmospheres. While electrical current density increases as RH does in the case of the ZnO nanoparticles, ZnO nanorods show inverse behaviour. These facts are related to the capillary condensation and water electric dipole moment effects, respectively. Additionally, a simultaneous validation between the sensor developed and a commercial device corroborates the potential application of this kind of low-cost sensing nanostructures presented in this work (Herran et al. 2014).
Ganesh Kumar Mani et al. (Ganesh Kumar and John Bosco Balaguru 2014) reported that, randomly interconnected zinc oxide (ZnO) nanoplatelets were successfully deposited on glass substrates using simple chemical spray pyrolysis technique. X-ray diffraction (XRD) pattern confirmed that the nanoplatelets were highly polycrystalline in nature with hexagonal wurtzite structure. Field emission scanning electron microscope (FE-SEM) image revealed the formation of randomly interconnected nanoplatelets with no visible defects on their surface. The thickness of the nanoplatelets was found to be in the range of 110–130 nm. The optical absorbance spectra showed no sharp absorption edge and the optical band gap was found to be 3.23 eV. Acetaldehyde sensing characteristics of ZnO nano platelet sat room temperature were investigated. The selectivity of ZnO nanoplatelets towards acetaldehyde was found to be significant in comparison with the other gases like ethanol, methanol, ammonia, acetone, formaldehyde and toluene.
Mohsen Asad, Mohammad Hossein Sheikhi reported that a surface acoustic wave (SAW) based H2S gas sensor with excellent selectivity and recovery/response time developed using single wall carbon nanotube decorated with copper nanoparticles (Cu NP-SWCNT). A thin film of Cu NP-SWCNT was deposited onto a lithium niobate (LiNbO3) piezoelectric substrate via a drop-casting technique. Sensing of H2S gas was carried out by measuring acousto electric perturbation of SAWs traveling along the LiNbO3 piezoelectric substrate and Cu NP-SWCNT sensing layer. H2S gas of concentrations as small as 5 ppm could be readily measured. The effect of temperature on the SAW sensor response was also investigated for a range of temperatures from 70 to 200 °C. The optimum operating temperature was 175 °C, in which, a relatively rapid response (7 s) and recovery time (9 s) was recorded. The selectivity of the proposed Cu NP-SWCNT gas sensor was examined by assessing the sensor response upon exposure to hydrogen, acetone, ethanol, and H2S gas species in air background and a large selectivity toward H2S gas was observed (Mohsen and Mohammad Hossein 2014).
In this research work, the ZnO-CNT composites are synthesized from spray pyrolysis method and their fundamental physical and optical properties have been investigated by X-ray diffraction (XRD), SEM, TEM, EDAX, PL spectra and FT-Raman analytical tools.
In the static position of this spray nozzle, the substrate size may be 1 cm × 1 cm for coating. But here we used 2.5 cm × 2.5 cm copper substrate for spraying. So a slight vertical and horizontal movement required for constant spraying. The droplets (mist) hit the copper substrate, where the solvent is entirely vaporized leading to the deposition of a rough film in which the transmission decreases markedly. At the optimum air flow rate the size of the mist particle is also optimum. So the thermal energy gained by the droplet is in such a way that it vaporizes just above the copper substrate and gives a good quality of powdered particles on the surface. They form a powdery precipitate on the substrate resulting in the decrease in transparency in the present work it has been observed that which gives highly transparent, good powdered particles by spraying (Shanti et al. 1999).
A specially designed glass tube is used as a carrier tube for the chemical mist generated by the perfume sprayer. The length of the tube is about 25 cm horizontal and 15 cm vertical length with diameter of 14 mm and the bottom of the vertical tube act as a spray nozzle with a diameter of 7 mm. In the above tube the spray nozzle glass walls cross section should be pure flat structure. i.e. the 7 mm nozzle outlet must be as a perfect circle. Then only the spray outlet will be a stream lined. The heat waves from the hot plate may affect the mist coming through vertical tube.
0.5 Molar solution of Zinc acetate dehydrate and 0.5 Molar solution of Glycene was dissolved in a 25 ml of distilled water and stirred for half an hour by using magnetic stirrer. The solution was well mixed with stirred then 5 ml of diethanolamine was added in it. This solution is filled with perfume sprayer of tube and sprayed continuously in equal time intervals on the hot plate. For the Zinc nanoparticles Zinc acetate dehydrate and diethanolamine was the solution for CNT Glycene was well stirred with zinc acetate dehydrate and sprayed on the copper plate without diethanolamine.
The crystalline phases of the materials were investigated using X-ray powder diffraction (XRD) PAN analytical X-ray diffractometer using CuKα radiation (λ =1.5406 nm). The morphological of the materials was observed using a scanning electron microscope (SEM, JEOL JSM 6500-F). A transmission electron microscope (TEM JEOL, JEM – 2010-F) was used to characterize the ZnO, ZnO-CNT and CNT powdered particles. A Raman spectrometer (Raman, Dongwoo, optron, Co) and an electron spectroscopy for chemical analysis (ESCA, VG Scientific Microlab 310 F) were used to investigate the surface chemical composition and characteristics of the samples.
Results and discussion
In CNT, the carbons are coupled directly and form the hexagonal chain. In the chain, the subsequent carbons are making themselves positive and negative and thus electrochemically connected continuously. In the case of ZnO structure, the Zn is positive and O is negative. The Zn is coupled by bond with negatively charged carbon and O is connected by bond with positively charged carbons in the hexagonal frame as in the Fig. 1. In this case, the sample is annealed at 300 °C and the XRD is also taken for the same, in the XRD pattern, the peaks are observed with weak intensity which is not preferred to take in to analysis. XRD signal pattern strongly represent the presence of ZnO and weakly symbolize the CNT.
Structural parameters of ZnO-CNT
Grain Size (D) (10−9) nm
Dislocation Density (δ) (1015) lines/m2
Strain (ε) (10−3)
Structural parameters of ZnO-CNT annealed at 300 °C
Grain Size (nm)
Dislocation density (δ) (1015) lines/m2
Strain (ε) (10−3)
Gas sensing applications
The PL intensity increases with the increase of sp2 content in the disordered carbon systems (Eda et al. 2010). This is certainly due to the presence of CNT aggregated ZnO nano dots. The blue shift is expected normally, whereas in this work, due to the presence of ZnO on CNT, the green photoluminescence shift is observed which is also due to the transition in defect states, particularly oxygen vacancies (Luo et al. 2009). In this case, blue shift is significantly quenched. This suggests that an additional pathways for the diminishing the charge carriers dominates because of the interactions between the excited ZnO and CNT. Since the ZnO act as n-type semiconductor due to oxygen vacancies and zinc interstitials (Look et al. 1999) and CNT behaves as a p-type semiconductor, hence, n-p depletion layer is formed at the ZnO: CNT interface. This set up making very narrow band gap and it is a root cause of the application involving opto-electronics.
The ZnO-CNT nano material has been prepared by simple perfume spray pyrolysis method on copper substrate. The effect of the structural, morphological, and sensor properties have been studied extensively. The XRD, SEM and TEM images evidenced the formation of crystalline ZnO-CNT with nano grained structure. The SEM examination of the present compound reveals that, there are numerous particles appear on the surface of the nanotubes like beads on a necklace which contributes in homogeneity over the surface of carbon nanotube due to ZnO coating. The Raman analysis confirmed that, the presence of CNT and adopted with ZnO which are capable of having semiconducting property. From the conductivity graph, it is found that, the conductivity of the material can be tuned by the controlling of the temperature. Simultaneously, the trans-conductance of the material also is controlled. From the analysis, it is observed that, the ZnO-CNT is active material for sensing gas.
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