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Synthesis of ZnO nanopetals and its application as NO2 gas sensor

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... It was observed that the hybrid sensor showed significant higher sensing performance toward 5-10 ppm NO 2 at low operating temperature of 150 °C. In other works [24][25][26], ZnO nanostructures in the form of nanopetals, nanowalls and composites were presented as room-temperature NO 2 sensors. Though a very high sensor response as well as fast response and recovery times were achieved in [24], only one NO 2 concentration was investigated (20 ppm), thus no information on the limit of detection was available. ...
... In other works [24][25][26], ZnO nanostructures in the form of nanopetals, nanowalls and composites were presented as room-temperature NO 2 sensors. Though a very high sensor response as well as fast response and recovery times were achieved in [24], only one NO 2 concentration was investigated (20 ppm), thus no information on the limit of detection was available. On the contrary, in [25], several concentrations were studied (5-50 ppm) but the sensor response was about 30 times lower under 20 ppm NO 2 , compared to the work [24]. ...
... Though a very high sensor response as well as fast response and recovery times were achieved in [24], only one NO 2 concentration was investigated (20 ppm), thus no information on the limit of detection was available. On the contrary, in [25], several concentrations were studied (5-50 ppm) but the sensor response was about 30 times lower under 20 ppm NO 2 , compared to the work [24]. Finally, in [26], the sensors were tested down to 1 ppm of NO 2 . ...
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In this paper, the great sensitivity and selectivity to NO2 detection at low temperature down to ppb level of zinc oxide (ZnO) thick-film sensors are reported. Sensor performances of ZnO films prepared by screen-printing technique were evaluated comparing two different ZnO nano-powders in wurtzite crystal structure. Powders were synthesized by hydrothermal route (HT-ZnO) and by auto-combustion sol–gel synthesis (AC-ZnO). After proper characterization of the nano-powders, the thick-film sensors were fabricated by screen-printing technique onto α-alumina substrates equipped with Pt interdigitated electrodes, followed by a thermal treatment. The sensor response was studied in the range 50–250 °C. Best results were reached at 150 °C, with sensor response R (Zg/Z0)—defined as the ratio between impedance under NO2 (Zg) and impedance under dry air (Z0)—equal to 42.92 for HT-ZnO and to 23.18 for AC-ZnO under 0.5 ppm of NO2 in dry conditions. Finally, response and recovery time were measured, and selectivity of the sensors was determined by exposing the film toward O3, CO2, CH4, N2O and humidity at the best working temperature. Both sensors showed great sensitivity for NO2 detection, supporting the exploitation of these sensors as NO2 detectors at ppb level.
... As these reactions progressed, a depletion region with low conductivity was created at the surface of the nanowires. Under UV illumination ( Fig. 12(b)), EHPs were generated and the photogenerated holes migrated to the surface of the ZnO nanowires and interacted with the negatively charged oxygen ions on the surface of the ZnO nanowires according to the following reactions [52,56]: ...
... Upon exposure to NO 2 gas, NO 2 molecules adsorbed on the surface of the nanowires because of their oxidizing nature according to the following reaction [54,56]: ...
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ZnO nanowires were prepared by oxidized ZnS nanowires. The sensing performance of these ZnO nanowires for NO2 gas was enhanced by decorating Au nanoparticles on their surface. The scanning electron microscopy results revealed that diameter and length of the ZnO nanowires showed 150–200 nm and up to a few hundreds of μm, respectively. The diameters of Au nanoparticles which were decorated on the ZnO nanowires were 5–20 nm and they were distributed evenly on the surface of the nanowires. The transmission electron microscopy results revealed that the ZnO nanowires obtained after 2 h of the oxidation treatment process were composed of lots of nanograins with a diameter of 50–100 nm, which rendered the surface of the nanowires rough and full of void spaces. The hierarchical structure of the nanowires increased their surface-to-volume ratio and contributed to the adsorption of gas on their surface, improving their sensing performance. In this study, the NO2 gas sensing mechanism of the Au nanoparticle-decorated ZnO nanowires sensors were investigated under UV illumination at room temperature.
... Since then, ZnO has been widely investigated for its good and stable gas sensing properties. Different morphologies provide different sensing performances [2][3][4][5]. ZnO nanopetals have a sensitivity (defined as R gas /R air , where R gas and R air are electrical resistance of the sensor in target gas and in dry air, respectively) of 119 to NO 2 gas at concentration of 20 ppm at room temperature [2]. Monodisperse ZnO hollow six-sided pyramids have a sensitivity of about 187 to ethanol and 15 to dimetylformamid (DMF), both at concentration of 200 ppm and at 240°C [3]. ...
... Different morphologies provide different sensing performances [2][3][4][5]. ZnO nanopetals have a sensitivity (defined as R gas /R air , where R gas and R air are electrical resistance of the sensor in target gas and in dry air, respectively) of 119 to NO 2 gas at concentration of 20 ppm at room temperature [2]. Monodisperse ZnO hollow six-sided pyramids have a sensitivity of about 187 to ethanol and 15 to dimetylformamid (DMF), both at concentration of 200 ppm and at 240°C [3]. ...
Article
In this study, we used a low-temperature hydrothermal technique to fabricate arrays of sensors with ZnO nanorods grown on-chip. The sensors on the glass substrate then were sputter decorated with Pd at thicknesses of 2, 4, and 8 nm and annealed at 650 °C in air for an hour. Scanning electron microscopy, high resolution transmission microscopy, X-ray diffraction, and surface analysis by X-ray photoelectron spectroscopy characterization demonstrated that decoration of homogenous PdO nanoparticles on the surface of ZnO nanorods had been achieved. The sensors were tested against three reducing gases, namely hydrogen, ethanol, and ammonia, at 350, 400, and 450 °C. The ZnO nanorods decorated with PdO particles from the 2 and 4 nm layers showed the highest responses to H2 at 450 and 350 °C, respectively. These samples also generally exhibited better selectivity for hydrogen than for ethanol and ammonia at the same concentrations and at all tested temperatures. However, the ZnO nanorods decorated with PdO particles from the 8 nm layer showed a reverse sensing behaviour compared with the first two. The sensing mechanism behind these phenomena is discussed in the light of the spillover effect of hydrogen in contact with the PdO particles as well as the negative competition of the PdO thin film formed between the sensor electrodes during sputter decoration, Pd–Zn heterojunction that forms at high temperature and thus influences the conductivity of the ZnO nanorods.
... MOS (metal oxide semiconductor) sensors which are surface-modified with different sensitive materials can detect different gases [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as carbon monoxide, sulfur dioxide, hydrogen sulfide, ammonia, and so on. Therefore, MOS sensors have become important environmental gas detectors and have attracted the attention of many researchers. ...
... In recent years, a large number of research papers on various MOS detectors have been reported. Nicoletti S and other research teams [4][5][6][7][8][9][10][11][12][13][14][15] have developed MOS gas detectors using nanocomposites as sensitive materials. Tomer V and other research teams [16,17] demonstrated MOS sensors with high performance that were doped with Ag or other catalytic materials. ...
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In this work, a mini monitoring system integrated with a microfabricated metal oxide array sensor and a micro packed gas chromatographic (GC) column was developed for monitoring environmental gases. The microfabricated packed GC column with a 1.6 m length was used to separate the environmental gas, and the metal oxide semiconductor (MOS) array sensor, fabricated with nano-sized SnO-SnO2 sensitive materials, was able to effectively detect each component separated by GC column. The results demonstrate that the monitoring system can detect environmental gas with high precision.
... 15 Polyaniline (PANI) as a typical conducting polymer has received 16 a great deal of attention recently [ 15 , 16 ]. With regard to the back- 17 ground, using a composite carrier composed of PANI and ferric ox- 18 ide nanoparticles could combine the excellent properties of ferric 19 oxide and polyaniline, in addition, a synergistic effect might play a 20 role in enhancing the properties of nanocomposite catalysts. They 21 have unique electronic properties due to the π -conjugation present 22 * Corresponding author. in their backbones and display improved characteristics over con- 23 ventional sensors based on nanometal oxides. ...
... thin film deposition is shown in Fig. 1 (b). 55 For studying the gas sensing properties, the home-made gas di-56 lution system was utilized and the sensing response of prepared 57 sensor structure was calculated using the formula [20] . in comparison to that observed for PANI thin films ( Fig. 4 (a) and 103 (b)). Both roughness and porosity are observed to be enhanced 104 in the Fe 2 O 3 -PANI composite thin films deposited with similar 105 growth conditions as that of Fe 2 O 3 and PANI thin films ( Fig. 4 106 (c ) and ( d)). ...
Article
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The iron oxide-polyaniline (α-Fe2O3–PANI) films were prepared by spin coating method on various corning glass substrates over Pt inter-digital electrodes (IDEs). The prepared film was characterised using XRD, SEM, AFM, UV-vis and FTIR. Also, it was employed for NO2 sensing. The nanostructured α-Fe2O3–PANI film showed a high sensing response ∼2.29 × 10² towards 20 ppm of NO2 gas. Besides giving the higher sensing response towards NO2 gas, α-Fe2O3–PANI sensor structure was found to be highly selective and exhibited the poor gas sensing response towards other interfering gases including e.g. Acetone, IPA, NH3, LPG and CO2. The investigated sensor can be used for the detection of NO2 at the industrial level.
... Zinc oxide (ZnO) is a promising material for application in optoelectronics [1], UV lasers [2], dye sensitized solar cells [3e5], photocatalysis [6,7] and etс. Furthermore, it has already found application as a sensitive layer of cheap resistive gas sensors [8,9]. Among different gases, the possibility to control propane-butane mixture (LPG) content in air is of high importance due to its high explosiveness. ...
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The aim of the work was to obtain ZnO nanostructures with heightened surface area and to study relationship between formation method and gas sensor properties towards propane-butane mixture (LPG). In order to synthesize ZnO nanostructures chemical and physical formation methods have been utilized. The first one was chemical bath deposition technology and the second one magnetron sputtering of Zn followed by oxidation. Optimal method and technological parameters corresponding to formation of material with the highest sensor response have been determined experimentally. Dynamical gas sensor response at different temperature values and dependencies of the sensor sensitivity on the temperature at different LPG concentrations in air have been investigated. It has been found, that sensor response depends on the sample morphology and has the highest value for the structure consisting of thin nanowires. The factors that lead to the decrease in the gas sensor operating temperature have been determined.
... Conduction electrons, e − , are then consumed and this leads to an increase of the surface resistance, in agreement with experimental results reported. The suggested sensing mechanism is in according with that proposed by other researchers [33,34]. Response, τ res , and recovery time, τ rec , have been calculated taking the NO 2 pulse of 1.4 ppm as reference, and results to be about 150 and 180 s, respectively. ...
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Zinc oxide nanoparticles (ZnO NPs) were prepared by sunflower pollen-assisted sol–gel method and successive annealing treatment in air at 500 °C. The morphology and microstructure of the synthesized nanoparticles were characterized by means of SEM, XRD, BET surface area and XPS. Characterization data showed that sunflower pollen leads to the formation of zinc oxide microspheres constituted by an ensemble of crystalline ZnO nanoparticles of about 35 nm in diameter. ZnO NPs synthesized by this method have been used to fabricate a conductometric gas sensor which resulted highly sensitive and selective for the monitoring of low concentrations of NO2 in air.
... Meanwhile, the observed values of gas response for our samples were larger than those observed for other ZnO based gas sensors. [46][47][48] Commercially available ZnO nanoparticles (Kojundo Co. Ltd) were spin coated onto a glass substrate and their measured gas response was found to be about 980% at 150 1C for 100 ppm of NO 2 gas. This shows that the gas responses for our materials are greater than that of the commercial ZnO nanopowder based gas sensor. ...
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Advancing the properties of selective and sensitive metal oxide based gas sensors is a challenging research topic for the detection of toxic, and pollutant gases. In the present research, we successfully deposited a three dimensional (3D) mesoporous ZnO nanostructure on a glass substrate by using a hydrothermal method, and tested the material for its gas sensing performance. These 3D mesoporous ZnO nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence techniques. Gas sensing performance analysis was carried out for nitrogen dioxide (NO2) gas at different temperatures and concentrations. The 3D mesoporous ZnO nanostructure revealed excellent gas sensing performance for NO2 gas because of its large surface area. The larger surface area led to an increase in the gas sensitivity. In addition, the sensor based on the 3D mesoporous ZnO nanostructure could be used at a low operating temperature of 150 °C. This work suggests that the 3D mesoporous ZnO nanostructure is a versatile material for NO2 gas sensing applications. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
... A literature Table 1. Figure 6b represents the resistance of the sensor after exposure to 10 ppm NO 2 , which shows that the sensor resistance increases after the exposure; this is expected in the case of the semiconducting MOX sensor. When ZnO film was exposed to NO 2 gas, NO 2 gas molecules gets absorbed by the sensing film and in this kind of reaction, NO 2 acts as an electron acceptor results in the increase of the resistance of the sensor [39]. The sensing mechanism of the MOX-based sensors includes two fundamental reactions: desorption and adsorption of oxygen species on the sensing layer. ...
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A three-dimensional flower-like ZnO nanostructured film decorated with the thin porous ‘petals’ is synthesized using an inexpensive sol–gel drop-casting method, and the NO2 detection characteristics of the nanostructured film are studied. The gas-sensing study shows higher sensitivity with selectivity toward NO2 gas, exhibiting good reproducibility and stability. The as-synthesized nanostructured 3D flower-like ZnO film shows excellent NO2 sensing performance, with a maximum gas response of 23.3 for 100 ppm NO2 gas at an operating temperature of 180 °C. A detailed gas-sensing study reveals that the enormous porous petals with various inter-connected pores fused on the flower-like ZnO nanostructure improve the adsorption of gas molecules; consequently, the synthesized ZnO nanostructure exhibits a superior level of NO2 gas-sensing activity. This study provides a promising path towards the development of a highly sensitive NO2 gas sensor and an easy way to fabricate the 3D morphology decorated with exceedingly porous ‘petals’.
... Other studies addressed some limitations of the gas sensors by improving the structure and morphology of the gas sensor films. Sonker et al. [12] successfully prepared a nano-petal like NO 2 sensor through a cheap and easy chemical route. Plecenik et al. [13] constructed a highly-sensitive room-temperature semiconductor gas sensor based on nanoscale Pt-TiO 2 -Pt sandwich. ...
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Key words In this study, a double frequency Q-switching Nd:YAG laser beam (1064 nm and λ= 532 nm, repetition rate 6 Hz and the pulse duration 10ns) have been used, to deposit TiO 2 pure and nanocomposites thin films with noble metal (Ag) at various concentration ratios of (0, 10, 20, 30, 40 and 50 wt.%) on glass and p-Si wafer (111) substrates using Pulse Laser Deposition (PLD) technique. Many growth parameters have been considered to specify the optimum condition, namely substrate temperature (300˚C), oxygen pressure (2.8×10-4 mbar), laser energy (700) mJ and the number of laser shots was 400 pulses with thickness of about 170 nm. The surface morphology of the thin films has been studied by using atomic force microscopes (AFM). The Root Mean Square (RMS) value of thin films surface roughness increased with increasing of Ag contents, while the crystallite size was found to decrease with increase in different silver content. The sensitivity toward NO 2 and NH 3 gas has been measured under different ppm concentrations. TiO 2 with noble metal has a sensitivity higher than pure TiO 2 where as TiO 2 with Ag metal deposited on glass substrate has maximum sensitivity to NO 2 gas with a value of ~(50 %) at the nanocomposite 90% TiO 2 / 10% Ag films with best operation temperature at 200 °C. In addition, noble metal like Ag to the titanium dioxide materials makes them sensitive to NO 2 gas. Titanium oxide, morphology and sensitivity properties, PLD technique. Article info.
... In order to monitor air pollution on a large scale, inexpensive, reliable and easy to use gas sensors are needed.The electrical resistance of semiconductor oxides, such as SnO 2 , ZnO, TeO 2 ,WO 3 and Fe 2 O 3 , has a strong dependence on the concentration of surrounding gases. According to this principle, these oxides are commercially designed as chemical sensors to detect toxic gases such as LPG, and NO 2 [3,4]. Ferric oxide is considered to be the most promising highly sensing materials of sensors due to the temperature dependent surface morphology and photo catalytic activity [5]. ...
... Metal oxide semiconductors are useful for the sensing of combustible gases by the change in the surface conductivity due to exposure of gases. The n-type semiconducting materials such as stannous oxide (SnO2), zinc oxide (ZnO), titanium dioxide (TiO2) are promising materials for gas and humidity sensors [1][2][3][4][5][6]. TiO2 is an important metal oxide for a broad range of gas sensing applications, because of its surface chemistry, charge transport, and electrical properties. ...
Conference Paper
The present work reports the preparation of Titania(TiO2) thin film by sol-gel technique and its Liquefied Petroleum Gas (LPG) sensing. TiO2 exists in numerous phases possessing different structural properties like amorphous, anatase or anatase/rutile mixed phases. The structural analysis confirmed the formation of TiO2 having an average crystallite size 21 nm. SEM showed the regular and porous surface morphology. The band gap of the material was found as 3.65 eV. This film was employed for LPG sensing and variations in resistance with exposure of LPG were observed. Sensor response (S) as a function of time was calculated and its maximum value was found as 2.8 for 4% vol. of LPG with a response and recovery times of 240 sec and 248 sec respectively.
... MOS sensors such as ZnO gas-sensing materials have been widely investigated and utilized for various types of gases due to their stable chemical transduction properties which can reversibly convert chemical interactions on a surface and lead to the change of the electrical conductivity. [3][4][5] In recent years, the remarkable sensing properties of ZnO and the possibility to fine tune its efficiency by a variety of doping technique and dopants has drawn many researchers' attention. In fact, doping with noble metals or other additives has been reported to enhance the sensitivity and selectivity of ZnO gas sensors. ...
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Herein we report Al-doped ZnO films (AZO) deposited on the ZnO seed layer by chemical bath deposition method. Al powder, Al oxide and Al chloride were used as sources for the deposition process and investigated for their different effects on the NH3 gas-sensing performance. The morphological and microstructural properties were investigated by employing x-ray powder diffraction, scanning electron microscopy analysis and energy-dispersive x-ray spectroscopy. The characterization studies showed that the AZO thin films are crystalline and exhibit a hexagonal wurtzite structure. Ammonia (NH3) gas-sensing measurements of AZO films were performed at different concentration levels and different operation temperatures from 50°C to 210°C. The sample based on powder-Al source showed a higher response, selectivity and short response/recovery time than the remaining samples. The powder Al sample exhibited 33% response to 10-ppm ammonia gas at 190°C, confirming a strong dependence on the dopant source type.
... The related spectrum was shown in Fig. 2(a). Estimated value of band gap for as-grown ZnO-NN film is found to be 3.34 eV and is close to the reported value [13]. ...
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Developing new technologies that could lead to alternatives to the traditional silicon-based solar panels and to efficiently light the world in the future, is critically important because of limited natural petroleum resources. Dye-sensitized solar cells (DSSCs) are promisingly efficient and clean hybrid, organic–inorganic, low-cost molecular solar cell devices. Because of their unique, multifunctional properties, zinc oxide (ZnO) nanostructures are promising materials to use to create photoanodes for DSSCs. ZnO was one of the first metal oxides which used in dye-sensitized solar cells. It exhibits a unique combination of potentially interesting properties such as high bulk electron mobility and probably the richest variety of nanostructures based on a very wide range of synthesis routes. The fabricated ZnO nanoneedle based DSSCs shows a short circuit current density (Jsc) of 20 mA/cm², open circuit voltage (Voc) of 0.48 V, fill factor (FF) of 0.44 and efficiency (ɳ) of 4.2% at one sun condition.
... The chemical methods for synthesis that are mostly employed for nanoscaled ZnO synthesis include hydrothermal, spray pyrolysis, sol-gel, sonochemical, solvothermal and electrodeposition. The physical methods that are usually employed for synthesis include thermal evaporation, pulsed laser deposition, chemical laser deposition and molecular beam epitaxy, etc. [16][17][18][19][20][21][22][23]. However, the physical and chemical means of synthesis possess considerable disadvantages. ...
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Aim: To investigate the physical and biological properties of bioinspired zinc oxide (ZnO) nanoparticles via aqueous leaf extracts of Sageretia thea. Experimental: Nanoparticles of size approximately 12.4 nm were extensively characterized. In vitro antimicrobial, cytotoxic, biocompatible and enzyme inhibition assays were performed. Results: Significant antimicrobial activities with and without UV illumination are reported. Bioinspired ZnO nanoparticles were found effective against fungal strains. MTT assay was performed to check the leishmanicidal activity against promastigotes (IC50: 6.2 μg/ml) and amastigotes (IC50: 10.87 μg/ml) of Leishmania tropica. Brine shrimp lethality was also indicated by bioinspired ZnO nanoparticles (IC50: 21.29 μg/ml). Conclusion: Hemocompatible nature of bioinspired nanoparticles was revealed. Furthermore, the antioxidant activities were performed. In addition, significant protein kinase while insignificant alpha amylase inhibition were recorded.
... When NO 2 enters the atmosphere, it also adsorbs at the semiconductor surface as presented in Figure 3b. By taking one negative charge from the conduction band, the NO 2 chemisorbs as NO 2 − (see Equation (2)) [33]. The electron affinity of NO 2 is significantly higher compared to the one of O 2 [34]. ...
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We present a gas sensitive thin-film transistor (TFT) based on an amorphous Indium–Gallium–Zinc–Oxide (a-IGZO) semiconductor as the sensing layer, which is fabricated on a free-standing flexible polyimide foil. The photo-induced sensor response to NO2 gas at room temperature and the cross-sensitivity to humidity are investigated. We combine the advantages of a transistor based sensor with flexible electronics technology to demonstrate the first flexible a-IGZO based gas sensitive TFT. Since flexible plastic substrates prohibit the use of high operating temperatures, the charge generation is promoted with the help of UV-light absorption, which ultimately triggers the reversible chemical reaction with the trace gas. Furthermore, the device fabrication process flow can be directly implemented in standard TFT technology, allowing for the parallel integration of the sensor and analog or logical circuits.
... Other studies addressed some limitations of the gas sensors by improving the structure and morphology of the gas sensor films. Sonker et al. [12] successfully prepared a nano-petal like NO 2 sensor through a cheap and easy chemical route. Plecenik et al. [13] constructed a highly-sensitive room-temperature semiconductor gas sensor based on nanoscale Pt-TiO 2 -Pt sandwich. ...
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Full-text available
Key words In this study, a double frequency Q-switching Nd:YAG laser beam (1064 nm and λ= 532 nm, repetition rate 6 Hz and the pulse duration 10ns) have been used, to deposit TiO 2 pure and nanocomposites thin films with noble metal (Ag) at various concentration ratios of (0, 10, 20, 30, 40 and 50 wt.%) on glass and p-Si wafer (111) substrates using Pulse Laser Deposition (PLD) technique. Many growth parameters have been considered to specify the optimum condition, namely substrate temperature (300˚C), oxygen pressure (2.8×10-4 mbar), laser energy (700) mJ and the number of laser shots was 400 pulses with thickness of about 170 nm. The surface morphology of the thin films has been studied by using atomic force microscopes (AFM). The Root Mean Square (RMS) value of thin films surface roughness increased with increasing of Ag contents, while the crystallite size was found to decrease with increase in different silver content. The sensitivity toward NO 2 and NH 3 gas has been measured under different ppm concentrations. TiO 2 with noble metal has a sensitivity higher than pure TiO 2 where as TiO 2 with Ag metal deposited on glass substrate has maximum sensitivity to NO 2 gas with a value of ~(50 %) at the nanocomposite 90% TiO 2 / 10% Ag films with best operation temperature at 200 °C. In addition, noble metal like Ag to the titanium dioxide materials makes them sensitive to NO 2 gas. Titanium oxide, morphology and sensitivity properties, PLD technique. Article info.
... Quantum-sized ZnO nanoparticles were synthesized using a mild sol-gel process by Bai et al. [16], the reported NO 2 gas response 280-40 ppm at 290°C operating temperature. Nanopetal structured ZnO was prepared by using chemical precipitation method reported by Sonker et al. [17], the fabricated nanopetals ZnO sensor gives high response 119 to NO 2 for 20 ppm concentration at room temperature. Direct growth of hierarchical ZnO nanostructure on chip patterned electrodes using evaporation method gives NO 2 gas response 32 for 20 ppm was reported by Pan et al. [18]. ...
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The 1D ZnO nanorods (NR's) were grown with Zinc (Zn) ion precursor concentration variation on seed layer glass substrate by the low temperature hydrothermal method and utilized for nitrogen dioxide (NO2) gas sensing application. Zn ion precursor concentration varied as 0.02, 0.03, 0.04, 0.05 and 0.06M and thin films were characterized for structural, morphological, optical, electrical, surface defect study and gas sensing properties. All the film showed dominant orientation along the (002) direction, the intensity of the peak vary with the length of the nanorods. SEM cross images confirmed that nanorods had vertical alignment perpendicular to the plane of the substrate surface. The PL intensity of oxygen vacancy related defects for prepared samples was found to be linearly proportional to gas sensing phenomena. This result in good agreement with the theoretical postulation that, oxygen vacancies plays the important role for adsorption sites to NO2 molecule. The gas sensing performance was studied as a function of operating temperature, Zn ion precursor concentration variation, and gas concentration. The maximum gas response is 113.32-100ppm NO2 gas at 150°C for 0.05M sample out of all prepared samples. Additionally, ZnO thin film sensor has potential to detect NO2 as low as 5ppm.
... The physical methods such 67 as metal-organic chemical vapor deposition, sputtering technique, 68 pulsed laser deposition, infrared irradiation, thermal decomposi-69 tion, thermal evaporation, and condensation are extensively used 70 to synthesize ZnO nanoparticles [6][7][8][9][10]. The chemical route 71 method, which requires high vacuum and energy, includes liquid 72 ultra sonication, sol-gel, and electrochemical reaction methods 73 [11][12][13][14]. These methods consume more energy and hazardous 74 chemical reagents, which may be hazardous in nature and may 75 yield by-products of non-eco-friendly nature [15]. ...
Article
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In this study, ZnO nanoparticles were green-synthesized from Acalypha indica leaf extract using zinc acetate as a precursor. The prepared ZnO nanoparticles were calcined at three different temperatures, namely 100, 300, and 600°C. The structure/morphology of the green-synthesized ZnO nanoparticles was ascertained through X-ray diffraction, particle size analysis, scanning electron microscopy, transmission electron microscopy, and surface area analysis techniques. It was observed from the physico-chemical and biological characterization studies that ZnO nanoparticles calcined at high temperature (600°C) exhibit high surface area (230m²g⁻¹) and small particle size (20nm) with good antibacterial activity against Escherichia coli (22.89±0.06mm) and Staphylococcus aureus (24.62±0.08mm). In addition, cotton fabrics coated with these nanoparticles showed higher UV-protection (87.8UPF), hydrophobicity (155°), and maximum zone of bacterial inhibition against E. coli and S. aureus (25.13±0.05 mm and 30.17±0.03mm) than those coated with particles calcined at 100°C and 300°C. High temperature calcination has a vital role in the crystallization of the particles towards nanoscale with increased resistivity to UV exposure, washing treatments, and microbial infection in fabrics. Thus, the cost-effective ZnO nanoparticles obtained through green synthesis method proves their potential applications in the field of biomedical, textile, and cosmetic applications.
... The electrical resistance of semiconductor oxides, such as SnO 2 , ZnO, TeO 2 ,WO 3 and Fe 2 O 3 , has a strong dependence on the concentration of surrounding gases. According to this principle, these oxides are commercially designed as chemical sensors to detect toxic gases such as LPG, and NO 2 [3,4]. Ferric oxide is considered to be the most promising highly sensing materials of sensors due to the temperature dependent surface morphology and photo catalytic activity [5]. ...
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Air pollution caused by toxic, flammable and explosive gases, detection of some hazardous gases is impossible for human, because some gases like CO and H 2 are odourless and tasteless as well as colourless. Furthermore in some cases absolute gas concentrations is very low to be detected by human nose. Therefore development and fabrication of a device for early detection of certain flammable, explosive, and toxic gases are extremely necessary. For this purpose, different devices have been developed toward tract detection of such pollution gases. Consequently, the development of cheap and reliable devices for detection of gases is considered to be a significant goal in science. In this study, iron oxide compound triple and quaternary iron oxide compounds with Zn, Co metal dopants were grown by using Chemical Spray Pyrolysis (CSP) technique. The structural, optical, magnetic properties of Co:Fe 2
... Synthesized ZnO nanostructures can be used for the fabrication of white light emitting diodes, display devices, biological labelling and detector etc [17]. ZnO SNSs possess significantly different properties from their bulk counterpart hence suitable for various applications such as light emitting diodes [18], polariton laser [19], field effect transistor [20], photo-catalyst [21], UV sensor [22] and gas sensor [23][24][25][26][27]. Yang et al. studied interesting optical properties of different types of ZnO nanostructures ranging from nanodots to tetrapods [28]. ...
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The present paper reports deviation in the intensity of light transmitted through the film of ZnO spherical nanostructure (SNSs) with the exposure of humidity at room temperature. For this purpose, the precursor of ZnO SNSs was prepared and used for coating thin film on borosilicate substrates. The efficient dye-sensitized solar cells (DSSCs) are promisingly low-cost molecular solar cell devices. ZnO SNSs are promising materials used to use to create photoanodes for DSSCs. The film was then investigated using SEM, HR-TEM, XRD and UV–visible transmittance techniques. Further, it was employed as transmission based optical humidity sensor, the maximum sensitivity of which was found a ∼ 1.81 μW/%RH with response and recovery time of 36 s and 124 s respectively. The sensor showed ∼97% reproducible results. The fabricated ZnO SPSs based DSSC shows a short circuit current density (Jsc) of 3 mA/cm2, open circuit voltage (Voc) of 0.62 V and efficiency (ɳ) of 1.3% at one sun condition.
... X-ray diffraction pattern of Fig. 1(a) [25]. Fig. 1(b) shows the diffraction peaks corresponding to reflection plane which was described in our previous report formation of the polycrystalline ZnO thin film [26]. Fig. 1(c) shows the XRD pattern of PANI, which shows broad peaks at 2θ = 24.61°and ...
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The present paper reports the in-situ chemical polymerization of nanocomposites thin film composed by titanium dioxide (TiO2), zinc oxide (ZnO) and polyaniline (PANI). It was found that nanocomposites sensor is highly selective and shows response to low concentration. To improve the sensing response characteristics of ZT thin film, PANI is incorporated. Thin film based LPG sensor of ZnO-TiO2-PANI composite was fabricated by spin coating of ZnO-TiO2 nanoparticles doped with PANI over inter digital electrodes (IDEs). The thin film was characterized by using XRD, SEM, TEM, UV–vis, BET and FTIR. It was also tested for gas sensing properties of LPG/NO2 which are well known flammable and toxic gases. The measured response for ZnO-TiO2-PANI based sensor was 87 for 2000 ppm of LPG and 412 for 20 ppm of NO2 at room temperature towards other testing gases together with Acetone, IPA, NH3 and CO2.
... The most commonly encountered methods used to produce these structures are: chemical vapour deposition (CVD), physical vapour deposition (PVD), galvanic displacement, or electrodeposition [23]. For example, Kong et al. [19] produced nanocubeaggregated cauliflower-like copper hierarchical 3D nanostructures by electroless deposition and used the deposits to study the electrocatalytic reduction of oxygen. ...
Article
In amperometric gas sensors, the flux of gas to electrode surfaces determines the analytical response and detection limit. For trace concentration detection, the resulting low current prevents the miniaturisation of such sensors. Therefore, in this study, we have developed repeating arrays of nanostructures which maximise flux towards their surface. Unique platinum 3D cauliflower-shaped deposits with individual floret-shaped segments have been produced in a single step electrodeposition process. The confined walls of recessed microelectrode arrays (10 μm in diameter, 90 electrodes) are utilized to produce these structures with a high surface area. Distinct segments are observed, with the gaps corresponding to electrodes adjacent in the microarray; thus the majority of the deposits face the primary diffusion zones. The sizes and shapes of the deposits are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and the largest structures are found to be 22 ± 1 μm in width and 7.9 ± 0.2 μm in height over the microhole. These modified electrodes are employed to detect ammonia using the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2mim][NTf2], as an electrolyte. Current responses on the cauliflower arrays were seven times higher for linear sweep voltammetry and ca. 12 times higher for chronoamperometry, relative to the bare microrrays, and limits of detection were less than 1 part per million of ammonia (gas phase concentration). This work highlights the use of modified microarrays with highly accessible 3D structures for enhanced electroanalytical detection of analyte species at ultra low concentrations.
... The extensive use of LPG in kitchen as well as in automobiles demands quick, reliable and selective detection of LPG leakage to prevent fatal accident. Gas sensor based on metal oxide nanostructures have been largely utilized for identifying oxidizing and reducing gases because they offer several advantages such as simple sensor structure, low production cost and high miniaturization potential etc. [2][3][4]. ZnO is n-type wide band gap semiconductor which is considered as one of the best materials for gas sensing application owing to its outstanding properties which includes high thermal and chemical stability, non-toxic nature, ability to grow into different morphologies etc. [5]. However, pure ZnO have several disadvantages such as poor sensitivity and selectivity, relatively high optimum operable temperature towards various gases. ...
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The fabrication of sensitive and selective liquefied petroleum gas (LPG) sensors is highly desirable for efficient detection of LPG. In this paper, we report fabrication of novel ZnO/NiO heterostructures for selective detection of LPG. X-ray diffraction (XRD) and Raman results indicated successful formation of ZnO/NiO heterostructures. Field emission scanning electron microscope (FESEM) results disclosed spherical shape of ZnO/NiO. The sensor based on ZnO/NiO heterostructures displayed higher sensor response, low detection limit and excellent selectivity towards 50 ppm of LPG. Interestingly, ZnO/NiO heterostructure based sensor presented elevated sensor response towards 50 ppm LPG at relatively low operable temperature. The response of ZnO–NiO heterostructures based sensor to 50 ppm of LPG was relatively higher than most of other reported LPG sensors. The excellent sensing property of present sensor towards LPG has been credited to creation of heterojunctions between ZnO and NiO nanoparticles. The gas sensing mechanism of ZnO/NiO heterostructure based sensor has been proposed and explained in detail which we claim that can be used for alarm applications with extremely high selectivity and sensitivity.
... Currently, ZnO-NPs are commonly synthesized through physical and chemical means. The chemical approaches include sol-gel, hydrothermal, spray pyrolysis, sonochemical, solvothermal, and electrodeposition while the commonly used physical techniques include thermal evaporation, pulsedlaser deposition, molecular beam epitaxy, and chemical laser deposition (Ameen et al., 2015;Fan et al., 2015;Mani and Rayappan, 2015;Sonker et al., 2015;Suntako, 2015;Wang et al., 2015). ...
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Herein, we report a facile, economic, one-pot green synthesis of Zinc Oxide nanoparticles (ZnO-NPs) for diverse biomedical applications. In the study, ZnO-NPs were synthesized using an aqueous extract of Aquilegia Pubiflora as an effective reducing and capping agent. The biomediated nanoparticles were characterized using various techniques including HPLC, XRD, FTIR, SEM, DLS, PL and RAMAN. The particles were highly pure, having an average size of 34. 23nm with spherical or elliptical shaped morphology and displayed good aqueous dispersion capability. FTIR and HPLC confirmed the successful capping of flavonoids and hydroxycinnamic acid derivatives. The characterized NPs were then explored for their antimicrobial and antileishmanial potential. Among the tested bacterial and fungal strains, ZnO-NPs were more potent towards Pseudomonas aeruginosa and Fusarium solani with inhibition zone of 10.3±0.19 mm and 13±1.4 mm, respectively. A dose-dependent cytotoxic effect was observed against Leishmania tropica (KWH23) with significant IC50 for both the promastigote (48 μg/mL) and amastigote form (51 μg/mL) of the parasite. In addition, bacterial kinase enzymes were inhibited by ZnO-NPs, thus allowing us to elaborate a possible action mechanism. Finally, remarkable biocompatible nature of the particles was confirmed against freshly isolated human red blood cells (hRBCs). All together these results affirmed the high antimicrobial and anti-parasitic potential of ZnO-NPs obtained through biogenic synthetic approach using aqueous extract of the Himalayan Columbine (Aquilegia Publifora).
... The high response of ZnO/rGO towards NO 2 gas could be realized by considering following factors. The ZnO plays very crucial role in sensing and acts as reactive sites for effective gas adsorption on its surface and hence, based on this some NO 2 gas sensors are also reported at low temperature [43,53,54]. In case of ZnO/rGO nanocomposite, the conduction path is controlled by the ZnO and with respect to addition of rGO and it clearly influences the electrical transport of electrons due to formation of heterojunction. ...
Article
In this work, we report parts per billion (ppb) NO2 gas detection by utilizing zinc oxide/reduced graphene oxide (ZnO/rGO) heterostructure through a chemiresistive approach. The sensing material is carefully investigated through numerous characterization techniques. The experimental results indicated that the designed sensor shown good linearity in low ppb range of nitrogen dioxide (NO2) gas. The sensor exhibited very high response of 33.11 at 2.5 ppm in 182 s with obtained detection limit down to ppb at relatively low optimal operating temperature of 110 °C. The remarkable performance of ZnO/rGO heterostructure towards NO2 and negligible cross-response to other interfering gases along with high repeatability and long-term stability of the sensor is investigated. Due to many reactive sites and high transport capability of rGO along with high gas adsorption of ZnO nanospheres which attributes to the favorable charge transfer at ZnO/rGO interface under exposure of NO2 gas which leads to modulate the energy band structure. This study shows that the simple, cost-effective synthesis method along with easy-fabricated and deployable sensor can be applied in many industrial and environmental applications.
... Zinc oxide is a promising semiconductor material, which is categorized in a wide bandgap semiconductor (Eg ~3.3 eV) at room temperature [14]. The ZnO has excellent optical and electronic properties [15,16] and has been widely used for sensors [17,18], solar cells [19,20], and other optoelectronic applications. In solar cell devices, ZnO was used as an active layer [21] and the transport layer [22] due to its high absorption and electron transport. ...
Conference Paper
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The main keys in developing solar cells are their optical absorption and electron transfer (optical conductivity) levels. To enhance these two characteristics, an electron transport layer (ETL) was added to the solar cell, which is used to prevent electron recombination. Zinc oxide nanorod (ZnO NR) is one of the potential ETL candidates in the new generation of solar cells due to its high electron transfer. To optimize the use of ZnO NR in new generation solar cells, we combine NR ZnO with graphene, into a hybrid ZnO NR/graphene system. Optical absorption and conductivity of hybrid ZnO NR/graphene were studied using spectroscopic ellipsometry. A significant change in ellipsometry spectra has been observed, which increases with a higher number of graphene in the hybrid systems. Furthermore, the role of graphene on the optical absorption and conductivity of hybrid systems was investigated through fittings by applying the effective medium approximation (EMA) model. This study will provide a good understanding of optical absorption and optical conductivity of hybrid ZnO NR/graphene, which is an important key in the development of high-performance new generation solar cells.
... Such materials combine the attractive properties of a polymer matrix, i.e., mechanical stability, chemical resistance [6], high porosity [7], and low hydrodynamic drag, with the unique sorption properties resulting from the high specific surface area [8] and chemical activity of a nanodimensional inorganic component [9]. Particles comprised of nanosheets [10] or nanopetals [11] are of special interest, due to their large specific surface area [12] and open-pore structure [13]. Strong adsorption properties (rate, capacity and selectivity) are not only demonstrated by graphene [9], a classic nanosheet material, but also by boron nitride nanosheets [14], zinc oxide [15] nanosheets and ferrous oxide nanopetals [16]. ...
Article
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In this work, in situ method of producing hybrid fibrous adsorbents in which boehmite nanosheets with high sorption properties formed on the surface of hydrophilic microfibres, such as cellulose acetate and glass fibre, was described. The boehmite nanosheets were fabricated by the reaction of composite AlN/Al nanoparticles with water at 60 °C. The synthesized samples were characterized by X-ray diffractometer, scanning, transmission electron microscopy, Fourier transform infrared spectrometer (FT-IR), zeta-potential and specific surface area analyzers. The introduction of microfibres into a diluted aqueous suspension of nanopowders causes heteroadagulation of the nanoparticles and accelerates their further transformation. This effect is most substantial with the glass microfibre, which is thought to have a higher concentration of surface groups capable of generating hydrogen bonds that act as heteroadagulation and nucleation centres. The experimental results showed that the morphology of the resultant hybrid fibrous adsorbents differed accordingly: the nanosheets were attached on-edge to the glass microfibre surface, while on the surface of the cellulose acetate microfibre, they were secured in the form of spherical “nanoflowers” of agglomerated nanosheets. The effect of the morphology of hybrid fibrous adsorbents on adsorption bacteria Escherichia coli was also investigated.
... Various ZnO morphologies provide different sensing performances [9]. For instance, ZnO nanopetals have a sensitivity of 119-20 ppm NO 2 gas at room temperature [10]. Monodisperse ZnO hollow six-sided pyramids have a sensitivity of about 15 to dimethylformamide (DMF) and 187 to ethanol [11]. ...
Chapter
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... Figure 3(c) shows a multi-cycle repeated injection of CO2 gas and result in no change of the maximum and minimum response of the resistance within 40 cycles. The sensing response is defined as the change in resistance between the presence of gas (Rg) to the resistance in the reference resistance (R0) [24], that is: ...
Chapter
The monitoring of CO2 concentration is important for the environment and health. The present work reports a printed silver electrodes CO2 sensor with TiO2 nanowires coated on the surface. The silver electrode sensor was printed with a Voltera PCB printer. TiO2 nanowires were attached to the electrodes by an electro-deposition method. Variations in resistance of the sensing element by the exposure of CO2 gas were successfully observed at room temperature without additional heat. The printed CO2 sensor shows responses from 78 ppm to more than 1055 ppm with a response time of 92 s and a recovery time of 25 s. The selectivity experiment displays that the printed sensor does not respond to methane, CO, NH3, H2, or H2S at 1000 ppm or higher concentration, but it is slightly sensitive to humidity. The response is 2% for 1000 ppm CO2, while the response is 0.7% when the relative humidity changes from 48 to 99%. The present results display a facile method to develop highly sensitive and selective CO2 sensors operating at room temperature.
... The chemical procedures used for preparing nanosized ZnO NPs include solvothermal, sol-gel, sonochemical, electrodeposition, hydrothermal and spray pyrolysis. [10][11][12][13][14] However, synthesis by physical and chemical means has disadvantages. Physical methods require large amounts of energy and are timeconsuming while chemical methods produce noxious chemicals, which are unfriendly for the environment. ...
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Biogenic synthesis using medicinal plants has less harmful effects as compared to chemically synthesized nanoparticles. Here, for the first time, we successfully demonstrated the eco-friendly synthesis of zinc oxide nanoparticles (ZnO NPs) using an aqueous extract of Papaver somniferum L. The phyto-mediated ZnO NPs were characterized using UV-visible spectroscopy, XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy) and TEM (transmission electron microscopy). They were also evaluated for anti-diabetic activity, biocompatibility with RBCs and bactericidal biological applications. The UV spectrum showed a strong surface plasmon peak for ZnO NPs at 360 nm. The optical band gap was observed to be 2.93 eV using UV spectroscopy data. The crystalline nature and the crystal size (48 nm) of the prepared ZnO NPs were confirmed by XRD. FT-IR analysis confirmed the formation of functional bio-molecules linked with ZnO NPs. SEM and TEM images revealed irregular and spherical morphology. The ZnO NPs demonstrated moderate enzyme inhibition (30.8%) at a concentration of 200 mg ml⁻¹. No potential damage was caused by ZnO NPs to red blood cells, if used in low doses. P. somniferum aqueous extract has the potency to combat drug-resistant bacteria but comparatively, ZnO NPs synthesized from the same plant were found to be more effective against resistant pathogenic strains. It is concluded from the above study that phyto-fabricated ZnO NPs have strong potential as theranostic agents and can be adopted in drug delivery systems.
... sensors owing to their low cost, simple fabrication, and good compatibility with microelectronic processes [5][6][7]. Metal oxide semiconductors such as SnO 2 , ZnO, and WO 3 have been widely used in gas sensors to detect NO 2 [8][9][10]. Among these semiconductors, WO 3 is a typical n-type semiconductor, and exhibits high sensitivity and selectivity towards NO 2 because of its superior physical and chemical properties [11,12]. ...
Article
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Metal oxide/graphene nanocomposites are emerging as promising materials for developing room-temperature gas sensors. However, the unsatisfactory performances owing to the relatively low sensitivity, slow response, and recovery kinetics limit their applications. Herein, a highly sensitive and rapidly responding room-temperature NO2 gas sensor based on WO3 nanorods/sulfonated reduced graphene oxide (S-rGO) was prepared via a simple and cost-effective hydrothermal method. The optimal sensor response of the WO3/S-rGO sensor toward 20 ppm NO2 is 149% in 6 s, which is 4.7 times higher and 100 times faster than that of the corresponding WO3/rGO sensors. In addition, the sensor exhibits excellent reproducibility, selectivity, and extremely fast recovery kinetics. The mechanism of the WO3/S-rGO nanocomposite gas sensor is investigated in detail. In addition to the high transport capability of S-rGO as well as its excellent NO2 adsorption ability, the superior sensing performance of the S-rGO/WO3 sensor can be attributed to the favorable charge transfer occurring at the S-rGO/WO3 interfaces. We believe that the strategy of compositing a metal oxide with functionalized graphene provides a new insight for the future development of room-temperature gas sensors.
... Employing this method, ionicities of inverse spinel ferrites were estimated. On the basis of this, the ion distributions at A site and B sites of NiLaFe 2 O 4 ((A) [B] 2 O 4 ) ferrites was calculated using ionicities values [30]. ...
Article
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Nanocrystalline NiLaFe2O4 exhibit unique properties, which make them promising candidates for an inclusive range of applications such as actuators, magnetic resonance imaging, including gas sensing element due to its inverse spinel structure. It is requisite to revamp its ionicity, phase and magnetic properties. A primal approach has been chosen to fabricate NiLaFe2O4nanocrystals by co-precipitation technique at different calcination temperatures (300 °C, 400 °C, 500 °C, 600 °C) phase, and ionicity as well as magnetic properties. Changes in the structural characteristics of as-synthesized samples have been found by the inclusion of rare-earth elements in X-ray diffraction studies. Fourier transform infrared spectral studies embrace two absorption bands peaked at 400 and 500 cm⁻¹representing the octahedral and tetrahedral sites. The transmission electron microscopy analysis depicts the tailored morphology of as-synthesized nanocrystal. The magnetization was determined by vibrating sample magnetometer and found that Hc increases with decrease in Ms and magnetostriction coefficient. These results can be partially described by the frailer nature of La³⁺–Fe³⁺ions which are equated to Fe³⁺–Fe²⁺ interaction. A model for inverse spinel ferrite has been used which refers as O2p itinerant electron model. The magnetization and the cation distributions of the La doped inverse spinel ferrites were elucidated using this model. The sensor designates with high selectivity, repeatability and fast transition at room temperature (305 K) towards ammonia gas in particular when related to ethanol, acetone and toluene. Low deposition cost makes it competent for developing a cost-effective ammonia sensor.
... 5 In general, the chemical-based bottom-up approaches are preferred for the synthesis of metal oxide nanostructures, owing to low growth temperature, cost-effectiveness, and better potential for mass production. [6][7][8][9][10] However, many chemical bottom-up methods typically employ hazardous solvents or toxic chemical compounds as surfactants or capping agents which are environmentally unfriendly and difficult to degrade. Furthermore, the chemical waste produced from the manufacture of metal oxides can have harmful effects on human health and environment. ...
Article
In recent years, naturally occurring compounds found in plants (also known as phytochemicals) have found increasing application in the synthesis of metal oxide nanostructures due to their multi-role as reducing agents, capping agents, and/or complexing agents. Furthermore, the utilization of natural agents, such as phytochemicals provide a green and sustainable way for fabricating metal oxide nanostructures compared to conventional chemical methods. This perspective will cover various types of plant-derived phytochemicals which have been employed in the preparation of metal oxide nanostructures, including their roles and the associated formation mechanisms. This review will also discuss some prospective applications of phytochemical-derived metal oxide nanostructures for energy storage, environmental remediation, and bio-related applications. Finally, some perspectives on the future direction of the synthesis of metal oxide nanostructures via green chemistry will be provided.
... A wide variety of physical and chemical processes have been used to synthesize ZnO: homogenous precipitation techniques [18], sol-gel [19], electrolytic deposition [20], organometallic synthesis [21], microbial wave [22], jet pyrolysis [23], thermal evaporation [24], spray method [25], pulsed laser deposition [26], thermal decomposition [27] and sono chemistry [28]. Several of them are not friendly environmental. ...
Article
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In this study, green synthesis of ZnO nanoparticles and single crystals were successfully prepared from Phoenix Dactylifera.L leaves extract. Effect of 0.01-0.6M zinc acetate concentration on the nanoparticles and single crystals ZnO formation was studied. UV-Vis, FT-IR spectrophotometer, X-ray diffraction (XRD), scanning electron microscopy (SEM), and EDAX techniques are used for this purpose. UV-Vis absorption spectra exhibited a maximum absorbance plate at 350nm related to the zinc oxide. Optical band gaps values of the ZnO products were closely equal to the bulk one. FT-IR spectra display a feeble peak at 593 and 674cm-1 , which are accredited to ZnO vibration. XRD showed a good crystalline quality of the ZnO product with very well defined highest peaks intensities along (002), (100), (101) indexing the hexagonal structure (wurtzite). Deduced grain sizes of the synthesized ZnO nanoparticles were in the range of 19.77-26.28nm. SEM showed that the green synthesizing nanoparticles contain sometimes micro single ZnO crystals. As a result, use of Phoenix Dactylifera. L leaves extract offers a low cost and kindly environmentally nanoparticles synthesizing process.
... In order to monitor air pollution on a large scale, inexpensive, reliable and easy to use gas sensors are needed. [Sonker and Yadav 2014;Sonker et al. 2015]. Ferric oxide is considered to be the most promising highly sensing materials of sensors due to the temperature dependent surface morphology and photo catalytic activity [Chaudhari 2008]. ...
Conference Paper
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Iron oxide semiconductor gas sensors are used in a variety of different applications. They are relatively cheap compared to other sensing technologies and benefit from high material sensitivity, reliable and quick response times. Spray pyrolysis (SP) is one of the solution based coating technique to grow thin or thick films. The technique of SP without the requirement of vacuum is a method that can be preferred in the industry, in order to allow the production of large size films in both cheap and fast. When we get the gas sensor measure we see that Mg:Fe2O3 is the p type semiconductors and Zn:Fe2O3, Fe2O3 are n type semiconductor. For Fe2O3 thin film, because of the electrons that emerge as a result of the reaction increase the carrier concentration. Thus resistance is reduced. For Mg:Fe2O3 thin films, because of the electrons that vanish as a result of the reaction decrease the carrier concentration. Thus resistance is increased. X-Ray Diffraction (XRD) measurements of the obtained films were taken. As a result of Atomic Force Microscope (AFM) measurements, was obtained information about surface morphology. Optical properties were measured by Double-Diffracted UV-VIS photoelectron spectroscopy. I-V (Van der Pauw) technique has ben used for respons of gas sensor.
... It has proven itself as one of the promising excellent candidates to replace the toxic and expensive material such as GaN, AlN, SnO 2 , ZnO, Fe 2 O 3 , TiO 2 -PANI etc. for the application of gas and humidity sensors. [1][2][3][4][5][6][7][8][9][10][11] Many efforts have been made in developing new sensing material with improved sensing properties by Zn doped TiO 2 . Various doping methods have been extensively utilised for modifying the electronic structure of TiO 2 nanoparticles to achieve a new or improved catalytic activity and other chemical and physical properties. ...
... At room temperature, the band gap energy of ZnO is 3.37 eV and a large exciton binding energy (60 meV) [4]. It has wide range of applications such as piezoelectricity, optical transparency and chemical stability in visible region [5], optoelectronic devices [6], gas sensors [7][8][9], transparent electrodes [10], solar cells, acoustic wave devices, ferroelectric memories [11] and so on. Its various morphological dependent properties have been reported in a number of studies which includes nanorods, nanosheets, nanotrees [12,13]. ...
Article
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Zinc oxide (ZnO) and ZnO–ZnS nanocomposite materials have been prepared by simple chemical co-precipitation method. The X-ray diffraction analysis revealed formation of ZnO and ZnO–ZnS crystalline materials. FESEM and HRTEM analyses indicated the formation of flake-like ZnO and sheet-like ZnO– ZnS structures. Energy dispersive X-ray (EDS) study further established formation of ZnO and ZnO–ZnS materials. In the FTIR spectrum the presence of Zn-O symmetric stretching vibration at 442 cm −1 and 809 cm −1 , due to weak vibration of ZnO, while the other peak at 687 cm −1 due to Zn-S symmetric bending vibration proved the formation of ZnO–ZnS composite material. Optical absorption spectrum showed that the band gap energy decreased for ZnO–ZnS composite compared to the pure ZnO NPs. The photoluminescence spectral analysis shows that the broad emissions spectrum caused due to several different bands, owing to presence of zinc vacancies, oxygen vacancies, and surface defects. The photocatalytic performance of these samples were tested for degradation of a dye methylene blue under UV light exposure. ZnS–ZnO composite shows the higher dye degradation efficiency (93%) than that of pure ZnO (55%).
Article
The hollow ZnO/ZnFe2O4 microspheres with heterogeneous structure are synthesized by direct pyrolysis of metal-organic frameworks. The as-prepared ZnO/ZnFe2O4 microspheres have well-defined spherical morphology with ∼1.5 μm in diameter and multiple porous shells constructed by interpenetrated ZnO and ZnFe2O4 heterogeneous nanoparticles. Interestingly, the hollow ZnO/ZnFe2O4 microspheres based gas sensors show interestingly temperature-dependent n-p-n type conductivity transition in detecting low-concentration VOC gases including ethanol, acetone, toluene and benzene. This interestingly n-p-n transition phenomenon is mainly ascribed to the trade-off of highly separated electron-hole pairs originated from the staggered type-II band alignment of in-shell ZnO-ZnFe2O4 hetero-interfaces, which is modulated by thermally-dependent ionization reaction of surface-absorbed oxygen molecules and extra electron injection due to surface reaction of reductive VOCs during gas-sensing process. This work presents a facile route to construct hollow nanostructures with heterogeneous feature and provides a new insight into sensing mechanism, exhibiting the potential application of ZnO/ZnFe2O4 microspheres in developing highly sensitive and selective gas-sensing materials in detecting low-concentration VOCs.
Article
Ultralong ZnO microbushes have been synthesized using a simple thermal evaporation and condensation method by Cu catalysts. The lengths of the ZnO microbushes range from several millimeters to more than one centimeter and the diameters of the branches’ teeth are about 300 nm. The growth mechanism of the ultralong microbushes and the catalytic behavior of the copper are discussed. Room temperature photoluminescence spectra of the ultralong ZnO microbushes showed a UV emission band at about 388 nm and wide green emissions at around 525 nm. It may be very attractive for commercial applications such as electrical devices, microelectromechanical systems and sensors.
Article
The special flower-like Pd-loaded indium oxide (In2O3) hierarchical microstructures with different Pd contents were successfully synthesized by a hydrothermal method, showing the features dimension of 5–7 μm diameter and 30 nm thick nanosheets. Developed NO2 sensors based on 1 mol% Pd-loaded In2O3 hierarchical microstructures demonstrated excellent NO2 detection at the ppb levels at lower operating temperature of 110 °C. These sensors also exhibited high response, fast response (180 s) and recovery (90 s) time and great reliability as well as simplicity in fabrication. Furthermore, selective detection of NO2 can be readily achieved with sensors attached with 1 mol% Pd-loaded In2O3 even with other common chemicals such as ethanol, CO, CH4 and H2 around. The electron depletion theory was used to explain the enhanced gas sensing mechanism.
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Nitrogen dioxide (NO 2 ), a hazardous gas with acidic nature, is continuously being liberated in the atmosphere due to human activity. The NO 2 sensors based on traditional materials have limitations of high-temperature requirements, slow recovery, and performance degradation under harsh environmental conditions. These limitations of traditional materials are forcing the scientific community to discover future alternative NO 2 sensitive materials. Molybdenum disulfide (MoS 2 ) has emerged as a potential candidate for developing next-generation NO 2 gas sensors. MoS 2 has a large surface area for NO 2 molecules adsorption with controllable morphologies, facile integration with other materials and compatibility with internet of things (IoT) devices. The aim of this review is to provide a detailed overview of the fabrication of MoS 2 chemiresistance sensors in terms of devices (resistor and transistor), layer thickness, morphology control, defect tailoring, heterostructure, metal nanoparticle doping, and through light illumination. Moreover, the experimental and theoretical aspects used in designing MoS 2 -based NO 2 sensors are also discussed extensively. Finally, the review concludes the challenges and future perspectives to further enhance the gas-sensing performance of MoS 2 . Understanding and addressing these issues are expected to yield the development of highly reliable and industry standard chemiresistance NO 2 gas sensors for environmental monitoring.
Article
In this study, a highly sensitive nitrogen dioxide (NO2) gas sensor based on titanium dioxide nanowires (TiO2-NWs) was successfully fabricated using a hydrothermal method. The structure of the sensor was investigated using scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The sensor properties were also investigated. We found that the TiO2-NW sensor showed excellent selectivity and high sensitivity down to 100 ppm NO2 at room temperature with rapid response and recovery times of 10 s and 19 s, respectively. Additionally, the TiO2-NWs displayed good repeatability and selectivity against various interfering gases such as NH3, H2, and CH4. We propose a possible mechanism for NO2 sensing by the TiO2-NW sensor.
Article
A high performance photocatalyst based on heterostructure using ZnO nanoparticles (NPs) decorating mesoporous anatase−TiO2 (B) biphase TiO2 nanowires (NWs) was synthesized by a facile water bath reflux method. The morphology, structure, and optical property of the prepared hybrid photocatalyst were well characterized. The results showed that the mesoporous biphase TiO2 NWs consisted of TiO2 (B) and anatase phase. When ZnO NPs was loaded on the surface of biphase TiO2 NWs, a heterojunction was formed between TiO2 NWs and ZnO NPs that could favor the separation of photogenerated electron-hole pairs. The TiO2-ZnO heterojunction exhibited remarkably enhanced photocatalytic activity and excellent stability for both the dyes degradation and H2 evolution compared with those of TiO2 NWs. The heterojunction with a 20 wt.% ZnO content exhibited the highest photocatalytic activity and the reaction rate constant was about 4.2 and 1.3 times higher than that of TiO2 NWs for dye degradation and H2 evolution, respectively. The main active species were found to be O2•- and •OH by electron paramagnetic resonance technique. This work may open a promising venue in producing highly-efficient heterojunction photocatalyst with special structure for large-scale environment and energy applications.
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In this work, a microfabricated metal oxide (MOX) array sensor based on nanosized SnO–SnO2 sensitive material was proposed. To maximize detection response and reduce power consumption, sensitive units supported by a multi-layer beam were suspended in center of micro reaction cell which could greatly improve thermal isolation. The sensitive units were fabricated with nanosized SnO–SnO2 sensitive material, and Au-doped sensitive material was proposed which was able to greatly increase selectivity and sensitivity of sensitive film. The results demonstrate that the sensitive unit has good specificity of benzene, and the MOX array sensor was able to detect benzene with an extremely low concentration, in which the lowest detectable concentration was less than 5 ppb.
Article
In the present study, we have deposited hierarchical flower-like microstructured zinc oxide (ZnO) thin films directly on a glass substrate by using the simplistic aqueous chemical route for different concentrations of triethanolamine (TEA) which acted like a complexing agent. The as-synthesized ZnO thin films were subsequently annealed at 300 °C and are characterized with characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and electrical resistivity. The hexagonal wurtzite crystal structure of as-synthesized ZnO thin films was confirmed by their XRD patterns and the well-resolved ZnO flowers-like morphology was revealed from the FESEM micrographs. From FESEM images it can be seen that the ZnO flower is composed of dozens of nanorods originating from the same core in a symmetric fashion with an average diameter of around 180-300 nm. The flower-like morphology was obtained at 0.3 M TEA concentration. Due to its hierarchical structure, the deposited ZnO thin films were employed for multiple applications such as gas sensing and anti-microbial activity. The ZnO thin films with micro-flowers like morphology showed the maximum gas sensor sensitivity ∼64.50 at 150 °C for 100 ppm of NO 2 gas. Moreover, the bacteria were completely destroyed in the presence of as-deposited ZnO thin films.
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A thermoelectric nitrogen dioxide gas sensor developed based on Fe2O3 nanowires is capable of outputting DC voltages of tens of millivolts, which facilitates signal amplification and processing. In this paper, the Fe2O3 nanowires were synthesized in a horizontal electrical furnace under air pressure at 600°C for 8 h. SEM and XRD techniques as well as gas sensing performance of prepared sensors towards NO2 gas were studied. The gas sensing studies demonstrate that, The voltage signal, corresponding to the 10 ppm of NO2 gas was 17.9 mV, the response time and the recovery time were 23 s and 17 s, respectively, when the temperature difference was set at 120°C. Furthermore, the plausible response mechanism of the thermoelectric gas sensor based on Fe2O3 was discussed that demonstrates a feasible method for nitrogen dioxide detection.
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During the past decade, the essential implications of nanotechnology have been proven and it has been established as emerging technology providing new directions of modern research broadly defined as “nanoscale science and technology”. With the birth of nanoscience and nanotechnology in the last two decades, the most exciting and fastest growing fields were formed to create the new functional nanoscale dimensions systems and materials. Nanotechnology; research development and commercialization offer high revolutionary instruments and techniques to investigate the material properties at the nanoscale. Such technological advances have inspired new pioneering experiments that have revealed new physical properties and effects of matter at an intermediate level between atomic and bulk. Due to the potential technological applications for nanomaterials, they have become the focus of intense investigations. These materials with different sizes and shapes, such as nanorods and nanocomposites, with identical compositions often possess special properties. The purpose of this book is to provide a perspective on the current status of nanorods and nanocomposites with the contents provided by the scientists and researchers in the related professions. As such, this book is categorized into Part I, with an emphasis on nanorods, and Part II, with the specific importance of nanocomposites. The book, NANORODS and NANOCOMPOSITES, provides the reader (students, scientists, and engineers working in the field of materials science and condensed matter physics) with an overview of the advances made on the synthesis of nanorods and nanocomposite materials and their emerging applications for a better lifestyle. The nanorods section covers advanced materials (metals, semiconductors, and organic materials) for nanorods, and growth/synthesis techniques of nanorods. There are six chapters in this section, which covers synthesis, characterizations and applications of gold nanorods, semiconducting oxide nanorods, and some composite nanorods. Emerging applications of the nanorods in various fields ranging from optoelectronic devices, sensors, and electro-optical devices are presented in the chapters. As all the contributing authors of the book are active researchers, they provide an up-to-date summary of their research topics. The readers will be presented with all the recent advances on the topics covered in this book. At the end of each chapter, important outputs of the topic covered and future research directions are provided. The perspective of the research on a special kind of nanostructures, nanorods, is presented in the Prologue. There is one chapter to introduce the growth process of nanorods and cover the important strategies developed for the growth of various nanorods. Alsultan et al. presented the growth strategies of carbon, ZnO, gold, and magnetic nanorods. In addition, there are four chapters that cover the gas sensing application of ZnO written by Wang et al.; application of carbon nanorods in EO/IR detectors written by Sood et al.; a theoretical study on the structural and melting properties of gold nanorods written by Rida et al.; and metallo-dielectric colloidal films by Ana et al. The nanocomposites section covers advanced nanocomposites. There are eight chapters in this section, which covers graphene, graphene like, polymer, and epoxy nanocomposites. In addition, the mechanical and tribological properties of epoxy nanocomposites have also be considered. Nanocomposite-based sensors are presented in one chapter by Baiju. The kinetic features of epoxy nanocomposites synthesis process is evaluated by Prof. Irzhak Vadim. Also, the classification and application of electrospinning methods are covered. One of the chapters deals with the study of the electrolysis synthesis of copper matrix nanocomposites developed for the fabrication of nano-particulate bulk materials. The editors hope that this book will contribute to increasing the availability of and access to new developments of nanomaterial synthesis and on nanostructureproperty relationships in a specific way, especially in nanorods and nanocomposites
Article
We successfully synthesized ultra-long ZnO nanocombs and nanobelts on Cu substrate for the first time. The morphology and structure of the as-grown ZnO nanocombs and nanobelts were characterized by means of scanning electron microscopy and X-ray diffraction. Scanning electron microscopy images show that Cu substrate is red and not oxidized, X-ray diffraction studies support Cu is present during the growth process, and we explained the growth mechanism for ultra-long ZnO nanostructures.
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In the present work an effort has been made to synthesize nanocrystalline composites (NCC) of Zinc oxide and Tin oxide (ZSO) using chemical route for efficient sensing of NO2 gas at lower operating temperature. The structural, microstructural and optical information have been revealed by X-ray diffraction (XRD), Atomic force microscopy (AFM) and UV-Visible spectroscopy respectively. Sensor structure showed a better sensing response (S ~ 6.64×102) at a relatively low operating temperature of 70 °C for 20 ppm NO2 gas with an average response time of about 2 min. The sensing response characteristics for NO2 gas has been compared with corresponding results obtained for pure SnO2 and ZnO thin film based sensor structure.
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In situ patterned zinc oxide (ZnO) thin films were prepared by precipitation of Zn(NO3)2/urea aqueous solution and by microcontact printing of self-assembled monolayers (SAMs) on Al/SiO2/Si substrates. The visible precipitation of Zn(OH)2 from the urea containing Zn(NO3)2 solution was enhanced by increasing the reaction temperature and the amount of urea. The optimized condition for the ZnO thin films was found to be the Zn(NO3)2/urea ratio of 1/8, the precipitation temperature of 80 °C, the precipitation time of 1 h and the annealing temperature of 600 °C, respectively. SAMs are formed by exposing Al/SiO2/Si to solutions comprising of hydrophobic octadecylphosphonic acid (OPA) in tetrahydrofuran and hydrophilic 2-carboxylethylphosphonic acid (CPA) in ethanol. The ZnO thin film was then patterned with the heat treatment of Zn(OH)2 precipitated on the surface of hydrophilic CPA. The ZnO gas sensor was exposed to different concentrations of C3H8 (5000 ppm), CO (250 ppm) and NO (1000 ppm) at elevated temperatures to evaluate the gas sensitivity of ZnO sensors. The optimum operating temperatures of C3H8, CO and NO gases showing the highest gas sensitivity were determined to be 350, 400 and 200 °C, respectively.
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A conductometric H<sub>2</sub>, NO<sub>2</sub>, and hydrocarbon gas sensor based on single-crystalline zinc oxide (ZnO) nanobelts has been developed. The nanobelt sensitive layer was deposited using a radio frequency (RF) magnetron sputterer. The microcharacterization study reveals that the nanobelts have a single crystal hexagonal structure with average thickness and width of about 10 and 50nm, respectively. The sensor was exposed to H<sub>2</sub>, NO<sub>2</sub> and propene gases at operating temperatures between 150 degC and 450 degC. The study showed that optimum operating temperatures for the sensor are in the range of 300 degC-400degC for H<sub>2</sub>, 300 degC-350 degC for NO<sub>2</sub>, and 350 degC-420 degC for propene sensing
Article
ZnO thin films have been deposited onto the glass substrates by the sol-gel spin coating method at different chuck rotation rates. This method was used for the preparation of thin films of the important semiconductors H-VI. The effect of deposition parameters on the structural, optical and electrical properties of the ZnO thin films was investigated. Zinc acetate dehydrate, 2-methoxethanol and monoethanolamine (MEA) were used as a starting material, solvent and stabilizer, respectively. Thermogravimetric analysis (TGA) of the dried gel showed that weight loss continued until 300 degrees C. The crystal structure and orientation of the ZnO thin films were investigated by X-ray diffraction (XRD) patterns, The grain size of the films was calculated using the Scherrer formula. The optical absorbance and transmittance measurements were recorded by using a double beam spectrophotometer with an integrating sphere in the wavelength range 190-900 nm. The optical absorption studies reveal that the transition is direct band gap energy. The optical band gaps and Urbach energies of the thin films were determined. The I-V plots of the ZnO thin films were carried out in dark and under UV-illumination. The obtained ZnO thin films can be used as a photovoltaic material.
Article
ZnO thin films have been deposited onto the glass substrates by the sol-gel spin coating method at different chuck rotation rates. This method was used for the preparation of thin films of the important semiconductors II-VI. The effect of deposition parameters on the structural, optical and electrical properties of the ZnO thin films was investigated. Zinc acetate dehydrate, 2-methoxethanol and monoethanolamine (MEA) were used as a starting material, solvent and stabilizer, respectively. Thermogravimetric analysis (TGA) of the dried gel showed that weight loss continued until 300°C. The crystal structure and orientation of the ZnO thin films were investigated by X-ray diffraction (XRD) patterns. The grain size of the films was calculated using the Scherrer formula. The optical absorbance and transmittance measurements were recorded by using a double beam spectrophotometer with an integrating sphere in the wavelength range 190-900 nm. The optical absorption studies reveal that the transition is direct band gap energy. The optical band gaps and Urbach energies of the thin films were determined. The I-V plots of the ZnO thin films were carried out in dark and under UV-illumination. The obtained ZnO thin films can be used as a photovoltaic material.
Article
In the present work, thick film of nanostructured zinc ferrite was prepared by screen printing method and its liquefied petroleum gas (LPG) sensing properties were investigated. The structural and surface morphological characterisations of the sample were analysed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The minimum crystallite size of ZnFe2O4 calculated from Scherrer’s formula is found to be 4 nm. SEM images exhibit the porous nature of the sensing material with a number of active sites. Optical characterisation of the film was carried out by ultraviolet–visible spectrophotometer. The estimated value of band gap of the film was found 1.91 eV. The LPG sensing properties of the zinc ferrite film were investigated at room temperature for different vol.% of LPG. The variations in electrical resistance of the film were measured with the exposure of LPG as a function of time. The maximum values of sensitivity and percentage sensor response were found 16 and 1785, respectively, for 5 vol.% of LPG. These experimental results show that nanostructured zinc ferrite is a promising material for LPG sensor.
In the present work chemical route method was used to deposit different catalyst (Pt and Pd) doped SnO2 thin films. After careful study of their physical properties, SnO2 thin films with suitable growth conditions were selected for probing their response to LPG and other common household gases. The prepared all sensor structures, Pt-doped SnO2 (SnO2-Pt) based sensor was found to give high sensing response of about 89 towards high concentration 1000 ppm of LP gas at operating temperature of 200 °C with response (∼20 sec) and recovery (∼27 sec) time. The structural, morphological and optical properties of the prepared sensor structures have been studied by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and UV-Visible spectroscopy.
Nanocrystalline composite thin films of Zinc oxide and Tin oxide (ZSO) have been synthesized using chemical route for the efficient trace level (20 ppm) detection of NO2 gas at lower operating temperature. The prepared ZSO sensor structure showed a high sensing response of about 1.578×103 towards 20 ppm of NO2 gas at a lower operating temperature of 70 °C with an average response and recovery time of 3.91 min. and 6.91 min. respectively. The structural, optical and surface morphological properties of the ZSO composite thin film have been studied by X-ray diffraction (XRD), UV-Visible spectroscopy, Atomic Force microscopy (AFM) images and have also been correlated with the observed enhancement in gas sensing properties of prepared sensor structure.
Article
Flexible, electrically conducting, high temperature stable ceramics with very high porosities are fabricated from interpenetrated metal oxide nano-microstructures in a versatile manner in a novel flame transport synthesis approach. The Young's modulus of these networks can be tuned from wool type to rubber like based on the density, type and interconnections of the building blocks. Semiconducting behavior allows multifunctional applications like the electrical readout of the mechanical history.
Article
Two flame-based synthesis methods- burner flame transport synthesis (B-FTS) and crucible flame transport synthesis (C-FTS) for fabricating ZnO nanostructure based UV photodetectors are presented. The B-FTS allows rapid growth of ZnO nanotetrapods and in situ bridging them into electrical contacts. The photodetector made from interconnected ZnO nanotetrapod networks exhibit fast response/recovery times and high current ratio under UV illuminations.
Article
Sensing characteristics of the drop-cast thin films of poly(3-hexylthiophene) (P3HT), ZnO nanowires, and P3HT:ZnO-nanowire hybrids with different compositions have been studied for various gases, namely, NO2, H2S, NH3, CH4, and CO. At room temperature, pure P3HT and ZnO-nanowire films were highly sensitive to NO2 and H2S, moderately sensitive to CO, and nearly insensitive to NH3 and CH4. P3HT:ZnO-nanowire hybrid films, with increasing ZnO-nanowire content, exhibited gradual enhancement in NO2 sensitivity, while reducing sensitivity for H2S. P3HT:ZnO-nanowire (1:1 ratio by weight) films were found to be highly selective for NO2. Plausible mechanisms explaining the enhanced NO2 selectivity by hybrid films are discussed.
Article
In this work, thin films of zinc oxide (ZnO) for gas-sensor applications were deposited on platinum coated alumina substrate, using electrostatic spray deposition (ESD) technique. As precursor solution zinc acetate in ethanol was used. Scanning electron microscopy (SEM) evaluation showed a porous and homogeneous film morphology and the energy dispersive X-ray analysis (EDX) confirmed the composition of the films with no presence of other impurities. The microstructure studied with X-ray diffraction (XRD) and Raman spectroscopy indicated that the ZnO oxide films are crystallized in a hexagonal wurtzite phase. The films showed good sensitivity to 1 ppm nitrogen dioxide (NO2) at 300 °C while a much lower sensitivity to 12 ppm hydrogen sulphide (H2S).
Article
Nitrogen dioxide (NO2) sensors based on sprayed zinc oxide (ZnO) thin films have been prepared. The effect of the film thickness and the In-doping on the sensor performance (sensor response and resistance) is analyzed. By adding 3 wt.% of indium nitrate to the spraying solution it is possible to enhance the film–gas response to 5 ppm of NO2 at 275 °C. At the same time the film resistance is sensibly reduced. The film crystallographic structure, morphology and additive content are studied by means of X-ray Diffraction, Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy and Atomic Force Microscopy. The possible sensitization mechanism is discussed.