As a hormone that determinates the level of fruit ripeness, ethylene concentration monitoring plays an important role in the agricultural field. One of the techniques that can be used to detect ethylene concentration is the sensing method. Zinc oxide (ZnO) is a multipurpose metal oxide semiconductor with a wide application in sensing area. Here, we use a ZnO-based flexible sensor to identify the presence of ethylene gas at certain concentrations. The as-synthesized ZnO layers were deposited on a polyethylene terephthalate-indium doped tin oxide (PET-ITO) flexible substrate using a simple electrochemical deposition method. To enhance the performance of the ethylene sensor, a small amount of silver (Ag) was added to the seeding solution. From the study, it was revealed that the ZnO-Ag layers were able to identify the presence of ethylene gas at the lowest concentration of 29 ppm. The most optimal result was obtained using 1 mM Ag. This layer demonstrated a response of 17.2% and 19.6% of ethylene gas at concentrations of 29 and 50 ppm, with recovery times of four and eight minutes, respectively.
Among semiconductors, zinc oxide (ZnO) has received great attention due to its wide band-gap and high electron mobility, resulting in various strategic applications. Controlling the physical properties of ZnO is therefore a critical issue in the fabrication of related electronic and optical devices. In this study, ZnO nanorods layers were grown on an ITO glass substrate via chemical bath deposition at low temperature. Prior to the growing process, the layers were deposited using a spin-coating technique. The seeding solution was made by dissolving zinc nitrate tetrahydrate and hexamethylene tetraamine in cold water (0 o C) for an hour using a cooler bath. The as-synthesized ZnOs were further subjected to different post-hydrothermal treatment series at a temperature of 150 o C for three hours at atmospheric pressure and at 100°C for one hour under one bar of nitrogen gas (N 2 ) pressure. The characterization was performed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and UV-Vis spectroscopy. The SEM results showed that the ZnO nanorods were grown as a vertically aligned hexagonal structure, while the XRD patterns showed a high intensity at the (002) plane. On the basis of investigation, it was found that under post-hydrothermal treatment at 150 o C for three hours with atmospheric pressure, the synthesis procedure resulted in nanostructures in the form of ZnO rods. Meanwhile, post-hydrothermal treatment at 100°C for one hour under one bar of nitrogen gas (N 2 ) produced ZnO rods and tubes. In general, the posthydrothermal process provided a high degree of crystallinity. The optimum ZnO layer was obtained after post-hydrothermal treatment at 150 o C for three hours at atmospheric pressure, with a crystallite size and band-gap energy of ~18 nm and 3.20 eV, respectively.
Zinc Oxide (ZnO) is an important semiconductor material due to its broad applications, such as in the fields of electronics, optoelectronics, photocatalysts, and solar cells. The main purpose of this work was to investigate the effect of pressure in post-hydrothermal treatment on crystallinity enhancement, crystallite growth, and band gap reduction of ZnO nanoparticles, which could be expected to improve their performance as the semiconductor oxide layer in the dye-sensitized solar cell application. For this purpose, ZnO nanoparticles have been successfully synthesized through the precipitation method, followed by a sequence of thermal treatments including drying, calcination, and Post-hydrothermal Treatment (PHT). For increasing the crystallinity of ZnO nanoparticles, PHT was carried out with a pressure variation of 1 and 3 bar. The resulting nanoparticles were further characterized with X-Ray Diffraction (XRD), Ultra-Violet Visible (UV-Vis) spectroscopy and a Scanning Electron Microscope (SEM). The study showed that by increasing the PHT pressure from 1 to 3 bar caused an adverse effect on the crystallinity, i.e. the crystallite size of ZnO nanoparticles slightly decreased from 27.42 to 26.88 nm. This was expected to be due to the increase of the boiling point of water causing less effective of vapor generated to improve the crystallinity by a cleavage mechanism on the inorganic framework. The band gap energy (E g ), however, was found to increase slightly from 3.25 to 3.26 eV, respectively. Considering the obtained properties, ZnO nanoparticles in this study have the potential to be used as the semiconductor oxide layer in the dye-sensitized solar cells.
As an emerging n-type semiconductor, ZnO has been widely applied in sensor area. In this study, we prepared an ethylene sensor using ZnO layer on FTO glass substrate. The seed layer was deposited using simple electrodeposition method using voltage of -1.1 V for 2 hours in cold bath (6°C). The ZnO layer was further grown using CBD technique at 90°C for 2 hours. In order to observe the effect of structural manipulation on the sensor performance, some of the ZnO layer samples were undergoing hydrothermal treatment at 100ºC for 1 hour under 1 bar N2 gas. After annealing process, all ZnO layers were exposed with 50 ppm ethylene gas in closed chamber. Based on the results, it is shown that the optimum ZnO layer has been successfully identified the ethylene gas in concentration of 50 ppm, with response value of 2.40% at 200°C.
ZnO nanorods were deposited on ITO glass substrate via chemical bath deposition at low temperature of 90°C. The seeding solution was made by dissolving zinc nitrate tetrahydrate and methenamine in cool water (5°C). The as-synthesized ZnOs were further subjected to post-hydrothermal treatment series.The results of scanning electron microscope (SEM) studies showed that the ZnO nanorods were grown as vertically-aligned hexagonal structure, while x-ray diffraction (XRD) patterns showed a high intensity of [002] peak. The absorption spectra of the as-synthesized sample indicated a strong absorption peak near the UV region. After post-hydrothermal treatments, the absorption was slightly shifted to visible region. The ZnO nanorods sample derived from post-hydrothermal treatment at 150°C for 12 hours has the largest crystallite size of 269.402 nm and the lowest band gap energy, Egvalue of 3.205 eV.
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