Abstract
The growth of uniformly distributed and densely packed array of zinc oxide (ZnO) nanorods (NRs) and nanorods (NRs)/nanopolypods (NPPs) was successfully achieved through microwave-assisted chemical route at low temperature. The ZnO NRs and NRs/NPPs were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), and UV-Vis absorption spectroscopy. The ZnO NRs were of 100–150 nm diameter and 0.5–1 μm length, while the NPPs were of diameter about 150–200 nm and 1.5–2 μm pod length. The prepared films are polycrystalline in nature and highly oriented along (002) plane with a hexagonal wurtzite structure. These films were studied for the sensing properties of liquefied petroleum gas (LPG), oxygen, and hazardous explosives, that is, 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramines (RDX), in the temperature ranges of 25–425 °C and 100–200 °C, respectively. The grown nanostructure films showed reliable stable response to several on-off cycles, and reduction in sensor recovery time was found with the increase in temperature. ZnO NRs and NRs/NPPs showed better sensitivity and recovery time for both LPG and oxygen, as compared to the literature-reported results for ZnO thin films.
Highlights
Numerous materials have been reported to be usable as metal-oxide chemical sensors including both single-component (e.g., zinc oxide (ZnO), SnO2, WO3, TiO2, and Fe2O3) and multicomponent oxides (BiFeO3, MgAl2O4, SrTiO3, and Sr1−yCayFeO3−x)
Uniform array of aligned ZnO NRs with diameter of about 3100–150 nm and length of 0.5–1 μm and ZnO NRs/NPPs with pod diameter of about 150–200 nm and length of about 1.5–2 μm were grown on glass substrates with microwaveassisted wet chemical synthesis
The sensing study of ZnO NRs and ZnO NRs/NPPs samples showed that the sensor response (S) increases with temperature for both liquefied petroleum gas (LPG) and oxygen, while with the increase in gas concentration from 0.2 to 0.4 vol%, the sensor response increases gradually and attains saturation for LPG, while for oxygen, the response was found to be linear with the increase in gas concentration
Summary
Numerous materials have been reported to be usable as metal-oxide chemical sensors including both single-component (e.g., ZnO, SnO2, WO3, TiO2, and Fe2O3) and multicomponent oxides (BiFeO3, MgAl2O4, SrTiO3, and Sr1−yCayFeO3−x). The ZnO is useful to gas sensors because of its typical properties such as resistivity control over the range of 10−3 to 105 Ωm, high electrochemical stability, absence of toxicity, and abundant availability in nature [5] This is primarily due to the high mobility of conduction electrons in the material and good chemical and thermal stability under operating conditions. The mechanism for gas detection in these conductometric materials is based, in large part, on reactions that occur at the sensor surface, resulting in a change in the concentration of adsorbed oxygen. On the other hand reducing gas decreases the oxygen surface concentration and the surface resistance; magnitude of the response depends on the nature and concentration of the volatile molecules and on the type of metal oxide This change in conductivity is directly related to the amount of a specific gas present in the environment, resulting in a quantitative determination of gas presence and concentration. The gas (LPG and oxygen) and RDX and TNT explosive sensing properties of ZnO NRs and NRs/NPPs have been investigated
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