Abstract
Recently, one-dimensional (1D) nanostructures have attracted the scientific community attention as sensitive materials for conductometric chemical sensors. However, finding facile and low-cost techniques for their production, controlling the morphology and the aspect ratio of these nanostructures is still challenging. In this study, we report the vapor-liquid-solid (VLS) synthesis of one dimensional (1D) zinc oxide (ZnO) nanorods (NRs) and nanowires (NWs) by using different metal catalysts and their impact on the performances of conductometric chemical sensors. In VLS mechanism, catalysts are of great interest due to their role in the nucleation and the crystallization of 1D nanostructures. Here, Au, Pt, Ag and Cu nanoparticles (NPs) were used to grow 1D ZnO. Depending on catalyst nature, different morphology, geometry, size and nanowires/nanorods abundance were established. The mechanism leading to the VLS growth of 1D ZnO nanostructures and the transition from nanorods to nanowires have been interpreted. The formation of ZnO crystals exhibiting a hexagonal crystal structure was confirmed by X-ray diffraction (XRD) and ZnO composition was identified using transmission electron microscopy (TEM) mapping. The chemical sensing characteristics showed that 1D ZnO has good and fast response, good stability and selectivity. ZnO (Au) showed the best performances towards hydrogen (H2). At the optimal working temperature of 350 °C, the measured response towards 500 ppm of H2 was 300 for ZnO NWs and 50 for ZnO NRs. Moreover, a good selectivity to hydrogen was demonstrated over CO, acetone and ethanol.
Highlights
Nowadays, domestic or industrial accidents caused by dangerous chemical compounds and pollutants demonstrate the real need for early detection systems
Among different types of chemical sensors, conductometric sensors based on metal oxides (MOXs) materials have several advantages, such as easy integration with current electronics, low production cost and suitability for a potential miniaturization
To the best of our knowledge, the present work is the first study reporting the use of Cu as a catalyst for the synthesis of zinc oxide (ZnO) nanowires
Summary
Domestic or industrial accidents caused by dangerous chemical compounds and pollutants demonstrate the real need for early detection systems. Among different types of chemical sensors, conductometric sensors based on metal oxides (MOXs) materials have several advantages, such as easy integration (compatibility) with current electronics, low production cost and suitability for a potential miniaturization These sensors still have some limitations such as selectivity and sensitivity at low working temperatures [5]. Many of them improved the detection capability, either by optimizing the synthesis method by modifying the surface properties, decorating with other materials, adding dopants or manufacturing p-n junctions to improve sensitivity to target gases An example of the latter is reported by Kaur et al who have enhanced the NiO sensitivity and selectivity by synthesizing a NiO/ZnO heterojunction [6,7,8]. A new approach was provided by Hu-Jun Le et al for designing versatile hydrogen sensors using alloy@oxide core-shell, such as PdAualloy@ZnO core-shell, as sensing material with high response and excellent selectivity to hydrogen [11]
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