Do Dang Trung

Effective decoration of Pd nanoparticles on the surface of SnO2 nanowires for enhancement of CO gas-sensing performance

Decoration of noble metal nanoparticles (NPs) on the surface of semiconducting metal oxide nanowires (NWs) to enhance material characteristics, functionalization, and sensing abilities has attracted increasing interests from researchers worldwide. In this study, we introduce an effective method for the decoration of Pd NPs on the surface of SnO2 NWs to enhance CO gas-sensing performance. Single-crystal SnO2 NWs were fabricated by chemical vapor deposition, whereas Pd NPs were decorated on the surface of SnO2 NWs by in situ reduction of the Pd complex at room temperature without using any linker or reduction agent excepting the copolymer P123. The materials were characterized by advanced techniques, such as high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Pd NPs were effectively decorated on the surface of SnO2 NWs. As an example, the CO sensing characteristics of SnO2 NWs decorated with Pd NPs were investigated at different temperatures. Results revealed that the gas sensor exhibited excellent sensing performance to CO at low concentration (1-25ppm) with ultrafast response-recovery time (in seconds), high responsivity, good stability, and reproducibility.

Selective detection of carbon dioxide using LaOCl-functionalized SnO2 nanowires for air-quality monitoring

In spite of the technical important of monitoring CO(2) gas by using a semiconductor-type gas sensor, a good sensitive and selective semiconductor CO(2) sensor has been not realized due to the rather unreactive toward CO(2) of conventional semiconductor metal oxides. In this work, a novel semiconductor CO(2) sensor was developed by functionalizing SnO(2) nanowires (NWs) with LaOCl, which was obtained by heat-treating the SnO(2) NWs coating with LaCl(3) aqueous solution at a temperature range of 500-700°C. The bare SnO(2) NWs and LaOCl-SnO(2) NWs sensors were characterized with CO(2) (250-4,000 ppm) and interference gases (100 ppm CO, 100 ppm H(2), 250 ppm LPG, 10 ppm NO(2) and 20 ppm NH(3)) at different operating temperatures for comparison. The SnO(2) NWs sensors functionalized with different concentrations of LaCl(3) solution were also examined to find optimized values. Comparative gas sensing results reveal that LaOCl-SnO(2) NWs sensors exhibit much higher response, shorter response-recovery and better selectivity in detecting CO(2) gas at 400°C operating temperature than the bare SnO(2) NWs sensors. This finding indicates that the functionalizing with LaOCl greatly improves the CO(2) response of SnO(2) NWs-based sensor, which is attributed to (i) p-n junction formation of LaOCl (p-type) and SnO(2) nanowires (n-type) that led to the extension of electron depletion and (ii) the favorable catalytic effect of LaOCl to CO(2) gas.

Comparative study on CO2 and CO sensing performance of LaOCl-coated ZnO nanowires

Carbon dioxide (CO(2)) and carbon monoxide (CO) emissions from industries and combustion fuels such as coal, oil, hydrocarbon, and natural gases are increasing, thus causing environmental pollution and climate change. The selective detection of CO(2) and CO gases is important for environmental monitoring and industrial safety applications. In this work, LaOCl-coated ZnO nanowires (NWs) sensors are fabricated and characterized for the detection of CO(2) (250-4000 ppm) and CO (10-200 ppm) gases at different operating temperatures. The effects of the LaCl(3) coating concentration and calcination temperature of the sensors are studied. They are found to have a strong influence on the sensing performance to CO(2) gas, but a relatively slight influence on that to CO. The LaOCl coating enhances the response and shortens the response and recovery times to CO(2) compared with those to CO. The enhanced response of the LaOCl-coated ZnO NW sensors is attributed to the extension of the electron depletion layer due to the formation of p-LaOCl/n-ZnO junctions on the surfaces of the ZnO NWs.

Comparison of NO2 Gas-Sensing Properties of Three Different ZnO Nanostructures Synthesized by On-Chip Low-Temperature Hydrothermal Growth

Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nanostructures were confirmed to have the same crystal type, but their dimensions and densities differed. The NO2 gas-sensing performance of the three ZnO nanostructures was investigated at different operation temperatures. ZnO nanorods had the lowest response to NO2 along with the longest response/recovery time, whereas sparse ZnO nanowires had the highest response to NO2 and the shortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200°C. The current–voltage curves of the three ZnO nanostructures were obtained at various temperatures, and the results clearly showed that sparse ZnO nanowires did not have the linear characteristics of the others. Analysis of this phenomenon in connection with the highly sensitive behavior of sparse ZnO nanowires is also presented.