Konjac glucomannan-templated synthesis of three-dimensional NiO nanostructures assembled from porous NiO nanoplates for gas sensors.

Biopolymer template synthesis has attracted extensive interest for fabricating highly porous metal oxide nanostructures. In this report, a green template-based approach for the synthesis of three-dimensional (3D) NiO nanostructures assembled from porous NiO nanoplates is introduced using a konjac glucomannan (KGM) template. The Ni-KGM composites, which were formed by the immersion of KGM nanofibrils in nickel nitrate solution, were annealed in air at 600 °C to obtain the highly porous NiO nanoplates. The KGM nanofibrils were used as a sacrificial template, which was combusted at a high temperature for the formation of the porous nanostructures. The gas sensor properties of the porous NiO architecture were systematically investigated with four reduced gases including hydrogen sulfide, ammonia, carbon monoxide and hydrogen. The results indicate that the porous NiO nanoplates show a good detection of hydrogen sulfide with a rapid response and recovery speed at low concentrations.

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.

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.

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.