Hyejoon Kheel

CO gas sensing properties of In4Sn3O12 and TeO2 composite nanoparticle sensors

A simple hydrothermal route was used to synthesize In4Sn3O12 nanoparticles and In4Sn3O12-TeO2 composite nanoparticles, with In(C2H3O2)3, SnCl4, and TeCl4 as the starting materials. The structure and morphology of the synthesized nanoparticles were examined by X-ray diffraction and scanning electron microscopy (SEM), respectively. The gas-sensing properties of the pure and composite nanoparticles toward CO gas were examined at different concentrations (5-100ppm) of CO gas at different temperatures (100-300°C). SEM observation revealed that the composite nanoparticles had a uniform shape and size. The sensor based on the In4Sn3O12-TeO2 composite nanoparticles showed stronger response to CO than its pure In4Sn3O12 counterpart. The response of the In4Sn3O12-TeO2 composite-nanoparticle sensor to 100ppm of CO at 200°C was 10.21, whereas the maximum response of the In4Sn3O12 nanoparticle sensor was 2.78 under the same conditions. Furthermore, the response time of the composite sensor was 19.73s under these conditions, which is less than one-third of that of the In4Sn3O12 sensor. The improved sensing performance of the In4Sn3O12-TeO2 nanocomposite sensor is attributed to the enhanced modulation of the potential barrier height at the In4Sn3O12-TeO2 interface, the stronger oxygen adsorption of p-type TeO2, and the formation of preferential adsorption sites.

Hydrogen gas sensing of Co3O4-Decorated WO3 nanowires

Co3O4 nanoparticle-decorated WO3 nanowires were synthesized by the thermal oxidation of powders followed by a solvothermal process for Co3O4 decoration. The Co3O4 nanoparticle-decorated WO3 nanowire sensor exhibited a stronger and faster electrical response to H2 gas at 300 °C than the pristine WO3 nanowire counterpart. The former showed faster response and recovery than the latter. The pristine and Co3O4-decorated WO3 nanowire sensors showed the strongest response to H2 gas at 225 and 200 °C, respectively. The Co3O4-decorated WO3 nanowire sensor showed selectivity for H2 gas over other reducing gases. The enhanced sensing performance of the Co3O4-decorated WO3 nanowire sensor was explained by a combination of mechanisms: modulation of the depletion layer width forming at the Co3O4-WO3 interface, modulation of the potential barrier height forming at the interface, high catalytic activity of Co3O4 for the oxidation of H2, active adsorption of oxygen by the Co3O4 nanoparticle surface, and creation of more active adsorption sites by Co3O4 nanoparticles.

Room-temperature hydrogen gas sensing properties of the networked Cr2O3-functionalized Nb2O5 nanostructured sensor

Cr2O3-functionalized Nb2O5 nanoparticles were synthesized via a facile hydrothermal route. The multiple-networked Cr2O3-functionalized Nb2O5 nanostructured sensor showed enhanced H2 gas sensing performance compared to its pristine Nb2O5 nanostructure counterpart. The Cr2O3-functionalized Nb2O5 nanostructure sensor showed responses of 5.24 to 2 ppm of H2 at room temperature, whereas the pristine Nb2O5 nanoparticle sensors showed responses of 2.29. The former also exhibited a faster response to H2. The multiple-networked pristine and Cr2O3-functionalized Nb2O5 nanostructured sensors were stronger and much shorter, respectively, than other nanomaterial-based Schottky diode-type sensors and Nb2O5-based Schottky diode-type sensors. The underlying mechanism for the enhanced sensing performance of the Cr2O3-functionalized Nb2O5 nanostructured sensor towards H2 gas is discussed in detail. Particular emphasis is placed on the role of the Cr2O3-Nb2O5 p-n junction in the Cr2O3-functionalized Nb2O5 nanostructure sensor.

Acetone gas sensing properties of a multiple-networked Fe 2 O 3 -functionalized CuO nanorod sensor

Fe2O3-decorated CuO nanorods were prepared by Cu thermal oxidation followed by Fe2O3 decoration via a solvothermal route. The acetone gas sensing properties of multiple-networked pristine and Fe2O3-decorated CuO nanorod sensors were examined. The optimal operating temperature of the sensors was found to be 240°C. The pristine and Fe2O3-decorated CuO nanorod sensors showed responses of 586 and 1,090%, respectively, to 1,000 ppm of acetone at 240°C. The Fe2O3-decorated CuO nanorod sensor also showed faster response and recovery than the latter sensor. The acetone gas sensing mechanism of the Fe2O3-decorated CuO nanorod sensor is discussed in detail. The origin of the enhanced sensing performance of the multiple-networked Fe2O3-decorated CuO nanorod sensor to acetone gas was explained by modulation of the potential barrier at the Fe2O3-CuO interface, highly catalytic activity of Fe2O3 for acetone oxidation, and the creation of active adsorption sites by Fe2O3 nanoparticles.

Hydrogen gas detection of Nb2O5 nanoparticle-decorated CuO nanorod sensors

Pristine and Nb2O5 nanoparticles-decorated CuO nanorods were prepared successfully by a two step process: the thermal evaporation of a Cu foil and the spin coating of NbCl5 solution on CuO nanorods followed by thermal annealing. X-ray diffraction was performed to examine the structure and purity of the synthesized nanoatuctures. Scanning electron microscopy was used to examine the morphology and shape of the nanostuctures. The Nb2O5 nanoparticles-decorated CuO nanorod sensor showed responses of ~217.05-862.54%, response times of ~161-199 s and recovery times of ~163-171 s toward H2 gas with concentrations in a range of 0.5 - 5% at the optimal working temperature of 300 °C. The Nb2O5 nanoparticle-decorated CuO nanorod sensor showed superior sensing performance to the pristine CuO nanorod sensor for the same H2 concentration range. The underlying mechanism for the enhanced hydrogen sensing performance of the CuO nanorods decorated with Nb2O5 nanoparticles is discussed.