Chan Woong Na

Highly sensitive and selective trimethylamine sensor using one-dimensional ZnO–Cr2O3 hetero-nanostructures

Highly selective and sensitive detection of trimethylamine (TMA) was achieved by the decoration of discrete p-type Cr(2)O(3) nanoparticles on n-type ZnO nanowire (NW) networks. Semielliptical Cr(2)O(3) nanoparticles with lateral widths of 3-8 nm were deposited on ZnO NWs by the thermal evaporation of CrCl(2) at 630 °C, while a continuous Cr(2)O(3) shell layer with a thickness of 30-40 nm was uniformly coated on ZnO NWs at 670 °C. The response (R(a)/R(g): R(a), resistance in air; R(g), resistance in gas) to 5 ppm TMA of Cr(2)O(3)-decorated ZnO NWs was 17.8 at 400 °C, which was 2.4 times higher than that to 5 ppm C(2)H(5)OH and 4.3-8.4 times higher than those to 5 ppm p-xylene, NH(3), benzene, C(3)H(8), toluene, CO, and H(2). In contrast, both pristine ZnO and ZnO (core)-Cr(2)O(3) (shell) nanocables (NCs) showed comparable responses to the different gases. The highly selective and sensitive detection of TMA that was achieved by the deposition of semielliptical Cr(2)O(3) nanoparticles on ZnO NW networks was explained by the catalytic effect of Cr(2)O(3) and the extension of the electron depletion layer via the formation of p-n junctions.

Design of highly sensitive volatile organic compound sensors by controlling NiO loading on ZnO nanowire networks

Highly sensitive detection of volatile organic compounds, such as C2H5OH and HCHO, has been achieved by decorating p-type NiO nanoparticles on n-type ZnO nanowire networks, whereas the incorporation of Ni into the lattice of the ZnO nanowires deteriorated the gas sensing characteristics.

Ultrasensitive and selective C2H5OH sensors using Rh-loaded In2O3 hollow spheres

Rh-loaded In2O3 hollow spheres with diameters of ∼2 μm were prepared by a one-pot hydrothermal reaction of aqueous solution containing indium nitrate, rhodium chloride, and glucose and subsequent heat treatment at 500 °C for 2 h. The response to 100 ppm C2H5OH (Ra/Rg, Ra: resistance in air, Rg: resistance in gas) of 1.67 at% Rh-loaded In2O3 hollow spheres was 4748, which was ∼180 times higher than that of pure In2O3 hollow spheres. Rh loading decreased the temperature for maximum gas response from 475 °C to 371 °C, which also enhanced the selectivity to C2H5OH 15.1–24.7 times and recovery speed. The ultrahigh sensitivity and selectivity to C2H5OH, the lower sensing temperature, and the reduced recovery time were attributed to electronic interactions between Rh and In2O3 and the promotion of catalytic dissociation of C2H5OH into reactive gases.

Transformation of ZnO Nanobelts into Single-Crystalline Mn3O4 Nanowires

Single-crystalline Mn(3)O(4) nanowires were prepared using the vapor-phase transformation of ZnO nanobelts. Mn(3)O(4)-decorated ZnO nanobelts and ZnO-ZnMn(2)O(4) core-shell nanocables (NCs) were also obtained as reaction intermediates. Heteroepitaxial growth of tetragonal spinel Mn(3)O(4) (or ZnMn(2)O(4)) on wurtzite ZnO is a possible reason for the growth of single-crystalline Mn(3)O(4) nanowires. Growth interfaces are possibly formed between the wurtzite (101[overline]0)/(21[overline]1[overline]0) and spinel (1[overline]01)/(4[overline]11) planes. Various one-dimensional homonanostructures and heteronanostructures consisting of n-ZnO, p-Mn(3)O(4), and p-ZnMn(2)O(4) can be used to design high-performance gas sensors.

Controlled transformation of ZnO nanobelts into CoO/Co3O4 nanowires

Highly crystalline CoO and Co3O4 nanowires were prepared by vapor-phase conversion of ZnO nanobelts. The ZnO nanobelts were successfully transformed into highly crystalline CoO nanowires by thermal evaporation of CoCl2 at 700 °C in Ar, which were subsequently converted to Co3O4 nanowires by oxidative annealing at 600 °C. The reactions at 500 and 550 °C in 0.5% O2 led to the formation of well-defined oxide p–n junction nanostructures such as Co3O4-decorated ZnO nanobelts and ZnO–ZnCo2O4 core–shell nanocables, respectively, as the reaction intermediates. The evolutions of phase and residual Zn component during the conversion were investigated in relation to the reaction temperature and oxygen partial pressure.

Preparation of highly porous NiO–gadolinium-doped ceria nano-composite powders by one-pot glycine nitrate process for anode-supported tubular solid oxide fuel cells

Abstract Highly porous NiO–gadolinium-doped ceria (GDC) nano-composite powders are synthesized by a one-pot glycine nitrate process and applied to the fabrication of Ni–YSZ (yttria-stabilized zirconia)-supported tubular solid oxide fuel cells (SOFCs) with a cell configuration of Ni–YSZ/Ni/Ni–GDC/GDC/LSCF (La0.6Sr0.4Co0.2Fe0.8O3−δ)–GDC/LSCF. The power density of the cell is as high as 413 mW cm−2 at 600 °C, which is 1.37 times higher than that of an identically configured cell fabricated using ball milling-derived NiO–GDC powders (301 mW cm−2). The high porosity of the powders and the good mixing between the NiO and GDC primary nanoparticles due to the abrupt combustion of the precursors effectively suppress the densification, coarsening, and agglomeration of NiO and GDC particles during sintering, resulting in a highly porous Ni–GDC anode layer with good dispersion of Ni and GDC particles and a cell with significantly enhanced power density.

Chemical synthesis of CoO-ZnO: Co hetero-nanostructures and their ferromagnetism at room temperature

One-dimensional CoO–ZnO:Co hetero-nanostructures were prepared by vapor phase growth. Ferromagnetism was observed at room temperature, which is ascribed to Co diffusion into ZnO nanorods grown over CoO nanowires. Strong enhancement in green emission intensity was also observed.