[show abstract][hide abstract] ABSTRACT: Ostwald ripening is an evolutionary mechanism that results in micro-scale carbon spheres from nano-scale spheres. Vapor-phase carbon elements from small carbon nanoparticles are transported to the surface of submicron-scale carbon spheres, eventually leading to their evolution to micro-scale spheres via well-known growth mechanisms, including the layer-by-layer, island, and mixed growth modes. The results obtained from this work will pave the way to the disclosure of the evolutionary mechanism of micro-scale carbon spheres and open a new avenue for practical applications.
[show abstract][hide abstract] ABSTRACT: Hydrothermally grown ZnO nanorods were used for enzyme immobilization in glucose sensors. In particular, the surface area of the ZnO nanorods was tailored by the use of a seed layer and/or by changing the concentration of the precursors. The glucose sensing capability was found to be strongly associated with the surface area of the nanorods. The results clearly demonstrated that hydrothermally grown ZnO nanorods be successfully applied to the electrode system for the detection of glucose. In addition, the growth conditions also need to be carefully optimized in order to grow ZnO nanorods that are as slim and long as possible in order to maximize the surface area.
Sensors and Actuators B Chemical 01/2014; 192:216–220. · 3.54 Impact Factor
[show abstract][hide abstract] ABSTRACT: Room temperature gas sensing ability for low concentrations of benzene was successfully realized with Pt nanoparticle-decorated networked ZnO nanowire sensors. For decoration of Pt nanoparticles, gamma-ray radiolysis was used. The Pt decoration greatly enhanced benzene sensing performances. Importantly, even at room temperature, ppm level benzene was clearly detected, which is likely to be due to the combined effect of electronic and chemical sensitizations by Pt nanoparticles.
Journal of Nanoscience and Nanotechnology 10/2013; 13(10):7097-9. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: We fabricated SnO2/Pt core-shell nanowires by means of a two-step process, in which Pt layers were sputtered onto the surface of networked SnO2 nanowires. For Pt-functionalization, we have synthesized the SnO2-Pt core-shell nanowires by depositing Pt layers using a sputtering method on bare SnO2 nanowires, subsequently annealing and thus transforming the continuous Pt shell layers into Pt nanoparticles. The NO2 gas sensing test demonstrated the ability of the Pt functionalization to attain the higher sensitivity and faster response than bare SnO2 nanowires. The possible mechanisms for improvment of the sensing properties by Pt-functionalization were discussed.
Journal of Nanoscience and Nanotechnology 09/2013; 13(9):6216-21. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: ZnO–SnO2 branch–stem nanostructures were realized on a basis of a two-step process. In step 1, SnO2-stem nanowires were synthesized. In step 2, ZnO-branch nanowires were successfully grown on the SnO2-stem nanowires through a simple evaporation technique. We have pre-deposited thin Au layers on the surface of SnO2 nanowire stems and subsequently evaporated Zn powders on the nanowires. The ZnO branches, which sprouted from the SnO2 stems, had diameters in a range of 30–35 nm. As-synthesized branches were of single crystalline hexagonal ZnO structures. Since the branch tips were comprised of Au-containing nanoparticles, the Au-catalyzed vapor–liquid–solid growth mechanism was more likely to control the growth process of the ZnO branches. To test a potential use of ZnO–SnO2 branch–stem nanostructures in chemical gas sensors, their sensing performances with respect to NO2 gas were investigated, showing the promising potential in chemical gas sensors.
Current Applied Physics 05/2013; 13(3):526–532. · 1.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: Highly sensitive and selective NO2 sensing performances were realized with the networked SnO2 microrods functionalized with Ag nanoparticles by applying γ-ray radiolysis. The Ag nanoparticles were transformed into nanoparticles of the Ag/Ag2O phase by thermal heating. The NO2 sensing characteristics of the Ag-functionalized SnO2 microrods were compared with those of bare SnO2 microrods. The cross-sensibility of the Ag-functionalized SnO2 microrods to other gases was tested for O2, SO2, CO, C6H6 and C7H8. The sensing results demonstrated not only that γ-ray radiolysis was an effective means of functionalizing the surface of oxide microrods with catalytic Ag nanoparticles, but also that the Ag functionalization greatly enhanced the SnO2 microrods' capability of detecting NO2 in light of response and selectivity. The special energy band structure built on the surface of SnO2 microrods associated with Ag nanoparticles leads to a superior response to oxidizing gases than reducing gases. Being combined with this, easy dissociation of NO2 into more active chemical species by the unique catalytic role of Ag is likely to be responsible for the selective, sensitive NO2 sensing performances of the Ag-functionalized SnO2 microrods.
[show abstract][hide abstract] ABSTRACT: We describe the preparation of superhydrophobic SiO2 layers through a combination of surface roughness and fluorination. Electrospraying SiO2 precursor solutions that were prepared by a sol–gel route and included trichloro(1H,1H,2H,2H-perfluorooctyl)silane as a fluorination source produced highly rough, fluorinated SiO2 layers. In sharp contrast to the fluorinated flat SiO2 layer, the fluorinated rough SiO2 layer showed much enhanced repellency toward liquid droplets of different surface tensions. The surface fraction and the work of adhesion of the superhydrophobic SiO2 layers were determined, respectively, based on Cassie–Baxter and Young–Dupre equations. The satisfactory long-term stability for 30 days, the ultraviolet resistance and the thermal stability up to 400 oC of the superhydrophobic SiO2 layers prepared in this work confirm a promising practical application.
Journal of Solid State Chemistry 01/2013; 197:23–28. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Networked SnO(2) nanowire sensors were achieved using the selective growth of SnO(2) nanowires and their tangling ability, particularly on on-chip V-groove structures, in an effort to overcome the disadvantages imposed on the conventional trench-structured SnO(2) nanowire sensors. The sensing performance of the V-groove-structured SnO(2) nanowire sensors was highly dependent on the geometrical dimension of the groove, being superior to those of their conventional trench-structured counterparts. Pt nanoparticles were decorated on the surface of the networked SnO(2) nanowires via γ-ray radiolysis to enhance the sensing performances of the V-groove sensors whose V-groove widths had been optimized. The V-groove-structured Pt-nanoparticle-decorated SnO(2) nanowire sensors exhibited outstanding and reliable sensing capabilities towards toluene and nitrogen dioxide gases, indicating their potential for use as a platform for chemical gas sensors.
[show abstract][hide abstract] ABSTRACT: This paper reports the preparation of superhydrophobic SiO(2) layers with a micro-nano hierarchical surface structure. SiO(2) layers, which were rough on the microscale, were prepared using an electrospraying method combined with a sol-gel chemical route. To create a nanoscale structure, the surface of the SiO(2) layers was coated with Au nanoparticles using an ultraviolet-enhanced chemical reduction process, resulting in a micro-nano hierarchical surface structure. A subsequent fluorination treatment with a solution containing trichloro(1H,1H,2H,2H-perfluorooctyl)silane resulted in fluorination of the micro-nano hierarchical SiO(2) layers. The resulting SiO(2) layers showed outstanding repellency toward a range of liquid droplets, for example, a water-repellency of 170°. The surface fraction and work of adhesion of the fluorinated, micro-nano hierarchical SiO(2) layers were estimated using the Cassie-Baxter and Young-Dupre equations, respectively. The long-term durability and ultraviolet resistance of the superhydrophobic SiO(2) layers prepared in this study highlight their potential in a range of practical applications.
Journal of Colloid and Interface Science 10/2012; · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Transmission electron microscopy studies were performed to reveal the underlying growth modes of ZnO nanorods by metalorganic chemical vapor deposition with respect to the type of substrates. On well-matched substrates, such as GaN/Al2O3 (0001) and ZnO (0001) substrates, a 2-dimensional (D) layer-by-layer growth occurs. During further growth after a certain critical thickness of ∼40 nm, 1D nanorods start to grow on the 2D layer. In contrast, only vertically-aligned ZnO nanorods grow on a partially-matched substrate, such as Al2O3 (0001), after the coalescence of 3D ZnO islands. On mismatched substrates, such as Si (111) and Si (001), an Si–O amorphous layer of ∼5 nm forms first, on which 3D ZnO islands grow. After their coalescence, 1D nanorods start to grow.
Journal of Crystal Growth 09/2012; 355(1):78–83. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: Platinum (Pt) nanoparticles were synthesized on tin dioxide (SnO2) nanowires by applying γ-ray radiolysis. The growth behavior of Pt nanoparticles was systematically investigated as a function of precursor concentration, illumination intensity and exposure time of the γ-rays. We found that these processing parameters greatly influenced the growth behavior of Pt nanoparticles in terms of size and formation density. Vapor-phase-grown SnO2 nanowires were uniformly covered with Pt nanoparticles by the radiolysis process. The Pt nanoparticle-functionalized SnO2 nanowires were tested as sensors for detecting reductive gases including carbon monoxide, toluene, and benzene. The results indicate that the γ-ray radiolysis is an efficient way of functionalizing the surface of oxide nanowires with catalytic Pt nanoparticles.
[show abstract][hide abstract] ABSTRACT: NiO nanofibers were synthesized by an electrospinning method with polyvinyl alcohol and nickel acetate tetrahydrate as precursor materials. Individual nanofibers consisted of nanograins. A gas sensor has been fabricated using these nanofibers. Its sensing properties to NO2 and benzene were investigated. The sensor exhibited good sensitivity and dynamic properties for the tested gases. All these results suggest that the electrospinning-synthesized NiO nanofibers hold promise for realizing sensitive and reliable gas sensors.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1288-91. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Selectively-grown networked SnO2 nanowires were functionalized with Pt nanodots by the radiolysis process. NO2 sensing characteristics of Pt-functionalized SnO2 nanowires were compared with those of bare SnO2 nanowires. The results demonstrate that the Pt functionalization greatly enhances the sensitivity and response time in SnO2 nanowire-based gas sensors. The enhancement is likely to be associated with the spillover effect and/or easy dissociation of NO2 into more active chemical species by the catalytic effect of Pt.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1526-9. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Highly stable TiO2 sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO3. Particularly, long-term stable TiO2 sols were prepared without adding any chemical additives. Anatase TiO2 nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO2 films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO2 sols and films are promising for use in flexible or dye-sensitized solar cells.
Journal of Sol-Gel Science and Technology 01/2012; 61(1). · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: A novel growth method for CuO-functionalized, branched tin oxide (SnO2) nanowires was developed on the basis of a Cu-triggered tip-growth vapour–liquid–solid (VLS) process during annealing of Cu-coated SnO2 nanowires. The variation in annealing temperature changed the morphology, in which higher temperatures (⩾500 °C) are favourable for the formation of branches. From the observation of tip nanoparticles, we revealed that the growth of branches at 500 and 700 °C was dominated by base-growth and tip-growth VLS processes, respectively. The tip nanoparticles at 700 °C were mainly comprised of a CuO phase. We have demonstrated the potential applicability of the CuO-functionalized, branched SnO2 nanowires to H2S sensors. CuO functionalization significantly enhanced the response to H2S. In sharp contrast, it degraded the response to NO2, suggesting their selective sensing performance to H2S.
Journal of Physics D Applied Physics 01/2012; 45(20). · 2.53 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hollow Silica (SiO2) fibers with porous walls were synthesized
by a coaxial electrospinning method. The SiO2 sol prepared by
a sol–gel route was blended with polyvinylacetate to prepare
precursor solutions for electrospinning. Electrospinning-synthesized
hollow SiO2 fibers were highly porous with pore
diameters of ~45 nm. A slow heating rate <5°C/min during
calcination was required to sustain the hollow and porous morphology.
In addition, aligned hollow SiO2 fibers were successfully
synthesized using a separate electrode configuration
Journal of the American Ceramic Society 01/2012; 95(2):553. · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: The preparation of superhydrophobic SiO(2) layers through a combination of a nanoscale surface roughness and a fluorination treatment is reported. Electrospraying SiO(2) precursor solutions that had been prepared by a sol-gel chemical route produced very rough SiO(2) layers. Subsequent fluorination treatment with a solution containing trichloro(1H,1H,2H,2H-perfluorooctyl)silane resulted in highly rough, fluorinated SiO(2) layers. The fluorinated rough SiO(2) layers exhibited excellent repellency toward various liquid droplets. In particular, water repellency of 168° was observed. On the bases of Cassie-Baxter and Young-Dupre equations, the surface fraction and the work of adhesion of the rough, fluorinated SiO(2) layers were respectively estimated. In light of the durability in water, ultraviolet resistance, and thermal stability, the superhydrophobic SiO(2) layers prepared in this work hold promise in a range of practical applications.
Journal of Colloid and Interface Science 12/2011; 368(1):599-602. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Networked ZnO nanowire sensors have been fabricated via selective growth of ZnO nanowires by the vapor growth method. The number of junctions per electrode pair (NJE) was deliberately controlled by changing the spacing of interdigital electrodes. Its effects on the sensing properties to NO2 and CO were investigated. As the NJE increased, superior sensing properties were attained. This novel method to fabricate gas sensors using vapor-phase grown nanowires may circumvent the drawbacks of single nanowire gas sensors. Importantly, the NJE needs to be tuned to fully exploit networked nanowires in gas sensors.
Journal of the American Ceramic Society 10/2011; 94(11):3922 - 3926. · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: Silica layers with different microstructures were prepared by electrospraying. The microstructure of the layers was changed by controlling the viscosity of the precursor solutions in the electrospray deposition. Precursor solutions of low viscosity produced particulated silica layers, exhibiting superhydrophobicity. In contrast, fibrous silica layers exhibiting superhydrophilicity were attained with viscous precursor solutions. In particular, the particulated silica layers showed a good durability and resistance to ultraviolet illumination. The dramatic change in the wettability of silica layers without any chemical treatment is promising in speeding up their use in many fields.
Journal of Colloid and Interface Science 09/2011; 364(2):561-5. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: We demonstrate that the size and crystallinity of grains in individual ZnO nanofibers greatly influence their sensing properties for CO. The sensing properties, including sensitivity, response and recovery times of a sensor fabricated with ZnO nanofibers composed of large grains are much superior to those of a sensor fabricated with nanofibers of small grains. The crystallinity, improved by the longer calcination time, is likely to be responsible for the higher sensitivity in the large-grained nanofibers. The facilitated occupancy and desorption of CO molecules at grain boundaries in the large-grained nanofibers are the most probable causes of the shorter response and recovery times in detecting CO, respectively. This work suggests not only that electrospinning-synthesized ZnO nanofibers hold promise for realizing sensitive and reliable gas sensors but also that the size as well as the crystallinity of the grains existing in individual nanofibers need to be optimized to obtain the best sensing properties.
Journal of Materials Research. 07/2011; 26(14):1662 - 1665.