Precise Fabrication and Manipulation of Individual Polymer Nanofibers.

Polymer nanofibers hold promise in a wide range of applications owing to their diverse properties, flexibility, and cost effectiveness. In this study, we introduce a polymer nanofiber drawing process in a scanning electron microscope and focused ion beam (SEM/FIB) instrument with in situ observation. We employed a nanometer-sharp tungsten needle and prepolymer microcapsules to enable nanofiber drawing in a vacuum environment. This method produces individual polymer nanofibers with diameters as small as ∼500 nm and lengths extending to millimeters, yielding nanofibers with an aspect ratio of 2000:1. The attachment to the tungsten manipulator ensures accurate transfer of the polymer nanofiber to diverse substrate types as well as fabrication of assembled structures. Our findings provide valuable insights into ultrafine polymer fiber drawing, paving the way for high-precision manipulation and assembly of polymer nanofibers.

In Situ Spectroscopic Studies of NH3 Oxidation of Fe-Oxide/Al2O3.

Simple temperature-regulated chemical vapor deposition was used to disperse iron oxide nanoparticles on porous Al2O3 to create an Fe-oxide/Al2O3 structure for catalytic NH3 oxidation. The Fe-oxide/Al2O3 achieved nearly 100% removal of NH3, with N2 as a major reaction product at temperatures above 400 °C and negligible NOx emissions at all experimental temperatures. The results of a combination of in situ diffuse reflectance infrared Fourier-transform spectroscopy and near-ambient pressure-near-edge X-ray absorption fine structure spectroscopy suggest a N2H4-mediated oxidation mechanism of NH3 to N2 via the Mars-van Krevelen pathway on the Fe-oxide/Al2O3 surface. As a catalytic adsorbent-an energy-efficient approach to reducing NH3 levels in living environments via adsorption and thermal treatment of NH3-no harmful NOx emissions were produced during the thermal treatment of the NH3-adsorbed Fe-oxide/Al2O3 surface, while NH3 molecularly desorbed from the surface. A system with dual catalytic filters of Fe-oxide/Al2O3 was designed to fully oxidize this desorbed NH3 to N2 in a clean and energy-efficient manner.

Surface Structures of Fe-TiO2 Photocatalysts for NO Oxidation.

Commercial rutile TiO2 particles capped with Al2O3 and ZrO2 layers, which are widely used in white pigments, can serve as a starting material for the fabrication of visible light-responsive photocatalysts toward gas-phase NO oxidation. The as-received TiO2 with iron impurities exhibited reduced photocatalytic activity, and the activity was boosted by the deposition of additional iron comparable in quantity to the intrinsic iron impurity level. Analyses using X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, and low-energy ion scattering spectroscopy revealed that the deposited iron and intrinsic impurity iron are dissimilar in terms of location, oxidation states, and interaction with TiO2. This suggests that tracking the structure and impurity levels of photocatalyst elements can be crucial for understanding structure-activity relationships of real catalysts.

Mesoporous SiO2 Particles Combined with Fe Oxide Nanoparticles as a Regenerative Methylene Blue Adsorbent.

Mesoporous SiO2 adsorbents were combined with Fe oxide nanoparticles (∼10 nm) that can catalyze thermal oxidation of organic compounds at low temperatures. Fe oxide nanoparticle (∼10 nm)-incorporated SiO2 adsorbents were prepared via a temperature-regulated chemical vapor deposition method followed by a thermal annealing process. The removal efficiency and reusability of Fe oxide/SiO2 particles were examined and compared to those of bare SiO2. Upon deposition of Fe oxide nanoparticles, not only the equilibrium adsorption capacity of mesoporous SiO2 for methylene blue (MB) was improved but also the reusability of SiO2 adsorbent was increased significantly. The adsorption ability of fresh Fe oxide/SiO2 particles can be almost fully recovered by simple thermal annealing at atmospheric conditions (400 °C), whereas that of bare SiO2 reduced significantly under same conditions. In addition, full recovery of initial MB adsorption ability of Fe oxide/SiO2 can be achieved by a 100 °C annealing process. Fourier transform infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopy analyses indicated that Fe oxide nanoparticles catalyzed thermal degradation of adsorbed MB molecules, resulting in the improved reusability of the Fe oxide/SiO2 adsorbent. In addition to reusability, the equilibrium adsorption capacity of mesoporous SiO2 particles for various cationic dye molecules, such as MB, malachite green, and rhodamine B, can be improved by combining Fe oxide nanoparticles.

TOF-SIMS Analysis Using Bi3 + as Primary Ions on Au Nanoparticles Supported by SiO2/Si: Providing Insight into Metal-Support Interactions.

Au nanoparticles with a mean diameter of 20 nm with a coverage of ∼20% of the surface were distributed on a Si wafer surface and studied both before and after being annealed (at 100 and 300 °C). The two types of samples were analyzed using secondary ion mass spectroscopy (SIMS) with Bi3 + clusters as the primary ions combined with surface etching using Ar1000 + clusters. We observed a substantial difference in the SIMS spectra combined with a relatively short sputtering time of Ar1000 +. In the nonannealed samples, bare Au cluster cations and Si+ were observed in the SIMS spectra; AuSi+ clusters were also observed in the annealed samples. These results indicate Au-silicide formation at a part of the periphery of the Au nanoparticles upon annealing. We suggest that SIMS experiments using cluster ions such as Bi3 + can not only be used for surface elemental analyses but also provide information on local chemical environments of elements on the surface. This is an important issue in heterogeneous catalysis (e.g., strong metal-support interactions). We also advise that one should be careful interpreting the SIMS data combined with a longer Ar1000 + sputtering time because this can deteriorate the surfaces from their original structures.

Adsorption and Oxidative Desorption of Acetaldehyde over Mesoporous Fe x O y H z /Al2O3.

Fe x O y H z nanostructures were incorporated into commercially available and highly porous alumina using the temperature-regulated chemical vapor deposition method with ferrocene as an Fe precursor and subsequent annealing. All processes were conducted under ambient pressure conditions without using any high-vacuum equipment. The entire internal micro- and mesopores of the Al2O3 substrate with a bead diameter of ∼2 mm were evenly decorated with Fe x O y H z nanoparticles. The Fe x O y H z /Al2O3 structures showed substantially high activity for acetaldehyde oxidation. Most importantly, Fe x O y H z /Al2O3 with a high surface area (∼200 m2/g) and abundant mesopores was found to uptake a large amount of acetaldehyde at room temperature, and subsequent thermal regeneration of Fe x O y H z /Al2O3 in air resulted in the emission of CO2 with only a negligibly small amount of acetaldehyde because Fe x O y H z nanoparticles can catalyze total oxidation of adsorbed acetaldehyde during the thermal treatment. Increase in the humidity of the atmosphere decreased the amount of acetaldehyde adsorbed on the surface due to the competitive adsorption of acetaldehyde and water molecules, although the adsorptive removal of acetaldehyde and total oxidative regeneration were verified under a broad range of humidity conditions (0-70%). Combinatory use of room-temperature adsorption and catalytic oxidation of adsorbed volatile organic compounds using Fe x O y H z /Al2O3 can be of potential application in indoor and outdoor pollution treatments.