We perform density functional theory calculations to study the CO and O2 adsorption chemistry of Pt@X core@shell bimetallic nanoparticles (X = Pd, Rh, Ru, Au, or Ag). To prevent CO-poisoning of Pt nanoparticles, we introduce a Pt@X core-shell nanoparticle model that is composed of exposed surface sites of Pt and facets of X alloying element. We find that Pt@Pd, Pt@Rh, Pt@Ru, and Pt@Ag nanoparticles spatially bind CO and O2, separately, on Pt and X, respectively. Particularly, Pt@Ag nanoparticles show the most well-balanced CO and O2 binding energy values, which are required for facile CO oxidation. On the other hand, the O2 binding energies of Pt@Pd, Pt@Ru, and Pt@Rh nanoparticles are too strong to catalyze further CO oxidation because of the strong oxygen affinity of Pd, Ru, and Rh. The Au shell of Pt@Au nanoparticles preferentially bond CO rather than O2. From a catalysis design perspective, we believe that Pt@Ag is a better-performing Ptbased CO-tolerant CO oxidation catalyst.

Gas detection is necessary for various reasons, including the prevention of gas leakages and the creation of necessary environmental conditions. Among the gas detection methods, leakage of gas can be confirmed using materials that undergo color changes that are easily distinguished by the naked eye. Metal nanoparticles (NPs) experience variations in their absorption wavelengths under the localized surface plasmon effect (LSPR) with mechanical stresses, which change the distance between NPs. In this study, we attempted to detect the presence of gas utilizing the LSPR-related color change of a chain of Au NPs. The assembly of Au NPs, arranged in a chain shape, experienced a color change from dark blue to purple with a change in the distance between the NPs by applying a physical force, i.e., compression, stretching, and gas pressure. As the force of compression and the degree of stretching increased, the absorption wavelength shifted from doublet peaks at 650 and 550 nm to a singlet peak at 550 nm. Further, applying gas pressure caused an identical color change. With this result, we propose a method that could be applied to all gases that require detection based on gas pressure.

Through density functional theory calculations, to provide insight into the origins of the catalytic activity of Au nanoparticles (NPs) toward oxidation reactions, we have scrutinized the oxygen adsorption chemistry of 9 types of small unsupported Au NPs of around 1 nm in size (Au13, Au19, Au20, Au25, Au38, and Au55) looking at several factors (size, shape, and coordination number). We found that these NPs, except for the icosahedral Au13, do not strongly bind to O2 molecules. Energetically most feasible O2 adsorption that potentially provides high CO oxidation activity is observed in the icosahedral Au13, our smallest Au NP. In spite of the chemical inertness of bulk Au, the structural fluxionality of such very small Au NP enables strong O2 adsorption. Our results can support recent experimental findings that the exceptional catalytic activity of Au NPs comes from very small Au species consisting of around 10 atoms each.

Superhydrophobic SiO2 layers with a micro-nano hierarchical surface structure were prepared. SiO2 layers depositedvia an electrospray method combined with a sol-gel chemical route were rough on the microscale. Au particles were decoratedon the surface of the microscale-rough SiO2 layers by use of the photo-reduction process with different intensities (0.11-1.9 mW/cm2) and illumination times (60-240 sec) of ultraviolet light. With the aid of nanoscale Au nanoparticles, this consequentlyresulted in a micro-nano hierarchical surface structure. Subsequent fluorination treatment with a solution containingtrichloro(1H,2H,2H,2H-perfluorooctyl)silane fluorinated the hierarchical SiO2 layers. The change in surface roughness factorwas in good agreement with that observed for the water contact angle, where the surface roughness factor developed as ameasure needed to evaluate the degree of surface roughness. The resulting SiO2 layers revealed excellent repellency towardvarious liquid droplets with different surface tensions ranging from 46 to 72.3mN/m. Especially, the micro-nano hierarchicalsurface created at an illumination intensity of 0.11mW/cm2 and illumination time of 60 sec showed the largest water contactangle of 170o. Based on the Cassie-Baxter and Young-Dupre equations, the surface fraction and work of adhesion for the micro-nano hierarchical SiO2 layers were evaluated. The work of adhesion was estimated to be less than 3×10−3N/m for all the liquiddroplets. This exceptionally small work of adhesion is likely to be responsible for the strong repellency of the liquids to themicro-nano hierarchical SiO2 layers.

The defect sites on chemical vapor deposition grown graphene are investigated through the selective electrochemical deposition (SED) of Au nanoparticles. For SED of Au nanoparticles, an engineered potential pulse is applied to the working electrode versus the reference electrode, thereby highlighting the defect sites, which are more reactive relative to the pristine surface. Most defect sites decorated by Au nanoparticles are situated along the Cu grain boundaries, implying that the origin of the defects lies in the synthesis of uneven graphene layers on the rough Cu surface.

In this study, we analyzed the effect of silicon oxynitride matrix on the optical properties of Au nanoparticles dispersed on composite film and explored the effectiveness of the silicon in fine tuning the refractive index of the composite film for applications in optical waveguide devices. The atomic fraction of nitrogen in SiOxNy films was controlled by varying the relative flow ratio of nitrogen gas in reactive sputtering and was evaluated optically using an effective medium theory with Bruggeman geometry consisting of a random mixture between SiO2 and Si3N4. The Au nanoparticles were embedded in the SiOxNy matrix by employing the alternating deposition technique and clearly showed an absorption peak due to the excitation of surface plasmon. With increasing nitrogen atomic fraction in the matrix, the surface plasmon resonance wavelength shifted to a longer wavelength (a red-shift) with an enhanced resonance absorption. These characteristics were interpreted using the Maxwell-Garnett effective medium theory. The formation of a guided mode in a slab waveguide consisting of 3 μm thick Au:SiOxNy nanocomposite film was confirmed at the telecommunication wavelength of 1550 nm by prism coupler method and compared with the case of using SiO2 matrix. The use of SiOxNy matrix provides an effective way of controlling the mode confinement while maintaining or even enhancing the surface plasmon resonance properties.

The electrochromic properties of Au nanoparticles (NPs) incorporating poly (3, 4-ethylenedioxythiphene) (PEDOT) film were investigated. Trisodium citrate was used for stabilizing Au NPs to control the size. The capping molecules of the Au nanoparticles were exchanged from citrate to 2-mercaptoethanol (2-ME). Water was removed by centrifuge and Au NPs were redispersed in methanol (MeOH). Finally, we obtained ca. 11.7 nm diameter of Au NPs. The effects of 0.15 at% of Au NPs incorporation on the optical, electrical, and eletrochromic properties of PEDOT films were investigated. The electrical property and switching speed of Au/PEDOT film was slightly improved over that of PEDOT film because Au NPs play a hopping site role and affect packing density of the PEDOT chain. Through the ultra violet-visible spectra of PEDOT and Au/PEDOT films at -0.7 V (vs Ag/AgCl), blue shift of maximum absorption peak was observed from PEDOT (585.4 nm) to Au/PEDOT (572.2 nm) due to a shortening of conjugated length of PEDOT. The Au NPs interfered with the degree of conjugation and the maximum absorption peak was shifted to shorter wavelength.