Shushi Suzuki

Synthesis of alloy AuCu nanoparticles with the L1₀ structure in an ionic liquid using sputter deposition.

Three-dimensional Au structures on bare and organic-compound-modified TiO₂(110) surfaces were interrogated by Au L₃-edge polarization dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) spectroscopy. On the bare TiO₂(110) surface, icosahedral Au₅₅ nanoclusters were the main product found. When the surfaces were modified with ortho or meso mercaptobenzoic acid (o-MBA or m-MBA), Au was atomically dispersed. Sulfur atoms in the o- and m- MBA formed strong covalent bonds with Au to produce stable Au-MBA (o- and m- forms) surface complexes. On the other hand, only oxygen atoms on the surface did not make a strong enough interaction to stabilize the Au species. We discuss how the Au species formed on the modified TiO₂(110) surface and the possibility to control the Au structure by the surface modification method.

Bimetallic alloy nanoparticles (NPs) are attractive materials for exploring advanced functions to reduce consumption of resources and energy. AuPt alloy NPs are of special interest for their potential applications to fuel cells, because of the reduction of CO poisoning on Pt. Here, we report the synthesis of AuPt alloy NPs by sputter deposition into (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) amide (TMPA-TFSA). Transmission electron microscopy (TEM), X-ray fluorescent spectroscopy (XRF) and X-ray diffraction (XRD) measurements showed that changes in particle diameters and compositions of AuPt bimetallic NPs, were controllable by choosing initial compositions of metal targets for the sputter deposition. By cyclic voltammetry measurements, the detection of an anodic peak corresponding to the methanol oxidation reaction on the AuPt NPs demonstrated the presence of an AuPt alloy phase in the NPs.

We found that the adsorption states of Au nanoparticles (NPs) on TiO₂(110) varied with the ionic liquids (ILs) that encapsulate the NPs during the entire process from synthesis of NPs to immobilization of the NPs on the surface at 323 K. Five kinds of ILs, including three 1-butyl-3-methylimidazolium ([C₄MIm]) cation-based ILs of tetrafluoroborate ([C₄MIm][BF₄]), hexafluorophosphate ([C₄MIm][PF₆]) and bis(trifluoromethylsulfonyl)amide ([C₄MIm][NTf₂]), and two [BF₄ ] anion-based ILs of 1-(methoxymethyl)-1-methylpyrrolidinium ([PY1,1O1][BF₄]) and N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium ([N122,1O2][BF₄]), were used. They provided different adsorption states of the Au NPs on the surface. We considered the determinant factor for the adsorption states of NPs on the surface from the viewpoint of electrostatic interactions between IL and IL and between IL and the surface. We deduced the influence of these interactions from the increments of NP's diameter and the amount of NPs after the immobilization, and obtained the order of anions as [BF₄ ] ≈ [NTf₂ ] > [PF₆ ] for the three [C₄MIm] based ILs and the order of cations as [PY1,1O1] > [C₄MIm] > [N122,1O2] for the three [BF₄ ] based ILs. Interestingly, the above orders were no match with the conventional physicochemical and chemical parameters but β of Kamlet–Taft solvent descriptors and Lewis basicity of anions in the case of anions of ILs. The results of anions indicate that the chemical natures of ILs might affect the immobilization of NPs through hydrogen bonding or coordination bonding with the surface. We suggested that such a trend in anions was ‘local viscosity’ of ILs in the vicinity of surface. Besides, layer formation of IL on the surface might be also an influential factor to control the size of NPs and the surface density of NPs. Our results show that the combination of a charged surface and charged molecules has the potential for controlling locations of the NPs on the surface preferentially with tuning the electrostatic interaction.

We have carried out ethanol conversion reactions on the MoO₃ under the pulse infrared irradiations (period = 2 s) with several wavelengths emitted from free-electron-laser. We found a piece of evidence to show the dependence of activities in the ethanol conversion rate on the infrared wavelengths. When the wavelength was tuned to 967 cm⁻¹, which corresponded to the absorption frequency of 0.167 nm Mo=O bond, C₂H₅OH was converted mainly to C₂H₄ with CH₃CHO as a minor product while no reaction occurred at 1200 cm⁻¹ where no resonant vibration mode of MoO₃ was present. The reaction products were different from those produced in thermal reactions.

We have observed MoO₃(010) surface on an atomic level by NC-AFM(Noncontact atomic force microscopy) for the first time. White arrays with 0.40 and 0.37 nm dimensions along [100] and [001], respectively, were observed, which corresponded to the topmost oxygen atoms of MoO₃(010).