Element-ratio dependence of the 5d-states of Au and Pt in solid-solution-type Au-Pt alloy nanoparticles studied by X-ray absorption spectroscopy and density functional theory.

Solid-solution-type Au-Pt alloy nanoparticles (NPs) were prepared from the nanoclusters of each metal using the polymer-conjugated fusion growth method. The elemental mapping analysis showed that the mixing state of the elements in the NPs drastically changed in the narrow reaction-temperature range from 100 °C to 180 °C. For their various mixing states, the 5d-states of Au and Pt atoms in the alloy NPs were investigated on the basis of the white line intensities of X-ray absorption near edge structure (XANES). Then, the 5d-states of Au and Pt atoms in a model crystalline ordered alloy structures were investigated on the basis of the theoretically calculated XANES spectra using density functional theory (DFT) in the whole composition range. The DFT calculation showed that the changes in the absorption spectra near the Pt and Au edges are caused by the change in the occupation of the Pt 5d-states and the orbital hybridisation of the Au 5d-states with the 5d-states of neighbouring Pt atoms around an Au atom, respectively.

Efficient and Selective Interplay Revealed: CO2 Reduction to CO over ZrO2 by Light with Further Reduction to Methane over Ni0 by Heat Converted from Light.

The reaction mechanism of CO2 photoreduction into methane was elucidated by time-course monitoring of the mass chromatogram, in situ FTIR spectroscopy, and in situ extended X-ray absorption fine structure (EXAFS). Under 13 CO2 , H2 , and UV/Vis light, 13 CH4 was formed at a rate of 0.98 mmol h-1 gcat -1 using Ni (10 wt %)-ZrO2 that was effective at 96 kPa. Under UV/Vis light irradiation, the 13 CO2 exchange reaction and FTIR identified physisorbed/chemisorbed bicarbonate and the reduction because of charge separation in/on ZrO2 , followed by the transfer of formate and CO onto the Ni surface. EXAFS confirmed exclusive presence of Ni0 sites. Then, FTIR spectroscopy detected methyl species on Ni0 , which was reversibly heated to 394 K owing to the heat converted from light. With D2 O and H2 , the H/D ratio in the formed methane agreed with reactant H/D ratio. This study paves the way for using first row transition metals for solar fuel generation using only UV/Vis light.

Dual Photocatalytic Roles of Light: Charge Separation at the Band Gap and Heat via Localized Surface Plasmon Resonance To Convert CO2 into CO over Silver-Zirconium Oxide.

Confirmation of 13CO2 photoconversion into a 13C-product is crucial to produce solar fuel. However, the total reactant and charge flow during the reaction is complex; therefore, the role of light during this reaction needs clarification. Here, we chose Ag-ZrO2 photocatalysts because beginning from adventitious C, negligible products are formed using them. The reactants, products, and intermediates at the surface were monitored via gas chromatography-mass spectrometry and FTIR, whereas the temperature of Ag was monitored via Debye-Waller factor obtained by in situ extended X-ray absorption fine structure. With exposure to 13CO2, H2, and UV-visible light, 13CO selectively formed, while 8.6% of the 12CO mixed in the product due to the formation of 12C-bicarbonate species from air that exchanged with the 13CO2 gas-phase during a 2 h reaction. By choosing the light activation wavelength, the CO2 photoconversion contribution ratio was charge separated at the ZrO2 band gap (λ < 248 nm): 70%, localized at the Ag surface plasmon resonance (LSPR) (330 < λ < 580 nm): 28%, and characterized by a thermal energy of 295 K: 2%. LSPR at the Ag surface was converted to heat at temperatures of up to 392 K, which provided an efficient supply of activated H species to the bicarbonate species, combined with separated electrons and holes above the ZrO2, which generated CO at a rate of 0.66 µmol h-1 gcat-1 with approximately zero order kinetics. Photoconversion of 13CO2 using moisture was also possible. Water photo-oxidation step above ZrO2 was rate-limited, and the side reactions that formed H2 above the Ag were successfully suppressed instead to produce CO via the Mg2+ addition to trap CO2 at the surface.

Restricted hydration structures of Rb and Br ions confined in slit-shaped carbon nanospace.

Hydration structures of "nanosolutions" around both cation and anion for rubidium bromide confined in nanospaces (pore width = 1.1 nm) of activated carbon fiber were determined with EXAFS measurements and related analysis. The analytical results indicate that the ionic solutions confined in hydrophobic nanospaces tend to form an incomplete dehydration structure, because of the spatial restriction by the nanospace and capturing water molecules in the ordered structure.