The Mn-oxide/Nb:SrTiO3 photoelectrode for oxygen evolution reaction was investigated by in situ Mn K-edge XAFS spectroscopy under UV irradiation. The oxidization of the Mn oxide was observed via photoexcited carrier transfer, which results in the positive potential shift of the Mn oxide cocatalyst toward oxygen evolution reaction.

Photoexcited hole transfer to MnO x cocatalysts on SrTiO3 photoelectrodes was examined under controlled potential conditions during UV irradiation using in situ Mn K-edge X-ray absorption fine structure (XAFS) spectroscopy. The absorption edges of spectra were found to shift to higher energies during irradiation, indicating that MnO x cocatalysts were oxidized by the migration of photoexcited holes accompanied by a positive potential shift of the MnO x cocatalysts. This oxidation process was promoted by the application of a positive applied potential, suggesting that the photoexcited hole transfer was enhanced by upward band bending at the cocatalyst–photoelectrode interface. Structural changes of the MnO x cocatalyst were found to depend on the UV photon intensity; thus, the observations of photoexcited electron transfer by XAFS are associated with the photoelectrochemical activity during water splitting.

The electrochromic transition of a nickel borate thin film between colorless and brown was examined by means of in situ XAFS and UV/vis spectroscopy. The XAFS spectra showed that the average valence state of the nickel species in the film changed from +2.1 to +3.8 following the application of an electrode potential. Additionally, a broad peak at 700 nm was observed during in situ UV/vis absorption measurements on the application of a positive potential. These results suggest that the nickel borate film reversibly forms a NiOOH structure with a domain size of several nanometers during the electrochromic reaction.

The reaction kinetics of laser-induced particle formation in an aqueous/EtOH solution of PdCl4 2– without a photoactivator was investigated by transmission electron microscopy (TEM) and dispersive X-ray absorption fine structure (DXAFS) measurements. Pd particles were generated by the irradiation of a nanosecond pulsed 266 nm laser with a fluence of 19.9–59.7 mJ/cm2. The TEM observation showed the dependence of the particle size on the laser fluence and the promotion of particle growth by the irradiation of a high-fluence laser. The DXAFS data were analyzed by three methods: deconvolution of the X-ray absorption near-edge structure (XANES) spectrum by a linear combination fitting, model fitting of the extended XAFS (EXAFS) oscillation of the PdCl4 2– ion, and fitting of the spectrum edge of XANES using an error function. These methods give the ratio of Pd2+, the coordination number of Pd–Cl bond, and the edge width of XANES, which are related to the Pd2+ concentration. Temporal changes of the Pd2+ concentration obtained by these three methods were analyzed on the basis of the Finke–Watzky two-step mechanism. The analysis elucidates that, in laser-induced particle formation in the absence of a photoactivator, the photons contribute to reduction of the PdCl4 2– ion by the one-photon process and to the autocatalytic growth of Pd particles by the multiphoton process.

Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, Pd, which can be found in radioactive wastes, is one of the difficult-to-measure nuclides and results in a deficit in experimentally determined contents. In this study, a precipitation-based separation method has been developed for the determination ofPd with inductively coupled plasma mass spectrometry. The photoreduction induced by pulsed laser irradiation at 355 nm provides short-time and one-step recovery of Pd. The proposed method was verified by applying it to a spent nuclear fuel sample. To recover Pd efficiently, a natural Pd standard was employed as the Pd carrier. Taking advantage of the absence of Pd in spent nuclear fuel,Pd in the Pd carrier was utilized as the internal standard. The chemical yield of Pd was about 90% with virtually no impurities, allowing accurate quantification of Pd. The amount ofPd in the Pd precipitate was 17.3 ± 0.7 ng, equivalent to 239 ± 9 ng per mg of U in the sample.