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The reaction mechanism of the direct photoreduction of a Rh3+ ion complex to a Rh0 species induced by pulsed ultraviolet laser irradiation was studied using dispersive X-ray absorption fine structure (DXAFS) spectroscopy. The time-resolved X-ray absorption near edge structure (XANES) showed the absence of isosbestic points and suggested that more than two Rhn+ species contribute toward the direct photoreduction of Rh3+. Analysis of the time-resolved XANES data by singular value deposition showed that the direct photoreduction involves three Rhn+ species. Multivariate curve resolution by alternating least-squares analysis (MCR-ALS) of the time-resolved XANES data gave pure spectra and concentration profiles of the three Rhn+ species. The Rhn+ species were assigned to Rh3+, Rh+, and Rh0 species based on the features of the pure XANES spectra. The concentration profiles suggested that the direct photoreduction proceeds in the order of Rh3+ → Rh+ → Rh0. A reaction mechanism, which was proposed involving photoreductions of Rh3+ and Rh+, photoinduced autocatalytic reductions of Rh3+ and Rh+, and photooxidation of Rh+, well reproduced the concentration profiles of three Rhn+ species.

Studtite and metastudtite are uranyl peroxides formed on nuclear fuel in water through the reaction with H2O2 produced by the radiolysis of water. However, it is unclear how the two types of uranyl peroxides are generated and distributed on the surface of nuclear fuel. Here, we used Raman imaging technique to exemplify distribution data of the two uranyl peroxides formed on the surface of a U3O8 pellet through immersion in a H2O2 aqueous solution. As a result, we observed that studtite and metastudtite are heterogeneously distributed on the U3O8 surface. No clear correlation between the distributions of studtite and metastudtite was observed, suggesting that the two uranyl peroxides are independently generated on the surface of U3O8. We anticipate that this Raman imaging technique could reveal how these uranyl peroxides are generated and distributed on the surface of the nuclear fuel debris in the Fukushima-Daiichi nuclear power plants.

The long-term safety assessment of spent Cs adsorbents produced during the decontamination of radiocesium-containing water at the Fukushima Daiichi nuclear power plant requires one to estimate thei...

In this study, we developed a simple and one-step Pd separation technique based on photoreduction with Xe lamp irradiation for the determination of

Dissipative structures often appear as an unstable counterpart of ordered structures owing to fluctuations that do not form a homogeneous phase. Even a multiphase mixture may simultaneously undergo one chemical reaction near equilibrium and another one that is far from equilibrium. Here, we observed in real time crystal seed formation and simultaneous nanocrystal aggregation proceeding from CeIV complexes to CeO2 nanoparticles in an acidic aqueous solution, and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges. The hierarchically assembled structures in solutions were CeO2 colloids, viz. primary core clusters (1–3 nm) of crystalline ceria and secondary clusters (20–30 nm) assembled through surface ions. Such self-assembly is widespread in multi-component complex fluids, paradoxically moderating hierarchical reactions. Stability and instability are not only critical but also complementary for co-optimisation around the nearby free energy landscape prior to bifurcation.

Previously, we showed that the irradiation of a nanosecond pulsed UV laser with high pulse energy into the Pd(II) solution forms the Pd particle with submicron size (100–500 nm), which has not been generated in the photo-induced particle formation using a UV lamp. It indicates that the laser irradiation with high pulse energy promotes the Pd particle growth, the mechanism of which is unclear. In this work, we studied the particle formation in the Pd(II) solution in the laser irradiation with high pulse energy using time-resolved X-ray absorption fine structure (XAFS) spectroscopy., 6th International Conference on Advanced Nanoparticle Generation & Excitation by Lasers in Liquids

The reaction kinetics of laser-induced particle formation in an aqueous/EtOH solution of PdCl42– 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 PdCl42– 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+ concentra...

Determination of radiopalladium 107Pd is required to ensure radiation safety of the Pd extracted from spent nuclear fuel for recycling or disposal. We employed nanosecond laser ablation inductively coupled plasma quadrupole mass spectrometry (ns-LA-ICP-QMS) to simplify the analytical procedure of 107Pd. Pd was separated through a selective Pd precipitation reaction induced by pulsed laser irradiation that reduces Pd(II) ions to metal Pd(0). Laser ablation facilitates direct measurement of the Pd precipitates, skipping the dissolution and dilution procedure with aqua regia and HCl, which causes serious corrosion damage to the introduction system of the ICP. In the present study, 102Pd in natural Pd standard solution was used as an internal standard owing to its absence in spent nuclear fuel. Pd precipitates with diameters ranging from 0.2 to 0.5 μm, obtained by pulsed laser irradiation, were embedded uniformly on the surface of the centrifugal filter to form a microscopically thin and flat Pd surface. The resulting homogeneous Pd layer is suitable for obtaining a stable signal ratio of 107Pd/102Pd (

We measured X-ray absorption fine structure (XAFS) and Raman spectra of isopolymolybdates(VI) in highly concentrated HNO3 solution (0.15 - 4.0 M), which change their geometries depending on the acid concentration, and performed the simultaneous resolution of the XAFS and Raman data using a multivariate curve resolution by alternating least-squares (MCR-ALS) analysis. In iterative ALS optimization, initial data matrices were prepared by two different methods. For low sensitivity of the XAFS spectra to the geometrical change of the isopolymolybdates, the MCR-ALS result of single XAFS data matrix shows a large dependence on the preparation method of the initial data matrices. This problem is improved by the simultaneous resolution of the XAFS and Raman data: the MCR-ALS result of an augmented matrix of these data has little dependence on the initial data matrices. This indicates that the augmentation method effectively improves the rotation ambiguities in the MCR-ALS analysis of the XAFS data.

The long-term safety assessment of spent Cs adsorbents produced during the decontamination of radiocesium-containing water at the Fukushima Daiichi nuclear power plant requires one to estimate their

An analytical procedure using micro-Raman spectroscopy (MRS) and secondary ion mass spectrometry (SIMS) was developed to elucidate both the chemical states and isotope ratios of individual micron-sized uranium particles. Each uranium particle was identified by scanning electron microscopy combined with energy dispersive X-ray detection and transferred onto each specific location on a substrate by micro-manipulation. After optimization of the analytical conditions, the chemical states of each uranium particle were determined with MRS non-destructively. The substrate containing each particle was then introduced into a SIMS instrument and uranium isotope ratios of each particle were determined. The developed method is expected to be used for clarifying the origin and history of each particle in environmental samples.

Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, 107Pd, 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 of 107Pd 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 102Pd in spent nuclear fuel, 102Pd 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 107Pd. The amount of 107Pd in the Pd precipitate w...

Determination of radiopalladium

The isotope ratio analysis of individual uranium particles in environmental samples taken at nuclear facilities is important to clarify their origins for nuclear safeguards. In the present study, automated particle screening was used to select uranium particles prior to precise isotope ratio analysis by thermal ionization mass spectrometry (TIMS). As a result, molecular ion interferences on the uranium mass region were able to be almost completely avoided in the analysis of real inspection samples using APM-TIMS. Therefore, the performance of APM-TIMS was sufficient for obtaining isotope ratio data of individual particles without molecular ion interferences., 原子力施設で採取された環境試料中の個々のウラン粒子の同位体比分析は、施設での未申告原子力活動を検知する上で重要である。本研究では、効率的な分析法の開発を目的として、自動粒子スクリーニングを利用して測定する粒子を選別し、表面電離質量分析法(TIMS)により同位体比分析を行う方法の開発を行った。本法により実際の査察試料を分析した結果、従来法に比べて分子イオンの影響を低減化して個々のウラン粒子の同位体比を決定することが可能なことが示され、本法の有効性が確かめられた。

Photoexcited hole transfer to MnOx 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 MnOx cocatalysts were oxidized by the migration of photoexcited holes accompanied by a positive potential shift of the MnOx 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 MnOx 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.

Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide

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.

The Mn-oxide/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. Introduction Photoelectrochemical water splitting is a candidate for the sustainable production of hydrogen gas using solar energy.1 Recently, MnO x have been shown to remarkably improve the photoelectrochemical activity for water splitting, because the MnO x on the semiconductors work as an efficient oxygen evolution cocatalyst.2 Thus, the surface modification of MnO x cocatalysts to a semiconductor photoelectrode is presently attracting attention as an efficient photoelectrochemical system for water splitting. However, the photoexcited carrier transfer processes at the photocatalyst/cocatalyst interface are not fully understood. In this study, photoexcited carrier transfer toward the MnO x cocatalyst from a SrTiO3 photoelectrode was investigated by in-situ Mn K-edge XAFS spectroscopy under UV irradiation (Fig. 1). Experimental n-Type SrTiO3 substrates were used after photodeposition of the Mn oxide cocatalysts, according to a previous work.2 The surface morphology of the MnO x cocatalysts was observed by scanning electron microscopy (SEM), confirming that the MnO x thin film was deposited on the SrTiO3 surface. A Teflon electrochemical cell was equipped with a Pt wire counter electrode and a Ag/AgCl (saturated KCl) reference electrode in 0.1 M Na2SO4aqueous solution with Ar bubbling. The in-situ XAFS measurements were performed at BL-12C of the Photon Factory and BL01B1 of SPring-8 as fluorescence excitation spectra using 19 element Ge detectors. XAFS spectra of the prepared samples were measured at various potentials under dark conditions or under UV irradiation using a Xe lamp.3 Results and discussion First,the in-situ XAFS measurements of the MnO x /SrTiO3 photoelectrode were tested at 0.5 V under UV irradiation (Fig. 2). The peak position at 6557.8 eV was gradually shifted to 6560.0 eV under irradiation, which suggests that the Mn3+ species changed to Mn4+ due to the migration of photoexcited holes, which is consistent with the photoelectrochemical reaction where the Mn oxide species acts as an oxygen evolution cocatalyst via the transfer of photoexcited holes. On the other hand, when the XAFS spectra were taken for the applied potential at 0.0 V or -0.5 V, the peak position shifted to 6559.2 eV or 6557.8 eV, respectively, indicating that the potential shift of MnO x via the photoexcited hole transfers from photoelectrode to MnO x cocatalyst is dependent on the applied electrode potential. These results demonstrate that the photoexcited carrier transfer into the cocatalyst from the photoelectrode can be probed under UV irradiation by in situ electrochemical XAFS measurement. References (1) Nocera, D. G. Acc. Chem. Res. 2012, 45, 767-776. (2) Wang, D.; Li, R.; Zhu, J.; Shi, J.; Han, J.; Zong, X.; Li, C. J. Phys. Chem. C 2012, 116, 5082-5089. (3) Yoshida, M.; Yomogida, T.; Mineo, T.; Nitta, K.; Kato, K.; Masuda, T.; Nitani, H.; Abe, H.; Takakusagi, S.; Uruga, T.; Asakura, K.; Uosaki, K.; Kondoh, H. Chem. Commun. 2013, 49, 7848-7850.