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Spinel-type inorganic pigments with intensive color and chemical/thermal stability are showing extensive applications that could be further broadened by color manipulation and improvement of the material properties through nanosizing. In this study, we report the supercritical hydrothermal synthesis of nonstoichiometric spinel-type cobalt gallate nanoparticles (Co–Ga NPs) with controlled color. Without the conventional calcination procedure, NPs with greenish-blue, blue, and yellowish-green colors were synthesized from precursor solutions at pH 7, 9, and 11, respectively, with a low Co/Ga molar ratio of 0.25. X-ray diffraction, scanning/transmission electron microscopy, and inductively coupled plasma-atomic emission spectroscopy methods suggest that the products were spinel-type cobalt gallate NPs with high crystallinity and a nonstoichiometric composition. Based on an X-ray absorption fine structure investigation, the prepared nonstoichiometric Co–Ga NPs were found to have different cationic configurations from stoichiometric CoGa2O4 produced by a solid-state reaction during calcination. Meanwhile, the degrees of distortions at tetrahedral and octahedral sites in the NPs were evaluated by Raman spectroscopy. In particular, nonstoichiometric Co–Ga NPs with a blue color were prepared without calcination for the first time and were found to have lower tetrahedral cobalt occupancy but comparable octahedral cobalt occupancy and larger polyhedral distortions at tetrahedral sites when compared to calcined CoGa2O4. We also discuss strategies that could realize Co–Ga NPs with a more brilliant blue color using the present technique based on an investigation of the growth process. [ABSTRACT FROM AUTHOR]

An efficient Johansson-type X-ray fluorescence spectrometer has been developed for advanced X-ray spectroscopic analysis with third-generation synchrotron radiation. K(alpha) and K(beta) X-ray fluorescence spectra for trace metals have been collected by a Ge(220) analyzing crystal with a Rowland radius of 150 ram, under monochromatic X-ray excitation at the undulator beamline at the SPring-8. The energy resolution is approximately 10 eV for most of the K lines for 3d transition metals. In light of the greatly improved efficiency, as well as the excellent signal-to-background ratio, the relative and absolute detection limits achieved are 1 ppm and 1.2 ng of copper in a carbon matrix, respectively. The energy resolution of the present spectrometer permits the observation of some chemical effects in K(beta) spectra. It has been demonstrated that the changes in K(beta)(sub 5) and K(beta)' intensity for iron and cobalt compounds can be used for the analysis of chemical states. Resonant X-ray fluorescent spectra are another important application of monochromatic excitation. In view of trace chemical characterization, the present spectrometer can be a good alternative to a conventional Si(Li) detector system when combined with highly brilliant X-rays.

Simple liquid-phase approaches for the synthesis of nanomaterials are attractive because their low costs, reduced nanoparticle aggregation, and compatibility with subsequent liquid processes widen the application scope of the resulting materials. This would be particularly interesting for β-Ga2O3 nanoparticles, which often suffer from aggregation issues during their synthesis processes. In this paper, we report a one-step synthesis of β-Ga2O3 nanoparticles in supercritical isopropanol. By simply heating Ga(NO3)3 in isopropanol at 400 °C for 24 hours, β-Ga2O3 nanoparticles with a size of ∼100 nm are obtained without requiring additional calcination in air. A structural characterization comprising X-ray diffraction, scanning electron microscopy, selected-area electron diffraction with transmission electron microscopy, and X-ray absorption fine structure measurements suggest that the synthesis process involves an initial conversion of Ga(NO3)3 to Ga(Oi-Pr)3 or a related species at 80 °C, which then transforms into γ-Ga2O3 nanoparticles upon increasing the temperature, to eventually produce β-Ga2O3 nanoparticles most likely via a dissolution and recrystallization process. [ABSTRACT FROM AUTHOR]

The Curiosity and Opportunity rovers have found depositions of manganese (Mn) (hydr)oxides within the veins of the sedimentary rocks at Gale and Endeavour craters. Since Mn is a redox sensitive element, revealing the chemical form of the Mn (hydr)oxide provides unique information on the redox state of the near‐surface/groundwater at the time of deposition. Here we report results of laboratory experiments that investigated scavenging patterns of trace metals (zinc, nickel, and chromium) on different Mn (hydr)oxides in order to constrain the chemical form of the Mn precipitates found on Mars. Our results show manganese dioxide (MnO2) scavenges zinc and nickel effectively but not for chromium. The agreement of this scavenging pattern with the observations strongly suggests that the Mn (hydr)oxides found on Mars are highly likely to be MnO2. To form MnO2, oxidizing aqueous environments are required (e.g., Eh > 0.5 V at pH ~ 8). The candidates of the oxidant include molecular oxygen, ozone, nitrates, and perchlorate acids; all of which are considered to be produced by photochemical processes. The presence of MnO2 veins in sediments suggests that such atmospheric high‐Eh oxidants may have been supplied to the subsurface, possibly through hydrological cycles activated by transient warming. Plain Language Summary: Early Mars is believed to have possessed an abundance of liquid water on its surface. The Mars rover Curiosity has found both complex organic matter and bio‐essential elements within the lake deposits at Gale crater. To further understand habitability on early Mars, knowledge of the redox states of the aqueous environments is essential because redox disequilibria in environments provide chemical energy to chemoautotrophic life. A key to constraining the redox states is the enrichment of "redox sensitive elements" within sediments. Manganese (Mn) is a redox‐sensitive element, changing its chemical form depending on the redox states. Curiosity and Mars Exploration Rover Opportunity have found Mn enrichments within the veins of ancient sediments on Mars; however, their chemical forms are poorly constrained. Here we constrain the chemical form of the Mn enrichments based on precipitation experiments. Our results suggest that the Mn enrichments on Mars were caused by deposition of MnO2, which requires highly oxidizing conditions in the aqueous environment at the time of deposition. The candidates of the oxidant include molecular oxygen, ozone, perchlorates, and nitrates. We suggest that these oxidants formed in the atmosphere and may have been supplied into reducing groundwater via hydrological cycles on early Mars. Key Points: Scavenging pattern of trace metals on Mn (hydr)oxides is investigated by precipitation experimentsThe scavenging pattern for MnO2 is consistent with the measurements of trace metals within Mn‐rich veins found on MarsTo form MnO2, high‐Eh oxidants formed in the atmosphere need to be supplied to groundwater on early Mars [ABSTRACT FROM AUTHOR]

An induction of polyacrylic acid-modified titanium dioxide with hydrogen peroxide nanoparticles (PAA-TiO2/H2O2NPs) to a tumor exerted a therapeutic enhancement of X-ray irradiation in our previous study. To understand the mechanism of the radiosensitizing effect of PAA-TiO2/H2O2NPs, analytical observations that included DLS, FE-SEM, FT-IR, XAFS, and Raman spectrometry were performed. In addition, highly reactive oxygen species (hROS) which PAA-TiO2/H2O2NPs produced with X-ray irradiation were quantified by using a chemiluminescence method and a EPR spin-trapping method. We found that PAA-TiO2/H2O2NPs have almost the same characteristics as PAA-TiO2. Surprisingly, there were no significant differences in hROS generation. However, the existence of H2O2was confirmed in PAA-TiO2/H2O2NPs, because spontaneous hROS production was observed w/o X-ray irradiation. In addition, PAA-TiO2/H2O2NPs had a curious characteristic whereby they absorbed H2O2molecules and released them gradually into a liquid phase. Based on these results, the H2O2was continuously released from PAA-TiO2/H2O2NPs, and then released H2O2assumed to be functioned indirectly as a radiosensitizing factor. [ABSTRACT FROM PUBLISHER]

Individual distribution constants (KD,A) of picrate ion (Pic−) and extraction constants (Kex±) of NaPic by some crown ethers (L) into benzene (Bz) at 25°C were calculated from data reported previously. These constants were defined as KD,Pic=Pic-o/[Pic-] and Kex±=NaL+oPic-o/(Na+Lo[Pic-]), respectively. Here, the subscript “o” denotes an organic (o) phase and practically o = Bz. 15-Crown-5 ether (15C5), 18-crown-6 one (18C6), and their monobenzo (B) derivatives (B15C5 and B18C6) were selected as L. Interfacial equilibrium-potential differences (Δϕeq) at extraction were estimated at 298 K. A plot of log⁡Kex± versus -Δϕeq for the four L extraction systems gave a straight line with slope = 84 V−1. This slope was compared with those, reported before, of the dichloromethane (DCM), 1,2-dichloroethane (DCE), and nitrobenzene (NB) extraction systems. The slopes of the regression lines were in the order NB < DCM ≤ DCE < Bz. Also, the individual distribution constants of the complex ion NaL+ and an ion-pair complex (NaL+Pic-) into Bz phase were calculated from the above extraction data. At least, a comparison between these values suggests that Bz molecules mainly interact with NaL+ moiety of NaL+Pic-. [ABSTRACT FROM AUTHOR]