In-depth analysis of embedded-type structures of NixMg4-xAl LDO-composited catalysts and the impacts on glycerol conversion under a base- and H2-free condition.

Core-shell composite catalysts composing of AgO@SnO2/ZSM-5 embedded by NixMg4-xAlO LDOs with various Ni/Mg ratios were characterized and tested for the activity on the conversion of glycerol to valuable chemicals under a base-free and external H2-free condition. As a result, the catalytic performance of an embedded composite was found greater than that of its individual constituents, owing to the synergy between a NixMg4-xAlO lodge and embedded AgO@SnO2/ZSM-5. The highest yield of 1,2-propanediol and lactic acid was achieved at the Ni/Mg ratio of 0.2/3.8. NixMg4-xAlO lodges were found to simultaneously drive glycerol dehydration to acetol and glycerol reforming, driven by Ni sites, forming in-situ H2 that enhances 1,2-propanediol formation whereas the AgO@SnO2/ZSM-5 clusters governed acetol oxidation and Cannizzaro reaction that led to the formation of lactic acid. At a high Ni/Mg ratio, the NixMg4-xAlO lodges completely covered AgO@SnO2/ZSM-5 clusters entirely, resulting in the suppression of lactic acid yield due to over-oxidation.

Charge transfer and X-ray absorption investigations in aluminium and copper co-doped zinc oxide nanostructure for perovskite solar cell electrodes.

This study explores influence of charge transfer and X-ray absorption characteristics in aluminum (Al) and copper (Cu) co-doped zinc oxide (ZnO) nanostructures for perovskite solar cell electrodes. Sol-gel technique was employed to synthesize the nanostructures, and their optical and morphological properties were investigated. X-ray diffraction (XRD) analysis confirmed high crystallinity and also single-phase composition of all the samples, particularly up to 5% Al co-doping. Field emission scanning electron microscopy (FESEM) exhibited the formation of pseudo-hexagonal wurtzite nanostructure and the transition to nanorods at 5% Al co-doping. Diffuse reflectance spectroscopy indicated a reduction in the optical band gap of co-doped zinc oxide from 3.11 to 2.9 eV with increasing Al doping. Photoluminescence spectra (PL) exhibited a decrease in peak intensity, suggesting enhanced conductivity in ZnO, also confirmed from I-V measurements. Near-edge X-ray absorption fine structure (NEXAFS) analysis depicts that charge transfer from Al to oxygen (O) species enhanced the photosensing properties of the nanostructure, which was supported by FESEM micrographs and PL spectra. Furthermore, the study discovered that 5% Al co-doping significantly reduced the density of emission defects (deep-level) in Cu-ZnO nanostructure. These findings highlight the potential of Cu and Al co-doped ZnO materials for perovskite solar cell electrodes, as their improved optical and morphological properties resulting from charge transfer could enhance device performance. The investigation of charge transfer and X-ray absorption characteristics provides valuable insights into the underlying mechanisms and behaviors of the co-doped ZnO nanostructures. However, further research is required to delve into the intricate hybridization resulting from charge transfer and explore the broader impact of co-doping on other properties of the nanostructures, enabling a comprehensive understanding of their potential applications in perovskite solar cells.

A new full-field XRF imaging station at Synchrotron Light Research Institute.

A full-field X-ray fluorescence imaging (FXI) station was recently developed at beamline BL8 of Synchrotron Light Research Institute (SLRI), Thailand. An unfocused, synchrotron X-ray beam from the bending magnet with a size of 2 mm (vertical) × 13 mm (horizontal) and photon energy of 10 keV was employed in the FXI experiments. A sample stage was tilted by 7.5° to enlarge the vertical beam size. X-ray fluorescence images were recorded by an energy-dispersive, 256 × 256 array, pn-type charge coupled device detector equipped with a polycapillary optics, providing a full-frame image size of 12.3 mm × 12.3 mm. The incident photon flux per pixel was 3 × 104 photons s-1 (100 mA)-1 and the experimental spatial resolution was 68 µm. Image processing was carried out offline using an in-house MATLAB program capable of elemental selection and inhomogeneity intensity correction. Elemental detection limits of FXI were found to decrease with increasing atomic number, i.e. 0.3 to 0.03 wt% for Z = 19 (K) to 30 (Zn). Compared with the BL6b microbeam imaging (µXI) station at SLRI with higher photon flux per pixel, 3 × 1010 photons s-1 (100 mA)-1, a tenfold sample area can be obtained and 13 times higher peak-to-background (PKB) ratio at Zn Kα measured with the same experimental time (8 h). Simultaneous measurement of FXI is more time-efficient against the long overhead times of µXI scanning over large pixel numbers, >65000. To demonstrate potential applications of the new FXI station, various types of samples were examined: dendritic limestone, ancient bronze and dried fish. Analyzed elemental images enabled us to identify areas rich in Mn on the limestone, Sn and Cu separation in the bronze, and Zn nutrition in the dried fish eye.

Synthesis and structural characterisation of solid titanium(IV) phosphate materials by means of X-ray absorption and NMR spectroscopy.

Solid titanium phosphate, TiP, materials hold great promise for wastewater treatment for removal of metal ions and complexes. A series of TiP materials, synthesised at mild conditions and short reaction times, have been structurally characterised using solid-state X-ray absorption spectroscopy, phosphorus and titanium K edge XANES and EXAFS, and 31P and 47/49Ti NMR spectroscopy. The titanium K edge EXAFS data of α-Ti(HPO4)2·H2O (α-TiP) revealed octahedral coordination of oxygens around titanium. Repeated washing of primary ß-/γ-TiP with hydrochloric acid results in formation of a weakly ordered solid, TiO(OH)(H2PO4)·H2O, TiP1-H. The structure of TiP1-H is shown by Ti EXAFS to be a titanyl compound, containing a short TiO bond. The analogous data for linked titanium phosphate compounds (LTP) disclosed that inter-linkage occurs between α-TiP and titanyl phosphate units, supported by 31P-31P NOESY NMR data. 47/49Ti NMR and Ti pre-edge XANES show evidence of two different titanium environments in LTP, one very similar to that observed in TiP1-H and a second more symmetric octahedral environment. Data are discussed in terms of induced acidic hydrolyses of titanium(IV) and phosphate counterpart during washings with hydrochloric acid and water. A straightforward relation between synthesis parameters/post synthetic treatment and structural re-arrangement in the materials is established.

Sulfur speciation in drained and restored minerotrophic peatland types of northeastern Germany.

Restoring drained peatlands has been practiced to mitigate climate change, regulate water quality, and restore biodiversity. However, no information is available on the long-term impact of drainage and restoration of peatlands on total sulfur (St), fractions, and S species. We investigated the long-term drained and restored forested and coastal peatlands and percolation mires using the sequential S fractionation and S K-edge X-ray near-edge absorption structure (XANES) spectroscopy analysis to address this knowledge gap. The St concentrations in the drained forested peatland and percolation mire were low by 4 and 1.5 folds compared to their respective restored peatlands at the topsoil horizons. Similarly, the H2O-S and NaH2PO4-S fractions in the drained forested peatland (28 and 18 mg kg-1) were lower than in the restored forested peatland (165 and 166 mg kg-1). However, the S fractions were higher in the drained percolation mire (449 and 247 mg kg-1) than in the restored percolation mire (150 and 41 mg kg-1). The relative proportion of the residual-S fraction (70-97% of St) was equivalent to the relative proportion of organic S species (76-97% of St) derived from the XANES analysis. The XANES analysis revealed the reduced organic S (44-62%), organic S with intermediate oxidation states (16-47%), strongly reduced (0-21%) and oxidized inorganic S species (4-12%) of the St. The results indicate that long-term restoration conserved St, decreased labile S fractions and enriched the strongly reduced inorganic and organic S species.

Insight into the Roles of Metal Loading on CO2 Photocatalytic Reduction Behaviors of TiO2.

The photocatalytic reduction of carbon dioxide (CO2) into value-added chemicals is considered to be a green and sustainable technology, and has recently gained considerable research interest. In this work, titanium dioxide (TiO2) supported Pt, Pd, Ni, and Cu catalysts were synthesized by photodeposition. The formation of various metal species on an anatase TiO2 surface, after ultraviolet (UV) light irradiation, was investigated insightfully by the X-ray absorption near edge structure (XANES) technique. CO2 reduction under UV-light irradiation at an ambient pressure was demonstrated. To gain an insight into the charge recombination rate during reduction, the catalysts were carefully investigated by the intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence spectroscopy (PL). The catalytic behaviors of the catalysts were investigated by density functional theory using the self-consistent Hubbard U-correction (DFT+U) approach. In addition, Mott-Schottky measurement was employed to study the effect of energy band alignment of metal-semiconductor on CO2 photoreduction. Heterojunction formed at Pt-, Pd-, Ni-, and Cu-TiO2 interface has crucial roles on the charge recombination and the catalytic behaviors. Furthermore, it was found that Pt-TiO2 provides the highest methanol yield of 17.85 µmol/gcat/h, and CO as a minor product. According to the IMPS data, Pt-TiO2 has the best charge transfer ability, with the mean electron transit time of 4.513 µs. We believe that this extensive study on the junction between TiO2 could provide a profound understanding of catalytic behaviors, which will pave the way for rational designs of novel catalysts with improved photocatalytic performance for CO2 reduction.

Soil phosphorus status and P nutrition strategies of European beech forests on carbonate compared to silicate parent material.

Sustainable forest management requires understanding of ecosystem phosphorus (P) cycling. Lang et al. (2017) [Biogeochemistry, https://doi.org/10.1007/s10533-017-0375-0] introduced the concept of P-acquiring vs. P-recycling nutrition strategies for European beech (Fagus sylvatica L.) forests on silicate parent material, and demonstrated a change from P-acquiring to P-recycling nutrition from P-rich to P-poor sites. The present study extends this silicate rock-based assessment to forest sites with soils formed from carbonate bedrock. For all sites, it presents a large set of general soil and bedrock chemistry data. It thoroughly describes the soil P status and generates a comprehensive concept on forest ecosystem P nutrition covering the majority of Central European forest soils. For this purpose, an Ecosystem P Nutrition Index (ENI P ) was developed, which enabled the comparison of forest P nutrition strategies at the carbonate sites in our study among each other and also with those of the silicate sites investigated by Lang et al. (2017). The P status of forest soils on carbonate substrates was characterized by low soil P stocks and a large fraction of organic Ca-bound P (probably largely Ca phytate) during early stages of pedogenesis. Soil P stocks, particularly those in the mineral soil and of inorganic P forms, including Al- and Fe-bound P, became more abundant with progressing pedogenesis and accumulation of carbonate rock dissolution residue. Phosphorus-rich impure, silicate-enriched carbonate bedrock promoted the accumulation of dissolution residue and supported larger soil P stocks, mainly bound to Fe and Al minerals. In carbonate-derived soils, only low P amounts were bioavailable during early stages of pedogenesis, and, similar to P-poor silicate sites, P nutrition of beech forests depended on tight (re)cycling of P bound in forest floor soil organic matter (SOM). In contrast to P-poor silicate sites, where the ecosystem P nutrition strategy is direct biotic recycling of SOM-bound organic P, recycling during early stages of pedogenesis on carbonate substrates also involves the dissolution of stable Ca-Porg precipitates formed from phosphate released during SOM decomposition. In contrast to silicate sites, progressing pedogenesis and accumulation of P-enriched carbonate bedrock dissolution residue at the carbonate sites promote again P-acquiring mechanisms for ecosystem P nutrition. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10533-021-00884-7.

Covalent Grafting of Ruthenium Complexes on Iron Oxide Nanoparticles: Hybrid Materials for Photocatalytic Water Oxidation.

The present environmental crisis prompts the search for renewable energy sources such as solar-driven production of hydrogen from water. Herein, we report an efficient hybrid photocatalyst for water oxidation, consisting of a ruthenium polypyridyl complex covalently grafted on core/shell Fe@FeOx nanoparticles via a phosphonic acid group. The photoelectrochemical measurements were performed under 1 sun illumination in 1 M KOH. The photocurrent density of this hybrid photoanode reached 20 µA/cm2 (applied potential of +1.0 V vs reversible hydrogen electrode), corresponding to a turnover frequency of 0.02 s-1. This performance represents a 9-fold enhancement of that achieved with a mixture of Fe@FeOx nanoparticles and a linker-free ruthenium polypyridyl photosensitizer. This increase in performance could be attributed to a more efficient electron transfer between the ruthenium photosensitizer and the Fe@FeOx catalyst as a consequence of the covalent link between these two species through the phosphonate pendant group.

Interfacial electronic structure engineering on molybdenum sulfide for robust dual-pH hydrogen evolution.

Molybdenum disulfide, as an electronic highly-adjustable catalysts material, tuning its electronic structure is crucial to enhance its intrinsic hydrogen evolution reaction (HER) activity. Nevertheless, there are yet huge challenges to the understanding and regulation of the surface electronic structure of molybdenum disulfide-based catalysts. Here we address these challenges by tuning its electronic structure of phase modulation synergistic with interfacial chemistry and defects from phosphorus or sulfur implantation, and we then successfully design and synthesize electrocatalysts with the multi-heterojunction interfaces (e.g., 1T0.81-MoS2@Ni2P), demonstrating superior HER activities and good stabilities with a small overpotentials of 38.9 and 95 mV at 10 mA/cm2, a low Tafel slopes of 41 and 42 mV/dec in acidic as well as alkaline surroundings, outperforming commercial Pt/C catalyst and other reported Mo-based catalysts. Theoretical calculation verified that the incorporation of metallic-phase and intrinsic HER-active Ni-based materials into molybdenum disulfide could effectively regulate its electronic structure for making the bandgap narrower. Additionally, X-ray absorption spectroscopy indicate that reduced nickel possesses empty orbitals, which is helpful for additional H binding ability. All these factors can decrease Mo-H bond strength, greatly improving the HER catalytic activity of these materials.

Highly porous Co-doped NiO nanorods: facile hydrothermal synthesis and electrocatalytic oxygen evolution properties.

Highly porous 3d transition metal oxide nanostructures are opening up the exciting area of oxygen evolution reaction (OER) catalysts in alkaline medium thanks to their good thermal and chemical stability, excellent physiochemical properties, high specific surface area and abundant nanopores. In this paper, highly porous Co-doped NiO nanorods were successfully synthesized by a simple hydrothermal method. The porous rod-like nanostructures were preserved with the added cobalt dopant ranging from 1 to 5 at% but were broken into aggregated nanoparticles at higher concentrations of additional cobalt. The catalytic activity of Co-doped NiO nanostructures for OER in an alkaline medium was assayed. The 5%Co-NiO sample showed a drastically enhanced activity. This result could originate from the combination of advantageous characteristics of highly porous NiO nanorods such as large surface area and high porosity as well as the important role of Co dopant that could provide more catalytic active sites, leading to an enhanced catalytic activity of the nanocatalyst.

Natural Kaolin-Based Ni Catalysts for CO2 Methanation: On the Effect of Ce Enhancement and Microwave-Assisted Hydrothermal Synthesis.

Natural kaolin-based Ni catalysts have been developed for low-temperature CO2 methanation. The catalysts were prepared via a one-step co-impregnation of Ni and Ce onto a natural kaolin-derived metakaolin using a microwave-assisted hydrothermal method as an acid-/base-free synthesis method. The influences of microwave irradiation and Ce promotion on the catalytic enhancement including the CO2 conversion, CH4 selectivity, and CH4 yield were experimentally investigated by a catalytic test of as-prepared catalysts in a fixed-bed tubular reactor. The relationship between the catalyst properties and its methanation activities was revealed by various characterization techniques including X-ray fluorescence, X-ray diffraction, Brunauer-Emmett-Teller, scanning electron microscopy, selected area electron diffraction, transmission electron microscopy, elemental mapping, H2 temperature-programmed reduction, and X-ray absorption near-edge structure analyses. Among the two enhancement methods, microwave and Ce promotion, the microwave-assisted synthesis could produce a catalyst containing highly dispersed Ni particles with a smaller Ni crystallite size and higher catalyst reducibility, resulting in a higher CO2 conversion from 1.6 to 7.5% and a better CH4 selectivity from 76.3 to 79.9% at 300 °C. Meanwhile, the enhancement by Ce addition exhibited a great improvement on the catalyst activities. It was experimentally found that the CO2 conversion increased approximately 7-fold from 7.5 to 52.9%, while the CH4 selectivity significantly improved from 79.9 to 98.0% at 300 °C. Though the microwave-assisted synthesis could further improve the catalyst activities of Ce-promoted catalysts, the Ce addition exhibited a more prominent impact than the microwave enhancement. Cerium oxide (CeO2) improved the catalyst activities through mechanisms of higher CO2 adsorption capacity with its basic sites and the unique structure of CeO2 with a reversible valence change of Ce4+ and Ce3+ and high oxygen vacancies. However, it was found that the catalyst prepared by microwave-assisted synthesis and Ce promotion proved to be the optimum catalyst in this study. Therefore, the present work demonstrated the potential to synthesize a nickel-based catalyst with improved catalytic activities by adding a small amount of Ce as a catalytic promoter and employing microwave irradiation for improving the Ni dispersion.

Incorporation of Al3+ Sites on Brønsted Acid Metal-Organic Frameworks for Glucose-to-Hydroxylmethylfurfural Transformation.

5-hydroxylmethylfurfural (HMF) is a bio-based chemical that can be prepared from natural abundant glucose by using combined Brønsted-Lewis acid catalysts. In this work, Al3+ catalytic site has been grafted on Brønsted metal-organic frameworks (MOFs) to enhance Brønsted-Lewis acidity of MOF catalysts for a one-pot glucose-to-HMF transformation. The uniform porous structure of zirconium-based MOFs allows the optimization of both acid strength and density of acid sites in MOF-based catalysts by incorporating the desired amount of Al3+ catalytic sites at the organic linker. Al3+ sites generated via a post-synthetic modification act as Lewis acid sites located adjacent to the Brønsted sulfonated sites of MOF structure. The local structure of the Al3+ sites incorporated in MOFs has been elucidated by X-ray absorption near-edge structure (XANES) combined with density functional theory (DFT) calculations. The cooperative effect from Brønsted and Lewis acids located in close proximity and the high acid density is demonstrated as an important factor to achieve high yield of HMF.

Influence of Physical-Chemical Soil Parameters on Microbiota Composition and Diversity in a Deep Hyperarid Core of the Atacama Desert.

The extreme environmental conditions and lack of water on the soil surface in hyperarid deserts hamper microbial life, allowing only highly specialized microbial communities to the establish colonies and survive. Until now, the microbial communities that inhabit or have inhabited soils of hyperarid environments at greater depths have been poorly studied. We analyzed for the first time the variation in microbial communities down to a depth of 3.4 m in one of the driest places of the world, the hyperarid Yungay region in the Atacama Desert, and we related it to changes in soil physico-chemical characteristics. We found that the moisture content changed from 2 to 11% with depth and enabled the differentiation of three depth intervals: (i) surface zone A (0-60 cm), (ii) intermediate zone B (60-220 cm), and (iii) deep zone C (220-340 cm). Each zone showed further specific physicochemical and mineralogical features. Likewise, some bacterial phyla were unique in each zone, i.e., members of the taxa Deinococcota, Halobacterota, and Latescibacterota in zone A; Crenarchaeota, Fusobacteriota, and Deltaproteobacterium Sva0485 in zone B; and Fervidibacteria and Campilobacterota in zone C, which indicates taxon-specific preferences in deep soil habitats. Differences in the microbiota between the zones were rather abrupt, which is concomitant with abrupt changes in the physical-chemical parameters. Overall, moisture content, total carbon (TC), pH, and electric conductivity (EC) were most predictive of microbial richness and diversity, while total sulfur (TS) and total phosphorous (TP) contents were additionally predictive of community composition. We also found statistically significant associations between taxa and soil properties, most of which involved moisture and TC contents. Our findings show that under-explored habitats for microbial survival and existence may prevail at greater soil depths near water or within water-bearing layers, a valuable substantiation also for the ongoing search for biosignatures on other planets, such as Mars.

Micro and nano sized particles in leachates from agricultural soils: Phosphorus and sulfur speciation by X-ray micro-spectroscopy.

Colloids and nanoparticles leached from agricultural land are major carriers of potentially bioavailable nutrients with high mobility in the environment. Despite significant research efforts, accurate knowledge of macronutrients in colloids and nanoparticles is limited. We used multi-elemental synchrotron X-ray fluorescence (XRF) microscopy with multivariate spatial analysis and X-ray atomic absorption near-edge structure (XANES) spectroscopy at the P and S K-edges, to study the speciation of P and S in two fractions of leached particles, >0.45 and <0.45 µm respectively, collected from four tile-drained agricultural sites in Sweden. P K-edge XANES showed that organic P, followed by P adsorbed to surfaces of aluminum-bearing particles were the most common forms of leached P. Iron-bound P (Fe-P) forms were generally less abundant (0-30 % of the total P). S K-edge XANES showed that S was predominantly organic, and a relatively high abundance of reduced S species suggests that redox conditions were adverse to the persistence of P bound to Fe-bearing colloids in the leachates. Acid ammonium-oxalate extractions suggested that P associated with Al and Fe (Al-P and Fe-P) in most cases could be explained by the adsorption capacity of non-crystalline (oxalate-extractable) oxides of Al and Fe. These results improve our understanding of particulate P and S speciation in the vadose zone and helps in developing effective technologies for mitigating colloidal driven eutrophication of water bodies near agricultural land.

The Adsorption of Per- and Polyfluoroalkyl Substances (PFASs) onto Ferrihydrite Is Governed by Surface Charge.

An improved quantitative and qualitative understanding of the interaction of per- and polyfluoroalkyl substances (PFASs) and short-range ordered Fe (hydr)oxides is crucial for environmental risk assessment in environments low in natural organic matter. Here, we present data on the pH-dependent sorption behavior of 12 PFASs onto ferrihydrite. The nature of the binding mechanisms was investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and by phosphate competition experiments. Sulfur K-edge XANES spectroscopy showed that the sulfur atom of the head group of the sulfonated PFASs retained an oxidation state of +V after adsorption. Furthermore, the XANES spectra did not indicate any involvement of inner-sphere surface complexes in the sorption process. Adsorption was inversely related to pH (p < 0.05) for all PFASs (i.e., C3-C5 and C7-C9 perfluorocarboxylates, C4, C6, and C8 perfluorosulfonates, perfluorooctane sulfonamide, and 6:2 and 8:2 fluorotelomer sulfonates). This was attributed to the pH-dependent charge of the ferrihydrite surface, as reflected in the decrease of surface ζ-potential with increasing pH. The importance of surface charge for PFAS adsorption was further corroborated by the observation that the adsorption of PFASs decreased upon phosphate adsorption in a way that was consistent with the decrease in ferrihydrite ζ-potential. The results show that ferrihydrite can be an important sorbent for PFASs with six or more perfluorinated carbons in acid environments (pH ≤ 5), particularly when phosphate and other competitors are present in relatively low concentrations.

Phosphate competition with arsenate on poorly crystalline iron and aluminum (hydr)oxide mixtures.

Phosphate competes with arsenate for sorption sites on poorly crystalline iron and aluminum (hydr)oxides. The competition has implications e.g. for the management of arsenic-contaminated soil and water. Phosphate competition with arsenate on mixed phases containing both iron and aluminum (hydr)oxides has rarely been investigated. Here, the phosphate competition with arsenate on mixtures of poorly crystalline aluminum hydroxide (Alhox) and ferrihydrite (Fh), was investigated in batch experiments at pH 6.5. X-ray absorption spectroscopy (XAS) was performed on the phosphorus and arsenic K edges, which offered a unique insight in the partitioning of arsenate and phosphate on mixed Alhox-Fh sorbents. Under the studied conditions the sorption capacity of the mixed sorbents (per mol Al or Fe) increased at higher Alhox to Fh ratios. The XAS measurements provided direct evidence that phosphate competed more effectively with arsenate for sorption sites on Alhox than on Fh. For example, in a mixture with 50% of both sorbents and with similar additions of arsenate and phosphate, 71% of the oxyanions adsorbed on Fh and 46% on Alhox were arsenate. Consequently, phosphate may mobilize arsenate more easily from mixed iron-aluminum matrices that are rich in aluminum.

Solvent-Free Hydrodeoxygenation of Triglycerides to Diesel-like Hydrocarbons over Pt-Decorated MoO2 Catalysts.

In the present work, the solvent-free hydrodeoxygenation of palm oil as a representative triglyceride model compound to diesel-like hydrocarbons was evaluated in a batch reactor using Pt-decorated MoO2 catalysts. The catalysts with various Pt loadings (0.5-3%) were synthesized by an incipient wetness impregnation method. The metallic Pt and MoO2 phases were detected in the XRD patterns of as-prepared catalysts after the reaction and acted as active components for the deoxygenation reactions. The XPS experiments confirmed the existence of metallic Pt and PtO x species. The XANES investigation of Mo L3-edge spectra elucidated a change in the valence state by the transformation of MoO3 into MoO2 species after the deoxygenation reaction. The TEM observation revealed the formation of Pt nanoparticles in the range of 1-3 nm decorated on MoO2 species. The number of acid sites increased with stronger metal-support interactions on increasing the Pt loading. The catalytic performance of the MoO2 catalyst significantly improved with a small amount of Pt decoration. However, the further increase in Pt loading did not relatively increase the deoxygenation activity due to the formation of the agglomerated Pt particles. The high performance of the decorated catalysts could be attributed to the moderate acidity from the Pt dispersed on MoO2 toward decarbonylation and decarboxylation reactions.

A Novel Approach for the Quantification of Different Inorganic and Organic Phosphorus Compounds in Environmental Samples by P L2,3-Edge X-ray Absorption Near-Edge Structure (XANES) Spectroscopy.

Phosphorus (P) is an essential element for life on Earth, with an important and oftentimes unaccounted organic biogeochemical component. Current methods for the quantification of different organic P compounds in environmental samples (e.g., soils, sediments) are based on extraction techniques and often associated with incomplete P recovery or sample changes. In this study, we present a protocol for the quantification of different organic and inorganic P species in soils using synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the P L2,3-edge. Its accuracy and precision was evaluated by analyzing 40 standard mixtures composed of seven different inorganic and organic P compounds (with a mean of R2 = 0.85). In addition, we quantified the P species of two soils and two agro-industrial byproducts using P L2,3-edge XANES spectroscopy and the results were compared with those obtained by P K-edge XANES or 31P NMR spectroscopy. Using the P L2,3-edge, we identified different organic P species, including those not identified by the common P K-edge XANES. However, there is a consistent underestimation of organic polyphosphates. Overall, the application of P L2,3-edge XANES provides a higher level of information than by P K-edge XANES, although the ubiquitous use of this novel methodology is still limited to samples with a phosphorus content above 3 mg g-1.

Transformation of Calcium Phosphates in Alkaline Vertisols by Acidified Incubation.

Acid-soluble soil phosphorus (P) is a potential resource in P-limited agricultural systems that may become critical as global P sources decrease in the future. The fate of P in three alkaline Vertisols, a major agricultural soil type, after acidic incubation was investigated using synchrotron-based K-edge X-ray absorption near-edge structure (XANES) spectroscopy, geochemical modeling, wet chemistry soil extraction, and a P sorption index. Increases in labile P generally coincided with decreased stability and dissolution of calcium phosphate (CaP) minerals. However, only a minor proportion of the CaP dissolved in each soil was labile. In two moderate-P soils (800 mg P kg-1), XANES indicated that approximately 160 mg kg-1 was repartitioned to sorbed phases at pH 5.1 of one soil and at pH 4.4 of the second; however, only 40 and 28% were labile, respectively. In a high-P soil (8900 mg P kg-1), XANES indicated a decrease in P of 1170 mg kg-1 from CaP minerals at pH 3.8, of which approximately only 33% was labile. Phosphorus mobilized by agricultural practices without concurrent uptake by plants may be repartitioned to sorbed forms that are not as plant-available as prior to acidification.

Phosphorus K-edge XANES spectroscopy has probably often underestimated iron oxyhydroxide-bound P in soils.

Phosphorus (P) K-edge X-ray absorption near-edge structure (XANES) spectra of orthophosphate (oPO4) bound to soil FeIII minerals (e.g. ferrihydrite, goethite) show a pre-edge signal at 2148-2152 eV. It is unknown whether organic P bound to FeIII oxyhydroxides also show this feature. Otherwise, Fe-bound soil P may be underestimated by P K-edge XANES spectroscopy, because a large portion of Fe oxyhydroxide-bound P in soils is organic P. K-edge XANES spectra were obtained for different organic P compounds present in soils [inositol hexaphosphate (IHP), glucose-6-phosphate (G6P), adenosine triphosphate (ATP)] after sorption to ferrihydrite or goethite and compared with spectra of oPO4 adsorbed to these minerals. P sorption to ferrihydrite increased in the sequence IHP ≪ G6P < oPO4 < ATP. P sorption to goethite increased in the sequence G6P < oPO4 ≪ ATP = IHP. Pre-edge signals in P K-edge XANES spectra of organic P adsorbed to Fe oxyhydroxides were markedly smaller compared with those of oPO4 adsorbed to these minerals and absent for FeIII oxyhydroxide-bound ATP as well as goethite-bound IHP. Linear combination fitting (LCF) performed on spectra of IHP, G6P or ATP adsorbed to ferrihydrite or goethite, using only spectra of FeIII oxyhydroxide-bound oPO4 as reference compounds for Fe-bound P, erroneously assigned >93% (ferrihydrite) or >41% (goethite) of Fe-bound P to non-Fe-bound P species. Inclusion of FeIII oxyhydroxide-bound IHP as reference compounds markedly increased the recovery of oxyhydroxide-bound organic P. Thus, Fe-bound soil P has probably often been underestimated by LCF in soil XANES studies where IHP adsorbed to ferrihydrite and to goethite were not included as reference compounds.