| 1. |
- Mäkie, Peter, et al.
(författare)
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Solar Light Degradation of Trimethyl Phosphate and Triethyl Phosphate on Dry and Water-Precovered Hematite and Goethite Nanoparticles
- 2012
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Ingår i: The Journal of Physical Chemistry C. - Washtington : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:28, s. 14917-14929
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Tidskriftsartikel (refereegranskat)abstract
- We report on the solar-light-mediated degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on hematite and goethite nanoparticles in synthetic air. Adsorption and photoreactions of TMP and TEP were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) on dry and water-precovered nanoparticles in dark and under simulated solar light irradiation. Two-dimensional correlation analysis of infrared spectra was used to identify surface products as a function of reaction time. The optical properties of the hematite and goethite nanoparticles were investigated with optical spectrophotometry. The optical band gap was determined by analysis of the Tauc relationship around the band gap energy, E-g, yielding band gap energies of 2.14 and 2.28 eV for hematite and goethite nanoparticles, respectively. It is found that both TMP and TEP are readily photodegraded upon solar light irradiation (employing AM1.5 filters with 1735 W m(-2)), yielding surface orthophosphate as the final product. The first step in the dissociation of TMP and TEP is displacement of the methoxy and ethoxy groups, respectively, yielding adsorbed dimethyl phosphate (DMP) and methoxy, and diethyl phosphate (DEP) and ethoxy intermediates. Further photodegradation displaces additional methoxy and ethoxy groups with adsorbed orthophosphate as final reaction product. Methoxy and ethoxy fragments are simultaneously oxidized to carboxylates and carbonates. Photodegradation of TMP and TEP is promoted by OH radicals, which is evidenced by the higher photodegradation rate on water-precovered surfaces. The rate of TMP degradation is higher than that for TEP contrary to what is expected from their corresponding bulk hydrolysis rates, but consistent with their surface reactivity in dark, where TMP is observed to dissociate at room temperature but not TEP (or only very slowly). The photodegradation rate is higher on the goethite nanoparticles than the hematite nanoparticles on both dry and water precovered surfaces. The TMP and TEP photodegradation rate constants are found to be 0.025 (0.058) and 0.008 (0.023) min(-1), respectively, on water-precovered hematite (goethite) nanoparticles.
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| 2. |
- Winter, Johannes, et al.
(författare)
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Charge transfer in alkali-metal-doped polymeric fullerenes
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54, s. 17486-17492
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Tidskriftsartikel (refereegranskat)abstract
- We present room-temperature Raman measurements of pressure-polymerized C60 and compare them with the spectra of RbC60 in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized C60 and the rubidium-doped orthorhombic compound, have the same overall structure and the AC60 compounds can be considered as the doped species of the C60, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency Hg(7) and Hg(8) modes. The low values for the coupling constants compared to the ones in the K3C60 can explain the lack of superconductivity in the AC60 compounds.
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| 3. |
- Rineau, F., et al.
(författare)
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Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus
- 2013
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Ingår i: The ISME Journal. - : nternational Society for Microbial Ecology. - 1751-7362 .- 1751-7370. ; 7:10, s. 2010-2022
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Tidskriftsartikel (refereegranskat)abstract
- The majority of nitrogen in forest soils is found in organic matter-protein complexes. Ectomycorrhizal fungi (EMF) are thought to have a key role in decomposing and mobilizing nitrogen from such complexes. However, little is known about the mechanisms governing these processes, how they are regulated by the carbon in the host plant and the availability of more easily available forms of nitrogen sources. Here we used spectroscopic analyses and transcriptome profiling to examine how the presence or absence of glucose and/or ammonium regulates decomposition of litter material and nitrogen mobilization by the ectomycorrhizal fungus Paxillus involutus. We found that the assimilation of nitrogen and the decomposition of the litter material are triggered by the addition of glucose. Glucose addition also resulted in upregulation of the expression of genes encoding enzymes involved in oxidative degradation of polysaccharides and polyphenols, peptidases, nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism. In contrast, the addition of ammonium to organic matter had relatively minor effects on the expression of transcripts and the decomposition of litter material, occurring only when glucose was present. On the basis of spectroscopic analyses, three major types of chemical modifications of the litter material were observed, each correlated with the expression of specific sets of genes encoding extracellular enzymes. Our data suggest that the expression of the decomposition and nitrogen assimilation processes of EMF can be tightly regulated by the host carbon supply and that the availability of inorganic nitrogen as such has limited effects on saprotrophic activities.
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| 4. |
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| 5. |
- Sundman, Anneli, et al.
(författare)
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XAS study of iron speciation in soils and waters from a boreal catchment
- 2014
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 364, s. 93-102
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Tidskriftsartikel (refereegranskat)abstract
- Iron (Fe) is a key element, strongly influencing the biogeochemistry of soils, sediments and waters, but the knowledge about the variety of Fe species present in these systems is still limited. In this work we have used X-ray absorption spectroscopy (XAS) to study the speciation of Fe in soils and waters from a boreal catchment in northern Sweden. The aim was to better understand the controls of Fe speciation across different, but adjacent landscape elements including soil, soil solution, groundwater and stream water draining catchments with contrasting land characteristics. Our results showed that all samples contained mixtures of Fe(II) and Fe(III). The soils consisted of Fe phyllosilicates, Fe (hydr)oxides and Fe complexed by natural organic matter (NOM). All aqueous samples contained Fe(II)– and Fe(III)–NOM complexes, often in combination with Fe(III) (hydr)oxides that were associated with NOM. The variation in contribution from Fe–NOM and Fe (hydr)oxides was controlled by pH and total concentrations of NOM. The XAS spectra suggested formation of mononuclear Fe–NOM complexes consisting of chelate ring structures, but it could not be determined whether they originated solely from Fe(III)– or from a mixture of Fe(II)/Fe(III)–NOM complexes. Our collective results showed that the Fe speciation was highly variable across the different landscape elements and streams. This variation was manifested both in the distribution between mononuclear Fe–NOM complexes and Fe (hydr)oxides associated with NOM and between Fe(II) and Fe(III). These results highlight the complexity of Fe speciation in natural environmental systems and thus the challenges in interpreting Fe reactivity.
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| 6. |
- Vincent, Andrea, et al.
(författare)
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Soil organic phosphorus transformations in a boreal forest chronosequence
- 2013
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Ingår i: Plant and Soil. - Dordrecht : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 367:1-2, s. 149-162
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Tidskriftsartikel (refereegranskat)abstract
- Soil phosphorus (P) composition changes with ecosystem development, leading to changes in P bioavailability and ecosystem properties. Little is known, however, about how soil P transformations proceed with ecosystem development in boreal regions. We used 1-dimensional P-31 and 2-dimensional H-1, P-31 correlation nuclear magnetic resonance (NMR) spectroscopy to characterise soil organic P transformations in humus horizons across a 7,800 year-old chronosequence in Vasterbotten, northern Sweden. Total soil P concentration varied little along the chronosequence, but P compounds followed three trends. Firstly, the concentrations of DNA, 2-aminoethyl phosphonic acid, and polyphosphate, increased up to 1,200-2,700 years and then declined. Secondly, the abundances of alpha- and beta-glycerophosphate, nucleotides, and pyrophosphate, were higher at the youngest site compared with all other sites. Lastly, concentrations of inositol hexakisphosphate fluctuated with site age. The largest changes in soil P composition tended to occur in young sites which also experience the largest shifts in plant community composition. The apparent lack of change in total soil P is consistent with the youth and nitrogen limited nature of the Vasterbotten chronosequence. Based on 2D NMR spectra, around 40 % of extractable soil organic P appeared to occur in live microbial cells. The observed trends in soil organic P may be related to shifts in plant community composition (and associated changes in soil microorganisms) along the studied chronosequence, but further studies are needed to confirm this.
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| 7. |
- Edo Gimenez, Mar, et al.
(författare)
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Fate of metals and emissions of organic pollutants from torrefaction of waste wood, MSW, and RDF
- 2017
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Ingår i: Waste Management. - Oxford : Elsevier. - 0956-053X .- 1879-2456. ; 68, s. 646-652
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Tidskriftsartikel (refereegranskat)abstract
- Torrefaction of municipal solid waste (MSW), refuse-derived fuel (RDF), and demolition and construction wood (DC) was performed at 220°C and a residence time of 90 min in a bench-scale reactor. The levels of toxic polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) contained in emission from the torrefaction process were evaluated. In addition, main ash-forming elements and trace metals in the raw feedstock and char were determined. The use of MSW in fuel blends with DC resulted in lower PCDD and PCDF emissions after torrefaction, compared with the RDF blends. The migration of chlorine from the feedstock to the gas phase reduces the chlorine content of the char which may reduce the risk of alkali chloride-corrosion in char combustion. However, trace metals catalytically active in the formation of PCDD and PCDF remain in the char, thereby may promote PCDD and PCDF formation during subsequent char combustion for energy recovery; this formation is less extensive than when the feedstock is used.
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| 8. |
- Jalilehvand, F., et al.
(författare)
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New class of oligonuclear platinum-thallium compounds with a direct metal-metal bond. 5. Structure determination of heterodimetallic cyano complexes in aqueous solution by EXAFS and vibrational spectroscopy
- 2001
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:16, s. 3889-3899
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Tidskriftsartikel (refereegranskat)abstract
- The structures of three closely related heterodimetallic cyano complexes, [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 1-3), formed in reactions between [Pt-II(CN)(4)](2-) and Tl-III cyano complexes, have been studied in aqueous solution. Multinuclear NMR data ((TI)-T-205, Pt-195, and C-13) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and TlLIII edges. The EXAFS data show, after developing a model describing the extensive multiple scattering within the linearly coordinated cyano ligands, short Pt-Tl bond distances in the [(NC)(5)Pt-Tl(CN)(n)](n-) complexes: 2.60(1), 2.62(1), and 2.64(1) Angstrom for n = 1-3, respectively. Thus, the Pt-Tl bond distance increases with increasing number of cyano ligands on the thallium atom. In all three complexes the thallium atom and five cyano ligands, with a mean Pt-C distance of 2.00-2.01 Angstrom, octahedrally coordinate the platinum atom. In the hydrated [(NC)(5)Pt-Tl(CN)(H2O)(4)](-) species the thallium atom coordinates one cyano ligand, probably as a linear Pt-TI-CN entity with a Tl-C bond distance of 2.13(1) Angstrom, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 Angstrom. In the [(NC)(5)Pt-Tl(CN)(2)](2-) species, the thallium atom probably coordinates the cyano ligands trigonally with two TI-C bond distances at 2.20(2) Angstrom, and in [(NC)(5)Pt-Tl(CN)(3)]Tl3- coordinates tetrahedrally with three TI-C distances at 2.22(2) Angstrom. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)(2)(H2O)(4)](+), [Tl(CN)(3)(H2O)], and [Tl(CN)(4)](-), and also for the solid K[TI(CN)(4)] compound. A comparison shows that the TI-C bond distances are longer in the dinuclear complexes [(NC)(5)Pt-TI(CN)(n)](n-) (it = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their Pt-195 and (TI)-T-205 chemical shifts, confirming that the I(NC)5Pt-TI(CN),]n- complexes can be considered as metastable intermediates in a two-electron-transfer redox reaction from platinum(II) to thallium(III). Vibrational spectra were recorded and force constants from normal-coordinate analyses are used for discussing the delocalized bonding in these species.
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| 9. |
- Karlsson, Torbjörn, et al.
(författare)
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Characterization of iron(III) in organic soils using extended X-ray absorption fine structure spectroscopy
- 2008
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 42:15, s. 5449-5454
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of different iron (Fe) species in soils, sediments, and surface waters has a large influence on the mobility and availability of Fe, other nutrients, and potentially toxic trace elements. However, the knowledge about the specific forms of Fe that occurs in these systems is limited, especially regarding associations of Fe with natural organic matter (NOM). In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize Fe(III) in organic soils (pH 4.6-6.0) with varying natural Fe content. The EXAFS data were subjected to wavelet transform analysis, to facilitate the identification of the nature of backscattering atoms, and to conventional EXAFS data fitting. The collective results showed the existence of two pools of iron: mononuclear Fe(III)-NOM complexes and precipitated Fe(III) (hydr)oxides. In the soil with lowest pH (4.6) and Fe content mononuclear organic complexes were the completely dominating fraction whereas in soils with higher pH and Fe content increasing amounts of Fe (hydr)oxides were detected. These results are of environmental importance, as the different iron pools most likely have markedly different reactivities.
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| 10. |
- Mäkie, Peter, et al.
(författare)
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Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 392, s. 349-358
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanoparticles of hematite (α-Fe(2)O(3)), maghemite (γ-Fe(2)O(3)), and goethite (α-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Brønstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy CO bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Brønstedt acid sites).
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