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  • 1.
    Feng, Wenting
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Thermal Stability of Goethite-Bound Natural Organic Matter Is Impacted by Carbon Loading2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 51, p. 12790-12796Article in journal (Refereed)
    Abstract [en]

    Dissolved natural organic matter (NOM) sorption at mineral surfaces can significantly affect the persistence. of organic carbon in soils and sediments. Consequently, determining the mechanisms that stabilize sorbed NOM is crucial for predicting the persistence of carbon in nature. This study determined the effects of loadings and pH on the thermal stability of NOM associated: With synthetic goethite (alpha-FeOOH) particle surfaces, as a proxy for NOM mineral interactions taking place in nature.. NOM thermal stability was investigated using temperature programmed desorption (TPD) in the 30-700 degrees C range to collect vibration spectra of thermally decomposing goethite NOM assemblages, and to concomitantly analyze evolved gases using mass spectrometry Results showed that NOM thermal stability, indicated by the range of temperatures in which CO2 evolved during thermal decomposition, was greatest in unbound NOM and lowest when NOM was bound to goethite. NOM thermal Stability was also loading dependent. It decreased:when loadings were in increased the 0.01 to 042 mg C m(-2) range, where the upper value corresponds to a Langmuirian adsorption maximum. Concomitant Fourier transform infrared (FTIR) spectroscopy measurement showed that these lowered stabilities could be ascribed to direct NOM-goethite interactions that dominated the NOM binding environment. Mineral surface interactions at larger loadings involved, on the contrary, a smaller fraction of the sorbed NOM, thus increasing thermal stability toward that of its unbound counterpart. This study thus identifies a sorption threshold below which NOM sorption to goethite decreases NOM thermal stability, and above which no strong effects are Manifested. This should likely influence the fate of organic carbon exposed to thermal gradients in natural environments.

  • 2.
    Glimsdal, Eirik
    et al.
    Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Carlsson, Marcus
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kindahl, Tomas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindgren, Mikael
    Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Lopes, Cesar
    Division of Information Systems, Swedish Defence Research Agency (FOI), Linköping, Sweden.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Luminescence, singlet oxygen production, and optical power limiting of some diacetylide platinum(II) diphosphine complexes2010In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, no 10, p. 3431-3442Article in journal (Refereed)
    Abstract [en]

    A series of four new trans-diphosphine Pt(II) diacetylide complexes, with a thiophene and two benzenoid rings in each acetylide ligand, have been synthesized and characterized with respect to optical absorption, spectrally and time-resolved luminescence, and optically nonlinear properties such as two-photon absorption cross section and optical power limiting. Density functional theory (DFT) calculations of a few ground state conformations of three Pt(II) diacetylide structures showed similar total energy for each geometry-optimized rotamer but some differences in the vertical excitation energies and in the ligand-to-metal charge-transfer character. The wavelengths of the calculated excitations were found to be red-shifted compared with peaks in the optical absorption spectra, but the general trends and shifts of wavelengths between the different structures are well reproduced. Static emission spectra for degassed samples in THF solution of the larger compounds showed small Stokes shifts and low fluorescence quantum yields, indicating fast intersystem crossing to the triplet manifold. More pronounced differences between the compounds were displayed in the phosphorescence data, in terms of spectral emission wavelengths and decay times. For instance, the phosphorescence decay of the compound with the thiophene ring close to the Pt center was found to be significantly faster than for the other compounds. A possible relationship between triplet lifetime and conformation of the compounds is discussed. It was also demonstrated that the quenching of the excited triplet states in air-saturated samples involves energy transfer to the oxygen triplet state, and subsequent generation of singlet oxygen showing the typical emission at approximately 1275 nm. The amount of produced singlet oxygen followed the phosphorescence yields of the solute molecules. Two-photon absorption cross sections (sigma(2)) were measured and showed values on the order of 10 GM at 780 nm for all compounds. Optical power limiting measurements of the new complexes in THF using 5 ns pulses, showed only slightly better performance at the wavelength of 532 nm compared to that of similar platinum compounds with only two aryl rings in each ligand. At 600 nm the complexes with three aryl rings were significantly better optical limiters than the smaller compounds with two aryl rings in the ligands.

  • 3.
    Glimsdal, Eirik
    et al.
    Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Dragland, Ingunn
    Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Carlsson, Marcus
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Melø, Thor Bernt
    Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Lindgren, Mikael
    Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Triplet excited states of some thiophene and triazole substituted platinum(II) acetylide chromophores2009In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 113, no 14, p. 3311-3320Article in journal (Refereed)
    Abstract [en]

    The photophysical properties of a series of platinum(II) acetylide compounds (trans-Pt(PBu(3))(2)(CC-R)(2)) with the R group consisting of two or three aryl rings (phenyl, phenyl/thiophenyl, phenyl/triazolyl) linked together with ethynyl groups were systematically investigated. Four new structurally similar compounds are reported with: (i) a bithiophene unit in the ligands, (ii) methyl or (iii) methoxy substituents on the aryl ring ligands that promote a more twisted conformation along the long axis of the molecule, and (iv) with two different alkynylaryl ligands giving rise to an asymmetric substitution with respect to the photoactive metal ion center. The spectroscopic studies include optical absorption, spectrally and time-resolved luminescence, as well as transient absorption spectra. The ground-state UV absorption between 300 and 420 nm gave rise to fluorescence with quantum efficiencies in the range of 0.1-1% and efficient intersystem crossing to triplet states. Phosphorescence decay times were in the order of 10-500 mus in oxygen-evacuated samples. The triplet states also lead to strong broadband triplet-triplet absorption between 400 and 800 nm. The complex with asymmetric substitution was found to populate two triplet states of different structure and energy.

  • 4. Karthikeyan, S.
    et al.
    Ramanathan, V.
    Kumar Mishra, Brijesh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Influence of the Substituents on the CH...pi Interaction: Benzene-Methane Complex2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 30, p. 6687-6694Article in journal (Refereed)
    Abstract [en]

    Recently we showed that the binding energy of the benzene...acetylene complex could be tuned up to 5 kcal/mol by substituting the hydrogen atoms of the benzene molecule with multiple electron-donating/electron-withdrawing groups (J. Chem. Theory Comput. 2012, 8, 1935). In continuation, we have here examined the influence of various substituents on the CH...pi interaction present in the benzene...methane complex using the CCSD(T) method at the complete basis set limit. The influence of multiple fluoro substituents on the interaction strength of the benzene...methane complex was found to be insignificant, while the interaction strength linearly increases with successive addition of methyl groups. The influence of other substituents such as CN, NO2, COOH, Cl, and OH was found to be negligible. The NH2 group enhances the binding strength similarly to the methyl group. Energy decomposition analysis predicts the dispersion energy component to be on an average three times larger than the electrostatic energy component. Multidimensional correlation analysis shows that the exchange-repulsion and dispersion terms are correlated very well with the interaction distance (r) and with a combination of the interaction distance (r) and molar refractivity (MR), while the electrostatic component correlates well when the Hammett constant is used in combination with the interaction distance (r). Various recently developed DFT methods were used to assess their ability to predict the binding energy of various substituted benzene...methane complexes, and the M06-2X, B97-D, and B3LYP-D3 methods were found to be the best performers, giving a mean absolute deviation of similar to 0.15 kcal/mol.

  • 5.
    Kindahl, Tomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ellingsen, Pal Gunnar
    Lopes, Cesar
    Brannlund, Carl
    Lindgren, Mikael
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Photophysical and DFT Characterization of Novel Pt(II)-Coupled 2,5-Diaryloxazoles for Nonlinear Optical Absorption2012In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 116, no 47, p. 11519-11530Article in journal (Refereed)
    Abstract [en]

    Several new bis-phosphine platinum(II) complexes with 2,5-diaryl-substituted oxazole-containing alkyne ligands have been synthesized and optically characterized in solution. Measurements of nonlinear absorption showed strong attenuation of laser light at 532 and 600 nm. The light absorption of the Pt complexes was shifted from the near-UV region for the ground state to the red region for the excited triplet state, and was associated with large extinction coefficients. The optical limiting effect can be explained by triplet-triplet excited state absorption in conjunction with fast excited singlet to-triplet intersystem crossing and slow triplet to-ground-state decay, in comparison with the pulse length of the laser. DFT calculations show good predictability of the S-0-S-1 and S-0-T-1 energy gaps and offer insight into the interaction strength between Pt and the alkyne ligands. The use of this type of ligand, with weak absorption for the Pt(II) complexes in the visual wavelength range as a key feature, enables the possibility to further improve these molecular systems for nonlinear absorption applications.

  • 6.
    Lind, Per
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Carlsson, Marcus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Eriksson, Anders
    Glimsdal, Eirik
    Lindgren, Mikael
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Structural, photophysical, and nonlinear absorption properties of trans-di-arylalkynyl Platinum(II) Complexes with Phenyl and Thiophenyl Groups2007In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 9, p. 1598-1609Article in journal (Refereed)
    Abstract [en]

    Optical power limiting and luminescence properties of two Pt(II) complexes with thiophenyl and phenyl groups in the ligands, trans-Pt(P(n-Bu)3)2(C[triple bond]C-Ar)2, where Ar = -C4H2S-C[triple bond]C-p-C6H4-n-C5H11 (1) and -p-C6H4-C[triple bond]C-C4H3S (2), have been investigated. The fluorescence lifetimes were found to be on the sub-nanosecond time scale, and the quantum yields were low, in accord with fast intersystem crossing from the excited singlet to triplet manifold. The phosphorescence lifetimes of 1 and 2 were shorter than that of a Pt(II) complex having two phenyl groups in the ligands. In order to elucidate the C-Pt bonding nature in the ground state, the 13C NMR chemical shift of the carbon directly bonded to Pt, the coupling constants 1JPtC, 2JPtC, and 1JPtP, and IR νC[triple bond]C wavenumbers were obtained for 1, 2, and three other trans-diarylalkynyl Pt(II) complexes. X-ray diffraction data of 1 and 2 and density functional theory calculated geometries of models of 1, 2, and trans-Pt(P(n-Bu)3)2(C[triple bond]C-p-C6H4-C[triple bond]C-C6H5)2 (3) show that 1 preferably exists in a different conformation from that of 2 and 3. The variations in photophysical, NMR, and IR data can be rationalized by differences in geometry and pi-backbonding from Pt to the alkynyl ligand.

  • 7.
    Mäkie, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Westin, Gunnar
    Department of Materials Chemistry, The Ångstrom Laboratory, Uppsala University.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Österlund, Lars
    Department of Engineering Sciences, The Ångstrom Laboratory, Uppsala University.
    Adsorption of Trimethyl Phosphate on Maghemite, Hematite and Goethite Nanoparticles2011In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 32, p. 8948-8959Article in journal (Refereed)
    Abstract [en]

    Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanoparticles was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy show that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Brønstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity towards TMP (hematite > maghemite > goethite): (i) Larger number of accessible Lewis acid adsorption sites on hematite, (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TMP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathways dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.

  • 8. Song, Xiaowei
    et al.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Surface and Bulk Thermal Dehydroxylation of FeOOH Polymorphs2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 31, p. 6249-6257Article in journal (Refereed)
    Abstract [en]

    In this study, bulk and surface thermal decomposition of synthetic iron oxyhydroxides to iron oxides was followed using the temperature programmed desorption (TPD) technique. Submicron-sized akaganeite beta-FeOOH), rod- and lath-shaped lepidocrocite (gamma-FeOOH), and goethite (alpha-FeOOH) particles were heated in vacuo in the 30-400 degrees C range, and their OH vibrational modes were monitored by Fourier transform infrared (FTIR) spectroscopy while H2O(g) release was monitored by quadrupole mass spectrometry. Peak thermal dehydroxylation temperatures were larger in the order of lath lepidocrocite (200 degrees C) < akaganeite (200/260 degrees C) < rod lepidocrocite (268 degrees C) < goethite (293 degrees C). Pre-equilibration of these particles to aqueous solutions of HCl increased dehydroxylation temperatures of all minerals except goethite by 13-40 degrees C. These shifts were explained by (1) the dissolution of particles or regions of particles of lower degree of crystallinity by HCl, as well as (2) the strengthening of the hydrogen bond environment in the akaganeite bulk. The latter is a means of facilitating H2O(g) formation via interactions between two adjacent OH groups. Strongly analogous forms of interactions at the FeOOH particle surfaces were also shown to facilitate the release of singly coordinated (-OH) hydroxo groups to the gas phase at temperatures lower than 125 degrees C, thus creating OH vacancies that may be actively involved in the transfer of bulk to surface OH groups during thermal dehydroxylation. Doubly- (mu-OH) and triply- (mu(3)-OH) coordinated hydroxo groups were however resilient to exchange under those conditions, and their dehydroxylation was strongly congruent with that of bulk OH groups. By resolving the bulk and surface thermal decomposition of FeOOH polymorphs, this work provides clearer insight into the fate of these materials in natural and technological settings where important thermal gradients are commonplace.

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