| 1. |
- Havenhand, Jonathan N., 1959, et al.
(författare)
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Ecological and functional consequences of coastal ocean acidification : Perspectives from the Baltic-Skagerrak System
- 2019
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 48:8, s. 831-854
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Forskningsöversikt (refereegranskat)abstract
- Ocean temperatures are rising; species are shifting poleward, and pH is falling (ocean acidification, OA). We summarise current understanding of OA in the brackish Baltic-Skagerrak System, focussing on the direct, indirect and interactive effects of OA with other anthropogenic drivers on marine biogeochemistry, organisms and ecosystems. Substantial recent advances reveal a pattern of stronger responses (positive or negative) of species than ecosystems, more positive responses at lower trophic levels and strong indirect interactions in food-webs. Common emergent themes were as follows: OA drives planktonic systems toward the microbial loop, reducing energy transfer to zooplankton and fish; and nutrient/food availability ameliorates negative impacts of OA. We identify several key areas for further research, notably the need for OA-relevant biogeochemical and ecosystem models, and understanding the ecological and evolutionary capacity of Baltic-Skagerrak ecosystems to respond to OA and other anthropogenic drivers.
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| 2. |
- Valter, Mikael, 1991, et al.
(författare)
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Electrooxidation of Glycerol on Gold in Acidic Medium: A Combined Experimental and DFT Study
- 2018
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:19, s. 10489-10494
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Tidskriftsartikel (refereegranskat)abstract
- Glycerol is a byproduct of biodiesel production and an abundant feedstock for synthesis of high-value chemicals. A promising approach for valorization of glycerol is electrooxidation on gold. In this work, we investigate electrooxidation of glycerol on gold in acidic media using cyclic voltammetry and density functional theory calculations. Experimentally, we observe activity for electrooxidation above a potential of 0.5 V vs. the reversible hydrogen electrode (RHE). A Pourbaix diagram is calculated to evaluate the surface coverage under reaction conditions, indicating that *O and *OH are not present at the measured onset potential. Computationally, we find that the onset potentials for partial dehydrogenation of glycerol to dihydroxyacetone, 2,3-dihydroxy-2-propenal and glyceraldehyde are 0.39, 0.39, and 0.60 V vs. RHE, respectively, while complete dehydrogenation to carbon monoxide requires 0.50 V vs. RHE. Our theoretical and experimental findings are in agreement and show the possibility of using gold as a catalyst for production of hydrogen and other valuable chemicals from glycerol.
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| 3. |
- Visibile, Alberto, et al.
(författare)
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Influence of Strain on the Band Gap of Cu2O
- 2019
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 31:13, s. 4787-4792
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Tidskriftsartikel (refereegranskat)abstract
- Cu2O has been considered as a candidate material for transparent conducting oxides and photocatalytic water splitting. Both applications require suitably tuned band gaps. Here we explore the influence of compressive and tensile strain on the band gap by means of density functional theory (DFT) modeling. Our results indicate that the band gap decreases under tensile strain while it increases to a maximum under moderate compressive strain and decreases again under extreme compressive strain. This peculiar behavior is rationalized through a detailed analysis of the electronic structure by means of density of states (DOS), density overlap region indicators (DORI), and crystal overlap Hamilton populations (COHP). Contrary to previous studies we do not find any indications that the band gap is determined by d10-d10 interactions. Instead, our analysis clearly shows that both the conduction and the valence band edges are determined by Cu-O antibonding states. The band gap decrease under extreme compressive strain is associated with the appearance of Cu 4sp states in the conduction band region.
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| 4. |
- Busch, Michael, 1983, et al.
(författare)
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Water Oxidation on MnOx and IrOx: Why Similar Performance?
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:1, s. 288-292
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Tidskriftsartikel (refereegranskat)abstract
- The critical steps in water oxidation at a binuclear Mn(II–IV) oxide site are revisited. Ideal stabilities of intermediates are confirmed by comparing to results for a binuclear Ir(III–V) system. The latter in turn is known to be an excellent water oxidation catalyst. The inefficiency of the binuclear Mn(II–IV) site is owing to the high activation energy for the chemical step whereby MnIV═O double bonds on adjacent sites are broken prior to forming the MnIII—O—O—MnIII peroxy moiety. A rationale for Mn(II–IV)—Mn(III–V) mixed oxidation state for water oxidation catalysis, analogous to mixed transition metal oxide systems, is offered. Possible virtues of the kinetic stability of the binuclear MnIV═O moiety are discussed, utilizing its oxidizing power by sidestepping oxygen evolution.
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| 5. |
- Hedenstedt, Kristoffer, 1979, et al.
(författare)
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Study of Hypochlorite Reduction Related to the Sodium Chlorate Process
- 2016
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Ingår i: Electrocatalysis. - : Springer Science and Business Media LLC. - 1868-2529 .- 1868-5994. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Reduction of hypochlorite is the most important side reaction in the sodium chlorate reactor leading to high energy losses. Today chromate is added to the reactor solution to minimize the hypochlorite reduction but a replacement is necessary due to health and environmental risks with chromate. In order to understand the effect of different substrates on the hypochlorite reduction, α-FeOOH, γ-FeOOH, Cr2O3 and CrOH3 were electrodeposited on titanium and subjected to electrochemical investigations. These substances are commonly found on cathodes in the chlorate process and can serve as model substances for the experimental investigation. The mechanism of hypochlorite reduction was also studied using DFT calculations in which the reaction at Fe(III) and Cr(III) surface sites were considered in order to single out the electrocatalytic properties. The experimental results clearly demonstrated that the chromium films completely block the reduction of hypochlorite, while for the iron oxyhydroxides the process can readily occur. Since the electrocatalytic properties per se were shown by the DFT calculations to be very similar for Fe(III) and Cr(III) sites in the oxide matrix, other explanations for the blocking ability of chromium films are addressed and discussed in the context of surface charging, reduction of anions and conduction in the deposited films. The main conclusion is that the combined effect of electronic properties and reduction of negatively charged ions can explain the reduction kinetics of hypochlorite and the effect of chromate in the chlorate process.
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| 6. |
- Steegstra, Patrick, 1978, et al.
(författare)
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Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:40, s. 20975-20981
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemistry of hydrous iridium oxide films (HIROF) is revisited. Cyclic voltammograms of HIROFs display two reversible redox couples commonly assigned to the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) transitions, respectively. However, compared to the first, the second redox couple has significantly less charge associated to it. This effect is interpreted as partial oxidation of Ir(IV) as limited by nearest neighbor repulsion of resulting Ir(V) sites. Thus, the redox process is divided into two steps: one preceding and one overlapping the oxygen evolution reaction (OER). Here, the ``super-nernstian'' pH dependence of the redox processes in the HIROF is used to expose how pH controls the overpotential for oxygen evolution, as evidenced by the complementary increased formation of Ir(V) oxide. A recently formulated binuclear mechanism for the OER is employed to illustrate how hydrogen bonding may suppress the OER, thus implicitly favoring Ir(V) oxide formation above the thermodynamic onset potential for the OER at low pH.
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| 7. |
- Wodrich, Matthew D., et al.
(författare)
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On the Generality of Molecular Volcano Plots
- 2018
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Ingår i: ChemCatChem. - : Wiley. - 1867-3899 .- 1867-3880. ; 10:7, s. 1586-1591
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Tidskriftsartikel (refereegranskat)abstract
- In homogeneous catalysis, the structure and electronic configuration of the active catalysts can vary significantly. Changes in ligation, oxidation, and spin states have the potential to influence the catalytic cycle energetics strongly that, to a large degree, dictate the catalytic performance. With the increased use of computational screening strategies aimed towards the identification of new catalysts, ambiguity surrounding structure/electronic configurations can be problematic, as it is unclear which species should be computed to determine a catalyst's properties. Here, we show that a single volcano plot constructed from linear free energy scaling relationships is able to account for variations in ligation, oxidation, and spin state. These linear scaling relationships can also be used to predict the free energies associated with a specific structure and electronic configuration of a catalyst based on a single descriptor. As a result, a single volcano plot can be used to screen prospective new catalysts rapidly.
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| 8. |
- Bauer, Susanne, et al.
(författare)
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Distribution of dissolved and suspended particulate molybdenum, vanadium, and tungsten in the Baltic Sea
- 2017
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Ingår i: Marine Chemistry. - : Elsevier. - 0304-4203 .- 1872-7581. ; 196, s. 135-147
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Tidskriftsartikel (refereegranskat)abstract
- In natural waters, dissolved oxyanions often dominate over the particle-bound element fraction. Still, the scavenging of oxyanions by suspended particles might contribute significantly to their dynamic cycling and distribution. To investigate how oxyanions are affected by manganese (Mn) redox cycling, detailed depth profiles across the pelagic redox zone at the Landsort Deep, Baltic Sea, were collected for molybdenum (Mo), vanadium (V), and tungsten (W), for both dissolved (<0.22 µm) and suspended particulate (>0.22 µm) fractions.All three oxyanions show a non-conservative behavior in the stratified Landsort Deep. Strong linear correlations with Mn in the particulate fraction in the redox zone of the Landsort Deep suggest that Mn redox cycling influences their distribution. In the dissolved fraction, Mo, V, and W exhibited rather different behavior. Molybdenum was depleted below the redox zone, while V was depleted only within the redox zone. Tungsten concentrations increased within the redox zone, being three times higher in the sulfidic zone than in the surface water. Unlike Mo, W shows no tendency for adsorption or co-precipitation under the prevailing weak sulfidic conditions in the deep water of the Landsort Deep and is, therefore, not exported to the underlying sediment.The Landsort Deep data were compared with data from the northern Baltic Sea (Bothnian Bay, Kalix River and Råne River estuaries), where particulate iron (Fe) occurs in high abundance. The particulate fractions of Mo, V, and W decreased during mixing in these estuaries. Vanadium showed the most drastic reduction, with a decrease in dissolved and particulate fractions, indicating that different processes influence the distribution of these oxyanions.
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| 9. |
- Conrad, Sarah, et al.
(författare)
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Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea
- 2019
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Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 16:6, s. 1305-1319
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Tidskriftsartikel (refereegranskat)abstract
- Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate ( > 0.22 μm), colloidal (0.22 μm–1 kDa), and truly dissolved (< 1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57μM with Fe dominantly as particulate Fe. The loss of > 99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about -0.20 ‰) and positive δ56Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. The positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.
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| 10. |
- Golets, M., et al.
(författare)
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Understanding the thermal decomposition mechanism of a halogen-free chelated orthoborate-based ionic liquid : a combined computational and experimental study
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18, s. 22458-22466
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Tidskriftsartikel (refereegranskat)abstract
- In the last few decades, ionic liquids (ILs) have gained significant attention as lubricants and lubricant additives due to their polar nature, low vapour pressure and tunable physicochemical properties. In this work, quantum chemistry calculations and atomistic Molecular Dynamics (MD) simulations were employed to predict thermal degradation mechanisms of a potential lubricating agent - the tributyloctylphosphonium bis(oxalato)borate ([P4,4,4,8][BOB]) IL. It was found that the onset of decomposition of the studied IL coincides with a cleavage of the B-O bonds in the [BOB](-) anion. Consequently, a series of chemical reactions of the [P4,4,4,8](+) cation with the [BOB](-) anion was triggered yielding alkylboranes, alkenes, trialkylphosphines, CO and CO2. Another ionic system, consisting of [P4,4,4,8][Cl], was also tested for a comparison. Thermogravimetric measurements have shown a higher thermal stability of [P4,4,4,8][BOB] compared to that of [P4,4,4,8][Cl] at least at the initial stage of decomposition, in accord with the presented calculations. Quantum chemical frequency calculations also agreed with the experimental Fourier Transform Infrared (FTIR) spectroscopy results.
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