| 1. |
- Iakunkov, Artem, et al.
(författare)
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Activated graphene as a material for supercapacitor electrodes : effects of surface area, pore size distribution and hydrophilicity
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : RSC Publishing. - 1463-9076 .- 1463-9084. ; 21:32, s. 17901-17912
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Tidskriftsartikel (refereegranskat)abstract
- Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.
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| 2. |
- Werner, Josephina
(författare)
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Exploring the surface of aqueous solutions : x-ray photoelectron spectroscopy studies on a liquid micro-jet
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The surface behavior of biologically or atmospherically relevant chemical compounds in aqueous solution has been studied using surface-sensitive X-ray photoelectron spectroscopy (XPS). The aim is to provide information on the molecular-scale composition and distribution of solutes in the surface region of aqueous solutions. In the first part, the distribution of solutes in the surface region is discussed, where in particular single molecular species are studied. Concentration-dependent studies on succinic acid and various alkyl-alcohols, where also parameters such as pH and branching are varied, are analyzed using different approaches that allow the quantification of surface concentrations. Furthermore, due to the sensitivity of XPS to the chemical state, reorientation of linear and branched alkyl-alcohols at the aqueous surface as a function of concentration is observed. The results are further discussed in terms of hydrophilic and hydrophobic interactions in the interfacial region, where the three-dimensional hydrogen bonded water structure terminates. In the second part, mixed solutions of compounds, both ionic and molecular, are inspected. Again concentration, but also co-dissolution of other chemical compounds, are varied and differences in the spatial distribution and composition of the surface region are discussed. It is found that the guanidinium ion has an increased propensity to reside at the surface, which is explained by strong hydration in only two dimensions and only weak interactions between the aromatic π-system and water. Ammonium ions, on the other hand, which require hydration in three dimensions, are depleted from the surface region. The presence of strongly hydrated electrolytes out-competes neutral molecules for hydrating water molecules leading to an enhanced abundance of molecules, such as succinic acid, in the interfacial region. The partitioning is quantified and discussed in the context of atmospheric science, where the impact of the presented results on organic loading of aerosol particles is emphasized.
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| 3. |
- Eckardt, Johanna, et al.
(författare)
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Long-term frozen storage of wheat bread and dough : Effect of time, temperature and fibre on sensory quality, microstructure and state of water
- 2013
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Ingår i: Journal of Cereal Science. - : Elsevier BV. - 0733-5210 .- 1095-9963. ; 57:1, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to determine effect of storage time, storage temperature and addition of fibre on sensory quality, state of water, microstructure and texture of bread and dough. Samples with and without fibre, were stored frozen for 2, 3.5 and 6 months at temperatures of -19, -16 and -8 °C as dough and bread. Sensory quality was evaluated by a trained analytical panel. Microstructure was analysed by light microscopy. Texture measurements were performed on bread, and the state of water was measured by differential scanning calorimetry. Bread without fibre stored as dough at -19 °C was the sample most like freshly baked bread. Sensory evaluation also confirmed that quality of the final bread was improved if samples were stored as dough compared to stored as bread. The microstructure had larger gaps between the starch and gluten phases when stored at warmer temperatures, due to retrogradation of starch, dehydration of gluten and water migration. DSC measurements showed that bread stored at -19 °C gained extra amount of freezable water, but lost ice after storage at -8 °C. Texture measurements showed that firmness increased with extended storage time. Bread stored at -8 °C had lowest quality in all measurements.
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| 4. |
- Grimm, Alejandro, et al.
(författare)
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Slagging and fouling characteristics during co-combustion of Scots pine bark with low-temperature dried pulp and paper mill chemical sludge
- 2019
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Ingår i: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 193, s. 282-294
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows how chemical sludge (CS) generated during wastewater treatment at a paperboard mill can be quickly dried at low-temperature and employed in bark-fired boilers to reduce slagging and corrosion problems. By using a cyclone-dryer operated at an inlet-air velocity of 110 m/s and a temperature of 90 degrees C, the dry-matter content of CS was increased from approximately 19 to 82%. The residence time of CS inside the cyclone was approximately 2 s when using the inlet-air velocity mentioned above. Disaggregation of the feedstock caused by collisions with the cyclone wall and between particles played a crucial role in enhancing the efficiency of heat and mass transfer. Three co-pelletized mixtures of Scots pine bark (SPB) and dried-CS were combusted in a 40 kW fixed-bed burner. Flue gas analysis was performed with a gas analyser. Coarse and fine ash were analysed by SEM-EDS and XRD. NOx, and SO2 emissions increased with increasing amount of CS in the mixtures. Mono combustion of SPB resulted in a large quantity of slag (i.e., molten ash) with a high degree of sintering (i.e., hardness of the slag), and ash deposits formed on heat transfer surfaces were rich in K2SO4 and KCI. Mixtures of SPB and CS were less prone to slagging, and the amount of alkali chloride in the deposits was reduced in favour of alkali sulphate formation.
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| 5. |
- Müller, Christian, et al.
(författare)
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Woven Electrochemical Transistors on Silk Fibers
- 2011
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Ingår i: ADVANCED MATERIALS. - : John Wiley and Sons, Ltd. - 0935-9648 .- 1521-4095. ; 23:7, s. 898-
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Tidskriftsartikel (refereegranskat)abstract
- Woven electrochemical transistors on silk fibers from the silkworm Bombyx mori are demonstrated. This is achieved with carefully chosen electrolyte chemistry: electrically conducting silk fibers are produced by dyeing silk fibers with a conjugated polyelectrolyte and gating is accomplished by use of an electrolyte mixture composed of imidazolium-based ionic liquids.
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| 6. |
- Nouhi, Shirin, et al.
(författare)
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Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry
- 2018
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 511, s. 474-481
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between perfluoroalkyl substances (PFASs) and a phospholipid bilayer (1,2-dimyristoyl-sn-glycero-3-phosphocholine) were investigated at the molecular level using neutron reflectometry. Representative PFASs with different chain length and functional groups were selected in this study including: perfluorobutane sulfonate (PFBS), perfluorohexanoate (PFHxA), perfluorohexane sulfonate (PFHxS), perfluorononanoate (PFNA), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonamide (FOSA). All PFASs were found to interact with the bilayer by incorporation, indicating PFAS ability to accumulate once ingested or taken up by organisms. The interactions were observed to increase with chain length and vary with the functional group as SO2NH2" role="presentation">(FOSA) > SO2O−" role="presentation">(PFOS) > COO−(PFNA). The PFAS hydrophobicity, which is strongly correlated with perfluorocarbon chain length, was found to strongly influence the interactions. Longer chain PFASs showed higher tendency to penetrate into the bilayer compared to the short-chain compounds. The incorporated PFASs could for all substances but one (PFNA) be removed from the lipid membrane by gentle rinsing with water (2 mL min−1). Although short-chain PFASs have been suggested to be the potentially less bioaccumulative alternative, we found that in high enough concentrations they can also disturb the bilayer. The roughness and disorder of the bilayer was observed to increase as the concentration of PFASs increased (in particular for the high concentrations of short-chain substances i.e. PFHxA and PFBS), which can be an indication of aggregation of PFASs in the bilayer.
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| 7. |
- O´brien, Nathan, et al.
(författare)
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In Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Growth of Indium Nitride by Atomic Layer Deposition
- 2020
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 32:11, s. 4481-4489
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Tidskriftsartikel (refereegranskat)abstract
- Indium nitride (InN) is characterized by its high electron mobility, making it a ground-breaking material for high frequency electronics. The difficulty of depositing high-quality crystalline InN currently impedes its broad implementation in electronic devices. Herein, we report a new highly volatile In(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial hexagonal InN by atomic layer deposition (ALD). The new In(III) precursor, the first example of a homoleptic triazenide used in a vapor deposition process, was easily synthesized and purified by sublimation. Thermogravimetric analysis showed single step volatilization with an onset temperature of 145 degrees C and negligible residual mass. Strikingly, two temperature intervals with self-limiting growth were observed when depositing InN films. In the high-temperature interval, the precursor underwent a gas-phase thermal decomposition inside the ALD reaction chamber to produce a more reactive In(III) compound while retaining self-limiting growth behavior. Density functional theory calculations revealed a unique two-step decomposition process, which liberates three molecules of each propene and N-2 to give a smaller tricoordinated In(III) species. Stoichiometric InN films with very low levels of impurities were grown epitaxially on 4H-SiC. The InN films deposited at 325 degrees C had a sheet resistivity of 920 Omega/sq. This new triazenide precursor enables ALD of InN for semiconductor applications and provides a new family of M-N bonded precursors for future deposition processes.
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| 8. |
- Palmqvist, Martin, et al.
(författare)
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Maghemite Nanoparticles Acts as Nanozymes, Improving Growth and Abiotic Stress Tolerance in Brassica napus
- 2017
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Ingår i: Nanoscale Research Letters. - : Springer Science and Business Media LLC. - 1931-7573 .- 1556-276X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Yttrium doping-stabilized γ-Fe2O3 nanoparticles were studied for its potential to serve as a plant fertilizer and, through enzymatic activity, support drought stress management. Levels of both hydrogen peroxide and lipid peroxidation, after drought, were reduced when γ-Fe2O3 nanoparticles were delivered by irrigation in a nutrient solution to Brassica napus plants grown in soil. Hydrogen peroxide was reduced from 151 to 83 μM g−1 compared to control, and the malondialdehyde formation was reduced from 36 to 26 mM g−1. Growth rate of leaves was enhanced from 33 to 50% growth compared to fully fertilized plants and SPAD-measurements of chlorophyll increased from 47 to 52 suggesting improved agronomic properties by use of γ-Fe2O3 nanoparticles as fertilizer as compared to chelated iron.
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| 9. |
- Rodriguez-Iruretagoiena, Azibar, et al.
(författare)
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A new procedure to quantify silver nanoparticles in sediments
- 2022
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Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X .- 1878-0571. ; 110, s. 264-269
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Tidskriftsartikel (refereegranskat)abstract
- Silver nanoparticles (AgNPs) are highly produced in developed countries for a variety of products. Consequently, AgNPs end up being introduced in aquatic systems all over the world, and usually deposited in riverine sediments, from where they can be taken up by aquatic organisms and transferred along the food chain. The analysis of AgNPs in natural samples is not an easy task, because of their low presence and complicated reactions, which can change their speciation. The objective of this work is to help in this challenge, developing a method applicable to analyse sediment samples from any place around the world where AgNPs are suspected to be present. Firstly, four methods for the synthesis of AgNPs were investigated by Ultraviolet-visible (UV-VIS) spectroscopy and particle size analysis. The methods differed in the reducing agent used and in the concentration of the stabilising agent applied. The method including NaBH4 and SDS (sodium dodecyl sulphate) resulted to be more adequate as the Surface Plasmon Resonance (SPR) band position and width indicated. This conclusion was corroborated considering the hydrodynamic diameters and polydispersity indices of the synthesised AgNPs. The Z-average hydrodynamic diameter and the UV-VIS spectrum of AgNPs synthesised using this method indicated that the AgNPs remained kinetically stable for at least 10 days. Finally, ten potential extraction solutions were investigated, in terms of maximal extraction efficiency, but minimal effects on AgNP dissolution and aggregation. The candidate solutions ranged from deionized water and salts to strong acids and bases. The intensity of the SPR band concluded that using NaOH media the synthesised AgNPs was kinetically stable. Moreover, TEM (Transmission Electron Microscopy) images showed that the AgNPs in NaOH retained their shape and size after 10 days. Therefore, NaOH media turned out to be the best potential extractant for the analysis of sediment samples.
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| 10. |
- Rouf, Polla, et al.
(författare)
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Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition
- 2021
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 33:9, s. 3266-3275
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Tidskriftsartikel (refereegranskat)abstract
- Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga-N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 degrees C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 degrees C were epitaxial on 4H-SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes.
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