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  • 251.
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Chapter 13: Characterization of Liquid-crystalline Materials by Separated Local Field Methods2018In: New Developments in NMR, Royal Society of Chemistry, 2018, no 15, p. 391-423Chapter in book (Refereed)
    Abstract [en]

    A unique feature of liquid crystals is a high degree of molecular mobility combined with orientational and positional order. Solid-state NMR contributes to fundamental understanding of diverse molecular organizations and complex dynamic processes in these exciting materials. The focus of this chapter is on the development and application of advanced solid-state NMR methodologies for liquid crystal studies, with emphasis on techniques for measuring anisotropic spin couplings. The discussion centers on applications of separated dipolar local field NMR spectroscopy, which is used in an increasing number of directions in studies of novel liquid-crystalline materials for emerging technological applications.

  • 252.
    Dvinskikh, Sergey
    Institute of Physics, St. Petersburg State University.
    Separated Local Field Nmr Spectroscopy In Columnar Liquid Crystals2007In: Thermotropic liquid crystals: recent advances / [ed] Ayyalusamy Ramamoorthy, Springer, 2007, p. 117-140Chapter in book (Refereed)
  • 253.
    Dvinskikh, Sergey
    et al.
    Institute of Physics, St. Petersburg State University.
    Sandström, Dick
    Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University.
    Zimmermann, Herbert
    Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany.
    Maliniak, Arnold
    Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University,.
    13C Nmr Studies Of Columnar Liquid Crystals2007In: New Research on Magnetic Resonance / [ed] Bernard C. Castleman, New York: Nova Science Publishers, Inc., 2007, p. 137-186Chapter in book (Refereed)
  • 254.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pulsed-Field-Gradient NMR Study of Anisotropic Molecular Translational Diffusion in nOCB Liquid Crystals2013In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 44, no 1-2, p. 169-180Article in journal (Refereed)
    Abstract [en]

    Pulsed-field-gradient nuclear magnetic resonance (NMR) combined with magic echo decoupling is applied to study anisotropic diffusion in samples with strong static dipolar spin interactions. The approach, due to its moderate demands on the NMR hardware, can be implemented on standard commercial equipment for routine diffusion studies of liquid crystals. Using a microimaging probe, measurement of diffusion in arbitrary spatial direction is possible. Hence, the principal components of the diffusion tensor are directly obtained. Anisotropic diffusion is investigated in the thermotropic mesophases of a homologous series of nOCB liquid crystals and an analogous compound with hydroxyl groups. The geometric average diffusion coefficient changes continuously at the isotropic-nematic phase transition. Experimental data are described in terms of the molecular translation models in the nematic phase and for the second-order nematic-smectic A phase transition. The diffusion anisotropy is higher for the sample with terminal hydroxyl groups suggesting significant molecular association via hydrogen bonding.

  • 255.
    Dédinaité, Andra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Iruthayaraj, Joseph
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Gorochovceva, Natalija
    Department of Polymer Chemistry, Vilnius University.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Interfacial Properties of Chitosan-PEO graft Oligomers: Surface Competition with Unmodified Chitosan Oligomers2006In: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 132, p. 124-130Article in journal (Refereed)
    Abstract [en]

    Oligomers of chitosan carrying 45 units long poly(ethylene oxide), PEO, chains grafted to the C-6 position of the sugar units were prepared using a novel synthesis route. The graft density was high, close to one poly(ethylene oxide) chain grafted to each sugar unit of the chitosan oligomer but a small fraction of unreacted chitosan remained in the sample. The molecular weight distribution of the sample was determined using GPC. The interfacial properties of the chitosan-PEO graft oligomers were evaluated using X-ray photoelectron spectroscopy and surface force measurements. It was found that the small fraction of unreacted chitosan was significantly enriched at the solid-solution interface on negatively charged muscovite mica surfaces. The interactions between chitosan-PEO oligomer coated surfaces were found to be dominated by the extended PEO chains, and at high coverage the measured forces were consistent with those expected for polymer brushes. Addition of salt up to 10 mM did not result in any significant desorption of preadsorbed oligomer layers.

  • 256.
    Dédinaité, Andra
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. KTH Royal Inst Technol, Sch Engn Sci Chem Biotechnol & Hlth, Dept Chem Surface & Corros Sci, Drottning Kristinas Vag 51, SE-10044 Stockholm, Sweden..
    Wieland, D. C. Florian
    Helmholtz Zentrum Geesthacht, Ctr Mat & Costal Res, Inst Mat Res, Max Planck Str 1, D-21502 Geesthacht, Germany..
    Beldowski, Piotr
    UTP Univ Sci & Technol, Inst Math & Phys, Al Kaliskiego 7, PL-85796 Bydgoszcz, Poland.;Friedrich Alexander Univ Erlangen Nurnberg, Cluster Excellence Engn Adv Mat, Inst Multiscale Simulat, Cauerstr 3, D-91058 Erlangen, Germany..
    Claesson, Per M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Biolubrication synergy: Hyaluronan - Phospholipid interactions at interfaces2019In: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 274, article id UNSP 102050Article in journal (Refereed)
    Abstract [en]

    The manner in which nature has solved lubrication issues has fascinated scientists for centuries, in particular when considering that lubrication is achieved in aqueous media. The most outstanding system in this respect is likely the synovial joint, where close to frictionless motion is realized under different loads and shear rates. This review article focuses on two components present in the synovial area, hyaluronan and phospholipids. We recapitulate what has been learned about their interactions at interfaces from recent experiments, with focus on results obtained using reflectivity techniques at large scale facilities. In parallel, modelling experiments have been carried out and from these efforts new detailed knowledge about how hyaluronan and phospholipids interact has been gained. In this review we combine findings from modelling and experiments to gain deeper insight. Finally, we summarize what has been learned of the lubrication performance of mixtures of phospholipids and hyaluronan.

  • 257. Ebadi, S. M.
    et al.
    Örtegren, J.
    Yan, Max
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    A Highly-Efficiency NIR Plasmonic Long-Wavelength Cut-Off Filter based on Stepped Impedance Resonators2021In: Optics InfoBase Conference Papers, Optica Publishing Group (formerly OSA) , 2021Conference paper (Refereed)
    Abstract [en]

    We report design and simulation results of a high-efficiency long-wavelength cut-off filter realized by stepped impedance resonators. Moreover, numerical results confirm by modulating the length of resonator, cut-off wavelength can be easily tuned.

  • 258.
    Edlund, Ulrica
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. RISE Bioecon, Drottning Kristinas Vag 61, SE-11428 Stockholm, Sweden..
    Lagerberg, Tove
    Alander, Eva
    Admicellar Polymerization Coating of CNF Enhances Integration in Degradable Nanocomposites2019In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 20, no 2, p. 684-692Article in journal (Refereed)
    Abstract [en]

    A water-based one-pot synthesis strategy for converting cellulose nanofibrils (CNF) into a hydrophobic and processable biopolymer grade is devised. CNF was chemically modified through admicellar polymerization, producing fibrils coated with fatty acrylate polymers. The proposed modification targets a change in the interfibrillar interactions and improved CNF compatibility with a degradable plastic composite matrix, poly(butylene adipate-co-terephthalate), PBAT in composites prepared by melt extrusion. CNF had a clear reinforcing effect on PBAT, increasing Young's modulus by at least 35% and 169% at 5 and 20% (w/w) CNF content, respectively. However, unmodified CNF showed aggregation, poor adhesion in the matrix, and severely impaired the ductility of PBAT. CNF modified by admicellar polymerization was homogeneously dispersed in the PBT matrix and showed significantly better preservation of the elongation properties compared to unmodified CNF, especially at 5% (w/w) addition level.

  • 259.
    Eita, Mohamed
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Arwin, Hans
    Granberg, Hjalmar
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films2011In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 363, no 2, p. 566-572Article in journal (Refereed)
    Abstract [en]

    Over the last decade, the use of nanocellulose in advanced technological applications has been promoted both due the excellent properties of this material in combination with its renewability. In this study, multilayered thin films composed of nanofibrillated cellulose (NFC), polyvinyl amine (PVAm) and silica nanoparticles were fabricated on polydimethylsiloxane (PDMS) using a layer-by-layer adsorption technique. The multilayer build-up was followed in situ by quartz crystal microbalance with dissipation, which indicated that the PVAm-SiO(2)-PVAm-NFC system adsorbs twice as much wet mass material compared to the PVAm-NFC system for the same number of bilayers. This is accompanied with a higher viscoelasticity for the PVAm-SiO(2)-PVAm-NFC system. Ellipsometry indicated a dry-state thickness of 2.2 and 3.4 nm per bilayer for the PVAm-NFC system and the PVAm-SiO(2)-PVAm-NFC system, respectively. Atomic force microscopy height images indicate that in both systems, a porous network structure is achieved. Young's modulus of these thin films was determined by the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) technique. The Young's modulus of the PVAm/NFC films was doubled, from 1 to 2 GPa, upon incorporation of silica nanoparticles in the films. The introduction of the silica nanoparticles lowered the refractive index of the films, most probably due to an increased porosity of the films.

  • 260.
    Ekholm, P.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per M
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Auflem, I. H.
    Department of Chemical Engineering, The Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Sjöblom, J.
    Department of Chemical Engineering, The Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Kornfeldt, A.
    ABB Corporate Research, Västerås, Sweden.
    A quartz crystal microbalance study of the adsorption of asphaltenes and resins onto a hydrophilic surface2002In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 247, no 2, p. 342-350Article in journal (Refereed)
    Abstract [en]

    The adsorption of extracted and purified samples of asphaltenes and resins onto gold surfaces has been studied as a function of bulk concentration using a quarts crystal microbalance with dissipation measurements (QCM-D). With this device, which works equally well in transparent, opaque, and nontransparent samples, the adsorbed amount is measured through a change in resonant frequency of the quartz oscillator. The measured change in dissipation reports on changes in layer viscoelasticity and slip of the solvent at the surface. The results show that the adsorbed amount for resins from heptane corresponds to a rigidly attached monolayer. The adsorbed amount decreases with increasing amount of toluene in the solvent and is virtually zero in pure toluene. Asphaltenes, on the other hand, adsorb in large quantities and the mass and dissipation data demonstrate the presence of aggregates on the surface. The aggregates are firmly attached and cannot be removed by addition of resins. On the other hand, resins and asphaltenes associate in bulk liquid and the adsorption from mixtures containing both resins and asphaltenes is markedly different from that obtained from the pure components. Hence, we conclude that preformed resin aggregates adsorb to the surface. These results are compared and discussed in relation to adsorption from crude oil diluted in heptane/toluene mixtures.

  • 261. El Haber, Manuella
    et al.
    Ferronato, Corinne
    Universite Claude Bernard Lyon 1, IRCELYON UMR 5256 CNRS, 69622, Villeurbanne, France.
    Giroir-Fendler, Anne
    Universite Claude Bernard Lyon 1, IRCELYON UMR 5256 CNRS, 69622, Villeurbanne, France.
    Fine, Ludovic
    Universite Claude Bernard Lyon 1, IRCELYON UMR 5256 CNRS, 69622, Villeurbanne, France.
    Nozière, Barbara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Salting out, non-ideality and synergism enhance surfactant efficiency in atmospheric aerosols2023In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, no 1, article id 20672Article in journal (Refereed)
    Abstract [en]

    In Earth’s atmosphere, the surface tension of sub-micron aerosol particles is suspected to affect their efficiency in becoming cloud droplets. But this quantity cannot be measured directly and is inferred from the chemical compounds present in aerosols. Amphiphilic surfactants have been evidenced in aerosols but experimental information on the surface properties of their mixtures with other aerosol components is lacking. This work explores experimentally the surface properties of aqueous mixtures of amphiphilic surfactants (SDS, Brij35, TritonX100, TritonX114, and CTAC) with inorganic salts (NaCl, (NH4)2SO4) and soluble organic acids (oxalic and glutaric acid) using pendant droplet tensiometry. Contrary to what could be expected, inorganic salts and organic acids systematically enhanced the efficiency of the surfactants rather than reduced it, by further lowering the surface tension and, in some cases, the CMC. Furthermore, all the mixtures studied were strongly non-ideal, some even displaying some synergism, thus demonstrating that the common assumption of ideality for aerosol mixtures is not valid. The molecular interactions between the mixture components were either in the bulk (salting out), in the mixed surface monolayer (synergy on the surface tension) or in the micelles (synergy on the CMC) and need to be included when describing such aerosol mixtures.

  • 262.
    El Jamal, Ghada
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. KTH.
    Redox Reactions of Uranium-Based Materials in Aqueous Systems and Under UHV Conditions.: Two models mimicking radiation-induced oxidation of spent nuclear fuel.2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The demand for clean electricity is a primary concern in Europe. Nuclear power isconsidered as a greenhouse gas-free technology for generation of electricity. However,compared to other energy sources, it generates a highly toxic waste.In Sweden, the long-term solution for the waste disposal issue is called the KBS-3 method.It is based on protective natural and engineered barriers surrounding the spent nuclear fuelin order to isolate it from the biosphere, thereby ensuring protection of the environmentfrom increased levels of radioactivity. The spent nuclear fuel problem also concernscountries that no longer make use of nuclear power but still have large amounts of wasteto deal with.In recent years, the safety research concerning deep geological repositories for spentnuclear fuel have attracted significant attention. Scientists have investigated differentaspects of the worst-case scenario where the integrity of the barrier system is lost. Ifgroundwater actually comes into contact with the fuel, water radiolysis will be induced andthe products formed have the potential of oxidizing and dissolving the fuel matrix whichwill risk spreading radionuclides into the environment.Not surprisingly, actinide oxides are at the heart of many experimental studies. In manyinstances, their surfaces interaction with water radiolysis products are key to explain thematrix response in different environments. The main goal is to understand the fuelcorrosion/dissolution process, however many of the studies were performed on fairlycomplex systems which makes it difficult to draw reliable detailed mechanisticconclusions.In this thesis, the chemical processes involved in radiation induced oxidative dissolutionof UO2 were experimentally modeled in two different ways: The H2O2-induced oxidativedissolution of UO2 in aqueous solution and the reactive plasma interaction with uraniumoxide thin films under UHV conditions. H2O2 is one of the main oxidants generated inwater radiolysis. The impact of groundwater components on the mechanism of H2O2consumption and UO2 oxidation were investigated.The plasma of water gas successfully generated products similar to the ones formed by theradiolysis of liquid water. Three different types of uranium oxide (UO2, U2O5 and UO3)were probed with X-ray and Ultra-Violet Photoelectron Spectroscopy before and after theexposure to water plasma, pure or mixed with H2. A comprehensive examination was madeof redox events which mimic the radiation effects. Analysis of U5f emission was used todetermine the surface oxidation state. The nature of hydroxyl species adsorbed to thedifferent uranium oxides was also investigated in order to identify the conditions underwhich hydroxyl radical binding to uranium oxide surfaces is favored.

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  • 263.
    El Jamal, Ghada
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Gouder, T.
    Eloirdi, R.
    Tereshina-Chitrova, E.
    Horákd, L.
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Mixed H2O/H2plasma-induced redox reactions of thin uranium oxide films under UHV conditions2021In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 36, p. 12583-12591Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) has been used to study the effect of mixed H2O/H2gas plasma on the surfaces of UO2, U2O5and UO3thin films at 400 °C. The experiments were performedin situunder ultra-high vacuum conditions. Deconvolution of the U4f7/2peaks into U(iv), U(v) and U(vi) components revealed the surface composition of the films after 10 min plasma exposure as a function of H2concentration in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analysed using grazing-incidence X-ray diffraction (GIXRD). The XPS results show that U(v) is formed as a major product upon 10 minutes exposure of UO3by a mixed H2O/H2plasma in a fairly wide H2concentration range. When starting with U(v) (U2O5), rather high H2concentrations are needed to reduce U(v) to U(iv) in 10 minutes. In the plasma induced oxidation of UO2, U(v) is never observed as a major product after 10 minutes and it would seem that once U(v) is formed in the oxidation of UO2it is rapidly oxidized further to U(vi). The grazing incidence X-ray diffraction analysis shows that there is a considerable impact of the plasma and heating conditions on the crystal structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(iv) and U(v) in both directions. 

  • 264.
    El Jamal, Ghada
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Gouder, Thomas
    Eloirdi, Rachel
    Evgenia, Tereshina-Chitrova
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Mixed H2O/H2 Plasma-Induced Redox Reactions of Thin Uranium Oxide Films under UHV ConditionsManuscript (preprint) (Other academic)
    Abstract [en]

    X-Ray Photoelectron Spectroscopy (XPS) has been used to study the effect of mixed H2O/H2 gas plasma on the surface of UO2, U2O5 and UO3 thin films at 400 °C. The experiments were performed in-situ under ultra-high vacuum conditions. Deconvolution of the U4f7/2 peaks into the U(IV), U(V) and U(VI) components revealed the surface composition of the films after 10 minutes plasma exposure as a function of the H2 concentration in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analysed using Grazing-Incidence X-Ray Diffraction (GIXRD). The XPS results show that U(V) is formed as a dominating product upon 10 minutes exposure of UO3 by a mixed H2O/H2 plasma in a fairly wide H2 concentration range. When starting with U(V) (U2O5), rather high H2 concentrations are needed to reduce U(V) to U(IV) in 10 minutes. In the plasma induced oxidation of UO2, U(V) is never observed as a major product after 10 minutes and it would seem that once U(V) is formed in the oxidation of UO2 it is rapidly oxidized further to U(VI). The Grazing Incidence X-Ray Diffraction analysis shows that there is a considerable impact of the plasma and heating conditions on the crystal structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(IV) and U(V) in both directions.

  • 265.
    El Jamal, Ghada
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Gouder, Thomas
    European Commission, Joint Research Centre, Postfach 2340, DE-76215 Karlsruhe, Germany, Postfach 2340.
    Eloirdi, Rachel
    European Commission, Joint Research Centre, Postfach 2340, DE-76215 Karlsruhe, Germany, Postfach 2340.
    Idriss, Hicham
    European Commission, Joint Research Centre, Postfach 2340, DE-76215 Karlsruhe, Germany, Postfach 2340; Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), DE-76215 Karlsruhe, Germany.
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Study of Water Interaction with UO2, U2O5, and UO3: Tracking the Unexpected Reduction of Uranium Cations and Characterization of Surface-Bound Hydroxyls2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 29, p. 14222-14231Article in journal (Refereed)
    Abstract [en]

    The interaction of water with the surfaces of metal oxides is important to many fields of research, extending from nuclear science to catalysis to energy and biomedical materials. One intriguing phenomenon is the observation that, for a few oxides, water seems to reduce (not oxidize) the oxide substrate. In this work, ultraviolet photoelectron spectroscopy (UPS) has been used to study the reactions of H2O with prototype oxide nuclear fuels: UO2, U2O5, and UO3. On UO2, water adsorbs largely in a molecular state. On U2O5, water partially dissociates at −60 °C, thus forming surface −OH groups, and a fraction of the uranium cations are reduced from U5+ to U4+. On UO3, a similar reduction process is seen (reduction of a fraction of uranium cations from U6+ to U5+), albeit less pronounced. The chemisorbed H2O and −OH states via their molecular orbitals (MOs), 1b2, 3a1, and 1b1 for H2O and 1σ and 1π for −OH, were further analyzed. The 3a1-1b1 binding energy difference (ΔE) was taken as a measure of the bond strength. It was found to be larger on UO2 and U2O5 (2.9-3.0 eV) than on UO3 (2.2 eV). The charge state of the surface hydroxyl was found to be related to the 1π /1σ intensity ratio, from which, and in conjunction with the created U 5f states, electron transfer to the conduction band under UPS collection was facilitated by the hole trapping capacity of surface −OH groups, at least in the case of UO3. An energy band diagram is constructed that may explain the redox process observed on UO3 under UV photon excitation.

  • 266.
    El Jamal, Ghada
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Li, Junyi
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    H2O2-Induced Oxidative Dissolution of UO2 in Saline Solutions2021In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 2021, no 40, p. 4175-4182Article in journal (Refereed)
    Abstract [en]

    H2O2 is one of the oxidants responsible for driving the process of radiation-induced dissolution of spent nuclear fuel in geological repositories for spent nuclear fuel. As the groundwater composition will vary depending on geographical location as well as on the age of the repository (in relation to glacial cycles, etc.), it is important to elucidate the impact of different groundwater constituents. While several studies have addressed the impact of HCO3− and halide ions on the radiation chemistry of water in general and radiation-induced oxidative dissolution of spent nuclear fuel in particular, very few studies have addressed the impact of halide ions on the mechanism of the reaction between H2O2 and UO2. In this work, the impact of Cl−, Br− and ClO4− on the mechanism and kinetics of H2O2-induced oxidative dissolution of UO2-powder in aqueous suspensions with and without added HCO3− has been studied experimentally. The experiments reveal both ionic strength effects and specific ion effects on the kinetics of the reactions involved. These are discussed in connection to the results.

  • 267.
    El Jamal, Sawsan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Stability of Alternative Nuclear Fuel Materials in Aqueous Systems2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nuclear power produces a large portion of the electricity worldwide. It has been the largest low-carbon energy source for more than 30 years and has played an essential role in the security of energy supplies for many countries. However, despite its advantages, its future is unknown mainly because of accidents that can happen under reactor operation and the high radioactivity of the fuel after use. Therefore, Generation IV nuclear power has been introduced as it promises a sustainable and economical way of producing energy and reduces some of the risks observed in current reactors. UC and UN have advantageous properties compared to conventional UO2-based fuel which makes them promising fuel candidates for Generation IV nuclear reactors. Even though the fuel for Generation IV reactors is planned to be reprocessed, unexpected political decisions may change these plans, and the used fuel could end up in a geological repository. Therefore, the behavior of these new fuel materials must be understood in accident scenarios in reactors as well as under deep geological repository conditions. The radioactivity of the used fuel will induce radiolysis of water that comes in contact with it. This will lead to oxidative dissolution of the fuel and this is one of the potential routes for radionuclide release in the environment.

    In the first part of this thesis, UC and UN have been investigated in aqueous solutions under anoxic conditions, and under the influence of external γ-radiation and H2O2, the latter mimicking the impact of α-radiolysis. The hydrolysis of these materials in aqueous systems resulted in matrix dissolution which is not observed for UO2. The oxidative dissolution induced by H2O2 is more prominent than hydrolysis in water with or without added HCO3- where higher concentrations of dissolved uranium can be detected. In addition, the differences in reactivity are discussed for these materials and H2O2 is most reactive towards UN followed by UC and finally UO2, yet the dissolution yield is the lowest for UN. The change in UC and UN behavior with consecutive exposure to H2O2 was attributed to a change in surface reactivity where catalytic decomposition of H2O2 becomes possible.  As it was observed for H2O2 additions, radiation induced oxidative dissolution also dominates over hydrolysis. Unexpectedly high concentrations of H2O2 were observed in the irradiated systems. This was found to be due to formation of nano-particulate studtite that could not be separated from the solutions samples by filtration. Hence, it turned out to be impossible to determine the free U(VI) and H2O2 concentrations in these systems.

    Finally, the stability of pure and ZrN containing UN pellet fragments was investigated in aqueous system under external γ-radiation or H2O2 exposure. The behavior of these pellet fragments was similar to the UN powder where the dissolution of uranium was enhanced under oxidizing conditions if compared with anoxic conditions (hydrolysis). Consecutive exposures of UN pellet fragments to H2O2 showed a change in surface reactivity. This change is attributed to the formation of an oxide layer on the surface of UN, as UO2 is less reactive towards H2O2 and UO2 pellets display lower dissolution yields than UN pellets. In addition, the impact of ZrN as a stabilizing additive to UN pellets was studied. The addition of ZrN to UN is expected to stabilize the UN matrix and thus render a more accident tolerant fuel. Interestingly, it was shown that under oxidizing conditions, ZrN did not have a significant impact on the stability of UN pellets in aqueous systems

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  • 268.
    El Jamal, Sawsan
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Li, Junyi
    Mishchenko, Yulia
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Johnsson, Mats
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Effects of Gamma Radiation on Oxidative Dissolution of Alternative Nuclear Fuel Materials in Aqueous Bicarbonate SolutionsManuscript (preprint) (Other academic)
  • 269.
    El Jamal, Sawsan
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Mishchenko, Yulia
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Stability of Pure and ZrN-containing UN Pellets in Aqueous Systems – Impact of Ionizing Radiation and Radiolytic OxidantsManuscript (preprint) (Other academic)
  • 270.
    El Jamal, Sawsan
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Mishchenko, Yulia
    KTH, School of Engineering Sciences (SCI), Centres, Centre for Nuclear Energy Technology, CEKERT.
    Jonsson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Uranium Nitride Stability in Aqueous Solutions under Anoxic and Oxidizing Conditions– Expected Behaviour under Repository Conditions in Comparison to Alternative Nuclear Fuel MaterialsIn: Article in journal (Other academic)
  • 271.
    Elawad, Mohammed
    et al.
    Dalian Univ Technol DUT, DUT KTH Joint Educ & Res Ctr Mol Devices, Inst Artificial Photosynth, State Key Lab Fine Chem, Dalian 116024, Peoples R China.;Omdurman Islamic Univ, Dept Chem, Fac Sci, POB 382, Omdurman, Sudan..
    Lee, Husileng
    Dalian Univ Technol DUT, DUT KTH Joint Educ & Res Ctr Mol Devices, Inst Artificial Photosynth, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Yu, Ze
    Dalian Univ Technol DUT, DUT KTH Joint Educ & Res Ctr Mol Devices, Inst Artificial Photosynth, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Sun, Licheng
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry. Dalian Univ Technol DUT, DUT KTH Joint Educ & Res Ctr Mol Devices, Inst Artificial Photosynth, State Key Lab Fine Chem, Dalian 116024, Peoples R China..
    Ionic liquid doped organic hole transporting material for efficient and stable perovskite solar cells2020In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 586, article id 412124Article in journal (Refereed)
    Abstract [en]

    As a hole transporting material (HTM), N2,N2,N2',N2',N7,N7,N7',N7'-octakis (4-methoxyphenyl) spiro [fluorene-9,9'-xanthene]-2,2',7,7'-tetraamine (X60) in mesoscopic perovskite solar cells (PSCs) has been widely utilized for substitution of the 2,2',7,7'-tetrakis (N,N-di-p-methoxyphenylamine)-9,9'-spiro-bi-fluorene (spiroOMeTAD). In this study, we have introduced an ionic liquid N-butyl-N'-(4-pyridylheptyl) imidazolium bis (trifluoromethane) sulfonamide (BuPyIm-TFSI) as a p-dopant to increase the hole conductivity and stability of the X60 based perovskite solar cells. As a result, based on the different concentrations of BuPyIm-TFSI in mesoscopic PSCs, the optimal condition (4.85 mM) showed the best power conversion efficiency (PCE) of 14.65%, which is extremely higher than the device without BuPyIm-TFSI. Moreover, the device based on X60: BuPyIm-TFSI composite HTM at ambient conditions with humidity of similar to 40% exhibited good PSCs performance with the long-term stability of 840 h. Hence, the use of BuPyIm-TFSI as a p-dopant for X60 played a significant role in enhancing the electrical properties, stability and efficiency of PSCs.

  • 272. Ellis, Hanna
    et al.
    Eriksson, Susanna K.
    Feldt, Sandra M.
    Gabrielsson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Lohse, Peter W.
    Lindblad, Rebecka
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Rensmo, Håkan
    Boschloo, Gerrit
    Hagfeldt, Anders
    Linker Unit Modification of Triphenylamine-Based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 41, p. 21029-21036Article in journal (Refereed)
    Abstract [en]

    Linker unit modification of donor-linker-acceptor-based organic dyes was investigated with respect to the spectral and physicochemical properties of the dyes. The spectral response for a series of triphenylamine (TPA)-based organic dyes, called LEG1-4, was shifted into the red wavelength region, and the extinction coefficient of the dyes was increased by introducing different substituted dithiophene units on the pi-conjugated linker. The photovoltaic performance of dye-sensitized solar cells (DSCs) incorporating the different dyes in combination with cobalt-based electrolytes was found to be dependent on dye binding. The binding morphology of the dyes on the TiO2 was studied using photoelectron spectroscopy, which demonstrated that the introduction of alkyl chains and different substituents on the dithiophene linker unit resulted in a larger tilt angle of the dyes with respect to the normal of the TiO2-surface, and thereby a lower surface coverage. The good photovoltaic performance for cobalt electrolyte-based DSCs found here and by other groups using TPA-based organic dyes with a cyclopentadithiophene linker unit substituted with alkyl chains was mainly attributed to the extended spectral response of the dye, whereas the larger tilt angle of the dye with respect to the TiO2-surface resulted in less efficient packing of the dye molecules and enhanced recombination between electrons in TiO2 and Co(III) species in the electrolyte.

  • 273. Ellis-Gibbings, Lilian
    et al.
    Johansson, Viktor
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Walsh, Rick B.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Quinton, Jamie S.
    Andersson, Gunther G.
    Formation of N719 Dye Multilayers on Dye Sensitized Solar Cell Photoelectrode Surfaces Investigated by Direct Determination of Element Concentration Depth Profiles2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 25, p. 9431-9439Article in journal (Refereed)
    Abstract [en]

    The structure of the dye layer adsorbed on the titania substrate in a dye-sensitized solar cell is of fundamental importance for the function of the cell, since it strongly influences the injection of photoelectrons from the excited dye molecules into the titania substrate. The adsorption isotherms of the N719 ruthenium-based dye were determined both with a direct method using the depth profiling technique neutral impact collision ion scattering spectroscopy (NICISS) and with the standard indirect solution depletion method. It is found that the dye layer adsorbed on the titania surface is laterally inhomogeneous in thickness and there is a growth mechanism already from low coverage levels involving a combination of monolayers and multilayers. It is also found that the amount of N719 adsorbed on the substrate depends on the titania structure. The present results show that dye molecules in dye-sensitized solar cells are not necessarily, as presumed, adsorbed as a self-assembled monolayer on the substrate.

  • 274.
    Elmlund, Hans
    KTH, School of Technology and Health (STH), Structural Biotechnology.
    Protein structure dynamics and interplay: by single-particle electron microscopy2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Single-particle cryo-electron microscopy (cryo-EM) is a method capable of obtaining information about the structural organization and dynamics of large macromolecular assemblies. In the late nineties, the method was suggested to have the potential of generating “atomic resolution” reconstructions of particles above a certain mass. However, visualization of secondary structure elements in cryo-EM reconstructions has so far been achieved mainly for highly symmetrical macromolecular assemblies or by using previously existing X-ray structures to solve the initial alignment problem. A factor that severely limits the resolution for low-symmetry (point group symmetry Cn) particles is the problem of ab initio three-dimensional alignment of cryo-EM projection images of proteins in vitreous ice.

    A more general problem in the field of molecular biology is the study of heterogeneous structural properties of particles in preparations of purified macromolecular complexes. If not resolved, structural heterogeneity limits the achievable resolution of a cryo-EM reconstruction and makes correct biological interpretation difficult. If resolved, the heterogeneity instead offers a tremendous biological insight into the dynamic behaviour of a structure, and statistical information about partitioning over subpopulations with distinct structural features within the ensemble of particles may be gained.

    This thesis adds to the existing body of methods in the field of single-particle cryo-EM by addressing the problem of ab initio rotational alignment and the problem of resolving structural heterogeneity without using a priori information about the structural variability within large populations of cryo-EM projections of unstained proteins. The thesis aims at making the single-particle cryo-EM method a generally applicable tool for generating subnanometer resolution reconstructions and perform heterogeneity analysis of biological macromolecules.

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  • 275.
    Elwinger, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Characterizing Chromatography Media: NMR-based Approaches2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Liquid chromatography is an essential technique in manufacturing biopharmaceuticals where it is used on all scales from analytical applications in R&D to full-scale production. In chromatography the target molecule, typically a protein, is separated and purified from other components and contaminants. Separation is based on different affinities of different molecules for the chromatographic medium and the physical and chemical properties of the latter determine the outcome. Controlling and designing those properties demand efficient analytical techniques.

    In this thesis the approach was to develop characterization methods based on nuclear magnetic resonance (NMR) spectroscopy for the assessment of various important physico-chemical properties. The rationale behind this strategy was that the versatility of NMR – with its chemical and isotopic specificity, high dynamic range, and direct proportionality between the integral intensity of the NMR signal and the concentration of spin-bearing atomic nuclei (e.g., 1H, 13C, 31P and 15N) – often renders it a very good choice for both qualitative and quantitative evaluations.

    These characteristics of NMR enabled us to develop two quantification methods for chromatography-media ligands, the functional groups that provide the specific interactions for the molecules being separated. Furthermore, a new method for measuring the distribution of macromolecules between the porous chromatographic beads and the surrounding liquid was established. The method, which we have named size-exclusion quantification (SEQ) NMR, utilizes the fact that it is possible to assess molecular size distribution from corresponding distribution of the molecular self-diffusion coefficient where the latter is accessible by NMR. SEQ-NMR results can also be interpreted in terms of pore-size distribution within suitable models. Finally, we studied self-diffusion of small molecules inside the pores of chromatographic beads. The results provided new insights into what affects the mass transport in such systems.

    The methods presented in this thesis are accurate, precise, and in many aspects better than conventional ones in terms of speed, sample consumption, and potential for automation. They are thus important tools that can assist a better understanding of the structure and function of chromatography media. In the long run, the results in this project may lead, via better chromatographic products, to better drugs and improved health.

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  • 276.
    Elwinger, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pourmand, Payam
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Diffusive Transport in Pores. Tortuosity and Molecular Interaction with the Pore Wall2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 25, p. 13757-13764Article in journal (Refereed)
    Abstract [en]

    The self-diffusion of neat water, dimethyl sulfoxide (DMSO), octanol, and the molecular components in a water-DMSO solution was measured by H-1 and H-2 NMR diffusion experiments for those fluids imbibed into controlled pore glasses (CPG). Their highly interconnected structure is scaled by pore size and shows invariant pore topology independent of the size. The nominal pore diameter of the explored CPGs varied from 7.5 to 72.9 nm. Hence, the about micrometer mean-square diffusional displacement during the explored diffusion tithes was much larger than the individual pore size, and the experiment yielded the average diffusion coefficient Great care was taken to establish the actual pore: volumes of the CPGs. Transverse relaxation experiments processed by inverse Laplace transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore size for the larger pores and becomes stronger toward the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes, while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. Deviation from the trends predicted by the Renkin equation indicates that the interaction with the pore wall is not a just simple steric one but is in part dependent on the specific features of the molecules explored here.

  • 277.
    Elwinger, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pourmand, Payam
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Diffusive transport in pores. Tortuosity and molecular interaction with the pore wallManuscript (preprint) (Other academic)
    Abstract [en]

    The self-diffusion of neat water, dimethylsulfoxide (DMSO), octanol and the molecular components in a water-DMSO solution were measured by 1H and 2H NMR diffusion experiments for those fluids imbibed into Controlled Pore Glasses (CPG). Their highly interconnected structure is scaled by pore size and shows the some pore topology independently of the size. The nominal pore diameter of the explored CPGs varied from 7.5 nm to 72.9 nm. Hence, the ∼μm mean-square diffusional displacement during the explored diffusion times was much larger than the individual pore size. Great care was taken to establish the actual pore volumes of the CPGs. In addition, transverse relaxation experiments processed by Inverse Laplace Transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore sizes for the larger pores and becomes larger towards the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. The interaction with the pore wall is not just simple steric one but must in part be dependent on the specific features of the molecules explored here.

  • 278.
    Elwinger, Fredrik
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. GE Healthcare Biosci AB, Bjorkgatan 31, SE-75184 Uppsala, Sweden..
    Wernersson, Jonny
    GE Healthcare Biosci AB, Bjorkgatan 31, SE-75184 Uppsala, Sweden..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. GE Healthcare Biosci AB, Bjorkgatan 31, SE-75184 Uppsala, Sweden..
    Quantifying Size Exclusion by Diffusion NMR: A Versatile Method to Measure Pore Access and Pore Size2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 19, p. 11431-11438Article in journal (Refereed)
    Abstract [en]

    Size-exclusion quantification NMR spectroscopy (SEQNMR) is introduced for measuring equilibrium distribution coefficients, K-eq, in porous media. The porous medium is equilibrated with a polydisperse polymer solution. The original bulk polymer solution and the polymer solution after equilibration but in the absence of the porous medium are analyzed by NMR diffusion experiments. The joint evaluation of the two diffusion attenuation curves under suitable constraints provides the extent by which polymer fractions of particular size were depleted from the solution by pore access. This procedure yields K-eq versus polymer probe size, the selectivity curve that in turn can provide the pore size and its distribution. Simulations probe the performance of the method that is demonstrated experimentally in chromatographic media using dextran polymers. SEQ-NMR and inverse size- exclusion chromatography (ISEC) yield selectivity curves that virtually coincide. Crucial advantages with SEQ-NMR, such as versatility with regard to both the polymer used and porous system explored, high speed, potential for automation, and small required sample volume, are discussed.

  • 279.
    Elwinger, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Wernersson, Jonny
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    SEQ-NMR: A new tool for measuring distribution coefficients and pore size in chromatography mediaManuscript (preprint) (Other academic)
    Abstract [en]

    We present a new method, SEQ-NMR (size-exclusion quantification NMR spectroscopy) for measuring equilibrium distribution coefficients, Keq, in chromatography media. The same method is also generally applicable to measure pore sizes in any porous media. Keq versus probe size, the selectivity curve, is obtained by equilibrating a chromatographic medium with a solution of polymers with a broad size distribution. The solution before and after equilibration is analyzed with NMR diffusion experiments. The joint least-squares analysis of the two diffusion attenuation curves under suitable constraints provides the extent by which the different polymer fractions are diluted upon equilibration that in turn yields the selectivity curve. The relation of the applied procedure to Inverse Laplace transformation is clarified. Simulations probe the performance of the method, in particular with respect to signal-to-noise ratio (SNR) and other parameters used in the data inversion process. The method is demonstrated experimentally using dextran polymers and the chromatographic medium Sephacryl™ S-200 High Resolution for which it yields, within a cylindrical pore model, 6.9 nm for the average hydrated pore size. Comparison is made to the analysis of the same system with inverse size-exclusion chromatography (ISEC). Advantages of the method, primarily that in speed, potential for automation, and small sample size, are discussed.

  • 280. El-Zohry, Ahmed M.
    et al.
    Cong, Jiayan
    KTH.
    Karlsson, Martin
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Zietz, Burkhard
    Ferrocene as a rapid charge regenerator in dye-sensitized solar cells2016In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 132, p. 360-368Article in journal (Refereed)
    Abstract [en]

    Using the reductive power of the ferrocene moiety (Fc), an ultrafast regeneration step via a covalent attachment of a Fc moiety to an organic triphenylamine-based dye (L1) when adsorbed on TiO2 is highlighted. Two modified dyes with one and two Fc moieties attached (L1Fc, and L1Fc2), respectively, were synthesized by addition to the L1 dye. These dyes have been studied spectroscopically using ultrafast transient absorption spectroscopy in the visible and the infrared (IR) regions. In acetonitrile, the results show an ultrafast excited state quenching of the modified dyes due to an expected electron transfer process from the Fc(s) to L1. Adsorbed onto TiO2, an electron transfer process is also detected from Fc to the oxidized dye (L1(+)). Despite the occurrence of an ultrafast regeneration step, the solar cell performance does not improve by the attachment of Fc(s) to the dye L1. Transient absorption measurements in the IR region revealed a fast electron recombination process to the Fc(+) moiety on an average time scale of ca. 300 ps, outcompeting the >12 ns process to L1(+). The reasons for the observed considerably faster recombination rate to Fc(+) than to L1(+) are discussed in detail. This study provides deep spectroscopic insights for such organic dyes utilized to afford ultrafast regeneration step without showing high performance in photovoltaic devices. In addition, this study will improve our understandings for the triangular relationship between the molecular design, electron kinetics, and the performance in photovoltaic devices. (C) 2016 Elsevier Ltd. All rights reserved.

  • 281.
    El-Zohry, Ahmed M.
    et al.
    Uppsala Univ, Dept Chem, Angstrom Lab, SE-75120 Uppsala, Sweden.;Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden..
    Orabi, Esam A.
    Univ Manitoba, Dept Chem, Winnipeg, MB R3T 2N2, Canada..
    Karlsson, Karl Martin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Zietz, Burkhard
    Uppsala Univ, Dept Chem, Angstrom Lab, SE-75120 Uppsala, Sweden..
    Twisted Intramolecular Charge Transfer (TICT) Controlled by Dimerization: An Overlooked Piece of the TICT Puzzle2021In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 125, no 14, p. 2885-2894Article in journal (Refereed)
    Abstract [en]

    Organic dyes have shown high efficiencies in solar cells, which is mainly attributed to the push-pull strategy present in such dyes upon attaching to the semiconductor surfaces. We deeply studied the fundamental photophysical properties of cyanoacrylic dyes, mostly the L1 dye, and found unique emission properties that depend on many factors such as the solvent polarity and the concentration of the dye and could present a complete emission picture about this family of dyes. The L1 dye shows an intramolecular charge transfer (ICT) emission state at low concentrations (approximately nanomolar scale) and shows a twisted intramolecular charge transfer (TICT) emission state in specific solvents upon increasing the concentration to the micromolar scale. Moreover, the associated emission lifetimes of the ICT and TICT states of the L1 dye depend on solvent basicity, highlighting the role of hydrogen bond formation on controlling such states. Density functional theory calculations are performed to gain insight into the photophysical properties of the dye and revealed that H-bonding between the carboxylic groups triggers the dimerization at low concentrations. Using femtosecond transient absorption, we assigned the rate of TICT formation to be in the range (160-650 fs)(-1), depending on the size of the studied cyanoacrylic dye. Therefore, we add herein a new dimension for controlling the formation of the TICT state, in addition to the solvent polarity and acceptor strength parameters. These findings are not limited to the studied dyes, and we expect that numerous organic carboxylic acids dyes show similar properties.

  • 282. Emanuelsson, Rikard
    et al.
    Löfas, Henrik
    Zhu, Jun
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Grigoriev, Anton
    Ottosson, Henrik
    In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 11, p. 5637-5649Article in journal (Refereed)
    Abstract [en]

    Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E-E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular "electrical cords" hang conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (sigma/pi-conjugation) between adjacent sigma(E-E) and pi(C=C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si-Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a sigma-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si-Si bond rotations when the electrode-electrode distance is locked (variation by factor similar to 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode-electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 A of electrode-electrode distances.

  • 283. Endrodi, Balazs
    et al.
    Bencsik, G.
    Darvas, F.
    Jones, R.
    Rajeshwar, K.
    Janáky, C.
    Continuous-flow electroreduction of carbon dioxide2017In: Progress in Energy and Combustion Science, ISSN 0360-1285, E-ISSN 1873-216X, Vol. 62, p. 133-154Article in journal (Refereed)
    Abstract [en]

    Solar fuel generation through electrochemical CO2 conversion offers an attractive avenue to store the energy of sunlight in the form of chemical bonds, with the simultaneous remediation of a greenhouse gas. While impressive progress has been achieved in developing novel nanostructured catalysts and understanding the mechanistic details of this process, limited knowledge has been gathered on continuous-flow electrochemical reactors for CO2 electroreduction. This is indeed surprising considering that this might be the only way to scale-up this fledgling technology for future industrial application. In this review article, we discuss the parameters that influence the performance of flow CO2 electrolyzers. This analysis spans the overall design of the electrochemical cell (microfluidic or membrane-based), the employed materials (catalyst, support, etc.), and the operational conditions (electrolyte, pressure, temperature, etc.). We highlight R&D avenues offering particularly promising development opportunities together with the intrinsic limitations of the different approaches. By collecting the most relevant characterization methods (together with the relevant descriptive parameters), we also present an assessment framework for benchmarking CO2electrolyzers. Finally, we give a brief outlook on photoelectrochemical reactors where solar energy input is directly utilized.

  • 284. Endrodi, Balazs
    et al.
    Hursán, D.
    Petrilla, L.
    Bencsik, G.
    Visy, C.
    Chams, A.
    Maslah, N.
    Perruchot, C.
    Jouini, M.
    Incorporation of cobalt-ferrite nanoparticles into a conducting polymer in aqueous micellar medium: Strategy to get photocatalytic composites2014In: Acta Chimica Slovenica, ISSN 13180207, Vol. 61, p. 376-381Article in journal (Refereed)
    Abstract [en]

    In this study an easy strategy for conducting polymer based nanocomposite formation is presented through the deposition of cobalt-ferrite (CoFe 2O4) containing poly(3,4-ethylenedioxythiophene) (PEDOT) thin layers. The electrochemical polymerization has been performed galvanostatically in an aqueous micellar medium in the presence of the nanoparticlesand the surface active Triton X-100. The nanoparticles have been characterized by Transmission electron microscopy (TEM), the thin layers has been studied by applying Scanning electron microscopy (SEM), and X-ray diffraction (XRD), and the basic electrochemical properties have been also determined. Moreover, electrocatalytic activity of the composite was demonstrated in the electrooxidation reaction of dopamine (DA). The enhanced sensitivity - related to the cobalt-ferritecontent - and the experienced photocatalyitic activity are promising for future application.

  • 285. Endrodi, Balazs
    et al.
    Mellar, J.
    Gingl, Z.
    Visy, C.
    Janaky, C.
    Reasons behind the improved thermoelectric properties of poly(3-hexylthiophene) nanofiber networks2014In: RSC Advances, E-ISSN 2046-2069, Vol. 4, no 98, p. 55328-55333Article in journal (Refereed)
    Abstract [en]

    Enhanced thermoelectric properties of poly(3-hexylthiophene) nanofiber networks, doped in their reaction with silver cations, are presented. The role of charge carrier concentration and mobility (influenced by the supramolecular structure and nanoscale morphology) is discussed. The nanonet structure leads to a six fold increase in the ZT value compared to the bulk polymer counterpart.

  • 286. Endrodi, Balazs
    et al.
    Mellár, J.
    Gingl, Z.
    Visy, C.
    Janáky, C.
    Molecular and supramolecular parameters dictating the thermoelectric performance of conducting polymers: A case study using poly(3-alkylthiophene)s2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, p. 8472-8479Article in journal (Refereed)
    Abstract [en]

    In this study, we investigated the impact of molecular and supramolecular structure of conducting polymers (CPs) on their thermoelectric properties. As a model system, poly(3-alkylthiophene)s (P3ATs) with different side-chain lengths were prepared through oxidative chemical polymerization and were recrystallized to a well-ordered lamellar structure, resulting in one-dimensional self-assembled nanofibers (evidenced by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopic measurements). Thermoelectric characterization was performed at different doping levels (precisely tuned by doping in the redox reaction with Ag+ and Fe3+ cations), and the highly doped samples exhibited the best performance for all studied polymers. By varying the length of the alkyl side chain, the supramolecular structure and consequently the electronic properties were varied. The highest electrical conductivity was measured for poly(3-butylthiophene), rooted in its densely packed structure. The established structure-property relationships, concerning the monotonous decrease of the electrical conductivity with the alkyl side chain length, highlight the importance of the supramolecular structure (interchain distance in this case). These findings may contribute to the rational design of organic thermoelectric materials.

  • 287.
    Endrődi, Balázs
    et al.
    University of Szeged, Hungary.
    Bíró, A.
    Janáky, C.
    Tóth, I. Y.
    Visy, C.
    Layer by layer growth of electroactive conducting polymer/magnetite hybrid assemblies2013In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 171, p. 62-68Article in journal (Refereed)
    Abstract [en]

    Poly(thiophene-acetic-acid)/magnetite nanocomposite electrodes were fabricated from aqueous solutions on PDADMA (polydiallyldimethylammonium chloride) pre-treated ITO covered glass electrodes, employing layer by layer (LBL) technique. This approach was selected on the ground of the interaction between the surface OH-groups of the magnetite and the carboxylic group of the thiophene derivative. The gradual development of the hybrid assembly was followed by UV-vis spectroscopy, and was found to be continuous up to 30 bilayers. Moreover, the absorbance increase at the characteristic wavelengths was linear in the whole examined region. Importantly, the LBL-prepared composites proved to be electroactive, in aqueous phosphate buffer the Fe3+/Fe2+ redox transformation was observed. The electrocatalytic activity of the modified electrodes was demonstrated for electrooxidation of dopamine (DA), and the role of both components as well as their synergistic contribution was elucidated. Preliminary results indicate possible utilization of such hybrid assemblies in the amperometric detection of this analyte.

  • 288.
    Endrődi, Balázs
    et al.
    University of Szeged, Hungary.
    Kormányos, A.
    Janáky, C.
    Berkesi, O.
    Visy, C.
    Fixation of laccase enzyme into polypyrrole, assisted by chemical interaction with modified magnetite nanoparticles: A facile route to synthesize stable electroactive bionanocomposite catalysts2014In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 122, p. 282-288Article in journal (Refereed)
    Abstract [en]

    Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioactive component. In this study, a novel and efficient method for specific binding of laccase enzyme onto magnetite nanoparticles (NPs) is presented. The interaction between the chemically modified magnetite NPs and the enzyme was evidenced by both infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the enzyme-coated magnetite NPs were successfully incorporated into polypyrrole (PPy) matrix during galvanostatic electropolymerization. The encapsulation of laccase covered NPs was proved by EQCN, TEM, and FT-IR spectroscopy; whereas the electrochemical behaviour of the formed bionanocomposite was characterized by cyclic voltammetiy. In oxygen saturated solution a cathodic charge surplus was observed, related to the electrochemical reduction of oxygen. This surplus was two times higher in the case of the laccase containing layer compared to its only magnetite containing counterpart. Kinetic aspects of the oxygen reduction reaction (ORR) on the laccase containing films were investigated by hydrodynamic voltammetry, and the four-electron route was found to be exclusive, which is promising from the fuel cell perspective. Such synergistic combination of inorganic NPs and enzymes may open new avenues in the application of these bio-nanocomposite materials.

  • 289.
    Endrődi, Balázs
    et al.
    University of Szeged, Hungary.
    Samu, G. F.
    Azam, M. A.
    Janáky, C.
    Visy, C.
    Electrochemical synthesis and characterization of poly(3-hexylthiophene)/single-walled carbon nanotube array hybrid materials2016In: Journal of Solid State Electrochemistry, ISSN 1432-8488, E-ISSN 1433-0768, Vol. 20, no 11, p. 3179-3187Article in journal (Refereed)
    Abstract [en]

    In this study, we demonstrate that by directly employing single-walled carbon nanotube arrays (SWCNT-arrays)-grown on conductive substrates-as working electrodes, selective and uniform electrodeposition of a conducting polymer, namely poly(3-hexylthiophene), can be achieved on the surface of the nanotubes. The overall kinetic pattern of the electrodeposition was studied by separating the deposition charge from the one related to the redox transformation of the polymer film deposited during the precedent cycles. Both the structure and the electrochemical properties of the hybrid materials were studied as a function of the electrodeposition cycles, thus the amount of the formed polymer. The hybrids were characterized by electron microscopic (SEM, TEM) and vibrational spectroscopic (Raman spectroscopy) means. The obtained results were compared and contrasted with those gathered on macroscopic-sized multi-walled carbon nanotube array-based composites in our group recently. Overall, we conclude that electrochemical polymerization is an attractive tool to synthesize conducting polymer/SWCNT hybrid materials with controlled composition and morphology.

  • 290. Endrődi, Balázs
    et al.
    Samu, Gergely Ferenc
    Fejes, Dora
    Németh, Zoltan
    Horváth, Endre
    Pisoni, Andrea
    Matus, Peter Krisztian
    Hernádi, Klara
    Visy, Csaba
    Forro, Laszlo
    Janáky, Csaba
    Challenges and rewards of the electrosynthesis of macroscopic aligned carbon nanotube array/conducting polymer hybrid assemblies2015In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 53, p. 1507-1518Article in journal (Refereed)
    Abstract [en]

    Hybrid assemblies based on conducting polymers and carbon nanomaterials with organized nanoscale structure are excellent candidates for various application schemes ranging from thermal management to electrochemical energy conversion and storage. In the case of macroscopic samples, however, precise control of the nanoscale structure has remained a major challenge to be solved for the scientific community. In this study we demonstrate possible routes to homogeneously infiltrate poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene), and polyaniline into macroscopic arrays of vertically aligned multiwalled carbon nanotubes (MWCNTAs). Electron microscopic images and Raman spectroscopic analysis (performed along the longitudinal dimension of the hybrid samples) both confirmed that optimization of the electropolymerization circumstances allowed fine tuning of the hybrid structure towards the targeted application. In this vein, three different application avenues were tested. The remarkable anisotropy in both the electrical and thermal conductivity of the nanocomposites makes them eminently attractive candidates to be deployed in thermal management. Thermoelectric studies, aimed to understand the effect of organized nanoscale morphology on the important parameters (Seebeck coefficient, electrical-, and thermal conductivity) compared to their non-organized hybrid counterparts. Finally, extraordinary high charge storage capacity values were registered for the MWCNTA/PANI hybrids (500 F g−1 and 1–3 F cm−2). 

  • 291. Engin, Ozge
    et al.
    Villa, Alessandra
    Sayar, Mehmet
    Hess, Berk
    Driving forces for adsorption of amphiphilic peptides to the air-water interface.2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 34, p. 11093-11101Article in journal (Refereed)
    Abstract [en]

    We have studied the partitioning of amphiphilic peptides at the air-water interface. The free energy of adsorption from bulk to interface was calculated by determining the potential of mean force via atomistic molecular dynamics simulations. To this end a method is introduced to restrain or constrain the center of mass of a group of molecules in a periodic system. The model amphiphilic peptides are composed of alternating valine and asparagine residues. The decomposition of the free energy difference between the bulk and interface is studied for different peptide block lengths. Our analysis revealed that for short amphiphilic peptides the surface driving force dominantly stems from the dehydration of hydrophobic side chains. The only opposing force is associated with the loss of orientational freedom of the peptide at the interface. For the peptides studied, the free energy difference scales linearly with the size of the molecule, since the peptides mainly adopt extended conformations both in bulk and at the interface. The free energy difference depends strongly on the water model, which can be rationalized through the hydration thermodynamics of hydrophobic solutes. Finally, we measured the reduction of the surface tension associated with complete coverage of the interface with peptides.

  • 292.
    Engström, Anders
    et al.
    Thermo-Calc Software AB, Råsundavägen 18, Solna, SE-169 67, Sweden.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Summary report of CALPHAD XLIX - Stockholm, Sweden, 20222023In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 80, p. 102528-, article id 102528Article in journal (Other academic)
    Abstract [en]

    The CALPHAD XLIX conference took place in Stockholm, Sweden, from May 22 to 27, 2022. 112 participants from 18 countries attended the conference. The scientific program included 69 oral presentations divided into 16 thematic topics and 27 posters.

  • 293.
    Engström, Joakim
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
    Reid, Michael S.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Brotherton, E. E.
    Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire, UK .
    Malmström, Eva
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
    Armes, S. P.
    Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire, UK .
    Hatton, F. L.
    Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire, UK .
    Investigating the adsorption of anisotropic diblock copolymer worms onto planar silica and nanocellulose surfaces using a quartz crystal microbalance2021In: Polymer Chemistry, ISSN 1759-9954, E-ISSN 1759-9962, Vol. 12, no 42, p. 6088-6100Article in journal (Refereed)
    Abstract [en]

    Electrostatic adsorption of cationic polyelectrolytes onto anionic cellulosic substrates is an attractive route for facile surface modification of biorenewable materials. Recently, attention has focused on adsorbing cationic spherical diblock copolymer nanoparticles onto model cellulose and/or nanocellulosic substrates. Herein, we investigate physical adsorption of highly anisotropic copolymer worms bearing either anionic or cationic charge onto planar silica, cellulose nanocrystal (CNC) or cellulose nanofibril (CNF) surfaces using quartz crystal microbalance with dissipation monitoring. Electrostatic interactions dominate in the case of anionic silica and CNC surfaces because the adsorbed mass of cationic worms was greater than that of anionic worms. However, either anionic or cationic worms could be adsorbed onto in situ generated CNF substrates, suggesting that additional interactions were involved: hydrogen bonding, van der Waals forces, and possibly covalent bond formation. Scanning electron and atomic force microscopy studies of the dried planar substrates after adsorption experiments confirmed the presence of adsorbed copolymer worms. Finally, composite worm/CNF films exhibited restricted swelling behavior when immersed in water compared to reference CNF films, suggesting that the worms reinforce CNF films by acting as a physical crosslinker. This study is the first investigation of the physical adsorption of highly anisotropic diblock copolymer worms onto cellulosic surfaces.

  • 294. Engvall, Klas
    et al.
    Holmlid, Leif
    Field ionisation of excited alkali atoms emitted from catalyst surfaces1992In: Applied Surface Science, Vol. 55, no 4, p. 303-308Article in journal (Refereed)
  • 295. Engvall, Klas
    et al.
    Holmlid, Leif
    Kotarba, Andrzej
    Pettersson, Jan B. C.
    Menon, P. Govind
    Skaugset, P.
    Potassium promoter in industrial ammonia synthesis catalyst: Studies by surface ionization1996In: Applied Catalysis A: General, Vol. 134, no 2, p. 239-246Article in journal (Refereed)
  • 296. Engvall, Klas
    et al.
    Holmlid, Leif
    Menon, P. Govind
    Comparative loss of alkali promoter by desorption from two catalysts for the dehydrogenation of ethyl benzene to styrene1991In: Applied Catalysis, Vol. 77, no 2, p. 235-241Article in journal (Refereed)
  • 297. Engvall, Klas
    et al.
    Holmlid, Leif
    Prinz, H.
    Hofmann, H.
    Loss of alkali promoter by desorption from promoted vanadium oxide catalysts1991In: Catalysis Letters, Vol. 11, no 1, p. 41-48Article in journal (Refereed)
  • 298. Engvall, Klas
    et al.
    Kotarba, Andrzej
    Holmlid, Leif
    Emission of excited potassium species from an industrial iron catalyst for ammonia synthesis1994In: Catalysis Letters, Vol. 26, no 1-2, p. 101-107Article in journal (Refereed)
  • 299. Engvall, Klas
    et al.
    Kotarba, Andrzej
    Holmlid, Leif
    Long-range diffusion of K promoter on an ammonia synthesis catalyst surface - Ionization of excited potassium species in the sample edge fields1999In: Journal of Catalysis, Vol. 181, no 2, p. 256-264Article in journal (Refereed)
  • 300.
    Enright, Michael J.
    et al.
    Univ Illinois, Dept Chem, Urbana, IL 61801 USA.;Western Washington Univ, Dept Chem, Bellingham, WA 98225 USA..
    Jasrasaria, Dipti
    Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA..
    Hanchard, Mathilde M.
    Univ Illinois, Dept Chem, Urbana, IL 61801 USA..
    Needell, David R.
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Phelan, Megan E.
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Weinberg, Daniel
    Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA.;Lawrence Berkeley Natl Lab, Div Mat Sci, Berkeley, CA 94720 USA..
    McDowell, Brinn E.
    Univ Illinois, Dept Chem, Urbana, IL 61801 USA..
    Hsiao, Haw-Wen
    Univ Illinois, Dept Mat Sci & Engn, Urbana, IL 61801 USA..
    Akbari, Hamidreza
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Kottwitz, Matthew
    Univ Illinois, Dept Chem, Urbana, IL 61801 USA..
    Potter, Maggie M.
    Univ Illinois, Dept Chem & Biomol Engn, Urbana, IL 61801 USA..
    Wong, Joeson
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Zuo, Jian-Min
    Univ Illinois, Dept Mat Sci & Engn, Urbana, IL 61801 USA..
    Atwater, Harry A.
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Rabani, Eran
    Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA.;Lawrence Berkeley Natl Lab, Div Mat Sci, Berkeley, CA 94720 USA.;Tel Aviv Univ, Sackler Ctr Computat Mol & Mat Sci, IL-69978 Tel Aviv, Israel..
    Nuzzo, Ralph G.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Univ Illinois, Dept Chem, Urbana, IL 61801 USA..
    Role of Atomic Structure on Exciton Dynamics and Photoluminescence in NIR Emissive InAs/InP/ZnSe Quantum Dots2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 17, p. 7576-7587Article in journal (Refereed)
    Abstract [en]

    The development of bright, near-infrared-emissive quantum dots (QDs) is a necessary requirement for the realization of important new classes of technology. Specifically, there exist significant needs for brighter, heavy metal-free, near-infrared (NIR) QDs for applications with high radiative efficiency that span diverse applications, including down-conversion emitters for high-performance luminescent solar concentrators. We use a combination of theoretical and experimental approaches to synthesize bright, NIR luminescent InAs/InP/ZnSe QDs and elucidate fundamental material attributes that remain obstacles for development of near-unity NIR QD luminophores. First, using Monte Carlo ray tracing, we identify the atomic and electronic structural attributes of InAs core/shell, NIR emitters, whose luminescence properties can be tailored by synthetic design to match most beneficially those of high-performance, single-band-gap photovoltaic devices based on important semiconductor materials, such Si or GaAs. Second, we synthesize InAs/InP/ZnSe QDs based on the optical attributes found to maximize LSC performance and develop methods to improve the emissive qualities of NIR emitters with large, tunable Stokes ratios, narrow emission linewidths, and high luminescence quantum yields (here reaching 60 +/- 2%). Third, we employ atomistic electronic structure calculations to explore charge carrier behavior at the nanoscale affected by interfacial atomic structures and find that significant exciton occupation of the InP shell occurs in most cases despite the InAs/InP type I bulk band alignment. Furthermore, the density of the valence band maximum state extends anisotropically through the (111) crystal planes to the terminal InP surfaces/interfaces, indicating that surface defects, such as unpassivated phosphorus dangling bonds, located on the (111) facets play an outsized role in disrupting the valence band maximum and quenching photoluminescence.

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