| 1. |
- Österlund, Lars, 1967-, et al.
(författare)
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Photocatalytic oxide films in the built environment
- 2014
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Ingår i: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. - : Institute of Physics (IOP). ; , s. 012009-
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Konferensbidrag (refereegranskat)abstract
- The possibility to increase human comfort in buildings is a powerful driving force for the introduction of new technology. Among other things our sense of comfort depends on air quality, temperature, lighting level, and the possibility of having visual contact between indoors and outdoors. Indeed there is an intimate connection between energy, comfort, and health issues in the built environment, leading to a need for intelligent building materials and green architecture. Photocatalytic materials can be applied as coatings, filters, and be embedded in building materials to provide self-cleaning, antibacterial, air cleaning, deodorizing, and water cleaning functions utilizing either solar light or artificial illumination sources – either already present in buildings, or by purposefully designed luminaries. Huge improvements in indoor comfort can thus be made, and also alleviate negative health effects associated with buildings, such as the sick-house syndrome. At the same time huge cost savings can be made by reducing maintenance costs. Photocatalytic oxides can be chemical modified by changing their acid-base surface properties, which can be used to overcome deactivation problems commonly encountered for TiO2 in air cleaning applications [2, 3]. In addition, the wetting properties oxides can be tailored by surface chemical modifications and made e.g. oleophobic and water repellent [5]. Here we show results of surface acid modified TiO2 coatings on various substrates. In particular, we show that advanced surface treatment of photocatalytic cement yields surfaces with beneficial self-cleaning properties by means of photo-fixation of surface sulfate groups. We propose that such approaches are feasible for a number of applications in the built environment, including windows, tiles, sheet metals, plastics, etc.
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| 2. |
- Karlsson, Stefan, 1984-, et al.
(författare)
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Effects of deposition temperature on the mechanical and structural properties of amorphous Al-Si-O thin films prepared by radio frequency magnetron sputtering
- 2023
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 787
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Tidskriftsartikel (refereegranskat)abstract
- Aluminosilicate (Al–Si–O) thin films containing up to 31 at.% Al and 23 at.% Si were prepared by reactive RF magnetron co-sputtering. Mechanical and structural properties were measured by indentation and specular reflectance infrared spectroscopy at varying Si sputtering target power and substrate temperature in the range 100 to 500 °C. It was found that an increased substrate temperature and Al/Si ratio give denser structure and consequently higher hardness (7.4 to 9.5 GPa) and higher reduced elastic modulus (85 to 93 GPa) while at the same time lower crack resistance (2.6 to 0.9 N). The intensity of the infrared Si-O-Si/Al asymmetric stretching vibrations shows a linear dependence with respect to Al concentration. The Al–O–Al vibrational band (at 1050 cm−1) shifts towards higher wavenumbers with increasing Al concentration which indicates a decrease of the bond length, evidencing denser structure and higher residual stress, which is supported by the increased hardness. The same Al–O–Al vibrational band (at 1050 cm−1) shifts towards lower wavenumber with increasing substrate temperature indicating an increase in the average coordination number of Al.
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| 3. |
- Langhammer, David Michael, 1991-
(författare)
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Capturing Air Pollutants : Photochemical Adsorption and Degradation of SO2, NO2 and CO2 on Titanium Dioxide
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Titanium dioxide (TiO2) is a material with many useful properties. It is used most widely as a pigment in white paint, although in technological research it is better known for its ability to catalyze chemical reactions during light absorption. This process is referred to as photocatalysis, where the energy of the light is used to power the chemical reactions. This has enabled several interesting applications of TiO2, where it can for instance be applied to windows or façade walls to make their surfaces self-cleaning. Another implementation that has received much attention lately is artificial photosynthesis, where the light energy is used to transform CO2 and H2O into synthetic fuels. This thesis work contributes to the development of both these applications, although the main ambition is to show how three of the most common ambient air pollutant molecules, SO2, NO2 and CO2, can be captured at the surface of TiO2 by means of photocatalysis. Specifically, infrared (IR) spectroscopy and density functional theory (DFT) has been used as complementary tools of analysis to study the photocatalytic reactions that enable transformation of SO2, NO2 and CO2 into strongly bound sulfates, nitrates and carbonates, respectively. This combined experimental and theoretical approach has enabled a detailed description of how these reactions proceed and has further shown how the fundamental reactivity of the TiO2 surface changes upon light absorption.The work presented herein contributes to an increased understanding of photocatalysis and shows, quite generally, how molecules can be effectively captured at the surface of metal oxides by forming surface-integrated ionic adsorbates.
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| 4. |
- Thyr, Jakob, 1979-, et al.
(författare)
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Energy Alignment of Quantum-Confined ZnO Particles with Copper Oxides for Heterojunctions with Improved Photocatalytic Performance
- 2022
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Ingår i: ACS Nanoscience Au. - : American Chemical Society (ACS). - 2694-2496. ; 2:2, s. 128-139
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Tidskriftsartikel (refereegranskat)abstract
- The ability to control electronic states by utilizing quantum confinement of one of the material components in heterojunctions is a promising approach to perform energy-level matching. In this work, we report the possibility to achieve optimum energy alignment in heterojunctions made from size-controlled quantum dots (Q-dots) of ZnO in combination with three copper oxides: Cu2O, Cu4O3, and CuO. Quantum confinement effects on the ZnO nanoparticles in the diameter range 2.6–7.4 nm showed that the direct optical band gap decreased from 3.99 to 3.41 eV, with a dominating shift occurring in the conduction band (CB) edge, and thus the possibility to obtain close to 0.6 eV CB edge shift by controlling the size of ZnO. The effect was utilized to align the electronic bands in the ZnO Q-dot/copper oxide heterojunctions to allow for charge transfer between the materials and to test the ability to improve the photocatalytic performance for the system, evaluated by the transformation of a dye molecule in water. The catalyst materials were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis), photoluminescence, and Raman spectroscopy. The most promising material combination was found to be the Cu2O copper oxide in combination with an energy aligned ZnO Q-dot system with approximately 7 nm diameter, showing strong synergy effects in good agreement with the energy-level analysis, outperforming the added effect of its individual components, ZnO-Q-dots and Cu2O, by about 140%. The results show that utilization of a heterojunction with controllable energy alignment can provide a drastically improved photocatalytic performance. Apart from increased photocatalytic activity, specific surface states of ZnO are quenched when the heterojunction is created. It is anticipated that the same approach can be utilized in several material combinations with the added benefit of a system with controllable overpotential and thus added specificity for the targeted reduction reaction.
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| 5. |
- Österlund, Lars, 1967-, et al.
(författare)
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Precise tuning of the photonic band gap using multilayered inverse opals
- 2014
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Ingår i: 12th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity and 9th International conference on Functional Materials and Nanotechnologies – RCBJSF–2014-FM&NT. - : Ulma, Riga.
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Konferensbidrag (refereegranskat)abstract
- Inverse opals are photonic band gap (PBG) structures with a periodic arrangement of voids with low refractive index (air) in a high-refractive index dielectric media with sub-wavelength periodicity. In analogy with electronic band gaps in solid state semiconductors these structures form forbidden energy ranges for light, irrespective of the photon’s momentum. Recently, inverse opal structures have been studied for photocatalysis applications. Here the idea is to match the edge of the PBG with the electronic band gap of a semiconductor to allow for efficient light absorption. Here we present a novel approach to tune the position and shape of the PBG by purposefully deposit multilayers of oxides with controlled thicknesses on the inside walls of the inverse opals. This avoids the technical problems of changing the periodicity and materials of the opals. The fabrication involves a three-step process: It consists of self-assembly by convective evaporation of polystyrene beads into close-packed fcc structures; atomic layer deposition (ALD) of metal oxides (Al2O3) to fill the voids between the beads; and subsequent Ar ion etching and calcination to crystallize and develop the inverse opal structure. ALD is then repeated to make multi-layer structures of TiO2 with controlled thickness. The inverse opal structures were characterized by optical spectroscopy, X-ray spectroscopy, electron microscopy, and profilometry. Theoretical modeling was performed to describe the optical properties. The results are analyzed and compared with band structure calculations made by the plane-wave expansion method together with finite-difference time-domain simulations of the transmission spectra (Fig. 1). Our method is versatile and can be used to fabricate reactive nanoparticles with different chemical composition on the inside walls; as well as plasmonic nanoparticles embedded in the layers to efficiently absorb slow light.
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| 6. |
- Johansson, Wilhelm, et al.
(författare)
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Transparent TiO2 and ZnO Thin Films on Glass for UV Protection of PV Modules
- 2019
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Ingår i: Frontiers in Materials. - Lausanne, Switzerland : Frontiers Media S.A.. - 2296-8016. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Failure of PV modules frequently occurs as a result of degradation of their encapsulation material by destructive UV radiation. Both the life expectancy and efficiency of PV modules can be improved by reducing the transmittance of the destructive UV radiation through the cover glass without compromising the transmittance in the visible wavelength region. In addition, if the absorbed UV photons can be down-shifted to wavelengths that can be more efficiently converted to electrical energy, an additional increase of the PV efficiency could be achieved. In this study we have investigated transparent ZnO and TiO2 thin films deposited by spray pyrolysis on soda lime silicate float glass as functional layers on PV cover glass. The optical bandgap, UV-cutoff, UV-Vis transmittance, reflectivity (total and diffuse) and photoluminescence have been determined. The ZnO coating shifted the optical bandgap to longer wavelengths, resulting in a reduction of the transmittance of destructive UV radiation by up to ∼85%. Distinct photoluminescence peaks at 377 nm and at 640 nm were observed for one of the ZnO samples. The TiO2 coated glasses also showed an increased UV cutoff, which resulted in a reduction of transmittance of destructive UV radiation by up to 75%. However, no photoluminescence peaks could be observed from the TiO2 films with 325 nm excitation laser, which can be explained by the fact that only indirect interband transitions are accessible at this excitation wavelength. Deposition of both ZnO and TiO2 coatings resulted in a reduction of the transmitted light convertible by PV modules, by up to 12.3 and 21.8%, respectively. The implication of the results is discussed in terms of lifetime expectancy and efficiency of PV modules.
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| 7. |
- Welearegay, Tesfalem, et al.
(författare)
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Exhaled air analysis as a potential fast method for early diagnosis of dengue disease
- 2020
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Ingår i: Sensors and actuators. B, Chemical. - Netherlands : Elsevier BV. - 0925-4005 .- 1873-3077. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- Dengue is a neglected tropical disease caused by arbovirus. Every year 390 million persons are infected with dengue, of which 96 million manifest clinically around the world, mainly in the Latin America, South-East Asia and Western Pacific. The disease manifests itself as a flu-like infection that generally is difficult to recognise from a normal flu or other viral infections. The mortality rate is around 20 % for the severe form of dengue, which readily could be decreased to below 1% with early, reliable diagnostic tools. Today there exist however no diagnostic tests for the early and rapid diagnosis of this disease. In this study, we report for the first time the possibility of identification of possible biomarkers associated with dengue disease in the exhaled air, and of the development of a breath test for fast, non-invasive and easy diagnosis of this disease. Further, we demonstrate a new deployable sensor technology based on a chemoresistive metal-ligand nanoassembly tailored for the identified possible biomarkers of dengue disease, which achieved 100 % accuracy for dengue diagnosis on our study group and can be used in both specialist and non-specialist settings. Nevertheless, as the present study was performed on a limited number of patients because of the difficulty to recruit a high number of patients because dengue is a neglected disease, future validation tests on a higher cohort are necessary for corroborating the results obtained in the present study.
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| 8. |
- Ahlinder, Linnea, et al.
(författare)
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Graphene oxide nanoparticle attachment and its toxicity on living lung epithelial cells
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 5:73, s. 59447-59457
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Tidskriftsartikel (refereegranskat)abstract
- Since its discovery, graphene and its oxidized form, graphene oxide (GO), have attracted interest in a wide range of technical applications. Concerns about their potential toxicity calls for scrutinized studies, but hitherto conflicting results have been reported which partly may be due to variations of synthesis and exposure procedures. Here we report on the attachment and toxicity of contamination-free graphene oxide nanoparticles (GONP) in living lung epithelial cells. The synthesis of chemically pure GONP was made by an improvement of the Hummer's method based on graphene exfoliated from graphite using high-intensity ultrasonication, resulting in two dimensional sheets with a lateral dimension in the range 200 nm to 3 mu m and thickness of 0.9 nm. Confocal Raman spectroscopy combined with multivariate analysis was used to study the interaction of GONP and living cells. It is shown that overlapping Raman bands due to GONPs and biomolecules in the cells can clearly be separated with this approach. Orthogonal partial least squares discriminant analysis was used to compare spectral data collected from cells exposed to GONP with spectral data collected from non-exposed control cells, and spectral data from cells exposed to a surfactant known to induce apoptosis. Our analyses show that GONP readily attach to the cells, forming sheets which cover a large fraction of the cell surfaces, and induce small chemical changes. In particular, chemical modifications of proteins and lipids in lung epithelial cells are inferred. GONPs do not, however, decrease cell viability. In contrast, enhanced cell proliferation is observed. Our results shed new light on the interactions of GO, and in contrast to some previous reports, suggest that GO is not toxic. The hyperspectral Raman spectroscopy analysis employed here should be applicable for other fields in nanomedicine as a label-free non-perturbing analytical method.
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| 9. |
- Henycha, Jiri, et al.
(författare)
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Reactive adsorption and photodegradation of soman and dimethyl methylphosphonate on TiO2/ nanodiamond composites
- 2019
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Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 259
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis and characterization of TiO2/Nanodiamond (ND) nanocomposites for rapid decontamination of chemical warfare agents (CWA) and toxic industrial compounds prepared by a simple water-based, low-temperature method using urea as a homogeneous precipitating agent. The excellent water-compatibility of NDs promoted their good dispersion within the TiO2 matrix resulting in intergrown TiO2/ND nanostructures. NDs with an abundance of oxygen-containing surface moieties increased the porosity of the composites resulting in their three times more efficient spontaneous degradation of the CWA soman in solution compared to pure TiO2. In situ DRIFT spectroscopy revealed the enhanced reactive adsorption and solar light photodecomposition of dimethyl methyl phosphonate vapor on TiO2/ND. The charge transfer across TiO2/ND interfaces that hinder recombination of photo-excited electron-hole pairs was inferred from surface potential measurements. The results indicate that well-dispersed NDs forming heterojunctions together with their high porosity contribute to the reactive properties of the nanocomposites.
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| 10. |
- Jansson, Jonas, 1973, et al.
(författare)
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On the catalytic activity of Co3O4 in low-temperature CO oxidation
- 2002
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 211:2, s. 387-397
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of CO over Co3O4 at ambient temperature was studied with flow reactor experiments, and in-situ spectroscopic and structural methods. The catalyst deactivates during the reaction. The rate of deactivation increased with increasing CO or CO2 gas-phase concentration but decreased with increased 02 concentration or increased temperature. Regeneration of the catalyst in 10% O-2/Ar was more efficient than regeneration in Ar alone. The presence of carbonates and surface carbon on the deactivated catalyst was concluded from TPO experiments. None of these species could, however, be correlated with the deactivation of the catalyst. In-situ FTIR showed the presence of surface carbonates, carbonyl, and oxygen species. The change in structure and oxidation state of the catalyst was studied by in-situ XRD, in-situ XANES, XPS, and flow reactor experiments. One possible explanation for the deactivation of the catalyst is a surface reconstruction hindering the redox cycle of the reaction. (C) 2002 Elsevier Science (USA).
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