| 1. |
- Iqbal, Muhammad Naeem, 1985-
(författare)
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Mesoporous Silica Particles for a Potential Therapeutic Application
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mesoporous silica particles (MSPs) have a high surface area, pore volume, and tunable pore size and surface properties, which makes them ideal for advanced therapeutic, biocatalytic, separation, and drug delivery applications. The work in this thesis shows that MSPs can be employed for therapeutic applications with minimal risk of adverse consequences. The MSPs in the study are of the SBA-15 type.Obesity is a serious health problem caused by an excess of adipose tissue (body fat) as a result of inadequate energy expenditure. Both in developed and developing countries, the prevalence is increasing rapidly. Type 2 diabetes (T2D) mellitus is going to be one of the most destructive consequences of the global obesity pandemic. Obesity and diabetes are anticipated to affect 783 million people by 2045, with diabetes being the leading cause of death for an estimated 6.7 million people in 2021 (according to International Diabetes Federation, IDF Diabetes Atlas 10th edition, 2021). People who are overweight or have diabetes are more likely to trigger other physiological conditions such as the development of dyslipidemia. Dyslipidemia is defined by a combination of risk factors for cardiovascular disease, including excessive plasma free fatty acids, cholesterol, and triglycerides; low levels of high density lipoprotein (HDL); and aberrant low-density lipoprotein (LDL). Public health expenditures and initiatives are under severe strain as a result of these situations. Researching therapies that are both safe and effective is in dire need.MSPs were produced at bench scale, and scaled to pilot (100L) and then at a relatively large demonstration scale (100-1000L) and tested in vitro, in vivo, ex vivo, and clinically. The results from these studies have shown that when administered orally, MSPs adsorb enzymes that break down carbohydrates and lipids (amylase and lipase), physically separating them from their large substrates. When administered orally, this consequently reduces the breakdown of carbohydrates and fats, leading to a lowering of the total energy intake in animals and humans. This occurs when the MSP has pore sizes which is typically in the range of 8–13 nm that are slightly larger than the food-digesting enzymes. The research carried out as part of this thesis showed that when the MSPs are in the micron size range, they operate locally in the gastrointestinal tract (GIT) and exit in the fecal mass without being absorbed by the body. The adsorbed enzymes aid in the safe transit of MSPs through the gastrointestinal system. Furthermore, the presence of these digestive enzymes within the pores was shown to have no effect on enzymatic function. It was also observed that when a large substrate (starch) was used to measure the activity of α-amylase adsorbed in the pores of MSPs, the activity appeared reduced. However, this was not related to an inactivation of α-amylase but to the fact that starch was molecularly too large to enter the pores of the MSPs.
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| 2. |
- Kapuscinski, Martin, 1989-
(författare)
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Following nanoparticle self-assembly in real-time : Small-angle X-ray scattering and quartz crystal microbalance study of self-assembling iron oxide nanocubes
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembly of nanoparticles is a widely used technique to produce nanostructured materials with crystallographic coherence on the atomic scale, i.e. mesocrystals, which can display useful collective properties. This thesis focusses on the underlying mechanism and dynamics of mesocrystal formation by using real-time techniques. Quartz-crystal microbalance with dissipation monitoring (QCM-D) as well as small-angle X-ray scattering (SAXS) in combination with optical microscopy were used to probe the temporal evolution of growing mesocrystals to elucidate the growth mechanism.Time-resolved small-angle X-ray scattering was used to probe the formation and how the structure and defects of the growing mesocrystals in levitating droplets evolve with time. Probing self-assembly of oleate-capped iron oxide nanocubes during evaporation-driven poor-solvent enrichment (EDPSE) showed that a low particle concentration in combination with a short nucleation period can generate large and well-ordered mesocrystals. Information on the formation and transformation of defects in mesocrystals were obtained by analysis of the temporal evolution of crystal strain. A transition from a rapidly increasing isotropic strain to a decreasing anisotropic strain towards the end of the growth stage was observed. The occurrence of anisotropic strain was assigned to the formation of stress-relieving dislocations in the crystal, which were induced by large internal stresses caused by superlattice contraction.Directed assembly of superparamagnetic iron oxide nanocubes, subjected to a weak magnetic field, produced one-dimensional mesocrystal fibers. Real-time SAXS as well as optical microscopy revealed a two-stage growth mechanism. The primary stage involved the growth of cuboidal mesocrystals by nanocube self-assembly. In a secondary stage, the cuboidal mesocrystals were assembled and aligned into fibers by the magnetic field. Evaluation of the magnetic dipole-dipole and van der Waals interactions showed that the dipolar forces arising between two nanocubes in a weak magnetic field are negligible compared to the van der Waals forces, but become the dominant force for larger mesocrystals, which drives the formation of fibers.QCM-D combined with optical microscopy provided simultaneously information on the rheological properties as well as on the mass of an adsorbed self-assembled layer of iron oxide nanocubes. We show that the iron oxide nanocubes rapidly assembled into an array with primarily viscous characteristics. This fluid-like behaviour can be assigned to a layer of solvent surrounding the nanocubes inside the assembly. Expulsion of the thin solvent layer from the assembled array is responsible for the increase in rigidity observed shortly after the beginning of self-assembly.
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| 3. |
- Wang, Xia, 1990-
(författare)
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Assemblies of Colloidal Hydrochar Nanoparticles and their Derived Activated Carbons for CO2 Sorption
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon-rich colloids are of great fundamental and technological interest and in this thesis, I tested a range of hypotheses and studied aspects of small hydrochar-based colloids and their colloidal and material chemistry. Crude hydrochar dispersions were synthesized by hydrothermal carbonization of glucose and purified by dialysis. After the purification, stable and monodisperse dispersions of colloidal hydrochar particles in water were obtained. Evaporation of water from the colloidal hydrochar dispersion led to that the hydrochar particles deposited into repeated strip patterns on glass substrates, or underwent directed assembly into macroscopic rods or yarn-shaped objects at the glass-water-air interface.In one study, we studied the strip patterns that comprised dense assemblies of hydrochar particles formed through directed assembly on the substrates during evaporation of water as a function of the sodium dodecylsulfate (SDS) addition, pH of the dispersion, geometry of the substrates, and concentration of the colloidal particle. The mechanisms were presented. In the published paper included in the thesis, the formation of the macroscopically large and assembled rods was studied during evaporation of water from the colloidal hydrochar dispersions. This assembly was studied along with the electrostatic stability of the dispersions at various pH and ion strengths and the redispersability of the assembled rods into the constituting colloidal particles. For matters of applications of the rod assemblies, pyrolysis and templating silicon carbide -tricopper silicide ((SiC-Cu3Si) by reactive infiltration with a copper silicon alloy by reaction infiltration were introduced.In two manuscripts, aspects of the dispersions of hydrochar particles were studied with means of KHCO3 activation into activated carbons (ACs). In one study, hydrochar particles were activated, and then the ACs were dispersed in a solvent after physical grinding. The morphology, porosity, and CO2 sorption properties, etc. of the activated carbons prepared by chemical activation were studied for freeze-dried hydrochar particles and the long bent yarn assemblies pretreated under different conditions. ACs of electrospun nanofibers of polyvinylpyrrolidone (PVP) and colloidal hydrochar were oxidized and chemically activated with KHCO3 or K2CO3 and studied for the adsorption of CO2.
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| 4. |
- Björnerbäck, Fredrik, 1984-
(författare)
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Sustainable porous organic materials : Synthesis, sorption properties and characterization
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The resources available to us humans, including metals, minerals, biomass, air, water, and anything else on the planet, are being used at an increasing rate. This anthropogenic use of resources both depletes the resources and has negative impacts on other resources, e.g. the biosphere. Thus, developing (more) sustainable chemical and industrial processes are of the utmost importance for the well-being of the creatures of Earth and for the long-term sustainability of human society.This thesis focuses on organic porous materials, and more specifically their synthesis and characterization. Porous materials are, for example, used in detergents, water treatment, bio gas upgrading, carbon dioxide capture, as catalysts, in sensors, and in various biological applications. The application of porous materials can contribute to the drive towards a more sustainable society. However, porous materials are typically not sustainable themselves. Thus, there is a need to develop more sustainable porous materials. The synthesis and characterization of three different groups of porous organic materials are described in this thesis.In pulp- and paper manufacturing, lignin is separated from desirable products and is typically combusted for heat. In one section of this thesis, lignin was used to produce bio-oil for potential use in fuels and chemicals. However, the bio-oil process produced a solid by-product. The by-product was used to synthesize and study activated carbons with very high porosities and magnetic properties, a combination of properties that may prove to be useful in applications.Sugar is known to produce solid and unwanted compounds through reactions with acids. It is shown here that it is possible to produce highly microporous humins, i.e. organic porous materials with a large amount of small pores, using sulphuric acid and a range of saccharides and bio-based polymers. This work supports that solid by-products in a wide range of biomass conversion processes can be of high value, both economically and as replacements for less sustainable alternatives.The biosphere contains vast amounts of molecules with aromatic structures. The last section of this thesis shows how such aromatic molecules can be used to produce highly porous materials through Friedel-Crafts type chemistry using sulfolane as a solvent and iron chloride as a catalyst. This synthesis strategy produces high-performance materials, improves upon the sustainability of traditional Friedel-Crafts chemistry, and makes use of typically underutilized and abundant bio-based molecules.
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| 5. |
- Cardenas, Edgar, 1990-
(författare)
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Synthesis of zeolites from economic raw materials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis methods using economic raw materials, such as kaolin and diatomite have been developed for the production of zeolites in the present work. Zeolite Y and ZSM-5 have been synthetized successfully from diatomite and kaolin, respectively. The synthesis of zeolite Y was extensively studied (Paper I) in order to obtain final products with high crystallinity and an appropriate SiO2/Al2O3 ratio to be suitable for application as catalyst. Then, the influence of the alkalinity (in terms of SiO2/Na2O ratio) on the outcome of the synthesis was studied. Thus, an optimum range of alkalinity that satisfies the requirements stated before was found. Additionally, the results also showed that diatomite produce similar products as colloidal silica, which may be expected since both silica sources are highly polymerized forms of silica.The synthesized zeolite Y crystals were also ion-exchanged with Lanthanum to obtain a Rare Earth zeolite Y (REY) catalyst (Paper V). The REY catalyst was shown to be thermally stable up to 800°C as expected for this catalyst. The REY catalyst was also evaluated in the reaction of Catalytic Cracking of cumene. The results of catalytic tests shown that the REY catalyst synthetized from diatomite holds activity towards the catalytic cracking of cumene.In addition, studies of synthesis of ZSM-5 zeolite from kaolin have been performed to understand the crystal growth and morphology, crystal size, and aluminum distribution. In particular, the influence of the gel on the morphology of the crystals (Paper II) has been studied. It was observed that when the crystal surface is in contact with the gel phase, dendritic features appear at the crystal surface, that become smoother as the reaction proceeds. On the contrary, when only liquid phase is in contact with crystal surface there is no presence of dendritic features and the growth rate is higher.Further studies demonstrated that the ZSM-5 crystals possess a non-homogeneous aluminum distribution, a phenomenon known as Al-zoning. A thorough characterization at distinct stages of the reaction has been performed (Paper III), on the different reaction mixture phases such as solid part, gel phase and liquid phase. The main finding was that the gel phase consists of a nanoparticle skeleton rich in alumina, filled by a silica rich matrix. In the beginning of crystallization, the silica rich matrix is preferentially consumed to form the crystals, leaving behind the alumina rich nanoparticle skeleton that is consumed later, resulting in the non-homogeneous distribution of aluminum in the crystals.Finally, studies of the microstructure of a TPA-ZSM-5 system using fumed silica as silicon source have been performed (paper IV). In this system, three stages of crystallization were observed. Stage I, formation of amorphous gel phase. Stage II formation of XRD amorphous spherical entities denoted as Condensed Agregates (CAs). Stage III, Crystallization of CAs into ZSM-5. This study was focused only in the stage III. Findings showed that ZSM-5 nanocrystals are formed in the core of the CA (beginning of stage III), surrounded by an amorphous shell composed of alumino-silica. As the crystallization proceeds, the amorphous shell crystallizes into ZSM-5 by competitive growth, but the nanocrystals of the core remain intact. Moreover, compositional analysis results showed that the silicon from the liquid phase provided most of the nutrients for growth of the ZSM-5 crystals resulting in polycrystalline ZSM-5 aggregates with an Al rich core - Si rich shell morphology.
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| 6. |
- Cheung, Ocean, 1986-
(författare)
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Narrow-pore zeolites and zeolite-like adsorbents for CO2 separation
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A range of porous solid adsorbents were synthesised and their ability to separate and capture carbon dioxide (CO2) from gas mixtures was examined. CO2 separation from flue gas – a type of exhaust gas from fossil fuel combustion that consists of CO2 mixed with mainly nitrogen and biogas (consists of CO2 mixed with mainly methane) were explicitly considered. The selected adsorbents were chosen partly due to their narrow pore sizes. Narrow pores can differentiate gas molecules of different sizes via a kinetic separation mechanism: a large gas molecule should find it more difficult to enter a narrow pore. CO2 has the smallest kinetic diameter in zeolites when compared with the other two gases in this study. Narrow pore adsorbents can therefore, show enhanced kinetic selectivity to adsorb CO2 from a gas mixture.The adsorbents tested in this study included mixed cation zeolite A, zeolite ZK-4, a range of aluminophosphates and silicoaluminophosphates, as well as two types of titanium silicates (ETS-4, CTS-1). These adsorbents were compared with one another from different aspects such as CO2 capacity, CO2 selectivity, cyclic performance, working capacity, cost of synthesis, etc. Each of the tested adsorbents has its advantages and disadvantages. Serval phosphates were identified as potentially good CO2 adsorbents, but the high cost of their synthesis must be addressed in order to develop these adsorbents for applications.
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| 7. |
- Engström, Olof
(författare)
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Carbohydrate dynamics and interactions studied by NMR spectroscopy
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The combination of NMR spectroscopy and molecular dynamics (MD) simulations are powerful tools in the studying of bioorganic molecules in solution. In this thesis two such studies are presented with focus on the NMR aspect. The caffeine association to sugars (D-glucose and sucrose) was investigated by NMR titrations and NOESY experiments in paper I. The observations from the NMR experiments confirmed MD simulations showing that the binding occurs by a face-to-face interaction between the aromatic surface of the caffeine and axial protons of the sugar ring. Different sugar molecules and residues have different preferences regarding which side of the sugar ring that are involved in the binding. The sucrose residues bind with only one ring face each whereas β-D-glucopyranose has two sides of similar binding probability and the α-D-glucopyranose has something in between. The MD simulations showed that the driving force of the binding is partly driven by hydration effects that favor the enthalpy of the system. A new approach to calculate NMR relaxation parameters (that is dependent on molecular motions) from computational simulations is presented in paper II. Each sugar residue is assumed to be a rigid unit connected by flexible joints in the approach, thus the name diffusive chain model (DCM). The simplified model together with a stochastic simulation approach lowers the computational cost which makes it possible to acquire long enough trajectories to the calculations of spin relaxation parameters. Two case studies with slightly different methodologies are presented. In one of them, spin relaxation parameters are reproduced for the human milk oligosaccharide LNF-1 in a feasible way by the use of Brownian dynamics.
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| 8. |
- Garcia Mendoza, Javier Gustavo, 1980-
(författare)
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Synthesis and applications of low silica zeolites from Bolivian clay and diatomaceous earth
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the present work was to develop synthesis routes to produce synthetic zeolites with industrial attractiveness from non-expensive Bolivian raw materials, such as clays and diatomite. In particular, the work was focused on the synthesis of low-silica zeolites with the LTA and FAU structures. The raw materials as well as intermediate and final zeolite products were structurally characterized by different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen gas adsorption, inductively coupled plasma mass spectrometry (ICP-MS). Besides, the final properties were evaluated for intended applications i.e. brightness by UV-VIS spectroscopy for LTA-type zeolite A in detergents and the CO2 breakthrough adsorption of FAU-type zeolite X for gas separation. The first part of this study deals with the synthesis of low silica zeolite A from Bolivian montmorillonite clay (Paper I). The clay was fused at high temperature with NaOH to render the material more reactive. The raw montmorillonite had a SiO2/Al2O3 ratio of 4 and sodium aluminate was added to the mixture to decrease this ratio to 2. An optimization of the synthesis time was performed. For the sake of comparison, the same treatment was applied to commercial kaolin. The final zeolite product from Bolivian montmorillonite exhibited high brightness despite the presence of iron in appreciable amount in the starting material and the final product. It was concluded that magnesium, present in the raw material, exerted a masking effect on iron. The latter was incorporated into extraneous magnesium aluminosilica compounds, thereby increasing brightness and strongly decreasing the overall yellowness. This simple method appears as a promising alternative to the complex and costly techniques suggested to reduce the iron content in natural raw materials, especially kaolin. The second part of the study addresses the synthesis, characterization and evaluation of FAU-type zeolites i.e. Y and X from diatomite and chemical grade reagents, respectively. With regard to the synthesis of zeolite Y, the diatomite was leached in sulfuric acid to remove impurities prior to synthesis, this step also resulted in dealumination, which rendered possible the synthesis of ZSM-5 zeolite (Paper II). However, extra aluminum had to be added in the form of aluminum sulfate for the synthesis of zeolite Y (Paper III). In this case, the raw materials were reacted hydrothermally at 100°C in aqueous medium with sodium hydroxide. Variations in parameters such as the Na2O/SiO2 ratio and synthesis time were investigated. As a result, micro-sized crystals of zeolite Y were obtained at a Na2O/SiO2 ratio of 0.9, which produced zeolite Y with a SiO2/Al2O3 ratio of 3.9. Also, zeolite Y with a SiO2/Al2O3 ratio of 5.3 in low yield at a Na2O/SiO2 ratio of 0.6 was achieved. In this way, diatomite behaved similarly to colloidal silica in traditional syntheses having a high degree of polymerization. Zeolite Y with a SiO2/Al2O3 ratio of 5.3 might be useful for the production of ultra-stable zeolite Y for use as FCC catalyst. Addition of NaCl to this system was also found to completely inhibit the formation of zeolite P and to retard the effects of overrunning by a synergic effect of Na and Cl ions (Paper IV). As an innovate application, FAU-type zeolite X films were growth on steel monoliths as structured adsorbent for CO2 removal (Paper V). Thicknesses 3 and 10 µm on steel monoliths of 1600 cells per square inches (c.p.s.i.) were investigated. The produced structured adsorbents showed reasonable CO2 adsorption capacity but with a very low pressure drop compared with traditional packed beds of zeolite beads. The CO2 breakthrough fronts were very sharp and the mass transfer resistance was very low compensating the presence of less adsorbing material by reducing cycle time and increased cycle frequency to increase throughput. To summarize, zeolites with promising characteristics were successfully synthesized from Bolivian raw materials in this thesis work. However, further characterization is required to qualify these products for industrial applications. Moreover, this study might help the development of poor regions of the Bolivian Altiplano and open up for large scale production, since the methods developed in this work are simple and non-expensive.
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| 9. |
- Li, Yunxiang, 1986-
(författare)
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Modification of zeolites and synthesis of SAPO-templated carbon
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons.In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications.The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons.Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail.In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores.
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| 10. |
- Papawassiliou, Wassilios, 1991-
(författare)
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Evaluation of NMR Knight shifts in metallic nanoparticles and topological matter
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Elucidating the surface electron states of transition metal compounds is of primary importance in main heterogeneous catalytic processes, such as the hydrogen and oxygen evolution reactions. Key property in all these processes is the position of the energy of the d-band center relative to the Fermi-level of the catalyst; it must be shifted close to the Fermi level to achieve balance between adsorption and desorption of the catalyst and the adsorbate. Often, these processes involve expensive metals such as Ru or Pt, limiting their applicability. The Nickel Phosphide (NixPy) family has recently emerged as an important catalyst family replacing noble metals; in these systems the surface electronic properties, may be tailored by doping with different transition metals, decreasing size, or by controlling the nanoparticle shape (facet engineering). It is thus crucial to be able to simultaneously monitor the evolution of the morphology as well as the electronic structure of the NP particles while scaling down the size.In most of these materials, surface electron states are extremely sensitive to local disturbances, such as impurities, surface defects, as well as surface termination. In contrast, 3D topological insulators like Bi2Se3, or Bi2Te3, exhibit exceptionally robust metallic surface electron states while the bulk interior is insulating. These extraordinary properties, which become dominant by reducing the system size to the nanometers, have been tied to enhancement of the Seebeck effect, i.e., the conversion of heat into electricity, catalytic activity, and electrochemical performance, the latter of these effects has been pursed in this thesis as well. An important question that has eluded however is the presence of the Dirac electrons themselves and to which extend the Dirac electrons penetrate the nanoparticles, controlling thus the overall electronic properties.In contrast to the TIs, Weyl semimetals (WSMs), another category of topological materials, host protected electron states in the bulk interior. The bulk conduction and valence bands of these systems cross linearly in pairs of conjugate nodal points, the so-called Weyl points, forming characteristic double cones. Remarkably, in specific WSMs, such as the WTe2 and MoTe2, known as type-II WSMs, the Weyl cones are strongly tilted, leading to the formation of electron and hole pockets at the Fermi level, strongly influencing their electronic properties. However, energy bands in these systems are shown to disperse in a very tiny region, rendering standard experimental techniques, such as Angle Resolved Photoemission Spectroscopy obsolete in detecting the Weyl bands. In this thesis all the issues mentioned for each case, were tackled by employing solid-state nuclear magnetic resonance (ssNMR) spectroscopy under various temperatures and magnetic fields, combined with high-resolution transmission electron microscopy and density functional theory calculations.
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| 11. |
- Rzepka, Przemyslaw, 1988-
(författare)
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The chemical nature of CO2 adsorption in zeolite A
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The climate changes are accelerated by increasing levels of carbon dioxide in the atmosphere connected to the fossil-fuel-based energy system. Substantial reforms of the system are needed immediately and could include the implementation of carbon capture and storage (CCS) technologies. Adsorption-driven CO2 capture is one of the most promising post-combustion CO2 capture techniques, which aim to remove CO2 from N2 in flue gas.The nature of adsorption of CO2 can vary. The process can act as physisorption with intermolecular interactions of the van der Waals type or as chemisorption with a significantly perturbed electronic structure of CO2 and for example the formation of CO32- and HCO3- species. The molecular details were elucidated by MAS NMR and IR studies for a zeolite, and the placement of adsorbed molecules was revealed by in situ diffraction data analysis.Adsorption-driven processes can be implemented only if highly functional adsorbent materials have been developed. Zeolite A seems to be a promising candidate. This thesis broadly discussed the potential enhancement of the selectivity of CO2 over N2 and CH4 by replacing Na+ with larger monovalent cation e.g. K+ in pore apertures of zeolite A. The positions of the extra-framework cations were analyzed by in situ X-ray diffraction using synchrotron light source. The cations were positioned at the 4- and 6-rings and the 8-ring apertures of the aluminosilicate framework of zeolite A. K+ was favored at the 8-ring sites, and this cation did also gradually substitute the 6-ring sites with and increasing x in |Na12-xKx|-A. Large cations did not fit the mirror plane of the 6-ring and were placed on both its sides. K+ at both positions, in 8-rings and 6-rings, seems to have tailored the size of pore openings.The effective pore aperture size was shown to depend on the K+ content and to partition small CO2 molecules from large N2 and CH4 because of, likely, differences in diffusivities. Various compositions of |Na12-xKx|-A demonstrated gradual decrease of CO2 uptake with x and an exclusion of N2 and CH4 already for low x. Although already absorbed CO2 molecules were revealed by in situ neutron diffraction to be coordinated mainly by the 8-ring cation or bridging adjacent 8-ring sites. Adsorbed CO2 molecules displaced the cations into the a-cages and resulted in a slight contraction of the overall distribution of extra-framework cations upon the adsorption of CO2.The kinetically-enhanced separation of CO2 from N2/CH4 seemed to be associated by a restrained diffusion also for the CO2 molecules. This is problematic for pressure swing adsorption processes. However, it could potentially be addressed by the reduction of size of zeolite crystals to increase the extent of accessible porous space over limited time.
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| 12. |
- Saadattalab, Vahid, 1991-
(författare)
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From blue hydrochars to activated carbons : Hydrothermal carbonization, chemical activation and gas adsorption
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrothermal carbonization (HTC) of carbohydrates and biomass is a straightforward method for preparing hydrochars at low temperatures of 180-250 °C. Hydrochars are more carbonized than their precursors. Increasing the carbonization degree of hydrochars at hydrothermal temperatures is a scientific quest that is addressed in this thesis. Hydrochars are known to have a spherical or irregular morphology. Here we address thin film hydrochars for the first time. Hydrochars themselves are carbon precursors for preparing activated carbons. Activated carbons are porous materials that can be used for gas adsorption applications. In this thesis, enhanced adsorption of VOCs at low pressures is addressed by using iron phosphate impregnated activated carbons. Finaly, any chemical process or product including those in this thesis such as HTC, activation, hydrochar and activated carbons may contribute to the issue of environmental degradation positively or negatively. Such environmental impacts are addressed by life cycle assessment of processes of HTC and activation and their related products in the last paper of this thesis. Briefly mentioned, in my first study (Paper I), I focused on the HTC of glucose in the presence of iron (II) sulfate. By changing the concentration of iron (II) sulfate, with a catalytic amount, blue hydrochars were formed at the bottom of the autoclave. The blueness was related to thin film interference. The thin film hydrochars were more carbonized than spherical hydrochars and the yield of HTC has increased in the presence of iron (II) sulfate. The second study (Paper II) is focused on the activation of hydrochars with H3PO4 and H3PO4+FeCl3. We showed that ultramicroporosity and impregnated iron phosphate species enhance the adsorption of VOCs at low pressure. The ACs were impregnated with Fe (PO3)2 and it was shown that Fe (PO3)2 acts as an activation agent which opens up for future studies. In the third study (Paper III), H3PO4-activated carbons were prepared and modified with FeS and FeSe and it was shown that the ACs were also impregnated with Fe2P, in the case of AC-FeS/Fe2P. FeSe and FeS were not detected by XRD. Only large crystals of Fe2P were detected in the sample AC-FeS/Fe2P. In the last study (Paper IV), prickly pear seed biomass from the agro sector in Tunisia was hydrothermally carbonized. The hydrochars were then activated into ACs by CO2 activation. The life cycle assessment of the HTC and activation process was investigated.
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| 13. |
- Saadattalab, Vahid, 1991-
(författare)
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From hydrothermal carbonization to blue hydrochars and activated carbons : Adsorption of volatile organic compounds and heavy metals
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrothermal carbonization of carbohydrate and biomass is a straightforward method for preparing hydrochars at low temperature. Hydrochars are more carbonized than their precursors. Hydrochars themselves are carbon precursors for preparing activated carbons. Activated carbons are porous materials that can be used for water and air purification. In my first study (Paper I), I have focused on hydrothermal carbonization of glucose in presence of iron (II)sulfate. By changing the concentration of iron (II) sulfate, with a catalytic amount, blue hydrochars were formed at the bottom of the autoclave. The blueness was related to thin film interference. The thin film hydrochars were more carbonized than spherical hydrochars and the yield of HTC has increased in presence of iron (II)sulfate. The second study (Paper II) is focused on the activation of hydrochars with H3PO4 and H3PO4+FeCl3. We showed that ultramicroporsity and impregnated iron phosphate species enhance the adsorption of VOCs at low pressure. The ACs were impregnated with Fe(PO3)2 and it is shown that Fe(PO3)2 acts as an activation agent which opens up for future studies. In the third study (Paper III), H3PO4 activated carbons were prepared and impregnated with FeS and FeSe. ACs were used for the removal of Cd2+ and Pb2+ in the third study. The uptake of heavy metals by FeS/AC and FeSe/ACs was significantly increased compared to other studies in the literature. In the last study (Paper IV), prickly pear seed biomass from agro sector in Tunisia was hydrothermal carbonized. The hydrochars were then activated into ACs by CO2 activation. The life cycle assessment of the HTC and activation process was investigated.
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| 14. |
- Xu, Chao, 1987-
(författare)
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Imine/azo-linked microporous organic polymers : Design, synthesis and applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microporous organic polymers (MOPs) are porous materials. Owing to their high surface area, tunable pore sizes and high physicochemical stability, they are studied for applications including gas capture and separation and heterogeneous catalysis. In this thesis, a series of imine/azo-linked MOPs were synthesized. The MOPs were examined as potential CO2 sorbents and as supports for heterogeneous catalysis.The MOPs were synthesized by Schiff base polycondensations and oxidative couplings. The porosities of the imine-linked MOPs were tunable and affected by a range of factors, such as the synthesis conditions, monomer lengths, monomer ratios. All the MOPs had ultramicropores and displayed relatively high CO2 uptakes and CO2-over-N2 selectivities at the CO2 concentrations relevant for post-combustion capture of CO2. Moreover, the ketimine-linked MOPs were moderately hydrophobic, which might increase their efficiency for CO2 capture and separation.The diverse synthesis routes and rich functionalities of MOPs allowed further post-modification to improve their performance in CO2 capture. A micro-/mesoporous polymer PP1-2, rich in aldehyde end groups, was post-synthetically modified by the alkyl amine tris(2-aminoethyl)amine (tren). The tethered amine moieties induced chemisorption of CO2 on the polymer, which was confirmed by the study of in situ infrared (IR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. As a result, the modified polymer PP1-2-tren had a large CO2 capacity and very high CO2-over-N2 selectivity at low partial pressures of CO2.Pd(II) species were incorporated in the selected MOPs by means of complexation or chemical bonding with the imine or azo groups. The Pd(II)-rich MOPs were tested as heterogeneous catalysts for various organic reactions. The porous Pd(II)-polyimine (Pd2+/PP-1) was an excellent co-catalyst in combination with chiral amine for cooperatively catalyzed and enantioselective cascade reactions. In addition, the cyclopalladated azo-linked MOP (Pd(II)/PP-2) catalyzed Suzuki and Heck coupling reactions highly efficiently.
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| 15. |
- Zhang, Peng
(författare)
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Mesoporous magnesium carbonate as a drug delivery vehicle for stabilising amorphous drugs and regulating their release rate
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In today’s drug discovery, the number of candidate drugs based on new molecular entities with poor aqueous solubility is increasing. Since poor aqueous solubility of an active pharmaceutical ingredients (APIs) is associated with low bioavailability and thus limite their therapeutic effect, this is often a great challenge in the development of new drugs when oral administration is the preferred route of administration. A number of different strategies have been developed to circumvent this problem where salt formulations of an API is the most widely employed method. However, new strategies are needed since there is no one solution that solves this issue for all substances. In recent time, the concept of stabilizing poorly soluble APIs in their amorphous form has gained a lot of attention since amorphous compounds exhibit a higher apparent solubility compared to their crystalline counterparts. Amorphous substances are prone to crystallize if left in a non-constricted environment and thus need to be stabilized if the amorphous state is to be conserved until administration. Inorganic mesoporous materials have been proposed as an interesting type of excipients that can conserve the amorphous state of APIs. In this work, the focus was to investigate the possibilities of using a mesoporous type of magnesium carbonate to stabilize the amorphous state of different APIs. Due to the nanometer sized pores in the material, complete conservation of amorphous APIs was obtained. This resulted in both an increase in in vitro release rate and a higher solubility of the substances which may translate to both a faster onset of action and an improved therapeutic effect of the APIs in a clinical situation. The long term stability of formulations was also investigated showing promising results.The results presented in this work show that mesoporous magnesium carbonate represents an interesting type of excipient for oral formulations of APIs with poor aqueous solubility.
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| 16. |
- Hao, Wenming, 1984-
(författare)
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Refining of hydrochars/ hydrothermally carbonized biomass into activated carbons and their applications
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrothermally treated biomass could not only be used as a fuel or a fertilizer but it can also be refined into high-value products. Activated carbons are one of those. In the studies of this thesis, four different hydrothermally carbonized (HTC) biomasses, including horse manure, grass cuttings, beer waste and biosludge, have been successfully made into activated carbons. The activated carbon materials were in the forms of powdered activated carbons, powdered composites of activated carbon and iron oxide nano-crystals, and activated carbon discs.The HTC biomasses and the activated carbons were characterized and analyzed using several methods. The biomasses were carbonized to different extent during the hydrothermal treatment, which depended on the different natures of the biomasses. The HTC biomasses were activated into powdered activated carbons by both physical activation, using CO2, and by chemical activation, using H3PO4. Full factorial design matrices were applied to design experiments and study the influence of different parameters used during both physical and chemical activation. Activated carbons with embedded iron oxide nanoparticles were synthesized through hydrothermal carbonization followed by CO2 activation. These composites had high surface areas and showed a strong magnetism, and the powders could be separated from liquid phase by applying a magnetic field. Strong and dense activated carbon discs were also prepared from powdered HTC beer waste by pulsed current processing (PCP) and a subsequent CO2 activation procedure. The potential for carbon dioxide separation from nitrogen, and methylene blue adsorption in aqueous solution, were assessed for the powdered activated carbons produced from HTC biomasses. They showed good performance in both applications.
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| 17. |
- Lu, Yuexia, 1983-
(författare)
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Experimental Studies on CO2 Absorption in Hollow Fiber Membrane Contactor
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Membrane gas absorption technology is considered as one of the promising alternatives to conventional techniques for CO2 separation from the flue gas of fossil fuels combustion. As a hybrid approach of chemical absorption and membrane separation, it may offer a number of important features, including operational flexibility, compact structure, linear scale up and predictable performance. The main challenge is the additional membrane mass transfer resistance, especially when this resistance increases due to the absorbent intruding into the membrane pores.In this thesis, the experimental was set up to investigate how the operating parameters affect the absorption performance when using absorbent in hollow fiber contactor, and to obtain the optimal range of operation parameters for the designated membrane gas absorption system . During 20 days’ continuous experiment, we observed that the CO2 mass transfer rate decreases significantly following the operating time, which is attributed to the increase of membrane mass transfer resistance resulting from partial membrane wetting.To better understand the wetting evolution mechanism, the immersion experiments were carried out to assume that the membrane fibers immersed in the absorbents would undergo similar exposure as those used in the membrane contactor. Various membrane characterization methods were used to illustrate the wetting process before and after the membrane fibers were exposed to the absorbents. The characterization results showed that the absorbent molecules diffuse into the polypropylene (PP) polymer during the contact with the membrane, resulting in the swelling of the membrane. In addition, the effects of operating parameters such as immersion time, CO2 loading, as well as absorbent type on the membrane wetting were investigated in detail. Finally, based on the analysis results, methods to smooth the membrane wetting were discussed. It was suggested that improving the hydrophobicity of PP membrane by surface modification may be an effective way to improve the membrane long-term performance.Modification of the polypropylene membrane by depositing a rough layer of PP was carried out in order to improve the non-wettability of membrane. The comparison of long-term CO2 absorption performance by PP membranes before and after modification proves that the modified polypropylene membranes retained higher hydrophobicity than the untreated polypropylene membrane. Therefore modification is likely to be more suitable for use in membrane gas absorption contactors for CO2 separation, particularly over long operation time.
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| 18. |
- Nobandegani, Mojtaba, 1988-
(författare)
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Adsorption and Mass Transport in Zeolite Membranes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are commonly used as adsorbents and catalysts in the industry due to their well-defined pores of molecular dimensions. Zeolites offer porous structure, which consists of interlinked alumina and silica tetrahedra with shared oxygen atoms. Zeolites can also be prepared as intergrown films on porous supports, which results in zeolite membranes. CHA and MFI are two promising zeolites that can be used as membranes for biogas and syngas separation and upgrading since their pore size is suitable.Membrane technology is considered an energy-lean gas separation method that offers a straightforward process with compact equipment and high efficiency. Compared with polymeric membranes, zeolite membranes offer higher permeance and stability due to their porous structure and ceramic nature. Since zeolite membranes are expensive and a higher flux would reduce the needed membrane area, thin membranes with high flux are of great interest. However, to enable the design of zeolite membrane processes, it is vital to enhance the fundamental understanding of the mass transport in the materials.In this study, zeolite membranes of different types, i.e., CHA and MFI, were evaluated for separation of various gas mixtures. MFI disc membranes were evaluated for the separation of equimolar CO2/H2 mixtures under both dry and humid conditions, as well as for the separation of ternary CH4/N2/He mixtures. High selectivity and high CO2 fluxes were observed during CO2/H2 separation under both dry and humid conditions. The MFI disc membrane also displayed a high performance for separation of ternary CH4/N2/He mixtures. The results indicated that MFI membranes are promising candidates for separation of CO2 from the gas mixtures and for helium recovery from natural gas. Tubular CHA membranes, with lengths of 10 and 50 cm, were also investigated for CO2/CH4 separation under industrially relevant conditions. A maximum CO2/CH4 separation selectivity of 198 combined with a CO2 permeance of 14×10-7 mol/(m2·s·Pa) was observed for humid gas. The results verified the feasibility of these membranes for industrial gas separations.After verifying the high performance of CHA zeolite membranes for gas separation under industrial conditions, CHA zeolite crystals with various Si/Al ratios were synthesized and the adsorption of CO2 and CH4 in the materials were studied. Subsequently, the mass transport through ultra-thin MFI and CHA zeolite disc membranes was measured and a model accounting for the adsorption and diffusion through the surface barriers and in the pores was developed. The model was successfully fitted to both single component and mixture permeation data. The fitted model indicates that the mass transport through ultra-thin membranes is controlled by the surface barriers. It revealed that the surface barrier is a surface diffusion process at the pore mouth with an activation energy that is higher than for the surface diffusion in the pores. Furthermore, the fitted model indicated that the high selectivity of CHA membranes is mostly due to a highly selective surface barrier and, to a lesser extent, is a result of adsorption selectivity.In the last part of the work, a process for upgrading biogas was designed by using the developed model. The process was compared with a process based on hollow fiber polymeric membranes. It was concluded that the zeolite membrane processes were much more compact and had a much lower demand for electricity than the polymeric membrane process.
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| 19. |
- Ohlin, Lindsay
(författare)
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An in-situ ATR-FTIR Spectroscopy Study of Adsorption in MFI Zeolites : A step towards effective upgrading of biofuels
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is believed to be caused by the extensive emission of greenhouse gases, for example carbon dioxide, into the atmosphere by combustion of fossil fuels, such as coal, oil and natural gas. To reduce the emission of carbon dioxide and hence avoid global warming, alternative fuels derived from renewable resources are desired. Another reason for the worldwide interest in finding alternative fuels is that the reserves of the fossil fuels are limited and the oil and gas sources will eventually run out. Biogas and biobutanol are renewable biofuels which are interesting alternatives to fossil fuels. Biogas is produced during degradation of organic material forming a mixture of mainly methane and carbon dioxide with water as a common trace component. Biobutanol is produced from ABE (acetone, butanol and ethanol) fermentation of biomass. Purification of biogas and biobutanol is essential to increase the heat value of the fuels. Traditional purification processes are energy demanding and expensive. Therefore, other separation processes are currently sought for. Zeolites are promising alternatives due to their great potential both as selective adsorbents and as membranes. Due to the unique pore structure, zeolites are capable of separating components based on their adsorption properties. In the present work, single component adsorption of biogas components such as methane, carbon dioxide and water in zeolite ZSM-5 was studied as well as adsorption of water and butanol in silicalite-1 using in-situ ATR-FTIR spectroscopy. The method was successfully further used to study multicomponent adsorption. For single gas adsorption experiments, recorded infrared spectra of adsorbed methane, carbon dioxide and water showed characteristic, well separated, bands for each gas. Adsorbed concentrations were determined from the recorded infrared spectra. The Langmuir model was fitted to the adsorption isotherms and the model matched the experimental data very well. The fitted Langmuir parameters obtained in the present work was in agreement with values reported in the literature. For multicomponent adsorption experiments, the Ideal Adsorbed Solution Theory (IAST) was used to predict the adsorbed concentrations of methane, carbon dioxide and water using the single component adsorption isotherm parameters as input. In general, the IAST was shown to be a fairly good model for predicting the adsorbed concentrations of methane and carbon dioxide from binary mixtures. For the amount of adsorbed methane from mixtures including water, the IAST predicted the values fairly well. However, for mixtures containing water and carbon dioxide, the IAST could not fully describe the adsorption behavior of the two components. The CO2/CH4 adsorption selectivity was determined for various gas compositions and temperatures showing a general increase in the selectivity with decreasing temperature. This indicates that the separation of carbon dioxide from biogas should be more efficient at lower temperatures. Compared to the literature, the selectivity observed in the present work is relatively high indicating that Na-ZSM-5 may be an effective membrane material for upgrading biogas. Moreover, butanol was preferentially adsorbed over water in silicalite-1, indicating that silicalite-1 may be a promising material for recovery of butanol from dilute water solutions.
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