Browsing by master's degree program "Master's Programme in Chemistry and Molecular Sciences"

As part of the SAFER2028, ABCRad (Alternative Buffer/Backfill Characterization and Radionuclide Interactions) research project, two alternative bentonite materials supplied by Posiva Oy were investigated in this thesis. The aim of the thesis was to investigate and determine the sorption behavior of these two buffer material candidates, with a deliberate reference to a well- known Na-Wyoming type bentonite serving as a benchmark. In order to closely imitate conditions relevant to repository settings, a synthetic reference water was prepared, and the experiments were conducted within a glove box in N2 atmosphere excluding CO2 and O2. This thesis provides valuable perspectives on the behavior and attributes of the alternative bentonite materials, which is crucial for guiding decisions in the design of repositories for radioactive waste and strategies for managing spent nuclear fuel. More specifically, this thesis provides thermodynamic sorption models (TMS) for two risk-driving radionuclides, uranium (U) and cesium (Cs). Batch sorption isotherms were made using a 1:20 solid-to-liquid ratio including 0.5 g of bentonite in 10 cm3 of reference water. Gamma spectroscopy and Liquid Scintillation Counting (LSC) were employed for the analysis of reaction supernatants. Complementary to these techniques, additional bentonite properties, including Cation Exchange Capacity (CEC) and Exchangeable Cations (EC), were determined. Pre-characterization was done for the bentonites using Fourier Transform Infrared Spectroscopy (FTIR) and the Specific Surface Areas (SSA) were determined. These analyses provide a comprehensive characterization of the alternative backfill materials under investigation. This thesis focuses on combining quantitative sorption data (e.g., distribution coefficient, Kd) with mechanistic understanding (e.g., FTIR spectroscopy). This contributes to an improved understanding of radionuclide sorption mechanisms, thereby bolstering safety considerations. The CEC determined for the bentonites, Laviosa, LMS, and Na-Wyoming were 87 (±0,048) meq/100 g, 95 (±0,34) meq/100 g, and 91 (± 1,23) meq/100 g, respectively. The distribution coefficient (Kd) values of uranium ranged from 130–135 cm3/g with Laviosa and 78–110 cm3/g with LMS, while those of cesium ranged from 130–280 cm3/g with Laviosa and from 150–425 cm3/g with LMS. Cesium demonstrated sorption of 95% within the 10-10 to 10-6 M range, decreasing slightly to 85–95% at concentrations up to 10-2 M. Uranium showed sorption in the range 80–100% across both clays, peaking at lower concentrations and declining at higher concentrations. These data align with those of the reference buffer material, indicating that these bentonites could potentially serve as feasible alternatives if they exhibit additional favorable sorption capacity with other risk-driving radionuclides (e.g., Eu, Ni, Th).

Plasmonic is an emerging field which has showed application for photocatlysis. Here we investigate a gold/platinum bimetallic catalytic system, and try to show how the catalytic properties of gold nanoparticles can be us to harvest visible light energy to increase the catalytic activity of platinum. Platinum being are rare and expensive metal, we also took the opportunity to find the optimal amount of catalyst to reduce platinum use. The catalyst is composed of a core spherical gold nanoparticles, of around 15 nm diameter. They were synthesized using an inversed Turkevich method, based on trisodium citrate, gold precursor salt and done in solution. Various amount of platinum was deposited on those nanoparticles using seeded growth method. The amount of platinum varied for single atoms to an atomic monolayer. This suspension of nanoparticles was deposited on ultrafine silica powder to be used for certain reaction and characterization. The material was characterized via several technics. UV-Visible and Diffuse Reflectance Spectroscopy were used to characterize its optical properties and showed a absorption peak around 524 nm characteristic of gold nanoparticles of this size. Imaging was done using electron microscopy (SEM and TEM) to study the morphology and showed monodisperse and spherical particles. The exact composition of the different catalyst were obtain using Atomic Emission Spectroscopy. The study was conducted by using reduction reaction as tests to investigate differences in conversion and selectivity under dark and monochromatic 525 nm and 427 nm light conditions. We chose to work on reduction of 4-nitrophenol, phenylacetylene and nitrobenzene, because they are widely used both in research and industry, and are easy to set up. Some catalyst showed good enhancement under 525 nm light, especially the one with the least amount of platinum. Different selectivity were also observed, indicating the presence of different reaction pathways under light conditions.

Development of machine learning models for reaction design has garnered growing interest. Notably, the benefits of predictive models include the elimination of trial and error in selecting suitable reaction conditions. In addition, mechanistic insight may be gained to help rational catalyst design. The aim of this study is to develop modeling and parametrization method for transition metal complexes which would enable the combined parametrization of mono- and bidentate ligands for the first time. Performance of novel parametrization method is demonstrated through a ligand classification model for Suzuki–Miyaura reaction. In this literature review, an overview of the computational catalyst modeling and performance prediction is presented. The history of physical and computational chemistry is reviewed, ranging from early structure-property relationships and linear models to modern physical organic density functional theory (DFT) parameters and machine learning models. The necessary theoretical background for reaction modeling is presented in terms of transition state theory, which can be used to model selectivity or reaction rate. Additionally, the reaction yield is discussed as typical performance score for reaction modeling. Furthermore, the initial structures of typical transition metal complexes used for modeling are presented, along with the methods employed for structure optimization and ligand parametrization. By utilizing this background, the evolution of modeling methods from linear free energy relationships to machine learning is discussed. Additionally, modern classification methods for catalyst design are reviewed. Finally, the mechanistic details of Suzuki–Miyaura reaction are explored to justify the modeling methodologies in the experimental part. In the experimental study, a novel method to combine parametrization for mono- and bidentate ligands was successfully invented. As a proof of concept, performance classification of ligands for Suzuki– Miyaura reaction was conducted. Suzuki–Miyaura reaction was chosen as the model reaction due to wide data availability. Initial transition metal complexes were built according to ligation state of nickel. The initial structures always included two carbonyl ligands and either one bidentate ligand, or two monodentate ligands, or one bulky monodentate ligand. The structures were optimized with semiempirical quantum mechanical method xTB and parametrized using a newly developed in-house parametrization method. Calculated parameters include global and local steric and electronic descriptors, and local geometric descriptors. Classification models were built with selected training data. Models were used to predict the performance of new ligands. Successful results were achieved, and ligands that provided better yields were identified. In addition, it was discovered that model reaction proceeds without the presence of phosphine ligand if superbase is used as a base. Nitrogen-containing bases were screened, additional active superbases were found, and correlating descriptor with activity was detected. Based on results, more active superbases were designed.

Nuclear power plant decommissioning is a difficult process that combines industrial decommissioning techniques, radiation safety standards, and legal requirements for the final disposal of nuclear waste. The goal of nuclear decommissioning is to completely purge the plant of all radioactive material so that it can be released from regulatory oversight. The range of corrosion products generated on the steel surface are known to have a significant impact on the corrosion process of steel. Corrosion products have a complicated structure. The corrosion products are created when metallic components, mostly iron, react with oxygen and water that are drawn from the atmosphere, and their structure is then significantly influenced by environmental factors. Quantitative characterisation of the atomic scale structure of corrosion products is critically needed for identifying the corrosion products reliably. This thesis provides the characterization process of corrosion products formed on the steel surfaces and this process was executed with the help of XRD (X-ray Diffraction), SEM/EDS Scanning Electron Microscope/ Energy Dispersive Spectrometry, and Raman spectroscopy. Within the scope of this project, besides characterization of steel samples, Loviisa ground water and synthetic water samples which have been in a long-term contact with activated steel samples were also examined. Separation processes was carried out for determining Fe-55 and Ni-63 in the waters and the presence of Co-60 was removed from the samples before the activity determination of Fe-55 and Ni-63 by LSC (Liquid Scintillation Counting). This master's thesis has been carried out in connection with the DEMONI project, which has been a coordinated project of VTT and the University of Helsinki (KYT2022 Research Program). The outcome of the thesis will benefit possible decommissioning and disposal strategies for the nuclear power plant's reactor pressure vessels.

The literature study of this thesis focuses on the different analytical methods used to analyse amino acids in food and beverage samples. Amino acids are essential organic molecules and their concentrations in foods and beverages constitute, inter alia, the product’s nutritional value, quality, freshness, and flavour. Amino acid analysis of foodstuff has various applications, which exploit several analytical methods. These reviewed methods are founded on academic articles published during the past two decades. This literature review discusses the different sample matrixes, sample preparation methods, ways to derivate analytes, and different separation and detection methods utilized in the recent amino acid studies. The experimental part of this thesis was a modification of L-asparagine and L-aspartic acid test (L-Asp/L-AspAc) in Thermo Fisher Scientific Oy industrial R&D laboratory. An enzymatic photometric method is used to determine L-Asp/L-AspAc amino acids in food samples. The modification process entailed pre-testing of several candidate methods, from which the most suitable one was selected. The feasibility of the chosen test was affirmed before verification and validation of the modified test.

Mercury is a toxic heavy metal that poses significant risks to human health. In many industrial and occupational settings, employees are at high risk of mercury exposure due to the nature of their work. Consequently, biomonitoring and routine testing mercury levels in the working environment are crucial to ensure occupational health and prevent adverse health effects. This master’s thesis reviews the literature on occupational exposure to mercury and its impact on human well-being. The review focuses on the pathways through which mercury enters the body and the transformations it undergoes. Protective strategies and adopted regulations are also investigated. The analytical methods used for detection of mercury in biological samples, such as cold vapor atomic absorption spectroscopy (CV-AAS) and inductively coupled plasma mass spectrometry (ICP-MS), are explored, including comparison of their efficacy. The primary objective of the experimental part of this research was to validate the use of flow injection mercury system (FIMS) as a method for determining mercury levels in human blood and urine samples. Additionally, ICP-MS was employed for comparative analysis of mercury levels in urine samples. The analytical parameters of FIMS and the potential for selective analysis of two reducing agents, stannous chloride (SnCl2) and sodium tetrahydroborate (NaBH4), were evaluated. This process included calibration, analysis of control materials, optimization of reductant concentration, and calculation of limits of detection (LODs) and quantification (LOQs). Various approaches for the preparation of blood samples were tested. Issues associated with the incompatibility of a particular FIMS setup with the intended goals were identified, and possible solutions were proposed. The study demonstrates practical value, as it clarifies the prospects for using FIMS in the biomonitoring of mercury.

Stimuli-responsive polymers have emerged as appealing compounds for the development of high-tech and functional materials. In particular, thermoresponsive polymers have been investigated for a variety of applications. Among these, hydrogel production for additive manufacturing is especially attractive. In fact, hydrogels obtained from synthetic and thermoresponsive polymers can be tailored to obtain biocompatible scaffolds for employment in the biomedical field. Poly(2-oxazolines) and poly(2-oxazines) stand out as promising starting materials for the production of novel hydrogels. In this work, a thermoresponsive and amphiphilic triblock copolymer composed of 2-methyl-2-oxazoline and 2-phenyl-2-oxazine was investigated to determine whether a suitable candidate for biofabrication purposes could be obtained. The copolymer was firstly synthetised, before partial hydrolysis and post-polymerization modification could be carried out. These further manipulations allowed to alter the substituent in position 2 of the 2-methyl-2-oxazoline unit and yield crosslinkable units. The mechanical properties of the triblock were investigated with numerous rheological studies before 3D printing and crosslinking were performed. Crosslinked hydrogels were obtained by using a photoinitiator (Irgacure 2959) and UV radiation. Lastly, swelling behaviour was investigated to determine the capacity of the hydrogels to absorb water and test their durability over time. Overall, this study provided results on specific conditions and parameters required for the fabrication of chemically crosslinked hydrogels, that can be optimised in the future to produce functional materials for additive manufacturing applications.

In this work, molecular mass determination by diffusion-ordered nuclear magnetic resonance spectroscopy was obtained for a series of poly(2-oxazoline)s, polypeptoids and poly(2-oxazine)s. The samples included linear, star like and cyclized homopolymers and block copolymers. The data was calibrated against polyethylene glycol, polystyrene and poly(methyl methacrylate) standards. The results were compared with those obtained by matrix-assisted laser desorption/ionization spectrometry, size exclusion chromatography, rolling-ball viscometry and end-group analyses based on proton nuclear magnetic resonance. It was concluded that in general diffusion-ordered spectroscopy tends to give a very accurate estimation of the masses up to 30 kg/mol in deuterated water and dimethyl sulfoxide, especially after viscosity correction. In addition, nuclear magnetic resonance spectroscopy provides a wealth of information about the samples including their structure and possible impurities. In summary, this methodology could be successfully applied to different polymers and it is invaluable in the case of absence of the standards with similar solubility to analyzed polymers since the viscosity correction enables a comparison of the results measured in different solvents.

Poly(2-oxazoline)/poly(2-oxazine)-based block copolymers have gained significant attention in recent years for their potential use in drug delivery systems. The architecture of amphiphilic poly(2-oxazoline)/poly(2-oxazine) based block copolymers, consisting of hydrophilic outer blocks and a hydrophobic inner block, allows the formation of micelles. The hydrophobic drug is encapsulated within the core, and the hydrophilic shell provides the stability and solubility in aqueous solution. The size and properties of the micelles can be tuned by adjusting the composition of the copolymer, making them a versatile platform for drug delivery. In this work, three different poly(2-oxazoline)/poly(2-oxazine)-based triblock, diblock and gradient copolymers were synthesized via cationic ring-opening polymerization and compared in terms of their drug formulation capability. Triblock copolymers consisting of three polymer blocks, can be tailored to have different hydrophobic and hydrophilic block ratios, allowing for tunable drug release profiles. However, triblock copolymers are more difficult to synthesize, especially if one aims to produce symmetrical ratio of hydrophilic blocks. Diblock copolymers, consisting of two polymer blocks, can also self-assemble into micelles in aqueous solutions and can encapsulate hydrophobic drugs, however, the lower stability of their formulations compared to that of triblock copolymers can limit their drug loading capacity and drug release profiles. In theory, entropy wise, when forming a micelle, the diblock copolymer should be favorable as it doesn’t need to fold, unlike the triblock copolymers, however, the drug formulations by triblock copolymers has shown to be more stable than that of diblock copolymers. Thus, more detailed analysis is needed since the lack of literature on the systematic comparison of these different architectures. Gradient copolymers, consisting of two or more types of monomers that are incorporated into a polymer chain with a gradually changing composition, have more variable properties and are easier to synthesize through one step, than block copolymers. This makes their usage in drug formulation very attractive. However, depending on the reactivity of monomers added, the resulting product can be very different, thus, the kinetics of the copolymerization deserves an attention of the study as well.

In Finland, the final disposal of spent nuclear fuel will start in the 2020s where spent nuclear fuel will be disposed 400-450 meters deep into the crystalline bedrock. Disposal will follow Swedish KBS-3 principle where spent nuclear fuel canisters will be protected by multiple barriers, which have been planned to prevent radionuclides´ migration to the surrounding biosphere. With multiple barriers, failure of one barrier will not endanger the isolation of spent nuclear fuel. Insoluble spent nuclear fuel will be stored in ironcopper canisters and placed in vertical tunnels within bedrock. Iron-copper canisters are surrounded with bentonite buffer to protect them from groundwater and from movements of the bedrock. MX-80 bentonite has been proposed to be used as a bentonite buffer in Finnish spent nuclear fuel repository. In a case of canister failure, bentonite buffer is expected to absorb and retain radionuclides originating from the spent nuclear fuel. If salinity of Olkiluoto island´s groundwater would decrease, chemical erosion of bentonite buffer could result in a generation of small particles called colloids. Under suitable conditions, these colloids could act as potential carriers for immobile radionuclides and transport them outside of facility area to the surrounding biosphere. Object of this thesis work was to study the effect of MX-80 bentonite colloids on radionuclide migration within two granitic drill core columns (VGN and KGG) by using two different radionuclides 134Cs and 85Sr. Batch type sorption and desorption experiments were conducted to gain information of sorption mechanisms of two radionuclides as well as of sorption competition between MX-80 bentonite colloids and crushed VGN rock. Colloids were characterized with scanning electron microscopy (SEM) and particle concentrations were determined with dynamic light scattering (DLS). Allard water mixed with MX-80 bentonite powder was used to imitate groundwater conditions of low salinity and colloids. Strontium´s breakthrough from VGN drill core column was found to be successful, whereas caesium did not breakthrough from VGN nor KGG columns. Caesium´s sorption showed more irreversible nature than strontium and was thus retained strongly within both columns. With both radionuclides, presence of colloids did not seem to enhance radionuclide´s migration notably. Breakthrough from columns was affected by both radionuclide properties and colloid filtration within tubes, stagnant pools and fractures. Experiments could be further complemented by conducting batch type sorption experiments with crushed KGG and by introducing new factors to column experiments. The experimental work was carried out at the Department of Chemistry, Radiochemistry in the University of Helsinki.