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1.
Integrating cultural heritage and urban subway infrastructures : spatial distribution, value assessment, and impacts of the Beijing metro line on cultural heritage regional development
Haisheng Hu, 2025, doktorska disertacija

Opis: This research examines the spatial patterns and economic significance of cultural heritage sites along Beijing’s metro lines, with an emphasis on how urban infrastructure influences heritage preservation. Using spatial analysis methods, including the nearest-neighbor index, geographic concentration index, and location entropy, the research identifies patterns in the distribution of cultural heritage sites - such as ancient architecture, industrial heritage, and tombs - particularly concentrated within Beijing’s second ring road. The study highlights the connectivity provided by key metro lines, including Lines 1, 2, 4, 5, 7, and 8, which link cultural sites in a point distribution pattern. On these premises, the research established a hierarchical framework to evaluate cultural heritage based on proximity to metro stations, with historical and artistic values being the most significant factors. The findings suggest that heritage sites within one kilometre of metro stations exert more significant influence on their surrounding areas and emphasize the importance of integrating metro infrastructure with cultural heritage preservation. This study contributes to understanding the spatial dynamics of cultural heritage in urban environments, offering a framework for assessing the impact of heritage within contemporary infrastructure systems. Practically, the study offers insights for urban planners, metro authorities, and cultural preservation bodies, proposing thematic routes along metro lines—such as Line 1 representing a fusion of Chinese and Western cultures and Line 5 emphasizing religious culture—to enhance cultural tourism. It also emphasizes the need for coordinated efforts between stakeholders to balance heritage conservation and urban development for sustainable growth.
Ključne besede: dissertations, linear cultural heritage, national cultural heritage, Beijing, spatial distribution, economic assessment
Objavljeno v RUNG: 31.03.2025; Ogledov: 431; Prenosov: 10
.pdf Celotno besedilo (12,56 MB)

2.
Modelling-assisted optimisation of hemicellulose-derived monosaccharide valorization : dissertation
Ana Jakob, 2025, doktorska disertacija

Opis: Hemicellulose, one of the key components of lignocellulosic biomass, and its sugar monomers offer significant potential as a substrate for producing value-added platform chemicals. With both pentoses (xylose and arabinose) and hexoses (glucose, galactose, and mannose), the conversion of hemicellulose can yield various products including furfural, hydroxymethylfurfural (HMF), and levulinic acid. This doctoral thesis investigates the dehydration of various hemicellulose-derived monosaccharides, utilizing catalyst-free systems, as well as homogeneous and heterogeneous catalysts, in both aqueous and organic solvents. Monosaccharide conversion was evaluated in a catalyst-free aqueous solution at temperatures ranging between 130 – 190 °C. Conducting dehydration reactions under simple, hydrothermal conditions highlighted the differences in the reactivity of individual monosaccharides. Experimental data from extensive activity testing enabled the development of accurate kinetic models. Aiming at the optimization of reaction parameters relevant to the post-Organosolv production of furanics and levulinic acid, sulfuric and formic acid were introduced into the reaction system as homogeneous acid catalysts. Reaction kinetics of acid catalysed conversion using sulfuric and formic acid indicated a significant reduction in the activation energy of ketose dehydration. In addition, the addition of both acids enhanced the dehydration rates and promoted the conversion of HMF towards levulinic acid due to its low activation energies 86 – 91 kJ mol−1 and high reaction rate constants. The established kinetic model for individual saccharides was proven to be robust and able to accurately predict optimal reaction conditions for two distinct industrially relevant hemicellulose streams. In pursuit of a more sustainable and recyclable catalyst, various zeolites, specifically H-BEA, were tested. Although H-BEA exhibited excellent catalytic activity, its selectivity towards furanics remained limited in aqueous media. The low activation energy for HMF rehydration facilitated the formation of levulinic acid even at a moderate reaction temperature of 165 °C. Notably, the addition of THF as an organic solvent in combination with H-BEA, drastically improved the product selectivity towards furanics, particularly furfural. In addition to H-BEA zeolite, various types of zeolites with different Si/Al ratios were studied. Catalyst characterization revealed a strong correlation between catalytic activity and acidity. The addition of THF resulted in 90 mol % of furfural after only 30 min, demonstrating an exponential increase in dehydration rates and a decrease in activation energies. This zeolite-THF system was therefore applied for tandem reactions involving both xylose dehydration and furfural hydrogenation. The addition of metallic active sites via a Ni/H-BEA catalyst, and a hydrogen atmosphere, resulted in the catalytic hydrogenation of xylose to tetrahydrofurfuryl alcohol. Adjusting reaction temperatures allowed the production of secondary hydrogenated (2-methylfuran and 2-methyltetrahydrofuran) and dehydration products (tetrahydropyran), while the addition of water as a co-solvent with THF resulted in the complete inhibition of dehydration reactions and the selective formation of xylitol. Through a systematic study of reaction conditions and the development of comprehensive kinetic models, this work provides an in-depth investigation of monosaccharide dehydration. This doctoral thesis represents a comprehensive study to systematically investigate both catalytic and non-catalytic dehydration of five relevant monosaccharides, providing a methodical kinetic modelling approach that addresses the challenges associated with the complexity related to hemicellulose conversion.
Ključne besede: hemicellulose, monosaccharides, kinetic modelling, furanics, catalysis, dissertations
Objavljeno v RUNG: 19.02.2025; Ogledov: 780; Prenosov: 18
.pdf Celotno besedilo (11,80 MB)

3.
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Modeling of solvent role in protein folding experiments : dissertation
Knarik Yeritsyan, 2025, doktorska disertacija

Opis: The Zimm-Bragg (ZB) model serves as a fundamental framework for elucidating conformational transitions in biopolymers, offering simplicity and efficacy in processing experimental data. This study provides a comprehensive review of the Zimm-Bragg model and its Hamiltonian formulation, with particular emphasis on incorporating water interactions and chain size effects into the computational framework. We propose a modified ZB model that accounts for water-polypeptide interactions, demonstrating its ability to describe phenomena such as cold denaturation and helix-coil transitions. In the realm of NanoBioTechnologies, the manipulation of short polypeptide chains is commonplace. Experimental investigation of these chains in vitro often relies on techniques like Circular Dichroism (CD) and timeresolved infrared spectroscopy. Determining interaction parameters necessitates processing the temperature dependence of the normalized degree of helicity through model fitting. Leveraging recent advancements in the Hamiltonian formulation of the Zimm and Bragg model, we explicitly incorporate chain length and solvent effects into the theoretical description. The resulting expression for helicity degree adeptly fits experimental data, yielding hydrogen bonding energies and nucleation parameter values consistent with field standards. Differential Scanning Calorimetry (DSC) stands as a potent tool for measuring the specific heat profile of materials, including proteins. However, relating the measured profile to microscopic properties requires a suitable model for fitting. We propose a novel algorithm for processing DSC experimental data based on the ZB theory of protein folding in water. This approach complements the classical two-state paradigm and provides insights into protein-water and intraprotein hydrogen bonding energies. An analytical expression for heat capacity, considering water interaction, is derived and successfully applied to fit numerous DSC experimental datasets reported in the literature. Additionally, we compare this approach with the classical two-state model, demonstrating its efficacy in fitting DSC data. Furthermore, we have developed and launched a free online tool for processing CD and DSC experimental data related to protein folding, aiming to support scientific research.
Ključne besede: Zimm-Bragg model, conformational transitions, helix-coil transitions, cold denaturation, circular dichroism, differential scanning calorimetry, protein folding, water-protein interaction, hydrogen bonding energy, degree of helicity, short polypeptide chains, protein heat capacity, protein data analysis, dissertations
Objavljeno v RUNG: 27.01.2025; Ogledov: 829; Prenosov: 13
.pdf Celotno besedilo (5,12 MB)

5.
Catalytic hydro(deoxy)genation of furfural and modelling of its reaction kinetics : dissertation
Rok Šivec, 2024, doktorska disertacija

Opis: In recent decades, there has been a growing interest in producing biofuels and biochemicals from renewable sources. Furfural stands as one of the ligno(hemi)cellulosic biomass derived platform chemical, which can be transformed into numerous value-added products. The goal of this PhD was to systematically study hydrotreatment reactions of furfural under varying operating conditions and to gain insights into the reaction mechanism and kinetics. An extensive experimental and computational study of hydrogenation, hydrodeoxygenation, oligomerisation and etherification of furfural in a three-phase batch reactor was performed. The goals were divided into three consecutive objectives. In the first part, hydrotreatment of furfural over Pd/C catalyst under various reaction conditions, including the solvent selection (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed, was studied. A reaction pathway network and a micro-kinetic model were developed, incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption, and surface reactions. These phenomena and their contribution to the surface coverages, TOF’s and global reaction rates were studied. The hydrogen presence on the catalyst surface was found to influence the main reaction pathway, leading to ring, aldehyde group or full hydrogenation. In the second part, various monometallic catalysts (Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C, Cu/C) were tested at 100 -200 °C with 60 bar of hydrogen and tetrahydrofuran as solvent. A generalized reaction pathway network was developed. H2 temperature-programmed reduction (H2-TPR) and CO temperature-programmed desorption (CO-TPD) were conducted, and a regression analysis of the results was subsequently performed by numerical modelling and optimisation. The obtained adsorption and desorption kinetic parameters for active metallic sites were further used in a generalized micro-kinetic model, applicable to all tested catalysts. Pd/C exhibited high activity and non-selective hydrogenation of furfural, while other catalysts showed selective aldehyde group hydrogenation followed by deoxygenation, consistent with density functional theory (DFT) calculations. Ru/C uniquely produced 2 methyltetrahydrofuran and ring-opening products at 200 °C. In silico optimization of reaction conditions for promising catalysts ((Pd/C, Pt/C, Re/C, Ni/C) aimed to maximize the yield of the target product. In the third part, the influence of support on catalytic activity was studied. Hydrotreatment of furfural over Pd/Al2O3, Pd/SiO2, Ru/Al2O3, Ru/SiO2, Ni/Al2O3, and Ni/SiO2 was performed between 150 - 200 °C, using 60 bar of hydrogen and tetrahydrofuran as solvent. The strength and rate of adsorption and desorption to/from acidic, metallic and interface site structures were determined, using H2-TPR, CO-TPD and NH3-TPD and subsequent regression analysis of the results by numerical modelling and optimisation. The resulting parameters were sequentially used in the generalized micro-kinetic model to quantify the contribution of the active metal (Ni, Pd, or Ru), support (Al2O3 or SiO2), interphase sites and their relationship on catalyst activity and selectivity. Evaluation of morphological and structural characteristics, adsorption/desorption and intrinsic reaction kinetics has indicated that the coverage of acidic sites (on alumina or silica) facilitated yielding ring hydrogenation and inhibited deoxygenation, decarbonylation and cyclic compound opening. The rates for aromatics or aldehyde functional groups were, nonetheless, affected in a different order. The used and developed methods and findings of this PhD offer useful guidelines for transforming furfural into high-value chemicals through catalytic hydrotreatment, with significant implications for future research and industrial applications.
Ključne besede: lignocellulosic biomass, furfural, catalytic hydrogenation, micro-kinetic mass transfer model, reaction kinetics, first-principle methods, furfuryl alcohol, tetrahydrofurfuryl alcoholv, dissertations
Objavljeno v RUNG: 08.11.2024; Ogledov: 1233; Prenosov: 23
.pdf Celotno besedilo (9,22 MB)

6.
Reaction mechanism and microkinetics of heterogeneously catalysed lignin depolymerisation and (de)functionalization : dissertation
Tina Ročnik, 2024, doktorska disertacija

Opis: Lignin, a complex aromatic polymer derived from lignocellulosic biomass, is a renewable resource for the production of aromatic-like chemicals and materials. However, its complex nature, depolymerisation and valorisation remain a major challenge for the bio-based community within biorefinery concepts. For this reason, lignin model compounds have been used to understand and design lignin depolymerisation, but insufficient attention has been paid to linking knowledge between simpler systems and applying it to a more complex problem. The objectives of this thesis were formulated accordingly to address the aforementioned gap in the literature. The objectives included a systematic approach correlating studies of lignin model compounds with lignin. Hydrodeoxygenation, cleavage of the β-O-4 bond and depolymerisation were investigated to evaluate the process- and structure-dependent correlations, effects on product distribution and kinetic parameters. The catalytic reactions were carried out in batch reactor and the conditions were applied and intensified according to the knowledge gained during the experimental work. The liquid samples for monomer yield evaluation were analysed by GC-MS, while the structural characteristics of lignin and oligomeric fragments, e.g. molecular weight, functionality/reactivity and structural features, were examined by SEC, quantitative 31P and 2D-HSQC NMR. Kinetic modelling was performed to determine the kinetic parameters (e.g. kinetic constants and activation energies) describing defunctionalisation, β-O-4 bond cleavage and depolymerisation. The study with monomeric lignin compounds contributed to the understanding of the key parameters leading to condensation during hydrotreatment. The unsaturated alkyl side-chain of eugenol and the reactive hydroxyl groups bound irreversibly and formed the carbonaceous species, while 4-propylphenol and 4-propylguaiacol provided important insights into the contribution of steric hindrances to a favourable reaction mechanism. An initial assessment of β-O-4 cleavage was performed with β-O-4-model compound, 2-phenoxy-1-phenylethanol, and linked to the lignin macromolecule by process- and structure-dependent correlations. Although the lignin model compound lacks the structural complexity of lignin, important insights into possible reaction processes were gained and accurate kinetic parameters were determined. Furthermore, lignin isolated in 50 vol% EtOH/H2O solutions was depolymerised and the optimal reaction conditions were defined at a temperature of 275 °C and a pressure of 1.5 MPa with regard to the product distribution and the changes in the structural characteristics of the corresponding oligomeric fragments. Depolymerisation of lignins isolated in different EtOH/H2O solutions showed the importance of the structural features, especially ethoxylation degree and the content of β-O-4 or α-ethoxylated β-O-4 bonds. A higher ethoxylation degree of lignin reduced its potential to depolymerise and achieve the theoretical monomer yield. Therefore, the structural characteristics of lignin play the main role in designing and prediction of lignin depolymerisation. The thesis represents a systematic approach of increasing the complexity of structures exposed to hydrodeoxygenation and depolymerisation. The approach contributed to incorporating the knowledge gained from less complex model compounds to real lignin samples by tailoring and designing lignin depolymerisation to exploit the potential of lignin for biorefinery concepts.
Ključne besede: model compounds, hydrodeoxygenation, organosolv lignin, depolymerisation, structural characteristics, kinetic modelling, dissertations
Objavljeno v RUNG: 08.11.2024; Ogledov: 1195; Prenosov: 17
.pdf Celotno besedilo (5,04 MB)

7.
Quantitative detection of Microcystis aeruginosa (cyanobacteria) in water using single domain antibodies (VHH) : dissertation
Gbenga Folorunsho Oginni, 2024, doktorska disertacija

Opis: Microcystis aeruginosa accumulation in freshwater poses a significant threat to aquatic organisms and human health. The toxicity of Cyanobacteria metabolites urges for the development of methods for their rapid and efficient detection but what is still almost completely missing is the availability of reagents for the quantification of M. aeruginosa cells in water to monitor the fluctuations of its population. In this study, nanobodies against cell surface antigens of the toxic Cyanobacteria M. aeruginosa were recovered bywhole-cell panning of a naive phage display library. Six unique sequences were identified and three of them sub-cloned and purified as fusion immunoreagents together with either green fluorescent protein or Avi-Tag to be used for diagnostics. Theirspecificity and sensitivity were evaluated by immunofluorescence, by fluorescent and colorimetric cell ELISA and by thermal lens spectrometry (TLS). No cross-reactivity with unrelated microalgae was detected, and both ELISA and TLS methods provided a linear range of detection of several logs. The limit-of-detection of TLS was as low as 1 cell/ml.
Ključne besede: cyanobacteria, nanobodies, phage display, thermal lens spectrometry, dissertations
Objavljeno v RUNG: 10.09.2024; Ogledov: 1348; Prenosov: 22
.pdf Celotno besedilo (3,80 MB)

8.
Green synthesis of Zeolitic Imidazolate Frameworks and their evaluation for ▫$CO_2$▫ capture in humid conditions : dissertation
Aljaž Škrjanc, 2024, doktorska disertacija

Opis: Emissions of green-house gasses have been in the forefront of scientific research in recent decades. One of the approaches towards reducing the amount of green gas CO2 in the atmosphere is its capture and storage with subsequent conversion where pure enough CO2 can be regenerated. While CO2 capture widely utilizes two mature technologies, amine absorption and cryogenic distillation, they both have significant downsides, in either cost or potential new danger to the environment. To that end an adsorption-based CO2 capture has seen quite a lot of interest in recently. Nanoporous materials have been extensively studied for this application, starting with zeolites, followed by aluminophosphates and also the new members of the porous materials group, the so called reticular porous materials. Metal-Organic Frameworks (MOFs), the first discovered reticular porous materials have shown very promising results for post combustion CO2 capture and recently also for in-door and direct air capture. MOFs are in general enough thermally stable for CO2 capture, their main weakness for wide applicability is sometimes lower selectivity for CO2 in real gas mixtures and lower stability in humid conditions. Zeolitic imidazolate frameworks (ZIFs), a subgroup of MOFs, have in recent years been extensively studied for sorption applications, also CO2, due to their superior stability and kinetics for vapour/gas adsorption if compared to carboxylate-based MOFs. While extensively studied, an overview of articles shows that most research is limited to a limited set group of frameworks, with ZIF-8 being used in more than half of ZIF papers. While ZIF-8 has successfully been prepared in water and even in solvent-free conditions, the rest of the ZIFs synthesis still heavily rely on solvothermal synthesis with formamide based solvent systems and synthesis times upwards of 5 days. Even in the case of ZIF-8, while greener synthesis approaches are available, dimethylformamide (DMF) synthesis still prevails in the cases tested for CO2 capture, mainly due to the increased CO2 uptake resulting from the synergistic contribution of the remaining DMF solvent in the pores. The goal of this thesis was to develop green synthesis approaches, both solvothermal and mechanochemical, for known ZIFs and then to extend the scope towards preparation of new ZIF materials. The goal for latter was to experimentally determine the optimal topology and functionality of ZIFs for CO2 adsorption in humid conditions. Model humid gas isotherms were developed and measured for a series of ZIFs with mostly SOD (sodalite) and RHO framework topologies and Zn and Ni as metal nodes. Finally, some novel bio-based binder materials were tested for the use with ZIFs. The sorption tests revealed than the SOD topology ZIFs have high potential for CO2 sorption applications, as the adsorption is rapid and further combination of terminally functionalised imidazoles in those frameworks drastically increases the frameworks affinity for CO2 at lower pressures. With most common 4,5- functionalised imidazole having hydrophilic functional groups, the challenge of competitive water sorption still remains. On the other hand some hydrophobic 4,5-substituted sodalite ZIFs, both with 4,5-dichloroimidazole, show excellent CO2 sorption and even complete hydrophobicity. The results led us to hypothesize that further research on ZIFs- for CO2 capture has to shift form 2 substituted sodalite frameworks to 4,5 substituted frameworks with strongly dipolar hydrophobic groups. The hydrophilic polar groups currently in use lead to issues with competitive water adsorption, due to their potential to form hydrogen bonds with water. Furthermore, some new agar and alginate based shaping methods were tested, as both potential binders are not environmentally toxic and are already used on the industrial scale world-wide for other applications.
Ključne besede: carbon capture, synthesis, metal-organic frameworks, zeolitic imidazolate frameworks, nanoporous materials, dissertations
Objavljeno v RUNG: 10.09.2024; Ogledov: 1383; Prenosov: 34
.pdf Celotno besedilo (15,56 MB)

9.
Detection of gamma-ray sources and search for dark matter signals with Cherenkov Telescope Array surveys : dissertation
Veronika Vodeb, 2024, doktorska disertacija

Opis: Gamma rays serve as important messengers in modern astrophysics, offering insights into the most energetic processes in the cosmos. Advancements in gamma-ray astronomy, facilitated by international scientific collaboration, have expanded its reach and capabilities. The Fermi-Large Area Telescope (Fermi-LAT) has so far contributed immensely to our understanding of the gamma-ray sky at GeV energies, surveying numerous source classes. At the same time, ground-based observatories like H.E.S.S., MAGIC, VERITAS, HAWC, and LHASSO, enable the exploration of high-energy (HE) phenomena across various energy scales, reaching the PeV range. The collective data from Fermi-LAT and ground-based instruments provide a comprehensive picture of cosmic phenomena across diverse energy regimes. Efforts to catalog HE gamma-ray sources have resulted in the detection of several thousand sources at GeV, including Pulsar Wind Nebulae (PWNe), Supernova Remnants (SNRs), pulsars, blazars, and Gamma-Ray Bursts (GRBs), with the observational capability to study their spectral and spatial morphology enhancing our understanding of their origin and evolution. Looking ahead, the Cherenkov Telescope Array (CTA) represents the next frontier in ground-based gamma-ray astronomy. Operating at very high energies (VHE) between 20 GeV and 300 TeV, CTA's improved sensitivity, angular resolution, and expanded field of view (FoV) promise enhanced imaging of extended sources and performance of large-scale surveys. CTA's Key Science Projects (KSPs) include the Extragalactic (EGAL) survey, a survey of a quarter of the extragalactic sky, and the Galactic Plane Survey (GPS), a survey of the entire Galactic Plane (GP). The KSPs will receive dedicated observation time and careful planning to ensure the optimization of their scientific output. As CTA is currently entering the construction phase, simulations are being extensively employed to predict its response to various signals, playing a vital role in comprehending CTA's response and sensitivity to different signals. The derived predictions are paving the way for estimating the CTA's scientific output, informing the observational strategy, and ensuring its success in maximizing the contribution to HE gamma-ray astronomy. In this thesis, I contribute to assessing the sensitivity of the CTA surveys, particularly the GPS and the EGAL survey, to diverse astrophysical sources and signals. Focusing on the GPS, I delve into understanding the detectability of pulsar halos, which emit multi-TeV gamma rays, the detection of which was recently reported by the HAWC Observatory. The study involves a spatial-spectral likelihood analysis, evaluating sensitivity to simple Gaussian extended sources and physically modeled sources. Employing a template-fitting approach, I analyze CTA's GPS sensitivity to extended sources and explore the prospects for pulsar halo detection and characterization. A preliminary population study addresses the visibility of pulsar halos to CTA's GPS and explores the angular sensitivity to extended sources. The thesis sets the detectability prospects of pulsar halos with CTA and investigates what fraction of the preliminary pulsar halo population CTA will be able to probe. The thesis extends its exploration into the persistent mystery of dark matter (DM), a fundamental puzzle in cosmology. The search for DM signals remains a vigorous pursuit in the physics community, utilizing various astrophysical messengers resulting from DM particle annihilation or decay. I investigate the potential of CTA's GPS to detect dark sub-halos within our galaxy, utilizing a similar approach as in the sensitivity assessment to pulsar halos, applied to recent sub-halo population simulations. Furthermore, the thesis addresses the intricate task of disentangling DM components from astrophysical contributions in the observed gamma-ray sky. In terms of the EGAL survey, employing advanced statistical methods such as the cross-correlation technique, I explore the prospects of using CTA's EGAL survey to correlate the Extragalactic Gamma-ray Background (EGRB) with galaxy catalogs, providing insights into DM properties. While traditional methods rely on likelihood analysis with background subtraction or template fitting, the emergence of supervised machine learning (ML) offers a novel, potentially more effective approach for cataloging the sky. The thesis touches upon the usability of ML in the high and VHE gamma-ray sky. My study focuses on CTA's GPS and utilizes deep-learning-based algorithms in a detection pipeline for the automatic classification of extended sources from gamma-ray data. As CTA stands at the forefront of gamma-ray astronomy as the next-generation observatory, the research presented in this thesis contributes a small step towards answering the open questions about pulsar halos and DM, showcasing the potential breakthroughs that may emerge from CTA's observations. The detailed likelihood analysis performed aims to advance our understanding of these enigmas, from the physical intricacies of pulsar halos to the elusive nature of DM, driven by curiosity about the continuous exploration of the Universe's mysteries.
Ključne besede: high-energy gamma-ray astronomy, astroparticle physics, Cherenkov Telescope Array, pulsar halos, dark matter, dissertations
Objavljeno v RUNG: 06.06.2024; Ogledov: 1673; Prenosov: 20
.pdf Celotno besedilo (36,25 MB)

10.
Degradation of microplastics in the environment : dissertation
Vaibhav Budhiraja, 2024, doktorska disertacija

Opis: Plastics are based on organic polymers that are sensitive to the environment in which they find themselves and will gradually decay through a variety of chemical reactions. This process is of great importance for the transformation and persistence of microplastics (MPs) that pollute the environment. The rate of degradation depends on two major factors: Firstly, the intrinsic properties of the polymers, such as chemical structure, molecular weight, crystallinity and the presence of additives, fillers or reinforcement and secondly, the environment to which they are exposed. The degradation rate of plastic will vary in different environmental matrices like soil, freshwater, seawater, wastewater, land etc., as well as in diverse environmental conditions like UV radiation, temperature, humidity, the effect of pollutants etc. Plastic mainly undergoes two fundamental reactions: oxidation and hydrolysis and the chemical structure of the polymer and its additives plays a key role in the degradation mechanism of plastic. Polyolefins having a carbon-only main chain are resistant to hydrolysis but susceptible to oxidation, whereas polyesters and polyamides containing heteroatoms are sensitive to hydrolysis and much more resistant to oxidation. In the context of the present work, five different studies were done involving both naturally degraded plastic and accelerated weathering of plastics in the form of small particles, MPs. In the first study, natural degraded polyethylene (PE) and polypropylene (PP) samples with a life span of more than forty years were collected from the environment and their physiochemical properties were analysed. The results show that red coloured PE samples were more degraded as compared to blue coloured samples, indicating that pigment plays a key role in the degradation. The PP sample shows extreme surface degradation, leading to fragmentation and the generation of MPs. In the second study, the effect of hydrodynamic cavitation on MPs in waste water treatment plant sludge was evaluated. PE, PP, polyethylene terephthalate and polyamide were extracted from the sludge. It was found that hydrodynamic cavitation does not disintegrate the MPs, although it removes some toxic metals and shows cell disruption mechanisms. Other studies were done with accelerated weathered MPs, which include PE, PP and tire wear particles (TWP), that were treated in accordance with an ISO 4892 standard weathering procedure that mimics natural weathered conditions. In the third study, we used weathered PE films to evaluate the synergistic adsorption behaviour of two pollutants, namely triclosan (TCS) and methylparaben (MeP). It was found that weathered MPs adsorb more pollutants and the adsorption behaviour of TCS is enhanced in the presence of MeP. In the fourth study, the magnetic extraction of pristine and weathered PE and TWP particles was performed. The results confirmed that the magnetic VI extraction of weathered MPs is difficult as compared to pristine MPs as their surface becomes more hydrophilic with weathering. In the fifth study, the effect of weathering on the density of PE and PP was evaluated. We found that weathering enhances the density of polyolefins, which is one of the main reasons for the observed sinking of polyolefin MPs in water.
Ključne besede: accelerated weathering, aging, density, magnetic separation, pigment, plastic degradation, pollutants, polyethylene, polyolefin, polypropylene, sinking, tire wear particles, dissertations
Objavljeno v RUNG: 04.06.2024; Ogledov: 3828; Prenosov: 14
.pdf Celotno besedilo (7,35 MB)

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