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1.
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: 341; Prenosov: 0
.pdf Celotno besedilo (7,35 MB)

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Photoelectrochemical activation of peroxymonosulfate using Sn-doped ▫$α-Fe_2O_3$▫ thin film for degradation of anti-inflammatory pharmaceutical drug
Manel Machreki, Georgi Tyuliev, Dušan Žigon, Qian Guo, Takwa Chouki, Ana Belén Jorge Sobrido, Stoichko Dimitrov, Saim Emin, 2024, izvirni znanstveni članek

Opis: Introduction of oxygen vacancies (OVs) has been investigated as a promising way to improve the electrical and catalytic characteristics of a hematite (α-Fe2O3) based photoelectrode. In this work, we develop a novel method for preparing porous Sn-doped α-Fe2O3 (Sn:Fe2O3) thin films with intrinsic OVs. The procedure included spin- coating an iron precursor onto a fluorine-doped tin oxide (FTO) substrate, followed by thermal treatment at elevated temperatures. The influence of Sn dopant on the optoelectronic properties of α-Fe2O3 was demonstrated by X-ray photoelectron spectroscopy and photoelectrochemical (PEC) measurements. The combined effect of OVs and Sn doping was found to play a synergistic role in reducing the charge recombination’s. The Sn:Fe2O3 photoanodes were used as a dual catalyst to oxidise water and break down an anti-inflammatory drug called 2-(4- isobutylphenyl)propanoic acid (IBPA). The Sn:Fe2O3 thin film with a 30-minute heat treatment time displayed the highest incident photon-to-current efficiency. For the first time, Sn:Fe2O3 thin films were utilised in the effective PEC degradation of IBPA employing peroxymonosulfate (PMS) under visible light illumination. The hydroxyl radicals (•OH), singlet oxygen (1O2), photogenerated holes (h+), and sulfate radicals (SO4 • ) were discovered to be the main reactive species during PEC degradation. IBPA degradation and the formation of new compounds were verified using liquid chromatography-mass spectrometry. The Lepidium sativum L phytotoxicity test reveals that PEC-treated wastewater with IBPA exhibits decreased toxicity.
Ključne besede: Sn-doped Fe2O3, oxygen vacancies, photoelectrochemical degradation, 2-(4-isobutylphenyl)propanoic acid, peroxymonosulfate
Objavljeno v RUNG: 10.01.2024; Ogledov: 777; Prenosov: 41
.pdf Celotno besedilo (2,44 MB)
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4.
Performance of copper - based catalysts for electrochemical CO2 reduction
Stefan Popović, 2023, doktorska disertacija

Opis: The industrial era has brought a never-ending problem to civilization through the emission of greenhouse gases (GHGs) while extracting energy from fossil fuels for a variety of processes. Among different GHGs, carbon dioxide (CO2) stood out as one of the most impactful and dangerous gases causing climatic disasters around the globe. However, CO2 as the abundant C1 building block, through the conversion pathways gives a plethora of opportunities to convert it into a wide range of commercial products and applications. The holistic approach among different conversion pathways is the electrochemical reduction of CO2 (eCO2R), ideally powered by renewable energy from intermittent sources such as wind and solar power. A silver bullet of the process is to find a catalyst that is active, selective, and stable. Copper has been recognized as the only monometallic catalyst that can produce products that require a transfer of >2e-. However, in recent years the increased awareness of its reconstructive nature under eCO2RR-relevant conditions multiplied the complexity of the parameters that can influence the reaction. Therefore overall thesis's approach to studying copper-based catalysts is based to understand the reconstructive aspect and the stability of Cu-based catalysts, and deeply comprehend their relationship with the activity/selectivity. Chapter 1 gives an introduction to the recent activities in the field of carbon capture, utilization and storage (CCSU) technologies, the fundaments of CO2 as a molecule, and its pathway toward state-of-the-art discoveries in the eCO2 R reaction. Afterward, the thesis focuses on the main experimental technique to produce nanostructured copper-based materials, namely, electrodeposition (Chapter 2). A big part of the thesis focuses on the establishment of an electrochemical setup for activity/selectivity measu rement. The setup consists of two parts: 1) construction of the custom-made gas-tight sandwich-type electrochemical cell and 2) optimization of the online gas and ex-situ liquid product detection. After the establishment of the reliable electrochemical setup, Chapter 3 focuses on electrochemically -grown Cu2O nanocubes catalyst and how the reconstructive nature induced by a particular electrochemical protocol influences on boost in activity/selectivity for methane production. The last part of the thesis consists contribution to the fundamental understanding of the degradation mechanisms and stability of Cu -based catalysts under eCO2RR conditions. A unique ex-situ approach, mirrored in identical location scanning electron microscopy (IL-SEM) method is employed to study electrodeposited spherical half-micron particles on the glassy carbon rotating disk electrode (GC-RDE). With this evidence, we could interpret the observed structural changes as two separate electrochemical processes occurring one after another, namely copper dissolution from pre-oxidized native nanoparticles and subsequent (electro -) redeposition of the dissolved copper species in a form of n ew smaller Cu fragments.
Ključne besede: electrocatalysts, electrochemical CO2 reduction, copper nanoparticles, IL-SEM, stability, degradation
Objavljeno v RUNG: 14.11.2023; Ogledov: 1097; Prenosov: 18
.pdf Celotno besedilo (5,55 MB)

5.
Defective ▫$TiO_2$▫ nanotube arrays for efficient photoelectrochemical degradation of organic pollutants
Manel Machreki, Takwa Chouki, Georgi Tyuliev, Dušan Žigon, Bunsho Ohtani, Alexandre Loukanov, Plamen Stefanov, Saim Emin, 2023, izvirni znanstveni članek

Opis: Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photo-electrodes. In this work, a simple procedure was applied to prepare reduced TiO 2 nanotube arrays (NTAs) (TiO 2−x) via a one-step reduction method using NaBH 4. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO 2−x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO 2−x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO 2−x NTAs was nearly 3 times higher than that of pristine TiO 2. It was found that increasing OVs in TiO 2 affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO 2−x photoanode was used in the photo-electrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products.
Ključne besede: TiO2, nanotube arrays, photoelectrochemical degradation, organic pollutants
Objavljeno v RUNG: 12.06.2023; Ogledov: 1212; Prenosov: 7
.pdf Celotno besedilo (4,22 MB)
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Reduced TiO2 nanotube arrays for photoelectrochemical degradation of pharmaceutical
Manel Machreki, Takwa Chouki, Georgi Tyuliev, Dušan Žigon, Bunsho Ohtani, Alexandre Loukanov, Plamen Stefanov, Saim Emin, 2022, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: TiO2, nanotube arrays, photoelectrochemical degradation, pharmaceuticals
Objavljeno v RUNG: 10.02.2023; Ogledov: 1208; Prenosov: 0
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Synthesis and application of transition metal phosphide nanomaterials as electrocatalysts for water splitting and chemical transformations : dissertation
Takwa Chouki, 2022, doktorska disertacija

Opis: In this thesis, we will focus on the solvothermal synthesis of iron phosphides (FeP, Fe2P) using triphenylphosphine (TPP) as an inexpensive and stable phosphorus source. The obtained iron phosphides were applied as electrocatalysts in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), Rhodamine B (RhB) degradation, Escherichia coli (E. coli) inactivation, nitrates reduction reaction (NO3RR) to ammonia (NH3), and as counter electrodes in dye-sensitized solar cells (DSSCs). Detailed characterizations of catalysts were carried out to investigate the correlations between the material structure and catalytic activity. The first part of the thesis gives an introduction to the topic which cover overview of literature about the use of transition metal phosphide as efficient electrocatalysts in water splitting studies, NO3RR to NH3 and DSSCs. The second part is a description of the experimental methods. The third part discusses the solvothermal synthesis of FeP and Fe2P catalysts using TPP precursor. The phase conversion of iron phosphides at elevated temperatures under reductive atmosphere was reported. Structural characterizations of the obtained materials were achieved using multiple techniques. The electrocatalytic activities of heat-treated iron phosphide films for HER were studied in acidic environment. The fourth part discusses the use of Fe2P nanoparticles (NPs) for OER. The fifth part outlines the use of Fe2P precatalyst in water treatment studies. Using a thin film of Fe2P precatalyst, RhB degradation and E. coli inactivation in the presence of in-situ generated reactive chlorine species were reported. Characterization of Fe2P electrocatalysts before and after the test was carried out using different techniques. The sixth part shows for the first time the use of FeP and Fe2P as a noble metal-free electrocatalysts for NO3RR to NH3. In this chapter we will emphasize the nitrate reaction pathways, which are highly complex and poorly understood. The seventh part demonstrates the use of FeP and Fe2P catalysts as robust and efficient counter electrodes in DSSCs.
Ključne besede: solvothermal synthesis, iron phosphides, electrocatalysis, HER, OER, RhB degradation, E. coli inactivation, NO3RR to NH3, DSSCs, dissertations
Objavljeno v RUNG: 29.08.2022; Ogledov: 2128; Prenosov: 104
.pdf Celotno besedilo (6,35 MB)
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