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Abstract: A study of magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys is reported. Amorphous Fe40Ni38Mo4B18, near its magnetic ordering temperature (600K) showed a magnetic entropy change ΔSM of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K) in a field change of 10 kOe. The decrease in ΔSM on partial crystallisation is attributed to the biphasic magnetic nature of the s
Keywords: magnetism, phase transitions, entropy, equations of state, alloys, amorphous materials, annealing
Published in RUNG: 07.11.2024; Views: 318; Downloads: 3
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Abstract: 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.
Keywords: carbon capture, synthesis, metal-organic frameworks, zeolitic imidazolate frameworks, nanoporous materials, dissertations
Published in RUNG: 10.09.2024; Views: 741; Downloads: 21
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Abstract: Fluorescent covalent organic frameworks (COFs) have emerged as promising candidates for imaging living cells due to their unique properties and adjustable fluorescence. In this mini-review, we provide an overview of recent advancements in fluorescent COFs for bioimaging applications. We discuss the strategies used to design COFs with desirable properties such as high photostability, excellent biocompatibility, and pH sensitivity. Additionally, we explore the various ways in which fluorescent COFs are utilized in bioimaging, including cellular imaging, targeting specific organelles, and tracking biomolecules. We delve into their applications in sensing intracellular pH, reactive oxygen species (ROS), and specific biomarkers. Furthermore, we examine how functionalization techniques enhance the targeting and imaging capabilities of fluorescent COFs. Finally, we discuss the challenges and prospects in the field of fluorescent COFs for bioimaging in living cells, urging further research in this exciting area.
Keywords: covalent organic frameworks, fluorescent materials, imaging, bioimaging, biosensors
Published in RUNG: 05.03.2024; Views: 1647; Downloads: 8
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Abstract: Complex systems are characterized by strong coupling between different microscopic degrees of freedom. Photoexcitation of such materials can drive them into new transient and metastable hidden phases that may not have any counterparts in equilibrium. By exploiting femtosecond time- and angle-resolved photoemission spectroscopy, we probe the photoinduced transient phase and the recovery dynamics of the ground state in a complex material: the charge density wave (CDW)–Mott insulator 1T-TaS2. We reveal striking similarities between the band structures of the transient phase and the (equilibrium) structurally undistorted metallic phase, with evidence for the coexistence of the low-temperature Mott insulating phase and high-temperature metallic phase. Following the transient phase, we find that the restorations of the Mott and CDW orders begin around the same time. This highlights that the Mott transition is tied to the CDW structural distortion, although earlier studies have shown that the collapses of Mott and CDW phases are decoupled from each other. Interestingly, as the suppressed order starts to recover, a metastable phase emerges before the material recovers to the ground state. Our results demonstrate that it is the CDW lattice order that drives the material into this metastable phase, which is indeed a commensurate CDW–Mott insulating phase but with a smaller CDW amplitude. Moreover, we find that the metastable phase emerges only under strong photoexcitation (∼3.6 mJ/cm2) and has no evidence when the photoexcitation strength is weak (∼1.2 mJ/cm2).
Keywords: angle resolved photoemission, time resolved photoemission, 2D materials, charge density wave, Mott insulator
Published in RUNG: 15.01.2024; Views: 1867; Downloads: 6
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Keywords: photopyroelectric calorimetry, thermal parameters, porous materials
Published in RUNG: 04.08.2023; Views: 2238; Downloads: 5
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