Synthesis and characterization of zinc imidazolate framework ZIF-8

V današnjem času, ko se še posebej osredotočamo na skrb za okolje, je ključno, da namesto fosilnih goriv poskušamo uveljaviti nove vire energije. Vodik je ena boljših alternativ, predvsem zaradi svoje čistosti in visoke količine energije na maso energenta. Poleg samega pridobivanja, je ena večjih težav tudi shranjevanje vodika in njegovo sproščanje pri standardni temperaturi in tlaku, saj shranjevanje vodika pod visokim tlakom ali utekočinjen vodik nista ekonomsko ugodni rešitvi. Rezervoarji so v teh primerih pod visokim tlakom, zato takšni načini shranjevanja predstavljajo tudi veliko nevarnost. V diplomskem delu sem sintetizirala porozno kovinsko-organsko ogrodje cinkov 2 metilimidazolat (ZIF-8), ki ima potencial za shranjevanje vodika. Želela sem najti optimalno sintezno pot za pripravo te spojine. S sintezo v vodni raztopini, evtektično metodo, sintezo v vodni raztopini v prisotnosti TEA in sintezo v metanolu sem poskušala pridobiti enak produkt, pri čemer sem kot izhodne spojine uporabila 2 metilimidazol in cinkov nitrat heksahidrat ali cinkov acetat dihidrat. Produkte sem analizirala z rentgensko praškovno difrakcijo in FTIR spektroskopijo in tako dobila potrditev, da so bili vsi nastali produkti različnih sinteznih poti spojina ZIF-8. Produkti različnih sintez se v strukturi bistveno niso razlikovali, torej organska topila za sintezo lahko zamenjamo tudi z vodno raztopino.Nowadays, environmental sustainability is of the utmost importance, therefore, it is crucial to use renewable sources of energy rather than fossil fuels. Hydrogen holds great promise as a zero-emission fuel, due to the highest energy density per unit mass. Along with the production, one of the major drawbacks, however, is a lack of effective hydrogen storage solutions at standard pressure and temperature as pressurized and liquid hydrogen are not considered as economically viable options for storage. Furthermore, reservoirs are, in these cases, under high pressure, which is also extremely dangerous. The aim of this work was to determine the most favourable synthetic pathway for porous metal-organic framework zinc 2 methylimidazolate (ZIF-8), which is a promising material for hydrogen storage. The synthesis of a zinc 2-methylimidazolate in an aqueous solution, with deep eutectic method, the synthesis in an aqueous solution in the presence of TEA and preparation in methanol were implemented. 2-methylimidazole and zinc nitrate hexahydrate or zinc acetate dihydrate were used as the reactants. X-ray powder diffraction and FTIR spectroscopy were also carried out in order to characterize all products. Both analysis confirmed that products of different synthetic pathways were the compound ZIF 8. Products did not differ significantly in their structure, which indicates water solutions can be used as an alternative to organic solvents

Kinetics of hydrogen adsorption and desorption on platinum catalyst

Poraba energije po vsem svetu vztrajno narašča, kar vodi v neizogibno izčrpavanje obstoječih virov energije, zato je ključno iskanje novih virov energije. Kot potencialni nosilec energije v prihodnosti, ima vodik pomembno vlogo na poti proti nizkoogljičnemu gospodarstvu. Zaradi svojih edinstvenih fizikalno-kemijskih lastnosti je platina pomemben element v tehnologijah, ki uporabljajo protonsko izmenjevalno membrano (PEM), ki se že uporablja tako v elektrolizerjih za proizvodnjo vodika kot tudi v vodikovih gorivnih celicah. Platina zato predstavlja ključ do brezemisijskega potenciala vodika. V magistrskem delu sem določevala kinetiko adsorpcije in desorpcije vodika na platinski katalizator Pt/SiO2, ki sem ga sintetizirala po metodi močne elektrostatske adsorpcije. Sintetizirani katalizator sem okarakterizirala z različnimi analiznimi tehnikami, in sicer z EDS, ICP OES, XRPD, TEM in TPD. S spreminjanjem temperature pri termični obdelavi sem pripravila različno velike platinske nanodelce na nosilcu za določitev vpliva velikosti nanodelcev na adsorpcijo vodika. Pri višjih temperaturah termične obdelave so nastali večji nanodelci, posledično pa se je na katalizator adsorbiralo manj vodika. Temperaturni maksimum desorpcijskega vrha nekoliko zavisi od hitrosti segrevanja in je pri hitrosti segrevanja 10 °C/min pri 190 °C. Hitrost adsorpcije je v temperaturnem območju med 0 °C in -100 °C temperaturno neodvisna, delež adsorbiranega vodika pa se ni bistveno spremenil. Rezultati kinetičnega modela so pokazali, da je množina aktivnih mest večja pri katalizatorju z manjšo velikostjo platinskih nanodelcev. Aktivacijska energija desorpcije je enaka 17 kJ/mol, kar je manj od pričakovane vrednosti, zato bi bilo kinetični model v prihodnje potrebno izboljšati.Energy consumption worldwide is steadily increasing which leads to an inevitable depletion of existing energy sources. Therefore, there is an ever-increasing demand for new sources of energy. Being a potential energy carrier of the future, hydrogen plays an important role in the path toward a low-carbon economy. Having unique chemical and physical properties, platinum is an important element of proton exchange membrane (PEM) technology, which is already in use in both electrolyzers to produce hydrogen and in hydrogen fuel cells and thus holds great promise in unlocking the zero-emission potential of hydrogen. In my master\u27s thesis I was determining kinetics of hydrogen adsorption and desorption on a platinum catalyst Pt/SiO2 synthesized using a strong electrostatic adsorption method. The synthesized catalyst was characterized by various analytical techniques, such as EDS, ICP-OES, XRPD, TEM and TPD. By varying the calcination temperature, platinum nanoparticles of different sizes on the support were generated, in order to determine the influence of nanoparticle size on hydrogen adsorption. At higher calcination temperatures, larger nanoparticles were formed and as a consequence, less hydrogen adsorbed onto the catalyst. The temperature maximum of the desorption peak depends on the heating rate and is at 190 °C for a heating rate of 10 °C/min. The adsorption rate is temperature-independent in the temperature range between 0 °C and -100 °C, and the proportion of adsorbed hydrogen did not change significantly. The result of the kinetic model showed that the number of active sites is greater for the catalyst containing smaller platinum nanoparticles. The activation energy of desorption is 17 kJ/mol, which is lower than the expected value, therefore, the kinetic model should be improved in the future

Understanding platinum-based H2 adsorption/desorption kinetics during catalytic hydrogenation or hydrogen storage-related reactions

Hydrogen is among the most promising energy carriers and plays an important role on the way to sustainable technologies. Platinum holds great promise for unlocking the potential of renewable hydrogen, as it is an essential component of proton exchange membrane technologies and in various hydrogenation reactions. For the variety of applications of energy harvesting, conversion, and storage, the optimization and reduction of Pt loading is crucial. In view of this, a platinum catalyst using a stable SiO$_2$ support is synthesized to investigate the adsorption/desorption behavior of hydrogen on platinum nanoparticles of different sizes, obtained by treating the sample at different calcination temperatures. Pulsed chemisorption and subsequent temperature-programmed desorption are described mathematically to obtain kinetic parameters. It is shown that higher adsorption capacities could be obtained using smaller particles. However, for particles smaller than 2.4 nm, higher Pt$^{2+}$ content decreases H$_2$ adsorption. Adsorption inhibition due to the presence of monatomic Pt cannot be excluded. The size of the Pt nanoparticles does not significantly affect the desorption/adsorption energy, but there is evidence that the hydrogen adsorbed per Pt atom at the surface varies with size: about 1 for single crystal planes and 2 for nanoparticles <3 nm

Organosolv lignin barrier paper coatings from waste biomass resources

The aim of the study was to isolate lignin from organosolv, beech tree (Fagus sylvatica), and Japanese knotweed (Reynoutria japonica), to use it for paper surface and to replace part of the non-renewable product resources with bio-based ones. A total of nine coated samples with different lignin formulations and starch were compounded, prepared, and evaluated. The basic (grammage, thickness, specific density), mechanical (elongation at break, tensile, burst and tear indices), and barrier properties (contact angle, water penetration, water vapour permeability, kit test) of the coated papers were investigated. The analysis showed no significant difference in tensile properties between uncoated and coated samples. Furthermore, the decrease in water vapour transmission rate and the lower contact angle for coated samples were nevertheless confirmed. The novel coating materials show promising products with very good barrier properties. Finally, the correlation between structural, morphological, and (other) natural lignin-based factors was revealed, highlighting the importance of parameters such as the equivalence ratio of aliphatic and phenolic hydroxyl groups or the average molecular weight. Tuning functionality by design could optimise performance in the future