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Kovinsko-organski mikroporozni materiali (ang. metal–organic frameworks ali MOF) sodijo med najbolj obetavne adsorbente za zajem CO2. V doktorskem delu sem podrobnopreučila tri strukturne tipe za ta namen, in sicer HKUST-1, ZnBDC in MOF-74. V prvem delu doktorskega dela sem se posvetila študiju vpliva modifikacije ogrodja HKUST-1 z etilendiaminom (ED) na jakost interakcije molekule CO2 z ogrodjem, selektivnost ogrodja za CO2 iz binarne mešanice plinov CO2/N2 ter kinetiko adsorpcije. Ugotovila sem, da modifikacija izboljša jakosti interakcije molekule CO2 z ogrodjem in selektivnosti ogrodja za adsorpcijo CO2 za 85 %, pri čemer sta oba parametra tesno povezana s poroznostjo materiala in dostopnostjo por. Večanje količine dodanega ED vpliva na nastanek t.i. hierarhičnega sistema por, kar nadalje izboljša tudi difuzijo in hitrost adsorpcije molekul CO2 v ogrodje modificiranih materialov. V drugem delu sem preučevala strukturo ZnBDC z negativno nabitim ogrodjem, katerega naboj kompenzirajo v porah prisotni di- in trimetilamonijevi kationi. Z namenom, da bi izboljšala tako sorpcijske kot tudi katalitske lastnosti izhodiščnega vzorca, sem izvedla ionsko izmenjavo v ogrodju ujetih kationov s kationi natrija, kalija, litija in magnezija. Glede na izhodiščni material, imajo ionsko izmenjani vzorci višjo adsorpcijsko kapaciteto za CO2, sorpcijske lastnosti pa se izboljšujejo z manjšanjem radija izmenjanih kationov. Ionska izmenjava vpliva tudi na povečanje katalitske aktivnosti, saj je osnovni ZnBDC katalitsko skoraj neaktiven, medtem ko Mg-ZnBDC brez uporabe ko-katalizatorja, ob prisotnosti CO2, uspešno pretvori približno 40 % propilen oksida v propilen karbonat. V tretjem sklopu doktorskega dela sem, z namenom lažjega rokovanja, M-MOF-74 (M=Zn, Co, Mg) pripravila v polimerni matrici poliHIPE s pomočjo sekundarne prekristalizacije iz kovinskih oksidov. Ugotovila sem, da vrsta kovinskih kationov v ogrodni strukturi, ne vpliva na uspešnost kristalizacije MOF-74 v polimerni matriki. Nadalje sem preučila dostopnost vgrajenega MOF-74 za adsorpcijo molekul CO2, ta je v primeru Mg-MOF-74@poliHIPE 98.6 %. Rezultati sorpcije CO2 so pokazali, da imajo prekristalizirani vzorci glede na delež vgrajenega MOF-a višje adsorpcijske kapacitete za CO2 ter da je kinetika adsorpcije in desorpcije v polimernih kompozitih boljša kot v praškastih vzorcih. Poleg kinetike sem z vgradnjo MOF-74 v polimerno matrico izboljšala tudi regeneracijo adsorbentov – pri temperaturi 150 °C se v primeru vzorca Zn-MOF-74@polyHIPE uspešno desorbira do 95 % CO2. Metal-organic frameworks (MOFs) are one of the most promising materials for CO2 capture and conversion. In my research, I have focused on three systems with high CO2 capture capabilities – HKUST-1, ZnBDC and MOF-74. The first part of my research was focused on the studies of HKUST-1 framework functionalization with ethylenediamine (ED) and the impact of the modification process on the CO2 capture parameters relevant for the post-combustion process. In the case of the modified materials, the isosteric heat of adsorption and CO2/N2 selectivity was improved by almost 85 %. Both parameters are closely related to the materials porosity and pore accessibility. The increase of ED loading caused the formation of hierarchical structure expanded over micro-, meso- and macropore range, which further improved the adsorption kinetics and diffusion of CO2 molecules within the framework of modified materials. In the second part of this research, I investigated the effect of cation exchange on the CO2 capture and conversion performances of the negatively charged ZnBDC framework, which was initially compensated by di- and trimethylammonium cations located within the material pores. The cation exchange was performed using sodium, potassium, lithium and magnesium cations to improve sorption and catalytic properties of the pristine material. In comparison with the pristine ZnBDC, all modified materials exhibited higher CO2 adsorption capacities, and the sorption properties are improved by decreasing the cation radius. The ionic exchange also had a positive effect on catalytic activity in comparison with the pristine ZnBDC, which was almost catalytically inactive, the exchanged materials exhibit significant improvement. Namely, Mg-modified material exhibited a 40% higher conversion of propylene oxide to propylene carbonate without the use of co-catalyst. The final part of the thesis is dedicated to the shaping of MOF materials by secondary recrystallization of metal-oxide initially incorporated in a polymeric matrix (polyHIPE) into M-MOF-74 (M=Zn, Co, Mg). All metal oxide precursors were efficiently recrystallized to MOF-74. Furthermore, incorporated MOF-74 phases exhibit unobstructed accessibility for the CO2 adsorption reaching up 98.6 % for the case of Mg-MOF-74@polyHIPE. All immobilized MOF-74 phases also showed an improvement in adsorption kinetics and temperature swing adsorption regeneration efficiency performed at 150 °C (up to 95 % for Zn-MOF-74@polyHIPE). |
