Dokument: Synthesis of metal-organic frameworks and monolithic composite materials for water sorption applications
| Titel: | Synthesis of metal-organic frameworks and monolithic composite materials for water sorption applications | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=34606 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20150623-102115-6 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Dr. Wickenheisser, Martin [Autor] | |||||||
| Dateien: |
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| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | Metal-organic frameworks (MOFs) have been well investigated as adsorbents for cyclic water ad-, desorption processes in potential heat transformation applications during the last years. In spite of their advantages over traditional adsorbents, the total water uptakes remain comparably low in environments of low to medium humidity. For intended practical applications, the water loading lifts have to be maximized in the partial pressure range of 0.05 < P∙P0–1 < 0.35 through increasing the hydrophilic nature of MOFs by chemical modifications.
Two water stable MOFs of the MIL-family ((MIL = Matériaux de l’Institut Lavoisier)), MIL 100(Cr) and MIL-101(Cr) were chosen and post-synthetically modified by substitution of terminal, coordinated water molecules through hydrophilic gylcols and amines, so-called ‘grafting’, at their coordinatively unsaturated metal sites. In spite of the decrease of the BET surface areas and total pore volumes of the modified MILs, MIL-100(Cr)-EG, MIL 100(Cr) DEG and MIL-100(Cr)-EN (EG = ethylene glycol, DEG = diethylene glycol, EN = ethylenediamine) showed almost unchanged water loading capacities with slightly favored water uptakes in the range of 0.17 < P∙P0–1 < 0.30 compared to non-modified MIL 100. The corresponding water adsorption isotherms could be shifted to lower partial pressures, accompanied with a higher slope of the adsorption isotherms in comparison to bulk MIL 100(Cr). The high water loading lifts in combination with the decrease of the surface areas can only be explained by the fact that the size of the MIL-100 pores is not the essential factor for high water uptakes. Ethylenediamine has shown a more stable bonding towards chromium(III) over glycols, but an ad-, desorption cycling stability test of MIL-100(Cr)-EN have shown that a practical application has to be critically regarded due to some degradation. We also focused on shaping of metal-organic frameworks into mechanically stable and manageable bodies due to the disadvantages of the powdery appearance of MOFs (e.g. dust problems). Shaping of MOFs into a more utilizable form, like monoliths, is an indispensable requirement for potential applications like heat transformation purposes. Therefore, different, water stable MOFs were embedded into porous organic and inorganic polymers (so-called binding agents), which can be manufactured in monolithic shape. These polymers can either be synthesized by high internal phase emulsions (HIPEs) or by xerogels. MOFs of the MIL-type such as MIL-100(Fe,Cr) and MIL-101(Cr) were incorporated into porous Si(HIPE), poly(HEMA)HIPE (HEMA = 2-hydroxyethyl methacrylate), poly(NIPAM)HIPE (NIPAM = N Isopropylacrylamide) and a xerogel, based on resorcinol and formaldehyde, through two different synthetic approaches: Firstly, the direct route, ‘Route A’, whereas activated MIL powders were added to the binding agents before curing and secondly an in situ route, ‘Route B’, in which MOF particles were in situ grown in the pores of monolithic polymers. The syntheses of MIL@Si(HIPE) composites has turned out to be problematic due to large shrinking effects during the drying process. Composites could only be obtained in granulated shape or monoliths with big cracks and relative low surface areas. MIL@poly(NIPAM)HIPE materials were also largely deformed during drying, although it could be shown that porous composites were obtained using the direct route, if the HIPE emulsion was highly pre-polymerized before addition of the powdery MILs. Only poly(HEMA)HIPE and R,F-xerogel have shown to be the most suitable candidates for monolithic composites with high MOF loadings. Pure polymers as well as the composite materials show negligible shrinking effects by conventional oven drying, resulting in mechanically stable monoliths. Pore blocking effects of the MIL pores by HIPE or xerogel monomers could be largely avoided in the direct route by pre-polymerization of the binding agents. Monolithic MIL@HEMA composites could also be synthesized by the in situ route, but this method yielded less porous materials in comparison to the direct route. Vapor sorption experiments have shown that MIL@HEMA composites favor the adsorption of methanol vapor over water due to the rather hydrophobic nature of the pure poly(HEMA)HIPE. Native R,F-xerogel reveals a more hydrophilic character in comparison to native poly(HEMA)HIPE, which explains the high water loading lifts in MIL@R,F-xerogels. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Anorganische Chemie und Strukturchemie | |||||||
| Dokument erstellt am: | 23.06.2015 | |||||||
| Dateien geändert am: | 23.06.2015 | |||||||
| Promotionsantrag am: | 16.04.2015 | |||||||
| Datum der Promotion: | 27.05.2015 |
