Nano-agglomerated capillary polymer monoliths for applications in micro-catalysis and separation science
Floris, Patrick (2013) Nano-agglomerated capillary polymer monoliths for applications in micro-catalysis and separation science. PhD thesis, Dublin City University.
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In this thesis, novel approaches to the preparation and characterisation of nanoagglomerated polymer monoliths are described. Polymer monoliths in various formats were prepared by availing of in-situ photopolymerisation techniques, with the modification of surface chemistry achieved via grafting selected amine-reactive monomers, facilitating the subsequent attachment of metal nano-materials. Traditional destructive characterisation methods such as field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy provided the qualitative confirmation of the presence of the nano materials. A very dense coverage of bimetallic Pd/Pt nano-flowers was achieved upon the surface of such polymer monoliths. The macro-porous structure of the monoliths and the high coverage of nano-particles facilitated catalytic applications, such as the oxidation of NADH to NAD+, in flow-through configuration. The rate of reaction was found to be dependant on the initial NADH concentration. Other polymer monoliths were functionalised with gold nano-particle (AuNPs) of various sizes in order to evaluate the effects of nano-particle size on catalytic efficiency. The catalytic properties of the immobilised AuNPs were retained following immobilisation, as demonstrated by the reduction of ferrocyanide from Fe(ІІІ) to Fe(ІІ). A 57% conversion rate was obtained when the reaction was performed on monolithic surfaces which had been functionalised with 16 nm AuNPs. Higher reaction yields (95 %) were obtained when 7 nm AuNPs were used. Non-invasive and non-destructive scanning capacitively coupled contactless conductivity detection (sC4D) was applied to monitor the temporal stability of surfactant and polyelectrolyte coatings in capillary columns which would traditionally be applied in capillary electrophoresis. The benefits of this technique were further illustrated by confirming the presence of AuNPs and PAA-grafted silica nano-particles (SiNPs) on previously aminated or quaternary ammonium functionalised monoliths. The movement of the nanoparticle’s plug was monitored at mm increments as it progressed along the column. Finally, an evaluation of the chromatographic properties of nano-agglomerated stationary phases was performed. Reversed-phase applications of AuNP functionalised monoliths were demonstrated upon further modification of the nanoparticles with alkylthiol and alkylamine chains. However, poor chromatographic performance was observed with a test mixture of alkylbenzenes due to the limited hydrophobicity of the stationary phase. Ion-exchange applications were also possible upon modification of the immobilised AuNPs with sulphonate groups, which was demonstrated by the retention of Ca2+ ions. PAA-grafted SiNPs were immobilised on the surface of a quaternary ammonium-functionalised polymer monolith and the anion-exchange properties of the stationary phase demonstrated by separating a mixture of Cl- and H2PO4 -. The immobilisation of negatively charged PAA-grafted SiNPs however, lead to the formation of a cation-exchange stationary phase as confirmed by the retention of Ca2+ and Mg2+.
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