Novel hybrid inorganic-organic materials : synthesis and advanced physico-chemical characterization of Periodic Mesoporous Organosilicas.
19 January 2015
Campus Drie Eiken, Promotiezaal Q.002 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk
Organization / co-organization:
Department of Chemistry
Pegie Cool & Sabine Van Doorslaer
PhD defense of Feng Lin - Department of Chemistry
The content of this thesis is mainly focused on the synthesis and characterization of ethane-bridged and benzene-bridged PMO materials. The aims of this study are to investigate the formation mechanism of PMOs and have a better control of the surface, structural and adsorption properties of the resulting materials. In addition, the incorporation of transition-metal ions into PMO materials is also a very important aspect of this work. Here, focus is put on the incorporation of copper ions and vanadium ions, which might offer special redox properties to the PMOs. The different aspects studied in this thesis are decribed from chapter 3 to 7.
In chapter 3, the effects of the synthesis conditions on the properties of ethane-bridged PMOs are studied by means of spin-probe EPR spectroscopy complemented with standard characterization techniques for porous materials. On the one hand, by dissolving spin probes into the synthesis mixture, these probes function as EPR spy molecules that allow monitoring the formation mechanism of the PMO materials. On the other hand, by absorbing the spin probes onto the surface of the surfactant-free PMO materials, the analysis of the EPR spectra allows the extraction of structural, mobility and polarity information of the spin probes, which further reflects the pore size, the accessibility, as well as the surface properties of the materials. In chapter 4, the adsorption of nitroxide radicals on three types of benzene-bridged PMOs with varying pore size and wall characteristics is monitored by spin-probe EPR. The study shows that the benzene-bridged PMO materials with amorphous walls allow an overall better adsorption of the spin probes than the one with crystalline walls, independent of the nature of the spin probe. Chapter 5 describes a facile meosphase control of ethane-bridged PMOs under basic conditions. A p6mm to mesophase evolution can be achieved simply by varying the counterions of the synthetic system. Furthermore, it is found that the hydrolysis and condensation rate of the organosilica precursor also plays a role in influencing the mesostructure of the final product. Chapter 6 studies the effects of the acidity and the addition of inorganic salt on the formation of the mesostructure of SBA-15-type ethane-bridged PMOs. Moreover, taking advantage of the mild acidic condition, vanadium-containing SBA-15-type ethane-bridged PMOs were successfully prepared through a direct synthesis approach. In chapter 7, copper-containing ethane-bridged PMO materials have been prepared through a direct-synthesis method at room temperature in the presence of CTABr as surfactant. The nature and distribution of the Cu2+ species in the materials were investigated through a wide number of physicochemical characterization techniques, including XRD, UV-Vis-Dr, TEM, CW-EPR and pulsed EPR spectroscopy.