Novel Periodic Mesoporous Silicas: Synthesis, Structure and Properties

Abstract

Hybrid organic-inorganic mesoporous silicas represent an important class of materials with a wide variety of potential applications due to their physical robustness and the chemical diversity. This work involves incorporating organic groups into mesoporous materials for the purpose of adding a useful functionality, and their characterization to gain more knowledge regarding the formation of the silicate network at different levels. A novel Gemini surfactant with a rigid organic spacer is synthesized and used to produce cubic MCM-48 silica mesophase by temperature induced phase transition. The transformation is studied under various pH and temperature conditions to understand the dynamics of the phase curvature change (Chapter 3). Further, to investigate the effect of high density of surface grafted amino groups, post-synthesis modification of grafted 3-halopropylsilane with amine is employed to generate long chain amines on the surface of pore-expanded MCM-41 silica (PE-MCM-41). The performance of such materials for CO2 adsorption is discussed in relation to the structural differences caused by the choice of the synthetic method (Chapter 4). For the first time, a bridged photoresponsive arylorganosilane 1,4'-bis(triethoxysilyl)azobenzene is used as a precursor for the synthesis of pure azobenzene-bridged organosilica. Reversible photoisomerization of the azobenzene moieties integrated in mesoporous organosilica network is demonstrated indicating that the organosilica remains flexible enough to undergo such contractions under UV irradiation (Chapter 5). Lastly, periodic mesoporous organosilica is synthesized using two silsesquioxane precursors containing bulky dimethylphenyl and a smaller ethylene spacer, and the 2D 29Si-1H heteronuclear correlation technique is employed to specifically address the issue of structural homogeneity in the bifunctional PMO (Chapter 6).