A structural study into the boundary surface and associated curvature of three-dimensional mesoporous silica crystals

Abstract: Since their first discovery in the early 1990s, mesoporous crystals (MCs) have fascinated researchers in various fields because of their interesting structures and their potential uses. Electron crystallography (EC) gives the direct three-dimensional (3D) realization of a crystal as a reconstructed electrostatic potential map (EPM). Various 3D-EPMs of silica MCs with cubic symmetry have been previously obtained by EC.The main task in this thesis is the development of structural analyses focusing on MCs and thus to evaluate the properties of periodic mesopores within EC data. How MC structures can be described and solved by EC is discussed in terms of the interpretation of the reconstructed 3D-EPM. Assuming a regime of an equi-potential surface (EPS), a structural description for MCs is suggested as a surface that optimizes the curvature elasticity evaluated on every EPS. The geometric properties of cubic MCs so far already reconstructed by EC, are then analyzed on the basis of the optimized EPSs. The analysis provides the property of the mesopores independently from gas adsorption measurements. A large cage-like MC is further studied by in-situ synchrotron powder X-ray diffraction to help understand the nitrogen adsorption process onto the mesopore wall.As an additional study, a silica MC showing its crystal morphologies of icosahedron, decahedron, etc. is studied. Results by EC suggest that the spherical uni-modal cages form the cubic close packing. The morphologies observed are explained in terms of the multiple twinning, which is analogous to metal nanoparticles. The occurrence of multiple twinning in MCs is discussed in light of the synthesis condition and the shape of micelles.