Structural and Morphological Studies of Mesoporous Crystals

Sammanfattning: Mesoporous silica and carbon have been synthesised and characterised by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM) and nitrogen adsorption. Surface structure, size and shape (morphology) of particles have been of special interest in this work. These parameters are of importance in understanding the growth mechanism and structural characteristics of mesoporous materials overall, which has been the main aim of this thesis.The novel synthetic system involving preparation of AMS (anionic surfactant-templated silica) crystals, where the non-toxic N-acyl-amino acids are used as surfactant together with a co-structure directing agent, was investigated in two different surfactant systems. Particle size and shape of AMS solids were controlled through the addition of a polymeric dispersant, which slowed down the system dynamics. However, the response for the two synthetic systems investigated, proved to be different. Nanoparticles of cage-type cubic Fd-3m crystals were obtained in one system, whereas facetted particles formed in a near-to-equilibrium growth in the bicontinuous cubic Ia-3d case. The surface fine structure of mesoporous silica was observed by high resolution SEM, leading to an understanding of the pore accessibility at the particle surface of SBA-15 silica. Furthermore, discrepancies in the XRD patterns of mesoporous tube-type carbon CMK-5 with different pore diameters were observed. XRD patterns displaying accidental extinction of the 10 reflection were observed in CMK-5 samples prepared with the widest pore diameter. An analytical approach was formulated in order to simulate the variation of XRD intensity for carbon crystals with p6mm symmetry. TEM observations of inner and outer diameter of the carbon tubes were used to interpret the diminishing of certain reflections and we observed good agreement between experimental observations and our calculations.