Electron microscopy of crystalline solids and non-classical crystal growth

Abstract

This project concerns the non-classical crystal growth of various porous and non-porous materials. In order to determine their crystal growth mechanism, the reaction was stopped at several different reaction times with the size, morphology, crystal structure and orientation of the particles analysed using scanning electron microscopy and high resolution transmission electron microscopy as the principal characterisation techniques. Other techniques used include X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron diffraction and thermal gravimetric analysis. Selected biomimetic systems include the early stage crystal growth of ZnO/gelatin composite twin-crystals and the time dependent microstructural evolution of CaCO₃/gelatin composite particles from spherulites into rods. Further investigations of the role of gelatin molecules were carried out by replacing gelatin by gum arabic. Using knowledge gained from synthetic systems, several travertine crust specimens collected from hot springs were investigated to gain an insight into the possible formation mechanisms of naturally occurring biominerals. Another form of ZnO investigated was the formation of core-shell ZnO hexagonal microdisks and selective dissolution of their core to form microstadiums followed by the selective growth of nanorods and nanocones onto the columnar surfaces of the microstadiums to generate branched-microstadiums. The formation mechanism of ultrasonically prepared BiOBr displaying a flower-like architecture was investigated. These BiOBr assemblies are found to exhibit excellent photocatalytic activity and stability during the photodegradation of Rh.B under visible-light irradiation. Finally mesoporous silicate plates displaying a single crystal-like property were re-investigated to clarify whether the previously reported mesoporous silicate plates exhibiting a single crystalline property were one-phase materials or a composite of non-crystalline mesoporous silicate and crystalline zeolite.