Studying the synthesis and reactivity of crystalline materials using in situ X-ray diffraction
Keywords: solid-state
X-ray diffraction
in situ
inorganic

The use of in situ X-ray diffraction (XRD) to investigate reactions involving crystalline materials is the focus of the work described in this thesis. The development of procedures for probing chemical reactions in situ, and the application of this technique for studying in detail the mechanisms and kinetics of solid-state processes, is reported.
The information in Chapter One provides a background to the in situ study of chemical reactions, with specific emphasis on the application of X-ray diffraction. Three distinct families of inorganic materials are introduced, including layered double hydroxides, Aurivillius phases, and metal-organic frameworks, and the relevance of each in contemporary technologies, is discussed.
Chapter Two incorporates an account of the design, construction, and development of a chemical reaction furnace, the Oxford-Diamond In Situ Cell (ODISC), for the in situ study of solid-state reactions. The capabilities of this apparatus are discussed, including the efficient and controlled heating of samples to temperatures in excess of 1000 °C, optional sample stirring, and successful incorporation of a range of different sample vessels. Details of the implementation and optimisation of this equipment for use at Beamline I12 at the Diamond Light Source are provided.
The synthesis and characterisation of a new series of ternary layered double hydroxides (LDHs) with general formula [MxM’2–xAl8(OH)24](NO3)4•yH2O (M, M’ = Zn, Ni or Co), is detailed in Chapter 3. It was discovered that these materials exhibit finely tuneable cation ratios in the intralayer regions. A study of the intercalation chemistry of this family is reported, including in situ energy-dispersive and angular-dispersive X-ray diffraction experiments. The chapter concludes with details of an in situ XRD investigation into the synthesis of these materials via direct reaction of metal salts with Al(OH)3, which was observed to proceed in four stages.
Chapter Four is concerned with the molten salt synthesis and characterisation of novel cation-doped compounds with the Aurivillius structure. The limited extent of substitution on the B-sites of the parent Bi5Ti3FeO15 material was observed to be highly dependent on the nature of the di- or tri-valent substituent. The impact of varying reaction conditions, such as dwell duration and nature of the molten salt, upon pure product formation is described. A comprehensive in situ XRD investigation into the molten salt synthesis of a novel doped Aurivillius phase is detailed in Chapter Five. A discussion of the synthesis mechanism, in addition to a description of the role of the molten salt in product formation, is provided.
A brief in situ XRD study of the mechanism and kinetics of crystallisation of metal-organic frameworks (MOFs) is detailed in Chapter Six. The use of ion-exchanged polymer resin beads to direct the synthesis of MOFs is probed in real time, and the route to formation is compared to that for the conventional solvothermal technique.
Experimental procedures pertaining to all of the above chapters are provided in Chapter Seven. Supplementary data are included in the Appendices.