Application of liquid state nuclear magnetic resonance techniques for the study of porous materials

Abstract

This thesis describes the work undertaken to develop and apply the liquid state NMR techniques of cryoporometry and diffusometry for the study of porous materials. Solid/liquid interfaces are at the heart of modern applied science. Understanding liquid dynamics, when located within a confining environment, such as a pore, is of utmost importance when expanding knowledge in this field. Thereare many novel solid/liquid systems that have yet to be studied; NMR offers the opportunity to probe these systems in their working states.The technique of cryoporometry was initially implemented using a series of highly ordered controlled pore glasses with varying pore diameters. This preliminary work built the foundations for further application. However, one key drawback in the thermoporometry area is the lack of consensus on the two key parameters for converting melting point data into pore size distributions. This work offers values for both. NMR cryoporometry is also limited by the lack of suitable liquids that can not only probe a wide range of pore size, but can also match the chemistry of the solid being studied. Two novel cryoporometric liquids are introduced here; t-butanol and menthol, with the aim of reducing the significance of this limitation. The suitability of these liquids is then investigated further by analysing the change in porosity, with swelling, of polymer systems.The physical and chemical behaviour of a confined liquid is often rate limiting in catalytic science.Diffusion NMR has been utilized for the first time to distinguish whether in-pore diffusion, or diffusion from the bulk media into a pore network, was the rate-limiting step for catalytic esterification over sulfonic acid silica analogues. Rate of reaction and liquid diffusion were found to be uncorrelated, discounting the former hypothesis.NMR spectrometers have near ubiquitous use in materials research. The work detailed here should offer to make NMR cryoporometry a more widely used technique in the analysis of porous materials. The future design of porous materials, such as the optimisation of silica architectures for catalytic activities,will also be aided by the physiochemical insights obtained here from diffusion NMR