Niet-standaard Karakterisatietechnieken voor Zeolieten: van formatie tot applicatie

At present, more than 230 different zeolite topologies have been characterised, each exhibiting different properties which lead to very specific applications. Due to the limited understanding of zeolite crystallisation, zeolite synthesis is arguably still more of an art than a science, with trial and error being one of the main strategies for discovery of new zeolites. A thorough understanding of zeolite formation is essential for unlocking their full potential: rational zeolite design. Since the early stages of zeolite formation strongly depend on convection and thus on gravity, dedicated hardware has been developed for microgravity experiments on board the International Space Station in order to shed more light on the underlying formation mechanism and the governing kinetics. Given the limited number of experimental techniques available for in situ investigation of zeolite formation, the potential of electrochemical impedance spectroscopy (EIS) to complement commonly used diagnostics has been explored. EIS allows to access multiple aspects of the precursor solution simultaneously by a relatively quick and simple in situ impedance measurement. Moreover, EIS firstly managed to observe the chemical exchange between oligomers and nano-aggregates during zeolite synthesis. This increased understanding of zeolite formation can be exploited in diverse industrial applications. Regioselectively breaking the interlayer bonds in a three-dimensional UTL crystal yields ultrathin zeolite nanosheets that overcome the typical diffusion limitations encountered in many industrial applications. An improved three-step process has been designed for the production of mixed-matrix membranes in which UTL layers are delaminated by extrusion in a polyethylene matrix and subsequently aligned by biaxial squeeze deformation. The mild processing conditions and the variation of the strain during the squeeze deformation additionally allow a precise control over the size and alignment of the zeolite layers. The result is a porous matrix containing well-aligned UTL sheets with aspect ratios exceeding the state of the art by an order of magnitude. This makes the UTL membranes, in combination with EIS or ellipsometry, a very interesting candidate for e.g. the development of more sensitive and faster-responding gas sensors.nrpages: 178status: publishe