A Computational and Atomic Force Microscopy Study on the Crystallisation of Disordered Zeolites

Abstract

Zeolites are porous, crystalline aluminosilicates which find commercial applications as catalysts and adsorbents. The presence of defects in these materials can interrupt porosity, thus influencing the diffusional and catalytic properties of these materials. Through understanding the distribution and formation of defects in these materials, there is potential to tailor experimental conditions and obtain forms with improved properties. This in turn requires methods for in-depth study of crystal growth processes occurring at the nanoscale. Previously, work in the University of Manchester's Centre for Nanoporous Materials has resulted in the development of the software CrystalGrower, which simulates crystal growth, outputting a predicted crystal habit and nanoscale surface topology. The software has been applied to a vast array of crystalline materials, including molecular crystals, zeolites and ionic crystals, but so far, simulations have been limited to materials which are defect free. This work describes the adaptation of the existing CrystalGrower software package to allow the crystallisation of materials with high levels of stacking faults to be simulated. The design and implementation of a graphical user interface for CrystalGrower is also described. In this work, the adapted software is applied to two zeolitic materials which possess high levels of structural disorder, namely zeolite beta and erionite-offretite intergrowths. Both materials are synthesised and characterised in order to image any surface features which may arise as a consequence of structural disorder. For erionite-offretite intergrowths, four samples are imaged using atomic force microscopy, revealing heavy faulting on some crystal facets. Crystallisation simulations for both erionite-offretite intergrowths and zeolite beta replicate surface faulting, and reproduce the surface structure and crystal habit to good effect. There is potential for CrystalGrower to be used in a wide range of fields and applications for the simulation of crystal habit and surface topology. By adapting the simulation software to allow for modelling of disordered materials, the results described here lay the groundwork for applying the software to a wider range of problems and materials.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Anderson (Supervisor) & Martin Attfield (Supervisor)