Crystal Growth on Complex Framework Structures

UoM administered thesis: Phd

  • Authors:
  • Nani Farida

Abstract

Newly discovered zeolite, IM-17 (UOV), with a complex structure directed by decamethonium dications, is fascinating owing to its very large unit cell (12.68 Å × 22.22 Å × 39.06 Å). This poses some interesting questions in crystal growth as to how the crystal memory is propagated over such a large distance. To investigate how such a large unit cell forms and allows stacking layers is the aim of this research. The investigation demands a powerful tool to study nanoscopic details, which can be reached employing Atomic Force Microscopy (AFM). Here we report results of our work on four crystals having complex structures: IM-17, DAF-1 (DFO), zeolite Rho (RHO) and NU-87 (NES). The outcomes are also compared to the crystal models simulated using CrystalGrower program. The PXRD technique was used to confirm the as-prepared crystal structures. From the SEM micrographs, the crystal morphologies were revealed. The AFM exhibits the presence of terraces on all of the crystal surfaces. Cross-section and histogram height measurements of the terraces correspond to the growth steps of the materials. The IM-17 crystal showed two mechanisms of growth: layer-by-layer on both (100) and (013) facets and spiral growth on the (100) facet. Layer-by-layer terraces dissolved in patches in alkaline solution while the spiral layer retreated during the dissolution. Meanwhile, the terraces on DAF-1 crystal surfaces demonstrated patches dissolution in solution combination of decamethonium hydroxide and phosphoric acid. Interestingly, these layers maintained their terrace positions throughout the dissolution time. Such phenomenon is called 'surface thinning'. Zeolite Rho possesses the simplest structure among the Rho-family zeolites. It has twelve {110} facets, on which the terraces grow with the same shape and orientation as the facet. The height of the small terraces did not decrease during the terrace retreat in alkaline solution until the critical surface area to maintain the structure together were achieved, after which the terrace height started to decrease. The NU-87 crystal was very resilient to the alkaline and acidic solution attack. In addition, the very thin crystal morphology of the NU-87 disadvantaged the crystal etching in basic solution. All crystals under study and several dissolution processes were also simulated using CrystalGrower software based on the natural tiles. The simulated crystals were in a good agreement with the experimental results. The crystal models also proved very important to understand the crystal habit and their structure which cannot be solved in the laboratory.

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Original languageEnglish
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Award date1 Aug 2019