Jonathan R. Agger

Growth models in microporous materials

Crystallisation pathways in framework materials, such as zeolites, have been monitored using a combination of atomic force microscopy, high-resolution electron microscopy and modelling. The principle conclusions of this study is that many open-framework crystals grow via a layer growth mechanism. The layers have a thickness which is related to the unit cell parameter in the direction of growth. The development of each layer can be sub-divided into a number of individual growth processes including nucleation of a new layer (or terrace), growth at edge sites and kink sites. Modelling of atomic force micrographs yields relative probabilities for these individual growth processes and reveals that growth at kink sites is favoured with nucleation of new terraces the slowest process. The layer mechanisms proposed explain the incorporation of defects in framework structures and further elucidate the role of structure directing agents.

Crystal growth in framework materials

Crystal-growth phenomena in open-framework microporous materials are explored using a combination of atomic force microscopy, high-resolution electron microscopy and modelling. Analogies are drawn between these open-framework systems and dense phase structures. In particular we discuss the role of organic structure-directing agents, commonly known as templates and suggest a new philosophy for predicting suitable molecules. We also discuss the role of defects in the crystallisation of open-framework materials and the effect of crystallisation processes on the incorporation of defects and intergrowths.

Fundamental Zeolite Crystal Growth Rates from Simulation of Atomic Force Micrographs

An accurate model of the surface growth of one of the most important industrial zeolites, zeolite A, has been created. Comparison of the simulation with experimental data in the form of atomic force micrographs highlights the non-diffusion-limited nature of zeolite growth and provides the first ever quantification of fundamental crystal growth processes in zeolites.

Cation sites in ETS-10: 23Na 3Q MAS NMR and lattice energy minimisation calculations

Second-order quadrupolar broadening has rendered the study of cation sites in microporous materials almost impossible until the recent advent of the 2D multiple-quantum NMR experiment. In conjunction with computer lattice-energy-minimisation calculations we employ this powerful new technique to study the complex microporous titanosilicate ETS-10 and titanium aluminosilicate ETAS-10 systems. Evidence is presented for five unique cation sites differing greatly in their behaviour towards dehydration. Strong evidence is also given for preferential potassium cation siting.

In situ atomic force microscopy of zeolite A dissolution.

In the present study, the {100} surface of zeolite A was exposed to a range of solutions and the response was monitored in real-time by means of atomic force microscopy (AFM). The zeolite dissolves by a well-defined layer process that is characterised by uncorrelated dissolution of units that are structurally unconnected and terrace retreat when building units are inter-connected. This process was observed to be coupled with the formation of nano-squares that are stabilized at the zeolite surface for a period before complete dissolution. Theoretical work suggests that three terminating structures are central to understanding the dissolution mechanism. Stripping the surface of the secondary building unit, the single 4-ring, is predicted to be a rate-determining step in dissolution, but this process occurs by removing monomeric rather than oligomeric units.

Atomic force microscopy study of the molecular sieve MnAPO-50

Atomic force microscopy (AFM) imaging of MnAPO-50 reveals multiply-nucleated, elliptical terraces, oriented in registry with the facet edges with step heights ranging from one to six template repeat distances on the [100] facets and terraces with step heights ranging from one to thirty three times the c unit cell parameter on the [001] facets.

Synthesis and characterisation of a microporous zirconium silicate with the structure of petarasite

The synthesis and structural characterisation of AV-3, a microporous sodium zirconium silicate with the structure of the mineral petarasite, are reported.

Modelling crystal growth in zeolite A

Abstract Zeolite A is one of most widely used and studied zeolites owing to its cation-exchange properties. Here, we present a computer program that simulates morphology as well as surface topology for zeolite A crystals. Results from simulations were compared with scanning electron microscopy and atomic force microscopy images on the {100}, {110} and {111} faces of synthetic crystals. This allowed to further refine the program by varying the relative attachment/detachment probabilities of individual growth sites.

02-O-05 - Atomic force microscopy (AFM) used to relate surface topography growth mechanisms in SSZ-42

Publisher Summary This chapter describes the atomic force microscopy (AFM) of the three faces of the microporous material SSZ-42. Interesting surface features have been observed on each face that is distinct and related to the structure of SSZ-42. These features have been used to determine the crystal growth mechanism of SSZ-42. This chapter describes a layer growth mechanism whereby the growth of crystals occurs at terrace sites and edges from nutrient in the solution and elucidates the templating mechanism.

3D computer simulation of zeolite A crystal growth

Abstract Atomic force microscopy (AFM) and recent developments in scanning electron microscopy (SEM) are helping improve our understanding of the surface of microporous materials. Computer simulation is an invaluable tool for probing chemical information from the images generated. Zeolites seem to grow via the deposition of layers. Nutrient presumably attaches until a minimum in surface energy, is reached at which point growth stops until nucleation of a fresh layer occurs. The height of these layers can always be related to some element of the zeolite structure Simulating crystal growth necessitates the definition of growth sites and corresponding nutrient attachment probabilities. Iteration of these probabilities to match simulation with experimental topography leads to values which reflect the surface chemistry occurring. This has been achieved successfully in two dimensions for zeolite A. Here we report the first ever three dimensional simulation of a growing zeolite. The simulation can currently generate zeolite A crystals up to 200 nm along each edge, corresponding, to 5 million array elements. The simulation can accurately mirror varying surface topographies and morphologies. Expression of facets, degree of terrace nucleation, terrace shape and behaviour upon coalescence can all be controlled based on choice of growth probabilities.