Crystal Growth of Open-framework Materials

In 1756 the Swedish Mineralogist Axel Cronstedt (1722-1765), better known for his discovery of the element nickel, dug an unknown mineral out of the ground. In his laboratory he heated the rock and observed water boiling out. He thus named it "zeolite" from the Greek words zeo and lithos meaning boiling stone. Today, zeolites form a family of well over 100 different structures with one all important, common property - porosity. Imagine a zeolite as a sponge with myriad holes so small that they cannot be seen with the naked eye. The pores actually range in size from 3 to 13 Å or from three to thirteen tenths of a millionth of a millimetre!

Why is porosity so important? The answer is two-fold. First, the pore structure itself permits zeolites to be used as molecular sieves and to exert shape selectivity on chemical process occuring inside the structure. Second, the existence of pores generates a vast internal surface. Approximately 10 g of zeolite can have a surface area equivalent in size to a football pitch! Since, chemical reactions necessitate contact between reacting entities, large surface area is a very desirable property.

Zeolites are of great industrial importance owing to their surface-area enhanced catalytic and ion exchange capabilities. They are used as cracking catalysts for the production of petrol from petroleum and as water-softening additives in washing powder. They are thus of paramount importance to the automotive and fashion/clothing industries. As molecular sieves they are used in the gas separation industry. They are now produced on both the laboratory and industrial scale by hydrothermal synthesis. However, the crystallisation processes controlling the synthesis of the product that underpins these multibillion pound industries is poorly understood at present.

My research involves the use of an array of solid-state analytical techniques to better understand crystallisation in porous materials: atomic force microscopy (AFM); scanning and transmission electron microscopies (SEM and TEM); powder X-ray diffraction (XRD); magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); computer simulation.