Colloidal zeolites and zeolite membranes

The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness. In order to optimise this process, an understanding of the nature of the sols and an insight into the structure of the consolidated layer so formed, is required. Such studies are illustrated here with silicalite and zeolite A. The formation and growth of silicalite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on sols at progressively higher concentrations have provided details of the colloid interactions which lead to zeolite gel-layer structures which are uniform and free of defects. Several techniques (XRD, small angle X-ray scattering (SAXS), and nitrogen adsorption isotherms) have also been used to characterize colloidal species extracted by ultracentrifugation at progressive stages from solutions during the hydrothermal synthesis of zeolite LTA.