Heterogeneous nucleation from colloidal precursor towards the growth of Beta zeolite membrane

Zeolites are stable under industrial operating condition of high temperature and pressure as they are crystalline with three-dimensional aluminosilicate framework that allows selective molecules to pass through their uniformly sized pores and therefore, they are ideal material for energy-efficient separation applications in harsh industrial conditions. In spite of their abundance availability in nature and synthesis of different types of framework structures, complexity of nucleation and growth mechanism limits the rational design of zeolite synthesis. The initial precursors can be monomers, nanoparticles, gel and crystals. The precursors are influential factors for optimal design of zeolite membrane that may allow for more energy-efficient separation processes than the thermally driven separation techniques. The present SANS study probed the underlying functional diversity of precursor nanoparticle depending on form and structure factor towards the crystal growth for Beta zeolite membrane formation. The data clearly distinguished nanoscale structural arrangements of the synthesis solution before the hydrothermal heat treatment, during the induction and nucleation periods. Initially, shells consisting of organic template, reactive Al species and other dissolved ions surrounded the colloidal silica nanoparticles. Some of the silica cores sizes reduced while the shell thicknesses increased resulting to a heterogeneous colloidal solution system consisting of particles of different core-shell dimensions. The heterogeneous nucleation system found by the SANS studies agreed with the XRD data. (author)