Characterization of tubular zeolite NaA membranes prepared from clear solutions by FTIR-ATR, GIXRD and FIB-TEM-SEM

Zeolite NaA (LTA) membranes supported by a porous alumina tube were hydrothermally synthesized under four clear solution synthesis conditions which are composed of seeding and regrowth from the clear solution. The clear solution method produced various LTA membrane surface morphologies and pervaporation (PV) dehydration performances of ethanol/water mixture. The aim of this paper is to present a novel and comprehensive structural characterization study of the tubular LTA membranes prepared from clear solutions. The four tubular LTA membranes were characterized by Fourier transform infrared attenuated total reflectance method (FTIR-ATR), grazing incidence 2θ scan X-ray diffraction analysis (GIXRD) and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with a focused ion beam (FIB) cross-section specimen preparation technique. By combining the four LTA membranes and the three characterization methods, amorphous-like adhered materials on membrane surface, depth profile of preferred orientation and an intermediate layer including many voids between columnar LTA layer and alumina support were presented. Furthermore, those relations with the PV dehydration performance were discussed. The structural information presented here pointed out a diversity and complexity of the LTA membranes prepared from clear solution. The present characterization study provides a novel information to discuss a relationship between fine structure of the membrane and ethanol/water separation mechanism.