Ionothermal synthesis of a CHA-type aluminophosphate molecular sieve membrane and its formation mechanism

A gas permeable CHA-type aluminophosphate molecular sieve membrane was ionothermally synthesized on a porous delta-alumina substrate through the so-called substrate surface conversion method. The synthetic conditions for this specific membrane were optimized. The temperature, time and the amounts of H3PO4 and HF in the initial synthesis solution were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation were performed to characterize the entire formation process for the CHA-type molecular sieve membrane. A formation mechanism of the substrate surface conversion method was proposed. The transformation of the gel layer to the CHA membrane via a solid transformation mechanism was suggested. (C) 2015 Elsevier Inc. All rights reserved.