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

• A gas permeable CHA-type AlPO4 membrane was ionothermally synthesized.
• The δ-alumina substrate acted as both support and Al source.
• The entire formation process of the CHA membrane was characterized in detail.
• A formation mechanism of the CHA membrane was proposed.

A gas permeable CHA-type aluminophosphate molecular sieve membrane was ionothermally synthesized on a porous δ-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.

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