Preparation of self-supporting NaA zeolite membranes using geopolymers

• The geopolymer was transformed into NaA zeolite by hydrothermal process.
• Relevant geopolymer could fabricate high-strength self-supporting zeolite membrane.
• The geopolymer micropore changed from 0 to 0.049 cc/g after hydrothermal process.
• The zeolite membrane possesses 99.5% Na+ rejection and 3.86 kg m−2 h−1 flux @90 °C.
• The desalination mechanisms are size exclusion, ion repulsion and adsorption.

In this paper, we fabricated a high-strength self-supporting NaA zeolite membrane from a geopolymer membrane through in situ hydrothermal transformation processing. The surface and inner amorphous geopolymer membrane was converted into the zeolite crystal phase after the hydrothermal process was applied, and the volume of the micropores of the hydrothermal sample changed from 0 to 0.049 cc/g after the hydrothermal process. We preliminarily studied the practicability and preparation of a self-supporting NaA zeolite membrane with a high compressive strength (approximately 57 MPa) for desalination through a pervaporation process. The results showed that the self-supporting NaA zeolite membranes exhibited improved high sodium ion rejection (approximately 99.5%) as the thickness gradually increased to a certain value (about 9.4 mm), and the flux (0.42 kg m−2 h−1 at 25 °C) gradually increased to 3.86 kg m−2 h−1 as the pervaporation temperature increased to 90 °C.