Innovative layer by layer and continuous growth methods for synthesis of ZIF-8 membrane on porous polymeric support using poly(ether-block-amide) as structure directing agent for gas separation

• Pebax 1657 was utilized as structure directing agent in fabrication of ZIF-8 membrane.
• Layer-by-layer and continues growth methods were used in ZIF-8 membrane preparation.
• Thicker selective layers of membranes lead to more selectivities and less permeances.
• Continuous growth method of synthesis lead to formation of more selective membranes.
• PDMS coating was very effective in enhancing ideal and real gas selectivities.

Poly(ether-bock-amide) (Pebax grade 1657) was utilized as structure directing agent for fabrication of ZIF-8 membranes on polyphenylsulfone (PPSU) by layer-by-layer and continuous methods of growth. N2 adsorption, SEM, XRD, TGA and FTIR tests were applied to characterize the synthesized membranes. Polydimethylsiloxane (PDMS) was utilized to cover the possible surface defects of ZIF-8 membranes by dip coating method. The ideal performances of uncoated and coated synthesized ZIF-8 membranes were evaluated in separations of CO2/CH4, CO2/N2, H2/CH4 and H2/N2. The results showed that: 1- The coating of membranes by PDMS significantly enhanced the selectivity and decreased the permeance in almost all separation tests. 2- Higher numbers of cycles of solution changing in layer-by-layer method resulted in less permeable and more selective membranes. 3- Continuous growth method with PDMS coating lead to observation of maximum separation factors in many permeation tests: In permeances of 2.5 × 10−7 mol m−2 s−2 Pa−1 for H2 and 1.9 × 10−7 mol m−2 s−2 Pa−1 for CH4, exceptional ideal selectivities of 22.8, 20.8, 17.3 and 15.8 were obtained for H2/CH4, H2/N2, CO2/CH4 and CO2/N2, respectively.

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