Aqueous solution synthesis of ZIF-8 films on a porous nylon substrate by contra-diffusion method

• ZIF-8 films are prepared on flexible porous nylon membrane in an aqueous solution by contra-diffusion method.
• A stoichiometric ratio of Zn2+ and 2-methylimidazole (1:2) is used.
• Ammonium hydroxide in the aqueous solution promotes the formation of ZIF-8 films.
• Continuous and compact ZIF-8 films are obtained.

ZIF-8 films were prepared on both sides of nylon membrane in aqueous solutions using a stoichiometric ratio of Zn2+ and 2-methylimidazole (hmim) by a contra-diffusion method. Both ammonium hydroxide solution and porous nylon membrane play a crucial role in promoting ZIF-8 crystallization and film formation. Ammonium hydroxide solution added in the hmim solution deprotonates hmim, and the nylon membrane separates the Zn2+ and hmim aqueous solutions with different diffusion rates through its pores, leading to appropriate concentration gradients of hmim and zinc nitrate required for ZIF-8 nucleation and growth. The synthesis conditions were systematically investigated. ZIF-8 films prepared with a Zn2+:hmim:NH4+ molar ratio of 1:2:32 at room temperature for 24 h exhibited an intergrown ZIF-8 layer on hmim side with a thickness of ca. 2.5 μm, and gas permeation confirmed the film was continuous and compact with a H2/N2 ideal selectivity of 4.6.

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