Preparation and gas separation performance of seeding-free aqueous synthesis ZIF-8 membrane by homologous-like ligands method

Due to the poor heterogeneous nucleation properties of MOFs crystal on ceramic substrates resulting from the absence of interaction of MOFs with support substrate surface, it is usually difficult to prepare well-intergrown MOF membranes on substrate by simple in situ growth. In this work, a novel synthesis strategy was used to prepare defect-free ZIF-8 membranes on α-Al2O3 supports by depositing gold particles modified with 2-mercaptoimidazole which creates pseudo-surfaces to bridge the metal centers with support. The end groups of the 2-mercaptoimidazole guides the heterogeneous nuclei to the support surface as homologous-like ligands. Furthermore, investigation of the metal sources revealed that the ZIF-8 membranes prepared with Zn(OAc)2 as the zinc source possessed more continuous and well-intergrown ZIF-8 membranes with a thickness of about 1 μm compared to other zinc sources. The results of gas separation performance show that the optimized ZIF-8 membranes possess high hydrogen permeance and thermal stability. The gas separation selectivity for binary H2/CH4 mixture reached 20.8 at 150 °C and 1 bar, with a high H2 permeance of about 6.15 × 10−7 mol m−2 s−1Pa−1, which is promising for hydrogen separation and purification. Moreover, free-organic solvents and room temperature growth by our strategy dramatically reduces the difficulty of preparation and environmental destruction, thus offering a new avenue to prepare MOFs membrane with good separation performance.