Synthesis of highly c-oriented ZIF-69 membranes by secondary growth and their gas permeation properties

• Published in: Journal of membrane science Vol. 379; no. 1; pp. 46 - 51
• Main Authors: Liu, Yunyang, Zeng, Gaofeng, Pan, Yichang, Lai, Zhiping
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2011; Elsevier
• Subjects: ambient temperature; artificial membranes; carbon dioxide; Chemistry; Colloidal state and disperse state; Exact sciences and technology; Gas permeation; General and physical chemistry; Membranes; microstructure; Orientation; Porous materials; Secondary growth; Separation; sowing; X-ray diffraction; ZIF-69 membranes; ZIF-69 membranes; Separation; Orientation; Gas permeation; Secondary growth; Methane; Binary compound; Growth; In situ; Permeation; X ray diffraction; Porous material; Substrate; Synthesis; Preparation; Membrane; Microstructure; Alumina; Microcrystal; Room temperature
• ISSN: 0376-7388
• DOI: 10.1016/j.memsci.2011.05.041

► A secondary growth process was developed to synthesize highly c-oriented ZIF-69 membranes. ► Improved membrane microstructure, particularly degree of the membrane orientation was achieved. ► Improved membrane performances in both permeability and selectivity were achieved. ► A facile synthesis method was developed to make ZIF-69 particles down to sub-micrometers. A seeded growth procedure was successfully developed to synthesize highly c-oriented and well-intergrown zeolitic imidazolate framework-69 (ZIF-69) membranes on porous α-alumina substrates. The synthesis conditions were optimized both for seed preparation and for secondary growth. For seeding, a facile method was developed to prepare smaller and flat ZIF-69 microcrystals in order to make thin and c-oriented seed layers. While for secondary growth, a synthesis condition that favored the growth along the c-direction was chosen in order to form highly c-oriented ZIF-69 membranes after growth. As a result, the majority of ZIF-69 grains inside the membrane have their straight channels along the crystallographic c-axis aligned perpendicularly to the substrate surface. Such alignment was confirmed by both XRD and pole figure analysis. The mixture-gas separation studies that were carried out at room temperature and 1 atm gave separation factors of 6.3, 5.0, 4.6 for CO 2/N 2, CO 2/CO and CO 2/CH 4 respectively, and a permeance of ∼1.0 × 10 −7 mol m −2 s −1 Pa −1 for CO 2 in almost all mixtures. Both the separation factor and permeance were better than the performance of the ZIF-69 membranes prepared by the in situ solvothermal method due to improvement in the membrane microstructure by the seeded growth method.