In-situ cross-linking and shear-driven coating enable defect-free tubular ZIF-8 membranes toward efficient C3H6/C3H8 separation

Abstract

Eliminating potential defects is crucial for making tubular ZIF-8 (T-ZIF-8) membranes widely adopted in chemical process industries. However, the geometric restriction of the inner T-ZIF-8 membrane and the high viscosity of cross-linked PDMS solution pose challenges in uniform polymer deposition and interfacial adhesion that traditional dip-coating methods may not effectively address. Herein, we propose an in-situ cross-linking and rolling coating (ISCL&RC) strategy to overcome these challenges. During the rolling coating process, the PDMS solution gradually solidifies on the surface of the T-ZIF-8 membrane under the shear force induced by gravity, forming a PDMS coating with uniform thickness. The in-situ cross-linking allows the low-viscosity PDMS solution to adequately infiltrate the surface of the T-ZIF-8 membrane, forming a desirable interface. Compared with the pristine T-ZIF-8 membrane, the T-ZIF-8/PDMS membrane demonstrates remarkable improvement in C₃H₆/C₃H₈ separation selectivity (2.6–18.5 times higher than the unmodified membrane), while the C₃H₆ permeance remains nearly unchanged. Notably, the T-ZIF-8/PDMS membrane sustains coating integrity under high pressure and industrial raw gas for 780 h without exhibiting bubbling or delamination. This work establishes a paradigm for defect engineering in confined tubular membrane systems, effectively bridging the gap between laboratory-scale synthesis and industrial module fabrication.