Metal‐doped Organosilica Membranes for Steam/Gas Separation Applications: From Permselectivity and Stability Perspectives

This study examines the effects of Al-, Ni-, and Co-doping on the steam/gas separation performance and hydrothermal stability of bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes. Doped and undoped powders and membranes were fabricated via a sol-gel route and characterized by X-ray diffraction (XRD), gas and vapor adsorption, solid-state NMR, and single-gas permeation. All metal dopants enhanced the hydrophilicity of organosilica, providing a "blocking effect" that suppressed non-condensable gas permeation and improved steam permselectivity, with the order Al > Ni > Co > undoped. Metal doping was also found to catalyze the cleavage of Si-C bonds, in the same order. Long-term testing under high-humidity (150 °C, 200 kPa-a, RH = 0.42) revealed that membrane performance stabilized within several 100 h and the degree of steam permeance loss correlated with the extent of Si-C bond cleavage. Contrary to the commonly assumed synergistic effect between metal doping and organosilica on hydrothermal stability, our results indicate that excessive Si-C cleavage can undermine hydrothermal stability. Among the metals tested, Co-doping achieved the best long-term steam permselectivity by balancing moderate hydrophilicity improvement with minimal Si-C cleavage. These findings provide new insights into the design of durable metal-doped organosilica membranes for steam/gas separation under severe conditions.