Room-temperature in situ fabrication of ultrathin undulating layered hydroxide salt membranes for efficient H2/CO2 separation

Abstract

Two-dimensional (2D) materials have demonstrated their superiorities as molecular sieve membranes for strategic gas separations. The promotion of these 2D membranes is confronted with great challenges such as elaborate fabrication procedures and expensive raw materials. Layered hydroxide salts (LHSs) are a kind of lamellar material involving economical ingredients and are quite easy-to-fabricate. However, they have yet to be developed into gas separation membranes and their separation potential has not been investigated, despite their merits. Here, we report the successful fabrication of ultrathin Zn5(OH)8(NO3)2·2H2O membranes by using a rapid and facile in situ growth strategy at room temperature. By virtue of the few-layered membrane thickness, the obtained membranes exhibited intriguing surface undulations, which endowed the membranes with extremely tortuous interlayer channels and therefore an auspicious molecular sieving ability. Consequently, these membranes showed an optimal H2/CO2 mixture separation selectivity of 792 ± 38 and a remarkable H2 permeance of 1607 ± 99 GPU. Moreover, with a demonstration of a gentle framework dehydration, the molecular sieving capacity of the LHS membrane was further sharpened at 150 °C owing to the narrowed interlayer channels. This work introduced a low-cost 2D membrane and manifested the advantages of fabricating few-layered 2D membranes, opening a new avenue for membrane future scale-up.