Ultrathin gutter layer for high-performance thin-film composite membranes for CO2 separation

Ultrathin film composite (TFC) membranes with selective layers less than 100 nm thick are highly desired to maximize the permeance of gas separation membranes for high energy efficiency. For membranes with ultrathin selective layers, a gutter layer is usually required to prevent pore penetration in the selective layers. Also, according to a recent model, the introduction of a gutter layer strongly improves TFC membrane performance by increasing the overall membrane performance up to an order of magnitude. Unfortunately, this improvement comes with an undesired decrease in selectivity unless the gutter layer is properly designed. This study found that the gutter layer permeability should be five- to tenfold that of the selective layer to minimize the decrease in selectivity. However, the most commonly used material for the gutter layer, polydimethylsiloxane, does not meet the requirements for high-performance membrane materials. Thus, here we report a gutter material with CO2 permeance sixfold that of polydimethylsiloxane, and prepare a TFC membrane with ultrathin gutter (75 nm) and selective layers (70 nm) for CO2/N2 separation. This work represents a guideline for developing next-generation TFC membranes and provides a comprehensive understanding of the impact of the gutter layer.