An integrated materials approach to ultrapermeable and ultraselective CO2 polymer membranes

Advances in membrane technologies that combine greatly improved carbon dioxide (CO2) separation efficacy with low costs, facile fabrication, feasible upscaling, and mechanical robustness are needed to help mitigate global climate change. We introduce a hybrid-integrated membrane strategy wherein a high-permeability thin film is chemically functionalized with a patchy CO2-philic grafted chain surface layer. A high-solubility mechanism enriches the concentration of CO2 in the surface layer hydrated by water vapor naturally present in target gas streams, followed by fast CO2 transport through a highly permeable (but low-selectivity) polymer substrate. Analytical methods confirm the existence of an amine surface layer. Integrated multilayer membranes prepared in this way are not diffusion limited and retain much of their high CO2 permeability, and their CO2 selectivity is concurrently increased in some cases by more than ~150-fold. Description Pulling carbon dioxide out of the air A challenge in the design of polymeric membranes for gas separation is the tradeoff between permeability, or how fast gases can flow through the membrane, and selectivity, the ability to separate one gas from another. In general, the more selective the membrane, the more slowly gases can flow through it. Sandru et al. overcame this tradeoff through a layered design. They used a bottom layer of porous polyacrylonitrile that acts as a physical support for the middle layer of either elastomer-like polydimethylsiloxane or glassy-type polytetrafluoroethylene. The authors then grafted a patchy layer of polyvinylamine, which selectively attracts carbon dioxide, thus pulling it into the membrane and leading to much higher separation from nitrogen. —MSL A patchy surface layer of polyvinylamine enhances the separation of carbon dioxide from nitrogen.