Synergistic dual-polymer blend membranes with molecularly mixed macrocyclic cavitands for efficient pre-combustion CO2 capture

•Synergistic polymer blends as the matrix with better gas transport properties.•Systematic investigation of molecular mixing in a three-component nanocomposite.•Molecularly mixed composite membranes with single phase morphologies.•The membranes with enhanced H2/CO2 molecular sieving ability.•The performance of H2/CO2 separation can surpass the upper bound.