Decoupled assembly of ultrathin, highly loaded mixed-matrix membranes for gas separations

Mixed-matrix membranes (MMMs) offer a promising route to efficient gas separation by synergizing the superior transport properties and stability of porous fillers with the scalability of polymeric matrix. However, fabricating ultrathin, high-loading MMMs remains a significant challenge, as conventional solution processing inevitably leads to filler agglomeration. Here, we report a decoupled assembly strategy to fabricate ultrathin, highly loaded MMMs by separating membrane formation into two distinct stages: filler monolayer assembly and subsequent matrix electropolymerization. This approach enables the formation of ordered, close-packed nanoparticle monolayers, facilitating the attainment of ultra-high filler loadings (>60 wt%) in the final membrane. Using metal-organic frameworks (MOF-801 and MOF-808) as fillers and a conjugated microporous polymer (CMP) as the matrix, we constructed robust MMMs with thicknesses of 390 nm and 550 nm, respectively. Applied to CO₂/CH₄ separation, the resulting membranes exhibited a 12-fold increase in CO₂ permeance (from 26 to 313 GPU) and a 120% enhancement in selectivity compared to the pristine polymer matrix.