Complexation induced highly loaded mixed-matrix membranes for organic azeotropic separation

Abstract

Mixed matrix membranes (MMMs), consisting of inorganic fillers in a polymer matrix, have shown great potential for molecular separation. Prussian blue analogues (PBAs) nanomaterials featuring regular and straight nanochannels are promising nanoporous fillers. However, fabricating defect-free PBA MMMs is challenging, particularly at a high loading. Herein, we proposed a complexation-assisted strategy to construct a highly loaded Cu–Fe PBA MMM for the pervaporation separation of a methanol (MeOH)/dimethyl carbonate (DMC) azeotropic mixture. The membrane casting solution was synthesized by pre-dispersing a complexing agent, sodium citrate (SC), and CuCl₂ in a polymer solution, followed by in situ coordination with potassium hexacyanoferrate (III) (K₃[Fe(CN)₆]) to form PBA nanocrystals in the polymer matrix. SC formed a complex with CuCl₂, preventing Cu²⁺ from crosslinking the polymer and reducing the coordination rate by slowing the release of Cu²⁺, thereby achieving the uniform growth and dispersion of PBA nanocrystals in the MMM. The introduced PBA provided interconnected transport nanochannels and enhanced the membrane's affinity for MeOH over DMC. The PBA MMM with 60% (mass) loading exhibited a total flux of 2910 g·m⁻²·h⁻¹ and a separation factor of 337, outperforming state-of-the-art membranes for MeOH/DMC separation, showing great potential for organic solvents separation and purification.