Mixed matrix membranes fabricated by a facile in situ biomimetic mineralization approach for efficient CO2 separation

• Biomineralization-inspired approach is used to fabricate MMMs.
• Silica nanoparticles are in situ formed within Pebax® 1657 matrix.
• The confined space within the polymer matrix leads to more uniform particle size.
• Permeability and selectivity of membranes are elevated in CO2/CH4(N2) systems.
• MMMs show improved CO2 separation performance, surpassing trade-off limit.

Inspired by the silica formation process mediated by silica deposition vesicle (SDV) in diatoms or sponges, a facile and efficient biomineralization-inspired approach is proposed to in situ fabricate MMMs. Silica nanoparticles are in situ formed within poly(ether-block-amide) (Pebax® 1657) matrix through the controlled biomimetic mineralization using protamine as the inducer. The size of the mineralized silica nanoparticles can be tailored by varying the silicon precursor/protamine ratio. It is found that the confined space within the polymer matrix controls the growth of the mineralized silica nanoparticles and the size of in situ generated mineralized silica nanoparticles is relatively uniform. The mineralized silica shows good interface compatibility with polymer matrix, and the interface interaction can be tuned by silicon precursor/protamine ratio. Effect of the in situ generated mineralized silica particles on the physicochemical structure of membranes is systematically investigated in terms of glass transition temperature (Tg), crystallinity, free volume properties and 29Si nuclear magnetic resonance (NMR). The as-prepared MMMs show simultaneously increased CO2 permeability and CO2/CH4(N2) selectivity. In particular, the Pebax-Pro(Silica)1 mixed matrix membrane displays an optimum gas separation performance with CO2 permeability of 161.5 Barrer and the selectivity of 65.5(82.8) for CO2/CH4(N2) system, surpassing the Robeson upper bound in 2008.

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