(368ca) Structural control of polyorganosilica (POSi) membrane for pre and post combustion carbon capture

Membrane material that exhibits robust molecular sieving ability, high degree of tunability for various separations, and simplicity in fabrication is hyper-attractive for industrial adaptation. In this work, we showcase that polyorganosilica (POSi) membrane prepared from rapid (< 2 minutes) oxygen plasma treatment of polysiloxane thin-film-composite (TFC) exhibits exceptional structural control and scalability for both pre and post combustion carbon capture. Specifically, polysiloxane of polydimethylsiloxane (PDMS) or hydroxide-modified and phenyl-modified PDMS are first fabricated into TFC on porous polymeric support, and subsequently exposed to oxygen plasma treatment to prepare an ultrathin (<10 nm) POSi skin layer. A thorough investigation of the effect of oxygen plasma treatment conditions (including plasma ionization power, ICP and RIE, chamber pressure, gas flow rate, and exposure time) and polysiloxane precursors on POSi membrane structure-transport properties provides a systematic and facile approach to POSi structural optimization for CO₂ capture. For example, using higher plasma ionization energy (ICP power > 50W and RIE > 20W) and 120s exposure time results tightened POSi network structure with the optimized H₂ permeance of 880 GPU and H₂/CO₂ selectivity of 67 at 150^oC. On the other hand, the POSi membrane prepared at lower ionization energy (ICP < 50W and RIE < 20W) and shorter exposure time (10s) induces loosened POSi structure with CO₂ permeance of 610 GPU, CO₂/N₂ of 40 and CO₂/CH₄ of 28 at 35^oC. The effect of the polysiloxane chemistry on the separation properties of the formed membranes is also investigated. For instance, the POSi membrane prepared from hydroxide-modified PDMS exhibits higher gas permeance than those prepared from PDMS and phenyl-modified PDMS, due to the readily available silanol group for POSi conversion. By contrast, the POSi prepared from PDMS exhibits stronger H₂/CO₂ selectivity than other POSi membranes due to the tighter polymer chain stacking. On the other hand, the POSi prepared from phenyl-modified PDMS exhibits the best hydrothermal stability, due to the enhanced network hydrophobicity. The robust and tunable gas separation properties of the POSi membrane in both pre and post-combustion carbon capture, coupled with the facile fabrication, present the exceptionality of the membrane for practical CO₂ capture processes.