Polydimethylsiloxane based mixed matrix membranes with pretreated fumed silica for efficient CO2 separation

Polydimethylsiloxane (PDMS) membranes exhibit significant potential for use in CO2 separation applications. However, the selectivity of CO2 over N2 and CH4 in a pure PDMS membrane is relatively low. Herein, we developed mixed matrix membranes (MMMs) by incorporating a surface-treated fumed silica (FS) into a PDMS polymer matrix to enhance the CO2 separation performance of PDMS membranes from N2, and CH4. The surface treatment of FS reduced its hydrophilicity, leading to more uniform dispersion within the PDMS matrix and increased fractional free volume by altering molecular packing, thereby enhancing CO2 permeability as well as CO2/N2 and CO2/CH4 selectivity. Structural, morphological, and thermal stability analyses demonstrated that the PDMS matrix remained intact even with the incorporation of fillers at higher loadings. Single gas permeation tests revealed that the highest CO2/N2 and CO2/CH4 selectivity were achieved at FS loading of 7.5 wt%. The optimized MMM, containing 7.5 wt% fillers in PDMS, exhibited a 1.42-fold increase in CO2 permeability and enhancements of 1.47-fold and 1.39-fold in CO2/N2 and CO2/CH4 selectivity, respectively, compared to neat PDMS. This study also indicates that feed pressure and time had no significant effect on CO2/N2 and CO2/CH4 separation performance.