Enhancing CO2-facilitated transport in PVAm membranes through the synergistic effect of porous molybdenum disulfide and mobilizable sulfonic groups

Abstract

The interlayer spacing of molybdenum disulfide nanosheets (MoS₂) can form gas transport channels in mixed matrix membranes, but the tortuous passageway simultaneously suppresses gas permeance and selectivity. Herein, porous nano-MoS₂(L) was synthesized via a hydrothermal reaction between L-cysteine and ammonium molybdate tetrahydrate using polysilicic acid as the template reagent. Next, sulfonated porous nano-MoS₂ (S-MoS₂(L)) was prepared via a thiol-click reaction between MoS₂(L) and sodium 3-mercapto-1-propanesulfonate (MPS). Thereafter, a mixed dispersion of polyvinylamine (PVAm) and S-MoS₂(L) was coated on a polysulfone (PSf) ultrafiltration membrane to obtain mixed matrix composite membranes (MMCMs). It exhibited a high CO₂ permeance of 554 GPU with a CO₂/N₂ selectivity of 74, which is higher by 104% and 90% compared with that of the pristine PVAm membrane (CO₂ permeance: 272 GPU; CO₂/N₂ selectivity: 39), respectively. This is because vacancies and defects on the MoS₂ surface enhanced the CO₂ affinity of MMCMs. Moreover, the CO₂-facilitated transport properties were enhanced by expanding the freely hopping space of amine groups with the help of mobilizable sulfonic groups. Noticeably, MMCMs revealed excellent CO₂ separation performance (CO₂ permeance: 346 GPU; selectivity: 48) under an acidic environment at 1 bar feed gas pressure due to the stabilizing effect of sulfonic groups. In addition, during a 360 h test with a CO₂/N₂ mixed gas, MMCMs maintained stable gas separation performance, revealing an average CO₂ permeance of 680 GPU with a CO₂/N₂ selectivity of 82.