Fabrication of Pd-Nb bimetallic doped organosilica membranes by different metal doping routes for H₂/CO₂ separation

Monometallic doping has proved its superiority in improving either permselectivity or H₂ permeability of organosilica membranes for H₂/CO₂ separation, but it is still challenging to break the trade-off effect. Herein, we report a series of Pd-Nb bimetallic doped 1,2-bis(triethoxysilyl)ethane (Pd-Nb-BTESE, PNB) membranes with different metal doping routes for simultaneously improving H₂ permeance and H₂/CO₂ permselectivity by the synergetic effects of Pd and Nb. The doped Pd can exist in the BTESE network as nanoparticles while the doped Nb is incorporated into BTESE network forming Nb-O-Si covalent bonds. The metal doping routes significantly influence the microstructure of PNB networks and gas separation performance of the PNB membranes. We found that the PNB membrane with Pd doping priority (PNB-Pd) exhibited the highest surface area and pore volume, comparing with Nb doping priority (PNB-Nb) or Pd-Nb simultaneous doping (PNB-PdNb). The PNB-Pd membrane could not only exhibit an excellent H₂ permeance of ~ 10⁻⁶ mol·m⁻²·s⁻¹·Pa⁻¹ but also a high H₂/CO₂ permselectivity of 17.2. Our findings may provide novel insights into preparation of bimetallic doped organosilica membranes with excellent H₂/CO₂ separation performance.