High Selective Mixed Membranes Based on Mesoporous MCM-41 and MCM-41-NH₂ Particles in a Polysulfone Matrix

The development of membrane technology for gas separation processes evolved with the fabrication of so-called mixed matrix membranes (MMMs) as an alternative to neat polymers, in order to improve the overall membrane effectiveness. Once the mixed matrix membranes are used, the gas separation properties of the porous materials used as fillers are combined with the economical processability and desirable mechanical properties of polymer matrix. Mixed mesoporous silica/polymer membranes with high CO₂ and O₂ permeability and selectivity were designed and prepared by incorporating MCM-41 particles into a polymer matrix. Ordered mesoporous silica MCM-41 with high surface confirmed by BET analysis were obtained and functionalized with amino groups. In order to obtain the mixed membranes, the mesoporous silica was embedded into the polysulfone matrix (PSF). Flat mixed matrix membranes with 5, 10, and 20 wt% MCM-41 and MCM-41-NH₂ loadings have been prepared via the polymer solution casting method. The phase's interactions were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TGA), while the gas separation performances were evaluated using pure gases (CO₂, O₂, N₂). The MCM-41/PSF and MCM-41-NH₂/PSF membranes exhibited increased permeabilities for O₂ (between 1.2 and 1.7 Barrer) and CO₂ (between 4.2 and 8.1 Barrer) compared to the neat membrane (0.8 Barrer). The loss of selectivity for the O₂/N₂ (between 6 and 8%) and CO₂/N₂ (between 25 and 41%) gas pairs was not significant compared with the pure membrane (8 and 39%, respectively). The MCM-41/PSF membranes were more selective for CO₂/N₂ than the O₂/N₂ pair, due to the size difference between CO₂ and N₂ molecules and to the condensability of CO₂, leading to an increase of solubility. Stronger interactions have been noticed for MCM-41-NH₂/PSF membranes due to the amino groups, with the selectivity increasing for both gas pairs compared with the MCM-41/PSF membranes.