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Stimuli-responsive membranes have been widely explored to mitigate fouling on the membrane surface to achieve the stable performance of water purification. Herein, a facile one-step coating of photo-mobile materials on membrane surface was developed to impart self-cleaning property upon exposure alternatively to ultraviolet (UV) and visible light. Specifically, photo-mobile 4,4′-azodianiline (AZO) and a bio-adhesive polydopamine (PDA) were co-deposited on the surface of ultrafiltration (UF) membranes. The effect of the coating layer on the surface hydrophilicity and pure water permeance was systematically evaluated. The photoresponsive properties of AZO in solutions and thin films with PDA was characterized using UV–Vis absorption spectroscopy. When exposed with UV light, AZO undergoes photoisomerization from trans-AZO to cis-AZO, decreasing the volume, while the exposure to visible light enables the transition from the cis- to trans- configuration, increasing the volume. The resulted self-cleaning behavior of the modified membranes through the reversible volume change is demonstrated in treating 1 g/L bovine serum albumin (BSA) solution. After exposure to the alternative UV/vis light, the AZO-coated UF membranes showed an increased water permeance by ~160%.

New polymeric blend membranes for CO2 separation were synthesized based on insights from molecular dynamics simulation. A molecular-level structure-property relationship in polymers of intrinsic microporosity (PIM) based blend membranes was investigated in detail computationally. Calculated local density profiles and energy of interaction of the blend membranes, composed of PIM-1 and various polyphosphazenes, showed that using the polyphosphazene with a higher concentration of ether side chains can improve the compatibility with PIM-1. Based on the findings of computational studies, blend membranes were experimentally fabricated from PIM-1 and polyphosphazenes with various polyether side chain concentrations. Polyether concentration in polyphosphazenes was correlated with the film properties and gas transport performance of the blend membranes. Blend membranes showed very high CO2 permeability (3100-5300barrer) and improved CO2/N2 selectivity (24–28), outperforming all other PIM-based blend membranes reported to date. Moreover, the CO2 permeability performance of the blend membranes was tested 566 h under real post-combustion flue gas from a coal-fired power plant, including CO2, N2, H2O, O2, SOx and NOx.

Thin film composite (TFC) membranes for industrial gas separation are often comprised of a thin selective layer (100 nm or less) on a porous support that provides mechanical strength. As the selective layer becomes thinner to increase gas permeance and thus reduce the capital cost, the support surface morphology restricts the concentration profile of the penetrant in the selective layer. Such geometric restriction has been demonstrated using modeling and computational simulations. However, there are no rigorous experimental studies that verify the modeling results. This study investigates model two-layer TFC membranes, which are comprised of track-etched polycarbonate (PC) nanofiltration membranes with uniform and straight cylindrical pores as porous supports, and AF1600 with excellent film formation and good stability as the selective layer. The presence of a support can decrease the gas permeance by as much as 85% compared to the freestanding thin film, when the PC support has a pore radius of 47 nm and porosity of 2.8%. The gas permeance increases with increasing porosity at a constant pore size and decreasing pore size at a constant porosity. The measured membrane permeances are consistent with the simulation values obtained using three-dimensional (3D) computational mass transport models that predict the steady-state penetrant concentration in the selective layer.

Fluorinated polymers exhibit unique gas separation properties. However, the effect of the degree of fluorination in polymers on gas transport properties has not been elucidated. Herein, the alkenyl groups in the polybutadiene (PB) block of polystyrene-b-polybutadiene-b-polystyrene (SBS) were modified with gem-difluorocyclopropanation via difluorocarbene (∶CF2). The F content in the fluorinated PB (FPB) phase ranges from 0 to 27 wt%, which was confirmed using 1H NMR spectroscopy, and physical properties of the polymers were determined, including density, fractional free volume (FFV), and glass transition temperature (Tg). The Maxwell and additive models are used to estimate gas permeability and solubility in the FPB phase, respectively. Increasing the F content from 0 to 27 wt% in the FPB phase increases the CO2 solubility from 0.58 to 1.1 cm3 (STP)/cm3 atm and CO2/C2H6 solubility selectivity from 0.45 to 1.1 at 35 °C, suggesting that the F groups have induced favorable interaction with CO2 and unfavorable interaction with C2H6 in these partially fluorinated polymers. However, a further increase of the F content in the perfluoropolymer (such as polytetrafluoroethylene) decreases CO2 solubility and CO2/gas solubility selectivity, indicating the unique CO2/gas separation properties in partially fluorinated polymers. The introduction of the F groups to the polymer also increases Tg and decreases FFV and gas diffusivity, which can be satisfactorily described using a free volume model.