RESUMO
Superglassy membranes synthesised by polymers of intrinsic microporosity (PIMs) suffer from physical aging and show poor gas permeance over time, especially thin membranes, due to the fast rearrangement of nonequilibrium polymer chains. Herein, we constructed a novel PIM-1 thin film nanocomposite membrane (TFN) using nanosized UiO-66-NH2 (≈10â nm)/carboxylated PIM-1 (cPIM-1) as the composite filler. Unlike conventional fillers, which interact with the polymer only via the surface, the UiO-66-NH2 /cPIM-1 forms a stable three-dimensional (3D) network intertwining with the polymer chains, being very effective to impede chain relaxation, and thus physical aging. Nanosizing of UiO-66-NH2 was achieved by regulating the nucleation kinetics using carbon quantum dots (CQD) during the synthesis. This led to increased surface area, and hence more functional groups to bond with cPIM-1 (via hydrogen bonding between -NH2 and -COOH groups), which also improved interfacial compatibility between the 3D network and polymer chains avoiding defect formation. As a result, the novel TFN showed significantly improved performance in gas separation along with reduced aging (i.e. ≈6 % loss in CO2 permeability over 63â days); the aged membranes had a CO2 permeance of 2504 GPU and ideal selectivity values of 37.2 and 23.8 for CO2 /N2 and CO2 /CH4 , respectively.
RESUMO
PIM-1/holey graphene oxide (GO) mixed matrix membranes (MMMs) have been prepared and their gas separation performance for CO2/CH4 mixtures assessed. Nanopores have been created in the basal plane of gas-impermeable GO by chemical etching reactions, and the resulting holey flakes have been further chemically functionalized, either with octadecylamine (ODA) or with PIM-1 moieties, to aid their dispersion in PIM-1. It is found that nanopores barely promote gas transport through the graphene-like nanofiller for fresh membranes (tested right after preparation); however, the prepared hybrid PIM-1/holey GO membranes exhibit higher CO2 permeability and CO2/CH4 selectivity than the pure polymer membrane 150 days after preparation and 13 and 15% higher CO2 permeability for filler contents of 0.1% of octadecylamine-functionalized holey GO and 1% of (PIM-1)-functionalized holey GO, respectively. The most significant improvement is observed for the mitigation of physical aging, as MMMs using 10% of (PIM-1)-functionalized holey GO nanofillers are capable of maintaining up to 70% of their initial CO2 permeability after 150 days, whereas only 53% is kept for pure PIM-1 after the same period. The gas permeability of the nanofiller has been rationalized with the aid of the Maxwell-Wagner-Sillars equation.
RESUMO
This work demonstrates very high removal rates (below the detection limit of 0.045 ppb) of inorganic arsenic from water using electrospun polyvinylidene difluoride (PVDF) membranes enhanced by the addition of functionalized graphene oxide in membrane distillation. This shows potential for applications in the many parts of the world suffering from arsenic-contaminated groundwater. These membranes were enhanced by the addition of reduced graphene oxide functionalized with superhydrophobic polyhedral oligomeric silsesquioxane molecules (POSS-rGO) into the spinning solutions. The flux of the best-performing rGO-enhanced membrane (containing 2 wt % POSS-rGO) was 21.5% higher than that of the pure PVDF membrane and almost double that of a commercial polytetrafluoroethylene (PTFE) membrane after 24 h of testing, with rejection values exceeding 99.9%. Furthermore, the flux of this membrane was stable over 5 days (â¼28 L m-2 h-1) of continuous testing and was more stable than those of the PTFE and control membranes when treating a concentrated fouling solution of calcium carbonate and iron(III) sulfate heptahydrate. It also achieved higher permeate quality in these conditions. The Young's modulus and ultimate tensile strength of the best-performing membrane increased by 38 and 271%, respectively, compared to the pure polymer membrane, while both had similar porosities of â¼91%.
