RETRACTED: Mixed matrix membrane O2/N2 selectivity enhancement by intercalation of iron-ferrite nanoparticles under moderate external magnetic fields; DFT assisted study

Abstract

Magnetic field-induced mixed matrix membranes (MMMs) were used for separation of O2 and N2 gas according to their different magnetic properties. The double-layered MMMs were made of polyethersulfone (PES) and Pebax-1657 and super-paramagnetic Fe3O4 nanoparticles (NPs) by simultaneous co-casting method. The PES served as the supporting layer while the Pebax layer (intercalated by the Fe3O4 NPs) acted as the selective parts of the MMMs. An external magnetic field (0–0.5 T) was applied to avoid the demagnetizing effects between the polymeric (because of monomer chains mobility) and the magnetic NPs components of the MMMs. In the presence of an external magnetic field (H = 0.4 T), the ideal selectivity of the fabricated MMMs (∼25 µm in thickness) was tested for O2/N2 separation, considering different concentrations of the NPs. The results indicated a substantial improvement up to 3.59 at room temperature for the sample containing 24 wt% Fe3O4 NPs under the gas feeding of 10 bar, whereas the selectivity for non-magnetic MMMs was ∼ 1.87. The results showed that the external magnetic field could facilitate the formation of magnetic channels by loosen hydrogen bonds of the carbonyl groups in the polymer and also alignment of the super-paramagnetic NPs.As a complimentary study, for better understanding of the rule of the magnetic NPs, Density Functional Theory (DFT) simulation was employed to investigate the general behavior of the O2 and N2 molecules near the Fe3O4 (magnetite) surface. Based on the results, the magnetic interactions between the NPs and O2 molecules could form a layered structure for oxygen accumulation, which in turn affects the gas flow rate within the pores and channels of the MMMs near the magnetic NPs.